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@@ -1,38 +1,4 @@ -The Project Gutenberg EBook of The Vertebrate Skeleton, by Sidney H. Reynolds - -This eBook is for the use of anyone anywhere at no cost and with -almost no restrictions whatsoever. You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org - - -Title: The Vertebrate Skeleton - -Author: Sidney H. Reynolds - -Release Date: August 9, 2013 [EBook #43431] - -Language: English - -Character set encoding: ASCII - -*** START OF THIS PROJECT GUTENBERG EBOOK THE VERTEBRATE SKELETON *** - - - - -Produced by Chris Curnow, Mark Young and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - - - - +*** START OF THE PROJECT GUTENBERG EBOOK 43431 *** CAMBRIDGE BIOLOGICAL SERIES. @@ -1675,12 +1641,12 @@ hypoblastic in origin. [3] See also p. 71. [4] It is usual to regard the clavicle as a membrane bone, but -Koelliker has shown that in rabbit embryos of about the 17th day it is +Kölliker has shown that in rabbit embryos of about the 17th day it is cartilaginous. [5] In compiling these paragraphs on Histology, free use has been made of Klein and Noble Smith's _Atlas of Histology_, the small Histologies -of Klein and Schaefer, Huxley's _Elementary Physiology_, and Lloyd +of Klein and Schäfer, Huxley's _Elementary Physiology_, and Lloyd Morgan's _Animal Biology_. [6] See Huxley's _Elementary Physiology_, Revised edition, London, @@ -1706,7 +1672,7 @@ Ray Soc. London, 1868. [12] See R. Wiedersheim, _Zeitschr. wiss. Zool._ vol. LIII. suppl. p. 43, 1892. -[13] G. Baur, _Beitraege zur Morphogenie des Carpus und Tarsus der +[13] G. Baur, _Beiträge zur Morphogenie des Carpus und Tarsus der Vertebraten_, Theil 1. Batrachia. Jena, 1888, and _Amer. Natural._, vol. XIX. 1885 (several papers). @@ -2239,7 +2205,7 @@ some respects that of von Zittel has been followed. Order 1. RATITAE. - Group =AEpyornithes=. _AEpyornis._ + Group =Æpyornithes=. _Æpyornis._ Group =Apteryges=. Apteryx--kiwi. @@ -2273,7 +2239,7 @@ some respects that of von Zittel has been followed. Subgroup Steganopodes. Sula--gannet. Pelicanus--pelican. - Phaethon--frigate bird. + Phaëthon--frigate bird. Phalacrocorax--cormorant. Subgroup Ardeae. Ardea--heron @@ -2456,7 +2422,7 @@ Order. MONOTREMATA. Suborder (3). ODONTOCETI. Family =Physeteridae=. Physeter--sperm whale. - Hyperoodon--bottlenose. + Hyperoödon--bottlenose. Ziphius. Mesoplodon. @@ -2631,7 +2597,7 @@ Order. MONOTREMATA. Suborder (2). CARNIVORA VERA or FISSIPEDIA. - Section AELUROIDEA. + Section ÆLUROIDEA. Family =Felidae=. Felis--cat, lion, tiger. _Machaerodus_--sabre-toothed lion. @@ -2730,7 +2696,7 @@ FOOTNOTES: [17] This classification of birds is essentially that of Gadow and Selenka in Bronn's _Classen und Ordnungen des Thierreichs_, Band VI., -Abth. IV., Voegel. Leipzig, 1891. +Abth. IV., Vögel. Leipzig, 1891. [18] The classification adopted is almost entirely that given in Flower and Lydekker's _Mammals Living and Extinct_. London, 1891. @@ -2799,7 +2765,7 @@ adult. SUBPHYLUM C. CEPHALOCHORDATA. [Illustration FIG. 3. DIAGRAM OF THE SKELETON OF _Amphioxus -lanceolatus_ x 3 (after a drawing in the Index collection at the Brit. +lanceolatus_ × 3 (after a drawing in the Index collection at the Brit. Mus.). 1. skeleton of dorsal fin. @@ -2984,7 +2950,7 @@ come nearer to the larval Lamprey or Ammocoete. SPINAL COLUMN. [Illustration FIG. 4. A, DORSAL; B, LATERAL AND C, VENTRAL VIEW OF THE -SKULL OF _Petromyzon marinus_ x 1 (after PARKER). +SKULL OF _Petromyzon marinus_ × 1 (after PARKER). 1. horny teeth. 2. labial cartilage. @@ -3558,7 +3524,7 @@ London, 1889-95. [32] See B. Dean, _J. Morphol._ vol. IX. pp. 87-114, 1894, and _Nat. Sci._ vol. VIII. p. 245, 1896. -[33] A. Guenther, _Phil. Trans._ vol. 161, Part II. 1871, p. 511. T.H. +[33] A. Günther, _Phil. Trans._ vol. 161, Part II. 1871, p. 511. T.H. Huxley, "On Ceratodus and the classification of fishes," _P.Z.S._ 1876, p. 24. @@ -3725,7 +3691,7 @@ below the large foramen just mentioned is a small hole through which the external carotid enters the orbit (fig. 6, 9). [Illustration Fig. 6. LATERAL VIEW OF THE SKULL OF A DOGFISH -(_Scyllium canicula_) x 2/3.] +(_Scyllium canicula_) × 2/3.] 1. nasal capsule. 2. rostrum. @@ -3892,7 +3858,7 @@ The meso-pterygium also supports only a single radial which divides distally. [Illustration FIG. 7. SEMIDORSAL VIEW OF THE PECTORAL GIRDLE AND FINS -OF A DOGFISH (_Scyllium canicula_) x 2/3. +OF A DOGFISH (_Scyllium canicula_) × 2/3. The gaps between the radiale are blackened. @@ -4541,7 +4507,7 @@ pterygoid and quadrate bones are the ossified representatives of the palato-pterygo-quadrate bar of the Dogfish. [Illustration FIG. 12. MANDIBULAR AND HYOID ARCHES OF A COD (_Gadus -morrhua_) x 1/2 (Brit. Mus.). +morrhua_) × 1/2 (Brit. Mus.). 1. palatine. 2. meso-pterygoid. @@ -4646,7 +4612,7 @@ developed, and the cartilage bones, the =scapula= and =coracoid=, are much reduced in size and importance. [Illustration FIG. 13. THE RIGHT HALF OF THE PECTORAL GIRDLE AND RIGHT -PECTORAL FIN OF A COD (_Gadus morrhua_) x 1/2 (Brit. Mus.). +PECTORAL FIN OF A COD (_Gadus morrhua_) × 1/2 (Brit. Mus.). 1. post-temporal. 2. supra-clavicle. @@ -4858,7 +4824,7 @@ type occurs, known as _osteodentine_; it is traversed by canals occupied by marrow, and is closely allied to bone. [Illustration FIG. 15. PART OF THE LOWER JAW OF A SHARK (_Galeus_) -(from OWEN after ANDRE). +(from OWEN after ANDRÉ). 1. teeth in use. @@ -5201,8 +5167,8 @@ a rostrum which is enormously developed in _Pristis_ and some Rays. The cartilaginous roof of the cranium is rendered incomplete by the presence of a large hole, the anterior fontanelle. -[Illustration FIG. 16. A. SKULL OF _Notidanus_ x 1/2 (Brit. Mus.). B. -SKULL OF _Cestracion_ x 1/3 (after GEGENBAUR). In neither case are the +[Illustration FIG. 16. A. SKULL OF _Notidanus_ × 1/2 (Brit. Mus.). B. +SKULL OF _Cestracion_ × 1/3 (after GEGENBAUR). In neither case are the branchial arches shown. 1. rostrum. @@ -5420,7 +5386,7 @@ _Lepidosiren_ have five, like most other fish. The branchial arches bear gill rakers. [Illustration FIG. 19. DORSAL (TO THE LEFT) AND VENTRAL (TO THE RIGHT) -VIEWS OF THE CRANIUM OF _Ceratodus miolepis_ (after GUeNTHER). +VIEWS OF THE CRANIUM OF _Ceratodus miolepis_ (after GÃœNTHER). 1. cartilaginous part of the quadrate with which the mandible articulates. @@ -5514,7 +5480,7 @@ at the margin of the fin[48] the cartilaginous endoskeletal radiale are replaced by horny exoskeletal fin-rays. [Illustration FIG. 20. LATERAL VIEW OF THE SKELETON OF _Ceratodus -miolepis_ (after GUeNTHER). +miolepis_ (after GÃœNTHER). 1. ethmoid. 2. scleroparietal. @@ -5661,7 +5627,7 @@ FOOTNOTES: [39] The following general works on fishes may be referred to: Bashford Dean, _Fishes, Living and Fossil_, New York, 1895. A. -Guenther, _An Introduction to the Study of Fishes_, Edinburgh, 1880. +Günther, _An Introduction to the Study of Fishes_, Edinburgh, 1880. A.A.W. Hubrecht and M. Sagemehl, _Fische_ in Bronn's _Classen und Ordnungen des Thierreichs_, Band VI. Leipzig, 1876. @@ -5673,8 +5639,8 @@ pp. 163-221. [42] C. Hasse, _Zeitschr. wiss. Zool._ LVII. 1893, p. 76. -[43] C. Hasse, _Das natuerliche System der Elasmobranchier auf -Grundlage des Baues und der Entwickelung ihrer Wirbelsaeule_, Jena, +[43] C. Hasse, _Das natürliche System der Elasmobranchier auf +Grundlage des Baues und der Entwickelung ihrer Wirbelsäule_, Jena, 1879 and 1885, and "Die fossilen Wirbel, Morph. Studien I.-IV.," _Morphol. Jahrb. Bd._ II., III. and IV. 1876-78. @@ -6006,7 +5972,7 @@ cranium and meet the orbitosphenoids. The _prefronto-lachrymals_ (fig. 21, A and C, 7) connect the frontals with the maxillae. [Illustration FIG. 21. A DORSAL, B VENTRAL, AND C LATERAL VIEWS OF THE -SKULL OF A NEWT (_Molge cristata_) x 2-1/2 (after PARKER). +SKULL OF A NEWT (_Molge cristata_) × 2-1/2 (after PARKER). The cartilage is dotted, the cartilage bones are marked with dots and dashes, the membrane bones are left white. @@ -6158,7 +6124,7 @@ portion=, and a ventral =coracoid portion= partially divided into an anterior part, the precoracoid, and a posterior part, the =coracoid=. [Illustration FIG. 22. A VENTRAL, AND B LATERAL VIEW OF THE SHOULDER -GIRDLE AND STERNUM OF AN OLD MALE CRESTED NEWT (_Molge cristata_) x 3 +GIRDLE AND STERNUM OF AN OLD MALE CRESTED NEWT (_Molge cristata_) × 3 (after PARKER). 1. scapula. @@ -6223,7 +6189,7 @@ the human hand, judging from the analogy of the frog probably being the one that is absent. [Illustration FIG. 23. A RIGHT POSTERIOR, AND B RIGHT ANTERIOR LIMB OF -A NEWT x 1-1/2 (_Molge cristata_). +A NEWT × 1-1/2 (_Molge cristata_). 1. femur. 2. tibia. @@ -6472,7 +6438,7 @@ the frog include the =epi-otic= and =opisthotic= elements of many skulls, in addition to the exoccipitals. [Illustration FIG. 24. A DORSAL, AND B VENTRAL VIEWS OF THE CRANIUM OF -A COMMON FROG (_Rana temporaria_) x 2 (after PARKER). +A COMMON FROG (_Rana temporaria_) × 2 (after PARKER). In this and the next two figs. cartilage is dotted, cartilage bones are marked with dots and dashes, membrane bones are left white. @@ -6545,7 +6511,7 @@ cranium. [Illustration FIG. 25. A DORSAL AND B VENTRAL VIEW OF THE CRANIUM OF A COMMON FROG (_Rana temporaria_) from which the membrane bones have -mostly been removed. x 2 (after PARKER). +mostly been removed. × 2 (after PARKER). 1. sphenethmoid. 2. palatine. @@ -6619,7 +6585,7 @@ its anterior end a short process which projects upwards and meets the nasal. [Illustration FIG. 26. A, LATERAL VIEW OF THE SKULL, B, POSTERIOR VIEW -OF THE CRANIUM OF A COMMON FROG (_Rana temporaria_) x 2 (after +OF THE CRANIUM OF A COMMON FROG (_Rana temporaria_) × 2 (after PARKER). 1. sphenethmoid. @@ -7234,7 +7200,7 @@ brain, its place being partly taken by a pair of orbitosphenoids, (4) there is no definite tympanic cavity. [Illustration FIG. 27. DORSAL VIEW OF THE SKULL OF A LABYRINTHODONT -(_Capitosaurus nasutus_) x 1/9 (from VON ZITTEL). +(_Capitosaurus nasutus_) × 1/9 (from VON ZITTEL). 1. premaxillae. 2. nasal. @@ -8086,7 +8052,7 @@ Clavicles and a T-shaped interclavicle are commonly present, but are absent in the Chamaeleons. [Illustration FIG. 33. A, LATERAL VIEW, AND B, LONGITUDINAL SECTION OF -THE SKULL OF A LIZARD (_Varanus varius_). x 3/5. (Brit. Mus.) +THE SKULL OF A LIZARD (_Varanus varius_). × 3/5. (Brit. Mus.) 1. premaxillae. 2. maxillae. @@ -8124,7 +8090,7 @@ There is no separate precoracoid but a precoracoidal process (fig. 34, 7) of the coracoid is generally prominent. [Illustration FIG. 34. LATERAL VIEW OF THE SHOULDER-GIRDLE OF -_Varanus._ x 3/5. +_Varanus._ × 3/5. (Brit. Mus.). @@ -8247,7 +8213,7 @@ spatulate and without serrated edges, they are always planted in distinct sockets, and some of them are borne by the premaxillae. [Illustration FIG. 35. RESTORED SKELETON OF _Ceratosaurus nasicornis_. -x 1/30. (After Marsh.) +× 1/30. (After Marsh.) 1. anterior nares. 2. prominence on the nasal bones which probably carried a horn. @@ -8524,7 +8490,7 @@ are there given. [74] The exact position of the suture between the prefrontal and postfrontal is not known. -[75] A. Guenther, On the Anatomy of Hatteria, _Phil. Trans_, vol. 157, +[75] A. Günther, On the Anatomy of Hatteria, _Phil. Trans_, vol. 157, 1867, p. 595. [76] =Zygosphenes= are extra articulating surfaces borne upon the @@ -8562,7 +8528,7 @@ are in the main those given by von Zittel. [86] See O.C. Marsh, _Amer. J. Sci._ (3), vol. 48, 1894, p. 85. -[87] See C.B. Bruehl, _Das Skelet der Krokodiliden_, Wien, 1862. C.K. +[87] See C.B. Brühl, _Das Skelet der Krokodiliden_, Wien, 1862. C.K. Hoffmann in Bronn's _Klassen und Ordnungen des Thierreichs_, Bd. VI. Abth. III. 1881-85. T.H. Huxley, _Proc. Linn. Soc._ (Zoology) 1860 vol. IV. p. 1. R. Owen, _History of British fossil Reptiles_. @@ -8702,7 +8668,7 @@ hyoplastra, hypoplastra and xiphiplastra are homologous with the abdominal ribs of Crocodiles. [Illustration FIG. 37. THE PLASTRON OF A GREEN TURTLE (_Chelone -midas_). x 1/7. (Camb. Mus.) +midas_). × 1/7. (Camb. Mus.) 1. epiplastron (clavicle). 2. entoplastron (interclavicle). @@ -8879,7 +8845,7 @@ the brain lies, and which is a direct continuation of the neural canal of the vertebrae. [Illustration FIG. 38. THE SKULL OF THE GREEN TURTLE (_Chelone -midas_). x 1/2. A, POSTERIOR HALF, B, ANTERIOR HALF. (Brit. Mus.) +midas_). × 1/2. A, POSTERIOR HALF, B, ANTERIOR HALF. (Brit. Mus.) 1. parietal. 2. squamosal. @@ -8983,7 +8949,7 @@ and quadratojugals. All three pairs of frontal bones, especially the postfrontals, take part in the bounding of the orbits. [Illustration FIG. 39. LONGITUDINAL VERTICAL SECTION THROUGH THE -CRANIUM OF A GREEN TURTLE (_Chelone midas_). x 2/3. (Camb. Mus.) +CRANIUM OF A GREEN TURTLE (_Chelone midas_). × 2/3. (Camb. Mus.) 1. parietal. 2. squamosal. @@ -9237,7 +9203,7 @@ united with the precoracoid, the two bones ossifying continuously. It tapers away distally, and is directed dorsalwards towards the carapace. -The =precoracoid= forms an angle of about 130 deg. with the scapula, with +The =precoracoid= forms an angle of about 130° with the scapula, with which it is completely fused at its proximal end. Its distal end is somewhat expanded and flattened, and is terminated by a fibrocartilaginous =epiprecoracoid= which meets its fellow. It takes @@ -9310,8 +9276,8 @@ the first digit is stout and curved, and bears a horny claw; those of the other digits are flattened and more or less pointed. [Illustration FIG. 40. A. ANTERIOR LIMB OF A YOUNG HAWKSBILL TURTLE -(_Chelone imbricata_) x 1/4 (Brit. Mus.). B. POSTERIOR LIMB OF A LARGE -GREEN TURTLE (_Chelone midas_) x 1/8 (Camb. Mus.). +(_Chelone imbricata_) × 1/4 (Brit. Mus.). B. POSTERIOR LIMB OF A LARGE +GREEN TURTLE (_Chelone midas_) × 1/8 (Camb. Mus.). 1. humerus. 2. radius (almost hidden by the ulna). @@ -9607,7 +9573,7 @@ ends of the transverse processes, at the same time becoming less prominent; otherwise these vertebrae are just like the third. [Illustration FIG. 42. ANTERIOR VIEW OF A, A LATE THORACIC AND B, THE -FIRST SACRAL VERTEBRA OF A YOUNG CROCODILE (_C. palustris_). x 1/3. +FIRST SACRAL VERTEBRA OF A YOUNG CROCODILE (_C. palustris_). × 1/3. 1. neural spine. 2. process bearing prezygapophysis. @@ -9712,7 +9678,7 @@ The =cranium= may again for purposes of description be divided into:-- 1. THE CRANIUM PROPER OR BRAIN CASE. [Illustration FIG. 43. PALATAL ASPECT A, OF THE CRANIUM, B, OF THE -MANDIBLE OF AN ALLIGATOR (_Caiman latirostris_). x 1/3. (Brit. Mus.) +MANDIBLE OF AN ALLIGATOR (_Caiman latirostris_). × 1/3. (Brit. Mus.) 1. premaxillae. 2. maxillae. @@ -9803,7 +9769,7 @@ the carotid arteries pass. Dorsolaterally the basisphenoid articulates with the =alisphenoids=. [Illustration FIG. 44. LATERAL VIEW OF THE SKULL OF AN ALLIGATOR -(_Caiman latirostris_). x 1/3. (Brit. Mus.) +(_Caiman latirostris_). × 1/3. (Brit. Mus.) 1. premaxillae. 2. maxillae. @@ -9987,7 +9953,7 @@ be converted into perforations. Pits of the same character occur between the maxillary and mandibular teeth. [Illustration FIG. 45. LONGITUDINAL SECTION THROUGH THE SKULL OF AN -ALLIGATOR (_Caiman latirostris_). x 1/3. (Brit. Mus.) +ALLIGATOR (_Caiman latirostris_). × 1/3. (Brit. Mus.) 1. premaxilla. 2. nasal. @@ -10295,7 +10261,7 @@ way homologous with true ribs, but correspond rather with the more posterior of the bones constituting the plastron of Chelonia. [Illustration FIG. 46. STERNUM AND ASSOCIATED MEMBRANE BONES OF A -CROCODILE (_C. palustris_) x 1/3. (Brit. Mus.) +CROCODILE (_C. palustris_) × 1/3. (Brit. Mus.) The last pair of abdominal ribs which are united with the epipubes by a plate of cartilage have been omitted. @@ -10313,7 +10279,7 @@ This includes the skeleton of the two pairs of limbs and their respective girdles. [Illustration: FIG. 47. LEFT HALF OF THE PECTORAL GIRDLE OF AN -ALLIGATOR (_Caiman latirostris_) x 2/3. (Brit. Mus.) +ALLIGATOR (_Caiman latirostris_) × 2/3. (Brit. Mus.) 1. scapula. 2. coracoid. @@ -10366,7 +10332,7 @@ articulates with the two bones of the fore-arm, the radius and ulna. [Illustration FIG. 48. A, RIGHT ANTERIOR, AND B, RIGHT POSTERIOR LIMB OF A YOUNG ALLIGATOR (_Caiman latirostris_). (Brit. Mus.) -A x 1/2. B x about 1/3.] +A × 1/2. B × about 1/3.] 1. humerus. 2. radius. @@ -10472,7 +10438,7 @@ ischium; it forms a small patch of unossified cartilage, interposed between the anterior parts of the ilium and ischium. [Illustration FIG. 49. PELVIS AND SACRUM OF AN ALLIGATOR (_Caiman -latirostris_) x 1/2. (Brit. Mus.) +latirostris_) × 1/2. (Brit. Mus.) 1. ilium. 2. ischium. @@ -10716,7 +10682,7 @@ way the new tooth comes to lie in the pulp cavity of the old one. This method of succession is well seen in the Crocodilia. [Illustration FIG. 50. PREPARATION OF PART OF THE RIGHT MANDIBULAR -RAMUS OF _Crocodilus palustris_ x 1/2. (Brit. Mus.) +RAMUS OF _Crocodilus palustris_ × 1/2. (Brit. Mus.) 1. tooth in use. 2. fairly old germ of future @@ -11093,7 +11059,7 @@ strongly developed, and the hyoid is often fairly large. THE RIBS. [Illustration FIG. 53. HYOIDS OF AN ALLIGATOR (_Caiman latirostris_) -(TO THE LEFT) AND OF A GREEN TURTLE (_Chelone midas_) (TO THE RIGHT) x +(TO THE LEFT) AND OF A GREEN TURTLE (_Chelone midas_) (TO THE RIGHT) × 5/8. (Brit. Mus.) The cartilaginous portions are dotted. @@ -11158,7 +11124,7 @@ it is keeled and bears some resemblance to that of birds. It may have been replaced by membrane bone. [Illustration FIG. 54. VENTRAL VIEW OF THE SHOULDER-GIRDLE OF STERNUM -OF A LIZARD (_Loemanctus longipes_) x 2. (After PARKER.) +OF A LIZARD (_Loemanctus longipes_) × 2. (After PARKER.) 1. interclavicle. 2. clavicle. @@ -11538,7 +11504,7 @@ not form a natural group. The Ratitae include the following groups:-- -_AEpyornithes_[98], huge extinct birds from Madagascar. +_Æpyornithes_[98], huge extinct birds from Madagascar. _Apteryges_, including the Apteryx of New Zealand. @@ -11606,13 +11572,13 @@ of manus.] FOOTNOTES: -[94] M. Fuerbringer, _Untersuchungen zur Morphologie und Systematik der -Voegel_, I. and II. Amsterdam, 1888. Cf. H. Gadow, _Nature_, XXXIX. +[94] M. Fürbringer, _Untersuchungen zur Morphologie und Systematik der +Vögel_, I. and II. Amsterdam, 1888. Cf. H. Gadow, _Nature_, XXXIX. 1888, pp. 150 and 177. T.H. Huxley, "On the classification of birds." _P.Z.S._, London, 1867. -E. Selenka and H. Gadow, _Voegel_ in Bronn's _Classen und Ordnungen des +E. Selenka and H. Gadow, _Vögel_ in Bronn's _Classen und Ordnungen des Thierreichs_ 1869-1890. [95] See p. 283. @@ -11710,7 +11676,7 @@ and is called the =remicle= (fig. 57, 11). [Illustration FIG. 56. THE WING OF A WILD DUCK (_Anas boschas_). The upper figure shows the dorsal side of a right wing, the lower -figure the ventral side of a left wing. x 1/3. (Brit. Mus.) +figure the ventral side of a left wing. × 1/3. (Brit. Mus.) 1. scapulars. 2. tectrices marginales. @@ -11736,7 +11702,7 @@ feathers, of varying length, attached to the anterior half of the humerus. [Illustration FIG. 57. WINGS OF A WILD DUCK WITH THE COVERTS REMOVED -(_Anas boschas_). x 1/3. +(_Anas boschas_). × 1/3. A. Right wing seen from the dorsal side. B. Left wing disarticulated and seen from the ventral side. (Brit. Mus.) @@ -11974,7 +11940,7 @@ Behind them come the six free caudal vertebrae, succeeded by a terminal piece, the =pygostyle=, formed of a number of vertebrae fused together; this bears the rectrices or tail quills. -[Illustration FIG. 59. SKULL OF A DUCK (_Anas boschas_). x 1. +[Illustration FIG. 59. SKULL OF A DUCK (_Anas boschas_). × 1. A. Dorsal view of the cranium. B. Palatal view of the mandible. C. The Hyoid. @@ -11985,7 +11951,7 @@ For numbers see Fig. 60.] B. THE SKULL. [Illustration FIG. 60. A. Ventral view of the cranium of a Duck (_Anas -boschas_). B. Cranium and mandible seen from the left side. x 1. +boschas_). B. Cranium and mandible seen from the left side. × 1. 1. maxillae. 2. premaxillae. @@ -12437,7 +12403,7 @@ the =antitrochanter= (fig 61, 8), with which the great trochanter of the femur articulates. [Illustration FIG. 61. LATERAL VIEW OF THE PELVIS AND SACRUM OF A DUCK -(_Anas boschas_) x 2/3. +(_Anas boschas_) × 2/3. 1. ilium. 2. ischium. @@ -12667,7 +12633,7 @@ the caudal vertebrae, the leg bones, and those of the antibrachium and manus; in Hornbills every bone contains air. [Illustration FIG. 62. THIRD CERVICAL VERTEBRA OF AN OSTRICH -(_Struthio camelus_). x 1. A anterior, B posterior, C dorsal view (A +(_Struthio camelus_). × 1. A anterior, B posterior, C dorsal view (A and B after MIVART). 1. neural spine. @@ -12789,7 +12755,7 @@ palatines and the pterygoids from the rostrum. Huxley uses the term the vomers are narrow behind, and the palatines and pterygoids converge posteriorly and articulate largely with the rostrum. Three modifications of this condition are distinguished by Huxley, and -termed =Schizognathous=, =AEgithognathous=, and =Desmognathous=. +termed =Schizognathous=, =Ægithognathous=, and =Desmognathous=. In the =Schizognathae= the vomers coalesce and form a narrow elongated bone, pointed in front, separating the maxillo-palatine processes of @@ -12798,7 +12764,7 @@ eagles, American vultures, some herons and many owls have the Schizognathous arrangement. In pigeons and sandgrouse there is no vomer, but the other bones have the Schizognathous arrangement. -In the =AEgithognathae= the arrangement is the same as in the +In the =Ægithognathae= the arrangement is the same as in the Schizognathae, except that the vomers are truncated in front. Passeres, swifts, woodpeckers, humming birds, rollers, hoopoes have this arrangement. @@ -12854,9 +12820,9 @@ PECTORAL GIRDLE. [Illustration FIG. 63. SHOULDER-GIRDLE AND STERNUM OF - A. BLACK VULTURE (_Vultur cinereus_) x 1/3. - B. PEACOCK (_Pavo cristatus_) x 3/8. - C. PELICAN (_Pelicanus conspicillatus_) x 1/3. (All Camb. Mus.) + A. BLACK VULTURE (_Vultur cinereus_) × 1/3. + B. PEACOCK (_Pavo cristatus_) × 3/8. + C. PELICAN (_Pelicanus conspicillatus_) × 1/3. (All Camb. Mus.) 1. carina of the sternum. 2. coracoid. @@ -12913,9 +12879,9 @@ PELVIC GIRDLE. [Illustration FIG. 64. BONES OF THE RIGHT WING OF - A. A PENGUIN x 1/3. (Camb. Mus.) - B. OSTRICH (_Struthio camelus_) x 1/7. (Partly after PARKER.) - C. GANNET (_Sula alba_) x 1/3. (Camb. Mus.) + A. A PENGUIN × 1/3. (Camb. Mus.) + B. OSTRICH (_Struthio camelus_) × 1/7. (Partly after PARKER.) + C. GANNET (_Sula alba_) × 1/3. (Camb. Mus.) In C the distal phalanges of the pollex and second digit have been omitted. @@ -12959,10 +12925,10 @@ greater or less extent. [Illustration FIG. 65. PELVIC GIRDLE AND SACRUM OF - A. CASSOWARY (_Casuarius galeatus_) x 1/8. - B. OWEN'S APTERYX (_A. oweni_) x 1/2. - C. BROAD BILLED RHEA (_R. macrorhyncha_) x 1/6. - D. OSTRICH (_Struthio camelus_) x 1/10. (All Camb. Mus.) + A. CASSOWARY (_Casuarius galeatus_) × 1/8. + B. OWEN'S APTERYX (_A. oweni_) × 1/2. + C. BROAD BILLED RHEA (_R. macrorhyncha_) × 1/6. + D. OSTRICH (_Struthio camelus_) × 1/10. (All Camb. Mus.) 1. ilium. 2. ischium. @@ -12978,14 +12944,14 @@ crest. The proximal tarsals are fused with its distal end, the whole forming a compound bone, the tibio-tarsus. There is frequently an oblique bar of bone crossing the anterior face of the tibio-tarsus at the distal end, just above the articular surface of the -tarso-metatarsus, this is absent in Ostriches and _AEpyornis_. The +tarso-metatarsus, this is absent in Ostriches and _Æpyornis_. The fibula though in the embryo and in _Archaeopteryx_ equal in length to the tibia, is in the adult of other birds always imperfect, its proximal end is often fused with the tibia, and its distal end is commonly atrophied. In the Penguins however the distal end is complete. The distal tarsals fuse with the second, third and fourth metatarsals, forming a compound bone, the tarso-metatarsus. The first -metatarsal is nearly always free but occasionally as in _Phaethon_ it +metatarsal is nearly always free but occasionally as in _Phaëthon_ it is fused with the others. No adult bird has more than four digits in the pes. In the Penguins the metatarsals are separate, and in many birds larger or smaller gaps exist between the fused metatarsals. In @@ -13166,7 +13132,7 @@ process resembling an olecranon. The limbs and their girdles bear a striking resemblance to those of some Theromorphous reptiles. [Illustration FIG. 66. VENTRAL VIEW OF THE SHOULDER-GIRDLE AND STERNUM -OF A DUCKBILL (_Ornithorhynchus paradoxus_) x 3/4 (after PARKER). +OF A DUCKBILL (_Ornithorhynchus paradoxus_) × 3/4 (after PARKER). 1 and 2. scapula. 3. coracoid. @@ -13379,7 +13345,7 @@ the animal is quite adult. None of the vertebrae are united to form a sacrum, but the caudal vertebrae have large chevron bones. [Illustration FIG. 67. CERVICAL VERTEBRAE OF A CA'ING WHALE -(_Globicephalus melas_) x 1/4. (Camb. Mus.) +(_Globicephalus melas_) × 1/4. (Camb. Mus.) 1. centrum of seventh cervical vertebra. 2. neural arch of seventh cervical vertebra. @@ -13869,7 +13835,7 @@ forms are plantigrade, some digitigrade, some subplantigrade. The group includes all the ordinary terrestrial Carnivora, and is divided into three sections:-- -AEluroidea[135], including the cats, civets, hyaenas, and allied forms. +Æluroidea[135], including the cats, civets, hyaenas, and allied forms. Cynoidea, including the dog tribe. @@ -13942,7 +13908,7 @@ specially to the phalanges of all the digits except the pollex. The pollex is clawed and so is sometimes the second digit; the other digits of the manus are without nails or claws. The teeth are divisible into the four usual types and the series never exceeds _i_ -2/3 _c_ 1/1 _pm_ 3/3 _m_ 3/3 x 2, total 38. The milk teeth are quite +2/3 _c_ 1/1 _pm_ 3/3 _m_ 3/3 × 2, total 38. The milk teeth are quite unlike the permanent teeth. The orbit is not divided by bone from the temporal fossa. The vertebral column is short, and in old animals the trunk vertebrae have a tendency to become partially fused together. @@ -14056,7 +14022,7 @@ O.C. Marsh, "Jurassic Mammals," _Amer. J. Sci._ 1878 _et seq._ [114] See Oldfield Thomas, _Brit. Mus. Cat. of Marsupialia and Monotremata_ (1888). -[115] W. Kuekenthal, _Anat. Anz._ VI. p. 364, 1891. C. Roese, _Anat. +[115] W. Kükenthal, _Anat. Anz._ VI. p. 364, 1891. C. Röse, _Anat. Anz._ VII. p. 639. [116] These bones however have no connection with the marsupium, being @@ -14065,7 +14031,7 @@ sesamoid bones forming ossifications in the inner tendon of the external oblique muscle, and are developed as supports for the abdominal wall. Very similar structures have been independently developed in various Amphibians, Reptiles and monodelphian Mammals. -See W. Leche, _Biol. Foeren._ III. p. 120. +See W. Leche, _Biol. Fören._ III. p. 120. [117] See H. Gadow, _P.Z.S._ 1892, p. 361. @@ -14082,13 +14048,13 @@ Trans._ 1865. [120] Epiphyses are fully developed in _Halitherium_, and traces occur in _Manatus_. -[121] See P.J. van Beneden and P. Gervais, _Osteographie des Cetaces_, +[121] See P.J. van Beneden and P. Gervais, _Ostéographie des Cétacés_, 1869-80. [122] H. Wincza, _Morphol. Jahrb._ XVI., p. 647. -[123] See M. Pavlow, "Etudes sur l'histoire paleontologique des -Ongules." _Bull. Soc. Moscou_, 1887--1890. +[123] See M. Pavlow, "Études sur l'histoire paléontologique des +Ongulés." _Bull. Soc. Moscou_, 1887--1890. [124] In a _plantigrade_ animal the whole of the foot is placed on the ground in walking. A _digitigrade_ animal places only its toes on the @@ -14167,7 +14133,7 @@ Each tooth, as has been already described, consists of three distinct tissues, dentine and cement of dermal origin, and enamel of epidermal origin. -[Illustration FIG. 68. DENTITION OF A DOG (_Canis familiaris_) x 1/2. +[Illustration FIG. 68. DENTITION OF A DOG (_Canis familiaris_) × 1/2. (Camb. Mus.) _i_ 2. second incisor. @@ -14188,7 +14154,7 @@ are three molars on each side of the lower jaw, the last is wanting in the upper jaw. The dentition of the dog may then be represented by the formula - _i_ 3/3 _c_ 1/1 _pm_ 4/4 _m_ 2/3 x 2 = 42. + _i_ 3/3 _c_ 1/1 _pm_ 4/4 _m_ 2/3 × 2 = 42. In each jaw there is one large specially modified tooth called the =carnassial=, the teeth in front of this are more or less pointed and @@ -14596,7 +14562,7 @@ drawn out into a strong ridge, which forms the anterior part of the [Illustration FIG. 72. VERTICAL LONGITUDINAL SECTION TAKEN A LITTLE TO THE LEFT OF THE MIDDLE LINE THROUGH THE SKULL OF A DOG (_Canis -familiaris_) x 3/5. (Camb. Mus.) +familiaris_) × 3/5. (Camb. Mus.) 1. supra-occipital. 2. interparietal. @@ -14657,7 +14623,7 @@ anterior part of the frontal is produced to form the long nasal process, which is wedged in between the nasal and maxillae. [Illustration FIG. 73. DORSAL VIEW OF THE CRANIUM OF A DOG (_Canis -familiaris_) x 2/3. +familiaris_) × 2/3. 1. supra-occipital. 2. parietal. @@ -14897,7 +14863,7 @@ of membrane bone. 3. THE UPPER JAW. [Illustration FIG. 75. VENTRAL VIEW OF THE CRANIUM OF A DOG (_Canis -familiaris_) x 3/5. (Camb. Mus.) +familiaris_) × 3/5. (Camb. Mus.) 1. supra-occipital. 2. foramen magnum. @@ -15140,7 +15106,7 @@ communicate. C. THE RIBS AND STERNUM. [Illustration FIG. 76. STERNUM AND STERNAL RIBS OF A DOG (_Canis -familiaris_) x 1/2. +familiaris_) × 1/2. 1. presternum. 2. first sternebra of mesosternum. @@ -15279,7 +15245,7 @@ slightly larger than its proximal end. The proximal end articulates with the trochlea, the distal end with the bones of the carpus. [Illustration FIG. 77. BONES OF THE LEFT UPPER ARM AND FORE-ARM OF A -DOG (_Canis familiaris_) x 1/2. +DOG (_Canis familiaris_) × 1/2. A, humerus (seen from the posterior side); B, radius, C, ulna, both seen from the anterior side. @@ -15384,7 +15350,7 @@ posterior part of the bone is flattened below, forming the narrow =iliac surface= (fig. 78, A, 5). [Illustration FIG. 78. RIGHT INNOMINATE BONE, A, OF A FULL-GROWN -TERRIER, B, OF A COLLIE PUPPY. x 1. +TERRIER, B, OF A COLLIE PUPPY. × 1. A is seen from the ventral side, B from the inner or sacral side. @@ -15412,7 +15378,7 @@ tuberosity= (fig. 78, A, 10). The ischium meets its fellow in a ventral symphysis, and forms about one-third of the acetabulum. [Illustration FIG. 79. FRONT VIEW OF THE LEFT LEG BONES OF A DOG -(_Canis familiaris_) x 1/2. +(_Canis familiaris_) × 1/2. A femur, B tibia, C fibula, D patella. @@ -15470,7 +15436,7 @@ The shaft of the tibia ossifies from one centre, the distal end from a second, and the proximal end from two more. [Illustration FIG. 80. A, RIGHT MANUS, B, RIGHT PES OF A DOG (_Canis -familiaris_) x 1/2 (after VON ZITTEL). +familiaris_) × 1/2 (after VON ZITTEL). 1. bone representing the fused scaphoid, lunar and centrale. 2. cuneiform. @@ -15744,7 +15710,7 @@ more or less flattened. The various terms used in describing some of the forms of the surface of grinding teeth are defined on page 345. [Illustration FIG. 81. SKULL OF A YOUNG INDIAN RHINOCEROS (_R. -unicornis_), SHOWING THE CHANGE OF THE DENTITION x 1/7. (Brit. Mus.) +unicornis_), SHOWING THE CHANGE OF THE DENTITION × 1/7. (Brit. Mus.) 1. nasal. 2. frontal. @@ -15770,7 +15736,7 @@ by which the dentition of any mammal can be briefly expressed as a formula has been already described. The regular mammalian arrangement of teeth for each side is expressed by the formula - _i_ 3/3 _c_ 1/1 _pm_ 4/4 _m_ 3/3 x 2; total, 44. + _i_ 3/3 _c_ 1/1 _pm_ 4/4 _m_ 3/3 × 2; total, 44. MONOTREMATA. In _Echidna_ teeth are quite absent. In the young _Ornithorhynchus_[146] functional molar teeth of a multi-tubercular @@ -15781,7 +15747,7 @@ plates. MARSUPIALIA[147] have a heterodont dentition, which has generally been regarded as almost monophyodont, the only tooth which has an obvious deciduous predecessor being the last premolar. The researches of -Roese[148] and Kuekenthal[149] tend to show that the teeth of Marsupials +Röse[148] and Kükenthal[149] tend to show that the teeth of Marsupials are developed in the same way as in other mammals, and are diphyodont. In the case of the premolars, teeth which are homologous with the permanent teeth of other mammals begin to develop as lateral @@ -15899,7 +15865,7 @@ probably belonging to the milk dentition are present in the embryo, but they are never functional, and are altogether absent in the adult. The anterior of these germs are simple, the posterior ones are originally complex, but subsequently split up into simple teeth like -those of the anterior part of the jaw. Hence according to Kuekenthal, +those of the anterior part of the jaw. Hence according to Kükenthal, who described these structures, the Cetacean dentition was originally heterodont. @@ -15914,7 +15880,7 @@ dentition is typically _piscivorous_, being adapted for seizing active slippery animals such as fish. The prey is then swallowed entire without mastication. Sometimes the teeth are excessively numerous, reaching two hundred or more (fifty to sixty on each side of each jaw) -in _Pontoporia_. This multiplication of teeth is regarded by Kuekenthal +in _Pontoporia_. This multiplication of teeth is regarded by Kükenthal as due to the division into three parts of numbers of trilobed teeth similar to those of some seals. @@ -16062,7 +16028,7 @@ absent. The dental formula is _i_ (0--2)/(0--1) _c_ 0/(0--1) _pm_ 4/4 _m_ 3/3. [Illustration FIG. 82. PALATAL ASPECT OF THE CRANIUM AND MANDIBLE OF A -DONKEY (_Equus asinus_) x 1/5. (Camb. Mus.) +DONKEY (_Equus asinus_) × 1/5. (Camb. Mus.) 1. supra-occipital. 2. occipital condyle. @@ -16117,7 +16083,7 @@ incisors (fig. 83, _i_ 1) are pectinate or partially divided by vertical fissures, and the grinding teeth are of the rhinocerotic type. -[Illustration FIG. 83. SKULL OF _Procavia (Dendrohyrax) dorsalis_ x +[Illustration FIG. 83. SKULL OF _Procavia (Dendrohyrax) dorsalis_ × 2/3. (Camb. Mus.) 1. nasal. @@ -16237,7 +16203,7 @@ with generally an inner cusp, and a heel or talon (fig. 84, 4) behind the blade. The most thoroughly carnivorous type of dentition is seen in the -AEluroidea, and especially in the cat tribe (Felidae). In the genus +Æluroidea, and especially in the cat tribe (Felidae). In the genus _Felis_ the dental formula is _i_ 3/3 _c_ 1/1 _pm_ 3/2 _m_ 1/1, total 30. The incisors are very small, so as not to interfere with the action of the large canines, the lower carnassial is reduced to simply @@ -16261,7 +16227,7 @@ The dentition of the Cynoidea is most closely linked with that of the Arctoidea by means of fossil forms. [Illustration FIG. 85. MANDIBLE OF ISABELLINE BEAR (_Ursus -isabellinus_) x 1/2. (Camb. Mus.) +isabellinus_) × 1/2. (Camb. Mus.) 1. condyle. 2. coronoid process. @@ -16276,10 +16242,10 @@ isabellinus_) x 1/2. (Camb. Mus.) should be four.] In the Arctoidea the dentition is not so typically carnivorous as in -the AEluroidea and Cynoidea. In the bears, Ursidae, the molars have +the Æluroidea and Cynoidea. In the bears, Ursidae, the molars have broad flat tuberculated crowns (fig. 85). The dental formula in _Ursus_ is _i_ 3/3 _c_ 1/1 _pm_ 4/4 _m_ 2/3, total 42. The upper -carnassial (fig. 84, III.) differs from that of the AEluroidea and +carnassial (fig. 84, III.) differs from that of the Æluroidea and Cynoidea in having no inner lobe supported on a third root. In the large group of Mustelidae there are generally two molars in the lower and one in the upper jaw. The grinding teeth commonly have large, @@ -16290,7 +16256,7 @@ In the _CREODONTA_ there are no specially differentiated carnassial teeth. [Illustration FIG. 86. LEFT MANDIBULAR RAMUS OF THE SEA LEOPARD -(_Ogmorhinus leptonyx_) WITH THE ROOTS OF THE TEETH EXPOSED x 1/3. +(_Ogmorhinus leptonyx_) WITH THE ROOTS OF THE TEETH EXPOSED × 1/3. (Camb. Mus.) 1. condyle. @@ -16459,7 +16425,7 @@ _Manatus_ however there are only six cervical vertebrae and they are very variable. [Illustration FIG. 87. CERVICAL VERTEBRAE OF A YOUNG FIN WHALE -(_Balaenoptera musculus_) x 1/10. (Camb. Mus.) +(_Balaenoptera musculus_) × 1/10. (Camb. Mus.) 1. surface on the atlas for articulation with the occipital condyle of the skull. @@ -16490,7 +16456,7 @@ and 4) which enclose between them a wide space. These processes are not completely ossified till the animal is adult. [Illustration FIG. 88. ATLAS (B) AND AXIS (A) VERTEBRAE OF AN OX (_Bos -taurus_) x 1/4. (Camb. Mus.) +taurus_) × 1/4. (Camb. Mus.) 1. neural canal. 2. transverse process. @@ -16601,7 +16567,7 @@ dugong there are nineteen thoracic and four lumbar, and in the manatee seventeen thoracic and two lumbar. In the CETACEA the number of thoracic vertebrae varies from nine in -_Hyperoodon_ to fifteen or sixteen in _Balaenoptera_, and the number +_Hyperoödon_ to fifteen or sixteen in _Balaenoptera_, and the number of lumbar vertebrae from three in _Inia_ to twenty-four or more in _Delphinus_. The lumbar vertebrae are often very loosely articulated together and the zygapophyses sometimes as in the Dolphins are placed @@ -16634,7 +16600,7 @@ these are thoracic and eight lumbar. In _Phenacodus_ the convergence of the neural spines to a centre of motion is well seen. [Illustration FIG. 89. FIRST AND SECOND THORACIC VERTEBRAE OF AN OX -(_Bos taurus_) x 1/3. (Camb. Mus.) +(_Bos taurus_) × 1/3. (Camb. Mus.) 1. neural spine. 2. neural canal. @@ -16841,9 +16807,9 @@ Sci._, Vol. XXIX. 1889; also Oldfield Thomas, _P.R.S._, XLVI. (1889). [147] W.H. Flower, _Phil. Trans._, vol. 156, pp. 631--641, 1867; also Oldfield Thomas, _Phil. Trans._, pp. 443--462, 1887. -[148] C. Roese, _Anat. Anz._ VII., p. 639. +[148] C. Röse, _Anat. Anz._ VII., p. 639. -[149] W. Kuekenthal, _Anat. Anz._ VI., p. 364. +[149] W. Kükenthal, _Anat. Anz._ VI., p. 364. [150] See p. 348. @@ -16921,8 +16887,8 @@ inferior dental and mental foramina of the mandible are all very large. [Illustration FIG. 90. HALF FRONT VIEW[165] OF THE SKULLS OF A -TASMANIAN WOLF (_Thylacinus cynocephalus_) (to the left) x 3/8; AND OF -A HAIRY-NOSED WOMBAT (_Phascolomys latifrons_) (to the right) x 3/8. +TASMANIAN WOLF (_Thylacinus cynocephalus_) (to the left) × 3/8; AND OF +A HAIRY-NOSED WOMBAT (_Phascolomys latifrons_) (to the right) × 3/8. (Camb. Mus.) 1. premaxillae. @@ -16979,7 +16945,7 @@ in a somewhat spout-like manner (fig. 91, 6). In both genera the thyro-hyals are ankylosed with the basi-hyal. [Illustration FIG. 91. SKULL OF A TWO-FINGERED SLOTH (_Choloepus -didactylus_) x 1/2. (Camb. Mus.) +didactylus_) × 1/2. (Camb. Mus.) 1. anterior nares. 2. postorbital process of the frontal. @@ -17035,7 +17001,7 @@ also for the roughness of the bones, and the irregular manner in which they are united together. [Illustration FIG. 92. LATERAL VIEW OF THE SKULL OF _Rhytina stelleri_ -x 1/8. (Brit. Mus.) +× 1/8. (Brit. Mus.) 1. frontal. 2. parietal. @@ -17135,7 +17101,7 @@ narrow and without turbinals and the nasals (fig. 93, 19) are almost as much reduced as in Sirenia. [Illustration FIG. 93. A, LATERAL VIEW, AND B, LONGITUDINAL SECTION OF -THE SKULL OF A YOUNG CA'ING WHALE (_Globicephalus melas_) x 1/6. +THE SKULL OF A YOUNG CA'ING WHALE (_Globicephalus melas_) × 1/6. (Brit. Mus.) 1. basi-occipital. @@ -17185,7 +17151,7 @@ are exceedingly long and narrow, and arising from the maxillae are two great plates of bone which nearly meet above. In the Physeteridae the skull is raised into a very prominent crest at -the vertex behind the nares. In front of this in _Hyperoodon_ a pair +the vertex behind the nares. In front of this in _Hyperoödon_ a pair of ridges occur, formed by outgrowths from the maxillae. In the old male these ridges reach an enormous size and almost meet in the middle line. In _Physeter_, the Sperm whale, these ridges are not developed; @@ -17216,7 +17182,7 @@ The skulls in the different groups of Artiodactyla differ considerably from one another. [Illustration FIG. 94. A, CRANIUM AND B, MANDIBLE OF A PIG (_Sus -scrofa_) x 1/5. (Camb. Mus.) +scrofa_) × 1/5. (Camb. Mus.) 1. jugal. 2. postorbital process of the frontal. @@ -17263,7 +17229,7 @@ portion and a small coronoid process (fig. 94, B, 13). The hyoid differs from that of most Ungulates, the stylo-hyal being very imperfectly ossified. -[Illustration FIG. 95. MANDIBLE OF A HIPPOPOTAMUS (_H. amphibius_) x +[Illustration FIG. 95. MANDIBLE OF A HIPPOPOTAMUS (_H. amphibius_) × 1/7. (Camb. Mus.) The second incisor of the left side is missing and the crowns of the @@ -17484,7 +17450,7 @@ not so small as in _Uintatherium_. [Illustration FIG. 96. SKULL OF A YOUNG INDIAN ELEPHANT (_Elephas indicus_), SEEN FROM THE RIGHT SIDE, THE ROOTS OF THE TEETH HAVE BEEN -EXPOSED. x 1/8. (Camb. Mus.) +EXPOSED. × 1/8. (Camb. Mus.) 1. exoccipital. 2. parietal. @@ -17538,7 +17504,7 @@ exceptional condition. [Illustration FIG. 97. LONGITUDINAL SECTION TAKEN RATHER TO THE RIGHT OF THE MIDDLE LINE OF THE SKULL OF A YOUNG INDIAN ELEPHANT (_E. -Indicus_) x 1/8. (Camb. Mus.) +Indicus_) × 1/8. (Camb. Mus.) 8. anterior nares. 10. periotic. @@ -17586,7 +17552,7 @@ shutting off from this vacuity a space which is the true infra-orbital foramen. [Illustration FIG. 98. HALF FRONT VIEW OF THE SKULL OF A PORCUPINE -(_Hystrix cristata_) x 1/2. (Camb. Mus.) +(_Hystrix cristata_) × 1/2. (Camb. Mus.) 1. nasal. 2. maxillo-turbinals. @@ -17783,7 +17749,7 @@ formed by the large supra-occipital and frontals, but mainly by the parietals (fig. 99, 1), which in Man are of enormous extent. [Illustration FIG. 99. HALF FRONT VIEW OF THE SKULLS, _A_ OF AN OLD, -_B_ OF A YOUNG GORILLA (_Gorilla savagei_) x 1/4. (Camb. Mus.) +_B_ OF A YOUNG GORILLA (_Gorilla savagei_) × 1/4. (Camb. Mus.) 1. parietal. 2. sagittal crest. @@ -17992,7 +17958,7 @@ Two distinct types of sternum are met with in the CETACEA. In the Odontoceti the sternum consists of a broad presternum followed by three or four mesosternal segments, but with no xiphisternum. Indications of the original median fissure can be traced, and are very -evident in _Hyperoodon_. In the Mystacoceti, on the other hand, the +evident in _Hyperoödon_. In the Mystacoceti, on the other hand, the sternum consists simply of a broad flattened presternum which is sometimes more or less heart-shaped, sometimes cross-shaped. Only a single pair of ribs are united to it. @@ -18082,7 +18048,7 @@ to twenty-two. The Elephant has nineteen to twenty-one pairs, seven of which may be floating ribs. [Illustration FIG. 101. SKELETON OF A CAPE BUFFALO (_Bubalus caffer_). -The left scapula is omitted for the sake of clearness x 1/17. (Brit. +The left scapula is omitted for the sake of clearness × 1/17. (Brit. Mus.) 1. premaxillae. @@ -18137,7 +18103,7 @@ Lacertilia. [Illustration FIG. 102. _A_, SIDE VIEW, _B_, DORSAL VIEW OF THE SHOULDER GIRDLE AND PART OR THE STERNUM OF THE SPINY ANTEATER -(_Echidna aculeata_) x 1. (After PARKER.) +(_Echidna aculeata_) × 1. (After PARKER.) 1. scapula. 2. suprascapula. @@ -18191,7 +18157,7 @@ acromion nor coracoid process is ever much developed. In no adult Ungulate except _Typotherium_ is there any trace of a clavicle, but a vestigial clavicle has been described in early embryos of sheep[171]. -[Illustration FIG. 103. SKELETON OF A LLAMA (_Auchenia glama_) x 1/18. +[Illustration FIG. 103. SKELETON OF A LLAMA (_Auchenia glama_) × 1/18. (Brit. Mus.) 1. hyoid. @@ -18257,7 +18223,7 @@ prescapular fossa being specially large, and being traversed by a ridge, which converges to meet the spine. [Illustration FIG. 104. DORSAL VIEW OF THE STERNUM AND RIGHT HALF OF -THE SHOULDER-GIRDLE OF _Mus sylvaticus_ x 4. (After PARKER.) +THE SHOULDER-GIRDLE OF _Mus sylvaticus_ × 4. (After PARKER.) 1. postscapular fossa. 2. prescapular fossa. @@ -18643,11 +18609,11 @@ and not with the scaphoid. There is no separate centrale. [Illustration FIG. 107. LEFT MANUS OF -_A. Coryphodon hamatus._ (After MARSH.) x 1/5. +_A. Coryphodon hamatus._ (After MARSH.) × 1/5. -_B. Phenacodus primaevus._ (After COPE.) x 1/3. +_B. Phenacodus primaevus._ (After COPE.) × 1/3. -_C. Procavia (Dendrohyrax) arboreus._ (After VON ZITTEL.) x 6/7. +_C. Procavia (Dendrohyrax) arboreus._ (After VON ZITTEL.) × 6/7. 1. scaphoid. 2. lunar. @@ -18856,7 +18822,7 @@ ischial tuberosities are large in the old world monkeys. [Illustration FIG. 108. LEFT ANTERIOR AND POSTERIOR LIMB AND LIMB GIRDLE OF _Uintatherium mirabile_. The anterior limb is to the left, -the posterior to the right x 1/10. (From casts, Brit. Mus.) +the posterior to the right × 1/10. (From casts, Brit. Mus.) 1. ilium. 2. head of femur. @@ -18914,7 +18880,7 @@ the pelvis by a definite acetabulum. [Illustration FIG. 109. LEFT FEMUR OF AN OX (_Bos taurus_) (to the left) AND OF A SUMATRAN RHINOCEROS (_R. sumatrensis_) (to the right). -x 1/6. (Camb. Mus.) +× 1/6. (Camb. Mus.) 1. head. 2. great trochanter. @@ -19103,10 +19069,10 @@ wanting. [Illustration - FIG. 110. _A._ LEFT PES OF A TAPIR (_Tapirus americanus_). x 1/6. - _B._ RIGHT PES OF A RHINOCEROS (_R. sumatrensis_). x 1/8. - _C._ (CAST OF) RIGHT PES OF _Hipparion gracile_. x 1/7. - _D._ RIGHT PES OF A HORSE (_Equus caballus_). x 1/10. (All Camb. Mus.) + FIG. 110. _A._ LEFT PES OF A TAPIR (_Tapirus americanus_). × 1/6. + _B._ RIGHT PES OF A RHINOCEROS (_R. sumatrensis_). × 1/8. + _C._ (CAST OF) RIGHT PES OF _Hipparion gracile_. × 1/7. + _D._ RIGHT PES OF A HORSE (_Equus caballus_). × 1/10. (All Camb. Mus.) 1. calcaneum. 2. astragalus. @@ -19252,7 +19218,7 @@ Ungulate foot," _T. Amer. Phil. Soc._ 1889. [174] See O.C. Marsh, various papers including "Fossil horses in America," _Amer. Natural._ 1874; "Polydactyl horses," _Amer. J. Sci._ -1879 and 1892. M. Pavlow, "Le developpement des Equides," _Bul. Soc. +1879 and 1892. M. Pavlow, "Le développement des Equidés," _Bul. Soc. Moscou_, 1887, and subsequent papers in the same. Osborn and Wortman, "On the Perissodactyls of the White River beds," _Bull. Amer. Mus._ Dec. 23rd, 1895. @@ -19301,7 +19267,7 @@ LIST OF AUTHORS REFERRED TO. Bridge, T.W., 123 - Bruehl, C.B., 210 + Brühl, C.B., 210 Burmeister, H., 351, 424 @@ -19327,7 +19293,7 @@ LIST OF AUTHORS REFERRED TO. Fritsch, A., 135 - Fuerbringer, M., 295 + Fürbringer, M., 295 Gadow, H., 40, 112, 190, 295, 343, 350 @@ -19336,7 +19302,7 @@ LIST OF AUTHORS REFERRED TO. Gervais, P., 353 - Guenther, A.C.L.G., 70, 104 + Günther, A.C.L.G., 70, 104 Haslam, G., 151 @@ -19367,9 +19333,9 @@ LIST OF AUTHORS REFERRED TO. Klein, E., 11 - Koelliker, A., 9 + Kölliker, A., 9 - Kuekenthal, W., 349, 422 + Kükenthal, W., 349, 422 Lankester, E. Ray, 51 @@ -19421,12 +19387,12 @@ LIST OF AUTHORS REFERRED TO. Ridewood, W.G., 106, 164 - Roese, C., 422 + Röse, C., 422 Sagemehl, M., 104 - Schaefer, E., 11 + Schäfer, E., 11 Scott, W.B., 368 @@ -19550,15 +19516,15 @@ INDEX. Adjutant, _41_; clavicles, 338 - AEgithognathous, 335 + Ægithognathous, 335 - AEluroidea, _48_, _369_; + Æluroidea, _48_, _369_; teeth, 437 - AEpyornis, _40_; + Æpyornis, _40_; tibio-tarsus, 341 - AEpyornithes, _40_, _299_ + Æpyornithes, _40_, _299_ Aftershaft, 328 @@ -20173,7 +20139,7 @@ INDEX. see Ox Bottlenose, _44_; - see _Hyperoodon_ + see _Hyperoödon_ Bovidae, _46_; pes, 523; @@ -22246,7 +22212,7 @@ INDEX. _Hyperodapedon_, _37_, _198_; premaxillae, 284 - _Hyperoodon_, _44_; + _Hyperoödon_, _44_; skull, 464; sternum, 489; thoracic vertebrae, 448 @@ -22505,7 +22471,7 @@ INDEX. pes, 522; tail, 453 - Kuekenthal, W., on teeth of Cetacea, 426; + Kükenthal, W., on teeth of Cetacea, 426; on teeth of Marsupials, 422 @@ -23672,7 +23638,7 @@ INDEX. _Phacochaerus_, _45_; teeth, 428 - _Phaethon_, _41_; + _Phaëthon_, _41_; metatarsals, 342 _Phalacrocorax_, _41_ @@ -24397,7 +24363,7 @@ INDEX. _Pristis_, 119; -- of sternum, duck, 321 - Roese, C., on teeth of Marsupials, 422 + Röse, C., on teeth of Marsupials, 422 Ruminantia, _46_, _359_; auditory ossicles, 487; @@ -25706,19 +25672,19 @@ KANTHACK, M.D., M.R.C.P. Crown 8vo. 6_s._ M.A., F.R.S., Fellow of Emmanuel College. In 2 vols. Demy 8vo. Vol. I. 12_s._ [Vol. II. _In the Press._] - _Revue Scientifique._ Nous ne pouvons entrer dans le detail; - mais il est evident que M. Seward, praticien distingue - lui-meme, est tres au courant des travaux des autres, il les + _Revue Scientifique._ Nous ne pouvons entrer dans le détail; + mais il est évident que M. Seward, praticien distingué + lui-même, est très au courant des travaux des autres, il les cite et utilise abondamment; et ceci est fait pour inspirer - confiance. Au total, son oeuvre est appuyee sur des bases - solides, et elle restera sans doute longtemps le breviaire, le - manuel de ceux qui veulent, non pas seulement s'initier a la - paleobotanique, mais retrouver les renseignements qui sont - epars dans des centaines de monographies qu'on a souvent peine - a se procurer. Le livre de M. Seward fait partie des _Cambridge + confiance. Au total, son oeuvre est appuyée sur des bases + solides, et elle restera sans doute longtemps le bréviaire, le + manuel de ceux qui veulent, non pas seulement s'initier à la + paléobotanique, mais retrouver les renseignements qui sont + épars dans des centaines de monographies qu'on a souvent peine + à se procurer. Le livre de M. Seward fait partie des _Cambridge Natural Science Manuals_, et il est digne de cette collection, - qui est elle-meme digne du foyer scientifique universellement - repute, ou il a vu le jour. + qui est elle-même digne du foyer scientifique universellement + réputé, où il a vu le jour. _Guardian._ We have already alluded to the spirit of caution which characterises the book, and we may add that it promises @@ -25846,361 +25812,4 @@ College. With numerous Illustrations. Demy 8vo. End of Project Gutenberg's The Vertebrate Skeleton, by Sidney H. 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You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org - - -Title: The Vertebrate Skeleton - -Author: Sidney H. Reynolds - -Release Date: August 9, 2013 [EBook #43431] - -Language: English - -Character set encoding: ISO-8859-1 - -*** START OF THIS PROJECT GUTENBERG EBOOK THE VERTEBRATE SKELETON *** - - - - -Produced by Chris Curnow, Mark Young and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - - - - - - CAMBRIDGE BIOLOGICAL SERIES. - - GENERAL EDITOR:--ARTHUR E. SHIPLEY, M.A. - - FELLOW AND TUTOR OF CHRIST'S COLLEGE, CAMBRIDGE. - - - - - THE - - VERTEBRATE SKELETON. - - - - - London: C.J. CLAY AND SONS, - CAMBRIDGE UNIVERSITY PRESS WAREHOUSE, - AVE MARIA LANE, - - AND - - H.K. LEWIS, - 136, GOWER STREET, W.C. - - [Illustration] - - Glasgow: 50, WELLINGTON STREET. - - Leipzig: F.A. BROCKHAUS. - - New York: THE MACMILLAN COMPANY. - - Bombay and Calcutta: MACMILLAN AND CO., LTD. - - - [_All Rights reserved._] - - - - - THE - - VERTEBRATE SKELETON - - BY - - SIDNEY H. REYNOLDS, M.A., - - TRINITY COLLEGE, CAMBRIDGE; - LECTURER AND DEMONSTRATOR IN GEOLOGY AND ZOOLOGY AT UNIVERSITY - COLLEGE, BRISTOL. - - Cambridge: - - AT THE UNIVERSITY PRESS. - - 1897 - - [_All Rights reserved._] - - - - - =Cambridge=: - - PRINTED BY J. & C.F. CLAY, - AT THE UNIVERSITY PRESS. - - - - -PREFACE. - - -IN the following pages the term skeleton is used in its widest sense, -so as to include exoskeletal or tegumentary structures, as well as -endoskeletal structures. It was thought advisable to include some -account of the skeleton of the lowest Chordata--animals which are not -strictly vertebrates, but it seemed undesirable to alter the title of -the book in consequence. - -The plan adopted in the treatment of each group has been to give first -an account of the general skeletal characters of the group in question -and of its several subdivisions; secondly to describe in detail the -skeleton of one or more selected types; and thirdly to treat the -skeleton as developed in the group organ by organ. - -A beginner is advised to commence, not with the introductory chapter, -but with the skeleton of the Dogfish, then to pass to the skeletons of -the Newt and Frog, and then to that of the Dog. After that he might -pass to the introductory chapter and work straight through the book. I -have endeavoured to make the account of each type skeleton complete in -itself; this has necessitated a certain amount of repetition,--a -fault that I have found it equally difficult to avoid in other parts -of the book. - -Throughout the book generic names are printed in italics; and italics -are used in the accounts of the type skeletons for the names of -membrane bones. Clarendon type is used to emphasise certain words. In -the classificatory table the names of extinct genera only, are printed -in italics. - -In a book in which an attempt is made to cover to some extent such a -vast field, it would be vain to hope to have avoided many errors both -of omission and commission, and I owe it to the kindness of several -friends that the errors are not much more numerous. I cannot however -too emphatically say that for those which remain I alone am -responsible. Messrs C.W. Andrews, E. Fawcett, S.F. Harmer, J. Graham -Kerr, and B. Rogers have all been kind enough to help me by reading -proofs or manuscript, while the assistance that I have received from -Dr Gadow during the earlier stages and from Prof. Lloyd Morgan and Mr -Shipley throughout the whole progress of the work has been very great. -To all these gentlemen my best thanks are tendered. - -All the figures except 1, 35, 55, and 84 were drawn by Mr Edwin -Wilson, to whose care and skill I am much indebted. The majority are -from photographs taken by my sister Miss K.M. Reynolds or by myself in -the British Museum and in the Cambridge University Museum of Zoology, -and I take this opportunity of thanking Sir W.H. Flower and Mr S.F. -Harmer for the facilities they have afforded and for permission to -figure many objects in the museums respectively under their charge. I -have also to thank (1) Prof. von Zittel for permission to reproduce -figs. 27, 41, 52, 69, 70, 80, 106 A, and 107 C; (2) Sir W.H. Flower -and Messrs A. and C. Black for figs. 1 and 84; (3) Prof. O.C. Marsh -and Dr H. Woodward for fig. 35; (4) Dr C.H. Hurst and Messrs Smith, -Elder, and Co. for fig. 55. - -A few references are given, but no attempt has been made to give -anything like a complete list. The abbreviations of the titles of -periodicals are those used in the _Zoological Record_. - -I have always referred freely to the textbooks treating of the -subjects dealt with, and in particular I should like to mention that -the section devoted to the skeleton of mammals is, as it could hardly -fail to be, to a considerable extent based on Sir W.H. Flower's -_Osteology of the Mammalia_. - - SIDNEY H. REYNOLDS. - - _March 10, 1897._ - - - - - CONTENTS. - - - PAGE - CHAPTER I. - - Introductory account of the skeleton in general 1 - - - CHAPTER II. - - Classification 30 - - - CHAPTER III. - - Skeleton of Hemichordata, Urochordata and Cephalochordata 50 - - - CHAPTER IV. - - Skeletal characters of the Vertebrata. The skeleton in the - Cyclostomata 53 - - - CHAPTER V. - - Skeletal characters of the Ichthyopsida. Characters of the - several groups of Pisces 59 - - - CHAPTER VI. - - The skeleton of the Dogfish (Scyllium canicula) 71 - - - CHAPTER VII. - - The skeleton of the Codfish (_Gadus morrhua_) and the skull of - the Salmon (_Salmo salar_) 83 - - - CHAPTER VIII. - - General account of the skeleton in Fishes 104 - - - CHAPTER IX. - - Characters of the several groups of Amphibia 133 - - - CHAPTER X. - - The skeleton of the Newt (_Molge cristata_) 138 - - - CHAPTER XI. - - The skeleton of the Frog (_Rana temporaria_) 151 - - - CHAPTER XII. - - General account of the skeleton in Amphibia 168 - - - CHAPTER XIII. - - Skeletal characters of the Sauropsida. Characters of the - several groups of Reptiles 189 - - - CHAPTER XIV. - - The skeleton of the Green Turtle (_Chelone midas_) 214 - - - CHAPTER XV. - - The skeleton of the Crocodile (_Crocodilus palustris_) 237 - - - CHAPTER XVI. - - General account of the skeleton in Reptiles 270 - - - CHAPTER XVII. - - Characters of the several groups of Birds 295 - - - CHAPTER XVIII. - - The skeleton of the Wild Duck (_Anas boschas_) 302 - - - CHAPTER XIX. - - General account of the skeleton in Birds 328 - - - CHAPTER XX. - - Characters of the several groups of Mammalia 343 - - - CHAPTER XXI. - - The skeleton of the Dog (_Canis familiaris_) 374 - - - CHAPTER XXII. - - General account of the skeleton in Mammalia. The exoskeleton - and vertebral column 416 - - - CHAPTER XXIII. - - General account of the skeleton in Mammalia (_continued_). The - skull and appendicular skeleton 455 - - - - - LIST OF ILLUSTRATIONS. - - - FIG. PAGE - - 1 Diagrammatic sections of various forms of teeth 6 - - 2 Cervical vertebrae of an Ox (_Bos taurus_) 15 - - 3 Diagram of the skeleton of _Amphioxus lanceolatus_ 51 - - 4 Dorsal, lateral, and ventral views of the skull of - _Petromyzon marinus_ 56 - - 5 Skull of a male _Chimaera monstrosa_ 65 - - 6 Lateral view of the skull of a Dogfish (_Scyllium canicula_) 75 - - 7 Semidorsal view of the pectoral girdle and fins of a Dogfish - (_Scyllium canicula_) 80 - - 8 Dorsal view of the pelvic girdle and fins of a male Dogfish - (_Scyllium canicula_) 81 - - 9 Dorsal and ventral views of the cranium of a Salmon (_Salmo - salar_) from which most of the membrane bones have been - removed 88 - - 10 Lateral view of the chondrocranium of a Salmon (_Salmo - salar_) 90 - - 11 Lateral view of the skull of a Salmon (_Salmo salar_) 92 - - 12 Mandibular and hyoid arches of a Cod (_Gadus morrhua_) 99 - - 13 Right half of the pectoral girdle and right pectoral fin of - a Cod (_Gadus morrhua_) 102 - - 14 Diagram of a section through the jaw of a Shark - (_Odontaspis americanus_) showing the succession of - teeth 107 - - 15 Part of the lower jaw of a Shark (_Galeus_) 108 - - 16 Skulls of _Notidanus_ and _Cestracion_ 118 - - 17 Dorsal view of the branchial arches of _Heptanchus_ 120 - - 18 Lateral view of the skull of a Sturgeon - (_Acipenser sturio_) 122 - - 19 Dorsal and ventral views of the cranium of - _Ceratodus miolepis_ 125 - - 20 Lateral view of the skeleton of _Ceratodus miolepis_ 128 - - 21 Dorsal, ventral and lateral views of the skull of a Newt - (_Molge cristata_) 142 - - 22 Ventral and lateral views of the shoulder-girdle and - sternum of an old male Crested Newt (_Molge cristata_) 146 - - - 23 Right posterior and anterior limbs of a Newt (_Molge - cristata_) 148 - - 24 Dorsal and ventral views of the cranium of a Common Frog - (_Rana temporaria_) 155 - - 25 Dorsal and ventral views of the cranium of a Common Frog - (_Rana temporaria_) from which the membrane bones have - mostly been removed 157 - - 26 Lateral view of the skull and posterior view of the - cranium of a Common Frog (_Rana temporaria_) 159 - - 27 Dorsal view of the skull of a Labyrinthodont (_Capitosaurus - nasutus_) 176 - - 28 Ventral view of the cranium, and lateral view of the - cranium and mandible of _Siphonops annulatus_ 178 - - 29 Visceral arches of Amphibia: A, _Molge cristata_; B, _Rana - temporaria_, adult; C, Tadpole of _Rana_; D, _Siredon - pisciformis_ 181 - - 30 Shoulder-girdle and sternum of an adult male Common Frog - (_Rana temporaria_), and of an adult female - _Docidophryne gigantea_ 183 - - 31 A, Right antibrachium and manus of a larval Salamander - (_Salamandra maculosa_); B, Right tarsus and adjoining - bones of _Molge sp._ 186 - - 32 Lateral and dorsal views of the skull of an _Ichthyosaurus_ 196 - - 33 Lateral view and longitudinal section of the skull of a - Lizard (_Varanus varius_) 201 - - 34 Lateral view of the shoulder-girdle of a Lizard (_Varanus_) 202 - - 35 Restored skeleton of _Ceratosaurus nasicornis_ 206 - - 36 Dorsal and ventral views of the carapace of a Loggerhead - Turtle (_Thalassochelys caretta_) 216 - - 37 Plastron of a Green Turtle (_Chelone midas_) 218 - - 38 The skull of a Green Turtle (_Chelone midas_) 223 - - 39 Longitudinal vertical section through the cranium of a - Green Turtle (_Chelone midas_) 226 - - 40 Anterior limb of a young Hawksbill Turtle (_Chelone - imbricata_), and posterior limb of a large Green Turtle - (_Chelone midas_) 234 - - 41 The first four cervical vertebrae of a Crocodile - (_Crocodilus vulgaris_) 239 - - 42 Anterior view of a late thoracic and the first sacral - vertebrae of a Crocodile (_Crocodilus palustris_) 242 - - - 43 Palatal aspect of the cranium and mandible of an Alligator - (_Caiman latirostris_) 245 - - 44 Lateral view of the skull of an Alligator (_Caiman - latirostris_) 248 - - 45 Longitudinal section through the skull of an Alligator - (_Caiman latirostris_) 253 - - 46 Sternum and associated membrane bones of a Crocodile - (_Crocodilus palustris_) 261 - - 47 Left half of the pectoral girdle of an Alligator - (_Caiman latirostris_) 262 - - 48 Right anterior and posterior limbs of an Alligator - (_Caiman latirostris_) 264 - - 49 Pelvis and sacrum of an Alligator (_Caiman latirostris_) 267 - - 50 Preparation of part of the right mandibular ramus of - _Crocodilus palustris_ 274 - - 51 Dorsal and ventral views of the skull of a Common Snake - (_Tropidonotus natrix_) 279 - - 52 Skull of Hatteria (_Sphenodon punctatus_) 282 - - 53 Hyoids of an Alligator (_Caiman latirostris_), and of a - Green Turtle (_Chelone midas_) 285 - - 54 Ventral view of the shoulder-girdle and sternum of - _Loemanctus longipes_ 287 - - 55 Left half of the skeleton of a Common Fowl (_Gallus - bankiva_) 301 - 56 The wing of a Wild Duck (_Anas boschas_) 304 - - 57 Wings of a Wild Duck with the coverts removed (_Anas - boschas_) 305 - - 58 Dorsal and ventral views of the pelvis and sacrum of a Duck - (_Anas boschas_) 311 - - 59 Skull of a Duck (_Anas boschas_) 312 - - 60 A, Ventral view of the cranium of a Duck (_Anas boschas_); - B, Cranium and mandible seen from the left side 313 - - 61 Lateral view of the pelvis and sacrum of a Duck (_Anas - boschas_) 325 - 62 Third cervical vertebra of an Ostrich (_Struthio camelus_) 331 - - 63 Shoulder-girdle and sternum of A, Black Vulture (_Vultur - cinereus_); B, Peacock (_Pavo cristatus_); C, Pelican - (_Pelicanus conspicillatus_) 337 - - 64 Bones of the right wing of A, a Penguin; B, an Ostrich - (_Struthio camelus_) and C, a Gannet (_Sula alba_) 339 - - 65 Pelvic girdle and sacrum of A, Cassowary (_Casuarius - galeatus_); B, Owen's Apteryx (_A. oweni_); C, - Broad-billed Rhea (_R. macrorhyncha_); D, Ostrich - (_Struthio camelus_) 340 - - 66 Ventral view of the shoulder-girdle and sternum of a - Duckbill (_Ornithorhynchus paradoxus_) 347 - - 67 Cervical vertebrae of a Ca'ing Whale (_Globicephalus - melas_) 354 - - 68 Dentition of a Dog (_Canis familiaris_) 375 - - 69 Atlas and axis vertebrae of a Dog (_Canis familiaris_) 379 - - 70 Second thoracic and second lumbar vertebrae of a Dog - (_Canis familiaris_) 382 - - 71 Diagram of the relations of the principal bones in the - Mammalian skull 385 - - 72 Vertical longitudinal section through skull of a Dog - (_Canis familiaris_) 387 - - 73 Dorsal view of the cranium of a Dog (_Canis familiaris_) 389 - - 74 Diagram of the mammalian tympanic cavity and associated - bones 391 - - 75 Ventral view of the cranium of a Dog (_Canis familiaris_) 396 - - 76 Sternum and sternal ribs of a Dog (_Canis familiaris_) 403 - - 77 Bones of the left upper arm and fore-arm of a Dog (_Canis - familiaris_) 407 - - 78 Right innominate bone, A, of a full-grown Terrier; B, of a - Collie Puppy 410 - - 79 Left leg bones of a Dog (_Canis familiaris_) 411 - - 80 A, Right manus; B, Right pes of a Dog (_Canis familiaris_) 413 - - 81 Skull of a young Indian Rhinoceros (_R. unicornis_) showing - the change of the dentition 421 - - 82 Palatal aspect of the cranium and mandible of a Donkey - (_Equus asinus_) 431 - - 83 Skull of _Procavia (Dendrohyrax) dorsalis_ 433 - - 84 Carnassial or sectorial teeth of Carnivora 436 - - 85 Mandible of Isabelline Bear (_Ursus isabellinus_) 438 - - 86 Left mandibular ramus of the Sea Leopard (_Ogmorhinus - leptonyx_) 439 - - 87 Cervical vertebrae of a young Fin Whale (_Balaenoptera - musculus_) 444 - - 88 Atlas and axis vertebrae of an Ox (_Bos taurus_) 445 - - 89 First and second thoracic vertebrae of an Ox (_Bos taurus_) 449 - - 90 Skulls of Tasmanian Wolf (_Thylacinus cynocephalus_) and - Hairy-nosed Wombat (_Phascolomys latifrons_) 456 - - 91 Skull of Two-fingered Sloth (_Choloepus didactylus_) 458 - - 92 Skull of _Rhytina stelleri_ 460 - - - 93 Lateral view and longitudinal section of the skull of a - young Ca'ing Whale (_Globicephalus melas_) 463 - - 94 Cranium and mandible of a Pig (_Sus scrofa_) 466 - - 95 Mandible of a Hippopotamus (_Hippopotamus amphibius_) 467 - - 96 Skull of a young Indian Elephant (_Elephas indicus_) 474 - - 97 Longitudinal section of the skull of a young Indian - Elephant (_Elephas indicus_) 475 - - 98 Half-front view of the skull of a Porcupine (_Hystrix - cristata_) 477 - 99 Skulls of an old and of a young Gorilla (_Gorilla savagei_) 483 - - 100 Malleus, stapes, and incus of Man, Dog, and Rabbit 485 - - 101 Skeleton of a Cape Buffalo (_Bubalus caffer_) 492 - - 102 Lateral and dorsal views of the shoulder-girdle and part - of the sternum of the Spiny Anteater (_Echidna - aculeata_) 494 - - 103 Skeleton of a Llama (_Auchenia glama_) 496 - - 104 Dorsal view of the sternum and right half of the shoulder - girdle of _Mus sylvaticus_ 498 - - 105 Anterior surface of the right humerus of a Wombat - (_Phascolomys latifrons_) 500 - - 106 Manus of Perissodactyles: A, Left manus of _Tapirus_; B, - Right manus of _Titanotherium_; C, Left manus of - _Chalicotherium giganteum_ 508 - - 107 Left manus of A, _Coryphodon hamatus_; B, _Phenacodus - primaevus_; C, _Procavia (Dendrohyrax) arboreus_ 510 - - 108 Left anterior and posterior limbs and limb girdles of - _Uintatherium mirabile_ 516 - - 109 Left femur of an Ox (_Bos taurus_) and of a Sumatran - Rhinoceros (_Rhinoceros sumatrensis_) 518 - - 110 Pes of A, a Tapir (_Tapirus americanus_); B, a Rhinoceros - (_Rhinoceros sumatrensis_); C, _Hipparion gracile_; D, - a Horse (_Equus caballus_) 524 - - - - -ERRATA. - - - p. 172, note, _for_ 14 _read_ 15. - - p. 279, description of figure, _for_ Tropidinotus _read_ - Tropidonotus. - - p. 287, description of figure, _for_ shoulder-girdle of sternum - _read_ shoulder-girdle and sternum. - - p. 393, middle of page, _for_ VIII _read_ VII. - - p. 427, line 2, _for_ Grampus _read_ Killer. - - - - -CHAPTER I. - -INTRODUCTORY ACCOUNT OF THE SKELETON IN GENERAL. - - -BY the term =skeleton= is meant the hard structures whose function is -to support or to protect the softer tissues of the animal body. - -The skeleton is divisible into - -A. The EXOSKELETON, which is external; - -B. The ENDOSKELETON, which is as a rule internal; though in some -cases, e.g. the antlers of deer, endoskeletal structures become, as -development proceeds, external. - -In Invertebrates the hard, supporting structures of the body are -mainly =exoskeletal=, in Vertebrates they are mainly =endoskeletal=; -but the endoskeleton includes, especially in the skull, a number of -elements, the =dermal= or =membrane= bones, which are shown by -development to have been originally of external origin. These membrane -bones are so intimately related to the true endoskeleton that they -will be described with it. The simplest and lowest types of both -vertebrate and invertebrate animals have unsegmented skeletons; with -the need for flexibility however segmentation arose both in the case -of the invertebrate exoskeleton and the vertebrate endoskeleton. The -exoskeleton in vertebrates is phylogenetically older than the -endoskeleton, as is indicated by both palaeontology and embryology. -Palaeontological evidence is afforded by the fact that all the lower -groups of vertebrates--Fish, Amphibia, and Reptiles--had in former -geological periods a greater proportion of species protected by -well-developed dermal armour than is the case at present. -Embryological evidence tends the same way, inasmuch as dermal -ossifications appear much earlier in the developing animal than do the -ossifications in the endoskeleton. - -Skeletal structures may be derived from each of the three germinal -layers. Thus =hairs= and =feathers= are =epiblastic= in origin, -=bones= are =mesoblastic=, and the =notochord= is =hypoblastic=. - -The different types of skeletal structures may now be considered and -classified more fully. - - -A. EXOSKELETAL STRUCTURES. - -I. EPIBLASTIC (epidermal). - -Exoskeletal structures of epiblastic origin may be developed on both -the inner and outer surfaces of the Malpighian layer of the -epidermis[1]. Those developed on the outer surface include =hairs=, -=feathers=, =scales=, =nails=, =beaks= and =tortoiseshell=; and are -specially found in vertebrates higher than fishes. Those developed on -the inner surface of the Malpighian layer include only the =enamel= of -teeth and some kinds of scales. With the exception of feathers, which -are partly formed from the horny layer, all these parts are mainly -derived from the Malpighian layer of the epidermis. - -=Hairs= are slender, elongated structures which arise by the -proliferation of cells from the Malpighian layer of the epidermis. -These cells in the case of each hair form a short papilla, which sinks -inwards and becomes imbedded at the bottom of a follicle in the -dermis. Each hair is normally composed of an inner cellular pithy -portion containing much air, and an outer denser cortical portion of a -horny nature. Sometimes, as in Deer, the hair is mainly formed of the -pithy portion, and is then easily broken. Sometimes the horny part -predominates, as in the bristles of Pigs. A highly vascular dermal -papilla projects into the base of the hair. - -=Feathers=, like hairs, arise from epidermal papillae which become -imbedded in pits in the dermis. But the feather germ differs from the -hair germ, in the fact that it first grows out like a cone on the -surface of the epidermis, and that the horny as well as the Malpighian -layer takes part in its formation. - -=Nails=, =claws=, =hoofs=, and the =horns of Oxen= are also epidermal, -as are such structures as the =scales= of reptiles, of birds' feet, -and of _Manis_ among mammals, the =rattle= of the rattlesnake, the -=nasal horns= of _Rhinoceros_, and the =baleen= of whales. All these -structures will be described later. - -=Nails= arise in the interior of the epidermis by the thickening and -cornification of the stratum lucidum. The outer border of the nail -soon becomes free, and growth takes place by additions to the inner -surface and attached end. - -When a nail tapers to a sharp point it is called a =claw=. In many -cases the nails more or less surround the ends of the digits by which -they are borne. - -Horny =beaks= of epidermal origin occur casing the jaw-bones in -several widely distinct groups of animals. Thus among reptiles they -are found in Chelonia (tortoises and turtles) as well as in some -extinct forms; they occur in all living birds, in _Ornithorhynchus_ -among mammals, and in the larvae of many Amphibia. - -In a few animals, such as Lampreys and _Ornithorhynchus_, the jaws -bear horny tooth-like structures of epidermal origin. - -The =enamel= of teeth and of placoid scales is also epiblastic in -origin[2], and it may be well at this point to give some account of -the structure of teeth, though they are partly mesoblastic in origin. -The simplest teeth are those met with in sharks and dogfish, where -they are merely the slightly modified scales developed in the -integument of the mouth. They pass by quite insensible gradations into -normal placoid scales, such as cover the general surface of the body. -A =placoid scale=[3] is developed on a papilla of the dermis which -projects outwards and backwards, and is covered by the columnar -Malpighian layer of the epidermis. The outer layer of the dermal -papilla then gradually becomes converted into dentine and bone, while -enamel is developed on the inner side of the Malpighian layer, forming -a cap to the scale. The Malpighian and horny layers of the epidermis -get rubbed off the enamel cap, so that it comes to project freely on -the surface of the body. - -As regards their attachment teeth may be (1) attached to the fibrous -integument of the mouth, or (2) fixed to the jaws or other bones of -the mouth, or (3) planted in grooves, or (4) in definite sockets in -the jaw-bones (see p. 107). - -Teeth in general consist of three tissues, =enamel=, =dentine= and -=cement=, enclosing a central pulp-cavity containing blood-vessels and -nerves. Enamel is, however, often absent, as in all living Edentates. - -=Enamel= generally forms the outermost layer of the crown or visible -part of the tooth; it is the hardest tissue occurring in the animal -body and consists of prismatic fibres arranged at right angles to the -surface of the tooth. It is characterised by its bluish-white -translucent appearance. - -II. MESOBLASTIC (mesodermal). - -=Dentine= or =ivory= generally forms the main mass of a tooth. It is a -hard, white substance allied to bone. When examined microscopically -dentine is seen to be traversed by great numbers of nearly parallel -branching tubules which radiate outwards from the pulp-cavity. In -fishes as a rule, and sometimes in other animals, a variety of dentine -containing blood-vessels occurs, this is called =vasodentine=. - -=Cement= or =crusta petrosa= forms the outermost layer of the root of -the tooth. In composition and structure it is practically identical -with bone. In the more complicated mammalian teeth, besides enveloping -the root, it fills up the spaces between the folds of the enamel. - -The hard parts of a tooth commonly enclose a central pulp-cavity into -which projects the pulp, a papilla of the dermis including -blood-vessels and nerves. As long as growth continues the outer layers -of this pulp become successively calcified and added to the substance -of the dentine. In young growing teeth the pulp-cavity remains widely -open, but in mammals the general rule is that as a tooth gets older -and the crown becomes fully formed, the remainder of the pulp becomes -converted into one or more tapering roots which are imbedded in the -alveolar cavities of the jaws. The opening of the pulp-cavity is then -reduced to a minute perforation at the base of each root. A tooth of -this kind is called a =rooted= tooth. - -But it is not only in young teeth that the pulp-cavity sometimes -remains widely open; for some teeth, such as the tusks of Elephants -and the incisor teeth of Rodents, form no roots and continue to grow -throughout the animal's life. Such teeth are said to be rootless or to -have persistent pulps. - -An intermediate condition is seen in some teeth, such as the grinding -teeth of Horses. These teeth grow for a very long time, their crowns -wearing away as fast as their bases are produced; finally however -definite roots are formed and growth ceases. - -[Illustration FIG. 1. DIAGRAMMATIC SECTIONS OF VARIOUS FORMS OF TEETH -(from FLOWER). - -I. Incisor or tusk of elephant, with pulp-cavity persistently open at -base. II. Human incisor during development with root imperfectly -formed, and pulp-cavity widely open at base. III. Completely formed -human incisor, with pulp-cavity contracted to a small aperture at the -end of the root. IV. Human molar with broad crown and two roots. V. -Molar of Ox, with the enamel covering the crown, deeply folded and the -depressions filled with cement. The surface is worn by use, otherwise -the enamel coating would be continuous at the top of the ridges. In -all the figures the enamel is black, the pulp white, the dentine -represented by horizontal lines, and the cement by dots.] - -The teeth of any animal may be =homodont=, that is, all having the -same general character, or =heterodont=, that is, having different -forms adapted to different functions. The dentition is heterodont in a -few reptiles and the majority of mammals. - -SUCCESSION OF TEETH. In most fishes, and many amphibians and reptiles -the teeth can be renewed indefinitely. In sharks, for example, -numerous rows of reserve teeth are to be seen folded back behind those -in use (see fig. 15). The majority of mammals have only two sets of -teeth, and are said to be =diphyodont=; some have only a single series -(=monophyodont=). - -DEVELOPMENT OF TEETH. A brief sketch of the method in which -development of teeth takes place in the higher vertebrates may here be -given. Along the surface of the jaws a thickening of the epiblastic -epithelium takes place, giving rise to a ridge, which sinks inwards -into the tissue of the jaw, and it is known as the primary enamel -organ. At the points where teeth are to be developed special ingrowths -of this primary enamel organ take place, and into each there projects -a vascular dental papilla from the surrounding mesoblast of the jaw. -Each ingrowth of the enamel organ forms an =enamel cap=, which -gradually embraces the dental papilla, and at the same time appears to -be pushed on one side, owing to the growth not being uniform. The -external layer of the dental papilla is composed of long nucleated -cells, the =odontoblasts=, and it is by these that the dentine is -formed. Similarly the internal layer of the enamel organ is formed of -columnar enamel cells, which give rise to the enamel. The mesoblastic -cells surrounding the base of the tooth give rise to the cement. - -=Bone= is in many cases exoskeletal, but it will be most conveniently -described with the endoskeleton. - -The =scales of fish= are wholly or in part mesoblastic in origin, -being totally different from those of reptiles. The =cycloid= and -=ctenoid= scales of Teleosteans (see p. 105) are thin plates coated -with epidermis. They are sometimes bony, but as a rule are simply -calcified. =Ganoid= scales are flat plates of bone coated with an -enamel-like substance, and articulating together with a peg and socket -arrangement; they are probably identical with enlarged and flattened -placoid scales. - -The =armour plates= of fossil Ganoids, Labyrinthodonts, and Dinosaurs, -and of living Crocodiles, some Lizards and Armadillos, are composed of -bone. They are always covered by a layer of epidermis. - -The =antlers of deer= are also composed of bone; they will be more -fully described in the chapter on mammals. It may perhaps be well to -mention them here, though they really belong to the endoskeleton, -being outgrowths from the frontal bones. - - -B. ENDOSKELETAL STRUCTURES. - -I. HYPOBLASTIC. - -(_a_) The =notochord= is an elastic rod formed of large vacuolated -cells, and is surrounded by a membranous sheath of mesoblastic origin. -It is the primitive endoskeleton in the Chordata, all of which possess -it at some period of their existence; while in many of the lower forms -it persists throughout life. Even in the highest Chordata it is the -sole representative of the axial skeleton for a considerable part of -the early embryonic life. A simple unsegmented notochord persists -throughout life in the Cephalochordata, Cyclostomata, and some Pisces, -such as Sturgeons and Chimaeroids. - -(_b_) The enamel of the pharyngeal teeth of the Salmon and many other -Teleosteans is hypoblastic in origin. The epiblast of the stomodaeum, -in which the other teeth are developed, passes into the hypoblast of -the mesenteron in which these pharyngeal teeth are formed. - - -II. MESOBLASTIC. - -The most primitive type of a mesoblastic endoskeleton consists of a -membranous sheath surrounding the notochord, as in _Myxine_ and its -allies. The first stage of complication is by the development of -cartilage in the notochordal sheath, as in _Petromyzon_. Often the -cartilage becomes calcified in places, as in the vertebral centra of -_Scyllium_ and other Elasmobranchs. Lastly, the formation of bone -takes place; it generally constitutes the most important of the -endoskeletal structures. - -=Bone= may be formed in two ways:-- - -(1) by the direct ossification of pre-existing cartilage, when it is -known as =cartilage bone= or =endochondral bone=; - -(2) by independent ossification in connective tissue; it is then known -as =membrane= or =dermal= or =periosteal bone=. - -With the exception of the _clavicle_[4] all the bones of the trunk and -limbs, together with a large proportion of those of the skull, are -preformed in the embryo in cartilage, and are grouped as cartilage -bones; while the clavicle and most of the roofing and jaw-bones of the -skull are not preformed in cartilage, being developed simply in -connection with a membrane. Hence it is customary to draw a very -strong line of distinction between these two kinds of bone; in reality -however this distinction is often exaggerated, and the two kinds pass -into one another, and as will be shown immediately, the permanent -osseous tissue of many of those which are generally regarded as -typical cartilage bones, is really to a great extent of periosteal -origin. The palatine bone, for instance, of the higher vertebrates in -general is preceded by a cartilaginous bar, but is itself almost -entirely a membrane bone. - -Before describing the development of bone it will be well to briefly -describe the structure of adult bone and cartilage. - -The commonest kind of =cartilage=, and that which preforms so many of -the bones of the embryo, is =hyaline= cartilage. It consists of oval -nucleated cells occupying cavities (=lacunae=) in a clear -intercellular semitransparent matrix, which is probably secreted by -the cells. Sometimes one cell is seen in each lacuna, sometimes -shortly after cell-division a lacuna may contain two or more cells. -The free surface of the cartilage is invested by a fibrous membrane, -the =perichondrium=. - -=Bone= consists of a series of lamellae of ossified substance between -which are oval spaces, the =lacunae=, giving rise to numerous fine -channels, the =canaliculi=, which radiate off in all directions. The -lacunae are occupied by the =bone cells= which correspond to cartilage -cells, from which if the bone is young, processes pass off into the -canaliculi. It is obvious that the ossified substance of bone is -intercellular in character, and corresponds to the matrix of -cartilage. - -Bone may be compact, or loose and spongy in character, when it is -known as =cancellous bone=. In compact bone many of the lamellae are -arranged concentrically round cavities, the =Haversian canals=, which -in life are occupied by blood-vessels. Each Haversian canal with its -lamellae forms a =Haversian system=. In spongy bone instead of -Haversian canals there occur large irregular spaces filled with -marrow, which consists chiefly of blood-vessels and fatty tissue. The -centre of a long bone is generally occupied by one large continuous -marrow cavity. The whole bone is surrounded by a fibrous connective -tissue membrane, =the periosteum=. - -THE DEVELOPMENT OF BONE. - -=Periosteal ossification.= An example of a bone entirely formed in -this way is afforded by the parietal. The first trace of ossification -is shown by the appearance, below the membrane which occupies the -place of the bone in the early embryo, of calcareous spicules of bony -matter, which are laid down round themselves by certain large cells, -the =osteoblasts=. These osteoblasts gradually get surrounded by the -matter which they secrete and become converted into bone cells, and in -this way a mass of spongy bone is gradually produced. Meanwhile a -definite periosteum has been formed round the developing bone, and on -its inner side fresh osteoblasts are produced, and these with the -others gradually render the bone larger and more and more compact. -Finally, the middle layer of the bone becomes again hollowed out and -rendered spongy by the absorption of part of the bony matter. - -=Endochondral ossification=[5]. This is best studied in the case of a -long bone like the femur or humerus. Such a long bone consists of a -shaft, which forms the main part, and two terminal portions, which -form the =epiphyses=, or portions ossifying from centres distinct from -that forming the shaft or main part of the bone. - -In the earliest stage the future bone consists of hyaline cartilage -surrounded by a vascular sheath, the perichondrium. - -Then, starting from the centre, the cartilage becomes permeated by a -number of channels into which pass vessels from the perichondrium and -osteoblasts. In this way the centre of the developing shaft becomes -converted into a mass of cavities separated by bands or trabeculae of -cartilage. This cartilage next becomes calcified, but as yet is not -converted into true bone. The osteoblasts in connection with the -cavities now begin to deposit true endochondral spongy bone, and then -after a time this becomes absorbed by certain large cells, the -osteoclasts, and resolved into marrow or vascular tissue loaded with -fat. So that the centre of the shaft passes from the condition of -hyaline cartilage to that of calcified cartilage, thence to the -condition of spongy bone, and finally to that of marrow. At the same -time beneath the perichondrium osteoblasts are developed which also -begin to give rise to spongy bone. The perichondrium thus becomes the -periosteum, and the bone produced by it, is periosteal or membrane -bone. So that while a continuous marrow cavity is gradually being -formed in the centre of the shaft, the layer of periosteal bone round -the margin is gradually thickening, and becoming more and more compact -by the narrowing down of its cavities to the size of Haversian canals. -The absorption of endochondral and formation of periosteal bone goes -on, till in time it comes about that the whole of the shaft, except -its terminations, is of periosteal origin. At the extremities of the -shaft, however, and at the epiphyses, each of which is for a long time -separated from the shaft by a pad of cartilage, the ossification is -mainly endochondral, the periosteal bone being represented only by a -thin layer. - -Until the adult condition is reached and growth ceases, the pad of -cartilage between the epiphysis and the shaft continues to grow, its -outer (epiphysial) half growing by the formation of fresh cartilage as -fast as its inner half is encroached on by the growth of bone from the -shaft. The terminal or articular surfaces of the bone remain -throughout life covered by layers of articular cartilage. - -Even after the adult condition is reached the bone is subject to -continual change, processes of absorption and fresh formation going on -for a time and tending to render the bone more compact. - -METHODS IN WHICH BONES ARE UNITED TO ONE ANOTHER. - -The various bones composing the endoskeleton are united to one another -either by =sutures= or by movable =joints=. - -When two bones are suturally united, their edges fit closely together -and often interlock, being also bound together by the periosteum. - -In many cases this sutural union passes into fusion or =ankylosis=, -ossification extending completely from one bone to the other with the -obliteration of the intervening suture. This feature is especially -well marked in the cranium of most birds. - -The various kinds of joints or articulations[6] may be subdivided into -imperfect joints and perfect joints. - -In =imperfect joints=, such as the intervertebral joints of mammals, -the two contiguous surfaces are united by a mass of fibrous tissue -which allows only a limited amount of motion. - -In =perfect joints= the contiguous articular surfaces are covered with -cartilage, and between them lies a synovial membrane which secretes a -viscid lubricating fluid. - -The amount of motion possible varies according to the nature of the -articular surfaces; these include-- - -_a._ =ball and socket joints=, like the hip and shoulder, in which the -end of one bone works in a cup provided by another, and movements can -take place in a variety of planes. - -_b._ =hinge joints=, like the elbow and knee, in which as in -ball-and-socket joints one bone works in a cup provided by another, -but movements can take place in one plane only. - - -THE ENDOSKELETON. - -The endoskeleton is divisible into =axial= and =appendicular= parts; -and the =axial= skeleton into-- - - 1. the spinal column, - - 2. the skull {_a._ the cranium, - {_b._ the jaws and visceral skeleton, - - 3. the ribs and sternum[7]. - - -I. THE AXIAL SKELETON. - -1. THE SPINAL COLUMN. - -The spinal column in the simplest cases consists of an unsegmented -rod, the notochord, surrounded by the =skeletogenous layer=, a sheath -of mesoblastic origin, which also envelops the nerve cord. Several -intermediate stages connect this simple spinal column with the -vertebral column characteristic of higher vertebrates. A typical -vertebral column may be said to consist of (1) a series of -cartilaginous or bony blocks, the vertebral =centra=, which arise in -the sheath surrounding the notochord. They cause the notochord to -become constricted and to atrophy to a varying extent, though a -remnant of it persists, either permanently or for a long period, -within each centrum or between successive centra. (2) From the dorsal -surface of each centrum arise a pair of processes which grow round the -spinal cord and unite above it, forming a =dorsal= or =neural arch=. -(3) A similar pair of processes arising from the ventral surface of -the centrum form the =ventral= or =haemal arch=. To the ventral arch -the ribs strictly belong, and it tends to surround the ventral -blood-vessels and the body cavity with the alimentary canal and other -viscera. - -A =neural spine= or spinous process commonly projects upwards from the -dorsal surface of the neural arch, and a pair of =transverse -processes= project outwards from its sides. When, as is commonly the -case, the two halves of the haemal arch do not meet, the ventral -surface of the centrum often bears a downwardly-projecting -=hypapophysis=. - -The character of the surfaces by which vertebral centra articulate -with one another varies much. Sometimes both surfaces are concave, and -the vertebra is then said to be =amphicoelous=; sometimes a centrum is -convex in front and concave behind, the vertebra is then -=opisthocoelous=, sometimes concave in front and convex behind, when -the vertebra is =procoelous=. Again, in many vertebrae both faces of -the centra are flat, while in others they are saddle-shaped, as in the -neck vertebrae of living birds, or biconvex, as in the case of the -first caudal vertebra of crocodiles. - -In the higher vertebrates pads of fibrocartilage--the =intervertebral -discs=--are commonly interposed between successive centra, these or -parts of them often ossify, especially in the trunk and tail, and are -then known as =inter centra=. - -[Illustration FIG. 2. CERVICAL VERTEBRAE OF AN OX (_Bos taurus_). - -A, is the fifth; B, the fourth; C, the third. x 1/4 (Camb. Mus.) - - 1. neural spine. - 2. transverse process. - 3. hypapophysis. - 4. convex anterior face of the centrum. - 5. concave posterior face of the centrum. - 6. prezygapophysis. - 7. postzygapophysis. - 8. vertebrarterial canal. - 9. neural canal. - 10. inferior lamella of transverse process.] - -The vertebrae of the higher forms can generally be arranged in the -following five groups, each marked by certain special characteristics: - -1. The =cervical= or =neck vertebrae=. These connect the skull with -the thorax, and are characterised by relatively great freedom of -movement. They often bear small ribs, but are distinguished from the -succeeding thoracic vertebrae by the fact that their ribs do not reach -the sternum. The first cervical vertebra which articulates with the -skull is called the =atlas=, but a study of the nerve exits shows that -the first vertebra is not serially homologous throughout the -Ichthyopsida, so that it is best to reserve the term atlas for the -first vertebra in Sauropsida and Mammalia. - -2. The =thoracic vertebrae= (often called dorsal) bear movably -articulated ribs which unite ventrally with the sternum. - -3. The =lumbar vertebrae= are generally large, and are often more -movable on one another than are the thoracic vertebrae. They bear no -ribs. - -4. The =sacral vertebrae= are characterised by the fact that they are -firmly fused together, and are united with the pelvic girdle by means -of their transverse processes and rudimentary ribs. - -5. The =caudal= or =tail vertebrae= succeed the sacral. The anterior -ones are often fused with one another and with the sacrals, but they -differ from true sacral vertebrae in that there are no rudimentary -ribs between their transverse processes and the pelvic girdle. They -often bear V-shaped =chevron bones=. - -In fish and snakes the vertebral column is divisible into only two -regions, an anterior trunk region, whose vertebrae bear ribs, and a -posterior tail region, whose vertebrae are ribless. - - -2. THE SKULL. - -Before giving a general account of the adult skull it will be well to -briefly describe its development. - - -GENERAL DEVELOPMENT OF THE CRANIUM[8]. - -Shortly after its appearance, the central nervous system becomes -surrounded by a membranous mesodermal investment which in the region -of the spinal cord is called the =skeletogenous layer= or =perichordal -sheath=, while in the region of the brain it is called the -=membranous cranium=. Ventral to the central nervous system is the -notochord, which extends far into the region of the future cranium, -and like the nervous system, is enclosed by the skeletogenous layer. -The primitive cartilaginous cranium is formed by histological -differentiation within the substance of the membranous cranium and -always consists of the following parts: - -(_a_) the =parachordals=. These are a pair of flat curved plates of -cartilage, each of which has its inner edge grooved where it comes in -contact with the notochord. The parachordals, together with the -notochord, form a continuous plate, which is known as the =basilar -plate=. The basilar plate is the primitive floor below the hind- and -mid-brain. In front the parachordals abut upon another pair of -cartilaginous bars, the trabeculae, the two pairs of structures being -sometimes continuous with one another from the first; - -(_b_) the =trabeculae= which meet behind and embrace the front end of -the notochord. Further forwards they at first diverge from one -another, and then converge again, enclosing a space, the =pituitary -space=. After a time they generally fuse with one another in the -middle line, and, with the parachordals behind, form an almost -continuous basal plate. The trabeculae generally appear before the -parachordals. They form the primitive floor below the fore-brain; - -(_c_) the cartilaginous =capsules= of the three pairs of =sense -organs=. At a very early stage of development involutions of the -surface epiblast give rise to the three pairs of special sense -organs--the olfactory or nasal organs in front, the optic in the -middle, and the auditory behind. The olfactory and auditory organs -always become enclosed in definite cartilaginous capsules, the eyes -often as in the Salmon, become enclosed in cartilaginous sclerotic -capsules, while sometimes, as in mammals, their protecting capsules -are fibrous. - -Each pair of sense capsules comes into relation with part of the -primitive cranium, and greatly modifies it. Thus the auditory or -periotic capsules press on the parachordals till they come to be more -or less imbedded in them. Perhaps owing to the pressure of the nasal -capsules the trabeculae fuse in front, and then grow out into an -anterior pair of processes, the =cornua trabeculae=, and a posterior -pair, the =antorbital processes=, which together almost completely -surround the nasal capsules. The sclerotic capsules of the eyes -greatly modify the cranium, although they never become completely -united with it. - -The cartilaginous cranium formed of the basal plate, together with the -sense capsules, does not long remain merely as a floor. Its sides grow -vertically upwards, forming the =exoccipital= region of the cranium -behind, and the =alisphenoidal= and =orbitosphenoidal= regions further -forwards. In many forms, such as Elasmobranchs, all these upgrowths -meet round the brain, roofing it in and forming an almost complete -cartilaginous cranium. But in most vertebrata, while in the occipital -region, the cartilaginous cranium is completed dorsally, in the -alisphenoidal and orbitosphenoidal regions the cartilage merely forms -the lateral walls of the cranium, the greater part of the brain having -dorsal to it a wide space, closed by merely membranous tissue in -connection with which the large frontal and parietal bones are -subsequently formed. - - -The SKULL includes - -_a._ the cranium, - -_b._ the jaws and visceral skeleton. - -The =cranium= can be further subdivided into - -(1) an axial portion, the =cranium proper= or =brain case=; - -(2) =the sense capsules.= The capsules of the auditory and olfactory -sense organs are always present, and as has been already mentioned, -in many animals the eye likewise is included in a cartilaginous -capsule. - - -(1) THE CRANIUM PROPER OR BRAIN CASE. - -The cranium varies much in form and structure. In lower vertebrates, -such as Sharks and Lampreys, it remains entirely cartilaginous and -membranous, retaining throughout life much of the character of the -embryonic rudiment of the cranium of higher forms. The dogfish's -cranium, described on pp. 73 to 76, is a good instance of a cranium of -this type. But in the majority of vertebrates the cartilage becomes -more or less replaced by cartilage bone, while membrane bones are also -largely developed and supplant the cartilage. - -The cranium of most vertebrates includes a very large number of bones -whose arrangement varies much, but one can distinguish a definite -=basicranial axis= formed of the basi-occipital, basisphenoid, and -presphenoid bones, which is a continuation forwards of the axis of the -vertebral column. From the basicranial axis a wide arch arises, -composed of a number of bones, which form the sides and roof of the -brain-case These bones are arranged in such a manner that if both -cartilage and membrane bones are included they can be divided into -three rings or segments. The hinder one of these segments is the -occipital, the middle the parietal, and the anterior one the frontal. - -The occipital segment is formed of four cartilage bones, the -=basi-occipital= below, two =exoccipitals= at the sides, and the -=supra-occipital= above. The parietal segment is formed of the -=basisphenoid= below, two =alisphenoids= at the sides and two membrane -bones, the _parietals_ above, and the frontal segment in like manner -consists of the =presphenoid= below, the two =orbitosphenoids= at the -sides, and two membrane bones, the _frontals_, above. The parietals -and frontals, being membrane bones, are not comparable to the -supra-occipital, in the way that the presphenoid and basisphenoid are -to the basi-occipital. - -The cartilage bones of the occipital segments are derived from the -parachordals of the embryonic skull, those of the parietal and frontal -segments from the trabeculae. - -In front of the presphenoid the basicranial axis is continued by the -=mesethmoid=. - - -(2) THE SENSE CAPSULES. - -These enclose and protect the special sense organs. - -(_a_) =Auditory capsule.= - -The basisphenoid is always continuous with the basi-occipital, but the -alisphenoid is not continuous with the exoccipital as the =periotic= -or =auditory capsule= is interposed between them. Each periotic -capsule has three principal ossifications; an anterior bone, the -=pro-otic=, a posterior bone, the =opisthotic=, and a superior bone, -the =epi-otic=. - -These bones may severally unite, or instead of uniting with one -another they may unite with the neighbouring bones. Thus the epi-otic -often unites with the supra-occipital, and the opisthotic with the -exoccipital. - -Two other bones developed in the walls of the auditory capsule are -sometimes added, as in Teleosteans; these are the =pterotic= and -=sphenotic=. - -(_b_) =Optic capsule.= - -The eye is frequently enclosed in a cartilaginous sclerotic capsule, -and in this a number of scale-like bones are often developed. - -Several membrane bones are commonly formed around the orbit or cavity -for the eye. The most constant of these is the _lachrymal_ which lies -in the anterior corner; frequently too, as in Teleosteans, there is a -_supra-orbital_ lying in the upper part of the orbit, or as in many -Reptiles, a _postorbital_ lying in the posterior part of the orbit. - -(_c_) =Nasal capsule.= - -In relation to the nasal capsules various bones occur. - -The basicranial axis in front of the presphenoid is ossified, as the -=mesethmoid=, dorsal to which there sometimes, as in Teleosteans, -occur a _median ethmoid_ and a pair of =lateral ethmoids=[9]. Two -pairs of membrane bones very commonly occur in this region, viz. the -_nasals_ which lie dorsal to the mesethmoid, and the _vomers_ -(sometimes there is only one) which lie ventral to it. - -The part of the skull lying immediately in front of the cranial cavity -and in relation to the nasal capsules constitutes the =ethmoidal -region=. - -There remain certain other membrane bones which are often found -connected with the cranium. Of these, one of the largest is the -_parasphenoid_ which, in Ichthyopsids, is found underlying the -basicranial axis. _Prefrontals_ often, as in most reptiles, occur -lying partly at the sides and partly in front of the frontal, and -_postfrontals_ similarly occur behind the orbit lying partly behind -the frontals and partly at their sides. Lastly a _squamosal bone_ is, -as in Mammals, very commonly developed, and lies external and partly -dorsal to the auditory capsules. - -THE JAWS AND VISCERAL SKELETON. - -In the most primitive fish these consist of a series of cartilaginous -rings or arches placed one behind another and encircling the anterior -end of the alimentary canal. Originally they are mainly concerned with -branchial respiration. - -The first or =maxillo-mandibular= arch forms the upper jaw and the -lower jaw or mandible. - -The second or =hyoid= arch bears gills and often assists in attaching -the jaws to the cranium. The remaining arches may bear gills, though -the last is commonly without them. - -The above condition is only found in fishes, in higher animals the -visceral skeleton is greatly reduced and modified. - -The first or maxillo-mandibular arch is divisible into a dorsal -portion, the =palato-pterygo-quadrate bar=, which forms the primitive -upper jaw and enters into very close relations with the cranium, and a -ventral portion, =Meckel's cartilage=, which forms the primitive lower -jaw. The cartilaginous rudiments of both these portions disappear to a -greater or less extent and become partly ossified, partly replaced by -or enveloped in membrane bone. - -The posterior part of the palato-pterygo-quadrate bar becomes ossified -to form the =quadrate=, the anterior part to form the palatine and -pterygoid, or the two latter may be formed partially or entirely of -periosteal bone, developed round the cartilaginous bar. Two pairs of -important membrane bones, the _premaxillae_ and _maxillae_ form the -anterior part of the upper jaw, and behind the maxilla lies another -membrane bone, the _jugal_ or _malar_, which is connected with the -quadrate by a _quadratojugal_. The premaxillae have a large share in -bounding the external nasal openings or anterior nares. - -In lower vertebrates the nasal passage leads directly into the front -part of the mouth cavity and opens by the posterior nares. In some -higher vertebrates, such as mammals and crocodiles, processes arise -from the premaxillae and palatines, and sometimes from the pterygoids, -which meet their fellows in the middle line and form the palate, -shutting off the nasal passage from the mouth cavity and causing the -posterior nares to open far back. - -The cartilage of the lower jaw is in all animals with ossified -skeletons, except the Mammalia, partly replaced by cartilage bone -forming the =articular=, partly overlain by a series of membrane bones -the _dentary_, _splenial_, _angular_, _supra-angular_ and _coronoid_. -In many sharks large paired accessory cartilages occur at the sides of -the jaws; and in a few reptiles and some Amphibia, such as the Frog, -the ossified representative of the anterior of these structures occurs -forming the =mento-meckelian= bone. In mammals the lower jaw includes -but a single bone. - -The quadrate in all animals with ossified skeletons, except the -Mammalia, forms the suspensorium of the mandible or the skeletal link -between the jaw and the cranium; in the Mammalia, however, the -mandible articulates with the squamosal, while the quadrate is greatly -reduced, and is now generally considered to be represented by the -tympanic ring of the ear. - -The second visceral or hyoid arch in fishes consists of two pieces of -cartilage, a proximal[1] piece the =hyomandibular=, and a distal[10] -piece the =cerato-hyal=. The cerato-hyals of the two sides are commonly -united by a median ventral plate, the =basi-hyal=. The hyoid arch -bears gills on its posterior border, but its most important function -in most fishes is to act as the suspensorium. In higher vertebrates -the representative of the hyomandibular is much reduced in size, and -comes into relation with the ear forming the =auditory ossicles=; the -cerato-hyal looses its attachment to the hyomandibular and becomes -directly attached to the cranium, forming a large part of the hyoid -apparatus of most higher vertebrates. - -Behind the hyoid arch come the branchial arches. They are best -developed in fishes, in which they are commonly five in number and -bear gills. Their ventral ends are united in pairs by median pieces, -the =copulae=. - -In higher vertebrates they become greatly reduced, and all except the -first and second completely disappear. In the highest vertebrates, the -mammals, the second has disappeared, but in birds and many reptiles it -is comparatively well developed. - -3. THE RIBS AND STERNUM. - -The =ribs= are a series of segmentally arranged cartilaginous or bony -rods, attached to the vertebrae; they tend to surround the body -cavity, and to protect the organs contained within it. Ribs are very -frequently found attached to the transverse processes of the -vertebrae, but a study of their origin in fish shows that they are -really the cut off terminations of the ventral arch, not of the -transverse processes which are outgrowths from the dorsal arch. In the -tail their function is to surround and protect structures like the -ventral blood-vessels which do not vary much in size, consequently -they meet one another, and form a series of complete ventral or haemal -arches. But the trunk contains organs like the lungs and stomach which -are liable to vary much in size at different times, consequently the -halves of the haemal arch do not meet ventrally, and then the ribs -become detached from the rest of the haemal arch. Having once become -detached, they are able to shift about and unite themselves to various -points of the vertebra. They frequently, as has been already -mentioned, become entirely attached to the transverse process, or they -may be attached to the transverse process by a dorsal or =tubercular= -portion and to the centrum or to the ventral arch by a ventral or -=capitular= portion. - -In all animals above fishes the distal ends of the thoracic ribs unite -with a median breast bone or sternum which generally has the form of a -segmented rod. The =sternum= is really formed by the fusion of the -distal ends of a series of ribs. In many animals elements of the -shoulder girdle enter into close relation with the rib elements of the -sternum. - -II. THE APPENDICULAR SKELETON. - -This consists of the skeleton of the anterior or =pectoral=, and the -posterior or =pelvic= limbs, and their girdles. In every case (except -in Chelonia) the parts of the appendicular skeleton lie external to -the ribs. - -1. THE LIMB GIRDLES. - -=The Pectoral girdle=[11]. In the simplest case the pectoral or -shoulder girdle consists of a hoop of cartilage incomplete dorsally. -It is attached by muscle to the vertebral column, and is divided on -either side into dorsal and ventral portions by a cavity, the =glenoid -cavity=, at the point where the anterior limb articulates. In higher -fishes this hoop is distinctly divided into right and left halves; it -becomes more or less ossified, and a pair of important bones, the -clavicles, are developed in connection with its ventral portion. - -In higher vertebrates ossification sets up in the cartilage and gives -rise on each side to a dorsal bone, the =scapula=, and frequently to -an anterior ventral bone, the =precoracoid=, and a posterior ventral -bone, the =coracoid=. The precoracoid is often not ossified, and upon -it is developed the clavicle which more or less replaces it. In some -forms a =T= shaped _interclavicle_ occurs, in others =epicoracoids= are -found in front of the coracoids. In all vertebrata above fish, except -the great majority of mammals, the coracoids are large and articulate -with the sternum. But in mammals the coracoids are nearly always quite -vestigial, and the pectoral girdle is attached to the axial skeleton -by the clavicle or sometimes by muscles and ligaments only. - -The =Pelvic girdle=[12] like the pectoral consists primitively of a -simple rod or hoop of cartilage, which in vertebrata above fishes is -divided into dorsal and ventral portions, by a cavity, the -=acetabulum=, with which the posterior limb articulates. In the pelvic -girdle as in the pectoral one dorsal, and (commonly) two ventral -ossifications take place. The dorsal bone is the =ilium= and -corresponds to the scapula. The posterior ventral bone is the -=ischium= corresponding to the coracoid. The anterior ventral bone is -the =pubis= and is generally compared to the precoracoid, but in some -cases a fourth pelvic element, the =acetabular= or =cotyloid= bone is -found, and this may correspond to the precoracoid. - -The pelvic girdle differs from the pectoral in the fact that the -dorsal bones--the ilia--are nearly always firmly united to transverse -processes of the sacral vertebrae, by means of rudimentary ribs. The -pubes and ischia generally meet in ventral symphyses. - -2. THE LIMBS. - -It will be most convenient to defer a discussion of the limbs of -fishes to chap. VIII. - -All vertebrates above fishes have the limbs divisible into three main -segments:-- - - =Anterior or Fore limb.= =Posterior or Hind limb.= - - Proximal segment. upper arm or _brachium_. thigh. - Middle segment. fore-arm or _antibrachium_. shin or _crus_. - Distal segment. _manus_. _pes_. - -The proximal segments each contain one bone, the =humerus= in the case -of the upper arm, and the =femur= in the case of the thigh. The middle -segments each contain two bones, the =radius= and =ulna= in the case -of the fore-arm, and the =tibia= and =fibula= in the case of the shin. - - * * * * * - -The manus and pes are further subdivided into - -(_a_) two or three proximal rows of bones forming the wrist or -=carpus= in the case of the manus, and the ankle or =tarsus= in the -case of the pes. - -(_b_) a middle row called respectively the =metacarpus= and -=metatarsus=. - -(_c_) a number of distal bones called the =phalanges= which form the -skeleton of the fingers and toes, or =digits=. - -Typically the manus and pes both have five digits (pentedactylate). -The first digit of the manus is commonly called the =pollex=, and the -first digit of the pes the =hallux=. - -In a very simple =carpus= such as that of _Chelydra_, there are nine -bones. They are arranged in a proximal row of three, the radiale, -intermedium, and ulnare,--the first being on the radial side of the -limb, and a distal row of five called respectively carpale 1, 2, 3, 4, -5, beginning on the radial side. Between these two rows is a single -bone the centrale, or there may be two. - -Similarly there are nine bones in a simple =tarsus= such as that of -_Salamandra_. They form a proximal row of three, the tibiale, -intermedium and fibulare, and a distal row of five, called -respectively tarsale 1, 2, 3, 4, 5, beginning on the tibial side. -Between the two rows there is a centrale as in the carpus, or there -may be two. - - * * * * * - -The following names derived from human anatomy are commonly applied to -the various carpal and tarsal bones: - - =Carpus.= - - radiale = scaphoid - intermedium = lunar - ulnare = cuneiform - centrale = central - carpale 1 = trapezium - " 2 = trapezoid - " 3 = magnum - " 4 } = unciform - " 5 } - - =Tarsus.= - - tibiale } - intermedium } astragalus - fibulare = calcaneum - centrale = navicular - tarsale 1 = internal cuneiform - " 2 = middle " - " 3 = external " - " 4 } = cuboid - " 5 } - - NOTE. The above is the view commonly accepted concerning the - homology of the carpal and tarsal bones. But with regard to the - proximal row of tarsal bones there is difference of opinion. - All anatomists are agreed that the calcaneum is the fibulare - and that the intermedium is contained in the astragalus, but - while the majority regard the astragalus as the fused tibiale - and intermedium, Baur considers that a small bone found on the - tibial side of the tarsus in _Procavia_, many Rodents, - Insectivores, and the male _Ornithorhynchus_, is the vestigial - tibiale, and regards the astragalus as the intermedium - alone[13]. He also considers that the mammalian scaphoid - represents a centrale. - - -MODIFICATIONS IN THE POSITIONS OF THE LIMBS[14]. - -In their primitive position the limbs are straight and are extended -parallel to one another at right angles to the axis of the trunk. Each -limb then has a dorsal surface, a ventral surface, an anterior or -=pre-axial= edge, and a posterior or =postaxial= edge. - -In the anterior limb the radius and the pollex are pre-axial, the ulna -and the fifth finger are postaxial. In the posterior limb the tibia -and the hallux are pre-axial, the fibula and the fifth toe are -postaxial. The Cetacea and various extinct reptiles, such as -_Ichthyosaurus_ and _Plesiosaurus_, have their limbs in practically -this primitive position. - -The first modification from it is produced by the bending ventrally of -the middle segments of both limbs upon the proximal segments, while -the distal segment is bent in the opposite direction on the middle -segment. Then the ventral surfaces of the antibrachium and crus come -to look inwards, and their dorsal surfaces to look outwards. The -brachium and manus, thigh and pes still have their dorsal surfaces -facing upwards and their ventral surfaces facing downwards as before, -and the relations of their pre-and postaxial borders remain as they -were. Many Amphibians and Reptiles, such as tortoises, carry their -limbs in this position. - -In all higher vertebrates, however, a further change takes place, each -limb is rotated as a whole from its proximal end, the rotation taking -place in opposite directions in the fore and hind limbs respectively. -The anterior limb is rotated backwards from the shoulder, so that the -brachium lies nearly parallel to the body, and the elbow points -backwards, the antibrachium downwards, and the manus backwards; the -pre-axial surface of the whole limb with the radius and pollex now -faces outwards, and the postaxial surface with the ulna and fifth -finger now faces inwards. In the Walrus and, to a certain extent, in -the Sea lions the anterior limb remains throughout life in this -position. The posterior limb is also rotated, but the rotation in this -case takes place forwards, so that the thigh lies nearly parallel to -the body, the knee-joint pointing forwards; the crus downwards and the -pes forwards. The pre-axial surface of the whole limb with the tibia -and hallux looks towards the middle of the body, the postaxial surface -with the fibula and fifth toe looks outwards. This is the position in -which the hind limb is carried in nearly all mammals. - -In nearly all mammals a further change takes place in the position of -the anterior limb. The radius and ulna have hitherto been parallel to -one another, but now the lower end of the radius, carrying with it the -manus, comes to be rotated forwards round the ulna, so that the manus, -as well as the pes, comes to be forwardly-directed, and its pre-axial -surface faces inwards. - -In the majority of mammals the radius and ulna are permanently fixed -in this, which is known as the =prone= position, but in man and some -other mammals the manus can be pronated or turned into this position -at will. When the radius and ulna are parallel throughout their whole -length the manus is said to be in the =supine= position. - -The =extensor= side of a limb is that to which the muscles which -straighten it are attached, the =flexor= side is that to which the -muscles which bend it are attached. - - -FOOTNOTES: - -[1] The skin consists of an outer layer of epiblastic origin, the -epidermis, and an inner layer of mesoblastic origin, the dermis. The -epidermis is divided into two principal layers, an outer one, the -horny layer or _stratum corneum_, and an inner one, the _stratum -Malpighii_. The innermost part of the stratum corneum is distinguished -as the _stratum lucidum_, and the outermost part of the stratum -Malpighii as the _stratum granulosum_. - -[2] The enamel of the pharyngeal teeth of some Teleosteans is -hypoblastic in origin. - -[3] See also p. 71. - -[4] It is usual to regard the clavicle as a membrane bone, but -Kölliker has shown that in rabbit embryos of about the 17th day it is -cartilaginous. - -[5] In compiling these paragraphs on Histology, free use has been made -of Klein and Noble Smith's _Atlas of Histology_, the small Histologies -of Klein and Schäfer, Huxley's _Elementary Physiology_, and Lloyd -Morgan's _Animal Biology_. - -[6] See Huxley's _Elementary Physiology_, Revised edition, London, -1886, p. 180. - -[7] Strictly speaking the jaws, visceral skeleton, ribs and sternum do -not form part of the axis, but it is convenient to group them as parts -of the axial skeleton. - -[8] F.M. Balfour, _Comparative Embryology_, vol. II., London, 1881, p. -465. W.K. Parker and G.T. Bettany, _The Morphology of the Skull_, -London, 1877. - -[9] Sometimes also called ectethmoids or parethmoids. - -[10] The _proximal_ end of anything is the one nearest the point of -origin or attachment, the _distal_ end is the one furthest from the -point of origin or attachment. - -[11] W.K. Parker, _A Monograph of the Shoulder Girdle and Sternum_, -Ray Soc. London, 1868. - -[12] See R. Wiedersheim, _Zeitschr. wiss. Zool._ vol. LIII. suppl. p. -43, 1892. - -[13] G. Baur, _Beiträge zur Morphogenie des Carpus und Tarsus der -Vertebraten_, Theil 1. Batrachia. Jena, 1888, and _Amer. Natural._, -vol. XIX. 1885 (several papers). - -[14] This account is based on Chapter XX. of Flower's _Osteology of -the Mammalia_. London 1876. - - - - -CHAPTER II. - -CLASSIFICATION. - - -THE following classification includes _only the forms mentioned in the -succeeding pages_. The relative value of some of the terms employed in -classification is not identical throughout the book. This remark -applies specially to the term _group_, which is a convenient one, -owing to its not having such a hard and fast zoological meaning as has -the term _family_, for instance. The term _group_ is applied in this -book to divisions of the animal kingdom of very different -classificatory importance. - - PHYLUM CHORDATA. - - SUBPHYLUM A. HEMICHORDATA. - - Balanoglossus. - Cephalodiscus. - Rhabdopleura. - ? Phoronis. - (? Actinotrocha--larval Phoronis). - - SUBPHYLUM B. UROCHORDATA (TUNICATA). - - Group LARVACEA and others. - - SUBPHYLUM C. CEPHALOCHORDATA. - - Amphioxus--lancelet. - - NOTE. In this chapter all the generic names printed in italics - are those of extinct animals. - - SUBPHYLUM D. VERTEBRATA. - - DIVISION (I). CYCLOSTOMATA. - - Order 1. MARSIPOBRANCHII. - - Family =Myxinoidei=. Myxine--hag-fish. - Bdellostoma. - - Family =Petromyzontidae=. Petromyzon--lamprey. - (Ammocoetes--larval lamprey.) - - Family =Palaeospondylidae=. _Palaeospondylus._ - - Order 2. OSTRACODERMI. - - Suborder 1. HETEROSTRACI. - - Family =Pteraspidae=. _Pteraspis._ - - Suborder 2. OSTEOSTRACI. - - Family =Cephalaspidae=. _Cephalaspis._ - - Suborder 3. ANTIARCHA. - - Family =Asterolepidae=. _Pterichthys._ - _Asterolepis._ - - - DIVISION (II). GNATHOSTOMATA. - - A. ICHTHYOPSIDA. - - CLASS I. PISCES. - - Order 1. ELASMOBRANCHII. - - Suborder (1). ICHTHYOTOMI. - - Family =Pleuracanthidae=. _Xenacanthus._ - - Suborder (2). PLEUROPTERYGII. - _Cladoselache._ - - Suborder (3). SELACHII. - - Group SQUALIDAE. - - Family =Notidanidae=. Heptanchus. - Hexanchus. - Chlamydoselache--frill-gilled shark. - - Family =Cochliodontidae=. _Cochliodus._ - - Family =Cestraciontidae=. Cestracion--Port Jackson shark. - _Acrodus._ - - Family =Scylliidae=. Scyllium--spotted dogfish. - - Family =Lamnidae=. Odontaspis. - - Family =Carcharidae=. Galeus--tope. - - Family =Spinacidae=. Acanthias--spiny dogfish. - Scymnus. - - Family =Squatinidae=. Squatina (Rhina)--angel fish. - - Group BATOIDEI. - - Family =Pristidae=. Pristis--saw-fish. - - Family =Raiidae=. Raia--skate. - - Family =Myliobatidae=. Myliobatis--eagle ray. - - Family =Trygonidae=. Trygon--sting ray. - - Family =Torpedinidae=. Torpedo--electric ray. - - Suborder (4). ACANTHODII. - - Family =Acanthodidae=. _Acanthodes._ - - Family =Diplacanthidae=. _Diplacanthus._ - - Order 2. HOLOCEPHALI. - - Family =Chimaeridae=. Chimaera--rabbit fish. - Harriotta. - Callorhynchus. - _Ischyodus._ - - Order 3. GANOIDEI. - - Suborder (1). CHONDROSTEI. - - Family =Palaeoniscidae=. _Palaeoniscus._ - _Trissolepis._ - - Family =Acipenseridae=. Acipenser--sturgeon. - Scaphirhynchus. - - Family =Polyodontidae=. Polyodon (Spatularia)--spoon-beaked sturgeon. - Psephurus--slender-beaked sturgeon. - - Suborder (2). CROSSOPTERYGII. - - Family =Holoptychiidae=. _Holoptychius._ - - Family =Rhizodontidae=. _Rhizodus._ - - Family =Osteolepidae=. _Osteolepis._ - - Family =Polypteridae=. Polypterus--bichir. - Calamoichthys--reed-fish. - - Suborder (3). HOLOSTEI. - - Family =Lepidosteidae=. Lepidosteus--gar pike. - - Family =Semionotidae=. _Lepidotus._ - - Family =Amiidae=. Amia--bow-fin. - - Order 4. TELEOSTEI. - - Suborder (1). PLECTOGNATHI. - - Family =Balistidae=. Balistes--file-fish. - - Family =Gymnodontidae=. Diodon--globe-fish. - - Family =Ostracionidae=. Ostracion--coffer-fish. - - Suborder (2). PHYSOSTOMI. - - Family =Siluridae=.--cat-fishes. - - Family =Cyprinidae=. Cyprinus--carp. - - Family =Esocidae=. Esox--pike. - - Family =Salmonidae=. Salmo--salmon. - - Family =Clupeidae=. Clupeus--herring. - Exocaetus--'flying fish'. - - Family =Muraenidae=. Anguilla--eel. - - Suborder (3). ANACANTHINI. - - Family =Gadidae=. Gadus--cod, haddock, whiting. - - Family =Pleuronectidae=. Solea--sole. - - Suborder (4). PHARYNGOGNATHI. - - Family =Labridae=. Labrus--wrasse. - Scarus--parrot fish. - - Suborder (5). ACANTHOPTERYGII. - - Family =Cataphracti=. Dactylopterus--flying gurnard. - - Family =Percidae=. Perca--perch. - - Order 5. DIPNOI. - - Suborder (1). SIRENOIDEI. - - Family =Dipteridae=. _Dipterus._ - - Family =Monopneumona=. Ceratodus--barramunda. - - Family =Dipneumona=. Protopterus--African mud-fish. - Lepidosiren. - - Suborder (2). ARTHRODIRA. - - Family =Coccosteidae=. _Coccosteus._ - _Dinichthys._ - - NOTE. Palaeontological research has disclosed the existence of - a great number of forms which seem to connect with one another - almost all the orders of fishes as usually recognised. Forms - connecting the living Ganoids with the Teleosteans have been - especially numerous, so that these terms Ganoid and Teleostean - can hardly be any longer used in a precise and scientific - sense. This has rendered the subject of the classification of - fishes a very difficult one. Though unsuitable for adoption in - a work like the present, by far the most natural classification - hitherto proposed seems to be that of Smith Woodward[15]. He - considers that the course of development of fishes has followed - two distinct lines, the autostylic and hyostylic (see p. 119), - and groups the various forms as follows: - - HYOSTYLIC. AUTOSTYLIC. - Subclass 1. ELASMOBRANCHII. Subclass 3. HOLOCEPHALI. - 1. Ichthyotomi. 1. (unknown). - 2. Selachii. 2. Chimaeroidei. - 3. Acanthodii. 3. (unknown). - - Subclass 2. TELEOSTOMI. Subclass 4. DIPNOI. - 1. Crossopterygii (Palaeozoic 1. Sirenoidei. - and Mesozoic). - 2. Crossopterygii (Cainozoic). 2. (unknown). - 3. Actinopterygii. 3. Arthrodira. - - The primitive forms in each of these four subclasses have the - fins archipterygia (see p. 127). - - CLASS II. AMPHIBIA. - - Order 1. URODELA. - - Suborder (1). ICHTHYOIDEA. - - Group A. PERENNIBRANCHIATA. - - Family =Menobranchidae=. Menobranchus. - - Family =Proteidae=. Proteus--olm. - - Family =Sirenidae=. Siren. - - Group B. DEROTREMATA. - - Family =Amphiumidae=. Megalobatrachus. - Cryptobranchus (Menopoma). - Amphiuma. - - Suborder (2). SALAMANDRINA. - - Family =Salamandridae=. Salamandra--salamander. - Molge--newt. - Onychodactylus. - Amblystoma. - (Siredon--axolotl, larval Amblystoma). - Batrachoseps. - Spelerpes (Gyrinophilus). - - Order 2. LABYRINTHODONTIA. - - Group =Lepospondyli=. _Branchiosaurus._ - - Group =Temnospondyli=. _Archegosaurus._ - _Nyrania._ - _Euchirosaurus._ - - Group =Stereospondyli=. _Capitosaurus._ - _Mastodonsaurus._ - - Order 3. GYMNOPHIONA. - - Family =Caeciliidae=. Siphonops. - Epicrium. - - Order 4. ANURA. - - Suborder (1). AGLOSSA. - - Family =Xenopidae=. Xenopus. - - Family =Pipidae=. Pipa--Surinam toad. - - Suborder (2). PHANEROGLOSSA. - - Group ARCIFERA. - - Family =Discoglossidae=. Discoglossus--painted frog. - Bombinator--fire-bellied frog. - Alytes--midwife frog. - - Family =Pelobatidae=. Pelobates--toad frog. - - Family =Hylidae=. Hyla--green tree-frog. - - Family =Bufonidae=. Bufo--toad. - Docidophryne. - - Family =Cystignathidae=. Ceratophrys--horned frog. - - Group FIRMISTERNIA. - - Family =Ranidae=. Rana--common and edible frogs. - - Family =Engystomatidae=. Brachycephalus. - - B. SAUROPSIDA. - - CLASS I. REPTILIA[16]. - - Order 1. THEROMORPHA. - - Group =Anomodontia=. _Dicynodon._ - _Udenodon._ - - Group =Placodontia=. _Placodus._ - - Group =Pariasauria=. _Pariasaurus._ - _Elginia._ - - Group =Theriodontia=. _Dimetrodon._ - _Galesaurus._ - _Cynognathus._ - - Order 2. SAUROPTERYGIA. - - Family =Mesosauridae=. _Mesosaurus._ - - Family =Nothosauridae=. _Nothosaurus._ - - Family =Plesiosauridae=. _Plesiosaurus._ - _Pliosaurus._ - - Order 3. CHELONIA. - - Suborder (1). TRIONYCHIA. - - Family =Trionychidae=. Trionyx--snapping turtle. - - Suborder (2). CRYPTODIRA. - - Family =Dermochelydidae=. Dermochelys (Sphargis)--leathery - turtle. - - Family =Chelonidae=. Chelone--green turtle. - - Family =Chelydridae=. Chelydra--terrapin. - - Family =Chersidae=. Testudo--tortoise. - - Suborder (3). PLEURODIRA. - - Family =Chelydae=. Chelys. - - Order 4. ICHTHYOSAURIA. - - Family =Ichthyosauridae=. _Ichthyosaurus._ - - Order 5. RHYNCHOCEPHALIA. - - Suborder (1). RHYNCHOCEPHALIA VERA. - - Family =Sphenodontidae=. Sphenodon (Hatteria). - - Family =Rhynchosauridae=. _Hyperodapedon._ - - Suborder (2). PROGANOSAURIA. - - Family =Proterosauridae=. _Proterosaurus._ - - Order 6. SQUAMATA. - - Suborder (1). LACERTILIA. - - Group =Lacertilia vera=. - - Family =Geckonidae=. Gecko. - - Family =Pygopodidae=. Lialis--scale-foot. - - Family =Agamidae=. Draco--flying lizard. - Agama. - - Family =Iguanidae=. Iguana. - - Family =Anguidae=. Ophisaurus (Bipes, Pseudopus). - Anguis--blindworm. - - Family =Varanidae=. Varanus--monitor. - - Family =Amphisbaenidae=. Chirotes. - Amphisbaena. - - Family =Scincidae=. Tiliqua (Cyclodus). - Scincus--skink. - Chalcides (Seps). - - - Group =Rhiptoglossa=. - - Family =Chamaeleonidae=. Chamaeleon. - - Suborder (2). OPHIDIA. - - Family =Typhlopidae=. Typhlops--blind snake. - - Family =Boidae=. Python. - - Family =Colubridae=. Tropidonotus--ringed snake. - - Family =Hydrophidae=--sea snakes. - - Family =Crotalidae=. Crotalus--rattlesnake. - - Suborder (3). PYTHONOMORPHA. - - Family =Mosasauridae=. _Mosasaurus._ - - Order 7. DINOSAURIA. - - Suborder (1). SAUROPODA. - - Family =Atlantosauridae=. _Brontosaurus._ - - Family =Cetiosauridae=. _Morosaurus._ - - Suborder (2). THEROPODA. - - Family =Megalosauridae=. _Megalosaurus_ (_Ceratosaurus_). - - Family =Compsognathidae=. _Compsognathus._ - - Suborder (3). ORTHOPODA. - - Section (_a_). STEGOSAURIA. - - Family =Scelidosauridae=. _Polacanthus._ - - Family =Stegosauridae=. _Stegosaurus._ - - Section (_b_). CERATOPSIA. - - Family =Ceratopsidae=. _Polyonax_ (_Ceratops_). - - Section (_c_). ORNITHOPODA. - - Family =Camptosauridae=. _Hypsilophodon._ - - Family =Iguanodontidae=. _Iguanodon._ - - Family =Hadrosauridae=. _Hadrosaurus._ - - Order 8. CROCODILIA. - - Suborder (1). PARASUCHIA. - - Family =Phytosauridae=. _Phytosaurus_ (_Belodon_). - - Suborder (2). EUSUCHIA. - - Family =Teleosauridae=. _Teleosaurus._ - _Metriorhynchus._ - - Family =Goniopholidae=. _Goniopholis._ - - Family =Alligatoridae=. Alligator. - Caiman. - Jacare. - - Family =Crocodilidae=. Crocodilus. - - Family =Garialidae=. Garialis (Gavialis). - - Order 9. PTEROSAURIA. - - Family =Pterodactylidae=. _Pterodactylus._ - - Family =Rhamphorhynchidae=. _Rhamphorhynchus._ - - Family =Pteranodontidae=. _Pteranodon._ - - -FOOTNOTES: - -[15] A. Smith Woodward, _Catalogue of Fossil Fishes in the British -Museum_, Part II., Introduction, p. xii. - -[16] This classification of reptiles is mainly based on that of -Lydekker (_Catalogue of Fossil Reptiles in the British Museum_) but in -some respects that of von Zittel has been followed. - - - - - CLASS II. AVES[17]. - - - Subclass (I). ARCHAEORNITHES. - _Archaeopteryx._ - - Subclass (II). NEORNITHES. - - Order 1. RATITAE. - - Group =Æpyornithes=. _Æpyornis._ - - Group =Apteryges=. Apteryx--kiwi. - - Group =Dinornithes=. Moas. - - Group =Megistanes=. Casuarius--cassowary. - Dromaeus--emeu. - - Group =Rheornithes=. Rhea--American ostrich. - - Group =Struthiornithes=. Struthio--ostrich. - - Order 2. ODONTOLCAE. - _Hesperornis._ - - Order 3. CARINATAE. - - Group =Ichthyornithiformes=. - _Ichthyornis._ - _Apatornis._ - _Odontopteryx._ - - Group =Colymbiformes=. - Subgroup Colymbi--divers. - - Group =Sphenisciformes=. - Subgroup Sphenisci--penguins. - - - Group =Ciconiiformes=. - - Subgroup Steganopodes. Sula--gannet. - Pelicanus--pelican. - Phaëthon--frigate bird. - Phalacrocorax--cormorant. - - Subgroup Ardeae. Ardea--heron - - Subgroup Ciconiae. Leptoptilus--adjutant. - Ciconia--white stork. - - Group =Anseriformes=. - - Subgroup Palamedeae. Palamedea } - } screamers. - Chauna } - - Subgroup Anseres. Anas--wild duck. - Anser--goose. - Plectropterus--spur-winged goose. - Cygnus--swan. - Mergus--merganser. - - Group =Falconiformes=. - - Subgroup Cathartae. Cathartes--American vulture. - - Subgroup Accipitres. Falco--falcon. - Vultur--vulture. - Harpagus. - Gypogeranus--secretary bird. - - Group =Tinamiformes=. - - Subgroup Tinami. Tinamus. - - Group =Galliformes=. - - Subgroup Galli. Gallus--fowl. - Pavo--peacock. - - Subgroup Opisthocomi. Opisthocomus--hoatzin. - - Group =Gruiformes=. - Gruidae--cranes. - - Group =Stereornithes=. _Phororhacos._ - - Group =Charadriiformes=. - - Subgroup Limicolae. Charadriidae--plovers. - Parra--jacana. - - Subgroup Lari. Laridae--gulls. - Alcidae--auks. - - Subgroup Pteroclidae. Pterocles--sandgrouse. - - Subgroup Columbidae. Columbae--pigeons. - _Didus_--dodo. - _Pezophaps_--solitaire. - - Group =Cuculiformes=. - - Subgroup Cuculi. Scythrops. - - Subgroup Psittaci. Stringops--owl-parrot. - - Group =Coraciiformes=. - - Subgroup Coraciae. Coracias--roller. - Buceros--hornbill. - Upupa--hoopoe. - - Subgroup Striges. Owls. - - Subgroup Cypseli. Cypselidae--swifts. - Trochilidae--humming-birds. - - Subgroup Trogonidae. Trogons. - - Subgroup Pici. Rhamphastos--toucan. - Picus--woodpecker. - - Group =Passeriformes=. Crows, finches, larks, warblers, - and many others. - -C. MAMMALIA[18]. - -Class MAMMALIA. - -Subclass (I). ORNITHODELPHIA or PROTOTHERIA. - -Order. MONOTREMATA. - - Family =Ornithorhynchidae=. Ornithorhynchus--duck-bill. - - Family =Echidnidae=. Echidna--spiny ant-eater. - - Group =Multituberculata=. _Tritylodon._ - - Subclass (II). DIDELPHIA or METATHERIA. - - Order. MARSUPIALIA. - - Suborder (1). POLYPROTODONTIA. - - Family =Amphitheriidae=. _Phascolotherium._ - - Family =Didelphyidae=. Didelphys--opossum. - - Family =Dasyuridae=. Thylacinus--Tasmanian wolf. - Sarcophilus--Tasmanian devil. - Dasyurus. - - Family =Peramelidae=. Perameles--bandicoot. - Choeropus. - - Family =Notoryctidae=. Notoryctes--marsupial mole. - - Suborder (2). DIPROTODONTIA. - - Family =Phascolomyidae=. Phascolomys--wombat. - - Family Phalangeridae. Tarsipes. - Phalanger--cuscus. - Phascolarctus--koala. - _Thylacoleo._ - - Family =Diprotodontidae=. _Diprotodon._ - - Family =Nototheriidae=. _Nototherium._ - - Family =Macropodidae=. Macropus--kangaroo. - - Family =Epanorthidae=. Coenolestes. - - Subclass (III). MONODELPHIA or EUTHERIA. - - Order 1. EDENTATA. - - Family =Bradypodidae=. Bradypus } - }--sloths. - Choloepus } - - Family =Megatheriidae=. _Megatherium_--ground sloth. - - Family =Myrmecophagidae=. Myrmecophaga--great ant-eater. - Cycloturus--two-toed ant-eater. - - Family =Dasypodidae=. Chlamydophorus } - Dasypus }--armadillos. - Priodon } - Tatusia } - - Family =Glyptodontidae=. _Glyptodon._ - - Family =Manidae=. Manis--pangolin. - - Family =Orycteropodidae=. Orycteropus--aard-vark. - - Order 2. SIRENIA. - - Family =Manatidae=. Manatus--manatee. - - Family =Rhytinidae=. _Rhytina_--Steller's sea-cow. - - Family =Halicoridae=. Halicore--dugong. - - Family =Halitheriidae=. _Halitherium._ - - Order 3. CETACEA. - - Suborder (1). ARCHAEOCETI. - - Family =Zeuglodontidae=. _Zeuglodon._ - - Suborder (2). MYSTACOCETI or BALAENOIDEA. - - Family =Balaenidae=. Balaena--right whale. - Megaptera--humpbacked whale. - Balaenoptera--rorqual. - - Suborder (3). ODONTOCETI. - - Family =Physeteridae=. Physeter--sperm whale. - Hyperoödon--bottlenose. - Ziphius. - Mesoplodon. - - Family =Physodontidae=. _Physodon._ - - Family =Squalodontidae=. _Squalodon._ - - Family =Platanistidae=. Platanista--Gangetic dolphin. - Inia. - Pontoporia. - - Family =Delphinidae=. Monodon--narwhal. - Phocaena--porpoise. - Orca--killer. - Globicephalus--Ca'ing whale. - Grampus. - Lagenorhynchus. - Delphinus--dolphin. - Tursiops. - Prodelphinus. - - Order 4. UNGULATA. - - Division A. UNGULATA VERA. - - Suborder (1). ARTIODACTYLA. - - Section (_a_). SUINA. - - Family =Hippopotamidae=. Hippopotamus. - - Family =Suidae=. Sus--pig. - Babirussa. - Phacochaerus--wart hog. - _Hyotherium._ - - Family =Cotylopidae=. _Cotylops (Oreodon)._ - _Cyclopidius._ - - Family =Agriochoeridae=. _Agriochoerus._ - - Family =Anoplotheriidae=. _Anoplotherium._ - - Section (_b_). TYLOPODA. - - Family =Camelidae=. Camelus--camel. - Auchenia--llama. - - Section (_c_). TRAGULINA. - - Family =Tragulidae=. Dorcatherium (Hyomoschus)--chevrotain. - - Section (_d_). RUMINANTIA or PECORA. - - Family =Cervidae=. Moschus--musk deer. - Cervus--deer. - Cervulus--muntjac. - Hydropotes--Chinese water deer. - - Family =Giraffidae=. Giraffa--giraffe. - _Sivatherium._ - - Family =Antilocapridae=. Antilocapra--prongbuck. - - Family =Bovidae=. Tetraceros--four-horned antelope. - Gazella--gazelle. - Bos--ox. - Bison. - Bubalus--buffalo. - - Suborder (2). PERISSODACTYLA. - - Family =Tapiridae=. Tapirus--tapir. - - Family =Lophiodontidae=. _Lophiodon._ - _Hyracotherium._ - - Family =Palaeotheriidae=. _Palaeotherium._ - - Family =Equidae=. _Hipparion._ - Equus--horse. - - Family =Rhinocerotidae=. Rhinoceros. - _Elasmotherium._ - - Family =Titanotheriidae=. _Titanotherium (Brontops)._ - _Palaeosyops._ - - Family =Chalicotheriidae=. _Chalicotherium._ - - Family =Macraucheniidae=. _Macrauchenia._ - - Division B. SUBUNGULATA. - - Suborder (1). TOXODONTIA. - - Family =Astrapotheriidae=. _Astrapotherium._ - - Family =Nesodontidae=. _Nesodon._ - - Family =Toxodontidae=. _Toxodon._ - - Family =Typotheriidae=. _Typotherium._ - - - Suborder (2). CONDYLARTHRA. - - Family =Phenacodontidae=. _Phenacodus._ - - Suborder (3). HYRACOIDEA. - - Family =Hyracidae=. Procavia (Hyrax). - - Suborder (4). AMBLYPODA. - - Family =Coryphodontidae=. _Coryphodon._ - - Family =Uintatheriidae=. _Uintatherium_ (_Dinoceras_). - - Suborder (5). PROBOSCIDEA. - - Family =Dinotheriidae=. _Dinotherium._ - - Family =Elephantidae=. _Mastodon._ - Elephas--elephant. - - Group Tillodontia. - - Order 5. RODENTIA. - - Suborder (1). SIMPLICIDENTATA. - - Section SCIUROMORPHA. - - Family =Castoridae=. Castor--beaver. - - Section MYOMORPHA. - - Family =Lophiomyidae=. Lophiomys. - - Family =Muridae=. Hydromys. - Acanthomys--spiny mouse. - Mus--mouse. - - Family =Spalacidae=. Bathyergus. - - Family =Dipodidae=. Dipus--jerboa. - Pedetes--Cape jumping-hare. - - Section HYSTRICOMORPHA. - - Family =Hystricidae=. Hystrix--porcupine. - - Family =Chinchillidae=. Chinchilla. - Lagostomus--viscacha. - - Family =Dasyproctidae=. Coelogenys--paca. - Dasyprocta--agouti. - - Family =Caviidae=. Cavia--guinea-pig. - Hydrochaerus--capybara. - - Suborder (2). DUPLICIDENTATA. - - Family =Leporidae=. Lepus--hare and rabbit. - - Order 6. CARNIVORA. - - Suborder (1). CREODONTA. - - Family =Hyaenodontidae=. _Hyaenodon._ - - Suborder (2). CARNIVORA VERA or FISSIPEDIA. - - Section ÆLUROIDEA. - - Family =Felidae=. Felis--cat, lion, tiger. - _Machaerodus_--sabre-toothed lion. - - Family =Viverridae=. Viverra--civet. - Paradoxurus--palm civet. - - Family =Protelidae=. Proteles--aard wolf. - - Family =Hyaenidae=. Hyaena. - - Section CYNOIDEA. - - Family =Canidae=. Canis--dog, wolf, fox. - - Section ARCTOIDEA. - - Family =Ursidae=. Ursus--bear. - - Family =Mustelidae=. Latax--sea otter. - - Suborder (3). PINNIPEDIA. - - Family =Otariidae=. Otaria--sea lion. - - Family =Trichechidae=. Trichechus--walrus. - - Family =Phocidae=. Ogmorhinus--sea leopard. - - Order 7. INSECTIVORA. - - Suborder (1). DERMOPTERA. - - Family =Galeopithecidae=. Galeopithecus--'flying lemur'. - - Suborder (2). INSECTIVORA VERA. - - Family =Macroscelidae=. Macroscelides--jumping shrew. - - Family =Erinaceidae=. Erinaceus--hedgehog. - Gymnura. - - Family =Soricidae=. Sorex--shrew. - - Family =Talpidae=. Talpa--mole. - - Family =Potamogalidae=. Potamogale. - - Family =Solenodontidae=. Solenodon. - - Family =Centetidae=. Microgale. - Centetes--tenrec. - - Family =Chrysochloridae=. Chrysochloris--golden mole. - - Order 8. CHIROPTERA. - - Suborder (1). MEGACHIROPTERA. - - Family =Pteropidae=. Pteropus--flying fox. - - Suborder (2). MICROCHIROPTERA. - - Family =Rhinolophidae=. Horseshoe bats. - - Family =Phyllostomatidae=. Desmodus--vampire. - - Order 9. PRIMATES. - - Suborder (1). LEMUROIDEA. - - Family =Tarsiidae=. Tarsius--tarsier. - - Family =Chiromyidae=. Chiromys--aye aye. - - Suborder (2). ANTHROPOIDEA. - - Family =Hapalidae=. Hapale--marmoset. - - Family =Cebidae=. Mycetes--howling monkey. - Ateles--spider monkey. - - Family =Cercopithecidae=. Cynocephalus--baboon. - Macacus. - Colobus. - - Family =Simiidae=. Hylobates--gibbon. - Simia--orang. - Gorilla. - Anthropopithecus--chimpanzee. - - Family =Hominidae=. Homo--man. - - -FOOTNOTES: - -[17] This classification of birds is essentially that of Gadow and -Selenka in Bronn's _Classen und Ordnungen des Thierreichs_, Band VI., -Abth. IV., Vögel. Leipzig, 1891. - -[18] The classification adopted is almost entirely that given in -Flower and Lydekker's _Mammals Living and Extinct_. London, 1891. - - - - -CHAPTER III. - -SKELETON OF HEMICHORDATA, UROCHORDATA, AND CEPHALOCHORDATA. - - -SUBPHYLUM A. HEMICHORDATA. - -THE subphylum includes three genera, _Balanoglossus_[19], -_Cephalodiscus_ and _Rhabdopleura_; and perhaps a fourth, _Phoronis_. - -The skeletal structures found in _Balanoglossus_[20] are all -endoskeletal. They include: - -(1) The =notochord=. This arises as a diverticulum from the alimentary -canal which grows forwards into the proboscis and extends beyond the -front end of the central nervous system. It is hypoblastic in origin -and arises in the same way as does the notochord of _Amphioxus_. Its -cells become highly vacuolated and take on the typical notochordal -structure[21]. The cavity of the primitive diverticulum becomes -obliterated in front, but behind it opens throughout life into the -alimentary canal. - -(2) The =axial skeletal rods=. These are a pair of chitinous rods -which lie ventral to the notochord and in the collar region unite to -form a single mass. - -(3) The =branchial skeleton=. The gill bars separating the gill slits -from one another are strengthened by chitinous rods in a way closely -similar to that in _Amphioxus_. But between one primary forked rod and -the next there are two secondary unforked rods--not one, as in -_Amphioxus_. - -(4) The =chondroid tissue=. This is of mesoblastic origin and may be -regarded as an imperfect sheath for the notochord. - -In _Cephalodiscus_ and _Rhabdopleura_ as in _Balanoglossus_ the -notochord forms a small diverticulum growing forwards from the -alimentary canal into the proboscis stalk. - -Recent researches on _Phoronis_[22] show the existence in the collar -region of the larva (_Actinotrocha_) of a paired organ, which is -regarded by its discoverer as representing a double notochord. - - -SUBPHYLUM B. UROCHORDATA (TUNICATA). - -Skeletal structures of epiblastic and hypoblastic origin occur in the -Urochordata. Most Tunicates are invested by a thick gelatinous test -which often contains calcareous spicules, and serves as a supporting -organ for the soft body. The cells of this test are mesodermal in -origin. - -In larval Tunicata and in adults of the group Larvacea the tail is -supported by a typical notochord, which is confined to the tail. In -all Tunicata except Larvacea all trace of the notochord is lost in the -adult. - - -SUBPHYLUM C. CEPHALOCHORDATA. - -[Illustration FIG. 3. DIAGRAM OF THE SKELETON OF _Amphioxus -lanceolatus_ × 3 (after a drawing in the Index collection at the Brit. -Mus.). - - 1. skeleton of dorsal fin. - 2. notochord. - 3. neural tube. - 4. buccal skeleton. - 5. branchial skeleton. - 6. septa separating the myotomes. - 7. skeleton of ventral fin.] - -This subphylum includes the well-known genus _Amphioxus_[23]. In -_Amphioxus_ the skeleton is very simple. It contains no trace of -cartilage or bone and remains throughout life in a condition -corresponding to a very early stage in Vertebrata. The skeleton of -_Amphioxus_ is partly hypoblastic, partly mesoblastic in origin. - -(_a_) =Hypoblastic skeleton.= - -The =notochord= (fig. 3, 2) is an elastic rod extending along the -whole length of the body past the anterior end of the nerve cord. It -lies ventral to the nerve cord, and shows no trace of segmentation. It -is chiefly made up of greatly vacuolated cells containing lymph, but -near the dorsal and ventral surfaces the cells are less vacuolated. -The notochord is immediately surrounded by a structureless cuticular -layer, the _chordal sheath_, and outside this comes the mesoblastic -_skeletogenous layer_, which also surrounds the nerve cord. - -The =branchial skeleton=. This consists of a series of chitinous -elastic rods which strengthen the gill bars and are alternately forked -and unforked ventrally. The forked rods are primary, and are U-shaped -in section, the unforked rods are secondary, and are circular in -section. All these rods are united at intervals by transverse rods. - -(_b_) =Mesoblastic skeleton.= - -The =buccal skeleton=. On each side of the mouth there is a curved bar -resembling the notochord in structure. The bars are segmented, and -each segment bears a smaller rod which supports a tentacle, the whole -forming the buccal skeleton (fig. 3, 4). - -The notochord is enclosed in a thick =sheath= of connective tissue -continuous with a thinner sheath round the nerve cord. The sheaths of -the notochord and nerve cord together form the skeletogenous layer, -and prolongations of it form the myomeres or septa between the -myotomes or segments of the great lateral muscles of the body. - -The =skeleton of each median fin= consists of small cubical masses of -a gelatinous substance arranged in rows (fig. 3, 1 and 7), and serving -to strengthen the fins. - - -FOOTNOTES: - -[19] The name _Balanoglossus_ is used here in its widest sense to -include all the Enteropneusta. - -[20] See W. Bateson, _Quart. J. Micr. Sci._ n. s. vol. XXIV. 1884, p. -208 and later; also E.W. Macbride, _Ibid._ vol. XXXVI. 1894, p. 385. - -[21] See p. 52. - -[22] A.T. Masterman, _P.R. Soc. Edinb._ 1895-96, p. 59; and _Anat. -Anz._ 1896, p. 266. - -[23] See E. Ray Lankester, _Quart. J. Micr. Sci._ vol. XXIX. n. s. -1889, p. 365. W.B. Benham, _Ibid._ vol. XXXV. n. s. 1893, p. 97. J.W. -Kirkaldy, _Ibid_. vol. XXXVII. n. s. 1895, p. 303. The last-named -writer divides the genus into three subgenera. - - - - -CHAPTER IV. - -SUBPHYLUM D. VERTEBRATA. - - -THE animals included in this great group all possess an internal axial -skeleton forming the vertebral column or back-bone; and a dorsal -spinal cord. The vertebral column is developed from the skeletogenous -layer, which surrounds the spinal cord together with the notochord and -its sheath; and in the great majority of cases the notochord becomes -more or less modified and reduced in the adult. In some cases the -notochord remains unmodified and the skeletogenous layer surrounding -it is not segmented to form vertebrae, but in every case the neural -arches which protect the spinal cord are segmented. The notochord -never extends further forwards than the mid-brain. - -All true vertebrates possess a cranium or skeletal box enclosing the -brain. - - -(I.) CYCLOSTOMATA. - -The mouth in living forms is suctorial and is not supported by jaws. -In some fossil forms the character of the mouth is unknown. - - -_Order I._ MARSIPOBRANCHII[24]. - -In these animals limbs and limb girdles are always completely absent. -They have no exoskeleton except horny teeth. - -The endoskeleton, excluding the notochord, is entirely cartilaginous -or membranous. The axial skeleton consists of a cartilaginous cranium -without jaws, succeeded by a thick persistent notochord enveloped in -a sheath. The notochord in living forms is unsegmented, but segmented -cartilaginous neural arches are present in some cases. A complicated -series of cartilaginous elements occurs in relation to the mouth, -gills, and sense organs. The median fins are supported by -cartilaginous pieces, the radiale. The order includes the Lampreys and -Hags. - - -_Order II._ OSTRACODERMI[25]. - -The forms included in this group have long been extinct, being known -only from beds of Upper Silurian and Lower Devonian age. They differ -much from all other known animals. The exoskeleton is always greatly -developed and includes (1) large bony plates covering the anterior -region; (2) scales covering the posterior region. The plates are -deeply marked by canals belonging to dermal sense organs. Jaws are -unknown, and arches for the support of the appendicular skeleton are -rudimentary or absent. The tail is heterocercal (see p. 60). - - -_Suborder_ (1). HETEROSTRACI. - -The exoskeleton consists principally of calcifications forming dorsal -and ventral shields which cover the head and abdominal region; the -dorsal shield is formed of a few plates firmly united, the ventral -shield of a single plate. The shields are composed of three layers, -the middle layer being traversed by canals belonging to the dermal -sense organs which open to the exterior by a series of pores. The tail -is sometimes covered by scales. The orbits are widely separated and -laterally placed. Paired appendages are absent. These curious forms -are found in beds of Upper Silurian and Lower Devonian age. One of the -best known genera is _Pteraspis_. - - -_Suborder_ (2). OSTEOSTRACI. - -The exoskeleton as in the Heterostraci consists of shields and scales, -the shields being divisible into three layers. The anterior part of -the body is covered dorsally by a single large shield which differs -from those of the Heterostraci in having the inner layer ossified. The -middle layer contains canals for the passage of blood vessels, but the -exoskeleton shows no impressions of dermal sense organs. The posterior -part of the body is covered by large quadrangular scales. Paired -appendages are absent, but median dorsal and caudal fins occur -supported by scales, not fin-rays. _Cephalaspis_, the best known of -these animals, occurs in beds of Lower Devonian age. - - -_Suborder_ (3). ANTIARCHA. - -The exoskeleton is formed of bony plates, the dorsal and ventral -shields each consisting of several symmetrically arranged pieces. The -tail may be covered with small scales or may be naked. The head is -articulated with the trunk, and its angles are drawn out into a pair -of segmented paddle-like appendages, covered with dermal plates. The -orbits are close together. A dorsal fin and traces of mouth parts -occur in _Pterichthys_, but the endoskeleton is unknown. The best -known forms _Pterichthys_[26] and _Asterolepis_ occur in beds of Lower -Devonian age. - - -GENERAL ACCOUNT OF THE SKELETON OF MARSIPOBRANCHII. - -The Marsipobranchii are worm-like animals. The living forms include -two families, the Myxinoidei (Hags)--genera _Myxine_ and -_Bdellostoma_--and the Petromyzontidae (Lampreys). - -Three species of _Petromyzon_ are known, _P. fluviatilis_, _P. -marinus_ and _P. planeri_. The larval forms were for a long time -thought to belong to a separate genus and were called _Ammocoetes_. - -The Myxinoids, although very highly specialised in their own way, are -at distinctly a lower stage of development than the adult Lamprey, and -come nearer to the larval Lamprey or Ammocoete. - -SPINAL COLUMN. - -[Illustration FIG. 4. A, DORSAL; B, LATERAL AND C, VENTRAL VIEW OF THE -SKULL OF _Petromyzon marinus_ × 1 (after PARKER). - - 1. horny teeth. - 2. labial cartilage. - 3. anterior dorsal cartilage. - 4. posterior dorsal cartilage. - 5. nasal capsule. - 6. auditory capsule. - 7. dorsal portion of trabeculae. - 8. lateral distal mandibular. - 9. lingual cartilage. - 10. branchial basket. - 11. cartilaginous cup supporting pericardium. - 12. sheath of notochord. - 13. neural plate.] - -In Myxinoids and larval lampreys, the notochord is enclosed in a thick -chordal sheath, in connection with which in the tail region there -occur cartilaginous pieces forming neural arch elements. In the trunk -region, however, no cartilage occurs in connection with the spinal -column, the only cartilage present being that forming the radiale of -the dorsal fin. On the other hand in most species of lamprey -(_Petromyzon_) cartilaginous pieces forming imperfect neural arches -(fig. 4, B, 13) are found lying in the tough skeletogenous layer -dorsal to the notochord, and extending throughout the whole length of -the trunk and tail. Two of these pieces, which are probably homologous -with the neural plates (see p. 72) of Elasmobranchs, occur to each -_neuromere_, or segment as determined by the spinal nerves. The -dorsal and caudal fins are supported by paired cartilaginous radiale -which are connected proximally with the skeletogenous layer. - -THE SKULL. - -In Myxinoids the cranium is a mere cartilaginous floor without side -walls or roof, and the trabeculae[27] end without growing forwards -into cornua. In Lampreys the trabeculae grow forwards and send up -plates of cartilage which meet above (fig. 4, 7) and form side walls -and a roof for part of the brain case. In Lampreys a labial suctorial -apparatus is well developed, including a large ring-like piece of -cartilage (fig. 4, 2) which supports the oral funnel and bears a large -armament of horny teeth. In Myxinoids on the other hand the labial -skeleton is small and consists merely of barbels round the mouth. - -The olfactory organ of Myxinoids has a very curious skeleton. It is -covered with a kind of grating of cartilage which is prolonged in -front into a tube composed of a series of imperfect cartilaginous -rings. In Lampreys the olfactory organ opens merely by a short -membranous passage. In correlation with the small development of the -labial suctorial apparatus in Myxinoids the lingual apparatus is very -greatly developed. The tongue in _Myxine_ has been said to 'dominate -the whole body' (Parker). It is supported by a great median -cartilaginous bar which when followed forwards first becomes bifid and -still further forwards becomes four-cleft. - -The horny teeth in Myxinoids are chiefly borne on the very large -supralingual apparatus. They form a double series arranged in the form -of an arch. In _Myxine_ there are seven large teeth and nine small -ones on each side. In _Bdellostoma_ the teeth of the two rows are more -equal in size. In _Bdellostoma_ and _Myxine_ it has been shown that -imperfect calcified teeth occur below the horny teeth. - -In Lampreys the lingual apparatus (fig. 4, C, 9) is well developed, -but not excessively so. It consists of a long median cartilaginous bar -which ends in front with a semicircular piece of cartilage supporting -the median part of the tongue. - -In both Myxinoids and Lampreys there is a complicated branchial basket -apparatus, but while in Myxinoids the basket apparatus is -interbranchial, formed deep within the head near the hypoblastic -lining of the throat, in Lampreys it is extra-branchial and formed -outside the head cavities (fig. 4, 10). The two sides of the basket -apparatus in _Myxine_ are not symmetrical. In the interbranchial -basket apparatus of Myxinoids the hyoid and first and second branchial -arches can be recognised. Traces of the interbranchial skeleton of -Myxinoids can be detected in Lampreys, and similarly in Myxinoids, -there are indications of the extra-branchial skeleton of _Petromyzon_. -The branchial basket in Lampreys forms at its posterior end a kind of -cup which supports the pericardium (fig. 4, 11). - -A remarkable Cyclostome named _Palaeospondylus_[28] has recently been -described from the Scottish Old Red Sandstone. It differs however from -all living Cyclostomes, in having a spinal column formed of distinct -vertebrae with well-developed neural arches. The caudal fin is well -developed and the dorsal radiale are forked as in lampreys. The skull -is well calcified and the auditory capsules are specially large. The -mouth is very similar to that of lampreys, being circular and without -jaws; it is provided with barbels or cirri. There is no trace of limbs -and the average length is only about 1-1-1/2 inches. - - -FOOTNOTES: - -[24] See W.K. Parker On the skeleton of the Marsipobranch fishes, -_Phil. Trans._ 1883, London. - -[25] See A. Smith Woodward, _Catalogue of Fossil Fish in the British -Museum_, Part II., 1891. A. Smith Woodward, _Nat. Sci._ vol. I. 1892, -p. 596. - -[26] See R.H. Traquair, _Ann. Nat. Hist._, ser. 6, vol. II. 1888, p. -485. - -[27] See p. 17. - -[28] R.H. Traquair, _Ann. Nat. Hist._ vol. VI. 1890, p. 485; _P. Phys. -Soc. Edinb._ vol. XII. 1892-93, pp. 87-94, and 312-320. A. Smith -Woodward, _Nat. Sci._ vol. III. p. 128, 1893. - - - - -CHAPTER V. - -(II.) GNATHOSTOMATA. - - -THE mouth is supported by definite jaws. - - -ICHTHYOPSIDA. - -The epiblastic exoskeleton is generally unimportant, the mesoblastic -exoskeleton is usually well developed. - -The notochord with its membranous sheath (1) may remain unmodified, or -(2) may be replaced by bone or cartilage derived from the -skeletogenous layer, or (3) may be calcified to a varying extent. - -The first vertebra is not homologous throughout the whole series and -so is not strictly comparable to the atlas of Sauropsids and Mammals. - -The centra of the vertebrae have no epiphyses. The skull may be (_a_) -incomplete and membranous, or (_b_) more or less cartilaginous, or -(_c_) bony. Membrane bones are not included in the cranial walls, and -there are large unossified tracts in the skull. When membrane bones -are developed in connection with the skull, a large parasphenoid -occurs. The basisphenoid is always small or absent. The skull may be -immovably fixed to the vertebral column, or may articulate with it by -a single or double occipital condyle. When the occipital condyle is -double, it is formed by the exoccipitals, and the basi-occipital is -small or unossified. The mandible may be (_a_) cartilaginous, (_b_) -partially ossified, or (_c_) membrane bones may be developed in -connection with it,--if so, there is usually more than one membrane -bone developed in connection with each half. - -There are at least four pairs of branchial arches present during -development. The sternum, if present, is not costal in origin. - - -CLASS I. PISCES. - -The exoskeleton is in the form of scales, which may be entirely -mesoblastic or dermal in origin (e.g. _cycloid_ and _ctenoid_ scales), -or may be formed of both mesoblast and epiblast (e.g. _placoid_ and -_ganoid_ scales). Large bony plates may be derived from both these -types of scale. In general fish with a greatly developed dermal armour -have the endoskeleton poorly developed; and the converse also holds -good. - -The integument of the dorsal and ventral surfaces is commonly -prolonged into longitudinal unpaired fins, supported by an internal -skeleton. These fins are distinguished according to their position as -dorsal, caudal and anal fins. The dorsal and anal fins are used -chiefly as directing organs, the caudal fin is however a most -important organ of propulsion. - -Three types of tail are found in fishes, viz.:-- - -1. The =diphycercal=, in which the axis is straight and the tail is -one-bladed and symmetrical, an equal proportion of radiale[29] being -attached to the upper and lower surfaces of the axis. - -2. The =heterocercal=, in which the tail is asymmetrical and the axis -is bent upwards, the proportion of radiale or of fin-rays attached to -its upper surface being much smaller than that attached to its lower -surface. - -3. The =homocercal=, in which the tail though externally symmetrical, -so far resembling the diphycercal type, is internally really -heterocercal, the great majority of the radiale or of the fin-rays -being attached to the lower surface of the axis. - -The cranium in the simplest cases (e.g. Selachii) forms a -cartilaginous box enclosing the brain and sense organs; in bony fishes -it is greatly complicated. When palatine or pterygoid bones are -present they are formed by the ossification of cartilage; in -Sauropsida and Mammalia they are laid down as membrane bones. There is -no tympanic cavity or auditory ossicle in relation to the ear. - -There are two principal types of suspensorium by means of which the -jaws are attached to the cranium:-- - -(1) The =Autostylic=. This is the primitive condition in which the -mandibular arch articulates with the base of the cranium in front of -the hyoid and in a similar manner. - -(2) The =Hyostylic=. In this case the mandibular arch becomes -connected with the hyomandibular and supported by the hyoid arch. -These terms are more fully discussed in Chapter VIII. - -There is always an internal framework supporting the gills; it usually -consists of the hyoid arch and five, rarely six or seven, pairs of -branchial arches. The limbs are represented by two pairs of fins, the -pectoral and the pelvic; they are not divided into proximal, middle -and distal portions. The ribs do not unite with a median ventral -sternum, or meet in the mid-ventral line in any other way in the trunk -region. - - -_Order I._ ELASMOBRANCHII. - -The exoskeleton is in the form of placoid scales which are sometimes -so numerous as to give the whole skin a rough surface forming -shagreen. In some cases the placoid scales are enlarged to form plates -or spines capped or coated with enamel. These spines may be imbedded -in the flesh in front of the paired or unpaired fins, or may be -attached to the tail. They are specially characteristic of the -suborder Acanthodii. The endoskeleton is cartilaginous and true bone -is never found. Much of the skeleton, especially of the vertebral -column, is however often calcified, this being especially well seen in -the anterior part of the vertebral column of Rays (Raiidae). In living -forms cartilaginous biconcave vertebrae are always well developed, but -in some extinct forms the notochord persists unconstricted. Neural and -haemal arches are however always developed; they sometimes remain -separate, sometimes fuse with the centra. Ribs are often wanting and -when present are often not separated off from the vertebrae. The -cranium is a simple cartilaginous box whose most prominent parts are -the capsules which enclose the sense organs. The skull is sometimes -immovably fixed to the vertebral column, sometimes articulates with it -by means of two condyles. There is no operculum and no representative -of the maxilla or premaxillae. The teeth are very variable. Large -pectoral and pelvic fins always occur. - -The Elasmobranchii may be divided into four suborders:-- - - (1) Ichthyotomi. - (2) Pleuropterygii. - (3) Selachii. - (4) Acanthodii. - - -_Suborder_ (1). ICHTHYOTOMI[30]. - -The members of this suborder range from the Devonian to the Permian -and so have long been extinct. - -The endoskeletal cartilage has granular calcifications evenly -distributed throughout it. The notochord is unconstricted, but the -neural and haemal arches are well-developed, and the neural spines are -long and slender. There is a continuous dorsal fin with separate -basalia and radiale. The tail is diphycercal, and the pectoral fins -are typical archipterygia[31]. The pelvic fins of the male are -prolonged to form claspers. - -The best known of these primitive Elasmobranchs are the -Pleuracanthidae. - - -_Suborder_ (2). PLEUROPTERYGII. - -This suborder was formed for the reception of _Cladoselache_, an -Elasmobranch found in the Lower Carboniferous of Ohio[32]. - -The exoskeleton is in the form of small, thickly-studded dermal -denticles. The vertebral centra are unossified, and the tail is -strongly heterocercal. There were certainly five, perhaps seven gill -slits, and the suspensorium is apparently hyostylic. The paired fins -are, according to the view which derives them by concentration from -continuous lateral folds, the most primitive known (see p. 129) and -claspers are absent. - - -_Suborder_ (3). SELACHII. - -Cartilaginous or partially calcified biconcave vertebrae are always -well developed; they constrict the notochord intervertebrally. The -neural and haemal arches and spines are stout and intercalary -cartilages (interdorsalia) are present. The tail is heterocercal, but -in some cases (_Squatina_) approaches the diphycercal condition. In -most cases the suspensorium is hyostylic, the jaws being attached to -the cranium by means of the hyomandibular, and the palato-pterygo -quadrate bar not being fused to the cranium. There are generally five -pairs of branchial arches, and gill rays are borne on the posterior -surface of the hyoid arch, and on both the anterior and posterior -surfaces of the first four branchial arches. The Notidanidae differ -from most Selachians in two respects, first as regards the -suspensorium,--Meckel's cartilage articulating directly with the -palato-pterygo-quadrate bar, and not being connected with the hyoid -arch; and secondly as regards the number of branchial arches,--six -pairs occurring in _Hexanchus_ and seven in _Heptanchus_. - -The pectoral fins are without the segmented axis of the -archipterygium. In most cases they are sharply marked off from the -body and lie almost at right angles to it; but in the Rays they have -the form of lateral expansions in the same plane as the body, from -which they are not sharply marked off. The pelvic fins in the male -bear long grooved cartilaginous rods which are accessory copulatory -organs or claspers. - -There are two principal groups of Selachii, the Squalidae or Sharks -and Dogfish, and the Batoidei or Skates and Rays. The Squalidae have -the shape of ordinary fish, the pectoral fins are vertically placed -and the body ends in a powerful heterocercal tail. The Batoidei have -flattened bodies owing to the great size and horizontal position of -the pectoral fins. The tail is long and thin and is often armed with -spines. The teeth in Selachii differ much in character in the -different forms, and are always arranged in numerous rows. They are -generally pointed and triangular or conical in the Squalidae, while in -the Batoidei they are often broad and flattened. - - -_Suborder_ (4). ACANTHODII. - -The fishes included in this group are all extinct and in some respects -are intermediate between Elasmobranchii and Ganoidei. The body is -elongated and closely covered with small scales consisting of dentine -enamelled at the surface. The notochord is persistent and the -calcification of the endoskeletal cartilage is only superficial. The -tail is heterocercal. The jaws bear small conical teeth, or in some -cases are toothless. The skeleton of all the fins differs from that of -modern Elasmobranchs in having the cartilaginous radiale much reduced, -and the fins are nearly always each provided with an anterior spine, -which except in the case of the pectoral fins is merely inserted -between the muscles. These spines are really enormous dermal fin-rays; -the pectoral fin-spine is articulated to the pectoral girdle. - -The suborder includes many well-known extinct forms like _Acanthodes_ -and _Diplacanthus_; it ranges from the Devonian to the Permian. - - -PISCES, HOLOCEPHALI. - -_Order II._ HOLOCEPHALI. - -This order includes a single suborder only. - - -_Suborder._ CHIMAEROIDEI. - -[Illustration FIG. 5. SKULL OF A MALE _Chimaera monstrosa_ (after -HUBRECHT). - - 1. nasal capsule. - 2. cartilaginous appendage to the fronto-nasal region. - 3. erectile appendage. - 4. foramen by which the ophthalmic nerves leave the orbit. - 5. foramen by which the ophthalmic branch of the Vth nerve enters - the orbit. - 6. auditory capsule. - 7. interorbital septum. - 8. mandible articulating with an outgrowth from the posterior part - of the palato-pterygo-quadrate. - 9. teeth. - 10. labial cartilage. - II. III. V. VII. IX. X. foramina for the passage of cranial nerves.] - -These singular fish have the skin smooth and in living forms almost or -quite scaleless. The palato-pterygo-quadrate bar and hyomandibular are -fused to the cranium, and Meckel's cartilage articulates directly with -the part corresponding to the quadrate. The skull is distinctly -articulated with the spinal column, the notochord is persistent and -unconstricted, and the skeletogenous layer shows no trace of metameric -segmentation, though in the neural arches this segmentation is -readily traceable. The neural arches of the first few vertebrae are -fused together and completely surround the notochord, while they do -not in other parts of the body. The tail is diphycercal. Of the living -genera, in _Callorhynchus_ there is no trace of calcification in the -skeletogenous layer, while in _Chimaera_ rings of calcification are -found, there being three to five for each vertebra as indicated by the -foramina for the exit of the spinal nerves. The pelvic fins are -produced into claspers. Besides the living genera _Chimaera_, -_Harriotta_ and _Callorhynchus_ a fair number of fossil forms are -known, e.g. _Ischyodus_. - - -_Order_ III. GANOIDEI. - -The fishes included under the term Ganoidei form a very heterogeneous -group, some of which closely approach the Dipnoi, others the -Elasmobranchii, others the Teleostei. The great majority of them are -extinct, only eight living genera being known; these are all -inhabitants of the northern hemisphere, and with the exception of -_Acipenser_, which is both fluviatile and marine, are entirely -confined to fresh water. - -The following is a list of the living genera of Ganoids with their -respective habitats:-- - - _Acipenser._ Rivers and seas of the northern hemisphere. - - _Scaphirhynchus._ Mississippi and rivers of Central Asia. - - _Polyodon_ (_Spatularia_). Mississippi. - - _Psephurus._ Yan-tse-kiang, and Hoangho. - - _Polypterus._ Rivers of tropical Africa. - - _Calamoichthys._ Some rivers of West Africa. - - _Lepidosteus._ Freshwaters of Central and North America and - Cuba. - - _Amia._ Rivers of Carolina. - -The exoskeleton is very variable, thus the body may be:-- - -(_a_) Naked or with minute stellate ossifications as in the -Polyodontidae. (_b_) Partially covered with large detached bony -plates as in _Scaphirhynchus_ and _Acipenser_. (_c_) Entirely covered -with rhomboidal ganoid scales as in _Lepidosteus_, _Polypterus_, -_Palaeoniscus_ and many extinct forms. (_d_) Covered with rounded -scales shaped like the cycloid scales of Teleosteans as in _Amia_. -(_e_) Having the trunk and part of the tail covered with rhomboidal -scales, and the remainder of the tail with rounded scales as in -_Trissolepis_. - -The teeth also are very variable. The endoskeleton shows every stage -of transition from an almost entirely cartilaginous state as in -_Acipenser_ to a purely bony state as in _Lepidosteus_. Sometimes, as -in _Acipenser_, the notochord persists, and its sheath is unsegmented; -sometimes, as in _Lepidosteus_, there are fully formed vertebrae. The -tail may be heterocercal, as in _Acipenser_, or diphycercal as in -_Polypterus_. The cartilaginous cranium is always covered with -external membrane bone to a greater or less extent, and the -suspensorium is markedly hyostylic. The pectoral girdle is formed of -two parts, one endoskeletal and cartilaginous, corresponding with the -pectoral girdle of Elasmobranchs, and one exoskeletal and formed of -membrane bones, corresponding with the clavicular bones of -Teleosteans. The pelvic fins are always abdominal. The fins often, as -in _Polypterus_, have spines (fulcra) attached to their anterior -borders. - -The order Ganoidei may be divided into three suborders: - - (1) CHONDROSTEI. Living genera _Acipenser_, _Scaphirhynchus_, - _Polyodon_ and _Psephurus_. - - (2) CROSSOPTERYGII. Living genera _Polypterus_ and - _Calamoichthys_. - - (3) HOLOSTEI. Living genera _Lepidosteus_ and _Amia_. - - -_Suborder_ (1). CHONDROSTEI. - -The skull is immovably fixed to the vertebral column. By far the -greater part of the skeleton is cartilaginous. The notochord is -persistent and unconstricted, its sheath is membranous, but -cartilaginous neural and haemal arches are developed. Intercalary -pieces (interdorsalia) occur between the neural arches, and similar -pieces (interventralia) between the haemal arches. The cranium is -covered with membrane bone, and teeth are but slightly developed. The -tail is heterocercal. Gill rays occur on the hyoid arch, and the gills -are protected by a bony operculum attached to the hyomandibular. The -skin (1) may be almost or quite naked, (2) may carry bony plates -arranged in rows, or may be covered (3) with rhomboidal scales, or (4) -partly with rhomboidal, partly with cycloidal scales. - - -_Suborder_ (2). CROSSOPTERYGII. - -The exoskeleton has the form of cycloidal or rhomboidal scales. The -condition of the vertebral column differs in the different genera. -Sometimes, as in _Polypterus_, there are well-developed ossified -vertebrae; sometimes, as in many extinct forms, the notochord persists -and is unconstricted. The tail may be diphycercal or heterocercal. The -pectoral and sometimes the pelvic fins consist of an endoskeletal axis -bearing a fringe of dermal rays. - - -_Suborder_ (3). HOLOSTEI. - -The exoskeleton has the form of cycloidal or rhomboidal scales. The -notochord is constricted and its sheath is segmented and ossified, -forming distinct vertebrae, which are generally biconcave, sometimes -opisthocoelous (_Lepidosteus_). The cartilaginous cranium is largely -replaced by bone, and in connection with it we find not only membrane -bone, but cartilage bone, as the basi-occipital, exoccipitals, and -pro-otic are ossified. The tail is heterocercal. The suspensorium -resembles that of Teleosteans, consisting of a proximal ossification, -the hyomandibular, which is movably articulated to the skull and a -distal ossification, the symplectic. The two are separated by some -unossified cartilage. The cartilaginous upper and lower jaws are to a -great extent surrounded and replaced by a series of membrane bones. - - -_Order_ IV. TELEOSTEI. - -The exoskeleton is sometimes absent but generally consists of -overlapping cycloid or ctenoid scales. Bony plates are sometimes -present, as in the Siluridae, or the body may be encased in a complete -armour of calcified plates, as in _Ostracion_. Enamel is however never -present, and the plates are entirely mesodermal. The skeleton is bony, -but in the skull much cartilage generally remains. The vertebral -centra are usually deeply biconcave, and the tail is of the masked -heterocercal type distinguished as _homocercal_. In the skull the -occipital region is always completely ossified, while the sphenoidal -region is generally less ossified. The skull has usually a very large -number of membrane bones developed in connection with it. The teeth -vary much in character in the different members of the order, but are -as a rule numerous and pointed, and are ankylosed to the bone. The -suspensorium is hyostylic and the jaws have much the same arrangement -as in the Holostei. There are five pairs of branchial arches, of which -all except the last bear gill rays. A series of dermal opercular bones -is developed in connection with these arches. The pectoral girdle -consists almost entirely of dermal clavicular bones. The pelvic girdle -has disappeared, its place being taken by the enlarged and ossified -dermal fin-rays of the pelvic fins. - -The group includes the vast majority of living fish (see p. 33). - - -_Order_ V. DIPNOI. - -The exoskeleton is of two types; dermal bones are largely developed in -the head region, while the tail and posterior part of the body may be -naked or may be covered with overlapping scales. The cranium remains -chiefly cartilaginous, the palato-pterygo-quadrate bar is fused with -the cranium, and the suspensorium is autostylic. The gill clefts are -feebly developed and open into a cavity covered by an operculum. The -notochord is persistent and unconstricted, and the limbs are -archipterygia. The pelvic fins are without claspers. - - -_Suborder_ (1). SIRENOIDEI[33]. - -The head has well developed membrane bones. The trunk is covered with -overlapping scales and bears no bony plates. Three pairs of teeth are -present, two in the upper and one in the lower jaw, the two principal -pairs of teeth are borne on the palato-pterygoids and splenials, while -the third pair are found in the vomerine region. The tail is -diphycercal in living forms. In the extinct Dipteridae it is -heterocercal. The pectoral girdle includes both membrane and cartilage -bones. The pelvic girdle consists of a single bilaterally symmetrical -piece of cartilage. - -This suborder is represented by the living genera _Ceratodus_, -_Protopterus_ and _Lepidosiren_, and among extinct forms by the -Dipteridae and others. - - -_Suborder_ (2). ARTHRODIRA. - -Bony plates are developed not only on the head but also on the -anterior part of the trunk, where they consist of a dorsal, a ventral, -and a pair of lateral plates which articulate with the cranial shield. -The posterior part of the trunk is naked. The tail is diphycercal. The -jaws are shear-like, and their margins are usually provided with -pointed teeth whose bases fuse with the tissue of the jaw and -constitute dental plates. There seem to have been three pairs of these -plates, arranged as in the Sirenoidei, the principal ones in the upper -jaw being borne on the palato-pterygoids. Small pelvic fins are -present, but pectoral fins are unknown. - -The Arthrodira occur chiefly in beds of Devonian and Carboniferous -age. Two of the best known genera are _Coccosteus_ from the European -Devonian and _Dinichthys_, a large predatory form from the lower -Carboniferous of Ohio. - - -FOOTNOTES: - -[29] See p. 79. - -[30] For this and other groups of extinct fish see A. Smith Woodward, -_Catalogue of Fossil Fish in the British Museum_, Parts I.-III. -London, 1889-95. - -[31] See p. 127. - -[32] See B. Dean, _J. Morphol._ vol. IX. pp. 87-114, 1894, and _Nat. -Sci._ vol. VIII. p. 245, 1896. - -[33] A. Günther, _Phil. Trans._ vol. 161, Part II. 1871, p. 511. T.H. -Huxley, "On Ceratodus and the classification of fishes," _P.Z.S._ -1876, p. 24. - - - - -CHAPTER VI. - -THE SKELETON OF THE DOGFISH[34]. - -_Scyllium canicula._ - - -I. EXOSKELETON. - -The exoskeleton of the dogfish is mainly composed of placoid scales, -each of which consists of a little bony base imbedded in the skin, -bearing a small backwardly-directed spine formed of dentine capped -with enamel. The scales are larger on the dorsal than on the ventral -surface, and on the jaws they are specially large and regularly -arranged in rows, there forming the teeth. The margins of the jaws or -lips are without scales. - -A second exoskeletal structure is found in the fins, all of which, -both paired and unpaired, have, in addition to their cartilaginous -endoskeleton, large numbers of long slender horny fibres, the -fin-rays, which are of exoskeletal origin. - - -II. ENDOSKELETON. - -The endoskeleton of the dogfish consists almost entirely of cartilage, -which however may become calcified in places, e.g. the centrum of each -vertebra is lined by a layer of calcified tissue. - -The endoskeleton is divisible into an =axial= portion consisting of -the vertebral column, skull, and skeleton of the median fins, and an -=appendicular= portion consisting of the skeleton of the paired fins -and their girdles. - - -1. THE AXIAL SKELETON. - -A. THE VERTEBRAL COLUMN AND RIBS. - -The vertebral column consists of a series of some hundred and thirty -vertebrae, each of which is united with its predecessor and successor -in such a way as to allow a large amount of flexibility. - -These vertebrae are developed round an unsegmented rod, the -=notochord=, which forms the axial support of the embryo. The -notochord remains continuous throughout the whole vertebral column, -but is greatly constricted opposite the middle of each vertebra, and -thus rendered moniliform. The vertebrae are divided into two groups, -an anterior group of trunk vertebrae, and a posterior group of caudal -or tail vertebrae. - -A typical vertebra consists of a middle portion, the =centrum=, a -dorsal portion, the =dorsal= or =neural arch=, which surrounds the -spinal cord, and a ventral portion, the =ventral= or =haemal arch=, -which similarly encloses a space. - -The tail vertebrae of the dogfish have this typical arrangement, the -trunk vertebrae have the haemal arches modified. - -Each =centrum= is a short cylinder of cartilage surrounding an -hourglass-shaped cavity occupied by the notochord. The =neural arches= -are composed of three separate elements, the =vertebral neural plates= -(basidorsalia), =intervertebral neural plates= (interdorsalia), and -=neural spines= (supradorsalia). - -The =vertebral neural plates= are in the adult fused with their -respective centra, and are notched behind for the exit of the ventral -(motor) roots of the spinal nerves. The =intervertebral neural plates= -are polygonal pieces alternating with the vertebral neural plates; -they are notched behind, but at a more dorsal level than are the -vertebral neural plates, for the exit of the dorsal or sensory roots -of the spinal nerves. - -The =neural spines= are small patches of cartilage filling up the gaps -between the dorsal ends of the neural plates. - -The =haemal arches= (basiventralia) differ much in the trunk and tail -portions of the vertebral column. In the trunk portion the centra are -flattened below, and the two halves of the haemal arch diverge from -one another as blunt =ventri-lateral processes= to -which short cartilaginous rods, the =ribs=, are attached. Further back -at about vertebra 37, the two halves of the haemal arch project -downwards and meet forming a complete arch. Further back still, -towards the hind end of the tail, the haemal arches bear median -=haemal spines= (ventrispinalia). - - -B. THE SKULL. - -The skull of the dogfish remains cartilaginous throughout the life of -the animal, and has consequently a far more simple structure than have -the skulls of higher animals, in which complication has been produced -by the development of bone. - -The skull consists of the following parts:-- - -(1) a dorsal portion, the =cranium=, which lodges the brain, and to -the sides of which the capsules of the auditory and olfactory sense -organs are united. The cranium may be compared to an unsegmented -continuation of the vertebral column; - -(2) a number of ventral structures, disconnected or only loosely -connected with the cranium. These together constitute the =visceral -skeleton= forming the jaws and supporting the gills. - -(1) THE CRANIUM. - -The =Cranium= is an oblong box, with a flattened floor and a more -irregular roof. Its sides are expanded in front owing to the -olfactory capsules, and behind owing to the auditory capsules, while -in the middle they are deeply hollowed to form the orbits. - -(_a_) On the dorsal surface of the cranium the following points should -be noticed. First at the anterior end, the large thin-walled =nasal= -or =olfactory capsules= (fig. 6, 1), each of which is drawn out into a -narrow cartilaginous process. - -The olfactory capsules have no ventral walls, and are separated from -one another by the =internasal septum=, which is drawn out into a -third slender process. These three processes together constitute the -=rostrum= (fig. 6, 2). - -Behind the olfactory capsules comes a large, nearly circular, hole, -the =anterior fontanelle=, slightly behind which are the two -=ophthalmic foramina=. The dorsal and ventral boundaries of the orbits -are respectively formed by the prominent =supra-orbital= and -=suborbital ridges=. Behind are the =auditory capsules= (fig. 6, 8), -each of which is marked by a pair of prominent ridges, converging -towards the middle line to a pair of apertures. These apertures -communicate with two canals, the =aqueductus vestibuli=, which lead -into the internal ear. The two ridges lodge respectively the =anterior -and posterior vertical semicircular canals= of the ear. - -(_b_) The principal structures to be noted in a side view of the -cranium are contained in the =orbit= or eye-cavity. Near the base of -the orbit at its anterior end is seen the small =orbitonasal foramen= -(fig. 6, 7), for the passage of blood-vessels, not nerves. Above it is -the large =ophthalmic foramen= (fig. 6, 5) so prominent in a dorsal -view of the skull; through it the ophthalmic branches of the fifth and -seventh nerves pass. Slightly further back near the ventral surface is -the large =optic foramen= (fig. 6, II.) for the passage of the second -nerve. Vertically above the optic foramen, near the dorsal surface, is -the very small =foramen for the fourth nerve= (fig. 6, IV.). Behind -and a little above the optic foramen is another small aperture, the -=foramen for the third nerve=. Behind and slightly below this is the -large =foramen for the sixth and main branches of the fifth and -seventh nerves= (fig. 6, V.). In front of and slightly below this -foramen are seen two other small apertures; the more anterior and -ventral of these (fig. 6, 4) is for the passage of a vessel connecting -the efferent artery of the hyoid gill with the internal carotid artery -inside the skull, the more posterior and dorsal is for the -=interorbital canal= (fig. 6, 3) which unites the two orbital sinuses. -Above and very slightly in front of the large foramen for the sixth -and main parts of the fifth and seventh nerves, are two small foramina -(fig. 6, Va., and VIIa.), through which the =ophthalmic branches of -the fifth and seventh nerves= enter the orbit. Behind and slightly -below the large foramen just mentioned is a small hole through which -the external carotid enters the orbit (fig. 6, 9). - -[Illustration Fig. 6. LATERAL VIEW OF THE SKULL OF A DOGFISH -(_Scyllium canicula_) × 2/3.] - - 1. nasal capsule. - 2. rostrum. - 3. interorbital canal. - 4. foramen for hyoidean artery. - 5. foramen for the exit of the - ophthalmic branches of - Vth and VIIth nerves. - 6. foramen through which the - external carotid leaves the - orbit. - 7. orbitonasal foramen. - 8. auditory capsule. - 9. foramen through which the - external carotid enters the - orbit. - 10. ethmo-palatine ligament. - 11. palato-pterygo-quadrate bar. - 12. Meckel's cartilage. - 13. hyomandibular. - 14. cerato-hyal. - 15. pharyngo-branchial. - 16. epi-branchial. - 17. cerato-branchial. - 18. gill filaments, nearly all have - been cut off short for the - sake of clearness. - 19. extra-branchial. - 20. pre-spiracular ligament. - II. III. IV. V. Va. VIIa. foramina - for passage of cranial nerves. - -Behind the orbit is the =auditory capsule=. This is marked below by a -prominent =surface for the articulation of the hyomandibular=, above -which is the deep =postorbital groove= for the passage of a -blood-vessel, connecting the orbital and anterior cardinal sinuses. - -(_c_) Passing to the posterior end of the cranium: in the centre is -seen the large =foramen magnum= through which the brain and spinal -cord communicate. The =notochord= enters the skull just below this -foramen, and on each side of the notochord is a projection, the -=occipital condyle=, by which the first vertebra articulates with the -skull. - -External to the condyles are the prominent =pneumogastric foramina= -for the passage of the tenth nerves, and further to the sides, just -beyond the posterior vertical semicircular canals, are a pair of deep -pits in which lie the =foramina for the ninth nerves= (fig. 6, IX). - -(_d_) The broad and flat ventral surface of the cranium is continued -in front as the =internasal septum= and terminated laterally by the -=suborbital ridges=. At a little behind the middle it is traversed by -two shallow grooves along which the internal carotid arteries run. At -the divergent ends of these grooves are seen two small apertures -through which the external carotids enter the orbit (fig. 6, 9), and -at the point where they meet is a single small aperture through which -the internal carotid enters the cranium. - -(2) THE VISCERAL SKELETON. - -The =Visceral skeleton= forms a series of seven cartilaginous arches -or hoops, surrounding the anterior part of the alimentary canal, and -enclosing a wide but rather shallow space. - -(_a_) The first or =mandibular arch= is the largest of the series, and -forms the upper and lower jaws. Each half of the upper jaw or -=palato-pterygo-quadrate= bar is formed by a thick cartilaginous rod -which meets its fellow in the middle line in front, the two being -united by ligament. Each half is connected to the cranium just in -front of the orbit by the =ethmo-palatine ligament= (fig. 6, 10), and -at its hind end articulates with one of the halves of the lower jaw. -Each half of the lower jaw or =Meckel's cartilage= (fig. 6, 12) is a -cartilaginous bar, wide behind but narrow in front, where it is united -to its fellow by a median ligament. Imbedded in the tissue external to -the upper jaw are a pair of =labial cartilages=, and a similar but -smaller pair are imbedded in the tissue external to the lower jaw. - -The jaws are developed from a structure whose dorsal and ventral -portions subsequently become of very different importance. The ventral -portion forms both upper and lower jaws, the former being developed as -an outgrowth from the latter. The dorsal portion forms only the -=pre-spiracular ligament= (fig. 6, 20), a strong fibrous band -containing a nodule of cartilage, and running from the anterior part -of the auditory capsule to the point where the jaws are connected with -the hyomandibular. - -(_b_) The =hyoid arch= consists of a pair of cartilaginous rods which -are attached at their dorsal ends to the cranium, and are united -ventrally by a broad median plate of cartilage, the =basi-hyal=. Each -rod is divided into a dorsal portion, the =hyomandibular= and a -ventral portion, the =cerato-hyal=. The =hyomandibular= (fig. 6, 13) -is a short stout rod of cartilage projecting outwards, and somewhat -backwards and downwards from the cranium, with which it articulates -behind the orbit and below the postorbital groove. Its distal end -articulates with a rather long slender bar, the =cerato-hyal= (fig. 6, -14), which is in its turn attached to the side of the =basi-hyal=. The -=basi-hyal= is a broad plate, rounded in front and drawn out behind -into two processes to which the two halves of the first branchial arch -are attached. The posterior surfaces of both hyomandibular and -cerato-hyal bear slender cartilaginous processes, the =gill rays=. The -hyoid arch forms the main =suspensorium= or means by which the jaws -are attached to the cranium. This attachment is chiefly brought about -by a series of short ligaments which connect the posterior ends of -both upper and lower jaws with the hyomandibular, but there is also a -ligament connecting the lower jaw with the cerato-hyal. The attachment -of the jaws to the cranium is also partially effected by the -pre-spiracular and ethmo-palatine ligaments. - -(_c_) Each of the five =branchial arches= is a hoop, incomplete above -and formed of four or more pieces of cartilage. The most dorsal -elements, the =pharyngo-branchials=, are flattened, pointed plates -whose free inner ends run obliquely backwards, and terminate below the -vertebral column. They are connected at their outer ends with the -short broad =epi-branchials= (fig. 6, 16) which lie at the sides of -the pharynx. From the epi-branchials arise the long =cerato -branchials= (fig. 6, 17) which run forwards and inwards along the -ventral wall of the pharynx. The first four cerato-branchials are -connected with small rods, the =hypo-branchials=, which run backwards -to meet one another in the middle line. The last two pairs of -hypo-branchials and the fifth cerato-branchials are connected with a -broad median plate, the =basibranchial=. Along the outer sides of the -second, third and fourth cerato-branchials are found elongated curved -rods, the =extra-branchials= (fig. 6, 19). The epi-branchials and -cerato-branchials bear gill rays along their posterior borders. - - -C. THE SKELETON OF THE MEDIAN FINS. - -The =dorsal fins= have a skeleton consisting of a series of short -cartilaginous rods, the =basals= or basalia, which slope obliquely -backwards. Their bases are imbedded in the muscles of the back, while -their free ends bear a number of small polygonal cartilaginous plates, -the =radials= or radiale. Associated with this cartilaginous skeleton -are a number of long slender horny fibres, the fin-rays, which have -been already referred to in connection with the exoskeleton. The -skeleton of the other median fins mainly consists of these fibres, the -cartilaginous portion being reduced or absent. - - -2. THE APPENDICULAR SKELETON. - -This includes the skeleton of the two pairs of limbs and of their -respective girdles. - -THE PECTORAL GIRDLE forms a crescent-shaped hoop of cartilage, -incomplete above and lying just behind the visceral skeleton. The -mid-ventral part of the hoop is the thinnest portion, and is drawn out -in front into a short rounded process which is cupped dorsally and -supports part of the floor of the pericardium (fig. 7, 1). On each -side of this flattened mid-ventral portion the arch becomes very thick -and bears on its outer border a surface with which the three basal -cartilages of the fin articulate. The dorsal ends or scapular portions -of the girdle form a pair of gradually tapering horns. - -THE PECTORAL FIN articulates with the pectoral girdle by means of -three basalia or basal cartilages, the =propterygium=, =meso -pterygium= and =meta-pterygium=. The most anterior and the smallest of -these is the =propterygium= (fig. 7, 5), while the most posterior -one, the =meta-pterygium= (fig. 7, 3), is much the largest. Along the -outer borders of the three basalia are arranged a series of close set -cartilaginous pieces, the =radiale=. The propterygium supports only a -single radial, which is however much larger than any of the others. -The meso-pterygium also supports only a single radial which divides -distally. - -[Illustration FIG. 7. SEMIDORSAL VIEW OF THE PECTORAL GIRDLE AND FINS -OF A DOGFISH (_Scyllium canicula_) × 2/3. - -The gaps between the radiale are blackened. - - 1. hollow in the mid-ventral part - of the pectoral girdle which - supports the pericardium. - 2. dorsal (scapular portion) of - pectoral girdle. - 3. meta-pterygium. - 4. meso-pterygium. - 5. propterygium. - 6. propterygial radial. - 7. meso-pterygial radial. - 8. meta-pterygial radial. - 9. outline of the distal part of - the fin which is supported - by horny fin-rays.] - -The meta-pterygium bears about twelve long narrow radials, the first -nine of which are traversed by a transverse joint at about two-thirds -of the way from their origin. Succeeding the radials are a series of -small polygonal pieces of cartilage arranged in one or more rows and -attached to the ends of the radials, and finally the fin is completed -by the dermal fin-rays. - -[Illustration FIG. 8. DORSAL VIEW OF THE PELVIC GIRDLE AND FINS OF A -MALE DOGFISH (_Scyllium canicula_). - - 1. pelvic girdle. - 2. basi-pterygium. - 3. clasper. - 4. radiale.] - -THE PELVIC GIRDLE is much smaller than the pectoral. It is formed of a -stout nearly straight bar of cartilage placed transversely across the -ventral region of the body. The bar has no dorsal or lateral -extensions, and is terminated by short blunt processes. It bears on -its posterior surface a pair of facets with which the pelvic fins -articulate. - -THE PELVIC FIN is smaller and more simply constructed than is the -pectoral. It consists of a long, somewhat curved rod, the -=basi-pterygium= (fig. 8, 2), running directly backwards on the inner -side of the fin, and articulating in front with the pelvic girdle. -From its outer side arise a series of about fourteen parallel -cartilaginous radials which bear smaller polygonal pieces. The -anterior one or two of these radials may articulate independently with -the pelvic girdle. In the adult male dogfish the distal end of the -basi-pterygium bears a stout rod nearly as long as itself, and grooved -on the dorsal surface. This is the skeleton of the =clasper= (fig. 8, -3). - -FOOTNOTE: - -[34] See Marshall and Hurst's _Practical Zoology_, 4th ed. London, -1895, p. 214. - - - - -CHAPTER VII. - -THE SKELETON OF THE CODFISH. (_Gadus morrhua._) - - -I. EXOSKELETON. - -The exoskeleton includes - -(1) =Scales.= These are of the type known as =cycloid= and consist of -flat rounded plates composed of concentrically arranged laminae of -calcified matter, with the posterior margin entire. The anterior end -of each scale is imbedded in the skin and is overlapped by the -preceding scales. - -(2) The =teeth=. These are small, pointed, calcified structures -arranged in large groups on the premaxillae, mandible, vomer, and -superior and inferior pharyngeal bones. - -(3) The =fin-rays=. These are delicate, nearly straight bony rods -which support the fins. - - -II. ENDOSKELETON. - -The endoskeleton of the Codfish, though partially cartilaginous, is -mainly ossified. - -It is divisible into an =axial portion=, including the skull, -vertebral column, ribs, and skeleton of the median fins, and an -=appendicular portion=, including the skeleton of the paired fins and -their girdles. - -1. THE AXIAL SKELETON. - -A. THE VERTEBRAL COLUMN. - -This consists of a series of some fifty-two vertebrae, all completely -ossified. - - -It is divisible into two regions only, viz. the =trunk= region, the -vertebrae of which bear movable ribs, and the =caudal= or =tail= -region, the vertebrae of which do not bear movable ribs. - -=Trunk vertebrae.= - -These are seventeen in number; the ninth may be described as typical -of them all. It consists of a short deeply biconcave =centrum= whose -two cavities communicate by a narrow central canal. From the dorsal -surface of the anterior half of the centrum arise two strong plates, -the dorsal or =neural processes=, which are directed obliquely -backwards and meet forming the dorsal or =neural arch=. This is -produced into a long backwardly-directed dorsal or =neural spine=. - -From the lower part of the anterior edge of each neural arch arise a -pair of blunt triangular projections which overhang the posterior half -of the preceding centrum, and bear a pair of flattened surfaces which -correspond to the anterior or =prezygapophyses= of most vertebrae, -they differ however from ordinary prezygapophyses in the fact that -they look downwards and outwards. From the posterior end of the -centrum arise a pair of short blunt processes each of which bears an -upwardly- and inwardly-directed articulating surface corresponding to -a =postzygapophysis=. - -The two halves of the ventral arch form a pair of large -=ventri-lateral processes= which arise from the anterior half of the -centrum and pass outwards and slightly backwards and downwards. - -Behind these there arises on each vertebra a second outgrowth which is -small and flattened, and like the ventri-lateral process serves to -protect the air-bladder. The surface of the centrum is marked by more -or less wedge-shaped depressions, one in the mid-dorsal line, and two -on the ventral surface immediately mesiad to the bases of the -ventri-lateral process. There are also a number of smaller -depressions. - -The space between one centrum and the next is in the fresh skeleton -filled up by the gelatinous remains of the =notochord=. - -The first few vertebrae differ from the others in having very short -centra and no ventri-lateral processes. - -The first vertebra comes into very close relation to the posterior -part of the skull, articulating with the exoccipitals. In the next few -vertebrae the centra gradually lengthen, and at the fourth or fifth -vertebra the ventri-lateral processes appear and gradually increase in -size as followed back. They likewise gradually come to arise at a -lower level on the centrum, and also become more and more downwardly -directed, till at the last trunk vertebra they nearly meet. - -The =neural spines= of the anterior trunk vertebrae are much longer -than those of the posterior ones, that of the first vertebra being the -largest and longest of all, and articulating with the skull. The -spinal nerves pass out through wide notches or spaces between the -successive neural arches. - -=Caudal vertebrae.= - -The caudal vertebrae are about thirty-five in number, each consists of -a centrum with a slender backwardly-directed dorsal or neural arch, -similar to those of the posterior trunk vertebrae. The two halves of -the ventral or haemal arch however do not form outwardly-directed -ventri-lateral processes, but arise on the ventral surface of the -centrum, and passing downwards meet and enclose a space; they thus -form a complete canal, and are prolonged into a backwardly-directed -ventral or =haemal spine=. The anterior haemal arches are much larger -than the corresponding neural arches, but when followed back they -gradually decrease in size, till at about the twenty-fourth caudal -vertebra they are nearly as small as the neural arches. The last -caudal vertebra is succeeded by a much flattened =hypural= bone or -=urostyle=, which together with the posterior neural and haemal spines -supports the tail-fin. - -B. THE RIBS. - -The =ribs= are slender, more or less cylindrical bones attached to the -poster-dorsal faces of the ventri-lateral processes of all the trunk -vertebrae except the first and second. The earlier ones are thicker -and more curved; the later ones thinner and more nearly straight. The -ribs are homologous with the distal parts of the haemal arches of the -caudal vertebrae. - -Associated with the ribs are a second series of rib-like bones, the -=intermuscular bones=. These are slender, curved bones which arise -from the ribs or from the ventri-lateral processes at a distance of -about an inch from the centra, and curve upwards, outwards and -backwards. In the anterior region where the ventri-lateral processes -are short they arise from the ribs, further back they arise from the -ventri-lateral processes. - -C. THE UNPAIRED OR MEDIAN FINS. - -These are six in number, three being =dorsal=, one =caudal= and two -=anal=. - -The =dorsal= and =anal= fins each consist of two sets of structures, -the =fin-rays= and the =interspinous bones=. Each fin-ray forms a -delicate, nearly straight, bony rod which becomes thickened and -bifurcated at its proximal or vertebral end, while distally it is -transversely jointed and flexible, frequently also becoming more or -less flattened. - -The first dorsal fin has thirteen rays, the second, sixteen to -nineteen, the third, seventeen to nineteen. The first anal fin has -about twenty-two, the second anal fourteen. In each fin the posterior -rays rapidly decrease in size when followed back. - -The =interspinous bones= of the dorsal and anal fins alternate with -the neural and haemal spines respectively, and form short, -forwardly-projecting bones, each attached proximally to the base of -the corresponding fin-ray. - -The =caudal fin= consists of a series of about forty-three rays which -radiate from the posterior end of the vertebral column, being -connected with the urostyle or hypural bone, and with the posterior -neural and haemal spines without the intervention of interspinous -bones. Like the other fin-rays those forming the caudal fin are -transversely jointed, and are widened and frayed out distally. - -The tail-fin in the Cod is =homocercal=, i.e. it appears to be -symmetrically developed round the posterior end of the vertebral -column, though in reality a much greater proportion is attached below -the end of the vertebral column than above it. It is a masked -heterocercal tail. - -THE SKULL. - -Owing to the fact that very little cartilage remains in the skull of -the adult Codfish, its relation to the completely cartilaginous skull -of the Dogfish is not easily seen. Before describing it therefore, the -skull of the Salmon will be described, as it forms an intermediate -type. - -THE SKULL OF THE SALMON[36]. - -The Salmon's skull consists of (1) the =chondrocranium=, which remains -partly cartilaginous and is partly converted into cartilage bone, -especially in the occipital region, (2) a large series of plate-like -membrane bones. - -THE CHONDROCRANIUM. - -This is an elongated structure, wide behind owing to the fusion of the -large auditory capsules with the cranium, and elongated and tapering -considerably in front; in the middle it is much contracted by the -large orbital cavities. - -DORSAL SURFACE OF THE CRANIUM. - -In the centre of the posterior end of the dorsal surface is the -=supra-occipital= (fig. 9, A, 1) with a prominent posterior ridge. -It is separated by two tracts of unossified cartilage from the large -series of bones connected with the =auditory organ=. The first of -these is the =epi-otic= (fig. 9, 2), which is separated by only a -narrow tract of cartilage from the supra-occipital, and is continuous -laterally with the large =pterotic= (fig. 9, A, 3) which overlaps in -front a smaller bone, the =sphenotic= (fig. 9, 4). Both epi-otic and -pterotic are drawn out into rather prominent backwardly-projecting -processes. - -[Illustration FIG. 9. A. DORSAL AND B. VENTRAL VIEW OF THE CRANIUM OF -A SALMON (_Salmo salar_) from which most of the membrane bones have -been removed (after PARKER). Cartilage is dotted. - - 1. supra-occipital. - 2. epi-otic. - 3. pterotic. - 4. sphenotic. - 5. frontal. - 6. median ethmoid. - 7. parietal. - 8. lateral ethmoid. - 9. parasphenoid. - 10. vomer. - 11. exoccipital. - 12. opisthotic. - 13. alisphenoid. - 14. orbitosphenoid. - 16. foramen for passage of an artery. - 17. pro-otic. - 18. articular surface for hyomandibular. - -II. VII. IX. X. foramina for the passage of cranial nerves.] - -The greater part of the remainder of the dorsal surface is formed of -unossified cartilage which is pierced by three large vacuities or -=fontanelles=. The anterior fontanelle is unpaired, and lies far -forward near the anterior end of the long cartilaginous snout, the two -larger posterior ones lie just in front of the supra-occipital and -lead into the cranial cavity. In front of the orbit the skull widens -again, and is marked by two considerable =lateral ethmoid= (fig. 9, 8) -ossifications. In front of these are a pair of deep pits, the =nasal -fossae=, at the base of which are a pair of foramina through which the -olfactory nerves pass out; they communicate with a space, the =middle -narial cavity=, seen in a longitudinal section of the skull. - -The long cartilaginous snout is more or less bifid in front, -especially in the male (fig. 9). - -POSTERIOR END OF THE CRANIUM. - -The =foramen magnum= forms a large round hole leading into the cranial -cavity, and is bounded laterally by the two =exoccipitals= and below -by them, and to a very slight extent by the =basi-occipital=, the -three bones together forming a concave =occipital condyle= by which -the vertebral column articulates with the skull. - -The exoccipitals are connected laterally with a fourth pair of -auditory bones, the =opisthotics=, and just meet the epi-otics -dorsolaterally, while dorsally they are separated by a wide tract of -unossified cartilage from the supra-occipital. - -The opisthotics are connected laterally with the pterotics. - -SIDE OF THE CRANIUM. - -At the posterior end is seen the =basi-occipital= in contact above -with the =exoccipital=, which is pierced by a prominent foramen for -the exit of the tenth nerve. In front of this lies a small foramen, -sometimes double, for the ninth nerve. - -[Illustration FIG. 10. LATERAL VIEW OF THE CHONDROCRANIUM OF A SALMON -(_Salmo salar_) (after PARKER). A few membrane bones are also shown. -Cartilage is dotted. - - 1. supra-occipital. - 2. epi-otic. - 3. pterotic. - 4. opisthotic. - 5. exoccipital. - 6. basi-occipital. - 7. parasphenoid. - 8. sphenotic. - 9. alisphenoid. - 10. orbitosphenoid. - 11. lateral- or ectethmoid. - 12. olfactory pit; the vomerine teeth are seen just below. - 14. pro-otic. - 15. basisphenoid. - 16. foramen for the passage of an artery. - 17. anterior fontanelle. - 18. posterior fontanelle. - -I. II. V. VII. IX. X. foramina for the passage of cranial nerves.] - -In front of the exoccipital is the large =pro-otic= pierced by two -prominent foramina. Through the more dorsal of these (fig. 10, VII.) -the facial nerve passes out, while the more ventral (fig. 10, 16) is -for the passage of an artery. Dorsal to the exoccipital are the -=opisthotic= and =pterotic=, and dorsal to the pro-otic is the -=sphenotic=. The =pterotic= is marked by a prominent groove often -lined by cartilage, which is continued forwards along a tract of -cartilage between the pro-otic and sphenotic. With this groove the -hyomandibular articulates. - -There are considerable ossifications in the sphenoidal region of the -side of the cranium. The anterior boundary of the posterior fontanelle -is formed by the large =alisphenoid=, which is continuous behind with -the pro-otic and sphenotic, and below with a slender =basisphenoid=. -Both in front of and behind the basisphenoid there are considerable -vacuities in the walls of the cranium; through the posterior of these -openings (fig. 10, V.) the main part of the trigeminal nerve passes -out, and through the anterior one, the optic (fig. 10, II.). The -alisphenoid is continuous in front with the =orbitosphenoid= (fig. 10, -10), which is pierced by the foramen for the exit of the first nerve -(fig. 10, I.), and in front of the orbitosphenoid there is a large -vacuity. The =lateral ethmoid= is seen in the side view as well as in -the dorsal view. Further forwards are seen the olfactory pits, and the -long cartilaginous snout. - -A =ventral view= of the cartilaginous cranium shows much the same -points as the side view. The basisphenoid appears on the surface -immediately in front of the basi-occipital. - -THE SKULL WITH MEMBRANE BONES. - -The =dorsal surface=. The greater part of the dorsal surface in front -of the supra-occipital is overlaid by a pair of large rough _frontals_ -(figs. 9, A, 5, and 10, 5). They cover the posterior fontanelles and -stretch over from the sphenotic to the lateral ethmoid, forming a roof -for the orbit. They meet in the middle line behind, but in front are -separated by a narrow tract of unossified cartilage, and are -overlapped by the _median ethmoid_ (figs. 9, A, 6, and 11, 6). At the -sides of the supra-occipital behind the frontals are a pair of small -_parietals_ (figs. 9, A, 7, and 11, 7). - -[Illustration FIG. 11. LATERAL VIEW OF THE SKULL OF A SALMON (_Salmo -salar_) (after PARKER). Cartilage is dotted. - - 1. supra-occipital. - 2. epi-otic. - 3. pterotic. - 4. sphenotic. - 5. frontal. - 6. median ethmoid. - 7. parietal. - 8. nasal. - 9. lachrymal. - 10. suborbital. - 11. supra-orbital. - 12. cartilaginous sclerotic. - 13. ossification in sclerotic. - 14. meso-pterygoid. - 15. meta-pterygoid. - 16. palatine. - 17. jugal. - 18. quadrate. - 19. maxillae - 20. premaxillae. - 21. articular. - 22. angular. - 23. dentary. - 24. hyomandibular. - 25. symplectic. - 26. epi-hyal. - 27. cerato-hyal. - 28. hypo-hyal. - 29. glosso-hyal. - 30. opercular. - 31. sub-opercular. - 32. infra-opercular. - 33. pre-opercular. - 34. supratemporal. - 35. branchiostegal rays. - 36. basi-branchiostegal.] - -In a =ventral view= the cranium is seen to be chiefly covered by two -large membrane bones, the _parasphenoid_ (fig. 9, B, 9) behind, the -_vomer_ in front. A view of the =posterior end= differs from that of -the cartilaginous cranium only in the fact that the end of the -_parasphenoid_ appears lying ventral to the basi-occipital. - -The =lateral view= differs very markedly from that of the -cartilaginous cranium, there being a great development of membrane -bone in connection with the jaws and branchial apparatus. Lying -dorsally are seen the _median ethmoid_, _frontal_, _parietal_, and -=supra-occipital= as before. Lying external to the middle of the -_median ethmoid_ is seen the small _nasal_ (fig. 11, 8), and below the -hinder part is the _lachrymal_. The _lachrymal_ (fig. 11, 9) forms the -first of a series of seven small bones which surround the orbit -forming the =orbital ring=. Of these the one lying immediately in the -mid-ventral line of the orbit is the _suborbital_, while the one lying -in the mid-dorsal line and attached to the frontal is the -_supra-orbital_ (fig. 11, 11). The orbit has a cartilaginous -_sclerotic_ in which are two small ossifications (fig. 11, 13) -laterally placed. - -BONES OF THE UPPER JAW. - -The =palato-pterygo-quadrate bar= is in a very different condition -from that of the dogfish, it is partially cartilaginous, partially -converted into cartilage bone, partially overlapped by membrane bone. -It is narrow in front but becomes much broader and deeper when -followed back. Its anterior end forms the =palatine= which bears -teeth, and in front is completely ossified, while behind the cartilage -is only sheathed by bone. - -Just behind the palatine the outer part of the cartilage is ossified, -forming two small bones, the =pterygoid= and =meso-pterygoid=, while -behind them is a larger, somewhat square bone, the =meta-pterygoid= -(fig. 11, 15). - -Below the meta-pterygoid is a tract of unossified cartilage, and then -comes the =quadrate= (fig. 11, 18). - -The lower angle of the quadrate bears a cartilaginous =condyle= with -which the mandible articulates. In front of the palatine the -cartilaginous snout is overlapped by three membrane bones, the -_jugal_, _maxilla_ and _premaxillae_. - -The _premaxillae_ (fig. 11, 20), the largest of these, overlaps the -maxilla behind; both bones bear teeth. The _jugal_ (fig. 11, 17) lies -above the maxilla and overlaps it in front. - -THE LOWER JAW. - -The =lower jaw= is a strong bar and is like the upper jaw, partly -cartilaginous, forming =Meckel's cartilage=, partly ossified, and -sheathed to a considerable extent in membrane bone. - -The outer side and posterior end is ossified, forming the large -=articular= (fig. 11, 21), but the condyle is cartilaginous and the -anterior part of the articular forms merely a splint on the outer side -of Meckel's cartilage, which extends beyond it for a considerable -distance. The angle of the jaw just below the condyle is formed by a -small _angular_ (fig. 11, 22), and the anterior two-thirds of the jaw -is sheathed in the large tooth-bearing _dentary_ (fig. 11, 23). - -THE HYOID ARCH. - -The =hyoid arch= has a number of ossifications in it and is closely -connected with the mandibular arch. - -The =hyomandibular= (fig. 11, 24) is a large bone which articulates -with a shallow groove lined by cartilage and formed partly in the -pterotic, partly in front of it. The hyomandibular is overlapped in -front by the meta-pterygoid, while below it tapers and is succeeded by -a small area of unossified cartilage followed by the forwardly -directed =symplectic= which fits into a groove in the quadrate. - -The unossified tract between the hyomandibular and symplectic is -continuous in front with a strong bar, which remains partly -cartilaginous and is partly converted into cartilage bone. The -proximal part is ossified, forming the =epi-hyal=, the middle part -forms the =cerato-hyal= (fig. 11, 27), in front of which is the small -=hypo-hyal=. The hyoid arches of the two sides are united by the large -tooth-bearing =glosso-hyal= (fig. 11, 29). Attached to the lower -surface of the hyoid arch are a series of twelve flat _branchiostegal -rays_ (fig. 11, 35). Each overlaps the one in front of it, the -posterior one being the largest. The branchiostegal rays of the two -sides are united in front by an unpaired membrane bone, the -_basi-branchiostegal_ (fig. 11, 36). - -=Opercular bones.= Behind the hyomandibular there is a large bony -plate, the =operculum=, formed of four large membrane bones. The -anterior of these, the _pre-opercular_ (fig. 11, 33), is crescentic in -shape, and with its upper end a small _supratemporal_ (fig. 11, 34) is -connected. - -Behind the upper part of the pre-opercular is the largest of the -opercular bones, the _opercular proper_. Its lower edge overlaps the -sub-opercular, and both opercular and sub-opercular are overlapped by -the _infra-opercular_ (fig. 11, 32) in front. The infra-opercular is -in its turn overlapped by the _pre-opercular_. - -BRANCHIAL ARCHES. - -There are five branchial arches, the first four of which bear gill -rays. Each of the first three consists of a shorter upper portion -directed obliquely backwards and outwards, and a longer lower portion -forming a right angle with the upper and directed obliquely forwards -and inwards. The greater part of each arch is ossified. - -The upper part of either of the first two consists of a short tapering -=pharyngo-branchial= directed inwards, and of a long =epi-branchial= -tipped with cartilage at both ends. The junction of the upper and -lower parts is formed by a cartilaginous hinge-joint between the -epi-branchial and cerato-branchial. The =cerato-branchial= is a long -bony rod separated by a short area of cartilage from the -=hypo-branchial=, which is succeeded by the =basibranchial= meeting -its fellow in the middle line. The =fourth arch= has a short -epi-branchial and no ossified pharyngo-branchial, while the fifth is -reduced to little more than the cerato-branchial, which bears a few -teeth on its inner edge. All the branchial arches have projecting from -their surfaces a number of little processes which act as strainers. -The first and fourth arches have one series of these, the second and -third have two. - - -THE SKULL OF THE CODFISH[37]. - -A full description having been already given of the Salmon's skull, -that of the Codfish will be described in a briefer manner. The skull -is very fully ossified, and the great number of plate-like bones -render it a very complicated structure. - -THE CRANIUM. - -At the posterior end of the dorsal surface is the large -=supra-occipital=, which is drawn out behind into the large blade-like -=occipital spine=. On each side of the supra-occipital are the small -irregular _parietals_, while in front of it the roof of the skull is -mainly formed by the very large unpaired _frontal_. - -A complicated series of bones are developed in connection with the -=auditory capsule=, which forms a large projecting mass united with -the side of the cranium and drawn out behind into a pair of strong -processes, the =epi-otic= and =parotic= processes. Both these -processes are connected behind with a large V-shaped bone, the -_post-temporal_ (fig. 13, 1), which will be described when dealing -with the pectoral girdle. The =epi-otic process= is formed by the -=epi-otic=, which is continuous in front with the parietal. The -=parotic process= is formed by two larger bones, a more dorsal one, -the =pterotic=, and a more ventral and internal one, the =opisthotic=, -which is continuous in front with the large =pro-otic=. Intervening -between the pterotic and frontal is another rather large bone, the -=sphenotic=, this articulates below with the pro-otic. The pterotic -and sphenotic together give rise to a large concave surface by which -the hyomandibular articulates with the cranium. Several of the cranial -nerves pass out through the bones of the auditory capsule. The ninth -leaves by a foramen near the posterior border of the opisthotic, the -fifth and seventh by a notch in the anterior border of the pro-otic. - -A number of bones are likewise developed in connection with the orbit -forming the =orbital ring=. Of these the most anterior, the -_lachrymal_, is much the largest, the others are five to seven in -number, the most ventral being the _suborbital_. The sclerotic coat of -the eye is cartilaginous. - -Two pairs of bones and one unpaired bone are developed in connection -with the =olfactory capsules=, of these, the _nasals_ are narrow bones -lying next the lachrymals, but nearer the middle line; they overlap -the second pair of bones, the irregular =lateral ethmoids=. These meet -one another in the middle line, and are overlapped behind by the -frontal. They articulate laterally with the lachrymal and palatine, -and ventrally with the parasphenoid. - -In a =posterior view= the foramen magnum and the four bones which -surround it and together form the occipital segment are well seen. On -the ventral side is the =basi-occipital=, terminated posteriorly by a -slightly concave surface which articulates with the centrum of the -first vertebra. The sides of the foramen magnum are formed by the -=exoccipitals=, a pair of very irregular bones, pierced by a pair of -prominent foramina for the exit of the tenth nerves. The exoccipitals -also bear a pair of surfaces for articulation with corresponding ones -on the neural arch of the first vertebra. The most dorsal of the four -bones is the supra-occipital. - -On the ventral surface of the cranium in front of the basi-occipital -is seen the _parasphenoid_, a very long narrow bone which underlies -the greater part of the cranium. Behind, it articulates dorsally with -the basi-occipital and dorsolaterally with the pro-otics and -opisthotics, in front it articulates dorsally with the lateral ethmoid -and ventrally with the vomer. At the sides of the parasphenoid are the -small =alisphenoids= articulating above with the postfrontals, in -front with the frontals, and behind with the pro-otics. - -The _vomer_ is an unpaired bone lying immediately in front of the -parasphenoid. In front it terminates with a thickened curved margin -bearing several rows of small teeth; behind it tapers out into a long -process which underlies the anterior part of the parasphenoid. -Immediately dorsal to the vomer is another median bone, the _median -ethmoid_; this is truncated in front and tapers out behind into a -process which fits into a groove on the ventral side of the frontal. - -BONES IN CONNECTION WITH THE UPPER JAW. - -These bear a close resemblance to those of the Salmon. The most -anterior bone is the _premaxillae_, a thick curved bone meeting its -fellow in the middle line. The point of junction of the two is drawn -out into a short process, and the oral surface is thickly covered with -small teeth. The dorsal ends of the premaxillae are seen in the fresh -skull to meet a large patch of cartilage. Behind the premaxillae is the -_maxilla_, a long rod-like toothless bone, somewhat expanded at the -upper end where it articulates with the premaxillae and vomer. - -Articulating in front with the anterior end of the maxilla and with -the =lateral ethmoid= is a very irregular bone, the =palatine= (fig. -12, 1); it articulates behind with two flat bones, the =pterygoid= and -=meso-pterygoid=. The pterygoid is united behind with two more bones, -the =quadrate= (fig. 12, 4) and =meta-pterygoid=. The =quadrate= is a -rather stout irregular bone, bearing on its lower surface a prominent -saddle-shaped articulating surface for the mandible. The palatine, -pterygoid and quadrate bones are the ossified representatives of the -palato-pterygo-quadrate bar of the Dogfish. - -[Illustration FIG. 12. MANDIBULAR AND HYOID ARCHES OF A COD (_Gadus -morrhua_) × 1/2 (Brit. Mus.). - - 1. palatine. - 2. meso-pterygoid. - 3. pterygoid. - 4. quadrate. - 5. symplectic. - 6. meta-pterygoid. - 7. hyomandibular. - 8. angular. - 9. articular. - 10. dentary. - 11. inter-hyal. - 12. epi-hyal. - 13. cerato-hyal. - 14. hypo-hyal. - 15. uro-hyal. - 16. branchiostegal rays.] - -The quadrate is united behind with the =symplectic= (fig. 12, 5), and -the meta-pterygoid with the symplectic and =hyomandibular=, both of -which bones will be described immediately in connection with the hyoid -arch. - - -THE LOWER JAW. - -The =lower jaw or mandible= like that of the Salmon is partly -cartilaginous, forming =Meckel's cartilage=, partly formed of -cartilage bone, partly of membrane bone. Meckel's cartilage is of -course not seen in the dried skull. - -The lower jaw includes one cartilage bone, the =articular= (fig. 12, -9), this is a large bone connected by a saddle-shaped surface with the -quadrate. Meckel's cartilage lies in a groove on its under surface, -and projects beyond it in front. The _angular_ is a small thick bone -united to the lower surface of the articular at its posterior end. The -_dentary_ (fig. 12, 10) is a large tooth-bearing bone meeting its -fellow in the middle line in front, while the articular fits into a -deep notch at its posterior end. - - -THE HYOID ARCH. - -The =hyomandibular= (fig. 12, 7) is a large irregular bone, -articulating by a prominent rounded head with the sphenotic and -pterotic. It is united in front with the meta-pterygoid and -symplectic, and sends off behind a strong process which articulates -with the opercular. The =symplectic= is a long somewhat triangular -bone drawn out in front into a process which fits into a groove on the -inner surface of the quadrate. The distal portion of the hyoid arch is -strongly developed and consists of first the =inter-hyal= (fig. 12, -11), a short bony rod, which articulates dorsally with a patch of -cartilage intervening between the posterior part of the hyomandibular -and the symplectic. Below it is united with the apex of the triangular -=epi-hyal=, a bone suturally connected with the large =cerato-hyal= -(fig. 12, 13) which unites distally with two small =hypo-hyals=. To -the cerato-hyal are attached a series of seven strong curved -cylindrical rods, the _branchiostegal rays_. The first of these is the -smallest and they increase in size up to the last. The four dorsal -ones are attached to the outer surface of the cerato-hyal, the three -ventral ones to its inner surface. Interposed between the hypo-hyals -of the two sides is an unpaired somewhat triangular plate, the -uro-hyal or _basi-branchiostegal_ (fig. 12, 15). - - -THE BRANCHIAL ARCHES. - -The =branchial arches= are five in number and consist of the following -parts on each side. The dorsal end is formed of the =supra-pharyngeal= -bone, a large irregular bone covered ventrally with teeth of a fair -size, and representing the fused =pharyngo-branchials= of the four -anterior arches. Its external surface is continuous with four small -=epi-branchials= which pass horizontally backwards and outwards. Their -distal ends meet four long =cerato-branchials= which are directed -forwards and inwards and form the principal part of the arches. - -Each of the first three cerato-branchials articulates ventrally with a -=hypo-branchial=, and the hypo-branchials of the two sides are united -in the middle line by an unpaired =basibranchial=. The third -hypo-branchial is much flattened. The fourth cerato-branchial is -united by cartilage with the posterior surface of the third -hypo-branchial, which it meets near the middle line. - -The fifth arch consists only of the cerato-branchial, a wide structure -covered with teeth and generally called the =inferior pharyngeal -bone=. - -The skeleton of the =operculum= consists of the same four bones as in -the Salmon, namely the _opercular_, the _infra-opercular_, the -_pre-opercular_ and the _sub-opercular_. Of these the anterior bone, -the _pre-opercular_, is the largest, while the _infra-opercular_ is -the smallest. The _opercular_ has a facet for articulation with the -hyomandibular. - - -2. THE APPENDICULAR SKELETON. - -THE PECTORAL GIRDLE. - -This is of a highly specialised type. Membrane bones are greatly -developed, and the cartilage bones, the =scapula= and =coracoid=, are -much reduced in size and importance. - -[Illustration FIG. 13. THE RIGHT HALF OF THE PECTORAL GIRDLE AND RIGHT -PECTORAL FIN OF A COD (_Gadus morrhua_) × 1/2 (Brit. Mus.). - - 1. post-temporal. - 2. supra-clavicle. - 3. clavicle. - 4. coracoid. - 5. scapula. - 6. post-clavicle. - 7. brachial ossicles. - 8. dermal fin-rays.] - -The largest bone in the shoulder girdle is the _clavicle_ (fig. 13, -3), which is irregularly crescent shaped, thick in front and tapering -off behind. To the outer side of its upper part is attached a thick -cylindrical bone, the _supra-clavicle_, which passes upwards and is -connected with a strong =V= shaped bone, the _post-temporal_. The apex -of the =V= meets the supra-clavicle, the inner limb articulates with -the epi-otic process, the outer with the parotic process. Projecting -downwards from the upper part of the clavicle is a long bony rod, -flattened proximally and cylindrical and pointed distally, this is -the _post-clavicle_ (fig. 13, 6). - -The =scapula= (fig. 13, 5) is a small irregular plate of bone attached -to the inner side of the middle of the _clavicle_. The =coracoid=[38] -is a larger plate of similar character, irregularly triangular in -shape, attached to the inner side of the clavicle immediately below -the scapula. The scapula and coracoid bear the pectoral fin. - -THE PECTORAL FINS. - -Each of these consists of four small irregular bones, the =brachial -ossicles= (fig. 13, 7), bearing a series of about nineteen dermal -_fin-rays_. The brachial ossicles represent the reduced and modified -radiale and basalia of cartilaginous fish such as the dogfish. The -fin-rays (fig. 13, 8) which form the whole external portion of the fin -are long slender rods having essentially the same character as those -of the unpaired fins. - -THE PELVIC GIRDLE. - -The =pelvic girdle= in the Cod as in other Teleosteans is entirely -absent, its place being taken by the enlarged basi-pterygia of the -fins. - -THE PELVIC FINS. - -These have a very anomalous position in the Cod, being attached to the -throat in front of the pectoral girdle. Each consists of a basal -portion, the =basi-pterygium=, and of a number of dermal rays. The -basi-pterygium consists of an expanded ventral portion which meets its -fellow below in the middle line, and to which the rays are attached, -and of an inwardly-directed dorsal portion which also meets its fellow -and is imbedded in the flesh. The rays are six in number and are long -slender structures similar to those of the other fins. - - -FOOTNOTES: - -[35] See T.J. Parker's _Zootomy_, London, 1884, p. 86. - -[36] See W.K. Parker and G.T. Bettany, _The Morphology of the Skull_, -London, 1877, chap. 3. - -[37] T.J. Parker, _Zootomy_, London, 1884, p. 91. - -[38] According to G. Swirski, _Schultergurtel des Hechtes_, Dorpat, -1880, the true coracoid is aborted, and the so-called coracoid of -Teleosteans is really the precoracoid. - - - - -CHAPTER VIII. - -GENERAL ACCOUNT OF THE SKELETON IN FISHES[39]. - - -EXOSKELETON. - -The most primitive type of exoskeleton is that found in Elasmobranchs -and formed of =placoid= scales; these are tooth-like structures -consisting of dentine and bone capped with enamel, and have been -already described (p. 4). In most Elasmobranchs they are small and -their distribution is fairly uniform, but in the Thornback skate, -_Raia clavata_, they have the form of larger, more scattered spines. -In adult Holocephali and in _Polyodon_ and _Torpedo_ there is no -exoskeleton, in young Holocephali, however, there are a few small -dorsal ossifications. - -The plates or scales of many Ganoids may have been formed by the -gradual fusion of elements similar to these placoid scales, and often -bear a number of little tooth-like processes. In _Lepidosteus_, -_Polypterus_, and many extinct species, these _ganoid_ scales, which -are rhomboidal in form and united to one another by a peg and socket -articulation, enclose the body in a complete armour. In _Trissolepis_ -part of the tail is covered by rhomboidal scales, while rounded scales -cover the trunk and remainder of the tail. _Acipenser_ and -_Scaphirhynchus_ have large dermal bony plates which are not -rhomboidal in shape and do not cover the whole body. In _Acipenser_ a -single row extends along the middle of the back and two along each -side. - -The majority of Teleosteans have thin flattened scales which differ -from those of Ganoids in being entirely mesodermal in origin, -containing no enamel. There are two principal types of Teleostean -scales, the cycloid and ctenoid. A =cycloid= scale is a flat thin -scale with concentric markings and an entire posterior margin. A -=ctenoid= scale differs in having its posterior margin pectinate. The -Dipnoi have overlapping cycloid scales. The rounded scales of _Amia_ -and of many fossil ganoids such as _Holoptychius_ are shaped like -cycloid scales, but differ from them in being more or less coated with -enamel. In Eels and some other Teleosteans the scales are completely -degenerate and have almost disappeared. Some Teleosteans, like _Diodon -hystrix_, have scales with triradiate roots from which arise long -sharp spines directed backwards. These scales, which resemble teeth, -contain no enamel; they become erect when the fish inflates its body -into a globular form. Many Siluroids have dermal armour in the form of -large bony plates which are confined to the anterior part of the body. -In _Ostracion_ the whole body is covered by hexagonal plates, closely -united together. - -The =fin-rays= are structures of dermal origin which entirely or -partially support the unpaired fins, and assist the bony or -cartilaginous endoskeleton in the support of the paired fins. - -In Elasmobranchs, Dipnoi, and Chondrosteous ganoids the skeletons of -the fins are, as a rule, about half of exoskeletal, half of -endoskeletal origin, the proximal and inner portion being -cartilaginous and endoskeletal, the distal and outer portion being -exoskeletal, and consisting of horny or of more or less calcified -fin-rays. In bony Ganoids and Teleosteans the endoskeletal parts are -greatly reduced and the fins come to consist mainly of the fin-rays, -which are ossified and frequently become flattened at their distal -ends. - -The fin-rays of the ventral part of the caudal fin are carried by the -haemal arches; those of the dorsal and anal fins and of the dorsal -part of the caudal fin generally by interspinous bones, which in adult -Teleosteans alternate with the neural and haemal spines. In Dipnoi -these interspinous bones articulate with the neural and haemal spines. -In many Siluroids the anterior rays of the dorsal and pectoral fins -are developed into large spines which often articulate with the -endoskeleton, or are sometimes fused with the dermal armour plates. -Similar spines may occur in Ganoids in front of both the dorsal and -anal fins. _Polypterus_ has a small spine or _fulcrum_ in front of -each segment of the dorsal fin. Such spines are often found -fossilised, and are known as _ichthyodorulites_. - -Similar spines are found in many Elasmobranchs, but they are simply -inserted in the flesh, not articulated to the endoskeleton. They also -differ from the spines of Teleosteans and Ganoids in the fact that -they are covered with enamel, and often have their edges serrated like -teeth. In the extinct Acanthodii they generally occur in front of all -the fins, paired and unpaired. - -In _Trygon_, the Sting-ray, the tail bears a serrated spine which is -used for purposes of offence and defence. Many ichthyodorulites may -have been spines of this nature fixed to the tail, rather than spines -situated in front of the fins. The spines, which are always found in -front of the dorsal fin in Holocephali, agree with those of -Elasmobranchs in containing enamel, and with those of Teleosteans in -being articulated to the endoskeleton. - -TEETH. - -The teeth of fish[40] are subject to a very large amount of variation, -perhaps to more variation than are those of any other class of -animals. Sometimes, as in adult Sturgeons, they are entirely absent, -sometimes they are found on all the bones of the mouth, and also on -the hyoid and branchial arches. The teeth are all originally developed -in the mucous membrane of the mouth, but they afterwards generally -become attached to firmer structures, especially to the jaws. In -Elasmobranchs, however, they are generally simply imbedded in the -tough fibrous integument of the mouth. Their attachment to the jaws -may take place in three different ways. - -[Illustration FIG. 14. DIAGRAM OF A SECTION THROUGH THE JAW OF A SHARK -(_Odontaspis americanus_) showing the succession of teeth (Brit. Mus. -from specimen and diagram). - - 1. teeth in use. - 2. teeth in reserve. - 3. skin. - 4. cartilage of the jaw. - 5. encrusting calcification of cartilage. - 6. connective tissue. - 7. mucous membrane of the mouth.] - -(1) By an elastic hinge-joint, as in the Angler (_Lophius_), and the -Pike (_Esox lucius_). In the Angler the tooth is held by a fibrous -band attaching its posterior end to the subjacent bone, in the Pike by -uncalcified elastic rods in the pulp cavity. - -(2) By ankylosis, i.e. by the complete union of the calcified tooth -substance with the subjacent bone. This is the commonest method among -fish. - -(3) By implantation in sockets. This method is not very common among -fish. The teeth are sometimes, as in _Lepidosteus_, ankylosed to the -base of the socket. In this genus there is along each ramus of the -mandible a median row of large teeth placed in perfect sockets, and -two irregular lateral rows of small teeth ankylosed to the jaw. - -Dentine, enamel and cement are all represented in the teeth of fishes, -but the enamel is generally very thin, and cement is but rarely -developed. Dentine forms the main bulk of the teeth; it is sometimes -of the normal type, but generally differs from that in higher -vertebrates in being vascular, and is known as _vasodentine_. A third -type occurs, known as _osteodentine_; it is traversed by canals -occupied by marrow, and is closely allied to bone. - -[Illustration FIG. 15. PART OF THE LOWER JAW OF A SHARK (_Galeus_) -(from OWEN after ANDRÉ). - -1. teeth in use. - -2. reserve teeth folded back. - -3. part of the caudal spine of a Sting-ray (_Trygon_) which has -pierced the jaw and affected the growth of the teeth.] - -The teeth are generally continually renewed throughout life, but -sometimes one set persists. - -The teeth of Selachii are fundamentally identical with placoid -scales. They are developed from a layer of dental germs which occurs -all over the surface of the skin, except in the region of the lips. At -this point the layer of tooth-producing germs extends back into the -mouth, being projected by a fold of the mucous membrane (fig. 14, 7). -Here new teeth are successively formed, and as they grow each is -gradually brought into a position to take the place of its predecessor -by the shifting outwards of the gum over the jaw. Owing to this -arrangement sharks have practically an unlimited supply of teeth -(figs. 14 and 15). - -Two principal types of teeth are found in ELASMOBRANCHS. In Sharks and -Dogfish, on the one hand, the teeth are very numerous, simple, and -sharp-pointed, and are with or without serrations and lateral cusps. -Many Rays and fossil Elasmobranchs, on the other hand, have broad -flattened teeth adapted for crushing shells. Intermediate conditions -occur between these two extremes. Thus in _Cestracion_ and many -extinct sharks, such as _Acrodus_, while the median teeth are sharp, -the lateral teeth are more or less flattened and adapted for crushing. -In various species belonging to the genus _Raia_ the teeth of the male -are sharp, while those of the female are blunt. A very specialised -dentition is met with in the Eagle-rays (Myliobatidae), in which the -jaws are armed with flattened angular tooth-plates, arranged in seven -rows, forming a compact pavement; the plates of the middle row are -very wide and rectangular, those of the other rows are much smaller -and hexagonal. Lastly, in _Cochliodus_ the individual crushing teeth -are fused, forming two pairs of spirally-coiled dental plates on each -side of each jaw. _Pristis_, the Saw-fish, has a long flat -cartilaginous snout, bearing a double row of persistently-growing -teeth planted in sockets along its sides. Each tooth consists of a -number of parallel dentinal columns, united at the base, but elsewhere -distinct. - -In the HOLOCEPHALI--_Chimaera_, _Hariotta_ and _Callorhynchus_--only -three pairs of teeth or dental plates occur, two pairs in the upper -jaw, one in the lower. These structures persist throughout life and -grow continuously. The upper tooth structures are attached -respectively to the ethmoid or vomerine region of the skull, and to -the palato-pterygoids. The vomerine teeth are small, while those -attached to the mandible and the palato-pterygoid region are large and -bear several roughened ridges adapted for grinding food. The teeth of -the two opposite sides of the jaw meet in a median symphysis. The -teeth of _Chimaera_ are more adapted for cutting, those of -_Callorhynchus_ for crushing. Many extinct forms are known, some of -whose teeth are intermediate in structure between those of _Chimaera_ -and _Callorhynchus_. - -The teeth of GANOIDS are also extremely variable. Among living forms, -the Holostei are more richly provided with teeth than are any other -fishes, as they may occur on the premaxillae, maxillae, palatines, -pterygoids, parasphenoid, vomers, dentaries, and splenials. Among the -Chondrostei, on the other hand, the adult Acipenseridae are toothless; -small teeth however occur in the larval sturgeon, and in _Polyodon_ -many small teeth are found attached merely to the mucous membrane of -the jaws. Many fossil Ganoids have numerous flattened or knob-like -teeth, borne on the maxillae, palatines, vomers and dentaries. Others -have a distinctly heterodont dentition. Thus in _Lepidotus_ the -premaxillae bear chisel-like teeth, while knob-like teeth occur on the -maxillae, palatines and vomers. In _Rhizodus_ all the teeth are -pointed, but while the majority are small a few very large ones are -interspersed. - -In TELEOSTEANS, too, the teeth are eminently variable both in form and -mode of arrangement. They may be simple and isolated, or compound, and -may be borne on almost any of the bones bounding the mouth cavity, and -also as in the Pike, on the hyoid and branchial arches. The splenial -however never bears teeth and the pterygoid and parasphenoid only -rarely, thus differing from the arrangement in the Holostei. - -The isolated teeth are generally conical in form and are ankylosed to -the bone that bears them. Such teeth are, with a few exceptions such -as _Balistes_, not imbedded in sockets nor replaced vertically. - -In some fish beak-like structures occur, formed partly of teeth, -partly of the underlying jaw bones. These beaks are of two kinds: (1) -In _Scarus_, the parrot fish, the premaxillae and dentaries bear -numerous small, separately developed teeth, which are closely packed -together and attached by their proximal ends to the bone, while their -distal ends form a mosaic. Not only the teeth but the jaws which bear -them are gradually worn away at the margins, while both grow -continuously along their attached edge. (2) In Gymnodonts, e.g. -_Diodon_, the beaks are formed by the coalescence of broad calcified -horizontal plates, which when young are free and separated from one -another by a considerable interval. - -In some Teleosteans the differentiation of the teeth into biting teeth -and crushing teeth is as complete as in _Lepidosteus_. Thus in the -Wrasse (_Labrus_), the jaws bear conical slightly recurved teeth -arranged in one or two rows, with some of the anterior ones much -larger than the rest. The bones of the palate are toothless, while -both upper and lower pharyngeal bones are paved with knob-like -crushing teeth; such pharyngeal teeth occur also in the Carp but are -attached only to the lower pharyngeal bone, the jaw bones proper being -toothless. - -In DIPNOI the arrangement of the teeth is very similar to that in -Holocephali. The mandible bears a single pair of grinding teeth -attached to the splenials, and a corresponding pair occur on the -palato-pterygoids. In front of these there are a pair of small conical -vomerine teeth loosely attached to the ethmoid cartilage. The -palato-pterygoid teeth of _Ceratodus_ are roughly semicircular in -shape with a smooth convex inner border, and an outer border bearing a -number of strongly marked ridges. The teeth of the extinct Dipteridae -resemble those of _Ceratodus_ but are more complicated. - - -ENDOSKELETON. - -SPINAL COLUMN[41]. - -The spinal column of fishes is divisible into only two regions, a -caudal region in which the haemal arches or ribs meet one another -ventrally, and a precaudal region in which they do not meet. - -The various modifications of the spinal column in fishes can be best -understood by comparing them with the arrangement in the simplest type -known, namely _Amphioxus_. In _Amphioxus_ the notochord is immediately -surrounded by a structureless cuticular layer, the _chordal sheath_. -Outside this is the _skeletogenous layer_, which in addition to -surrounding the notochord and chordal sheath embraces the nerve cord -dorsally, and laterally sends out septa forming the _myomeres_. - -The CARTILAGINOUS GANOIDS[42] _Acipenser_, _Polyodon_ and -_Scaphirhynchus_ are the simplest fishes as regards their spinal -column. The notochord remains permanently unconstricted and is -enclosed in a chordal sheath, external to which is the skeletogenous -layer. In this layer the development of cartilaginous elements has -taken place. In connection with each _neuromere_, or segment as -determined by the points of exit of the spinal nerves, there are -developed two pairs of ventral cartilages, the ventral arches -(basiventralia) and intercalary pieces (interventralia); and at least -two pairs of dorsal pieces, the neural arches (basidorsalia) and -intercalary pieces (interdorsalia). The lateral parts of the -skeletogenous layer do not become converted into cartilage, so there -are no traces of vertebral centra. The ventral or haemal arches meet -one another ventrally and send out processes to protect the ventral -vessels. The neural arches do not meet, but are united by a -longitudinal elastic band. - -In Cartilaginous ganoids the only indications of metameric -segmentation are found in the neural and haemal arches. The case is -somewhat similar with the Holocephali and Dipnoi. - -In the HOLOCEPHALI the notochord grows persistently throughout life, -and is of uniform diameter throughout the whole body except in the -cervical region and in the gradually tapering tail. The chordal sheath -is very thick and includes a well-marked zone of calcification which -separates an outer zone of hyaline cartilage from an inner zone. There -are also a number of cartilaginous pieces derived from the -skeletogenous layer which are arranged in two series, a dorsal series -forming the neural arches and a ventral series forming the haemal -arches. These do not, except in the cervical region, meet one another -laterally round the notochord and form centra. To each neuromere there -occur a pair of basidorsals, a pair of interdorsals, and one or two -supradorsals. In the tail the arrangement is irregular. - -In the DIPNOI as in the Holocephali the notochord grows persistently -and uniformly, and the chordal sheath is thick and cartilaginous -though there are no metamerically arranged centra. The neural and -haemal arches and spines are cartilaginous and interbasalia -(intercalary pieces) are present. The basidorsalia and basiventralia -do not in _Ceratodus_ meet round the notochord and enclose it except -in the anterior part of the cervical and posterior part of the caudal -region. - -In ELASMOBRANCHII the chordal sheath is weak and the skeletogenous -layer strong. Biconcave cartilaginous vertebrae are developed, and as -is the case in most fishes, constrict the notochord _vertebrally_. - -Two distinct types of vertebral column can be distinguished in -Elasmobranchs[43]: - -1. In many extinct forms and in the living Notidanidae, _Cestracion_, -and _Squatina_, the dorsal and ventral arches do not meet one another -laterally round the centrum, and consequently readily come away from -it. - -2. In most living Elasmobranchs the arches meet laterally round the -centrum. - -The vertebrae are never ossified but endochondral calcification nearly -always takes place, though it very rarely reaches the outer surface of -the vertebrae. Elasmobranchs are sometimes subdivided into three -groups according to the method in which this calcification takes -place: - -1. =Cyclospondyli= (_Scymnus_, _Acanthias_), in which the calcified -matter is deposited as one ring in each vertebra. - -2. =Tectospondyli= (_Squatina_, _Raia_, _Trygon_), in which there are -several concentric rings of calcification. - -3. =Asterospondyli= (Notidanidae, _Scyllium_, _Cestracion_), in which -the calcified material instead of forming one simple ring, extends out -in a more or less star-shaped manner. - -In _Heptanchus_ the length of the vertebral centra in the middle of -the trunk is double that in the anterior and posterior portions, and -as the length of the arches does not vary, the long centra carry more -of them than do the short centra. - -In many Rays the skull articulates with the vertebral column by -distinct occipital condyles. - -In BONY GANOIDS the skeletogenous layer becomes calcified -ectochondrally in such a way that the notochord is pinched in at -intervals, and distinct vertebrae are produced. Ossification of the -calcified cartilage rapidly follows. In _Amia_ the vertebrae are -biconcave, in _Lepidosteus_ they are opisthocoelous, cup and ball -joints being developed between the vertebrae in a manner unique among -fishes. The notochord entirely disappears in the adult _Lepidosteus_, -but at one stage in larval life it is expanded vertebrally and -constricted intervertebrally in the manner usual in the higher -vertebrata, but unknown elsewhere among fishes. - -The tail of _Amia_ is remarkable from the fact that as a rule to each -neuromere, as determined by the exit of the spinal nerves, there are -two centra, a posterior one which bears nothing, and an anterior one -which bears the neural and haemal arches, these being throughout the -vertebral column connected with the centra by cartilaginous discs. - -In most TELEOSTEANS but not in the Plectognathi the neural arches are -continuous with the centra, which are nearly always deeply biconcave. - -In some cases many of the anterior vertebrae are ankylosed together -and to the skull. The vertebrae often articulate with one another by -means of obliquely placed flattened surfaces, the zygapophyses. The -centrum in early stages of development is partially cartilaginous, but -the neural arches and spines in the trunk at any rate, pass directly -from the membranous to the osseous condition. - - -FINS. - -The most primitive fins are undoubtedly the unpaired ones, which -probably originally arose as ridges or folds of skin along the -mid-dorsal line of the body, and passed thence round the posterior end -on to the ventral surface, partially corresponding in position and -function to the keel of a ship. - -In long 'fish' which pass through the water with an undulating motion -such simple continuous fins may be the only ones found, as in -_Myxine_. To support these median fins skeletal structures came to be -developed; these show two very distinct forms, viz. cartilaginous -endoskeletal pieces, the _radiale_, and horny exoskeletal fibres, the -_fin-rays_. Mechanical reasons caused the fin to become concentrated -at certain points and reduced at intervening regions. Thus a terminal -caudal fin arose and became the chief organ of propulsion, and the -dorsal and ventral fins became specialised to act as balancing organs. - -In some of the earlier Elasmobranchs, the Pleuracanthidae, the -endoskeletal cartilaginous radiale are directly continuous with -outgrowths from the dorsal and ventral arches of the vertebrae, and -form the main part of the fin. In later types of Elasmobranchs the -horny exoskeletal fin-rays have comparatively greater prominence. In -bony fish, as has been already stated, the horny fibres are replaced -by bony rays of dermal origin, and at the same time complete reduction -and disappearance of the cartilaginous radiale takes place. - -THE CAUDAL FIN. - -The caudal region of the spinal column in fishes is of special -importance. It is distinctly marked off from the rest of the spinal -column by the fact that the ventral or haemal arches meet one another -and are commonly prolonged into spines, while in the trunk region they -do not meet but commonly diverge from one another. - -In some fish the terminal part of the caudal region of the spinal -column retains the same direction as the rest of the spinal column. -The blade of the caudal fin is then divided into two nearly equal -portions, and is said to be =diphycercal=. This condition is generally -regarded as the most primitive one; it occurs in the Ichthyotomi, -Holocephali, all living Dipnoi, _Polypterus_ and some extinct -Crossopterygii, and a few Selachii and Teleostei. It occurs also in -deep-sea fish belonging to almost every group, and under these -conditions obviously cannot be regarded as primitive, but must be -looked on as a feature induced by the peculiar conditions of life. - -In the great majority of fish the terminal part of the caudal region -of the spinal column is bent dorsalwards, and the part of the blade of -the caudal fin which arises on the dorsal surface is much smaller than -is that arising on the ventral surface. Such a fin is said to be -=heterocercal=. - -Strictly speaking all fish whose tails are not diphycercal have -heterocercal tails, but the term is commonly applied to two-bladed -tails in which the spinal column forms a definite axis running through -the dorsal blade, while the ventral blade is enlarged and generally -forms the functional part of the tail. Such heterocercal tails are -found in nearly all Elasmobranchii, together with the living -cartilaginous Ganoidei, and many extinct forms belonging to the same -order; _Lepidosteus_, _Amia_, and the Dipteridae among Dipnoi, have -tails which, though obviously heterocercal, are not two-bladed. - -The vast majority of the Teleostei and some extinct Ganoidei have -heterocercal tails of the modified type to which the term =homocercal= -is applied. The hypural bones which support the lower half of the tail -fin become much enlarged, and frequently unite to form a wedge-shaped -bone which becomes ankylosed to the last ossified vertebral centrum. -The fin-rays then become arranged in such a way as to produce a -secondary appearance of symmetry. Some homocercal fish such as the -Perch have the end of the notochord protected by a calcified or -completely ossified sheath, the =urostyle=, to which several neural -and haemal arches may be attached, and which becomes united with the -centrum of the last vertebra; in others such as the Salmon the end of -the notochord is protected only by laterally placed bony plates. - -THE SKULL. - -It is often impossible to draw a hard and fast line between the -cranium and the vertebral column. This is the case for instance in -_Acipenser_ (fig. 18, 16) among Chondrostei, in _Amia_ among Holostei, -and in _Ceratodus_ and _Protopterus_ among Dipnoi. The occipital -region of the skull in _Amia_ is clearly formed of three cervical -vertebrae whose centra have become absorbed into the cranium, while -the neural arches and spines are still distinguishable. - -The simplest type of cranium is that found in ELASMOBRANCHS: it -consists of a simple cartilaginous box, which is generally immovably -fixed to the vertebral column, though in some forms, like _Scymnus_ -and _Galeus_, a joint is indicated, and in others, such as the -Rays, one is fairly well developed. The cranium in Elasmobranchs -is never bony, though the cartilage is sometimes calcified. It is -drawn out laterally into an antorbital process in front of the eye, -and a postorbital process behind it. The nasal capsules are always -cartilaginous, and the eye, as a general rule, has a cartilaginous -sclerotic investment. The cranium is often prolonged in front into -a rostrum which is enormously developed in _Pristis_ and some Rays. -The cartilaginous roof of the cranium is rendered incomplete by the -presence of a large hole, the anterior fontanelle. - -[Illustration FIG. 16. A. SKULL OF _Notidanus_ × 1/2 (Brit. Mus.). B. -SKULL OF _Cestracion_ × 1/3 (after GEGENBAUR). In neither case are the -branchial arches shown. - - 1. rostrum. - 2. olfactory capsule. - 3. ethmo-palatine process. - 4. palatine portion of palato-pterygo-quadrate bar. - 5. quadrate portion of bar. - 6. Meckel's cartilage. - 7. teeth. - 8. labial cartilage. - 9. hyomandibular. - 10. postorbital process. - II. optic foramen.] - -Two pairs of labial cartilages (fig. 16, B, 8) are often present. They -lie imbedded in the cheeks outside the anterior region of the jaws, -and are specially large in _Squatina_. - -As regards the visceral arches[44] the simplest and most primitive -condition of the jaws is that of the Notidanidae, in which the -mandibular and hyoid arches are entirely separate. In these primitive -fishes the palato-pterygo-quadrate bar articulates with the -postorbital process (fig. 16, 10), while further forwards it is united -to the cranium by the ethmo-palatine ligament. The hyoid arch is small -and is broadly overlapped by the mandibular arch. The term -=autostylic= is used to describe this condition of the suspensorium. -From this condition we pass in the one direction to that of -_Cestracion_ (fig. 16, B), in which the whole of the palato-pterygo -quadrate bar has become bound to the cranium, and in the other to that -of _Scyllium_. In _Scyllium_ (fig. 6), while the ethmo-palatine -ligament is retained, the postorbital articulation of the palato -pterygo-quadrate has been given up, so that the palato-pterygo -quadrate comes to abut on the hyomandibular and is attached to it by -ligaments. The pre-spiracular ligament (fig. 16, 20) running from the -auditory capsule also assists in supporting the jaws. - -Lastly we come to the purely =hyostylic= condition met with in Rays, -in which the mandibular arch is entirely supported by the -hyomandibular. In some Rays the hyoid is attached to the posterior -face of the hyomandibular near its proximal end, and may even come to -articulate with the cranium. - -The =visceral arches of Elasmobranchs= may be summarised as follows:-- - -1. The =mandibular arch=, consisting of a much reduced dorsal portion, -the pre-spiracular ligament, and a greatly developed ventral portion -from which both upper and lower jaws are derived. The mandible -(Meckel's cartilage) is the original lower member of the mandibular -arch, and from it arises an outgrowth which forms the upper jaw or -palato-pterygo-quadrate bar. In _Scymnus_ this bears a few -branchiostegal rays. - -2. The =hyoid arch=, which consists of the hyomandibular and the -hyoid, and bears branchiostegal rays on its posterior face. - -[Illustration FIG. 17. DORSAL VIEW OF THE BRANCHIAL ARCHES OF -_Heptanchus_. (From GEGENBAUR). - - 1. basi-hyal. - 2. cerato-hyal. - 3. second hypo-branchial. - 4. first cerato-branchial. - 5. first epi-branchial. - 6. first pharyngo-branchial. - 7. pharyngo-branchial, common to the sixth and seventh arches. - 8. basibranchial of second arch. - 9. basibranchial, common to the sixth and seventh arches.] - -3. The =branchial arches=, generally five in number, all of which -except the last bear branchiostegal rays. In the Notidanidae the -number of branchial arches is increased beyond the normal series, -thus in _Hexanchus_ there are six, and in _Heptanchus_ seven. There -are six also in _Chlamydoselache_ and _Protopterus_. - -4. The so-called external branchial arches which are cartilaginous -rods attached to all the visceral arches. They are especially large in -_Cestracion_. - -The skull in HOLOCEPHALI is entirely cartilaginous. The -palato-pterygo-quadrate bar is fixed to the cranium, and to it the -mandible articulates. There is a well-marked joint between the skull -and the spinal column. - -In living Cartilaginous GANOIDS the primitive cartilaginous cranium is -very massive, and is greatly prolonged anteriorly, while posteriorly -it merges into the spinal column. Although it is mainly cartilaginous -a number of ossifications take place in the skull, and membrane bones -are now found definitely developed, especially in connection with the -roof of the cranium. In _Acipenser_ (fig. 18) the ossifications in the -cartilage include the pro-otic, which is pierced by the foramen for -the fifth nerve, the alisphenoid, orbitosphenoid, ectethmoid, -palatine, pterygoid, meso-pterygoid, hyomandibular (fig. 18, 11), -cerato-hyal, all the cerato-branchials, and the first two -epi-branchials. Most of these structures are, however, partly -cartilaginous, though they include an ossified area. The membrane -bones too of _Acipenser_ are very well developed, they include a bone -occupying the position of the supra-occipital, and form a complete -dorsal cephalic shield. Resting on the ventral surface are a vomer and -a very large parasphenoid (fig. 18, 3). There is a bony operculum -attached to the hyomandibular, and membrane bones representing -respectively the maxilla and dentary are attached to the jaws. The -suspensorium is most markedly hyostylic. The palato-pterygo-quadrate -bar has a very curious shape and is quite separate from the cranium. -It is connected to the hyomandibular by a thick symplectic ligament -containing a small bone homologous with the symplectic of -Teleosteans. - -_Polyodon_ differs much from _Acipenser_, the membrane bones not being -so well developed though they cover the great cartilaginous snout. - -[Illustration FIG. 18. LATERAL VIEW OF THE SKULL OF A STURGEON -(_Acipenser sturio_). Nearly all the membrane bones have been removed -(Brit. Mus.). - - 1. nasal cavity. - 2. orbit. - 3. parasphenoid. - 4. vomer. - 5. pterygoid. - 6. maxilla. (The dotted line running from 6 passes into the mouth - cavity.) - 7. dentary. - 8. symplectic. - 10. palatine. - 11. hyomandibular. - 12. pharyngo-branchial. - 13. epi-branchial. - 14. cerato-branchial. - 15. hypo-branchial. - 16. coalesced anterior vertebrae. - 17. inter-hyal. - 18. cerato-hyal. - 19. rib.] - -The skull in _Polypterus_ (Crossopterygii) shows a great advance -towards the condition met with in Teleostei. The cranium remains to a -great extent unossified, and large dorsal and ventral fontanelles -pierce its walls. It is covered by a great development of membrane -bones, paired nasals, frontals, parietals, supra- and post-temporals, -and dermo-supra-occipitals among others being present. The -palato-pterygo-quadrate bar is fused to the cranium, and in connection -with it the following paired membrane bones appear, palatine, ecto-, -meso- and meta-pterygoid, and further forwards jugal, vomer, maxilla -and premaxillae. The membrane bones developed in connection with each -ramus of the mandible are the dentary, angular, and splenial, in -addition to the cartilage bone the articular. Several large opercular -bones occur. There are also a pair of large jugular or gular plates, -and several large opercular bones. - -In Bony Ganoids both cartilage bone and membrane bone is well -developed. The pro-otics and exoccipitals are well ossified, but the -supra-occipital and pterotics are not. Lateral ethmoids are developed, -and there are ossifications in the sphenoidal region which vary in -different forms. The place of the cartilaginous palato-pterygo -quadrate is taken by a series of bones, the quadrate behind and the -palatine, ecto-, meso- and meta-pterygoids in front. In _Lepidosteus_, -however, the palatine and pterygoid are membrane bones, as they are in -_Polypterus_ and the Frog. Paired maxillae, premaxillae, vomers and a -parasphenoid occur forming the upper jaw and roof of the mouth, and a -series of membrane bones are found investing the mandible and forming -the operculum. - -In _Amia_[45] membrane bones are as freely developed as they are in -Teleosteans; they include on each side a squamosal, four opercular -bones, a lachrymal, a pre-orbital, one or two suborbitals, two large -postorbitals and a supratemporal; while investing the mandible, -besides the dentary, splenial, angular, and supra-angular, there is an -unpaired jugular. The articular too is double and a mento-meckelian -occurs. In _Amia_ teeth are borne on the premaxillae, maxillae, vomers, -palatines and pterygoids. - -Bony Ganoids are the lowest animals in which squamosal bones are -found, and they do not occur in Teleosteans. - -The suspensorium in bony Ganoids, as in the Chondrostei, is hyostylic, -and there are two ossifications in the hyomandibular cartilage, viz. -the hyomandibular, and the symplectic. - -The skull of TELEOSTEI is very similar to those of _Lepidosteus_ and -_Amia_. Although the bony skull is greatly developed and very -complicated, much of the original cartilaginous cranium often -persists. Membrane bones are specially developed on the roof of the -skull where they include the parietal, frontal, and nasal bones. The -same bones are developed in connection with the upper jaw and roof of -the mouth as in bony Ganoids, but only two membrane bones occur in the -lower jaw, viz. the angular and dentary. A number of large -ossifications take place in the cartilage of the auditory capsules. In -some forms parts of the last pair of branchial arches are broadened -out and form the pharyngeal bones which bear teeth. The opercular -bones and those of the upper and lower jaws are quite comparable to -those of bony Ganoids. - -A full account of the Teleostean skull has been given in the case of -the Salmon (pp. 87-96) and the Cod (pp. 96-101). - -In DIPNOI the skull is mainly cartilaginous, but both cartilage- and -membrane-bone occur also. Cartilage-bone is found in the ossified -exoccipitals, while of membrane-bones _Protopterus_ has among unpaired -bones a fronto-parietal, a median ethmoid, and a parasphenoid, and -among paired bones nasals and large supra-orbitals. The skull of -_Ceratodus_ (fig. 19) has an almost complete roof of membrane bones, -including some whose homology is doubtful. The ethmo-vomerine region -is always cartilaginous, but bears small teeth. The palato-pterygo -quadrate bar is ossified and firmly united to the cranium, and the -mandible articulates directly with it (autostylic). Membrane bones are -freely developed in connection with the mandible, dentary, splenial, -and angular bones being all present. There are two opercular bones. - -In the extinct Dipteridae the cranium is very completely covered with -plates of dermal bone, and the skeleton in general is more ossified -than is the case in recent Dipnoi. - -Six pairs of branchial arches occur in _Protopterus_; _Ceratodus_ and -_Lepidosiren_ have five, like most other fish. The branchial arches -bear gill rakers. - -[Illustration FIG. 19. DORSAL (TO THE LEFT) AND VENTRAL (TO THE RIGHT) -VIEWS OF THE CRANIUM OF _Ceratodus miolepis_ (after GÜNTHER). - - 1. cartilaginous part of the quadrate with which the mandible - articulates. - 2. scleroparietal. - 3. frontal. - 4. ethmoid. - 5. nares. - 6. orbit. - 7. pre-opercular (squamosal). - 8. second rib. - 9. first rib. - 10. vomerine tooth. - 11. palato-pterygoid tooth. - 12. palato-pterygoid. - 13. parasphenoid. - 14. interopercular.] - -RIBS. - -As has been already mentioned (p. 24), although ribs commonly appear -to be the cut-off ends of the transverse processes, they are really -elements derived from the ventral or haemal arch. - -In Elasmobranchii and other cartilaginous fish they have the form of -small cartilaginous structures imperfectly separated from the -diverging halves of the ventral arch, and are often absent. - -In Teleostei and bony Ganoids they often have different attachments in -different parts of the body. In the tail region they are not -differentiated from the two halves of the ventral arch, which meet in -the middle line, and are prolonged into a haemal spine. In the -posterior trunk region they sometimes form distinct processes -diverging from the two halves of the ventral arch; while further -forward they may shift their attachment so as to arise from the dorsal -side of the two halves of the ventral arch and at some distance from -their ends, which now diverge as ventri-lateral processes. - -APPENDICULAR SKELETON. - -PECTORAL GIRDLE. - -The simplest type of pectoral girdle is found in Elasmobranchs. It is -entirely cartilaginous and consists of a curved ventrally-placed rod, -ending dorsally in two horn-like scapular processes which are -sometimes attached to the cranium or vertebral column. In Rays the -shoulder girdle is very large, and has a distinct suprascapular -portion forming a broad plate attached to the neural spines of the -vertebrae. There is often a cup-like glenoid cavity for the -articulation of the limb; this cavity is specially large in Rays and -is much pierced by holes. In Dipnoi the cartilaginous girdle still -occurs, but on it there is a deposit of membrane bone forming the -clavicle, infraclavicle, and supra-clavicle. These bones, which with -the exception of the clavicle, are unknown in higher vertebrates, are -better developed in Ganoids, and best of all in Teleosteans. They are -connected by the supratemporal with the epi-otic and opisthotic -regions of the cranium. Owing to this development of dermal bone, the -original cartilaginous arch becomes much reduced, but ossifications -representing the scapula and coracoid occur in bony Ganoids and -Teleosteans. - -PELVIC GIRDLE. - -In Elasmobranchs the pelvic girdle consists of a short ventral rod of -cartilage representing the ischium and pubis, which does not send up -dorsal iliac processes. In _Chimaera_ the pelvic girdle has a -flattened pointed iliac portion, and ventrally an unpaired movable -cartilaginous plate which bears hooks and is supposed to be copulatory -in function. Claspers of the usual type are present as well. The -Dipnoi have a primitive kind of pelvis in the form of a cartilaginous -plate lying in the mid-ventral line and drawn out into three horns -anteriorly. In Ganoids the pelvis has almost entirely disappeared, -though small cartilaginous vestiges of it remain in _Polypterus_. In -Teleosteans even these vestiges are gone, and in these fish and -Ganoids the place of the pelvis is taken by the enlarged basi-pterygia -(meta-pterygia) of the fins. - -PAIRED FINS[46]. - -As regards the origin of the limbs or paired fins of fishes there are -two principal views. One view, that of Gegenbaur, considers that limbs -and their girdles are derived from visceral arches which have migrated -backwards. The other view, which probably now has the greater number -of supporters, considers that the paired fins of fishes are of -essentially the same nature as the median fins. - -According to Gegenbaur's view[47] the =archipterygium= of _Ceratodus_ -(fig. 20) represents the lowest type of fin; it consists of a central -cartilaginous axis bearing a large number of radiale. The dorsal or -pre-axial radiale are more numerous than the ventral or postaxial, and -at the margin of the fin[48] the cartilaginous endoskeletal radiale -are replaced by horny exoskeletal fin-rays. - -[Illustration FIG. 20. LATERAL VIEW OF THE SKELETON OF _Ceratodus -miolepis_ (after GÜNTHER). - - 1. ethmoid. - 2. scleroparietal. - 3. frontal. - 4. cartilaginous posterior part of cranium. - 5. pre-opercular (squamosal). - 6. opercular. - 7. suborbital. - 8. orbit. - 9. pectoral girdle. - 10. proximal cartilage of pectoral fin. - 11. pectoral fin. - 12. pelvic girdle. - 13. pelvic fin. - 14. spinal column. - 15. caudal fin (diphycercal).] - -It is impossible here to give a full discussion of the rival views, -but some of the points which support Gegenbaur's view may be -mentioned. The fact that migration of visceral arches has to be -assumed is no difficulty, as it is obvious that migration in the -opposite direction has taken place in many Teleosteans such as the -Cod, whose pelvic fins are attached to the throat in front of the -pectorals. If migration did take place, the pelvic fins being older -than the pectoral should be the more modified, and this is the case. -Again, if the pectoral girdle is a modified branchial arch, it must at -some period have carried a gill, and in _Protopterus_ it does bear a -vestigial gill. - -According to the view more prevalent at the present time, the paired -fins have been derived from two continuous folds of skin and their -skeletal supports running forward from the anal region along the sides -of the body, their character being similar to the fold that gave rise -to the median fins. In support of this view it may be argued that the -paired and unpaired fins are often identical in structure, and that -some Elasmobranch embryos do show a ridge running between the pectoral -and pelvic fins. Then from this continuous fold two pairs of smaller -folds may have been specialised off, and in each a number of -cartilaginous radiale may have been developed. The fin of -_Cladoselache_ from the Carboniferous of Ohio apparently illustrates -this condition. It consists of certain basal pieces which do not -project beyond the body wall and bear a number of unsegmented -cartilaginous radiale, which show crowding together and are sometimes -bifurcated distally; they extend throughout the whole fin from the -body wall to the margin. From this fin the archipterygium might be -easily derived by the enlargement of one of the middle radiale and the -segmentation and partial fusion of them all. - -Whether the archipterygium be a primitive or secondary type of fin, -when it is once reached it is easy to derive all the other types from -it. The fins of the other living Dipnoi,--_Protopterus_ and -_Lepidosiren_--are simply archipterygia from which the radiale have -almost or completely disappeared, leaving only the segmented axes. -Archipterygia too are found in the pectoral fins of the Ichthyotomi, -but the postaxial radiale are much reduced. - -The =ichthyopterygium=, or type of fin, characteristic of many modern -Elasmobranchs such as _Scyllium_, may have been derived from the -archipterygium by the gradual reduction of the rays on the postaxial -side of the axis and their condensation on the pre-axial side. The -Ichthyotomi such as _Xenacanthus_ show one stage in the reduction of -the postaxial rays, and a further stage is seen in the Notidanidae and -some other sharks like _Scymnus_ and _Acanthias_, in which a few -postaxial rays still remain. The condensation of the pre-axial rays -when further continued leads to one of the rays getting an attachment -to the girdle. Thus the fin comes to articulate with the girdle by two -basalia or basal pieces; a third attachment is formed in the same way -and the three basalia are called respectively pro-, meso-, and -meta-pterygia. By some authors the meta-pterygium and by others the -meso-pterygium is regarded as homologous with the axis of the -archipterygium. - -The pectoral fins of Elasmobranchs vary very much in their mode of -attachment. In some of the sharks, including the Notidanidae and -_Scyllium_, all three basalia articulate with the pectoral girdle, -while in others such as _Cestracion_ the meta-pterygium is excluded. -In Rays the propterygium and the meta-pterygium are long and narrow -and diverge much from one another; other basalia work their way in -between the meso-pterygium and meta-pterygium, and come to articulate -with the pectoral girdle. Sometimes they fuse and form a second -meso-pterygium. The radiale are greatly elongated and are segmented. - -In _Chimaera_ all three basalia are present, but the meso-pterygium -is shifted and does not articulate with the pectoral girdle[49]. - -In _Acipenser_ and _Polyodon_ the pectoral fin is built on the same -type as in Elasmobranchs, but becomes modified from the fact that the -propterygium is replaced by dermal bone which forms a large =marginal -ray=. Extra meso-pterygia are formed in the same way as in Rays. - -In _Polypterus_ the pro-and meta-pterygia have ossified while the -meso-pterygium remains chiefly cartilaginous; the fin-rays are also -chiefly ossified. - -In _Amia_, _Lepidosteus_, and certain Teleosteans like _Salmo_, not -only the propterygium but the meso-pterygium is almost suppressed by -the marginal ray. - -In the great majority of Teleosteans a still further stage is reached, -the endoskeletal elements, the basalia and radiale are almost entirely -suppressed and the fin comes to consist entirely of ossified fin-rays -of dermal origin. - -In some Teleosteans--_Exocaetus_, a herring, and _Dactylopterus_, a -gurnard--the pectoral fins are so enormously developed that by means -of them the fish is able to fly through the air for considerable -distances. The skeleton of these great fins is almost entirely -composed of dermal bone. - -PELVIC FIN. - -The pelvic fin is almost always further removed from the -archipterygial condition, and is in general more modified than is the -pectoral. Thus in the Ichthyotomi, while the pectoral fins are -archipterygia similar to those of _Ceratodus_, the pelvic fins consist -of an axis bearing rays on the postaxial side only, and prolonged -distally into a clasper. In Dipnoi however the pelvic fins are very -similar to the pectoral. In Elasmobranchs the meso-pterygium is -missing, the propterygium is small or absent, and the fin is mainly -composed of the meta-pterygium (generally called basi-pterygium) and -its radiale. The males in Elasmobranchii and Holocephali have the -distal end of the meta-pterygium prolonged into a clasper. - -In Ganoids and in Teleosteans the loss of the pelvic girdle causes the -pelvic fin to be still further removed from the primitive state. There -is always a large basi-pterygium which lies imbedded in the muscles -and meets its fellow at its proximal end. In Cartilaginous Ganoids it -has a secondary segmentation. Its relation to its fellow is subject to -much variation in Teleosteans, sometimes as in the Perch the two are -in contact throughout, sometimes as in the Salmon they meet distally -as well as proximally, but are elsewhere separated by a space, -sometimes as in the Pike and Bony Ganoids they diverge widely. The -radiale are articulated to the basi-pterygium. In Cartilaginous -Ganoids and _Polypterus_ they are well developed, in other Ganoids and -in Teleosteans they are in the main replaced by dermal fin-rays. - -In some Teleosteans such as the Cod the pelvic fins have migrated from -their usual position and come to be attached to the throat in front of -the pectoral fins. Fish with this arrangement are grouped together as -=jugulares=. - - -FOOTNOTES: - -[39] The following general works on fishes may be referred to: -Bashford Dean, _Fishes, Living and Fossil_, New York, 1895. A. -Günther, _An Introduction to the Study of Fishes_, Edinburgh, 1880. -A.A.W. Hubrecht and M. Sagemehl, _Fische_ in Bronn's _Classen und -Ordnungen des Thierreichs_, Band VI. Leipzig, 1876. - -[40] See W.G. Ridewood, _Nat. Sci._ vol. VIII. 1896, p. 380. Full -references are there given to the literature of the subject. - -[41] See H. Gadow and E.C. Abbott, _Phil. Trans._ vol. 186 (1895) B. -pp. 163-221. - -[42] C. Hasse, _Zeitschr. wiss. Zool._ LVII. 1893, p. 76. - -[43] C. Hasse, _Das natürliche System der Elasmobranchier auf -Grundlage des Baues und der Entwickelung ihrer Wirbelsäule_, Jena, -1879 and 1885, and "Die fossilen Wirbel, Morph. Studien I.-IV.," -_Morphol. Jahrb. Bd._ II., III. and IV. 1876-78. - -[44] See H.B. Pollard, _Anat. Anz._ X. 1894. - -[45] T.W. Bridge, "The Cranial Osteology of _Amia calva_," _J. Anat. -Physiol. norm. path._ 1876, vol. XI. p. 605. R. Shufeldt, "The -Osteology of _Amia calva_," _Ann. Rep. of the Commissioner for Fish -and Fisheries_, Washington, 1885. - -[46] A. Smith Woodward, _Nat. Sci._ vol. I. 1892, p. 28. Further -references are here given on the literature of the subject. - -[47] C. Gegenbaur, Ueber das Archipterygium, _Jena Zeitschr. der -Wirbelthiere_, 2^e Heft, 1873, vol. 7, and _Morphol. Jahrb._ XXII. -1894, p. 119. - -[48] The fins of _Ceratodus_ are very variable, no two being exactly -alike. Sometimes even the main axis bifurcates. See W.A. Haswell, -_Linn. Soc. N. S. Wales_, vol. VII. 1882. - -[49] Some of these views with regard to the homologies of the parts of -the fins are not accepted by all anatomists. - - - - -CHAPTER IX. - -CLASS II. AMPHIBIA[50]. - - -AMPHIBIA differ markedly from Pisces in the fact that in the more -abundant and familiar forms the skin is naked, and that when the -integument is prolonged into median fins they are devoid of fin-rays. -The notochord may persist, but bony vertebral centra are always -developed. These are sometimes biconcave, sometimes procoelous, -sometimes opisthocoelous. There is only one sacral vertebra, except in -rare cases. The cartilaginous cranium persists to a considerable -extent but is more or less replaced by cartilage bone, and overlain by -membrane bone. The basi-occipital is not completely ossified, and the -skull articulates with the vertebral column by means of two occipital -condyles formed by the exoccipitals. - -There is a large parasphenoid, but there are no ossifications in the -basisphenoidal, presphenoidal, and alisphenoidal regions. In most -cases the epi-otics and opisthotics are ossified continuously with the -exoccipitals. - -The palato-pterygo-quadrate bar is firmly united to the cranium, so -the skull is autostylic. The palatines and pterygoids are membrane -bones. Teeth are nearly always borne on the vomers and commonly on the -maxillae and premaxillae. There are no sternal ribs, and the sternum is -very intimately related to the pectoral girdle. There are no obturator -foramina. The limbs are as in the higher vertebrata, divisible into -upper arm, fore-arm, and manus (wrist and hand), and into thigh, shin, -and pes (ankle and foot) respectively. The posterior limb is, as a -rule, pentedactylate, but in nearly every case the pollex is vestigial -or absent. - - -_Order 1._ URODELA[51]. - -The Urodela are elongated animals with a naked skin, a persistent -tail, and generally four short limbs. - -The vertebral centra are opisthocoelous or biconcave, and there are -numerous precaudal vertebrae. Portions of the notochord commonly -persist in the intervertebral spaces. In the skull there is no -sphenethmoid forming a ring encircling the anterior end of the brain, -its place being in many cases partly taken by a pair of -orbitosphenoids. There is no quadratojugal, and the quadrate is more -or less ossified. The mandible has a distinct splenial, and the -articular is ossified. - -There is no definite tympanic cavity. The hyoid apparatus is -throughout life connected to the quadrate by ligament, and a large -basilingual plate does not occur. The ribs are short structures with -bifurcated proximal ends. In the pelvis the pubis remains -cartilaginous, and there is a bifid cartilaginous epipubis. The bones -of the fore-arm and shin remain distinct, and the manus never has more -than four digits. - -_Suborder_ (1). ICHTHYOIDEA. - -The vertebrae are amphicoelous, but the notochord remains but little -constricted throughout the whole length of the vertebral column. Three -or four branchial arches nearly always persist in the adult. The -cartilages of the carpus and tarsus remain unossified. - -The Ichthyoidea may be subdivided again into two groups:-- - -A. _Perennibranchiata_, whose chief distinguishing skeletal characters -are that the skull is elongated, the premaxillae are not ankylosed, the -maxillae are vestigial or absent; there are sometimes no nasals, and -the palatines bear teeth; - - e.g. _Siren_, _Proteus_, _Menobranchus_. - -B. _Derotremata_, whose chief distinguishing skeletal characters are -that there are large maxillae and nasals; teeth are borne by both -maxillae and premaxillae; there are no palatines; and both pectoral and -pelvic limbs are always present; - - e.g. _Amphiuma_, _Megalobatrachus_, _Cryptobranchus_. - -_Suborder_ (2). SALAMANDRINA. - -The vertebrae are opisthocoelous. The skull is broad, and teeth are -borne by both premaxillae and dentaries. Nasal bones are present. The -remains of only two branchial arches are found in the adult. The -carpus and tarsus are more or less ossified. - -This suborder includes the Newts (_Molge_), Salamanders -(_Salamandra_), and _Amblystoma_. - - -_Order_ 2. LABYRINTHODONTIA[52]. - -These are extinct Amphibia with a greatly developed dermal -exoskeleton, which is generally limited to the ventral surface. The -body and tail are long and in some cases limbs are absent. The teeth -are pointed and often have the dentine remarkably folded. The -vertebrae are amphicoelous, and are generally well ossified. The skull -is very solid, and has a greatly-developed secondary roof which hides -the true cranium and is very little broken up by fossae. Paired -dermal supra-occipitals are found, and there is an interparietal -foramen. The epi-otics and opisthotics form a pair of bones distinct -from the exoccipitals. Four simple limbs of moderate length are -generally present, and in some cases all four limbs are -pentedactylate. Among the better known genera of Labyrinthodonts are -_Mastodonsaurus_, _Nyrania_, and _Archegosaurus_. - - -_Order 3._ GYMNOPHIONA[53]. - -These animals form a group of abnormal worm-like Amphibia having an -exoskeleton in the form of subcutaneous scales arranged in rings. The -vertebrae are biconcave and are very numerous; very few however belong -to the tail. The skull has a complete secondary bony roof, the -mandible bears teeth and has an enormous backward projection of the -angular. The hyoid arch has very slender cornua and no distinct body, -it is attached neither to the cranium nor to the suspensorium. The -ribs are very long and there are no limbs or limb girdles. - - -_Order 4._ ANURA. - -These are tailless Amphibia, which except in a few instances, are -devoid of an exoskeleton. The vertebrae are as a rule procoelous, and -are very few in number. The post-sacral part of the spinal column -ossifies continuously, forming an unsegmented cylindrical rod, the -urostyle. Remains of the notochord persist, lying _vertebrally_, i.e. -enclosed within the centra of the several vertebrae, and not as in -Urodela lying between one vertebra and the next. The skull is very -short and wide. The mandible is almost always, if not invariably, -toothless. - -The frontals and parietals on each side are united so as to form a -pair of fronto-parietals, and a girdle-like sphenethmoid is present. - -The quadrate is not generally ossified. A predentary or -mento-meckelian bone is commonly present in the mandible, and a single -bone represents the angular and splenial. The branchial arches are -much reduced in the adult, and the distal ends of the cornua unite to -form a flat basilingual plate of a comparatively large size. - -Ribs are very little developed. Clavicles are present. The ilia are -very greatly elongated. The anterior limb has four well-developed -digits and a vestigial pollex, and is of moderate length; the radius -and ulna have fused. The posterior limb is greatly elongated and is -pentedactylate; the tibia and fibula are fused, while the calcaneum -and astragalus are greatly elongated, and it is largely owing to them -that the length of the limb is so great. The group includes the Frogs -and Toads, the predominant Amphibia of the present time. - - -FOOTNOTES: - -[50] T.H. Huxley, _Amphibia_ (_Encyclopaedia Britannica_). - -[51] See R. Wiedersheim, _Morphol. Jahrb._ Bd. III. 1877, p. 459. - -[52] See A. Fritsch, _Fauna der Gaskohle_, Prague, 1883-85-86, also -writings of Cope, Credner, Huxley, H. v. Meyer, Miall. - -[53] See R. Wiedersheim, _Anatomie der Gymnophionen_, Jena, 1879. - - - - -CHAPTER X. - -THE SKELETON OF THE NEWT (_Molge cristata_). - - -I. EXOSKELETON. - -The skin of the Newt is quite devoid of any exoskeletal structures. -The only exoskeletal structures that the animal possesses are the -teeth, and these are most conveniently described with the -endoskeleton. - - -II. ENDOSKELETON. - -The endoskeleton of the Newt, though ossified to a considerable -extent, is more cartilaginous than is that of the frog. It is -divisible into an =axial portion= including the vertebral column, -skull, ribs, and sternum, and an =appendicular portion= including the -skeleton of the limbs and their girdles. - -1. THE AXIAL SKELETON. - -A. THE VERTEBRAL COLUMN. - -This consists of about fifty vertebrae arranged in a regular -continuous series. The first vertebra differs a good deal from any of -the others; the seventeenth or sacral vertebra and the eighteenth or -first caudal also present peculiarities of their own. The remaining -vertebrae are divided by the sacrum into an anterior series of =trunk= -vertebrae which bear fairly large ribs, and a posterior series of -=caudal= vertebrae, all of which except the first few are ribless. - -THE TRUNK VERTEBRAE. - -Any vertebra from the second to the sixteenth may be taken as a type -of the trunk vertebrae. - -The general form is elongated and somewhat hour-glass shaped, and the -=centra= are convex in front and concave behind; an opisthocoelous -condition such as this is quite exceptional in Anura. The =notochord= -may persist intervertebrally[54], but in the centre of each vertebra -it becomes greatly constricted or altogether obliterated, and replaced -by marrow. The superficial portion of the centrum is ossified, while -the articular surfaces are cartilaginous. The =neural arches= are low -and articulate together by means of =zygapophyses= borne on short -diverging processes. The anterior zygapophyses look upwards, the -posterior downwards. Each neural arch is drawn out dorsally into a -very slight cartilaginous =neural spine=. - -On each centrum, at a little behind the middle line, there arise a -pair of short backwardly-directed =transverse processes=; each of -which becomes divided into two slightly divergent portions, a dorsal -portion which meets the tubercular process of the rib and is derived -from the neural arch, and a ventral portion which meets the capitular -process of the rib and is derived from the ventral or haemal arch. The -division between these two parts of the transverse processes can be -traced back as far as the sacrum. - -The =first vertebra= as already mentioned differs much from all the -others. It has no ribs, and presents anteriorly two slightly divergent -concave surfaces which articulate with the occipital condyles of the -skull. Between these surfaces the dorsal portion of the anterior face -of the centrum is drawn out into a prominent =odontoid process=, the -occurrence of which renders it probable that the first vertebra of -the newt is really the axis, and that the atlas with the exception of -the odontoid process has become fused with the skull. The sacral -vertebra or =sacrum= differs from the vertebrae immediately in front -of it only in the fact that its transverse processes are stouter and -more obviously divided into dorsal and ventral portions. - -THE CAUDAL VERTEBRAE. - -The =caudal vertebrae= are about twenty-four in number. The anterior -ones have hour-glass shaped centra, and short backwardly-directed -transverse processes. The middle and posterior ones have rather -shorter centra, and are without transverse processes. The neural -arches resemble those of the trunk vertebrae, but each is drawn out -into a rather high cartilaginous neural spine abruptly truncated -anteriorly. All the caudal vertebrae except the first have also a -haemal arch, which is very similar to the neural arch, and is drawn -out into a haemal spine quite similar to the neural spine. Both neural -and haemal arches are ossified continuously with the centra. - -B. THE SKULL. - -The skull of the newt is divisible into three principal parts:-- - -(1) an axial part, the =cranium proper=, which encloses the brain and -to which - -(2) the =capsules= of the =auditory and olfactory sense organs= are -fused; - -(3) the skeleton of the =jaws and hyoid apparatus=. The skull is much -flattened and expanded, though not so much as in the frog. - -(1) THE CRANIUM PROPER. - -The =cranium proper= or =brain case= is an unsegmented tube which -remains partly cartilaginous, and is partly converted into cartilage -bone, partly sheathed by membrane bone. The roof and floor of the -cartilaginous cranium are, as is the case also in the frog, pierced -by holes or fontanelles, and these are so large that the main part of -the roof and floor comes to be formed by membrane bone. - -Two pairs of large ossifications take place in the cranial walls. Of -these the more posterior on each side represents the =exoccipital= and -all three =periotic= bones. It bears a small convex patch of cartilage -for articulation with the atlas, and with its fellow forms the -boundary of the foramen magnum. - -Two foramina pierce the exoccipital just in front of the occipital -condyle and transmit respectively the glossopharyngeal and -pneumogastric (fig. 21, X) nerves. Lying laterally to these nerve -openings is seen a patch of cartilage, the =stapes=, which is -homologous with the stapes or proximal element of the columellar chain -in the frog. Further forward in front of the stapes is the small -opening for the exit of the facial nerve, and seen in a lateral view -close to the orbitosphenoid, that for the trigeminal (fig. 21, C, 5). - -In front of these large bones the lateral parts of the cranial walls -remain cartilaginous for a short distance, and then there follow two -elongated bones, the =orbitosphenoids= (fig. 21, B and C, 11), pierced -by the foramina for the exit of the optic nerves. These bones partly -correspond to the sphenethmoid of the frog. - -The _membrane bones_ connected with the cranium are the _parietals_, -_frontals_ and _prefronto-lachrymals_ on the dorsal surface, and the -_parasphenoid_ on the ventral surface. - -The _parietals_ (fig. 21, A and C, 6) roof over the posterior part of -the great dorsal fontanelle and overlap the exoccipito-periotics. They -meet one another along a sinuous suture in the middle line, as do also -the _frontals_ which overlap them in front. The _frontals_ and -_parietals_ both extend for a short distance down the sides of the -cranium and meet the orbitosphenoids. The _prefronto-lachrymals_ (fig. -21, A and C, 7) connect the frontals with the maxillae. - -[Illustration FIG. 21. A DORSAL, B VENTRAL, AND C LATERAL VIEWS OF THE -SKULL OF A NEWT (_Molge cristata_) × 2-1/2 (after PARKER). - -The cartilage is dotted, the cartilage bones are marked with dots and -dashes, the membrane bones are left white. - - 1. premaxillae. - 2. anterior nares. - 3. posterior nares. - 4. nasal. - 5. frontal. - 6. parietal. - 7. prefronto-lachrymal. - 8. maxillae. - 9. vomero-palatine. - 10. parasphenoid. - 11. orbitosphenoid. - 12. pterygoid. - 13. squamosal. - 14. pro-otic region of exoccipito-periotic. - 15. quadrate. - 16. quadrate cartilage. - 17. exoccipital region of exoccipito-periotic. - 18. articular. - 19. articular cartilage. - 20. dentary. - 21. splenial. - 22. middle narial passage. - II. V. VII. IX. X. foramina for the exit of cranial nerves.] - -On the ventral surface is the large _parasphenoid_ (fig. 21, B, 10), -which is widest behind and overlapped anteriorly by the -vomero-palatines. - -(2) THE SENSE CAPSULES. - -The =auditory capsules= become almost completely ossified continuously -with the exoccipitals; they have been already described. - -The =nasal capsules= are large and quite unossified though they are -overlain by membrane bone. They appear on the dorsal surface between -the anterior nares and the nasal process of the premaxillae. They -enclose the nasal organs, bound the inner side of the anterior narial -opening, and are connected with one another posteriorly by a -cartilaginous area. - -Developed in connection with the nasal capsules are a pair of rather -large _nasals_ (fig. 21, A and C, 4), which lie on the dorsal surface -immediately in front of the frontals. Each forms part of the posterior -boundary of one of the anterior nares, and the two are separated from -one another in the middle line by the nasal process of the premaxillae -(fig. 21, A, 1), and the opening of the =middle narial passage= (fig. -21, A and B, 22), which passes right through the skull. - -On the ventral surface of the skull and forming the greater part of -the boundary of the posterior nares are two large bones, the -_vomero-palatines_ (fig. 21, B and C, 9). Each consists of a wide -anterior portion, partly separated from its fellow in the middle line -by the ventral opening of the middle narial passage, and of a long -pointed posterior portion which is separated from its fellow by the -_parasphenoid_, and bears a row of small pointed teeth formed of -dentine capped with enamel. - -(3) THE JAWS. - -The =upper jaw= of the newt is a discontinuous structure divided into -two parts, an anterior part which consists of membrane bones, the -_maxillae_ and _premaxillae_, and a posterior part which remains mainly -cartilaginous. - -The _premaxillae_ are united, forming a single bone, which in a -ventral view is seen to meet the maxillae and vomero-palatines, and in -a dorsal view to send back a nasal process (fig. 21, A, 1) between the -nasals. - -The _maxillae_ are large bones, each terminating in a point -posteriorly. A single row of teeth similar to those on the -vomero-palatines runs along the outer margin of the maxillae and -premaxillae. - -The posterior part of the upper jaw forms a mass of cartilage which -extends forwards towards the maxillae as a long pointed process whose -ventral surface and sides are overlapped by a membrane bone, the -_pterygoid_ (fig. 21, 12). - -The suspensorial bones include the =quadrate= and _squamosal_. The -=quadrate= (fig. 21, 15) which forms the true =suspensorium= is -directed forwards and outwards, and is terminated by a patch of -cartilage with which the mandible articulates. - -The lower jaw or mandible remains partly cartilaginous, while its -ossifications include two membrane bones and one cartilage bone. The -cartilage bone is the =articular= (fig. 21, C, 18), it forms the -posterior part of the ramus, extends forwards for some distance along -its inner side, and is terminated posteriorly by a patch of cartilage -which articulates with the quadrate. The _dentary_ (fig. 21, C, 20) is -a large bone which forms the anterior part and nearly all the outer -half of each ramus, and bears teeth similar to those of the upper jaw. -Attached to its inner face is a long slender _splenial_ (fig. 21, C, -21). - -THE HYOID APPARATUS. - -This consists of the hyoid arch and part of the first two branchial -arches. - -The =hyoid arch= (fig. 29, A, 2) consists of a pair of =cornua=, each -of which is divided into two halves. The dorsal half forming the -=cerato-hyal= is mainly ossified though tipped with cartilage, and is -connected by ligament with the suspensorium. The ventral half -(=hypo-hyal=) is cartilaginous, and is connected with the -basibranchial. - -The =branchial arches= consist of a median piece, the =basibranchial=, -which is ossified in the centre and cartilaginous at either end, and -of two pairs of =cerato-branchials= which are attached to the -cartilaginous part (fig. 29, A, 8) of the basibranchial. The first -cerato-branchial is chiefly ossified, the second (fig. 29, A, 4) is a -good deal smaller and is cartilaginous. Both are united dorsally to a -single =epi-branchial=, which is terminated by a small cartilaginous -area at the free end but is elsewhere well ossified. - -C. THE RIBS. - -The ribs are short imperfectly ossified structures, bifid at their -proximal end where they articulate with the transverse processes, and -tipped both proximally and distally with cartilage. The dorsal portion -of the proximal end corresponds to the =tuberculum= of the ribs of -higher animals, and the ventral portion to the =capitulum=. Some of -the anterior ribs have a step-like notch on their dorsal surfaces. - -The second to twelfth ribs are fairly equal in size, but further back -they decrease slightly. The ribs which connect the sacral vertebrae -with the ilia are however large. The short ribs borne on the anterior -caudal vertebrae are cartilaginous. - -D. THE STERNUM. - -The sternum (fig. 22, A, 6) is a rather broad plate of cartilage, -drawn out posteriorly into a median process marked by a prominent -ridge. On its antero-lateral margins it bears surfaces for -articulation with the pectoral girdle. - -2. THE APPENDICULAR SKELETON. - -A. THE PECTORAL GIRDLE. - -This is of a very simple character, and remains throughout life in an -imperfectly ossified condition. It consists of a dorsal =scapular -portion=, and a ventral =coracoid portion= partially divided into an -anterior part, the precoracoid, and a posterior part, the =coracoid=. - -[Illustration FIG. 22. A VENTRAL, AND B LATERAL VIEW OF THE SHOULDER -GIRDLE AND STERNUM OF AN OLD MALE CRESTED NEWT (_Molge cristata_) × 3 -(after PARKER). - - 1. scapula. - 2. suprascapula. - 3. coracoid. - 4. glenoid cavity. - 5. precoracoid. - 6. sternum.] - -The =scapular portion= is a slightly curved oblong plate; its proximal -third the =scapula= (fig. 22, 1) is ossified and bounds part of the -well-marked =glenoid cavity= (fig. 22, 4); its distal portion forms a -large oblong cartilaginous plate, the =suprascapula= (fig. 22, 2). - -The =precoracoid= (fig. 22, 5) forms a small forwardly-directed -cartilaginous plate. The =coracoid= (fig. 22, 3) forms a much larger -plate, the greater part of which is unossified and overlaps its fellow -in the middle line, the two being overlapped by the sternum. Around -the glenoid cavity is an area which is mainly ossified and is -continuous with the scapula. - -B. THE ANTERIOR LIMB. - -This is divisible into three parts, the =upper arm= or =brachium=, the -=fore-arm= or =antibrachium=, and the =manus=. - -The =upper arm= includes a single bone, the =humerus=. - -The =humerus= is a slender bone cylindrical in the middle and expanded -at either end, the proximal part forms a rounded =head= which -articulates with the glenoid cavity. Along the proximal part of the -anterior or pre-axial surface runs a strong =deltoid ridge=. The -proximal part of the postaxial surface also bears a small outgrowth. - -The =fore-arm= contains two bones, the =radius= and =ulna=, both of -which are small and imperfectly ossified at their terminations. - -The =radius= (fig. 23, B, 11) or pre-axial bone is rather the larger -of the two, and is considerably expanded at its proximal end. The -=ulna= or postaxial bone is somewhat expanded distally, but is not -drawn out proximally into an olecranon process. - -The =manus= consists of two parts, a group of small bones forming the -=carpus= or =wrist=, and the =hand=. - -The =carpus= is in a very simple unmodified condition as compared with -that of the Frog. It consists of a proximal row of two bones and a -distal row of four, with one, the =centrale=, interposed between. All -these bones are small and polygonal and are imbedded in a plate of -cartilage. - -The bones of the proximal row are a smaller pre-axial bone, the -=radiale= (fig. 23, B, 13), and a larger postaxial bone, which -represents the fused =ulnare= and =intermedium= of the very simple -carpus described on pp. 26 and 27. - -The four bones of the distal row are respectively =carpalia= 2, 3, 4 -and 5. - -The =hand= consists of four digits, that corresponding to the thumb of -the human hand, judging from the analogy of the frog probably being -the one that is absent. - -[Illustration FIG. 23. A RIGHT POSTERIOR, AND B RIGHT ANTERIOR LIMB OF -A NEWT × 1-1/2 (_Molge cristata_). - - 1. femur. - 2. tibia. - 3. fibula. - 4. tibiale. - 5. intermedium. - 6. fibulare. - 7. centrale of tarsus. - 8. tarsale 1. - 9. tarsalia 4 and 5 fused. - 10. humerus. - 11. radius. - 12. ulna. - 13. radiale. - 14. intermedium and ulnare fused. - 15. centrale of carpus, the pointing line passes across carpale 2. - 16. carpale 3. - 17. carpale 5. - I. II. III. IV. V. digits.] - -Each digit consists of a somewhat elongated =metacarpal= and of two or -three phalanges. The metacarpals are contracted in the middle and -expanded at either end. They are connected with the carpus by -cartilage, and the articulations between the several phalanges, and -between the metacarpals and phalanges are also cartilaginous. The -second, third, and fifth digits have two phalanges apiece, the fourth, -which is the longest, has three. The second metacarpal in the -specimen examined and figured articulates partly with carpale 2, -partly with carpale 3. - -C. THE PELVIC GIRDLE. - -The pelvic girdle of the Newt is in a much less modified condition -than is that of the Frog (see p. 165). It consists of a dorsal -element, the =ilium=, a posterior ventral element, the =ischium=, and -an anterior ventral element, the =pubis=, to which is attached an -=epipubis=. - -The =ilium= is a somewhat cylindrical bone which at its ventral end -meets the ischium, and forms part of the =acetabulum=. It is then -directed upwards and slightly backwards, and is attached to the ribs -of the sacral vertebra. - -The =ischia= are a pair of somewhat square bones which meet one -another in the middle line; they form part of the acetabulum, and are -united to the ilia above. - -In front of the ischia is a narrow cartilaginous area which represents -the =pubes=. Projecting forwards from it is a bifid cartilaginous -=epipubis=. - -D. THE POSTERIOR LIMB. - -This is divisible into a proximal portion, the =thigh=, a middle -portion, the =crus= or =shin=, and a distal portion, the =pes=. - -The =thigh= consists of a single bone, the =femur= (fig. 23, A, 1), -which has a thin shaft and expanded ends. The anterior part of the -pre-axial border and posterior part of the postaxial border bear -slight outgrowths. - -The =crus= or =shin= includes two short bones, the =tibia= and -=fibula=, which are nearly equal in length. The pre-axial bone or -tibia is a straight bone thickest at its proximal end, the postaxial -bone or =fibula= (fig. 23, A, 3) is a rather stouter curved bone of -nearly equal diameter throughout. - -The =pes= includes the =tarsus= or =ankle=, and the =foot=. - -The =tarsus= consists of eight small bones arranged in a proximal row -of three, the =tibiale=, =intermedium= and =fibulare=, and a distal -row of four =tarsalia=, with one bone, the =centrale= (fig. 23, A, 7), -interposed between the two rows. In the specimen examined, the -=tibiale=, is a small bone articulating with the tibia, the -=intermedium= (fig. 23, A, 5) is larger and articulates with both -tibia and fibula, the =fibulare= is the largest of the three and -articulates with the fibula. - -The bones of the distal row are =tarsalia 1=, =2=, =3=, and a bone -representing =4= and =5= fused. In the specimen examined tarsale 1 is -pushed away dorsally (fig. 23, A, 8), so as to lie between the tibiale -and tarsale 2. All the tarsal bones are small and somewhat polygonal, -and are connected with one another, and with the tibia and fibula on -the one hand, and with the metatarsals on the other by a thin layer of -cartilage. - -The five =digits= of the foot each consist of a =metatarsal= and of a -certain number of =phalanges=. In the specimen examined, owing to the -shifting of tarsale 1, the first metatarsal as well as the second -articulates with tarsale 2, while the fifth metatarsal articulates -partially with the bone representing the fused tarsalia 4 and 5, -partially with the fibulare. All the bones of the digits except the -distal phalanges are terminated at each end by cartilaginous -epiphyses, the distal phalanx of each digit has a cartilaginous -epiphysis only on its proximal end. - -The first, second, and fifth digits have two phalanges apiece, the -third and fourth have three. - -Figure 31 B, showing a Newt's tarsus copied from Gegenbaur, has -precisely the arrangement generally regarded as primitive for the -higher vertebrates, except that tarsalia 4 and 5 are fused. - - -FOOTNOTES: - -[54] i.e. between one vertebra and the next. - - - - -CHAPTER XI. - -THE SKELETON OF THE FROG[55] (_Rana temporaria_). - - -I. EXOSKELETON. - -The skin of the frog is smooth and quite devoid of scales or other -exoskeletal structures. The only exoskeletal structures met with in -the frog are:-- - -1. The =teeth=, which are most conveniently described with the -endoskeleton. - -2. The horny covering of the calcar or prehallux (see p. 167). - - -II. ENDOSKELETON. - -The endoskeleton of the adult frog consists partly of cartilage, -partly of bone and each of these types of tissue occurs in two forms. -The cartilage may be hyaline, as in the omosternum and xiphisternum, -or may be more or less calcified as in part of the suprascapula and -the epiphyses of the limb bones. The bone may be cartilage bone, or -membrane bone. - -The skeleton is divisible into an =axial portion= consisting of the -skull, vertebral column, and sternum, and an =appendicular portion= -consisting of the skeleton of the limbs and their girdles. - -1. THE AXIAL SKELETON. - -A. THE VERTEBRAL COLUMN. - -The vertebral column is a tube, formed of a series of ten bones which -surround and protect the spinal cord. Of these ten bones nine are -vertebrae, while the tenth is a straight rod, the =urostyle=, and is -almost as long as all the vertebrae put together. The second to eighth -vertebrae inclusive have a very similar structure, but the first and -ninth differ from the others. - -Any one of the second to eighth vertebrae forms a bony ring with a -somewhat thickened floor, the =centrum= or body, which articulates -with the centra of the immediately preceding and succeeding vertebrae. -The articulating surfaces are covered with cartilage and are -procoelous, or convex in front and concave behind. The eighth vertebra -is however amphicoelous or biconcave. The centrum of each vertebra -encloses an isolated vestige of the notochord. The =neural arch= forms -the roof and sides of the neural canal, which is very spacious in the -anterior vertebrae, but becomes more depressed in the posterior ones. -The arch bears the =neural spine=, a low median ridge of variable -character, and is drawn out in front and behind, forming the two pairs -of articulating surfaces or =zygapophyses= by means of which the -vertebrae are attached together. Of these the anterior articulating -surfaces or =prezygapophyses= look upwards and slightly inwards, while -the posterior articulating surfaces or =postzygapophyses= look -downwards and slightly outwards. The sides of the neural arches are -drawn out into a pair of prominent =transverse processes=. Those of -the second vertebra look somewhat forwards, those of the third look -directly outwards or somewhat forwards, while those of the fourth, -fifth, and sixth are directed slightly backwards, and those of the -seventh and eighth nearly straight outwards. All the transverse -processes are terminated by very small cartilaginous =ribs=. - -SPECIAL VERTEBRAE. - -The =first vertebra= is a ring-like structure with a much depressed -centrum. It bears in front two oval concave surfaces for articulation -with the condyles of the skull, while the centrum is terminated behind -by a prominent convex surface. There are as a rule no transverse -processes, and the postzygapophyses look downwards and outwards. -Occasionally however transverse processes do occur. Projecting -forwards from the centrum is a minute process better developed in the -Newt. This resembles an odontoid process, and it has hence been -supposed that the first vertebra is homologous with the axis of -mammalia, and that the atlas of the frog is fused with the skull. - -The =ninth vertebra= has very stout transverse processes directed -backwards and somewhat upwards. They articulate with the pelvic girdle -and hence this vertebra is regarded as the =sacrum=. The neural arch -is much depressed, the centrum is convex in front and bears on its -posterior surface two short rounded processes for articulation with -the urostyle. - -The =urostyle= is a long rod-like bone forming the posterior -unsegmented continuation of the vertebral column. It is probably -equivalent to three vertebrae, the tenth, eleventh, and twelfth fused -together, and to an unsegmented rod of cartilage which lies ventral to -the notochord. The anterior end is expanded and bears two concave -articular surfaces by means of which it articulates with the sacrum. A -prominent ridge runs along the dorsal surface, but gradually -diminishes when traced back. The anterior portion contains a canal -which is a continuation of the neural canal. At a point not far from -the anterior end, this canal communicates with the exterior by a pair -of minute holes which correspond with the intervertebral foramina. - -B. THE SKULL[56]. - -The skull of the Frog consists of three principal parts:-- - -(1) an axial part, the =cranium proper=, which encloses the brain. To -it are firmly fused - -(2) the =capsules of the olfactory and auditory sense organs=, - -(3) lastly there is the =hyoid apparatus= and the =skeleton of the -jaws=. - -The skull is by no means so completely ossified as is the vertebral -column, but in addition to the cartilage bone, there is a great -development of membrane bone in connection with it. - -The skull has a peculiarly flattened and expanded form depending on -the wide lateral separation of the jaws from the cranium. - - -(1) THE CRANIUM PROPER or Brain case. - -This is an unsegmented tube, which is widest behind. It remains to a -considerable extent cartilaginous, but is partly converted into -cartilage bone, partly sheathed in membrane bone. Its roof is -imperfect, being pierced by three holes or =fontanelles=, one large -anterior fontanelle (fig. 25, A, 9), and two smaller posterior -fontanelles (fig. 25, A, 10). - -The cartilage bones of the cranium proper are the two =exoccipitals= -and the =sphenethmoid=. - -The =exoccipitals= (figs. 24, 25, and 26, 6) are a pair of irregular -bones bounding the foramen magnum at the posterior end of the skull. -They almost completely surround the foramen magnum, and bear a pair of -oval convex surfaces, the =occipital condyles=, with which the first -vertebra articulates. The bones generally called the exoccipitals of -the frog include the =epi-otic= and =opisthotic= elements of many -skulls, in addition to the exoccipitals. - -[Illustration FIG. 24. A DORSAL, AND B VENTRAL VIEWS OF THE CRANIUM OF -A COMMON FROG (_Rana temporaria_) × 2 (after PARKER). - -In this and the next two figs. cartilage is dotted, cartilage bones -are marked with dots and dashes, membrane bones are left white. - - 1. sphenethmoid. - 2. fronto-parietal. - 3. pterygoid. - 4. squamosal. - 6. exoccipital. - 7. parasphenoid. - 8. pro-otic. - 9. quadratojugal. - 10. maxillae. - 11. nasal. - 12. premaxillae. - 13. anterior nares. - 14. vomer. - 15. posterior nares. - 16. palatine. - 18. columella. - 19. quadrate. - 20. occipital condyle. - II. optic foramen. - V. VII. foramen for exit of trigeminal and facial nerves. - IX. X. foramina for exit of glossopharyngeal and pneumogastric - nerves.] - -The patch of unossified cartilage immediately external to the -occipital condyle is pierced by two small foramina, through which the -ninth and tenth nerves leave the cranial cavity. The ninth nerve -passes through the more external of these foramina, the tenth through -the one nearer the condyle. The foramina lie however very close -together and are sometimes confluent. The cranial walls for a -considerable distance in front of the occipitals are unossified, but -the anterior end of the cranial cavity is encircled by another -cartilage bone, the =sphenethmoid= (figs. 24 and 25, 1) or girdle -bone. This partly corresponds to the orbitosphenoids of the Newt's -skull. Anteriorly it is pierced by a pair of small foramina through -which the ophthalmic branches of the trigeminal nerve pass out. - -The anterior part of the cranial cavity is divided into two halves by -a vertical plate, the =mesethmoid=. Some little distance behind the -sphenethmoid the ventro-lateral walls of the cartilaginous cranium are -pierced by a pair of rather prominent holes, the =optic foramina= -(figs. 24 and 25, B, II), and at a similar distance further back, -occupying a kind of notch in the pro-otic are the large =trigeminal -foramina=, through which the fifth and seventh nerves leave the -cranium. Between the trigeminal and optic foramina are the very small -foramina for the sixth nerves (fig. 25, B, VI). - -The _membrane bones_ of the cranium proper include the -_fronto-parietals_ and the _parasphenoid_. - -The _fronto-parietals_ (figs. 24 and 26, A, 2) form a pair of long -flat bones closely applied to one another in the middle line, the line -of junction being the =sagittal suture=. They cover over the -fontanelles and overlap the sphenethmoid in front. - -The _parasphenoid_ (figs. 24 and 26, B, 7) is a bone shaped like a -dagger with a very short handle. It lies on the ventral surface of the -cranium, the blade being directed forwards and underlying the -sphenethmoid; its lateral processes underlie the auditory capsules. - - -(2) THE SENSE CAPSULES. - -The sense capsules are cartilaginous or bony structures which surround -the olfactory and auditory organs and are closely united to the -cranium. - -[Illustration FIG. 25. A DORSAL AND B VENTRAL VIEW OF THE CRANIUM OF A -COMMON FROG (_Rana temporaria_) from which the membrane bones have -mostly been removed. × 2 (after PARKER). - - 1. sphenethmoid. - 2. palatine. - 3. pterygoid. - 4. quadrate. - 5. columella. - 6. exoccipital. - 7. ventral cartilaginous wall of cranium. - 8. pro-otic. - 9. anterior fontanelle. - 10. right posterior fontanelle. - 11. quadratojugal. - 12. nasal capsule. - II. V. VI. IX. X. foramina for exit of cranial nerves.] - -The =auditory capsules= are fused with the sides of the posterior -end of the cranium just in front of the exoccipitals. They are -largely cartilaginous, but include in their anterior walls a pair -of irregular cartilage bones, the =pro-otics= (figs. 24 and 25, 8). -The cartilaginous area lying ventral to the pro-otic and external -to the exoccipital is pierced by a rather prominent hole, the -=fenestra ovalis=, which forms a communication between the internal -ear cavity, and a space the tympanic cavity, which lies at the side -of the head, and is bounded externally by the tympanic membrane. The -fenestra ovalis is occupied by a minute cartilaginous structure, the -=stapes=, and articulated partly to this and partly to a slight recess -in the pro-otic is the =columella= (fig. 25, B, 5), a rod in part -bony and in part cartilaginous, whose outer end is attached to the -tympanic membrane. The columella and stapes are together homologous -with the mammalian auditory ossicles and with the hyomandibular of -Elasmobranchs. Sometimes the term columella is used to include the -whole ossicular chain,--the columella together with the stapes. - -The =olfactory= or =nasal capsules= (fig. 25, B, 12) are fused with -the anterior end of the cranium and differ from the auditory capsules -in being to a great extent unossified. There are however two pairs of -membrane bones developed in connection with them, the _vomers_ and the -_nasals_. They are drawn out into three pairs of cartilaginous -processes, on the dorsal surface into the =prenasal= and =alinasal= -processes which bound the external nares, and on the ventral surface -towards the middle line into the forwardly-projecting =rhinal= -processes. - -The _nasals_ (figs. 24 and 26, 11) form a pair of triangular bones -lying dorsolaterally in front of the fronto-parietals. Their bases are -turned towards one another and their apices are directed outwards and -backwards. They correspond in position with the prefrontals of the -reptilian skull as well as with the nasals. - -The _vomers_ are a pair of irregular bones lying on the ventral -surface of the olfactory capsules. Each bears on its inner and -posterior angle a group of minute pointed teeth, while its outer -border is drawn out into three or four small slightly diverging -processes, the two posterior of which form the inner boundary of the -=posterior nares= (fig. 24, B, 15). - -(3) THE JAWS. - -The =upper jaw= consists of a rod of cartilage connected with the -cranium near its two ends, but widely separated from it in the middle. -It is almost completely overlain by membrane bone. With its posterior -end the lower jaw articulates. - -The membrane bones of the upper jaw include first the _premaxillae_, a -small bone meeting its fellow in the middle line, and forming the -extreme anterior end of the upper jaw. It gives off on its dorsal -surface a backwardly-projecting process. It is connected behind with -the _maxillae_ (figs. 24 and 26, 10), a long flattened bone which forms -the greater part of the margin of the upper jaw, and gives off near -its anterior end a short process which projects upwards and meets the -nasal. - -[Illustration FIG. 26. A, LATERAL VIEW OF THE SKULL, B, POSTERIOR VIEW -OF THE CRANIUM OF A COMMON FROG (_Rana temporaria_) × 2 (after -PARKER). - - 1. sphenethmoid. - 2. fronto-parietal. - 3. pterygoid. - 4. squamosal. - 5. tympanic membrane. - 6. exoccipital. - 7. parasphenoid. - 8. pro-otic. - 9. quadratojugal. - 10. maxillae. - 11. nasal. - 12. premaxillae. - 13. anterior nares. - 14. mento-meckelian. - 15. dentary. - 16. angulo-splenial. - 17. basilingual plate. - 19. quadrate. - 20. columella. - 21. occipital condyle. - 22. anterior cornu of the hyoid (cerato-hyal). - 23. foramen magnum. - - II. IX. X. foramina for the exit of cranial nerves.] - -Both maxillae and premaxillae are grooved ventrally, and bear, attached -to the outer more prominent margin of the groove, a row of minute -conical teeth. These teeth are =pleurodont=, that is, are ankylosed by -their bases and outer sides to the margin of the jaw. Each tooth is a -hollow cone, the basal part of which is formed of bone, the apical -part of dentine, capped by a very weak development of enamel. - -The posterior end of the maxillae is overlapped by a small bone, the -_quadratojugal_ (figs. 24 and 26, 9), whose posterior end forms part -of the articular surface for the lower jaw. Just behind the -quadratojugal there is a small unossified area which lies at the angle -of the mouth, and is connected by a narrow bar of cartilage with the -cranium; this forms the =quadrate= (figs. 24 and 26, 19). A -backwardly-directed outgrowth from the cartilaginous bar more or less -completely surrounds the tympanic membrane, forming the tympanic ring. -When followed back the maxillae and quadratojugal diverge further and -further from the cranium, till the angle of the mouth comes to be -separated from the foramen magnum by a space nearly double the width -of the cranium. This space is bridged over to a considerable extent by -two triradiate bones, the _pterygoid_ and _squamosal_. - -The _pterygoid_ (figs. 24 and 26, 3) is a large bone, whose anterior -limb runs forwards meeting the maxillae and palatine; while its inner -limb meets the auditory capsule and parasphenoid, and its outer limb -runs backwards and outwards to the angle of the mouth. The _palatine_ -is a small transversely-placed bone, which connects the pterygoid with -the anterior part of the sphenethmoid. The _squamosal_ (figs. 24 and -26, 4) is a T-shaped bone whose anterior arm is pointed and passes -forwards to meet the pterygoid. The posterior upper arm is closely -applied to the pro-otic, while the posterior lower arm meets the -pterygoid and quadratojugal at the angle of the jaw, and surrounds the -narrow cartilaginous bar of the quadrate which goes to join the -cranium. The squamosal is probably homologous with the squamosal -together with the pre-opercular of Bony Ganoids. - -The quadrate and squamosal form the =suspensorium= by which the lower -jaw is connected with the cranium. - -The =lower jaw= or =mandible= consists of a pair of cartilaginous rods -(=Meckel's cartilages=) in connection with each of which there are -developed two membrane bones and one cartilage bone. The cartilage -bone is the =mento-meckelian= (fig. 26, A, 14), a very small -ossification at the extreme anterior end. The membrane bones are the -_angulo-splenial_ and the _dentary_. The _angulo-splenial_ is a strong -flat bone which forms the inner and lower part of the mandible for the -greater part of its length. Its dorsal surface is produced into a -slight =coronoid process=. The _dentary_ (fig. 26, A, 15) is a flat -plate which covers the outer surface of the anterior half of the -mandible, as far forwards as the mento-meckelian. The lower jaw is -devoid of teeth. The part of Meckel's cartilage which in most -vertebrates ossifies, forming the articular bone, remains unossified -in the Frog. - -THE HYOID APPARATUS. - -The =hyoid= of the adult Frog is formed of the modified hyoid and -branchial arches of the tadpole. It consists of a broad thin plate of -cartilage, the =basilingual plate= (fig. 29, B, 1), drawn out into two -pairs of long processes, the =cornua=. The basilingual plate is -broader in front than behind, and is formed from the fused ventral -ends of the hyoid and branchial arches of the tadpole. - -The =anterior cornua= (fig. 29, B, 2) form a pair of long slender -cartilaginous rods which project from the body of the hyoid at first -forwards, then backwards, and finally upwards and somewhat forwards -again, to be united to the auditory capsules just below the fenestrae -ovales. They are formed from the dorsal portion of the hyoid arch of -the tadpole and are homologous with the cerato-hyals of the Dogfish. - -The =posterior cornua= form a pair of straight bony rods diverging -outwards from the posterior end of the basilingual plate. They are -formed from the fourth branchial arches of the tadpole, and differ -from the rest of the hyoid apparatus in being well ossified. - -The =columellar chain=, which has been already described (p. 157), -should be mentioned with the hyoid as it is homologous to the -hyomandibular of fishes. - -The =sternum= of the =Frog=, though regarded as part of the axial -skeleton, is so intimately connected with the pectoral girdle, that it -will be described with the appendicular skeleton. - - -2. THE APPENDICULAR SKELETON. - -This consists of the skeleton of the two pairs of limbs and their -respective girdles. It is at first entirely cartilaginous but the -cartilage becomes later on mainly replaced by bone. The only bone -developed in connection with the appendicular skeleton, which has no -cartilaginous predecessor, is the _clavicle_. - - -A. THE PECTORAL GIRDLE. - -This consists originally of two half rings of cartilage encircling the -sides of the body a short way behind the head. These two halves meet -one another in the ventral middle line, and separate the anterior -elements of the sternum from the posterior ones. - -Each half-ring bears on the middle of its outer and posterior surface -a prominent cup, the =glenoid cavity=, with which the proximal -arm-bone articulates. This cup divides the half-arch into a dorsal -=scapular= and a ventral =coracoid= portion. - -The =scapular portion= consists of two parts, the =suprascapula= and -the =scapula=. - -The =suprascapula= (fig. 30, A, 2) is a wide, thin plate attached by -its ventral and narrowest border to the scapula. Its proximal and -anterior half is imperfectly ossified, its whole border or sometimes -only its dorsal and posterior borders consist of unaltered hyaline -cartilage, while the rest of it is composed of calcified cartilage. -The =scapula= (fig. 30, A, 3) is a fairly stout rod of bone -constricted in the middle, and forming the dorsal half of the glenoid -cavity. - -The =coracoid portion= consists of three parts, the =coracoid=, -=precoracoid= and _clavicle_. - -The largest and most posterior of these is the _coracoid_ (fig. 30, A, -4) which like the scapula, is contracted in the middle and expanded at -the ends, especially at the ventral end. It forms a large part of the -glenoid cavity. The ventral ends of the coracoids which meet one -another in the middle line are unossified, and form narrow strips of -calcified cartilage, the =epicoracoids= (fig. 30, A, 5); these are -often regarded as sternal elements. - -The =precoracoid= forms a narrow strip of cartilage lying in front of -the coracoid, from which it is separated by the wide =coracoid -foramen= (fig. 30, A, 9). The dorsal end is continuous with an area of -unossified cartilage which separates the coracoid and scapula and -forms part of the glenoid cavity. - -The _clavicle_ is a narrow membrane bone closely attached to the -anterior surface of the precoracoid, its dorsal end is expanded. - - -THE STERNUM. - -The sternum consists of four parts arranged in two groups; two parts -to each group. The anterior members are the episternum and omosternum. - -The =episternum= (fig. 30, A, 10) is a thin almost circular plate of -cartilage much of which remains hyaline. - -The =omosternum= (fig. 30, A, 11) is a slender bony rod widest at its -posterior end; it connects the episternum with the ventral ends of the -precoracoids. - -The =sternum proper= is a short rod of cartilage sheathed in bone; it -is contracted in the middle and expanded at each end. It bears -attached to its posterior end a broad somewhat bilobed plate of -partially calcified cartilage, the =xiphisternum= (fig. 30, A, 13). - -B. THE ANTERIOR LIMB. - -This is divisible into three parts, the =upper arm= or =brachium=, the -=fore-arm= or =antibrachium=, and the =manus=. - -All the larger bones have their ends formed by prominent epiphyses -which do not unite with the shaft till late in life. Their -articulating surfaces are covered by hyaline cartilage. - -In the =upper arm= there is a single bone, the =humerus=. - -This has a more or less cylindrical shaft and articulates by a -prominent rounded =head= with the glenoid cavity. The distal end shows -a large rounded swelling on either side of which is a =condylar -ridge=, the inner or postaxial one being the larger. A prominent -=deltoid ridge= runs along the proximal half of the anterior surface, -and in the male frog a second equally prominent ridge runs along the -distal half of the posterior surface. - -The =fore-arm= consists of two bones, the =radius= and =ulna=, united -together and forming the =radio-ulna=. The two bones are quite fused -at their proximal ends where they form a deep cup which articulates -with the distal end of the humerus, and is drawn out into a rather -prominent backwardly-projecting =olecranon process=, which ossifies -from a centre distinct from that of the shaft. The distal end is -distinctly divided by a groove into an anterior radial and a posterior -ulnar portion. - -The =manus= consists of two parts, the =wrist= or =carpus= and the -=hand=. - -The =carpus=[57] consists of six small bones arranged in two rows. The -three bones of the proximal row are the =ulnare=, =radiale= and -=centrale=. The =ulnare= and =radiale= are about equal in size and -articulate regularly with the radio-ulna. The =centrale= is pushed out -of its normal position and lies partly on the pre-axial side, partly -in front of the radiale. Of the three bones of the distal row the two -pre-axial ones, =carpalia 1= and =2=, are small; carpale 2 articulates -with the second metacarpal, carpale 1 with both the first and second. -The third bone is large and articulates with the third, fourth and -fifth metacarpals, it represents =carpalia 3-5=, with probably in -addition the representative of a second centrale. - -The =hand= consists of four complete digits, and a vestigial =pollex= -reduced to a short metacarpal. - -Each of the four complete digits consists of a =metacarpal= and a -variable number of =phalanges=. The first digit, as just mentioned, -has no phalanges, the second and third have two, and the fourth and -fifth have three. - -C. THE PELVIC GIRDLE. - -The pelvic girdle of the Frog is much modified from the simple or -general type found in the Newt (p. 149). - -It is a V-shaped structure consisting of two halves which are fused -together in the middle line posteriorly, while in front they are -attached to the ends of the transverse processes of the sacral -vertebra. Each half bears at its posterior end a deep cup, the -=acetabulum=, with which the head of the femur articulates. - -Each half of the pelvis ossifies from two centres. The anterior and -upper half of the acetabulum, and the long laterally compressed bar -extending forwards to meet the sacral vertebra ossify from a single -centre and are generally called the =ilium=; it is probable however -that they represent both the =ilium= and =pubis= of mammals[58]. The -posterior part of this bone meets its fellow in a median symphysis. - -The posterior third of the acetabulum is formed by a small bone, the -=ischium=, which likewise meets its fellow in a median symphysis. - -The ventral portion of the pelvic girdle never ossifies, even in old -animals being formed only of calcified cartilage. This is generally -regarded as the pubis, but it perhaps corresponds to the =acetabular -bone= of mammals. - - -D. THE POSTERIOR LIMB. - -This corresponds closely to the anterior limb and, like it, is -divisible into three parts, the =thigh=, the =shin= or =crus= and the -=pes=. - -As was the case with the anterior limb, all the long bones have their -ends formed by prominent epiphyses which do not unite with the shaft -till late in life. - -In the =thigh= there is only a single bone, the =femur=. - -The =femur= is a moderately long, slender bone with a well-ossified -hollow shaft slightly curved in a sigmoid manner. Both ends are -expanded, the proximal end is hemispherical and articulates with the -acetabulum, the distal end is larger and more laterally expanded. - -The =shin= likewise includes a single bone, the =tibio-fibula=, but -this, as can be readily seen by the grooves at the proximal and distal -ends of the shaft, is formed by the fusion of two distinct bones, the -=tibia= and =fibula=. The tibio-fibula is longer and straighter than -the femur. - -The =pes= consists of two parts, the =ankle= or =tarsus= and the -=foot=. - -The =tarsus= consists of two rows of structures, very different in -size. The proximal row consists of two long bones, the =tibiale= and -=fibulare=, which are united by common epiphyses at the two ends, -while in the middle they are widely separated. The tibiale lies on the -tibial or pre-axial side, and the fibulare which is the larger of the -two bones on the fibular or postaxial side. The distal row of tarsals -consists of three very small pieces of calcified cartilage. The -postaxial of these is the largest, it articulates with the second and -third metatarsals and is probably homologous with tarsalia 2 and 3 -fused. The middle one is very small, it articulates with the first -metatarsal and is probably tarsale 1. The pre-axial one articulates -with the metatarsal of the calcar, a structure to be described -immediately, and has been regarded as a =centrale=. - -The =foot= includes five complete digits and a supplemental toe as -well. Each of the five digits consists of a long =metatarsal= with -epiphyses at both ends, and of a variable number of phalanges. The -first digit or =hallux= and the second have two phalanges, the third -three, the fourth, which is the largest, four, and the fifth, three. -The distal phalanges have epiphyses only at their proximal ends, the -others at both ends. - -On the pre-axial side of the hallux is the supplemental digit, the -=prehallux= or =calcar=. It consists of a short metatarsal and one or -two phalanges, and is terminated distally by a horny covering of -epidermal origin. - - -FOOTNOTES: - -[55] See A. Ecker, _Die anatomie des Frosches_, Braunschweig 1864, -translated by G. Haslam, Oxford, 1889, also A.M. Marshall, _The Frog_, -5th edition, Manchester and London, 1894. - -[56] W.K. Parker, _Phil. Trans._ 161, 1871, p. 137, and W.K. Parker -and G.T. Bettany, _The Morphology of the Skull_, London, 1877, p. 136. - -[57] See G.B. Howes and W. Ridewood, _P.Z.S._, 1888, p. 141. - -[58] See bottom of p. 187. - - - - -CHAPTER XII. - -GENERAL ACCOUNT OF THE SKELETON IN AMPHIBIA. - - -EXOSKELETON. - -The exoskeleton, at any rate in most living forms, is very slightly -developed in Amphibia. The only representatives of the epidermal -exoskeleton are (1) the minute horny beaks found coating the -premaxillae and dentaries in _Siren_ and the tadpoles of most Anura, -(2) the nails borne by the first three digits of the pes in _Xenopus_ -and by the Japanese Salamander _Onychodactylus_, (3) the horny -covering of the calcar or prehallux of frogs. The Urodela and nearly -all the Anura, which form the vast majority of living Amphibia, have -naked skins. A few Anura belonging to the genera _Ceratophrys_ and -_Brachycephalus_ have bony dermal plates developed in the skin of the -back, and these plates become united with some of the underlying -vertebrae. - -In the Gymnophiona the integument bears small cycloid scales arranged -in rings which are equal in number to the vertebrae. These scales -contain calcareous concretions. Scales also occur between the -successive rings. - -In the Labyrinthodontia the dermal exoskeleton is in many genera -greatly developed. It is generally limited to the ventral surface and -consists principally of a buckler formed of three bony plates, one -median and two lateral. These plates protect the anterior part of the -thorax, and are closely connected with the adjacent endoskeleton. They -probably represent the interclavicle and clavicles. Behind this -buckler numerous scutes are generally developed, which often cover the -whole ventral surface, and may cover the whole body. - - -TEETH[59]. - -In Amphibia teeth are generally present on the maxillae, premaxillae and -vomers, and except in Anura on the dentaries; sometimes they occur on -the palatines as in many Urodela, most Labyrinthodontia, and the -Gymnophiona; less commonly on the pterygoids as in _Menobranchus_, -_Siredon_, some Labyrinthodontia, and _Pelobates cultripes_[60], or on -the splenials as in _Siren_ and _Menobranchus_, or parasphenoid as in -_Pelobates cultripes_, _Spelerpes belli_ and _Batrachoseps_. In some -Anura such as _Bufo_ and _Pipa_ the jaws are toothless. - -In Gymnophiona, _Menobranchus_, and _Siredon_, the teeth are arranged -in two concentric curved rows. The teeth of the outer row are borne on -the premaxillae and maxillae if present, (the maxillae are absent in -_Menobranchus_), the teeth of the second row on the vomers and -pterygoids in _Menobranchus_ and _Siredon_, and on the vomers and -palatines in Gymnophiona. In some Gymnophiona there is a double row of -mandibular teeth. The vomerine, palatine and parasphenoid teeth of all -forms are numerous and are not arranged in rows. - -The teeth of all living Amphibia are simple conical structures -ankylosed to the bone, and consisting of dentine, coated or capped -with a thin layer of enamel. In the Labyrinthodontia teeth of more -than one size are sometimes present. The dentine of the basal part of -the larger teeth is in some genera very greatly folded, causing the -structure to be highly complicated. These folds, the intervals between -which are filled with cement, radiate inwards from the exterior and -outwards from the large pulp cavity. The basal part of the teeth of -_Ceratophrys_ (Anura) has a similar structure. - - -ENDOSKELETON. - -VERTEBRAL COLUMN. - -Four regions of the vertebral column can generally be recognised in -Amphibia, viz. the cervical, the trunk or thoraco-lumbar, the sacral -and the caudal regions. In the limbless Gymnophiona, however, only -three regions, the cervical, thoracic, and post-thoracic can be made -out. The cervical region is limited to a single vertebra which -generally differs from the others in having no transverse processes or -indication of ribs. It is generally called the atlas, but it commonly -bears a small process arising from the anterior face of the centrum -which resembles the odontoid process of higher animals, and renders it -probable that the first vertebra of Amphibia corresponds to the axis, -not to the atlas. Amphibia generally have a single sacral vertebra. - -Three elements go to make up the vertebral column in Amphibia, viz. - -1. the notochord, - -2. the long vertebral centra, - -3. intervertebral cartilage which forms the joints between successive -centra. - -The relations which these three elements bear to one another are -subject to much variation. The successive stages can be well traced in -the Urodela. - -1. The first stage is found in larval Urodeles in general and in adult -Ichthyoidea, and some Salamandrina. In these forms the notochord -persists and retains approximately the same diameter throughout the -whole length of the vertebral column. Bony biconcave centra are -present and constrict it to a certain extent vertebrally, while -intervertebrally there is a development of cartilage. The connection -between the bony vertebrae is effected mainly by the expanded -notochord. - -2. In the next stage, as seen in _Gyrinophilus porphyriticus_, the -growth of intervertebral cartilage has caused the almost complete -obliteration of the notochord intervertebrally, and its entire -disappearance vertebrally, i.e. in the centre of each vertebra. The -intervertebral cartilage now forms the main connection between -successive vertebrae, and sometimes cases are found whose condition -approaches that of definite articulations. Readily recognisable -remains of the notochord are still found at each end of the -intervertebral constriction. - -3. In the third stage differentiation and absorption of the -intervertebral cartilage has given rise to definitely articulating -opisthocoelous vertebrae. These are found in most adult Salamandrina. - - * * * * * - -The transverse processes of the earlier trunk vertebrae are divided -into two parts, a dorsal part which meets the tubercular process of -the rib and is derived from the neural arch, and a ventral part which -meets the capitular process of the rib, and is derived from the -ventral or haemal arch. In the caudal vertebrae and often also in the -posterior trunk vertebrae the two processes are fused. - -_Siren_ and _Proteus_, although they possess minute posterior limbs, -have no sacral vertebrae, while _Cryptobranchus lateralis_ has two. -The caudal vertebrae, except the first, have haemal arches very -similar to the neural arches. - -In Labyrinthodontia the centra of the vertebrae are generally well -ossified biconcave discs. In some forms however, like _Euchirosaurus_, -the centra are imperfectly ossified, and consist of bony rings -traversed by a wide notochordal canal. Each ring is formed of four -pieces, a large well-ossified neural arch, a basal piece, and a pair -of lateral pieces. Vertebrae of this type are called _rachitomous_. - -In the tail region of other forms each vertebra consists of an -anterior centrum bearing the neural arch, and a posterior -intercentrum[61] bearing chevron bones. Vertebrae of this type are -called _embolomerous_. Haemal arches similar to the neural arches are -often found as in Urodela. The transverse processes are sometimes well -developed and are divided into tubercular and capitular portions. - -In Gymnophiona the vertebrae are biconcave and are very numerous, they -sometimes number about two hundred and thirty. Only quite the last few -are ribless and so can be regarded as post-thoracic vertebrae. The -first vertebra has nothing of the nature of an odontoid process. - -In Anura the number of vertebrae is very greatly reduced, only nine -and the urostyle being present. Of these, eight are presacral and one -sacral. The urostyle is post-sacral and corresponds to three or more -modified vertebrae. The first vertebra is without transverse -processes, the remaining presacral vertebrae have the transverse -processes fairly large, while the sacral vertebra has them very large, -forming in some genera widely expanded plates. The urostyle is a long -cylindrical rod which articulates with the sacrum generally by two -facets. Ankylosed to its anterior end are the remains of two neural -arches. - -In Anura remains of the notochord are found in the centre of each -vertebra, i.e. vertebrally, while in the Urodela they only occur -intervertebrally. - -The vertebrae in Anura are, as a rule, procoelous. The eighth vertebra -is however generally amphicoelous, while the ninth commonly has one -convexity in front, and two behind. - -In some forms such as _Bombinator_, _Pipa_, _Discoglossus_ and -_Alytes_ they are opisthocoelous; in others like _Pelobates_ they are -variable. - - -THE SKULL[62]. - -CRANIUM AND MANDIBLE. - -In the Amphibian skull there are as a rule far fewer bones than in the -skull of bony fish. The primordial cartilaginous cranium often -persists to a great extent. Only quite a few ossifications take place -in it; namely in the occipital region--the exoccipitals, further -forwards--the pro-otics, and at the boundary of the orbital and -ethmoidal regions--the sphenethmoid. The basi-occipital and -basisphenoid are never ossified. As in Mammalia there are two -occipital condyles formed by the exoccipitals. - -Large vacuities commonly occur in the cartilage of both floor and roof -of the primordial cranium. These are roofed over to a greater or less -extent by the development of membrane bone. Thus on the roof of the -cranium there are paired parietals, frontals, and nasals, and on its -floor are paired vomers, and a median unpaired parasphenoid. - -In all living forms the parietals meet and there is no interparietal -foramen, though this exists in Labyrinthodonts. - -The palato-pterygo-quadrate bar is united at each end with the -cranium, but elsewhere in most cases forms a wide arch standing away -from it. The suspensorium is, as in Dipnoi and Holocephali, -autostylic. The palato-pterygo-quadrate bar sometimes remains entirely -cartilaginous, sometimes its posterior half is ossified forming the -quadrate. In connection with it a number of membrane bones are -generally developed, viz. the maxillae, premaxillae, palatines, -pterygoids, quadratojugals, and squamosals. The pterygoids are, -however, sometimes partially formed by the ossification of cartilage. -The cartilage of the lower jaw and its investing membrane bones -generally have much the same relations as in bony fishes. - -URODELA. The skulls of the various Urodeles show an interesting series -of modifications and differ much from one another, but all agree in -the absence of the quadratojugals, in the fact that the palatines lie -parallel to the axis of the cranium, and in the large size of the -parasphenoid. - -The lower types _Menobranchus_, _Siren_, _Proteus_, and _Amphiuma_ -have longer and narrower skulls than do the higher types. - -_Menobranchus_ has a very low type of skull which remains throughout -life in much the same condition as that of a young tadpole or larval -salamander. The roof and floor of the cranium internal to the membrane -bones are formed of fibrous tissue, not of well-developed cartilage. -The epi-otic regions of the skull are ossified, forming a pair of -large bones which lie external to, and distinct from, the -exoccipitals. _Proteus_ and the Labyrinthodonts are the only other -Amphibia which have these elements separately ossified. The parietals -send a pair of long processes forwards along the sides of the -frontals. Nasals and maxillae are absent, as is likewise the case in -_Proteus_. Teeth are borne on the vomers, premaxillae, pterygoids, -dentaries and angulo-splenials. The suspensorium is forwardly -directed. - -The skull of _Siren_ resembles that of _Menobranchus_ in several -respects, as in the forward direction of the suspensorium and in the -absence of maxillae, but differs in the possession of nasals, in the -toothless condition of the premaxillae and dentaries, and in the fusion -and dentigerous condition of the vomers and palatines. - -_Amphiuma_ has a skull which, though narrow and elongated, differs -from those of _Menobranchus_, _Proteus_, and _Siren_, and resembles -those of higher types in the following respects:-- - -(1) the suspensorium projects nearly at right angles to the cranium -instead of being directed forwards, (2) the maxillae are well -developed, and the premaxillae are completely ankylosed together, (3) -there are no palatines. - -The skulls of _Megalobatrachus_, _Cryptobranchus_ and _Siredon_ -resemble those of the highest Urodeles the Salamanders in their wide -form, in having the pro-otics distinct from the exoccipitals which are -ossified continuously with the epi-otics and opisthotics, and in -having no palatines, but differ in having the two premaxillae -separate, and in the arrangement of the vomerine teeth which in -_Megalobatrachus_ and _Cryptobranchus_ are placed along the anterior -boundaries of the bones, these meeting in the middle line. In -_Siredon_ the vomers are separated by the very large parasphenoid. - -The suspensorium in _Megalobatrachus_ and _Cryptobranchus_ projects at -right angles to the cranium; in _Siredon_ it projects somewhat -downwards and forwards as in the Salamandrina. - -Modifications of the vomers, pterygoids and palatines accompany the -changes of the larval ichthyoid _Siredon_ into the adult salamandroid -_Amblystoma_, the vomers especially come to resemble to a much greater -extent those of the Salamandrina. - -The ossification of the skull in the Salamandrina is carried further -than in the Ichthyoidea, though the supra-occipital and basi-occipital -are not ossified. The skull differs from that in the Ichthyoidea in -the size of the part of the vomero-palatines which lies in front of -the teeth, in the frequent union of the two premaxillae and in the -ossification of all the periotic bones continuously with the -exoccipital. - -The skull differs from that of Anura in the following respects:-- - -(1) the bones of the upper jaw do not form a complete arch standing -away from the cranium, and the maxillae are not united to the quadrates -by quadratojugals, (2) the long axis of the suspensorium passes -obliquely downwards and forwards instead of downwards and backwards, -(3) there is no sphenethmoid encircling the anterior end of the -brain, its place being partly taken by a pair of orbitosphenoids, (4) -there is no definite tympanic cavity. - -[Illustration FIG. 27. DORSAL VIEW OF THE SKULL OF A LABYRINTHODONT -(_Capitosaurus nasutus_) × 1/9 (from VON ZITTEL). - - 1. premaxillae. - 2. nasal. - 3. maxillae. - 4. anterior nares. - 5. frontal. - 6. prefrontal. - 7. lachrymal. - 8. jugal. - 9. orbit. - 10. parietal. - 11. postfrontal. - 12. postorbital. - 13. interparietal foramen. - 14. squamosal. - 15. supratemporal. - 16. quadratojugal. - 17. quadrate. - 18. epi-otic. - 19. dermo-supra-occipital. - 20. exoccipital. - 21. foramen magnum.] - -LABYRINTHODONTIA. The skull in Labyrinthodontia is remarkable for its -extreme solidity, the large number of bones which are present, and the -extent to which the roofing over of the temporal and other fossae has -taken place. In many forms the surface of the bones is as in -Crocodiles, strongly sculptured (fig. 27, right half) with ridges and -grooves which probably lodged sensory organs. The bones forming the -roof of the skull are generally very uniform in size, perhaps the most -noticeable of them being the paired dermo-supra-occipitals (fig. 27, -19). Paired dermo-supra-occipitals occur also in certain Ganoids. The -Labyrinthodont skull also bears resemblance to that of many fish in -the development of a pair of long pointed epi-otics (fig. 27, 18), -which remain permanently distinct from the surrounding bones. The -parietals are small and enclose between them the interparietal foramen -(fig. 27, 13). In some forms in which the head is protected with an -armour of scutes, these do not roof over the interparietal foramen, -and from this fact it has been inferred that the Labyrinthodonts had a -functional pineal eye. Both supra- and infra-temporal fossae are -partially or completely roofed over by the postorbitals and large -supra-temporals (fig. 27, 15). - -There is generally a ring of bones in the sclerotic coat of the eye. -The pterygoids do not meet in the middle line, being separated by the -parasphenoid. The palatines bear teeth, and in some genera -(_Archegosaurus_) form long splints lying along the inner side of the -maxillae and more or less surrounding the posterior nares. In others -(_Nyrania_) they lie in the normal position near the middle line, one -on each side of the parasphenoid. The vomers bear teeth and sometimes -meet in the middle line; they are sometimes confluent with the -parasphenoid. On the ventral surface of the cranium there are -generally large palatal vacuities. - -In the mandible there is often a well-marked postglenoid process, and -the articular is generally completely ossified. - -[Illustration FIG. 28. A, VENTRAL VIEW OF THE CRANIUM; B, LATERAL VIEW -OF THE CRANIUM AND MANDIBLE OF _Siphonops annulatus_ (after -WIEDERSHEIM). - - 1. anterior nares. - 2. naso-premaxillae. - 3. frontal. - 4. parietal. - 5. maxillae. - 6. vomer. - 7. orbit. - 8. quadrate united with the pterygoid in front. - 9. squamosal. - 10. exoccipital. - 11. dentary. - 12. angular. - 13. basi-occipital and basisphenoid fused. - 14. posterior narial opening surrounded by the palatine. - X. pneumogastric foramen.] - -GYMNOPHIONA. The skull bears a considerable resemblance to that of -Labyrinthodonts, especially in the arrangement of the bones which -bound the mouth cavity. The cranium is very hard, and is covered by -a complete bony roof formed mainly of the exoccipitals, parietals, -frontals, prefrontals, nasals and premaxillae. The nasals and -premaxillae are sometimes ossified continuously. There is a median -unpaired ethmoid whose dorsal end appears at the surface wedged in -between the frontals and parietals. The bone generally regarded as the -squamosal[63] is very large, and it and the maxillae generally together -surround the orbit, which, in _Epicrium_, has in it a ring of bones. -The palatines form long tooth-bearing bones fused with the inner sides -of the maxillae; they nearly surround the posterior nares. - -The quadrate bears the knob, and the angular the cup for the -articulation of the mandible,--a very primitive feature. The mandible -is also noticeable for the enormous backward projection of the -angular. - - * * * * * - -ANURA. In Anura the skull is very short and wide owing to the -transverse position of the suspensorium. There is often a small -ossification representing the quadrate. Sometimes as in _Hyla_ and -_Alytes_ there is a fronto-parietal fontanelle. - -As compared with the skull in Urodela the chief characteristics of the -skull of Anura are:-- - -1. the presence of a sphenethmoid, - -2. the union of the frontals and parietals on each side, - -3. the occasional occurrence of small supra- and basi-occipitals, - -4. the backward growth of the maxillae and its connection with the -suspensorium by means of the quadratojugal, - -5. the dagger-like shape of the parasphenoid, - -6. the occurrence of a definite tympanic cavity, - -7. the frequent occurrence of a predentary or mento-meckelian -ossification in the mandible. - -The skull of _Pipa_ is abnormal, being greatly flattened and -containing little cartilage. The fronto-parietals are fused, and there -is no sphenethmoid. The quadrates are well developed and the -squamosals and parasphenoid differ much from those of other Anura. - - -HYOID AND BRANCHIAL ARCHES. - -In larval Amphibia the hyoid and four branchial arches are generally -present, and in adult Ichthyoidea they are frequently almost as well -represented as in the larva, and are of use in strengthening the -swallowing apparatus. They are very well seen in _Siredon_, and -consist of a hyoid attached by ligaments to the suspensorium, followed -by four branchial arches of which the first and second are united by a -copula (fig. 29, D, 8), while the third and fourth are not. The hyoid -is not always the largest and best preserved of the arches, for -sometimes as in _Spelerpes_ one of the branchials is far larger than -the hyoid. Four branchial arches occur in _Siren_ as in _Siredon_, but -in _Proteus_ there are only three. - -In some larval Labyrinthodontia (_Branchiosaurus_) four branchial -arches are known to occur, and their arrangement is almost precisely -similar to that in _Siredon_. - -In Gymnophiona the remains of only three branchial arches occur in -addition to the hyoid. The four arches are all very similar to one -another, each consists of a curved rod of uniform diameter throughout. -The hyoid is united with the first branchial arch, but has no -attachment to the cranium. - -In larval Anura (fig. 29, C) the arrangement of the hyoid and -branchial arches is much as in Urodela. In the adult, however, the -ventral parts of all the arches unite, forming a compact structure, -the _basilingual plate_ (fig. 29, B, 1). - -[Illustration FIG. 29. VISCERAL ARCHES OF AMPHIBIA. - - A. _Molge cristata_ (after PARKER). - B. _Rana temporaria_ adult (after PARKER). - C. Tadpole of _Rana_ (after MARTIN ST ANGE). - D. _Siredon pisciformis_ (after CREDNER). - -In each case the ossified portions are slightly shaded, while the -cartilaginous portions are left white. - - 1. basilingual plate. - 2. hyoid arch. - 3. first branchial arch. - 4. second do. - 5. third branchial arch. - 6. fourth do. - 7. thyro-hyal. - 8. copula.] - -The dorsal parts of the first three branchial arches disappear, but -those of the fourth become ossified and form the short, stout -thyro-hyals or posterior cornua. The dorsal parts of the hyoid arch in -the adult form a pair of long bars, the anterior cornua, which are -united to the periotic region of the skull in front of the fenestra -ovalis either by short ligaments or by fusion as in _Bufo_. In _Pipa_ -and _Xenopus_ the first and second branchial arches persist as well as -the fourth (thyro-hyal), but in _Pipa_ the hyoid is wanting. - - -RIBS. - -Ribs are generally very poorly developed in Amphibia. In Anura they -are in most cases absent; when present they generally form minute -unossified appendages attached to the transverse processes, but in -_Discoglossus_ and _Xenopus_ the anterior vertebrae are provided with -distinct ribs. In Urodela and Labyrinthodontia they are generally -short structures, each as a rule attached to the vertebra by a -bifurcated proximal end. The number of rib-bearing vertebrae varies, -but the first and the posterior caudal vertebrae are always ribless. -The anterior caudal vertebrae too are generally ribless, but sometimes -a few of them bear small ribs. In _Spelerpes_ the last two trunk -vertebrae are ribless, and hence may be regarded as lumbar vertebrae. - -In Gymnophiona ribs are better developed than in any other Amphibia; -they occur on all the vertebrae except the first and last few, and are -attached to the transverse processes, sometimes by single, sometimes -by double heads. - -Sternal ribs are almost unknown in Amphibia, but traces of them occur -in _Menobranchus._ - - -STERNUM. - -In Amphibia the sternum is not very well developed; sometimes as in -Gymnophiona and _Proteus_ no traces of it occur, and in the Urodela it -is never ossified. It is always very intimately related to the -pectoral girdle. In the Salamandrina it has the form of a broad thin -plate of cartilage, grooved and overlapped by the coracoid. - -[Illustration FIG. 30. SHOULDER-GIRDLE AND STERNUM OF - - A. An old male common Frog (_Rana temporaria_). - B. An adult female _Docidophryne gigantea_ (after PARKER). - -In both A and B the left suprascapula is removed. The parts left -unshaded are ossified; those marked with small dots consist of hyaline -cartilage, those marked with large dots of calcified cartilage. - - 1. calcified cartilage of suprascapula. - 2. ossified portion of suprascapula. - 3. scapula. - 4. coracoid. - 5. epicoracoid. - 6. precoracoid. - 7. clavicle. - 8. glenoid cavity. - 9. coracoid foramen. - 10. episternum. - 11. omosternum. - 12. sternum. - 13. xiphisternum.] - -In most Anura the sternum consists of a number of parts arranged in -series. At the anterior end is a flat cartilaginous plate with a -bony basal stalk. This plate is called the episternum, and its stalk -the omosternum. The continuity of the sternum is now interrupted -by a pair of cartilaginous structures, the epicoracoids, which are -shoulder-girdle elements, and represent the unossified ventral ends of -the coracoids. In some cases cartilaginous epiprecoracoids can also -be distinguished. Further back is the long sternum proper, while last -comes the xiphisternum, a broad expanded plate of cartilage. - -In some Anura such as _Pipa_ and _Hyla_ the number of sternal elements -is considerably reduced. - - -APPENDICULAR SKELETON. - - -PECTORAL GIRDLE. - -The most primitive Amphibian shoulder-girdle is found in the Urodela. -It consists of a dorsal element, the scapula, a posterior ventral -element, the coracoid, and an anterior ventral element, the -precoracoid. The clavicle is not developed, and the two coracoids -overlap in the middle line. The shoulder-girdle remains largely -cartilaginous but the proximal end of the scapula is ossified, and the -ossification may extend through part of the coracoid and precoracoid. - -In Labyrinthodontia there is an exoskeletal ventral buckler formed of -three plates, a median one, which probably represents an -interclavicle, and two lateral ones, which are probably clavicles. -Traces of endoskeletal structures, probably corresponding to the -precoracoid and scapula, are also known in some cases. The Gymnophiona -and some of the Labyrinthodontia have lost the pectoral girdle and -limbs. - -The ossification of the shoulder-girdle has gone on much further in -Anura than it has in Urodela. Clavicles are present and the scapula -and coracoid of each side are ossified from separate centres. The -distal part of the scapula forms a large imperfectly ossified plate, -the suprascapula. - -The shoulder-girdle of Anura is however subject to considerable -variations. In the Toads (Bufonidae) the epicoracoids or unossified -ventral ends of the coracoids and precoracoids overlap in the middle -line (fig. 30, B, 5). This arrangement is called _Arciferous_. In the -Frogs,--Ranidae, and other forms belonging to the group -_Firmisternia_,--the epicoracoids do not overlap but form a narrow -cartilaginous bar separating the ventral ends of the coracoids (fig. -30, A, 5). - - -ANTERIOR LIMB. - -In many Amphibia and especially in the Urodela the anterior limb has a -very simple unmodified arrangement. The humerus is straight and of -moderate length, its ends are rounded for articulation on the one hand -with the shoulder-girdle, and on the other hand with the radius and -ulna. In the Urodela the radius and ulna are distinct. In the Anura -they have fused, though the line of junction of the two is not -obliterated. Their proximal ends are hollowed for articulation with -the convex end of the humerus. - -The manus in all recent Amphibia agrees in never having more than four -complete digits, but is subject to considerable variation, this -statement applying especially to the carpus. - -In the larva of Salamandra (fig. 31, A), except that the pollex is -absent[64], the manus retains completely the condition which is -generally regarded as primitive for the higher Vertebrata. It consists -of an anterior row of three elements, the ulnare, intermedium, and -radiale, and a posterior row of four, the carpalia 2, 3, 4, and 5. -Interposed between the two rows is a centrale. _Menobranchus_ has a -similar very simple carpus. In most other Amphibia this simplicity is -lost. This loss may be due to:-- - -(_a_) fusion of certain structures, e.g. in the adult _Salamandra_ the -intermedium and ulnare have fused, - -(_b_) displacement of structures, e.g. in _Bufo viridis_, the centrale -has been pushed up till it comes to articulate with the radius, - -(_c_) the development of supernumerary elements, especially of extra -centralia. In _Megalobatrachus_ two or even three centralia sometimes -occur. - -[Illustration FIG. 31. A, RIGHT ANTIBRACHIUM AND MANUS OF A LARVAL -SALAMANDER (_Salamandra maculosa_) (after GEGENBAUR). - -B, RIGHT TARSUS AND ADJOINING BONES OF _Molge sp._ (after GEGENBAUR). - - 1. radius. - 2. ulna. - 3. radiale. - 4. intermedium. - 5. ulnare. - 6. centrale. - 7. carpale 2. - 8. " 3. - 9. " 4. - 10. " 5. - 11. tibia. - 12. fibula. - 13. tibiale. - 14. intermedium. - 15. fibulare. - 16. centrale. - 17. tarsale 1. - 18. tarsalia 4 and 5 fused. - I. II. III. IV. V. digits.] - -In the great majority of Amphibia while one digit, probably the first, -is absent, the other four digits are well developed. In the forms -however with degenerate limbs like _Amphiuma_, _Siren_ and _Proteus_ -the number of digits is still further reduced. In _Siren_ there are -three or four, in _Proteus_ three, and in _Amphiuma_ two or three -digits in the manus. - -In Anura the pollex is represented only by a short metacarpal. There -are sometimes traces of a prepollex. The carpus often has two -centralia and the intermedium is absent. - -In Labyrinthodontia the limbs are generally very simple and resemble -those of Urodela. In some forms, however, the manus differs from that -of all living Amphibia in possessing five well-developed digits. - - -PELVIC GIRDLE. - -The simplest Amphibian pelvis is that of some of the Labyrinthodontia; -thus in _Mastodonsaurus_ it consists dorsally of a short broad ilium -placed vertically and attached to the sacrum, and ventrally of a small -pubis and of a large ischium meeting its fellow in the middle line. In -some Labyrinthodonts the pubes as well as the ischia meet in a ventral -symphysis, and in many there are no obturator foramina. In _Siren_, -Gymnophiona and some Labyrinthodontia the pelvic girdle and limbs are -absent. - -In Urodela the ventral element of the pelvis on each side forms a flat -plate which meets its fellow of the opposite side. The anterior part -of the plate, representing the pubis, generally remains cartilaginous -throughout life; the posterior part representing the ischium is in -almost every case well ossified. Attached to the anterior end of the -pubes there is an unpaired bifid cartilaginous structure, the -epipubis. The ilia are vertically placed. - -In most Anura the pelvis is peculiarly modified in correlation with -the habits of jumping. The long bone generally called the ilium is -placed horizontally and is attached at its extreme anterior end to the -sacrum. The ischium is ossified and distinct. Ventrally in front of -the ischium there is a tract of unossified cartilage which is often -regarded as the pubis. In _Xenopus_, however, the bone corresponding -to the ilium of the Frog is seen to ossify from two centres, one -forming the ilium, the other, which lies at the symphysis, being -apparently the pubis. This makes it probable that the so-called ilium -of the Frog is really to be regarded as an ilio-pubis, and renders the -homology of the cartilaginous part uncertain, but it probably -corresponds to the acetabular bone of mammals. In _Xenopus_ also there -is a minute epipubis similar to that of Urodeles. - - -POSTERIOR LIMB. - -In Urodela the posterior limb (fig. 31, B) closely resembles the -anterior limb, but is even less removed from the primitive condition -of the higher vertebrates in the fact that all five digits are -commonly present. The tibia and fibula are short bones approximately -equal in size. In some cases the number of digits is reduced. Thus in -_Menobranchus_ the pes has four digits, in _Proteus_ it has two, and -in _Amphiuma_ two or three, while in _Siren_ the posterior limbs have -atrophied. - -In correlation with their habits of jumping, the posterior limbs in -Anura are much lengthened and considerably modified. The tibia and -fibula are completely fused. The intermedium is absent, while the -tibiale and fibulare are greatly elongated. Tarsalia 4 and 5 are -absent. Five digits are always present, and there is a prehallux -formed of two or more segments. - -In general the posterior limbs in Labyrinthodontia bear the closest -resemblance to the anterior limbs; in some cases three centralia are -found. - -In Ichthyoidea, and in most Labyrinthodontia, the cartilages of the -carpus and tarsus remain unossified; in Salamandrina and in Anura they -are generally ossified. - - -FOOTNOTES: - -[59] O. Hertwig. Ueber das Zahnsystem der Amphibien. _Arch. mikr. -Anat._ supplem. Bd. XI. 1875. - -[60] G.A. Boulenger, _P.Z.S._ 1890, p. 664. - -[61] See p. 14. - -[62] See many papers by W.K. Parker published in the _Phil. Trans._ of -the Royal Soc. - -[63] Perhaps this bone includes supra-orbital and postorbital -elements. - -[64] The first digit present is sometimes regarded as the pollex, but -from analogy with Anura it is probable that the pollex is the missing -digit. - - - - -CHAPTER XIII. - -SAUROPSIDA. - - -This great group includes the Reptiles and Birds and forms the second -of the three into which the Gnathostomata may be divided. There is -nearly always a strongly-developed epiblastic exoskeleton which has -the form of scales or feathers, and in some cases a dermal exoskeleton -is also well developed. In living forms the notochord never persists, -being replaced by vertebrae, but in some extinct forms the centra are -notochordal. The vertebral centra are ossified, and only in -exceptionally rare cases have terminal epiphyses. The skull is well -ossified and has membrane bones incorporated in its walls. - -The occipital segment is completely ossified, and an interorbital -septum or bony partition separating the two orbits is usually -developed to a greater or less extent. The skull generally articulates -with the vertebral column by a single occipital condyle into the -composition of which the exoccipitals and basi-occipital enter in -varying proportions. The pro-otic ossifies, and either remains -distinct from the epi-otic[65] and opisthotic throughout life, or -unites with them only after they have fused with the adjacent bones. -The hyoid and branchial arches are much reduced; and the -representative of the hyomandibular is connected with the auditory -apparatus, forming the auditory ossicles[66]. Each ramus of the -mandible always consists of a cartilage bone, the articular, and -several membrane bones. The mandible articulates with the cranium by -means of a quadrate. The ribs in Birds and some Reptiles bear -_uncinate processes_, i.e. small, flat, bony or cartilaginous plates -projecting backwards from their posterior borders. The sternum is not -transversely segmented as in mammals, and there are commonly distinct -cervical ribs. The ankle joint is intertarsal, or situated between the -proximal and distal row of tarsal bones, not cruro-tarsal as in -Mammalia. - - -CLASS I. REPTILIA[67]. - -The axial skeleton is generally long, and that of the limbs frequently -comparatively short, or sometimes absent. - -The exoskeleton generally has the form of epidermal scales, which are -often combined with underlying bony dermal plates or scutes and may -sometimes form a continuous armour. Neither feathers nor true hairs -are ever present. The vertebral column is generally divisible into the -five usual regions. The centra of the vertebrae vary enormously, and -may be amphicoelous, procoelous, opisthocoelous or flat, but they -never have saddle-shaped articulating surfaces. The quadrate is always -large, and is sometimes fixed, sometimes movable. A transpalatine bone -uniting the pterygoid and maxillae is generally present. - -Free ribs are often borne along almost the whole length of the trunk -and tail, and often occur attached to the cervical vertebrae. The -sacrum is generally composed of two vertebrae which are united with -the ilia by means of expanded ribs. The sternum is rhomboidal, and may -either be cartilaginous or formed of cartilage bone, but never of -membrane bone; it differs from that of birds also in the fact that it -does not ossify from two or more centres. An interclavicle is -generally present. There are always more than three digits in the -manus, and never less than three in the pes. In all living reptiles -the ilia are prolonged further behind the acetabula than in front of -them, and the bones of the pelvis remain as a rule, distinct from one -another throughout life. - -The pubes (pre-pubes) and ischia both commonly meet in ventral -symphysis, and the acetabula are wholly or almost wholly ossified. The -metatarsals are not ankylosed together. - - -_Order 1._ THEROMORPHA[68]. - -This order includes a number of mainly terrestrial, extinct reptiles, -which differ much from one another, and show remarkable points of -affinity on the one hand with the Labyrinthodont Amphibia, and on the -other with the Mammalia. The vertebrae are nearly always amphicoelous -and sometimes have notochordal centra. The skull is short and has the -quadrate immovably fixed. There is an interparietal foramen, and -generally large supratemporal fossae bounded by supratemporal[2] -arcades, but with no infratemporal[69] arcades; _Elginia_ however has -the whole of the temporal region completely roofed over. - -The teeth are placed in distinct sockets and are very variable in -form, the dentition sometimes resembling the heterodont dentition of -mammals. The humerus has distinct condyles and an ent-epicondylar -foramen[70] as in many mammals. - -The pubis is fused with the ischium, and both pectoral and pelvic -girdles are remarkably solid. The obturator foramen is remarkably -small or even absent. The anterior ribs have two articulating -surfaces, and each articulates by its tuberculum with the transverse -process, and by its capitulum with the centrum as in mammals. - -These reptiles occur chiefly in deposits of Triassic and Permian age. -Some of the best known genera are _Dicynodon_, _Udenodon_, _Placodus_, -_Pariasaurus_ and _Galesaurus_. They will be noticed in the general -account of the skeleton in reptiles. - - -_Order 2._ SAUROPTERYGIA. - -This order includes a number of extinct marine reptiles, devoid of an -exoskeleton. The tail is short, the trunk long, and the neck in the -most typical forms extremely long. The vertebrae have slightly -biconcave, or nearly flat centra. The skull is relatively small and -has large supratemporal fossae. The teeth are placed in distinct -sockets, and are generally confined to the margins of the jaws; they -are sharp and curved and are coated with grooved enamel. The -premaxillae are large, and there is an interparietal foramen. The -quadrate is firmly united to the cranium. The anterior nares are -separate and are placed somewhat close to the orbits. There is no -ossified sclerotic ring. The palatines and pterygoids meet the vomers, -and more or less completely close the palate, and in some forms, e.g. -_Plesiosaurus_, there is a distinct parasphenoid. Thoracic ribs are -strongly developed and each articulates with its vertebra by a single -head. The cervical vertebrae have well-marked ribs, which articulate -only with the centra, in this respect differing from those of -Crocodiles. The caudal vertebrae bear both ribs and chevron bones, and -abdominal splint-ribs are largely developed. - -In the shoulder-girdle the coracoids are large and meet in a ventral -symphysis; precoracoids and a sternum are apparently absent, but parts -generally regarded[71] as the clavicles and interclavicle are well -developed. In the pelvis, the pubes and ischia meet in a long -symphysis. The limbs are pentedactylate, and in the best known forms, -the Plesiosauridae, form swimming paddles. - -The Sauropterygia occur in beds of Secondary age, and some of the best -known genera are _Plesiosaurus_, _Pliosaurus_ and _Nothosaurus_. - - -_Order 3._ CHELONIA. - -In the Tortoises and Turtles the body is enclosed in a bony box, -formed of the dorsal carapace, and a flat ventral buckler, the -plastron. Except in _Dermochelys_ the carapace is partly formed from -the vertebral column and ribs, partly from dermal bones. Both carapace -and plastron are, except in _Dermochelys_, _Trionyx_ and their allies, -covered with an epidermal exoskeleton of horny plates, which are -regularly arranged, though their outlines do not coincide with those -of the underlying bones. The thoracic vertebrae have no transverse -processes, and are quite immovably fixed, but the cervical and caudal -vertebrae are very freely movable. There are no lumbar vertebrae. The -skull is extremely solid, and frequently has a very complete false -roof. Teeth have been detected in embryos of _Trionyx_ but with this -exception the jaws are toothless, and are encased in horny beaks. The -quadrate is firmly fixed. The facial part of the skull is very short, -and the alisphenoidal and orbitosphenoidal regions are unossified. In -living forms there are no separate nasal bones, while large -prefrontals and postfrontals are developed. There is a comparatively -complete bony palate chiefly formed of the palatines and pterygoids. -The anterior nares are united and placed at the anterior end of the -skull, and the premaxillae are very small. There is no transpalatine -bone and the vomer is unpaired. The dentaries are generally fused -together. - -There are ten pairs of ribs, and each rib has only a single head and -is partially attached to two vertebrae; there are no cervical or -sternal ribs. There is no true sternum. - -The three anterior elements of the plastron are respectively -homologous with the interclavicle and two clavicles of other reptiles, -while the remaining elements of the plastron are probably homologous -with the abdominal ribs of Crocodiles. The pectoral girdle lies within -the ribs, and the precoracoids and coracoids do not meet in ventral -symphyses. The scapula and precoracoid are ossified continuously. The -pubis probably corresponds with the pre-pubis of Dinosaurs. There are -four limbs each with five digits. - -The order includes three suborders:-- - - -_Suborder (1)._ TRIONYCHIA. - -The carapace and plastron have a rough granular surface covered with -skin and without any horny shields. - -The plastron is imperfectly ossified, and marginal bones may be -absent, or if present are confined to the posterior portion of the -carapace. The pelvis is not united to the plastron. The cranium has -not a complete false roof and the head can be drawn back under the -carapace. - -The first three digits of both manus and pes bear claws, and the -fourth digit in each case has more than three phalanges. The most -important genus is _Trionyx_. - - -_Suborder (2)._ CRYPTODIRA. - -The carapace and plastron vary in the extent to which they are -ossified, and except in _Dermochelys_[72] and its allies are covered -by horny plates. Marginal bones are always present. The head can -generally be drawn back under the carapace. The pelvis is not firmly -united to the plastron. The cranium often has a complete false roof, -and in the mandibular articulation the cup is borne by the cranium, -and the knob by the mandible. Among the more important genera are -_Dermochelys_, _Chelone_, and _Testudo_. - - -_Suborder (3)._ PLEURODIRA. - -The carapace and plastron are strongly ossified, and firmly united to -the pelvis. The head and neck can be folded laterally under the -carapace, but cannot be drawn back under it. The cranium has a more or -less complete false roof, and in the mandibular articulation the knob -is borne by the cranium, and the cup by the mandible. _Chelys_ is a -well-known genus. - - -_Order 4._ ICHTHYOSAURIA[73]. - -The order includes a number of large extinct marine reptiles whose -general shape is similar to that of the Cetacea. The skull is -enormously large, and the neck short. The tail is very long, and is -terminated by a large vertically-placed bilobed fin, the vertebral -column running along the lower lobe. The very numerous vertebrae are -short and deeply biconcave. The vertebral column can be divided into -caudal and precaudal regions only, as the ribs which begin at the -anterior part of the neck are continued to the posterior end of the -trunk without being connected with any sternum or sacrum. The precaudal -vertebrae bear two surfaces for the articulation of the ribs, while -in the caudal vertebrae the two surfaces have coalesced. The caudal -region is also distinguished by its chevron bones. The vertebrae have -no transverse processes, and the neural arches are not firmly united -to the centra, and have only traces of zygapophyses. The atlas and -axis are similar to the other vertebrae, but there is a wedge-shaped -intercentrum between the atlas and the skull, and another between -the atlas and the axis. The skull is greatly elongated (fig. 32) and -pointed, mainly owing to the length of the premaxillae. The orbits -are enormous, and there is a ring of bones in the sclerotic (fig. 32, -15). The anterior nares are very small; and are placed far back just -in front of the orbits. There is an interparietal foramen, and the -supratemporal fossae (fig. 32, 9) are very large, while there are no -infratemporal fossae. An epipterygoid occurs. The quadrate is firmly -fixed to the cranium, and there is a large parasphenoid. There are -large prefrontals, but the frontals are very small. The very numerous -teeth are large and conical, and are placed in continuous grooves -without being ankylosed to the bone. They are confined to the jaw-bones. - -[Illustration FIG. 32. LATERAL (BELOW) AND DORSAL (ABOVE) VIEWS OF THE -SKULL OF AN _Ichthyosaurus_. (Modified from Deslongchamps.) - - 1. premaxillae. - 2. maxillae. - 3. nasal. - 4. prefrontal[1]. - 5. frontal. - 6. postfrontal[74]. - 7. anterior nares. - 8. orbit. - 9. supratemporal fossa. - 10. interparietal foramen. - 11. parietal. - 12. squamosal. - 13. supratemporal. - 14. quadratojugal. - 15. sclerotic ring. - 16. postorbital. - 17. jugal. - 18. lachrymal. - 19. dentary. - 20. articular. - 21. angular.] - -The ribs are long, and the anterior ones have capitula and tubercula. -There is no sternum, but the ventral body wall is strengthened by a -complex system of abdominal splint ribs. - -The pectoral girdle is strongly developed, the scapulae are narrow, -the coracoids broad, and meet ventrally without overlapping. There are -probably no precoracoids, but clavicles and a T-shaped interclavicle -are well developed. - -The limbs are very short, and completely modified into swimming -paddles. The humerus and femur are both short, while the radius and -ulna, tibia and fibula are generally still further reduced to the form -of short polygonal bones. - -The digits are formed of longitudinal series of very numerous small -bones. The number of digits is five, but there sometimes appear to be -more owing to the bifurcation of certain of them, or to the addition -of marginal bones, either to the radial or ulnar side of the limb. The -humerus has no foramen, and both humerus and femur are unique in that -they are distally terminated by concave surfaces instead of by convex -condyles. The pelvic limb is much smaller than the pectoral. The -pelvis has no bony connection with the vertebral column, and all the -component bones are small and rod-like. - -The Ichthyosauria are confined to beds of Secondary age and by far the -best known genus is _Ichthyosaurus_. - - -_Order 5._ RHYNCHOCEPHALIA. - -This order includes the living _Sphenodon_ (_Hatteria_) and various -extinct forms. The general shape of these animals is lizard-like and -the tail is long. - -The vertebrae are amphicoelous or sometimes nearly flat, and the -notochord sometimes persists to some extent. _Proterosaurus_ differs -from the other members of the order in having opisthocoelous cervical -vertebrae. - -The sacrum is composed of two vertebrae. Ossified inter centra -(interdorsalia) generally occur in the cervical and caudal regions, -and sometimes throughout the whole vertebral column. In the skull the -quadrate is immovably fixed and united to the pterygoid. The palate is -well ossified, while the premaxillae which are often beak-like are -never ankylosed together. The jaws may be toothless or may be provided -with teeth which are usually acrodont (see p. 199). The palatines -frequently bear teeth, and in _Proterosaurus_ teeth occur also on the -pterygoids and vomers. The rami of the mandible are united by ligament -at the symphysis except in the Rhynchosauridae, in which the union is -bony. Superior and inferior temporal arcades occur. - -The ribs have capitula and tubercula, and often uncinate processes -(see p. 190) as in birds. A pectoral girdle and sternum, with -clavicles and a T-shaped interclavicle are developed, and abdominal -ribs are always found. The precoracoid is however absent. The limbs -are pentedactylate. - -_Sphenodon_[75] (Hatteria) now living in some of the islands of the -New Zealand group, is certainly the most generalised of all living -reptiles. Though lizard-like in form it differs from all living -lizards in the possession of two temporal arcades, abdominal ribs and -a fixed quadrate; and is often considered to be nearly allied in many -respects to the type of reptile from which all the others took their -origin. - -Among the better known extinct forms are _Proterosaurus_ of Permian -and _Hyperodapedon_ of Triassic age. - - -_Order 6._ SQUAMATA. - -This order includes the extinct Mosasaurians, and the lizards and -snakes which form the vast majority of living reptiles. The trunk may -be moderately elongated and provided with four short limbs as in -lizards, or it may be limbless, extremely elongated, and passing -imperceptibly into the tail. The surface is generally completely -covered with overlapping horny epidermal scales, below which bony -dermal scutes may be developed. - -The vertebrae are procoelous, rarely amphicoelous. There are no inter -centra, and the neural arches are firmly united to the centra. -Additional articulating surfaces, the zygosphenes and zygantra, are -often developed[76]. The sacrum is formed of two or rarely three -vertebrae, or may be wanting as in Ophidia. In the skull an -infratemporal arcade forming the lower boundary of the infratemporal -fossa is absent, and the quadrate, except in the Chamaeleons, is -movably articulated to the squamosal. The palatal vacuities are large -and the nares are separate. There is often a distinct parasphenoid. -The teeth are either _acrodont_ (i.e. ankylosed to the summit of the -jaw), or _pleurodont_, i.e. ankylosed to the inner side of the jaw. -The thoracic ribs each have a single head which articulates with the -centrum of the vertebra; while uncinate processes and abdominal ribs -never occur. - -A pectoral girdle and sternum may be present, or may be completely -absent as in snakes. Except in snakes there are generally four -pentedactylate limbs which may either form paddles or be adapted for -walking. - - -_Suborder (1)._ LACERTILIA[77]. - -The body is elongated, and as a rule four short pentedactylate limbs -are present, but sometimes limbs are vestigial or absent. The -exoskeleton generally has the form of horny plates, spines, or scales; -while sometimes as in the Chamaeleons and Amphisbaenians it is absent. -In other forms such as _Tiliqua_ and _Scincus_, the body has a -complete armour of bony scutes, whose shape corresponds with that of -the overlying horny scales. - -The vertebrae are procoelous, rarely as in the Geckos amphicoelous; -they are usually without zygosphenes and zygantra, but these -structures occur in the Iguanidae. The sacral vertebrae of living -forms are not ankylosed together, and the caudal vertebrae usually -have well-developed chevron bones. - -In the skull[78] the orbits are separated from one another, only by an -imperfectly developed interorbital septum, the cranial cavity not -extending forwards between them, while the alisphenoidal region is -unossified. The premaxillae may be paired or united (Amphisbaenidae), -and there is usually an interparietal foramen. There may be a complete -supratemporal[79] arcade bounding the lower margin of the -supratemporal fossa, or the supratemporal fossa may be open below. The -quadratojugal is not ossified, and the quadrate articulates with the -exoccipital. There is no infratemporal arcade. There is commonly a -rod-like epipterygoid[80] (fig. 33, 14) connecting the pterygoid and -parietal. - -Teeth are always present, and may be confined to the jaws or may be -developed also on the pterygoids and rarely on the palatines; they are -either acrodont or pleurodont. The rami of the mandible are suturally -united. - -A pectoral girdle is always present, and generally also a sternum. -Clavicles and a T-shaped interclavicle are commonly present, but are -absent in the Chamaeleons. - -[Illustration FIG. 33. A, LATERAL VIEW, AND B, LONGITUDINAL SECTION OF -THE SKULL OF A LIZARD (_Varanus varius_). × 3/5. (Brit. Mus.) - - 1. premaxillae. - 2. maxillae. - 3. nasal. - 4. lateral ethmoid. - 5. supra-orbital. - 6. lachrymal. - 7. frontal. - 8. postfrontal. - 9. prefrontal. - 10. basisphenoid. - 11. pro-otic. - 12. epi-otic. - 13. pterygoid. - 14. epipterygoid (columella cranii). - 15. jugal. - 16. transpalatine. - 17. parasphenoid. - 18. quadrate. - 19. parietal. - 20. squamosal. - 21. supratemporal. - 22. exoccipital. - 23. dentary. - 24. splenial. - 25. supra-angular. - 26. angular. - 27. coronoid. - 28. articular. - 29. vomer. - 30. basi-occipital. - 31. orbitosphenoid.] - -There is no separate precoracoid but a precoracoidal process (fig. 34, -7) of the coracoid is generally prominent. - -[Illustration FIG. 34. LATERAL VIEW OF THE SHOULDER-GIRDLE OF -_Varanus._ × 3/5. - -(Brit. Mus.). - - 1. suprascapula. - 2. scapula. - 3. glenoid cavity. - 4. coracoid. - 5. clavicle. - 6. interclavicle. - 7. precoracoidal process.] - -Sternal ribs are present in chamaeleons and scinks. The limbs are in -the great majority of cases pentedactylate and the digits are clawed. -The phalanges articulate by means of condyles. Sometimes one or both -pairs of limbs are absent. When the posterior limbs are absent the -pelvis is also wanting, though the loss of the anterior limbs does not -lead to a corresponding loss of the pectoral girdle. - -The pubis corresponds to the pre-pubis of Dinosaurs, and both pubes -and ischia meet in ventral symphyses. - -The suborder includes the Lizards, Chamaeleons and Amphisbaenians. - - -_Suborder (2)._ OPHIDIA[81]. - -The Ophidia or snakes are characterised by their greatly elongated -body and want of limbs. The body is covered with overlapping horny -scales and bony dermal scutes are never present. The vertebrae are -procoelous, and are distinguishable into two groups only, precaudal or -rib-bearing, and caudal or ribless. The atlas vertebra is also -ribless. The neural arches are always provided with zygosphenes and -zygantra. Many of the vertebrae have strong hypapophyses, and the -caudal vertebrae are without chevron bones. - -In the skull the cranial cavity extends forwards between the orbits, -and is closed in front by downgrowths from the frontals and parietals -which meet the well-ossified alisphenoids and orbitosphenoids[82]. The -cranium is strongly ossified, and there are no parotic processes or -interparietal foramen. There are no temporal arcades and no -epipterygoid. The premaxillae if present are very small (fig. 51, 1) -and usually toothless. The quadrates articulate with the squamosals, -and do not as in Lacertilia meet the exoccipitals. The palatines do -not unite directly with the vomers or with the base of the cranium, -and the whole palato-maxillary apparatus is more loosely connected -with the cranium than it is in Lacertilia. The pterygoids, and in most -cases also the palatines, bear teeth. The dentition is acrodont, and -the rami of the mandible are united only by an elastic ligament--an -important point serving to distinguish the Ophidia from the -Lacertilia. There is an imperfectly developed interorbital septum, the -ventral part of which is formed by the parasphenoid. The postfrontal -is generally well developed, while the jugals and quadratojugals are -absent. There are never any traces of the anterior limbs or pectoral -girdle, but occasionally there are vestiges of a pelvis and posterior -limbs. - - -_Suborder (3)._ PYTHONOMORPHA[83]. - -This suborder includes _Mosasaurus_ and its allies, a group of -enormous extinct marine reptiles found in beds of Cretaceous age. - -The skin is in most forms at any rate unprovided with dermal scutes. -The vertebrae may be with or without zygosphenes and zygantra. The -skull resembles that of lizards, having an interparietal foramen, and -a cranial cavity open in front. The squamosal takes part in the -formation of the cranial wall, and the quadrate articulates with the -squamosal, not as in Lacertilia with the exoccipital. There are large -supratemporal fossae, bounded below by supratemporal arcades. The -teeth are large and acrodont, and occur on the pterygoids as well as -on the jaws. The two rami of the mandible are united by ligament only. -Pectoral and pelvic girdles are present, but clavicles are wanting, -and the pelvis is not as a rule united to any sacrum. - -The limbs are pentedactylate, and are adapted for swimming, while all -the limb bones except the phalanges are relatively very short. The -number of phalanges is not increased beyond the normal, and they -articulate with one another by flat surfaces. The terminal phalanges -are without claws. - - -_Order 7._ DINOSAURIA[84]. - -The extinct reptiles comprising this order were all terrestrial, and -include the largest terrestrial animals known. They vary greatly in -size and in the structure of the limbs, some approach close to the -type of structure met with in birds, others are allied to crocodiles. - -Passing to the more detailed characters:--there is sometimes a -well-developed exoskeleton having the form of bony plates or spines. -The vertebrae may be solid or their centra may be hollowed internally; -their surfaces may be flat, biconcave or opisthocoelous. The sacrum is -composed of from two to six vertebrae. - -As regards the skull, the quadrate is large and fixed, and -supratemporal and infratemporal fossae bounded by bone occur. The -teeth are more or less laterally compressed, and often have serrated -edges; they may be placed in distinct sockets or in a continuous -groove. The ribs have capitula and tubercula, and sternal ribs often -occur. The scapula is very large, the coracoid small, and there is no -precoracoid, or T-shaped interclavicle. Clavicles are only known in a -few cases. In the pelvis the ilium is elongated both in front of, and -behind, the acetabulum, sometimes the pre-pubis, sometimes the -post-pubis is the better developed. The anterior limbs are shorter -than the posterior, and the long bones are sometimes solid, sometimes -hollow. - -There are three well-marked suborders of the Dinosauria. - - -_Suborder (1)._ SAUROPODA[85]. - -The reptiles belonging to this group were probably quadrupedal and -herbivorous. - -They have the cervical and anterior trunk vertebrae opisthocoelous, -while the posterior vertebrae are biconcave; all the presacral, and -sometimes the sacral vertebrae are hollowed internally. The teeth are -spatulate and without serrated edges, they are always planted in -distinct sockets, and some of them are borne by the premaxillae. - -[Illustration FIG. 35. RESTORED SKELETON OF _Ceratosaurus nasicornis_. -× 1/30. (After Marsh.) - - 1. anterior nares. - 2. prominence on the nasal bones which probably carried a horn. - 3. pre-orbital vacuity. - 4. orbit. - 5. scapula. - 6. coracoid. - 7. ilium. - 8. pubis (pre-pubis). - 9. ischium.] - -The nares have the form of long slits and there are large pre-orbital -vacuities. - -The limb bones are solid, and the anterior limbs are not much shorter -than the posterior ones. All the limbs are plantigrade and -pentedactylate, and the digits of the pes are clawed. There is a large -pre-pubis directed downwards and forwards, meeting its fellow in a -ventral symphysis, but there is no post-pubis. - -The Sauropoda are found in the secondary rocks of Europe and N. -America and include the largest land animals that are known to have -existed. Many of the best known forms such as _Brontosaurus_ and -_Morosaurus_ are North American. - - -_Suborder (2)._ THEROPODA. - -The members of this suborder were all carnivorous, and from the small -comparative size of the anterior limbs many of them were probably -bipedal. - -The vertebrae are opisthocoelous or amphicoelous, their neural arches -are provided with zygosphenes and zygantra, and their centra are -frequently hollowed internally; the limb bones are also hollow, and in -fact the whole skeleton is extremely light. The tail is of great -length. The teeth are pointed and recurved, and have one or both -borders serrated; they are always planted in distinct sockets, and -some of them are borne by the premaxillae. There are large pre-orbital -vacuities. The digits of both manus and pes are terminated by pointed -ungual phalanges which must have borne claws. In the pelvis the -pre-pubes and ischia are slender bones, the former meeting in a -ventral symphysis. The ilia are very deep vertically and there are no -post-pubes. The astragalus is closely applied to the tibia, in front -of which it sends an ascending process, sometimes the two bones appear -to have been ankylosed together, as in birds. The metatarsals are -elongated and the feet digitigrade. - -The Theropoda vary greatly in size, one of the best known genera -_Compsognathus_ was about as large as a cat, another, _Megalosaurus_, -perhaps as large as an elephant. _Ceratosaurus_ is the name of a -well-known North American form regarded by many authorities as -identical with _Megalosaurus_. - - -_Suborder (3)._ ORTHOPODA. - -This suborder includes the most specialised of the Dinosaurs, certain -of which resemble the Theropoda in being bipedal. In some of them such -as _Stegosaurus_ the exoskeleton is strongly developed, in others such -as _Iguanodon_ it is absent. - -The vertebrae are solid and may be opisthocoelous, biconcave, or flat. -The teeth are compressed and serrated, often irregularly, and are -frequently not set in distinct sockets. The anterior part of the -premaxillae is without teeth, and a toothless predentary or -mento-meckelian bone is present. The pre-orbital vacuities are small -or absent, and the nares are large and placed far forwards. - -The most characteristic features of the group are found in the pelvis -which, except in the Ceratopsia, bears a striking resemblance to that -of birds. The ischium and post-pubis are long slender bones directed -backwards parallel to one another, and the pre-pubis is also well -developed. The ischium has an obturator process. The limb bones are -sometimes hollow, sometimes solid. The anterior limbs are much shorter -than the posterior, pointing to a bipedal method of progression. The -pes is digitigrade or plantigrade, and has three, rarely four, -digits. - -The suborder Orthopoda may be further subdivided into three -sections:-- - - -A. STEGOSAURIA. - -A dermal exoskeleton is strongly developed. The vertebral centra are -flat or biconcave, and neither they nor the limb bones are hollowed -out by internal cavities. The limbs are plantigrade, the anterior ones -short, the posterior ones very large and strong. The post-pubis is -well developed; - -e.g. _Stegosaurus_ from the Upper Jurassic of Colorado. - - -B. CERATOPSIA. - -There is sometimes a well-developed dermal exoskeleton formed of small -granules and plates of bone. The bones are solid, and the vertebral -centra flat. The cranium bears a pair of enormous pointed frontal -horns, and the parietal is greatly expanded and elevated behind, -forming with the squamosals a shield which overhangs the anterior -cervical vertebrae. The premaxillae are united, and in front of them is -a pointed beak-like bone which bites upon a toothless predentary -ossification of the mandible. The teeth have two roots. The anterior -limbs are but little shorter than the posterior ones. There is no -post-pubis; - -e.g. _Polyonax_ from the uppermost Cretaceous of Montana. - - -C. ORNITHOPODA[86]. - -There is no dermal exoskeleton. The cervical vertebrae are -opisthocoelous, and so are sometimes the thoracic. The limb bones are -hollow and the anterior limbs are much shorter than the posterior -ones. The feet are digitigrade and provided with long pointed claws. -The post-pubis is long and slender and directed back parallel to the -ischium; - -e.g. _Iguanodon_ from the European Cretaceous. - - -_Order 8._ CROCODILIA[87]. - -This order includes the Crocodiles, Alligators and Garials and various -extinct forms, some of which are closely allied to the early -Dinosaurs. - -There is always a more or less complete exoskeleton formed of bony -scutes overlain by epidermal scales; these bony scutes are specially -well developed on the dorsal surface but may occur also on the -ventral. The vertebral column is divisible into the five regions -commonly distinguishable. In all living forms the vertebrae, with the -exception of the atlas and axis, the two sacrals, and first caudal, -are procoelous, but in many extinct forms they are amphicoelous. The -atlas (fig. 71) is remarkable, consisting of four pieces, and the -first caudal is biconvex. - -The teeth are, in the adult, planted in separate deep sockets. The -skull is very dense and solid, and all the component bones including -the quadrate are firmly united. The dorsal surface of the skull is -generally characteristically sculptured. There is an interorbital -septum, and the orbitosphenoidal and presphenoidal regions are -imperfectly ossified. Supratemporal, infratemporal, and post-temporal -fossae occur, but no interparietal foramen. In living genera there is -a long secondary palate formed by the meeting in the middle line of -the palatines, pterygoids and maxillae (fig. 43, A). - -Cervical ribs (fig. 41, 8 and 9) are well developed, and articulate -with rather prominent surfaces borne on the neural arches and centra -respectively. The thoracic ribs articulate with the long transverse -processes, and sternal ribs and abdominal splint ribs (fig. 46, 4) -occur. The sternum is cartilaginous, and both it and the -shoulder-girdle are very simple. The precoracoid is represented by -merely a small process on the coracoid, while the clavicles are -absent, except in the Parasuchia. In the pelvis (fig. 49) there is a -large ilium, and an ischium meeting its fellow in a ventral symphysis; -these two bones form almost the whole of the acetabulum. In front of -the acetabulum, in the Eusuchia, projects a bone which is generally -called the pubis, but is in reality rather an epipubis (fig. 49, 4), -the true pubis being probably represented by a fourth element which -remains cartilaginous for some time, and later on ossifies and -attaches itself to the ischium. The limbs are small in proportion to -the size of the body, and are adapted for swimming or for shuffling -along the ground; they are plantigrade and the bones are all solid. In -living forms the anterior limbs have five digits and the posterior -four, the fifth being represented only by a short metatarsal. The -first three digits in each case are clawed. The calcaneum has a large -backwardly-projecting process. - -The order Crocodilia may be subdivided into two suborders. - - -_Suborder (1)._ PARASUCHIA. - -The vertebral centra are flat or biconcave. The premaxillae are very -large, and the nares are separated, and placed far back. The posterior -narial openings lie comparatively far forward between the anterior -extremities of the palatines. - -The palatines and pterygoids do not form a secondary palate. The -supratemporal fossae are small, and open posteriorly, the lateral -temporal fossae are very large. The parietals and frontals are paired. -Clavicles are present. The best known and most important genus of -these extinct crocodiles is _Belodon_. - - -_Suborder_ (2). EUSUCHIA. - -The vertebrae are either biconcave or procoelous. The premaxillae are -small, and the anterior nares are united and placed far forwards. The -posterior nares lie far back, the palatines and in living genera the -pterygoids, meeting in the middle line, and giving rise to a closed -palate. The supratemporal fossae are surrounded by bone on all sides, -and the parietals, and often also the frontals are united. There are -no clavicles. The suborder includes the genera _Crocodilus_, -_Alligator_, _Garialis_ and others living and extinct. - - -_Order 9._ PTEROSAURIA[88]. - -These animals, called also the pterodactyles or Ornithosauria, are a -group of extinct reptiles, whose structure has been greatly modified -from the ordinary reptilian type for the purpose of flight. - -The skin was naked and they vary greatly in size and in the length of -the tail. The vertebrae and limb bones are pneumatic just as in birds. -The presacral vertebrae are procoelous and have their neural arches -firmly united to the centra. The neck is long, the caudal vertebrae -are amphicoelous, and from three to five vertebrae are fused together -in the sacral region. The skull is large and somewhat bird-like, the -facial portion being much drawn out anteriorly, and the sutures being -obliterated. It resembles that of other reptiles in having large -supratemporal fossae; large pre-orbital vacuities also occur. The jaws -may be toothed or toothless, and the teeth, when present, are imbedded -in separate sockets. The premaxillae are large, and the quadrate is -firmly attached to the skull. The rami of the mandible are united at -the symphysis, and there is an ossified ring in the sclerotic. The -occurrence of a postfrontal and its union with the jugal behind the -orbit, are characteristic reptilian features. - -The ribs have capitula and tubercula, and sternal and abdominal ribs -occur. The sternum has a well-developed keel, and the scapula and -coracoid are large and bird-like. There are no clavicles or -interclavicle. - -The anterior limbs are modified to form wings by the great elongation -of the fifth digit, to which a membrane was attached. The second, -third and fourth digits are clawed and are not elongated in the way -that they are in bats. The pollex, if present at all, is quite -vestigial. - -The pelvis is weak and small, and though the ilia are produced both in -front of and behind the acetabula, in other features the pelvis is not -bird-like. The ischia are short and wide, and the pubes are -represented only by the pre-pubes. The posterior limbs are small and -the fibula is much reduced. The pes is quite reptilian in type, and -has five separate slender metatarsals. The two best known genera are -_Pterodactylus_, in which the tail is short, and _Rhamphorhynchus_, in -which it is long. The Pterosauria are found throughout the Jurassic -and Cretaceous formations in both Europe and North America. - - -FOOTNOTES: - -[65] According to Baur a distinct epi-otic is not recognisable in the -reptilian skull. - -[66] H. Gadow, _Phil. Trans._, vol. 179, 1888. - -[67] See G. Baur, _J. Morph._, vol. I., 1887. R. Lydekker, _Catalogue -of the Fossil Reptilia and Amphibia in the British Museum_, Parts I. & -II. C.K. Hoffmann, _Reptilien_, in Bronn's _Classen und Ordnungen des -Thierreichs_, Bd. VI., 3 abth. 1879-90. - -[68] T.H. Huxley, _Quart. J. Geol. Soc._, vol. XV. p. 649, 1859. R. -Owen, _Catalogue of Fossil Reptiles of S. Africa in the British -Museum_, London, 1876. H.G. Seeley, various papers published in the -_P.R. Soc. London_, and _Phil. Trans._ - -[69] See pp. 281-283. - -[70] An ent-epicondylar foramen is one piercing the humerus on its -inner side just above the condyle. - -[71] According to Hulke they should be regarded as the -omosternum,--the clavicles and interclavicle being wanting. - -[72] See p. 272. - -[73] R. Lydekker, _Nat. Sci._ vol. I. p. 514, 1892. Further references -are there given. - -[74] The exact position of the suture between the prefrontal and -postfrontal is not known. - -[75] A. Günther, On the Anatomy of Hatteria, _Phil. Trans_, vol. 157, -1867, p. 595. - -[76] =Zygosphenes= are extra articulating surfaces borne upon the -anterior face of the neural arch; they fit into corresponding -structures, the =zygantra=, which are borne on the posterior surface -of the neural arch of the preceding vertebra. Ordinary zygapophyses -always accompany them. - -[77] See E.D. Cope, _P. Amer. Phil. Soc_. vol. xxx. p. 185. - -[78] See W.K. Parker, _Phil. Trans._ vol. 170, 1879, p. 595. - -[79] See p. 281. - -[80] Often called the columella cranii. - -[81] See C.K. Hoffmann, in Bronn's _Klassen und Ordnungen des -Thierreichs_, Bd. VI., 3 abth. 1885-90. - -[82] Some anatomists consider that the closing in of the brain case in -front is entirely due to the frontals and parietals. - -[83] E.D. Cope, _Rep. U.S. Geol. Surv._, 1875, vol. II., The -vertebrata of the Cretaceous formations of the west. E.D. Cope, _P. -Boston Soc._ 1862, XII. p. 250. O.C. Marsh, _Amer. J. Sci._, 1872, -vol. 3. R. Owen, _Quart. J. Geol. Soc._, 1877, and 1878. - -[84] J.W. Hulke, _Presidential address to the Geol. Soc. of London_, -1883 and 1884. O.C. Marsh, many papers in the _Amer. J. Sci._ from -1878 onwards, also in the _Geol. Mag._ R. Owen, _History of British -fossil reptiles: Dinosauria_ (Palaeont. Soc.). - -[85] The diagnostic characters of the different groups of Dinosaurs -are in the main those given by von Zittel. - -[86] See O.C. Marsh, _Amer. J. Sci._ (3), vol. 48, 1894, p. 85. - -[87] See C.B. Brühl, _Das Skelet der Krokodiliden_, Wien, 1862. C.K. -Hoffmann in Bronn's _Klassen und Ordnungen des Thierreichs_, Bd. VI. -Abth. III. 1881-85. T.H. Huxley, _Proc. Linn. Soc._ (Zoology) 1860 -vol. IV. p. 1. R. Owen, _History of British fossil Reptiles_. -_Crocodilia_ (Palaeont. Soc.). A. Smith Woodward, _Geol. Mag._ 1885, -3rd dec. II. p. 496. A. Smith Woodward, _Proc. of Geologists' Assoc._ -vol. IX. p. 288, 1886. - -[88] See H.G. Seeley, On the Organisation of the Ornithosauria, -_Journ. Linn. Soc._ (Zoology) vol. XIII. p. 84. K.A. Zittel, Ueber -Flugsaurier aus dem lithographischen schiefer, _Palaeontograph._ XXIX. -p. 49. - - - - -CHAPTER XIV. - -THE SKELETON OF THE GREEN TURTLE. - -(_Chelone midas._) - - -The most striking feature as regards the skeleton of the Turtle is -that the trunk is enveloped in a bony box, the dorsal portion of which -is called the =carapace=, while the ventral portion is the =plastron=. - - -I. EXOSKELETON. - -_a._ The =epidermal exoskeleton= in the Green Turtle as in all other -Chelonia except _Dermochelys_, _Trionyx_ and their allies is strongly -developed, its most important part consisting of a series of horny -=shields= which cover over the bony plates of the carapace and -plastron but do not at all correspond to them in size and arrangement. - -The shields covering over the =carapace= consist of three rows of -larger central shields,--five (=vertebral=) shields being included in -the middle row and four (=costal=) in each lateral row,--and of a -number of smaller =marginal= shields. - -Of the marginal shields, that lying immediately in front of the first -vertebral is termed the =nuchal=, while the two succeeding the last -vertebral are called sometimes =pygal=, sometimes =supracaudal=; the -remainder are the marginal shields proper. - -The epidermal covering of the =plastron= consists principally of six -pairs of symmetrically arranged shields, called respectively the -=gular=, =humeral=, =pectoral=, =abdominal=, =femoral=, and =anal=, -the gular being the most anterior. In front of the gular shields is an -unpaired =intergular=, and the shields of the plastron are connected -laterally with those of the carapace, by five or six pairs of rather -irregular =infra-marginal= shields. Smaller horny plates occur on -other parts of the body, especially on the limbs and head. - -Two other sets of structures belong also to the epidermal exoskeleton, -viz. (_a_) horny =beaks= with denticulated edges which ensheath both -upper and lower jaws, (_b_) =claws=, which as a rule are borne only by -the first digit of each limb. Sometimes in young individuals the -second digit is also clawed. - -_b._ The =dermal exoskeleton= is strongly developed, and is combined -with endoskeletal structures derived from the ribs and vertebrae to -form the carapace. - -The =Carapace= (fig. 36) consists of a number of plates firmly united -to one another by sutures. They have a very definite arrangement and -include: - -(_a_) the =nuchal= plate (fig. 36, 1), a wide plate forming the whole -of the anterior margin of the carapace. It is succeeded by three -series of plates, eight in each series, which together make up the -main part of the carapace. Of these the small - -(_b_) =neural plates=[1] (fig. 36, A, 2) form the middle series. They -are closely united with the neural arches of the underlying vertebrae; - -(_c_) the =costal plates=[89] (fig. 36, A, 3) are broad arched plates -united to one another by long straight sutures. They are united at -their inner extremities with the neural plates, but the boundaries of -the two sets of plates do not regularly correspond. Each is united -ventrally with a rib which projects beyond it laterally for some -distance; (_d_) the =marginal plates= (fig. 36, 4) are twenty-three -in number, eleven lying on each side, while an unpaired one lies in -the middle line posteriorly. Many of them are marked by slight -depressions into which the ends of the ribs fit; - -(e) the =pygal= plates (fig. 36, 5) are two unpaired plates lying -immediately posterior to the last neural. - -[Illustration Fig. 36. A, DORSAL AND B, VENTRAL VIEW OF THE CARAPACE -OF A LOGGERHEAD TURTLE (_Thalassochelys caretta_), (after Owen). - - 1. nuchal plate. - 2. first neural plate. - 3. second costal plate. - 4. marginal plate. - 5. pygal plate. - 6. rib. - 7. thoracic vertebra. - 8. first vertebral shield. - 9. costal shield.] - -The sculpturing due to the epidermal shields is very obvious on the -carapace. - -The =plastron= (fig. 37) consists of one unpaired ossification, the -=entoplastron=, and four pairs of ossifications called respectively -the =epiplastra=, =hyoplastra=, =hypoplastra=, and =xiphiplastra=. - -The =epiplastra= (fig. 37, 1) are the most anterior, they are expanded -and united to one another in the middle line in front, while behind -each tapers to a point which lies external to a process projecting -forwards from the hyoplastron. They are homologous with the -_clavicles_ of other vertebrates. - -The =entoplastron= or =episternum= (fig. 37, 2) which is homologous -with the _interclavicle_ of other reptiles, is expanded at its -anterior end and attached to the symphysis of the epiplastra, while -behind it tapers to a point and ends freely. - -The =hyoplastra= are large irregular bones each closely united -posteriorly with the corresponding hypoplastron, and drawn out -anteriorly into a process which lies internal to that projecting -backwards from the epiplastron. Each gives off on its inner surface a -slender process which nearly meets its fellow, while the anterior half -of the outer surface is drawn out into several diverging processes. - -The =hypoplastra= (fig. 37, 4) are flattened bones resembling the -hyoplastra, with which they are united by long sutures; the posterior -half of both outer and inner surfaces is drawn out into a number of -pointed processes. - -The =xiphiplastra= are small flattened elongated bones meeting one -another in the middle line posteriorly. In front they are notched and -each interlocks with a process from the hypoplastron of its side. The -hyoplastra, hypoplastra and xiphiplastra are homologous with the -abdominal ribs of Crocodiles. - -[Illustration FIG. 37. THE PLASTRON OF A GREEN TURTLE (_Chelone -midas_). × 1/7. (Camb. Mus.) - - 1. epiplastron (clavicle). - 2. entoplastron (interclavicle). - 3. hyoplastron. - 4. hypoplastron. - 5. xiphiplastron.] - - -II. ENDOSKELETON. - -1. THE AXIAL SKELETON. - -The axial skeleton includes the vertebral column, the ribs, and the -skull. - -A. THE VERTEBRAL COLUMN AND RIBS. - -The number of vertebrae in the Green Turtle is thirty-eight, not a -great number as compared with that in many reptiles, and of these -eighteen are caudal. - -The vertebral column is divisible into four regions only--=cervical=, -=thoracic=, =sacral=, and =caudal=. - - -THE CERVICAL VERTEBRAE. - -These are eight in number, and are chiefly remarkable for the great -variety of articulating surfaces which their centra present, and for -their mobility upon one another. - -The first or =atlas= vertebra differs much from all the others and -consists of the following parts:-- - -_a._ the =neural arch=, formed of two separate ossifications united in -the mid-dorsal line; - -_b._ the =inferior arch=; - -_c._ the =centrum=, which is detached from the rest and forms the -odontoid process of the second vertebra. - -Each half of the =neural arch= consists of a ventral portion, the -=pedicel=, which lies more or less vertically and is united ventrally -to the inferior arch, and of a dorsal portion, the =lamina=, which -lies more or less horizontally and meets its fellow in the middle line -in front, partially roofing over the neural canal. Each pedicel bears -a facet on its anterior surface, which, with a corresponding one on -the inferior arch, articulates with the occipital condyle of the -skull. Three similar facets occur also on the posterior surface of the -pedicel and inferior arch, and articulate with the odontoid process. -The laminae meet one another in front, but do not fuse, while behind -they are separated by a wide triangular space. They bear a pair of -small downwardly-directed facets, the =postzygapophyses=, for -articulation with the prezygapophyses of the second vertebra. - -The =inferior arch= is a short irregular bone bearing two converging -facets for articulation with the occipital condyle and odontoid -process respectively. - -The =centrum= or =odontoid process= has a convex anterior surface for -articulation with the neural and inferior arches, and a concave -posterior surface by which it is united with the centrum of the second -or axis vertebra. It bears posteriorly a small epiphysis which is -really a detached portion of the inferior arch. - -The second or =axis= and following five cervical vertebrae, though -showing distinct differences, resemble one another considerably, each -having a fairly elongated centrum with a keel-like =hypapophysis=, -each having also a neural arch with prominent articulating surfaces, -the anterior of which, or =prezygapophyses=, look upwards and inwards, -while the posterior ones, the =postzygapophyses=, look downwards and -outwards. They however, as was previously mentioned, differ very -remarkably in the character of the articulating surfaces of the -centra. Thus the second and third vertebrae are convex in front and -concave behind, the fourth is biconvex, the fifth is concave in front -and convex behind. The sixth is concave in front and attached to the -seventh by a flat surface behind, the seventh has a flat anterior face -and two slightly convex facets behind. The vertebrae all have short -blunt transverse processes and the second has a prominent =neural -spine=. - -The =eighth cervical vertebra= is curiously modified, the centrum is -very short, has a rather prominent hypapophysis, and is convex behind, -while in front it articulates with the preceding centrum by two -concave surfaces. The neural arch is deeply notched in front and bears -two upwardly-directed prezygapophyses, while behind it is very massive -and is drawn out far beyond the centrum, bearing a pair of flat -postzygapophyses. The top of the neural arch almost or quite meets a -blunt outgrowth from the nuchal plate. - - -THE THORACIC VERTEBRAE. - -These are ten in number and are all firmly united with the ribs and -elements forming the carapace. - -The first thoracic vertebra differs from the others, the centrum is -short and has a concave anterior surface articulating with the centrum -of the last cervical vertebra, and a pair of prezygapophyses borne on -long outgrowths. The neural spine arises only from the anterior half -of the centrum, and is not fused to the carapace. Arising laterally -from the anterior part of the centrum are a small pair of ribs each of -which is connected with a process arising from the rib of the -succeeding vertebra. - -The next seven thoracic vertebrae are all very similar, each has a -long cylindrical centrum, expanded at the ends, and firmly united to -the preceding and succeeding vertebrae. The neural arches are -flattened and expanded dorsally, and are united to one another and to -the overlying neural plates; each arises only from the anterior half -of its respective centrum, and overlaps the centrum of the vertebra in -front of it. Between the base of the neural arch and its successor is -a small foramen for the exit of the spinal nerve. There are no -transverse processes or zygapophyses. - -To each thoracic vertebra from the second to ninth inclusive, there -corresponds a pair of =ribs= (fig. 36, 6) of a rather special -character. Each is suturally united with the anterior half of the edge -of its own vertebra, and overlaps on to the posterior half of the edge -of the next preceding vertebra. The ribs are much flattened, and each -is fused with the corresponding costal plate, beyond which it projects -to fit into a pit in one of the marginal plates. - -The tenth thoracic vertebra is smaller than the others, and its neural -arch does not overlap the preceding vertebra, it bears a pair of small -ribs which are without costal plates, but meet those of the ninth -vertebra. - -There are no =lumbar= vertebrae. - - -THE SACRAL VERTEBRAE. - -The =sacral vertebrae= are two in number, they are short and wide, -their centra are ankylosed together, and their neural arches are not -united to the carapace. - -The first has the anterior face of the centrum concave and the -posterior flat, while both faces of the second are flat. Each bears a -pair of short ribs which meet the ilia, but are not completely -ankylosed either with them or the centra. - - -THE CAUDAL VERTEBRAE. - -The =caudal vertebrae= are eighteen in number. The centrum of the -first is flat in front and is ankylosed to the second sacral; behind -it is convex. The others are all very similar to one another, and -decrease gradually in size when followed back. Each has a moderately -long centrum, concave in front and convex behind, both terminations -being formed by epiphyses. The neural arch arises only from the -anterior half of the vertebra; it bears a blunt truncated neural spine -and prominent pre- and post-zygapophyses. The first seven caudal -vertebrae bear short ribs attached to their lateral margins, the -similar outgrowths on the succeeding vertebrae do not ossify from -distinct centres, and are transverse processes rather than ribs. - - -B. THE SKULL. - -The skull of the Turtle is divisible into the following three parts:-- - -(1) the cranium; - -(2) the lower jaw or mandible; - -(3) the hyoid. - -(1) THE CRANIUM. - -The =cranium= is a very compact bony box, containing a cavity in which -the brain lies, and which is a direct continuation of the neural canal -of the vertebrae. - -[Illustration FIG. 38. THE SKULL OF THE GREEN TURTLE (_Chelone -midas_). × 1/2. A, POSTERIOR HALF, B, ANTERIOR HALF. (Brit. Mus.) - - 1. parietal. - 2. squamosal. - 3. quadrate. - 4. basisphenoid. - 5. basi-occipital. - 6. quadratojugal. - 7. opisthotic. - 8. exoccipital. - 9. foramen magnum. - 10. splenial. - 11. articular. - 12. dentary. - 13. angular. - 14. supra-angular. - 15. premaxilla. - 16. maxilla. - 17. jugal. - 18. postfrontal. - 19. vomer. - 20. prefrontal. - 21. frontal. - 22. external auditory meatus leading into tympanic cavity.] - -Like those of the skull as a whole its component bones may be -subdivided into three sets:-- - -1. those forming the brain-case or =cranium proper=; - -2. those developed in connection with the special sense organs; - -3. those forming the upper jaw and suspensorial apparatus. - -Both cartilage and membrane bones take part in the formation of the -skull, and a considerable amount of cartilage remains unossified, -especially in the ethmoidal and sphenoidal regions. - - -1. THE CRANIUM PROPER OR BRAIN-CASE. - -The cartilage and membrane bones of the brain-case when taken together -can be seen to be more or less arranged in three rings or segments, -called respectively the occipital, parietal, and frontal segments. - -The =occipital segment= is the most posterior of these, and consists -of four cartilage bones, the =basi-occipital=, the two =exoccipitals= -and the =supra-occipital=; these bound the =foramen magnum=. - -The =basi-occipital= (figs. 38 and 39, 5) lies ventral to the foramen -magnum and only bounds a very small part of it; it forms one-third of -the =occipital condyle= by which the skull articulates with the atlas -vertebra. It unites dorsally with the exoccipitals and anteriorly with -the basisphenoid. - -The =exoccipitals= are rather small bones, which form the sides and -the greater part of the floor of the foramen magnum, and two-thirds of -the occipital condyle. Laterally each is united with the pterygoid and -opisthotic of its side. At the sides of the occipital condyle each -exoccipital is pierced by a pair of foramina, the more dorsal and -posterior of which transmits the hypoglossal nerve. - -The =supra-occipital= (fig. 39, 14) is a larger bone than the others -of the occipital segment. It forms the upper border of the foramen -magnum and is drawn out dorsally into a large crest which extends back -far beyond the occipital condyle. In the adult the supra-occipital is -completely ankylosed with the epi-otics. - - -The =Parietal segment=. - -The ventral portion of the parietal segment is formed by the -=basisphenoid= (figs. 38 and 39, 4) which lies immediately in front of -the basi-occipital. A triangular portion of it is seen in a ventral -view of the skull, but it is quickly overlapped by the pterygoids. It -gives off dorsally a pair of short processes which meet the pro-otics. - -The alisphenoidal region is unossified and the only other constituents -of the parietal segment are the _parietals_ (fig. 39, 1). These are -large bones which, after roofing over the cranial cavity, extend -upwards and become expanded into a pair of broad plates which unite -with the squamosal and bones of the frontal segment to form a wide, -solid, false roof to the skull. Each also sends ventralwards a plate -which meets an upgrowth from the pterygoid and acts as an alisphenoid. - - -The =Frontal segment=. - -Of the frontal segment the basal or presphenoidal and lateral or -orbitosphenoidal portions do not become ossified, the dorsal portion -however includes three pairs of membrane bones, the _frontals_, -_prefrontals_ and _postfrontals_. - -The _frontals_ are a pair of small bones lying immediately in front of -the parietals, and in front of them are the _prefrontals_ (figs. 38 -and 39, 20), a pair of similar but still smaller bones, which are -produced ventrally to meet the vomer and palatines. They form also the -dorsal boundary of the anterior nares. The _postfrontals_ (figs. 38 -and 39, 18) are larger bones, united dorsally to the frontals and -parietals, posteriorly to the squamosals, and ventrally to the jugals -and quadratojugals. All three pairs of frontal bones, especially the -postfrontals, take part in the bounding of the orbits. - -[Illustration FIG. 39. LONGITUDINAL VERTICAL SECTION THROUGH THE -CRANIUM OF A GREEN TURTLE (_Chelone midas_). × 2/3. (Camb. Mus.) - - 1. parietal. - 2. squamosal. - 3. quadrate. - 4. basisphenoid. - 5. basi-occipital. - 6. quadratojugal. - 7. pro-otic. - 8. opisthotic. - 9. pterygoid. - 10. palatine. - 11. rod passed into narial passage. - 12. exoccipital. - 13. epi-otic fused to supra-occipital. - 14. supra-occipital. - 15. premaxillae. - 16. maxillae. - 17. jugal. - 18. postfrontal. - 19. vomer. - 20. prefrontal. - 21. frontal. - V, VII, VIII, IX, X, XI, XII, - foramina for the exit of - cranial nerves.] - - -2. THE SENSE CAPSULES. - -Skeletal structures occur in connection with each of the three special -sense organs of hearing, sight, and smell. - - -The =Auditory capsules=. - -The auditory or periotic capsule of the turtle is rather large and its -walls are well ossified, epi-otic, pro-otic and opisthotic bones being -present. - -The =epi-otic= (fig. 39, 13) is the more dorsal of the three bones, -and in the adult is completely ankylosed with the supra-occipital. - -The =opisthotic= (fig. 39, 8) is the ventral posterior element. On its -inner side it is united to the supra-occipital above, and to the -exoccipital below; it sometimes becomes completely fused with the -exoccipital. In front it meets the pro-otic, and on its outer side the -squamosal and quadrate. Its anterior portion is hollowed out by the -cavity in which the auditory organ lies, it gives off also a process -which is separated from the exoccipital by an oval foramen through -which the glossopharyngeal, pneumogastric, and spinal accessory nerves -leave the cranial cavity. - -The =pro-otic= is the anterior element; it meets the supra-occipital -and opisthotic posteriorly, while anteriorly it is separated from the -alisphenoidal plate of the parietal and pterygoid by a large oval -foramen through which the maxillary and mandibular branches of the -trigeminal nerve pass out (fig. 39, V 1 & 2). It is hollowed out -posteriorly by the cavity in which the auditory organ lies, and its -inner wall as seen in longitudinal section is pierced by a foramen -through which the external carotid artery and facial nerve leave the -cranial cavity,--the nerve finally leaving the skull through a small -oval foramen on the anterior face of the pro-otic near its junction -with the quadrate. - -Between the pro-otic and opisthotic as seen in a longitudinal section -of the skull is a large opening constricted in the middle. This is -the =internal auditory meatus= (fig. 39, VIII.). Through it the -auditory nerve leaves the cranial cavity and enters the ear. The ramus -vestibularis leaves through the dorsal part of the hole, the ramus -cochlearis through the ventral. - -The cavity of the auditory or periotic capsule communicates with the -exterior by a fairly large hole, the =fenestra ovalis=, which lies -between the opisthotic and pro-otic, and opens into a deep depression, -the =tympanic cavity=, which is seen in a posterior view of the skull -lying just external to the exoccipital. The cavity communicates with -the exterior by a large opening, the =external auditory meatus= (fig. -38, 22). - -Several other openings are seen in the tympanic cavity; through one at -the extreme posterior end the pneumogastric and spinal accessory -nerves leave the skull, and through another, a little further -forwards, the glossopharyngeal. - -The auditory ossicles consist of a long bony =columella=, whose inner -end fits into the fenestra ovalis, while the outer end is attached to -a small cartilaginous plate, the =extra-columella=, which is united to -the tympanum. - - -The =Optic capsules=. - -The skeletal structures developed in connection with the optic capsule -do not become united to the skull. They consist of:-- - -(_a_) the =sclerotic=, a cartilaginous sheath investing the eye and -bearing - -(_b_) a ring of ten small bony scales. - -There is no _lachrymal_ bone. - - -The =Olfactory= or =Nasal capsules=. - -The basicranial axis in front of the basisphenoid remains -cartilaginous, neither presphenoid nor mesethmoid bones are developed, -and the orbits in a dry skull communicate by a wide space through -which the second, third, fourth, and sixth cranial nerves pass out. -Separate _nasal_ bones also do not occur, the large prefrontals -extending over the area usually occupied by both nasals and -lachrymals. - -The only bone developed in connection with the nasal capsules is the -_vomer_ (fig. 39, 19), an unpaired bone lying ventral to the -mesethmoid cartilage, and in contact laterally with the maxillae, -premaxillae and palatines. - - -3. THE UPPER JAW AND SUSPENSORIAL APPARATUS. - -A number of pairs of bones are developed in connection with the upper -jaw and suspensorial apparatus, one pair, the =quadrates=, being -cartilage bones, while the rest are all membrane bones. - -The _squamosals_ (fig. 38, 2) are large bones which, lying external to -the auditory bones, extend dorsalwards to meet the parietals and -postfrontals, and form a large part of the false roof of the skull. -They are united ventrally with the quadrates and quadratojugals. - -Each =quadrate= (fig. 38, 3) forms the outer boundary of the tympanic -cavity, and is firmly united on its inner side with the opisthotic, -exoccipital, and pterygoid. Dorsally it is fixed to the squamosal and -anteriorly to the quadratojugal. Its outer surface is marked by a deep -recess, and it ends below in a strong condyle with which the mandible -articulates. In front of the quadrates are a pair of thin plate-like -bones, the _quadratojugals_ which are united in front to the jugals or -malars. - -The _jugals_ (fig. 38, 17) are also thin plate-like bones, and form -part of the posterior boundary of the orbit. They are attached -dorsally to the postfrontals, and anteriorly to the maxillae, while -each also sends inwards a horizontal process which meets the pterygoid -and palatine. - -The _maxillae_ (figs. 38 and 39, 16) are a pair of large -vertically-placed bones, each drawn out ventrally into a straight, -sharp, cutting edge. They form the lateral boundaries of the anterior -nares, and each sends dorsalwards a process which meets the -postfrontal. Each also sends inwards a horizontal =palatine process=, -which meets the palatine and vomer, and also forms much of the floor -of the narial passage. - -The _premaxillae_ (figs. 38 and 39, 15) are a pair of very small bones -forming the floor of the anterior narial opening, they are wedged in -between the two maxillae, and send back processes which meet the vomer -and palatines. - -The _palatines_ (fig. 39, 10) are a pair of small bones firmly united -with the pterygoids behind, with the maxillae and jugals externally, -and with the vomer in the middle line. Each also gives off a palatine -plate which unites with the expanded lower edge of the vomer, and -forms the ventral boundary of the posterior nares. Anteriorly the -palatines form the posterior boundary of a large foramen through which -the ophthalmic branches of the fifth and seventh nerves pass to the -olfactory organs. - -The _pterygoids_ (fig. 39, 9) are a pair of large bones which unite -with one another by a long median suture. They are united also with -the palatines in front, and with the quadrate, basisphenoid, -basi-occipital, and exoccipitals behind. Each also sends dorsalwards a -short =alisphenoid plate= which meets that from the parietal. - -Piercing the posterior end of the _pterygoid_ is the prominent opening -of the carotid canal; a bristle passed into this hole emerges through -a foramen lying between the pro-otic and the alisphenoid process of -the pterygoid. - - -(2) THE LOWER JAW OR MANDIBLE. - -The =mandible= consists of one unpaired bone, formed by the fusion of -the two _dentaries_, and five pairs of bones, called respectively the -=articular=, _angular_, _supra-angular_, _splenial_ and _coronoid_. - -The fused _dentaries_ (fig. 38, 12) form by far the largest of the -bones; they constitute the flattened anterior part of the mandible, -and extend back below the other bones almost to the end of the jaw. - -The _coronoid_ is the most anterior of the paired bones, it forms a -prominent process to which the muscles for closing the jaw are -attached. - -The =articular= (fig. 38, 11) is expanded, and with the -_supra-angular_ forms the concave articulating surface for the -quadrate. - -The _splenial_ (fig. 38, 10) is a thin plate applied to the inner -surface of the posterior part of the mandible. - -The _angular_ (fig. 38, 13) is a slender plate of bone lying below the -supra-angular and splenial. - - -(3) THE HYOID. - -The hyoid apparatus is well developed, parts of the first two -branchial arches being found, as well as of the hyoid proper. It -consists of a more or less oblong flattened =basilingual plate= or -=body of the hyoid= which represents the fused ventral ends of the -hyoid and branchial arches of the embryo, and is drawn out into a -point anteriorly. The greater part is formed of unossified cartilage, -but at the posterior end it is bilobed, and a pair of ossified tracts -occur. To its sides are attached three pairs of structures, which are -portions of the hyoid and first and second branchial arches -respectively. - -The free part of the =hyoid= consists of a small piece of cartilage -attached to the anterior part of the basilingual plate at its widest -portion (fig. 53, 2). - -The =anterior cornu= or free part of the =first branchial arch= is -much the largest of the three structures. Its proximal portion -adjoining the basilingual plate is cartilaginous, as is its distal -end; the main part is however ossified. - -The =posterior cornu= or free part of the =second branchial arch= -(fig. 53, 4) consists of a short flattened cartilaginous bar arising -from the bilobed posterior end of the basilingual plate. - -The hyoid apparatus has no skeletal connection with the rest of the -skull. - - -2. THE APPENDICULAR SKELETON. - -This includes the skeleton of the two pairs of limbs and their -girdles. - - -THE PECTORAL GIRDLE. - -The pectoral girdle has an anomalous position, being situated -internal or ventral to the ribs. It consists of three bones, a dorsal -bone, the =scapula=, an anterior ventral bone, the =precoracoid=, and -a posterior ventral bone, the =coracoid=. - -The =scapula= is a small somewhat rod-shaped bone forming about -two-thirds of the glenoid cavity. At its proximal end it is closely -united with the precoracoid, the two bones ossifying continuously. It -tapers away distally, and is directed dorsalwards towards the -carapace. - -The =precoracoid= forms an angle of about 130° with the scapula, with -which it is completely fused at its proximal end. Its distal end is -somewhat expanded and flattened, and is terminated by a -fibrocartilaginous =epiprecoracoid= which meets its fellow. It takes -no part in the formation of the glenoid cavity. - -The =coracoid= is a large flattened blade-shaped bone forming about -one-third of the glenoid cavity. It does not meet its fellow in a -ventral symphysis, and is terminated by a cartilaginous =epicoracoid=. -The glenoid articulating surfaces of both scapula and coracoid are -lined by a thick pad of cartilage. - - -THE ANTERIOR LIMB. - -This is divisible into three portions, the =upper arm=, =fore-arm= and -=manus=. - -The =upper arm= contains a single bone, the =humerus=. - -The =humerus= (fig. 40, A, 1) is a stout, nearly straight, somewhat -flattened bone widely expanded at both ends. At the proximal end is -the large hemispherical =head=, which articulates with the glenoid -cavity. Behind the head the bone is drawn out into another large -rounded process. Below the head the shaft bears a small outgrowth -which is continuous with a larger one on the flexor surface (see p. -29). The bone is terminated distally by the =trochlea=, consisting of -three partially distinct convex surfaces which articulate with the -bones of the fore-arm. - -The =fore-arm= includes two bones, the =radius= and =ulna=; both these -are small bones, and are immovably fixed to one another proximally and -distally. - -The =radius= or pre-axial bone is the larger of the two, and is a -rod-like bone terminated at either end by an epiphysis. It articulates -at its proximal end with the humerus, and at its distal end with the -radiale or scaphoid bone of the carpus. - -The =ulna= (fig. 40, A, 3) or postaxial bone is shorter than the -radius, and more expanded at its proximal end, where it articulates -with the humerus. It articulates distally with the intermedium (lunar) -and the ulnare (cuneiform) bones of the carpus. All three bones of the -arm have their terminations formed by epiphyses which ossify from -centres distinct from those forming the shafts. - -The =Manus= consists of the =carpus= or =wrist= and the =hand= which -includes the metacarpals and phalanges. - -The =carpus= consists of a series of ten small bones, one of which, -the =pisiform= (fig. 40, A, 10), differs from the others in being -merely an ossification in the tendon of a muscle. The remaining nine -bones are arranged in a proximal row of three, the =ulnare= (fig. 40, -A, 6), =intermedium=, and =radiale=, and a distal row of five -(carpalia 1-5), each of which supports one of the metacarpals. A ninth -bone, the =centrale= (fig. 40, A, 7), is wedged in between the two -rows. The ulnare, intermedium and pisiform are comparatively large -flattened bones, the others are small and cubical. - -The =hand=. This is composed of five digits, each of which consists of -a metacarpal and of a varying number of phalanges. - -The =metacarpals=. The first metacarpal (fig. 40, A, 11) is a short -flattened bone, the others are all elongated and cylindrical, and are -terminated proximally by slightly concave surfaces, and distally by -slightly convex ones. - -The =phalanges=. The first and fifth digits both have two phalanges, -the second, third, and fourth have each three. The distal phalanx of -the first digit is stout and curved, and bears a horny claw; those of -the other digits are flattened and more or less pointed. - -[Illustration FIG. 40. A. ANTERIOR LIMB OF A YOUNG HAWKSBILL TURTLE -(_Chelone imbricata_) × 1/4 (Brit. Mus.). B. POSTERIOR LIMB OF A LARGE -GREEN TURTLE (_Chelone midas_) × 1/8 (Camb. Mus.). - - 1. humerus. - 2. radius (almost hidden by the ulna). - 3. ulna. - 4. radiale. - 5. intermedium. - 6. ulnare. - 7. centrale. - 8. carpale I. - 9. carpale IV. - 10. pisiform. - 11. first metacarpal. - 12. femur. - 13. tibia. - 14. fibula. - 15. tibiale intermedium and centrale fused. - 16. fibulare. - 17. tarsale 1. - 18. tarsale 2. - 19. tarsalia 4 and 5 fused. - 20. first metatarsal. - 21. fifth metatarsal. - I, II, III, IV, V, digits.] - - -THE PELVIC GIRDLE. - -The pelvic girdle consists of three bones; a dorsal bone, the =ilium=, -an anterior ventral bone, the =pubis=, and a posterior ventral bone, -the =ischium=. All three bones contribute largely to the formation of -the =acetabulum=, with which the head of the femur articulates. - -The =ilium= is a small slightly curved bone, which unites ventrally -with the pubis and ischium, and extends dorsalwards and backwards to -meet the distal ends of the sacral ribs. - -The =pubis= is the largest bone of the three; its distal end forms a -wide bilobed plate, the inner lobe meeting its fellow in a median -symphysis, while the other lobe or lateral process extends outwards. -Attached to the symphysis in front is a cartilaginous =epipubis=, -while behind, the two pubes are terminated by a wide rounded -cartilaginous area. - -The =ischium=, the smallest bone of the three, is flattened and like -the pubis meets its fellow in a median symphysis. A narrow band of -cartilage connects the symphysis pubis with the symphysis ischii, and -separates the two =obturator foramina= from one another. - - -THE POSTERIOR LIMB. - -This is divisible into three portions, the =thigh=, the =crus= or -=shin=, and the =pes=. - -The =thigh= includes a single bone, the =femur=. - -The =femur= (fig. 40, B, 12) is a short thick bone, with a prominent -rounded =head= articulating with the acetabulum. Behind this head is a -deep pit, beyond which is a roughened area corresponding with the -great trochanter of mammals. The distal end is expanded and somewhat -convex. - -The bones of the =crus= or =shin= are the =tibia= and =fibula=. These -are both straight rod-like bones with expanded terminations which -closely approach one another, while elsewhere the bones diverge -considerably. - -The terminations of all three of the leg bones are formed by -epiphyses. - -The =Pes= consists of the =tarsus= or =ankle=, and the =foot=, which -is made up of five digits. - -The =tarsus=. The tarsal bones of the Turtle do not retain their -primitive arrangement to such an extent as do the carpals. They are -arranged in a proximal row of two and a distal row of four. Of the -bones in the proximal row the postaxial one is much the smaller and is -the =fibulare=; the larger pre-axial one (fig. 40, B, 15) represents -the =tibiale=, =intermedium=, and =centrale= fused, and articulates -with both tibia and fibula. The first three distal tarsalia are all -small bones and are very similar in size, and each articulates -regularly with the corresponding metatarsal. The fourth bone (fig. 40, -B, 19) is much larger, and represents tarsalia 4 and 5 fused. The -first two distal tarsalia articulate with the pre-axial tarsal of the -proximal row, the third only with its neighbours the second, and the -fused fourth and fifth. The latter articulates with both bones of the -proximal row. - -Each =digit= consists of a metatarsal and of a varying number of -phalanges. - -The =metatarsals=. The first metatarsal (fig. 40, B, 20) is broad and -flattened, the second, third and fourth, are all elongated bones with -nearly flat terminations formed by small epiphyses. The fifth is large -and flattened, and the articular surface for the phalanx is situated -somewhat laterally. - -The =phalanges=. The first digit has two phalanges and is the stoutest -of them all; its distal phalanx is sheathed in a large horny claw. The -other digits, of which the third is the longest, have each three -phalanges. The distal phalanges of the second and third digits are -flattened and pointed and bear small horny claws. - - -FOOTNOTES: - -[89] Another view commonly held is that the neural and costal plates -are respectively formed by the expanded neural arches and ribs. - - - - -CHAPTER XV. - -THE SKELETON OF THE CROCODILE. - - -The species chosen for description is _C. palustris_, a form occurring -throughout the Oriental region, but the description would apply almost -equally well to any of the other species of the genus _Crocodilus_, -and with comparatively unimportant modifications to any of the living -Crocodilia. - - -I. EXOSKELETON. - -The exoskeleton of the Crocodile is strongly developed and includes -elements of both epidermal and dermal origin. - -_a._ The =epidermal exoskeleton= is formed of a number of horny -=scales= or plates of variable size covering the whole surface of the -body. Those covering the dorsal and ventral surfaces are oblong in -shape, and are arranged in regular rows running transversely across -the body. The scales covering the limbs and head are mostly smaller -and less regularly arranged, and are frequently raised into a more or -less obvious keel. Those covering the dorsal surface of the tail are -very prominently keeled. - -The epidermal exoskeleton also includes the horny =claws= borne by the -first three digits of both manus and pes. - -_b._ The =dermal exoskeleton=. This has the form of bony =scutes= -which underlie the epidermal scales along the dorsal surface of the -trunk and anterior part of the tail. Except in very young individuals -the epidermal scales are rubbed off from these scutes, which -consequently come to project freely on the surface of the body. Each -scute is a nearly square bony plate, deeply pitted or sculptured, and -marked by a strong ridge on its dorsal surface, while its ventral -surface is smooth. Contiguous scutes are united to one another by -interlocking sutures. - -The scutes are arranged in two distinct areas, viz. (1) a small -anterior =nuchal shield= which lies just behind the head and is formed -of six large scutes more or less firmly united together, and (2) a -larger posterior =dorsal shield= covering the whole of the back and -anterior part of the tail, and formed of smaller scutes, which are -arranged in regular transverse rows, and progressively diminish in -size when followed back. - -The =teeth= are exoskeletal structures, partly of dermal, partly of -epidermal origin. They lie along the margins of the jaws and are -confined to the premaxillae, maxillae and dentaries. They are simple -conical structures, without roots; each is in the adult placed in a -separate socket, and is replaced by another which as it grows comes to -occupy the pulp cavity of its predecessor. In the young animal the -teeth are not placed in separate sockets but in a continuous groove. -This feature is met with also in the Ichthyosauria. The groove -gradually becomes converted into a series of sockets by the ingrowth -of transverse bars of bone. The anterior teeth are sharply pointed and -slightly recurved, the posterior ones are more blunt. - -The upper jaw bears about nineteen pairs of teeth, the lower jaw about -fifteen pairs. The largest tooth in the upper jaw is the tenth, and in -the lower jaw the fourth. - -The three living families of Crocodilia, the Crocodiles, Alligators -and Garials, can be readily distinguished by the characters of the -first and fourth lower teeth. In Alligators both first and fourth -lower teeth bite into pits in the upper jaw; in Garials they both bite -into notches or grooves in the upper jaw. In Crocodiles the first -tooth bites into a pit, the fourth into a notch in the upper jaw. - - -II. ENDOSKELETON. - -1. THE AXIAL SKELETON. - -This includes the vertebral column, the skull, and the ribs and -sternum. - -A. THE VERTEBRAL COLUMN. - -The vertebral column is very long, consisting of some sixty vertebrae. -It can be divided into the usual five regions, the cervical, thoracic, -lumbar, sacral, and caudal regions. - -[Illustration FIG. 41. FIRST FOUR CERVICAL VERTEBRAE OF A CROCODILE -(_C. vulgaris_). (Partly after VON ZITTEL.) - - 1. pro-atlas. - 2. lateral portion of atlas. - 3. odontoid process. - 4. ventral portion of atlas. - 5. neural spine of axis. - 6. postzygapophysis of fourth vertebra. - 7. tubercular portion of fourth cervical rib. - 8. first cervical rib. - 9. second cervical rib. - 10. convex posterior surface of centrum of fourth vertebra.] - -THE CERVICAL VERTEBRAE. - -Counting as cervical all those vertebrae which are anterior to the -first one whose ribs meet the sternum, there are nine cervical -vertebrae, all of which bear ribs. - -As a type of the cervical vertebrae the fifth may be taken. It has a -short cylindrical =centrum= deeply concave in front and convex behind. -From the anterior part of the ventral surface of the centrum arises a -short =hypapophysis=, and on each side is a facet with which the lower -limb (=capitulum=) of the cervical rib articulates. The =neural arch= -is strongly developed and drawn out dorsally into a long =neural -spine=, in front of which are a pair of upstanding processes bearing -the prominent upwardly and inwardly directed =prezygapophyses=. At the -sides and slightly behind the neural spine are a corresponding pair of -processes bearing the =postzygapophyses=, which look downwards and -outwards. At the point where it joins the centrum the neural arch is -drawn out into a short blunt =transverse process= with which the upper -limb (=tuberculum=) of the cervical rib articulates. The sides of the -neural arch are slightly notched behind for the exit of the spinal -nerves. - -The first or =atlas= vertebra differs much from any of the others, and -consists of four quite detached portions, a ventral arch, with two -lateral portions and one dorsal. The =ventral arch= (fig. 41, 4) is -flat below and slightly concave in front, forming together with two -flattened surfaces on the lateral portions a large articulating -surface for the occipital condyle of the skull. Its posterior face is -bevelled off and forms with a second pair of facets on the lateral -portions a surface with which the odontoid process of the second -vertebra articulates. The postero-lateral surfaces of the ventral arch -also bear a pair of little facets with which the cervical ribs -articulate. The lateral portions are somewhat flattened and expanded, -and bear in addition to those previously mentioned a pair of small -downwardly directed facets, the postzygapophyses, which articulate -with the prezygapophyses of the second vertebra. The dorsal portion -(fig. 41, 1) is somewhat triangular in shape, and overhangs the -occipital condyle. It is often regarded as the neural arch of a -vertebra in front of the atlas and is called the _pro-atlas_; but as -it is a membrane bone it is not properly a vertebral element. - -The second or =axis vertebra= also differs a good deal from the other -cervicals. The centrum is massive, and is terminated in front by a -very large slightly concave articulating surface formed by the -=odontoid process= (fig. 41, 3) which is united with the centrum by -suture only, and is really the detached centrum of the first vertebra. -The cervical rib (fig. 41, 9) articulates with two little -irregularities on the odontoid process. The posterior surface of the -centrum is convex. The neural arch is strongly developed and -terminated dorsally by a long neural spine (fig. 41, 5), its sides are -notched, slightly in front and more prominently behind for the exit of -the spinal nerves. It is drawn out in front into two little processes -bearing a pair of upwardly and outwardly directed prezygapophyses, -while the postzygapophyses are similar to those of the other cervical -vertebrae. - -The last two cervical vertebrae resemble the succeeding thoracic -vertebrae, in the increased length of the transverse processes, and -the shifting dorsalwards of the facet with which the capitulum of the -rib articulates. - -THE THORACIC VERTEBRAE. - -The thoracic vertebrae commence with the first of those that bears -ribs reaching the sternum. They are ten in number, and the first eight -are directly connected with the sternum by ribs. - -The =third= of them may be taken as a type. It has a thick cylindrical -centrum, concave in front and convex behind, there is a slight -hypapophysis, and the centrum is suturally united with a strong neural -arch enclosing a narrow neural canal. The neural arch is drawn out -dorsally into a wide truncated neural spine, and laterally into two -prominent transverse processes, with the ends of which the tubercula -of the ribs articulate, while the capitulum articulates in each case -with a step-like facet (fig. 42, A, 3) on the anterior face of the -transverse process. The prezygapophyses (fig. 42, A, 2) are borne on -outgrowths from the bases of the transverse processes, and the -postzygapophyses on outgrowths at the base of the neural spine. - -The thoracic vertebrae behind the third have no hypapophyses, and the -capitular facets gradually come to be placed nearer and nearer the -ends of the transverse processes, at the same time becoming less -prominent; otherwise these vertebrae are just like the third. - -[Illustration FIG. 42. ANTERIOR VIEW OF A, A LATE THORACIC AND B, THE -FIRST SACRAL VERTEBRA OF A YOUNG CROCODILE (_C. palustris_). × 1/3. - - 1. neural spine. - 2. process bearing prezygapophysis. - 3. facet for articulation with the capitulum of the rib. - 4. sacral rib. - 5. surface which is united with the ilium. - 6. concave anterior face of centrum.] - -In the first and second thoracic vertebrae the capitulum of the rib -articulates, not with a facet on the transverse process, but with a -little elevation borne at the line of junction of the centrum and -neural arch. - -THE LUMBAR VERTEBRAE. - -These are five in number, and are precisely like the posterior -thoracic vertebrae, except in the fact that the transverse processes -have no facets for the articulation of ribs. - -THE SACRAL VERTEBRAE. - -These are two in number, and while the centrum of the first is concave -in front (fig. 42, B, 6) and nearly flat behind, that of the second is -flat in front and concave behind. Each has a pair of strong =ribs= -(fig. 42, B, 4) firmly ankylosed in the adult with a wide surface -furnished partly by the centrum, partly by the neural arch. The distal -ends of these ribs are united with the ilia. The character of the -neural spines and zygapophyses is the same as in the thoracic -vertebrae. - -THE CAUDAL VERTEBRAE. - -These are very numerous, about thirty-four in number. The first -differs from all the other vertebrae of the body in having a biconvex -centrum. The succeeding ones are procoelous and are very much like the -posterior thoracic and lumbar vertebrae, having high neural spines and -prominent straight transverse processes. They differ however in having -the neural spines less strongly truncated above, and the transverse -processes arise from the centra and not from the neural arches. When -followed further back the centra and neural spines gradually lengthen -while the transverse processes become reduced, and after the twelfth -vertebra disappear. Further back still the neural spines and -zygapophyses gradually become reduced and disappear, as finally the -neural arch does also, so that the last few vertebrae consist simply -of cylindrical centra. - -Each caudal vertebra, except the first and the last eleven or so, has -a =V=-shaped =chevron bone= attached to the postero-ventral edge of -its centrum. The anterior ones are the largest and they gradually -decrease in size till they disappear. - -B. THE SKULL[90]. - -The skull of the Crocodile is a massive depressed structure -presenting a number of striking characteristics, some of the more -important of which are:-- - -1. All the bones except the mandible, hyoid, and columella are firmly -united by interlocking sutures. In spite of this, however, growth of -the whole skull and of the component bones goes on continuously -throughout life, this growth being especially marked in the case of -the facial as opposed to the cranial part of the skull. - -2. All the bones appearing on the dorsal surface are remarkable for -their curious roughened and pitted character; this feature is -prominent also in many Labyrinthodonts. - -3. The size of the jaws and teeth is very great. - -4. The mandibular condyle is carried back to some distance behind the -occipital condyle. - -5. The occipital plane (see p. 386) of the skull is vertical. - -6. The length of the secondary palate is remarkably great, and the -vomer takes no part in its formation. - -7. The posterior nares are placed very far back, the nasal passages -being as in mammals separated from the mouth by the long secondary -palate. - -8. There is a complicated system of Eustachian passages communicating -at one end with the tympanic cavity and at the other end with the -mouth cavity. - -9. The interorbital septum is mainly cartilaginous, the presphenoidal -and orbitosphenoidal regions remaining unossified. - -The =skull= is divisible into three parts:-- - -(1) the cranium, (2) the lower jaw, (3) the hyoid. - -The =cranium= may again for purposes of description be divided into:-- - -1. the cranium proper or brain case; - -2. the bones connected with the several special sense organs; - -3. the bones of the upper jaw, and suspensorial apparatus. - - -1. THE CRANIUM PROPER OR BRAIN CASE. - -[Illustration FIG. 43. PALATAL ASPECT A, OF THE CRANIUM, B, OF THE -MANDIBLE OF AN ALLIGATOR (_Caiman latirostris_). × 1/3. (Brit. Mus.) - - 1. premaxillae. - 2. maxillae. - 3. palatine. - 4. pterygoid. - 5. posterior nares. - 6. transpalatine. - 7. posterior palatine vacuity. - 8. anterior palatine vacuity. - 9. basi-occipital. - 10. opening of median Eustachian canal. - 11. jugal. - 12. quadratojugal. - 13. quadrate. - 14. dentary. - 15. splenial. - 16. coronoid. - 17. supra-angular. - 18. angular. - 19. articular. - 20. lateral temporal fossa. - 21. openings of vascular canals leading into alveolar sinus.] - -The cartilage and membrane bones of the cranium proper when taken -together can in most vertebrates be seen to be more or less arranged -in three rings or segments called respectively the =occipital=, -=parietal= and =frontal= segments; in the Crocodile however only the -occipital and parietal segments are clearly seen. - -The =occipital segment= consists of four cartilage bones, three of -which together surround the =foramen magnum=. - -The most ventral of these, the =basi-occipital= (figs. 43 and 45, 9), -forms the single convex =occipital condyle= for articulation with the -atlas, bounds the base of the foramen magnum, and is continuous -laterally with two larger bones, the =exoccipitals= (fig. 45, 24), -which meet one another dorsally and form the remainder of the boundary -of the foramen magnum. Each is drawn out externally into a strong -process, which is united below with the quadrate, and above with the -squamosal by a surface seen in a disarticulated skull to be very rough -and splintered. In a longitudinal section the anterior face of the -exoccipital is seen to be closely united with the opisthotic. - -The exoccipital is pierced by a number of foramina, four lying on the -posterior surface. Just external to the foramen magnum is a small -foramen for the exit of the hypoglossal nerve (figs. 44 and 45, XII). -External to this is the foramen for the pneumogastric (fig. 44, X), -while more ventrally still is the foramen (fig. 44, 15) through which -the internal carotid artery enters the skull. Some distance further to -the side, and more dorsally, is a larger foramen which gives passage -to the facial nerve and certain blood-vessels. - -In a median longitudinal section of the skull the hypoglossal foramen -is seen, and just in front of it a small foramen for a vein. Further -forwards the long slit-like opening between the exoccipital and -opisthotic is the =internal auditory meatus= (fig. 45, VIII) through -which the auditory nerve leaves the cranial cavity and enters the -internal ear. - -The =supra-occipital= (fig. 45, 5) is a small bone which takes no part -in the formation of the foramen magnum, and is closely united in front -with the epi-otic. It is characteristic of Crocodiles that all the -bones of the occipital segment have their longer axes placed -vertically, and that they scarcely if at all appear on the dorsal -surface. - -In front of the occipital segment is the =parietal segment=. The -dorsal and ventral portions of the two segments are in contact with -one another, but the lateral portions are widely separated by the -interposition of the =auditory= and =suspensorial bones=. - -The =basisphenoid= (fig. 45, 12) is an unpaired wedge-shaped bone, -united along a deep vertical suture with the basi-occipital. The two -bones are, however, partially separated in the mid-ventral line by a -foramen, the opening of the =median Eustachian canal=, which leads -into a complicated system of Eustachian passages ultimately -communicating with the tympanic cavity. - -The dorsal surface of the basisphenoid is well seen in a section of -the skull, but owing to the way it tapers ventrally, it appears on the -ventral surface only as a very narrow strip of bone wedged in between -the basi-occipital and pterygoids. In a lateral view it is seen to be -drawn out in front into an abruptly truncated process, the =rostrum=, -which forms part of the =interorbital septum.= On the anterior part of -the dorsal surface is a deep pit, the =pituitary fossa= or =sella -turcica=, at the base of which are a pair of foramina, through which -the carotid arteries pass. Dorsolaterally the basisphenoid articulates -with the =alisphenoids=. - -[Illustration FIG. 44. LATERAL VIEW OF THE SKULL OF AN ALLIGATOR -(_Caiman latirostris_). × 1/3. (Brit. Mus.) - - 1. premaxillae. - 2. maxillae. - 3. lachrymal. - 4. prefrontal. - 5. jugal. - 6. postfrontal. - 7. squamosal. - 8. quadrate. - 9. palatine. - 10. pterygoid. - 11. transpalatine. - 12. quadratojugal. - 13. exoccipital. - 14. basi-occipital. - 15. foramen by which carotid artery enters skull. - 16. external auditory meatus. - 17. frontal. - 18. supra-angular. - 19. articular. - 20. dentary. - 21. coronoid. - 22. angular. - III, VI, opening for exit of oculomotor and abducens nerves. - V, foramen ovale. - X, pneumogastric foramen. - XII, hypoglossal foramen.] - -The =alisphenoids= (fig. 45, 13) are a pair of irregular bones which -arise from the basisphenoid antero-laterally, and are united dorsally -with the parietal, frontal, and postfrontals. They bound most of the -anterior part of the brain case, and each presents on its inner face a -deep concavity which lodges the cerebral hemisphere of its side. -Viewed from the ventral side the two alisphenoids are seen to almost -or quite meet one another immediately below the frontal, and then to -diverge, forming an irregular opening--partially closed by cartilage -in the fresh specimen,--through which the optic nerves leave the -cranial cavity. Further back the alisphenoids meet one another for a -narrow area, and then diverge again, so that between each and the -rostrum of the basisphenoid there appears an opening (fig. 44, III, -VI) through which the oculomotor and abducens nerves leave the -cranium. Further back still each is united for a short space with the -basisphenoid, pterygoid and quadrate, and then becomes separated from -the quadrate by a large foramen, the =foramen ovale= (fig. 44, V), -through which the whole of the trigeminal nerve passes out. - -The dorsal portion of the parietal segment is formed by the _parietal_ -(fig. 45, 4), which though double in the embryo, early comes to form a -single bone. It extends over the posterior part of the cranial cavity, -and is continuous in front with the frontal, behind with the -supra-occipital, and laterally with the postfrontals, squamosals, -alisphenoids, pro-otics and epi-otics. It forms the inner boundary of -a large rounded vacuity on the roof of the skull, the =supratemporal -fossa=. - -The =frontal segment= is very imperfectly ossified, there being no -certain representatives of either the ventral member, the presphenoid, -or the lateral members, the orbitosphenoids. On the dorsal side there -is, however, a large development of membrane bones. There is a large -_frontal_ (fig. 45, 3), unpaired, except in the embryo, united behind -with the parietal and postfrontal, and drawn out in front into a long -process which is overlapped by the prefrontals and posterior part of -the nasals. The frontal ends off freely below, owing to the -orbitosphenoidal region being unossified, it forms a considerable part -of the roof of the cranial cavity, but takes no part in the formation -of the wall. - -Each _prefrontal_ (fig. 45, 14) forms part of the inner wall of the -orbit and sends ventralwards a process which meets the palatine. - -The _postfrontals_ (fig. 44, 6) are small bones lying at the sides of -the posterior part of the frontal. Each is united with a number of -bones, on its inner side with the frontal and parietal, behind with -the squamosal, and ventrally with the alisphenoid. It also unites by -means of a strong descending process with an upgrowth from the jugal, -and thus forms a =postorbital bar= separating the orbit from the -lateral temporal fossa. The postfrontal forms also part of the outer -boundary of the supratemporal fossa. - - -2. THE SENSE CAPSULES. - -Skeletal capsules occur in connection with each of the three special -sense organs of sight, of hearing and of smell. - -The =Auditory capsules= and associated bones. - -Three bones, the =epi-otic=, =opisthotic= and =pro-otic=, together -form the auditory or =periotic= capsule of each side. They are wedged -in between the lateral portions of the occipital and parietal segments -and complete the cranial wall in this region. Their relations to the -surrounding structures are very complicated, and many points can be -made out only in sections of the skull passing right through the -periotic capsule. The relative position of the three bones is, -however, well seen in a median longitudinal section. The =opisthotic= -early becomes united with the exoccipital, while the =epi-otic= -similarly becomes united with the supra-occipital, the =pro-otic= -(fig. 45, 7),--seen in longitudinal section to be pierced by the -prominent =trigeminal foramen=--alone remaining distinct throughout -life. The three bones together surround the essential organ of hearing -which communicates laterally with the deep tympanic cavity by the -=fenestra ovalis=. - -The =tympanic cavity=, leading to the exterior by the =external -auditory meatus= (fig. 44, 16), is well seen in a side-view of the -skull; it is bounded on its inner side by the periotic bones, -posteriorly in part by the exoccipital, and elsewhere mainly by the -quadrate. A large number of canals and passages open into it. On its -inner side opening ventro-anteriorly is the =fenestra ovalis=, opening -ventro-posteriorly the =internal auditory meatus= (fig. 45, VIII), -while dorsally there is a wide opening which forms a communication -through the roof of the brain-case with the tympanic cavity of the -other side. On its posterior wall is the prominent foramen through -which the facial nerve passes on its way to its final exit from the -skull through the exoccipital, this foramen is bounded by the -quadrate, squamosal, and exoccipital. - -The opening of the fenestra ovalis is in the fresh skull occupied by -the expanded end of the auditory ossicle, the =columella=, whose outer -end articulates by a concave facet with a trifid =extra-columellar= -cartilage which reaches the tympanic membrane. The lower process of -this extra-columella passes into a cartilaginous rod which lies in a -canal in the quadrate and is during life continuous with Meckel's -cartilage within the articular bone of the mandible. - -The columella and extra-columella are together homologous with the -chain of mammalian auditory ossicles. - - * * * * * - -The =Optic capsules= and associated bones. - -Two pairs of bones are associated with the optic capsules, viz. the -_lachrymals_ and the _supra-orbitals_. The _lachrymal_ (fig. 44, 3) is -a fairly large flattened bone lying wedged in between the maxillae, -nasal, jugal, and prefrontal. It forms a considerable part of the -anterior boundary of the orbit, and is pierced by two foramina. On the -orbital edge is a large hole leading into a cavity within the bone -which lodges the naso-lachrymal sac, and communicates with the narial -passage by a wide second foramen near the anterior end of the bone. -The _supra-orbital_ is a very small loose bone lying in the eyelid -close to the junction of the frontal and prefrontal. - - * * * * * - -The =Olfactory capsules= and associated bones. - -Two pairs of membrane bones, the _vomers_ and _nasals_, are developed -in association with the olfactory organ, but the =mesethmoid= is not -ossified. - -The _vomers_ form a pair of delicate bones, each consisting of a -vertical plate (fig. 45, 15), which with its fellow separates the two -narial passages, and of a horizontal plate which forms much of their -roof. The vomers articulate with one another and with the pterygoids, -palatines, and maxillae. - -The _nasals_ (fig. 45, 2) are very long narrow bones extending along -the middle line from the frontal almost to the anterior nares. They -are continuous laterally with the premaxillae, maxillae, lachrymals and -prefrontals. They form the roof of the narial passages. - -3. THE UPPER JAW AND SUSPENSORIAL APPARATUS. - -These are enormously developed in the Crocodile and are firmly united -to the cranium. It will be most convenient to begin by describing the -bones at the anterior end of the jaw and to work back thence towards -the brain-case. The most anterior bones are the _premaxillae_. The -_premaxillae_ (figs. 44 and 45, 1) are small bones, each bearing five -pairs of teeth, set in separate sockets in their alveolar borders. -They constitute almost the whole of the boundary of the =anterior -nares=, which are confluent with one another and form a large -semicircular opening in the roof of the skull, leading into the wide -narial passage. They are also partially separated from one another in -the ventral middle line, by the small =anterior palatine vacuity= -(fig. 43, A, 8). They form the anterior part of the broad =palate=. -The alveolar border on each side between certain of the teeth is -marked by pits which receive the points of the teeth of the other jaw. -The first pair of these pits in the premaxillae are often so deep as to -be converted into perforations. Pits of the same character occur -between the maxillary and mandibular teeth. - -[Illustration FIG. 45. LONGITUDINAL SECTION THROUGH THE SKULL OF AN -ALLIGATOR (_Caiman latirostris_). × 1/3. (Brit. Mus.) - - 1. premaxilla. - 2. nasal. - 3. frontal. - 4. parietal. - 5. supra-occipital. - 6. epi-otic. - 7. pro-otic. - immediately in front of the figure 7 is the prominent foramen - for the trigeminal nerve. - 8. opisthotic. - 9. basi-occipital. - 10. quadrate. - 11. pterygoid. - 12. basisphenoid. - 13. alisphenoid. - 14. prefrontal. - 15. vomer. - 16. maxilla. - 17. palatine. - 18. dentary. - 19. splenial. - 20. angular. - 21. supra-angular. - 22. articular. - 23. coronoid. - 24. exoccipital. - 25. squamosal. - 26. jugal. - 27. external mandibular foramen. - 28. internal mandibular foramen. - VIII. internal auditory meatus. - XII. hypoglossal foramen.] - -The _maxillae_ (figs. 43, A, 2 and 44, 2) are a pair of very large -bones and bear the remaining teeth of the upper jaw, set in sockets -along their alveolar borders. On the dorsal side each maxillae is -continuous with the premaxillae, nasal, lachrymal, and jugal, while -ventrally it meets its fellow in a long straight suture and forms the -greater part of the long bony palate. The maxillae are separated in the -middle line posteriorly by processes from the palatines, while further -back they meet the transpalatines. The internal or nasal surface, like -that of the premaxillae, is excavated by a deep longitudinal groove, -the =narial passage=. In a ventral view of the skull a number of small -openings (fig. 43, A, 21) are seen close to the alveolar border, these -are the openings of small vascular canals which lead into the -=alveolar sinus=, a passage traversing the maxillae, and transmitting -the superior maxillary branch of the trigeminal nerve and certain -blood-vessels. This alveolar sinus opens posteriorly by the more -external of the two large holes in the maxillae, which lie close to the -anterior edge of the posterior palatine vacuity, to be described -immediately. The more internal of these holes, on the other hand, -leads into a cavity lodging the nasal sac. Behind the maxillae the -completeness of the palate is broken up by the large oval =posterior -palatine vacuities= (fig. 43, A, 7); these are separated from one -another in the middle line by the palatines, and are bounded elsewhere -by the maxillae, transpalatines, and pterygoids. - -The _palatines_ (fig. 43, A, 3) are long and rather narrow bones -interposed between the maxillae in front and pterygoids behind. They -meet one another in a long suture and form much of the posterior part -of the palate, while the whole length of their dorsal surface -contributes to the floor of the narial passage. The dorsal surface of -each bone is also drawn out on its outer side into a prominent ridge -which forms much of the side and roof of the narial passage, being in -contact with the vomer and pterygoid, and at one point by means of a -short ascending process with the descending process of the -prefrontal. - -The _pterygoids_ (figs. 43, A, 4, and 45, 11) are a pair of large -bones, each consisting of a median more or less vertical part, which -becomes ankylosed to its fellow in the middle line early in life, and -of a wide horizontal part which meets the transpalatine. They -completely surround the posterior nares (fig. 43, A, 5) and their -median portions form the whole boundary of the posterior part of the -narial passage, and assist the palatines and vomers in bounding the -middle part. The horizontal parts form the posterior part of the -secondary palate, while the dorsal surface of each looks into the -=pterygoid fossa=, a large cavity lying below the quadrate and -quadratojugal at the side of the skull. The lateral margin adjoining -the transpalatine is in the fresh skull terminated by a plate of -cartilage against which the mandible plays. Dorsally the pterygoid -articulates with the basisphenoid, quadrate, and alisphenoid. - -The _transpalatines_ (fig. 44, 11) connect the pterygoids with the -jugals and maxillae, articulating with each of the three bones by a -long pointed process. The jugal process meets also a down-growth from -the postfrontal. - -The _jugals_ or _malars_ (fig. 44, 5) are long somewhat flattened -bones which are united to the lachrymals and maxillae in front, while -passing backwards each is united behind to the _quadratojugal_ (fig. -44, 12), the two forming the =infratemporal arcade= which constitutes -the external boundary of the orbit and lateral temporal fossa. The -jugal is united below to the transpalatine, and the two bones together -form an outgrowth, which meeting that from the postfrontal forms the -=postorbital bar=, and separates the orbit from the lateral temporal -fossa. The quadratojugals are small bones and are united behind with -the quadrates. - -The =quadrate= (figs. 43, A, 13 and 44, 8) of each side is a large -somewhat flattened bone firmly fixed in among the other bones of the -skull. It is terminated posteriorly by an elongated slightly convex -surface, coated with cartilage in the fresh skull, by which the -mandible articulates with the cranium. The dorsal surface of the -quadrate is flat behind, further forwards it becomes much roughened -and articulates with the exoccipital and squamosal; further forwards -still it becomes marked by a deep groove which forms the floor of the -external auditory meatus and part of the tympanic cavity. The anterior -boundary of the quadrate is extremely irregular, it is united dorsally -with the postfrontal, pro-otic, and squamosal, and more ventrally with -the alisphenoid. The smooth ventral surface looks into the pterygoid -fossa. In front the quadrate forms the posterior boundary of the -supratemporal fossa and foramen ovale, and is continuous with the -alisphenoid, while it sends down a thin plate meeting the pterygoid -and basisphenoid. On the inner side of the dorsal surface of the -quadrate near the condyle, is a small foramen which leads into a tube -communicating with the tympanic cavity, by a foramen lying in front of -and ventral to that for the exit of the facial nerve. By this tube air -can pass from the tympanic cavity into the articular bone of the -mandible. - -The _squamosal_ (fig. 44, 7) meets the quadrate and exoccipital below, -and forms part of the roof of the external auditory meatus, while -above it forms part of the roof of the skull and has a pitted -structure like that of the other bones of the roof. It is continuous -with the postfrontal in front, forming with it the =supratemporal -arcade= which constitutes the outer boundary of the supratemporal -fossa. It meets also the parietal on its inner side, forming the -=post-temporal bar=, the posterior boundary of the supratemporal -fossa. - -It may be useful to recapitulate the large vacuities in the surface of -the Crocodile's cranium. - -_Dorsal surface._ - -1. =The Supratemporal fossae=. Each is bounded internally by the -parietal, behind by the =post-temporal bar= formed by the parietal and -squamosal, and externally by the =supratemporal arcade= formed by the -squamosal and postfrontal. The postfrontal meets the parietal in front -and forms the anterior boundary of the supratemporal fossa. - -2. The =Lateral temporal= or =infratemporal fossae=. These lie below -and to the outer side of the supratemporal fossae. Each is bounded -dorso-internally by the supratemporal arcade; and behind by a -continuation of the post-temporal bar formed by the quadrate and -quadratojugal. The external boundary is the =infratemporal arcade= -formed of the quadratojugal and jugal, while in front the fossa is -separated from the orbit by the =postorbital bar= formed by the -junction of outgrowths from the postfrontal and jugal. - -3. The =Orbits=. Each is bounded behind by the postorbital bar, -externally by the jugal forming a continuation of the infratemporal -arcade, in front by the lachrymal, and internally by the frontal and -prefrontal. - -4. The =Anterior nares=. These form an unpaired opening bounded by the -premaxillae. - -_Posterior surface._ - -5. The =Foramen magnum=. The exoccipitals form the chief part of its -boundary, but part of the ventral boundary is formed by the -basi-occipital. - -6. The =Pterygoid fossae=. These form a pair of large cavities at the -sides of the occipital region of the skull. The dorsal boundary is -formed by the quadrate and quadratojugal, the ventral by the -pterygoid, the internal chiefly by the quadrate, pterygoid, -alisphenoid, and basisphenoid. The transpalatine forms a small part of -the external boundary which is incomplete. - -_Ventral surface._ - -7. The =Posterior nares=. These form a median unpaired opening (fig. -43, A, 5) bounded by the pterygoids. - -8. The =Posterior palatine vacuities=. Each is bounded by the maxillae -in front, the maxillae and transpalatine externally, the transpalatine -and pterygoid behind, and the palatine on the inner side (fig. 43, A, -7). - -9. The =Anterior palatine vacuity=. This is unpaired and is bounded by -the premaxillae (fig. 43, A, 8). - - -(_b_) THE LOWER JAW OR MANDIBLE. - -The mandible is a strong compact bony structure formed of two halves -or =rami=, which are suturally united at the symphysis in the middle -line in front. Each ramus is formed of six separate bones. - -The most anterior and largest of these is the _dentary_ (figs. 44, 20, -and 45, 18), which forms the symphysis, and greater part of the -anterior half of the jaw, and bears along the outer part of its dorsal -border a number of sockets or =alveoli= in which the teeth are placed. -Lying along the inner side of the dentary is a large splint-like bone, -the _splenial_ (fig. 45, 19), which does not extend so far forwards as -the symphysis, and is separated from the dentary posteriorly by a -large cavity. Forming the lower part of all the posterior half of the -jaw is the large _angular_ (figs. 44, 22, and 45, 20), which underlies -the posterior part of the dentary in front and sends a long process -below that bone to the splenial. On the inner side of the jaw there is -an oval vacuity, the =internal mandibular foramen= (fig. 45, 28), -between the angular and the splenial; through this pass blood-vessels -and branches of the inferior dental nerve. Lying dorsal to the angular -is another large bone, the _supra-angular_ (figs. 44, 18, and 45, 21). -It extends back as far as the posterior end of the jaw and forwards -for some distance dorsal to the dentary and splenial. It forms part of -the posterior margin of a large vacuity, the =external mandibular -foramen=, which is bordered above and in front by the dentary and -below by the angular; it gives passage to the cutaneous branch of the -inferior dental nerve. The concave surface for articulation with the -mandible and much of the posterior end of the jaw is formed by a short -but solid bone, the =articular= (fig. 45, 22), which in young skulls -rather readily becomes detached. The remaining mandibular bone is the -_coronoid_ (fig. 45, 23), a very small bone of irregular shape -attached to the angular below, and to the supra-angular and splenial -above. - -(_c_) THE HYOID. - -The hyoid of the Crocodile consists of a wide flattened plate of -cartilage, the =basilingual plate= or =body of the hyoid=, and a pair -of =cornua=. - -The =basilingual plate= (fig. 53, 1) is rounded anteriorly and marked -by a deep notch posteriorly. The =cornua= (fig. 53, 3), which are -attached at a pair of notches near the middle of the outer border of -the basilingual plate, are partly ossified, but their expanded ends -are formed of cartilage. They pass at first backwards and then upwards -and inwards. They are homologous with part of the first branchial -arches of Selachians. - -The columella and extra-columella have been already described (p. -251). - -C. THE RIBS AND STERNUM. - -=Thoracic ribs.= - -The Crocodile has ten pairs of =thoracic ribs=, all except the last -one or two of which consist of three parts,--a vertebral rib, an -intermediate rib and a sternal rib. - -Of the =vertebral ribs= the third may be taken as a type, it consists -of a curved bony rod which articulates proximally with the transverse -process of the vertebra by two facets. The terminal one of these, the -=capitulum= or =head=, articulates with a notch on the side of the -transverse process; the other, the =tuberculum=, which lies on the -dorsal surface a short distance behind the head, articulates with the -end of the transverse process. From near the distal end an imperfectly -ossified uncinate =process= (see p. 190) projects backwards. - -The =intermediate ribs= are short and imperfectly ossified; they are -united with the =sternal ribs= (fig. 46, 3), which are large, -flattened, likewise imperfectly ossified structures, and articulate at -their distal ends with a pair of long divergent =xiphisternal horns= -(fig. 46, 5), which arise from the posterior end of the sternum -proper. The last pair of sternal ribs are attached to the preceding -pair, not to the xiphisternal horns. - -The first and second vertebral ribs differ from the others in the fact -that the tuberculum forms a fairly long outstanding process. - - -=Cervical ribs.= - -Movable ribs are attached to all the cervical as well as to the -thoracic vertebrae. Those borne by the atlas and axis are long, narrow -structures attached by a fairly broad base, and tapering gradually. -The ribs borne by the third to seventh cervical vertebrae are shaped -like a =T= with a double base, one limb of which, corresponding to the -tuberculum (fig. 41, 7), articulates with a short transverse process -arising from the neural arch, while the other, corresponding to the -capitulum, articulates with a surface on the centrum. The ribs -attached to the eighth and ninth cervical vertebrae are intermediate -in character between the =T=-shaped ribs and the ordinary thoracic ribs. -The anterior limb of the =T= is shortened, the posterior one is drawn -out, forming the shaft of the rib. The distal portion of the rib of -the ninth cervical vertebra is unossified. - -The =Sacral ribs= have been described in connection with the sacral -vertebrae. - - -THE STERNUM. - -The =sternum= of Crocodiles is a very simple structure, consisting of -a plate of cartilage (fig. 46, 2) lying immediately dorsal to the -interclavicle, and drawn out posteriorly into a pair of long -=xiphisternal horns= (fig. 46, 5). - - -THE ABDOMINAL SPLINT RIBS. - -Lying superficially to the recti muscles of the ventral body-wall, -behind the sternal ribs, are seven or eight series of slender curved -bones, the _abdominal ribs_ (fig. 46, 4). Each series consists of four -or more bones, arranged in a =V=-like form with the angle of the =V= -directed forwards. They show a considerable amount of variability in -number and character. They are really membrane bones, and are in no -way homologous with true ribs, but correspond rather with the more -posterior of the bones constituting the plastron of Chelonia. - -[Illustration FIG. 46. STERNUM AND ASSOCIATED MEMBRANE BONES OF A -CROCODILE (_C. palustris_) × 1/3. (Brit. Mus.) - -The last pair of abdominal ribs which are united with the epipubes by -a plate of cartilage have been omitted. - - 1. interclavicle. - 2. sternum. - 3. sternal rib. - 4. abdominal splint rib. - 5. xiphisternal horn.] - - -2. THE APPENDICULAR SKELETON. - -This includes the skeleton of the two pairs of limbs and their -respective girdles. - -[Illustration: FIG. 47. LEFT HALF OF THE PECTORAL GIRDLE OF AN -ALLIGATOR (_Caiman latirostris_) × 2/3. (Brit. Mus.) - - 1. scapula. - 2. coracoid. - 3. interclavicle. - 4. glenoid cavity.] - - -THE PECTORAL GIRDLE. - -The pectoral girdle of the Crocodile is less complete than is that of -most reptiles. It consists of a dorsal bone, the =scapula=, and a -ventral bone, the =coracoid=, with a median unpaired element, the -_interclavicle_; but there is no separate representative either of the -clavicle or precoracoid. - -The =scapula= (fig. 47, 1) is a large bone, flattened and expanded -above where it is terminated by an unossified margin, the -=suprascapula=, and thickened below where it meets the coracoid. The -scapula forms about half the =glenoid cavity= (fig. 47, 4) for -articulation with the humerus, and has the lower part of its anterior -border drawn out into a roughened ridge. - -The =coracoid= (fig. 47, 2) is a flattened bone, much expanded at -either end; it bears on its upper posterior border a flattened surface -which forms half the glenoid cavity, and is firmly united to the -scapula at its dorsal end. Its ventral end meets the sternum. - -The _interclavicle_ (figs. 46, 1, and 47, 3) is a long narrow -blade-shaped bone lying along the ventral side of the sternum; about a -third of its length projects beyond the sternum in front. - - -THE ANTERIOR LIMB. - -This is as usual divisible into three portions, the upper arm, -fore-arm and manus. - -The =upper arm= or =brachium= contains one bone, the =humerus.= - -The =humerus= (fig. 48, A, 1) is a fairly long stout bone, -considerably expanded at either end. The proximal end or head is -evenly rounded and is formed by an epiphysis ossifying from a centre -different from that forming the shaft. It articulates with the glenoid -cavity. The shaft bears on the flexor surface, at some little distance -behind the head, a prominent rounded protuberance, the =deltoid -ridge.= The distal end or trochlea is also formed by an epiphysis and -is partially divided by a groove into two convex surfaces; it -articulates with the two bones of the fore-arm, the radius and ulna. - -[Illustration FIG. 48. A, RIGHT ANTERIOR, AND B, RIGHT POSTERIOR LIMB -OF A YOUNG ALLIGATOR (_Caiman latirostris_). (Brit. Mus.) - -A × 1/2. B × about 1/3.] - - 1. humerus. - 2. radius. - 3. ulna. - 4. radiale. - 5. ulnare. - 6. pisiform. - 7. patch of cartilage representing carpalia 1 and 2; between it - and the radiale should be another flattened patch, the centrale. - 8. carpalia 3, 4, and 5 (fused). - 9. first metacarpal. - 10. proximal phalanx of second digit. - 11. second phalanx of fifth digit. - 12. femur. - 13. tibia. - 14. fibula. - 15. tibiale, intermedium and centrale (fused). - 16. fibulare. - 17. tarsalia 1, 2, and 3 (fused). - 18. tarsalia 4 and 5 (fused). - 19. first metatarsal. - 20. ungual phalanx of second digit. - 21. fifth metatarsal. - -The =radius= and =ulna= are nearly equal in size and each consists of -a long shaft terminated at either end by an epiphysis. - -The =radius= (fig. 48, A, 2) or pre-axial bone is slightly the smaller -of the two. It has a straight cylindrical shaft and is slightly and -nearly evenly expanded at either end. The proximal end which -articulates with the humerus is flat or slightly concave, the distal -end which articulates with the carpus is slightly convex. - -The =ulna= (fig. 48, A, 3) or postaxial bone is a curved bone rather -larger than the radius. Its proximal end is large and convex, but is -not drawn out into an olecranon process. - -The =Manus= consists of the =carpus= or =wrist=, and the =hand=. - -The =Carpus=. This differs considerably from the more primitive type -met with in the Turtle. It consists of six elements arranged in a -proximal row of three and a distal row of two, with one intervening. -The bones of the proximal row are the radiale, the ulnare, and the -pisiform. The =radiale= (fig. 48, A, 4) is the largest bone of the -carpus: it is a somewhat hour-glass shaped bone, with its ends formed -by flattened epiphyses. It articulates by its proximal end with the -whole of the radius, and partly also with the ulna, and by its distal -end with the centrale. - -The =ulnare= (fig. 48, A, 5) is a smaller bone, also somewhat -hour-glass shaped; it articulates proximally with the pisiform and -radiale, not quite reaching the ulna. The third bone of the proximal -row is the =pisiform= (fig. 48, A, 6), an irregular bone, articulating -with the ulna, radiale, and fifth metacarpal. The =centrale= is a -flattened cartilaginous element applied to the distal surface of the -radiale. - -The distal row of carpals consists of two small structures. The first -of these forms a small cartilaginous patch, which is wedged in between -the first and second metacarpals, the centrale and the bone -representing carpalia 3, 4 and 5; this cartilaginous patch represents -=carpalia 1 and 2= (fig. 48, A, 7). The bone representing =carpalia 3, -4 and 5= is a good deal larger, rounded, and well-ossified; it -articulates with the ulnare, the pisiform, and the third, fourth, and -fifth metacarpals. - -The =hand=. Each of the five digits consists of an elongated -metacarpal, terminated at each end by an epiphysis, and of a varying -number of phalanges. The terminal phalanx of each digit has an -epiphysis only at its proximal end, the others have them at both ends. - -The first digit, or =pollex=, is the stoutest, and has two phalanges, -the second has three, the third four, the fourth three, and the fifth -two. The terminal phalanx of each of the first three digits is pointed -and sheathed in a horny claw; and is also marked by a pair of -prominent lateral grooves. - -THE PELVIC GIRDLE. - -The pelvic girdle of the Crocodile consists of four parts, a dorsal -element, the =ilium=, an anterior ventral element, the =pubis=, a -posterior ventral element, the =ischium=, and an accessory anterior -ventral element, the =epipubis=. All except the epipubis take part in -the formation of the =acetabulum=, which is perforated by a prominent -hole. - -The =ilium= (fig. 49, 1) is a thick strong bone, firmly united on its -inner side with the two sacral ribs. Its dorsal border is rounded, its -ventral border bears posteriorly two irregular surfaces, completed by -epiphyses, which are united respectively with the ischium and pubis. - -The =ischium= (fig. 49, 2)--the largest bone of the pelvis, is -somewhat contracted in the middle and expanded at either end. Its -proximal end, which is formed by an epiphysis, bears two surfaces, one -of which is united to the ilium, while the other forms part of the -acetabulum. The anterior border is also drawn out dorsally into a -strong process, which is terminated by a convex epiphysis, and is -united to the pubis. The ventral end of the ischium forms a flattened -blade, meeting its fellow in a median symphysis. - -The =pubis= (fig. 49, 3) is much smaller than either the ilium or -ischium; it forms a small patch of unossified cartilage, interposed -between the anterior parts of the ilium and ischium. - -[Illustration FIG. 49. PELVIS AND SACRUM OF AN ALLIGATOR (_Caiman -latirostris_) × 1/2. (Brit. Mus.) - - 1. ilium. - 2. ischium. - 3. true pubis. - 4. epipubis (so-called pubis). - 5. acetabular foramen. - 6. neural spines of sacral vertebrae. - 7. symphysis ischii. - 8. process bearing prezygapophysis.] - -The =epipubis= (fig. 49, 4) is a large bone with a thickened proximal -end, which is loosely articulated to the ischium, and a flattened -expanded distal end, which is united with its fellow, and with the -last pair of abdominal ribs by a large plate of cartilage. This bone -is generally described as the pubis. - - -THE POSTERIOR LIMB. - -This is as usual divisible into three portions, the =thigh=, the -=crus= or =shin=, and the =pes=. - -The =thigh= is formed by the =femur= (fig. 48, B, 12), a moderately -long stout bone, not unlike the humerus; it articulates with the -acetabulum by a fairly prominent rounded =head=. The distal end -articulating with the tibia and fibula is also expanded, and is -partially divided into equal parts by anterior and posterior grooves. -The flexor surface bears a fairly prominent trochanteric ridge. Each -end of the femur is formed by an epiphysis. - -The =crus= or =shin= includes two bones, the =tibia= and =fibula=. -Both are well developed, but the tibia is considerably the larger of -the two. - -The =tibia= (fig. 48, B, 13) is a strong bone with a flattened -expanded proximal end articulating with almost the whole of the end of -the femur, and a similarly expanded distal end articulating with a -bone representing the fused astragalus and centrale. - -The =fibula= (fig. 48, B, 14) is flattened proximally, and articulates -with only quite a small part of the femur, while distally it is more -expanded, and articulates with the fibulare (calcaneum) and with a -facet on the side of the fused astragalus and centrale. - -The =Pes= consists of the =tarsus= or =ankle=, and the =foot=. - -The =Tarsus=. This, like the carpus, is much reduced and modified from -the primitive condition. It consists of only four bones, arranged in -two rows of two each. The two bones of the proximal row are much -larger than are those of the distal row. The pre-axial of them (fig. -48, B, 15) representing the fused =astragalus= (tibiale and -intermedium) and =centrale=, articulates proximally with the tibia and -fibula, and distally with the first metatarsal, and a small bone -representing the first three tarsalia. The postaxial bone, the -=calcaneum= (fibulare) (fig. 48, B, 16), is drawn out into a -prominent posterior process forming a heel such as is almost unknown -elsewhere except in mammals. It articulates with the fibula, the -tibiale-centrale, and distally with a bone representing the fourth and -fifth tarsalia, and with the fifth metatarsal. - -The two bones forming the distal row of tarsals are both small and -rounded; one represents the first three tarsalia fused together, the -other tarsalia 4 and 5. - -The =Foot=. The =foot= has five digits, but the fifth is much reduced, -consisting only of a short metatarsal. The first four =metatarsals= -are all long bones, slightly expanded at each end, and terminated by -small epiphyses. The first digit has two phalanges, the second three, -the third four, and the fourth five. The terminal or =ungual phalanx= -in each instance is grooved and pointed, and in the case of the first -three digits bears a horny claw. The ungual phalanx progressively -decreases in size from the first to the fourth. The fifth digit -consists only of a small, somewhat square metatarsal (fig. 48, B, 21), -attached to the bone representing the fused fourth and fifth -tarsalia. - - -FOOTNOTES: - -[90] Free use has been made of L.C. Miall's _Studies in Comparative -Anatomy_, I., _The Skull in Crocodilia_, London, 1878. See also W.K. -Parker, _Tr. Z.S._, vol. XI. 1885, p. 263. - - - - -CHAPTER XVI. - -GENERAL ACCOUNT OF THE SKELETON IN REPTILES. - - -EXOSKELETON. - -The exoskeleton both epidermal and dermal is exceedingly well -developed in reptiles. - - -EPIDERMAL EXOSKELETON. - -This generally has the form of overlapping horny =scales= which invest -outgrowths of the dermis, and are found covering the whole body in -most Rhynchocephalia, Ophidia, and Lacertilia, and many Crocodilia. In -the Ophidia the ventral surface of the tail is commonly covered by a -double row of broad scales, while the ventral surface of the precaudal -part of the body is covered by a single row. In the burrowing snakes -(Typhlopidae) and some sea snakes (Hydrophidae) these broad scales do -not occur, the scales of the ventral surface being similar to those of -the dorsal. - -In the Chelonia with the exception of _Dermochelys_, _Trionyx_ and -their allies there is a well-developed system of horny shields having -a regular arrangement which has been described in the account of the -Turtle's skeleton[91]. - -The =rattle of the rattlesnake= is an epidermal structure formed of -several loosely articulated horny rings, produced by the modification -of the epidermal covering of the end of the tail, which instead of -being cast off when the rest of the outer skin is shed is retained -loosely interlocked with the adjoining ring or joint. New rings are -thus periodically added to the base of the rattle, and in old animals -the terminal ones wear away and are lost. - -Horny claws occur on the ends of some or all of the digits in most -living reptiles. - -Owen's Chameleon bears three epidermal horns, one arising from the -nasal and two from the frontal region. - -In the Chelonia, some of the Theromorpha such as _Udenodon_ and -_Dicynodon_, probably also in the Pterosauria and _Polyonax_ among the -Dinosaurs, the jaws are more or less cased in horny beaks. The horny -beaks of Chelonia are variable; sometimes they have cutting edges, -sometimes they are denticulated, sometimes they are adapted for -crushing. - - -DERMAL EXOSKELETON. - -Nearly all Crocodilia, many Dinosauria, some Rhynchocephalia and -Pythonomorpha, and some Lacertilia such as _Tiliqua_, _Scincus_ and -_Anguis_ have a dermal exoskeleton of bony scutes, developed below and -corresponding in shape to the epidermal scales. Sometimes as in -_Caiman sclerops_, _Jacare_ and _Teleosaurus_, the scutes completely -invest the body, being so arranged as to form a dorsal and a ventral -shield, and a continuous series of rings round the tail. In -_Crocodilus_ they are confined to the dorsal surface, and in -_Alligator_ to the dorsal and ventral surfaces. The scutes of some -extinct forms articulate with one another by a peg and socket -arrangement as in some Ganoid fish. - -The =carapace= of most Chelonia is a compound structure, being partly -endoskeletal and formed from the ribs and vertebrae, partly from -plates derived from the dermal exoskeleton. The common arrangement is -seen in fig. 36. All the surface plates are probably exoskeletal in -origin, but united with the ventral surfaces of the costal and neural -plates respectively are the expanded ribs and neural arches of the -vertebrae. - -The =plastron= in the common genus _Chelone_ (fig. 37) includes nine -plates of bone, one unpaired and four pairs; they will be referred to -in connection with the ribs and pectoral girdle. - -In the Leathery Turtle (_Dermochelys_) the carapace and plastron -differ completely from those of any other living form. The carapace -consists of a number of polygonal ossifications fitting closely -together and altogether distinct from the vertebrae and ribs. The -plastron is imperfectly ossified, and not united with the pelvis, and -the whole surface of both carapace and plastron is covered with a -tough leathery skin, without horny shields. - -Some of the extinct Dinosauria have an enormously developed dermal -exoskeleton. Thus in _Stegosaurus_ and _Omosaurus_ the dorsal surface -is provided with flattened plates or with spines reaching a length of -upwards of two feet. In _Polacanthus_ the posterior part of the body -is protected by a bony shield somewhat recalling that of the little -armadillo _Chlamydophorus_. No exoskeleton is known in Ichthyosauria, -Sauropterygia, Pterosauria, many Dinosauria and Theromorpha, and some -Lacertilia, such as _Chamaeleon_ and _Amphisbaena_. - - -TEETH. - -The teeth of reptiles are generally well developed, and in the great -majority of forms are simple conical structures, uniform in character, -generally somewhat recurved, and often with serrated edges. Another -common type of tooth is that with a laterally compressed triangular -crown provided with a double cutting edge which may or may not be -serrated. The teeth are mainly formed of dentine, with usually an -external layer of enamel, and often a coating of cement on the root. -Vasodentine is found below the dentine in _Iguanodon_. The teeth of -reptiles never have the enamel deeply infolded, nor do they have -double roots. - -Teeth may be present not only on the jaw-bones, but as in many -_Squamata_, also on the palatines, pterygoids or vomers. The method -by which they are attached to the bones varies much. Sometimes as in -_Iguana_ and some other lizards, they are pleurodont[1], sometimes -they are acrodont[92], as in the Rhynchocephalia, Pythonomorpha, -Ophidia and some Lacertilia such as _Agama_. Again they may be set in -a continuous groove as in the Ichthyosauria and young Crocodilia. -Finally the teeth may be _thecodont_ or placed in distinct sockets as -in the Theromorpha, Sauropterygia, adult Crocodilia, Sauropoda and -Theropoda. In _Iguanodon_ the teeth are set in shallow sockets in a -groove one side of which is higher than the other; the method of -attachment thus shows points of resemblance to the thecodont -condition, the pleurodont condition, and that met with in the -Ichthyosauria. - -In _Ichthyosaurus_ the teeth are marked by a number of vertical -furrows, and it is from a furrow of this nature greatly enlarged and -converted into a tube that the channel down which flows the poison of -venomous snakes is derived. - -In most reptiles the dentition is more or less homodont. The only -reptiles in which a definite heterodont dentition is known are the -extinct Theromorpha, and in them the teeth vary greatly. Thus -_Udenodon_ is toothless, the jaws having been probably cased in a -horny beak. In _Dicynodon_ the jaws are likewise toothless with the -exception of a pair of permanently growing tusks borne by the maxillae. -_Dicynodon_ is the only known reptile whose teeth have permanently -growing pulps. In _Pariasaurus_ the teeth are uniform and very -numerous, and though placed in distinct sockets are ankylosed to the -jaw. In _Galesaurus_ and _Cynognathus_ three kinds of teeth can be -distinguished, slender conical incisor-like teeth, large canine-like -teeth, and cheek teeth with two or three cusps. The teeth in -_Galesaurus_ are confined to the jaws, in _Placodus_ and its allies, -however, large flat crushing teeth are attached to the palatines as -well as to the jaw-bones, and in _Pariasaurus_ the vomer, palatine and -pterygoid all bear teeth as well as the jaw bones. The upper jaw of -_Sphenodon_ and other Rhynchocephalia is provided with two parallel -rows of teeth, one borne on the maxillae and one on the palatines, the -mandibular teeth bite in a groove between these two rows. The bone of -the jaws in _Sphenodon_ is so hard that when the teeth get worn away, -it can act as a substitute. In the young _Sphenodon_ the vomers bear -teeth, as they do also in _Proterosaurus_. - -There is generally a continuous succession of teeth throughout life, -the new tooth coming up below, or partly at the side of the one in -use, and causing the absorption of part of its wall or base. In this -way the new tooth comes to lie in the pulp cavity of the old one. This -method of succession is well seen in the Crocodilia. - -[Illustration FIG. 50. PREPARATION OF PART OF THE RIGHT MANDIBULAR -RAMUS OF _Crocodilus palustris_ × 1/2. (Brit. Mus.) - - 1. tooth in use. - 2. fairly old germ of future - tooth. - 3. symphysial surface of the - mandible.] - -Teeth have been detected in embryos of _Trionyx_, but otherwise no -teeth are known to occur in Chelonia, or in _Pteranodon_ -(Pterosauria), while the anterior part of the jaw is edentulous in -_Iguanodon_, _Polyonax_ and some other Dinosaurs, and in -_Rhamphorhynchus_. - - -ENDOSKELETON. - - -VERTEBRAL COLUMN. - -The vertebral column is commonly divisible into the usual five -regions, but in the Ophidia, Ichthyosauria, and Amphisbaenidae among -Lacertilia, only into caudal and precaudal regions. In the Chelonia -there are no lumbar vertebrae. - -The form of the vertebral centra is very variable. A large proportion -of extinct reptiles,--several entire orders,--and the earlier and more -primitive forms in some of the other groups have amphicoelous -vertebrae. Vertebrae of this type occur in the Theromorpha, -Ichthyosauria, most Sauropterygia and Rhynchocephalia, and many -Dinosauria, also in some of the early Crocodilia such as _Belodon_, -_Teleosaurus_ and _Goniopholis_, and the Geckonidae among Lacertilia. - -The majority of living reptiles have procoelous vertebrae. Thus they -occur in the Lacertilia (excluding the Geckos), the Ophidia, and the -Crocodilia, also among extinct forms in the Pterosauria and many -Dinosauria. On the other hand some Dinosauria such as _Iguanodon_ have -opisthocoelous cervical vertebrae, while others have opisthocoelous -thoracic vertebrae. The vertebrae of the Ceratopsidae and some -Sauropterygia, the thoracic vertebrae of _Iguanodon_, and the sacral -vertebrae of Crocodilia have flat centra. The first caudal vertebra of -modern Crocodilia is biconvex, and in the Chelonia all types of -vertebral centra are found. The cervical vertebrae of _Sphenodon_ are -noticeable for the occurrence of a small pro-atlas, which may -represent the neural arch of a vertebra in front of the atlas. - -In most reptiles the vertebrae are fully ossified, but in some of the -more primitive forms the notochord persists in the centre of the -vertebra (i.e. intervertebrally), this is the case for instance in -many of the Theromorpha and Rhynchocephalia, and also in the Geckos. -In other reptiles it persists longest intravertebrally. - -The centrum of each of the caudal vertebrae of most Lacertilia is -traversed by an unossified septum along which it readily breaks. - -Chevron bones occur below the caudal vertebrae in Lacertilia, -Chelonia, Ichthyosauria, many Dinosauria, and _Sphenodon_, -articulating with quite the posterior part of the centrum which bears -them. In Lacertilia and Crocodilia (fig. 41, 3) the axis has a -well-marked odontoid process. The ventral portions of the -intervertebral discs are sometimes ossified, forming wedge-shaped -inter centra, as in Geckos, and the cervical vertebrae of _Sphenodon_. - -In snakes, Theropod Dinosaurs, and the iguanas among lizards, the -neural arches are provided with _zygosphenes_, and _zygantra_. - -The neural arches are usually firmly ankylosed to the centra, but in -the Crocodilia and some Chelonia, Sauropterygia, and Dinosauria, the -suture between the centrum and neural arch persists at any rate till -late in life. In the Ichthyosauria the neural arches were united to -the centra by cartilage only. - -The thoracic vertebrae of some of the Theromorpha (_Dimetrodon_) are -remarkable for the extraordinary development of the neural spine, and -those of Chelonia for the absence of transverse processes. - -In living reptiles the number of sacral vertebrae is nearly always -two, but in the Theromorpha, Dinosauria, and Pterosauria, as many as -five or six bones may be ankylosed together in the sacral region. In -Crocodiles the two halves of the pelvis sometimes articulate with -different vertebrae. The vertebrae of some of the great Sauropoda are -remarkably hollowed out, having a large vacuity on each side of the -centrum communicating with a series of internal cavities. The whole -structure of these vertebrae shows a combination of great strength -with lightness. - - -THE SKULL. - -The reptilian skull is well ossified and the bones are noticeable for -their density. The true cranium is often largely concealed by a -secondary or false roof of membrane bones, which is best seen in the -Ichthyosauria and some of the Chelonia. In other reptiles the false -roof is more or less broken up by vacuities exposing the true cranial -walls. The ethmoidal region is the only one in which much of the -primordial cartilaginous cranium remains. The lateral parts of the -sphenoidal region are also as a rule not well ossified. - -In some reptiles, such as most Lacertilia and Chelonia, the orbits are -separated only by the imperfect interorbital septum, while in others, -such as the Ophidia, Crocodilia and Amphisbaenidae, the cranial cavity -extends forwards between the orbits. - -In the occipital region all four bones are ossified. The great -majority of reptiles have a single convex occipital condyle, but some -of the Theromorpha such as _Cynognathus_ have two distinct condyles as -in mammals. Sometimes, as in Chelonia, Ophidia and Lacertilia, the -exoccipitals, as well as the basi-occipital, take part in the -formation of the single condyle; sometimes, as in Crocodiles, it is -formed by the basi-occipital alone, as in birds. The relations of the -bones to the foramen magnum vary considerably, in Chelonia the -basi-occipital generally takes no part in bounding it, and in the -Theromorpha, Crocodilia, and Ophidia, the supra-occipital is excluded. -The parietals are paired in Geckos and Chelonia alone among living -forms, and in the extinct Ichthyosauria and some Theromorpha; in all -other reptiles they are united. - -The frontals are paired in Ichthyosauria (fig. 32, 5), Chelonia, -Ophidia, _Sphenodon_ (fig. 52, B, 4) and some extinct crocodiles, such -as _Belodon_. They are completely fused in living Crocodilia and some -Lacertilia and Dinosauria. In the gigantic _Polyonax_ they are drawn -out into a pair of enormous horns, and the parietals and squamosals -are greatly expanded behind. - -An interparietal foramen occurs in the Theromorpha, the Ichthyosauria -(fig. 32, 10), _Sphenodon_, the Sauropterygia and most Lacertilia. -The posterior part of the skull is curiously modified in some -Chamaeleons, the parietals and supra-occipitals being drawn out into a -backwardly-projecting sagittal crest which unites with the two -prolongations from the squamosals. In other Chamaeleons (_C. bifidus_) -prolongations of the prefrontals and maxillae form large -forwardly-projecting bony processes. - -The roof of the skull is characterised by the development of -prefrontals and postfrontals, which lie respectively near the anterior -and posterior extremity of the orbit. In Theromorpha, Squamata, -Crocodilia, and some Dinosauria lachrymals are developed. There is a -ring of bones in the sclerotic in the Ichthyosauria (fig. 32, 15), the -Metriorhynchidae among Crocodiles and some Rhynchocephalia, -Dinosauria, and Pterosauria. - -The pro-otic lies in front of the exoccipital and together with the -opisthotic forms the hind border of the fenestra ovalis. In Chelonia -the opisthotic remains separate, in all other living reptiles it fuses -with the exoccipital. The epi-otic fuses with the supra-occipital. - -The parasphenoid, so important in Ichthyopsids, has very often -disappeared completely; it is present, however, in the Ichthyosauria, -the Plesiosauridae, and a number of Squamata, in many Ophidia its -anterior part forming the base of the interorbital septum. - -In the Plesiosauridae and most Lacertilia, but not in the -Amphisbaenidae, a slender bone, the epipterygoid, occurs uniting the -parietal or the anterior end of the pro-otic with the pterygoid. A -homologous arrangement occurs in the Ichthyosauria and some Chelonia. - -In most reptiles a transpalatine occurs, connecting the maxillae with -the pterygoid, but this is absent in the Chelonia, and some -Dinosauria, and in the Typhlopidae among snakes. - -The quadrate is always well developed, and except in the Squamata is -firmly fixed to the surrounding bones. The Chamaeleons also, among the -Squamata, have a fixed quadrate, and in them too the quadratojugal is -absent. Separate nasal bones do not occur in any living Chelonia. - -The vomers are generally paired as in Squamata, sometimes unpaired as -in Chelonia. - -[Illustration FIG. 51. DORSAL (TO THE LEFT) AND VENTRAL (TO THE RIGHT) -VIEWS OF THE SKULL OF THE COMMON SNAKE (_Tropidinotus natrix_). (After -PARKER.) - - 1. premaxillae (fused). - 2. anterior nares. - 3. nasal. - 4. prefrontal. - 5. frontal. - 6. parietal. - 7. maxillae. - 8. transpalatine. - 9. palatine. - 10. pterygoid. - 11. pro-otic. - 12. exoccipital. - 13. supra-occipital. - 14. opisthotic. - 15. epi-otic. - 16. quadrate. - 17. parasphenoid. - 18. basisphenoid. - 19. basi-occipital. - 20. occipital condyle. - 21. splenial. - 22. dentary. - 23. angular. - 24. articular. - 25. supra-angular. - 26. coronoid. - 27. vomer. - 28. squamosal. - - IX, X foramina for the ninth - and tenth cranial nerves.] - -The disposition of the bones of the jaws is subject to much -modification in the Ophidia in order to adapt them for swallowing very -large prey. The arrangements again differ greatly in the venomous and -non-venomous snakes. In the non-venomous snakes, such as _Python_ and -_Tropidonotus_, the palatine is large and is fixed to the pterygoid -which extends outwards (fig. 51, 10) so as to be united to the -quadrate, and is at the same time firmly connected by the -transpalatine with the maxillae. The quadrate is united to the -squamosal, which is loosely attached to the cranium. The premaxillae is -moderately developed and bears teeth, and the maxillae forms a long bar -loosely connected with the rest of the skull. The rami of the mandible -are united only by an extremely elastic ligament. It is as regards the -maxillae and premaxillae that the skulls of venomous and non-venomous -snakes differ most. In the rattlesnake (_Crotalus_) and other venomous -snakes the premaxillae is extremely small and toothless. The maxillae is -small and subcylindrical, and is movably articulated to the lachrymal, -which also is capable of a certain amount of motion on the frontal. -The maxillae is connected by means of the transpalatine with the -pterygoid, which in its turn is united to the quadrate. When the mouth -is shut the quadrate is directed backwards, and carrying back the -pterygoid and transpalatine pulls at the maxillae and causes its -palatal face, to which the poison teeth are attached, to lie back -along the roof of the mouth. When the mouth opens the distal end of -the quadrate is thrust forward, and this necessitates the pushing -forward of the pterygoid and transpalatine, causing the tooth-bearing -surface of the maxillae to look downwards and the tooth to come into -the position for striking. - -The Ophidian skull is also noticeable for the absence of the jugals -and quadratojugals. In poisonous snakes the place of the jugal is -taken by the zygomatic ligament which connects the quadrate and -maxillae. - -The extent to which the palate is closed in reptiles varies much. In -many reptiles, such as the Squamata and Ichthyosauria, the palate is -not complete, both palatines and pterygoids being widely separated in -the middle line. In others, such as the Crocodilia, Sauropterygia, and -Chelonia, there is a more or less complete bony palate. In many -Chelonia this is chiefly formed of the vomer, palatines, and -pterygoids, the posterior nares being mainly bounded by the palatines. -In living Crocodilia, however, outgrowths are formed from the -pterygoids and palatines which arch round and meet one another -ventrally, forming a secondary palate (fig. 43, A), which completely -shuts off the true sphenoidal floor of the skull, and causes the -posterior nares which are bounded by the pterygoids to open very far -back. Though this feature is common to all postsecondary crocodiles, -it is interesting to notice that it is not found in the earlier forms, -but that its gradual evolution can be traced. In the Triassic -_Belodon_, for instance, the posterior nares open far forwards, and -are not surrounded by either the palatines or pterygoids. In the -Jurassic crocodile, _Teleosaurus_, the posterior nares lie further -back, being surrounded by the palatines, but the pterygoids do not -meet them. Finally, in the Tertiary forms the arrangements are as in -living crocodiles. - -A short secondary hard palate is found also in the Theriodontia. The -palatines of _Ichthyosaurus_ are noticeable for their transverse -position, which recalls that in the Frog. - -The various =fossae= or =vacuities= in the false roof of the skull are -important, and their relations may best be understood by a description -of their mode of occurrence in _Sphenodon_, a form in which they are -very completely developed. - -[Illustration FIG. 52. SKULL OF HATTERIA. (_Sphenodon punctatus_). A, -lateral; B, dorsal; C, ventral; D, posterior. (After VON ZITTEL.) - - 1. premaxillae. - 2. nasal. - 3. prefrontal. - 4. frontal. - 5. postfrontal. - 6. parietal. - 7. squamosal. - 8. quadratojugal. - 9. quadrate. - 10. postorbital. - 11. jugal. - 12. maxillae. - 13. vomer. - 14. palatine. - 15. pterygoid. - 16. transpalatine. - 17. exoccipital. - 18. epipterygoid. - 19. basisphenoid. - 20. supratemporal fossa. - 21. infratemporal or lateral temporal - fossa. - 22. orbit. - 23. post-temporal fossa. - 24. foramen magnum. - 25. anterior nares. - 26. interparietal foramen. - 27. dentary. - 28. supra-angular. - 29. articular.] - -In _Sphenodon_, then, on the dorsal surface of the skull, are the -large =supratemporal fossae= (fig. 52, 20). Their inner margins are -separated from one another by the parietal walls of the cranium, while -externally each is bounded by a bony arch, the =supratemporal arcade=, -formed of the postfrontal, postorbital, and squamosal. Posteriorly the -boundary is formed by a =post-temporal bar=, formed by the parietal -and squamosal. Below the supratemporal arcade is another large -vacuity, the =infratemporal= or =lateral temporal fossa= (fig. 52, -21). This is bounded above by the supratemporal arcade, and is -separated from the orbit in front by the =postorbital bar=, formed by -the union of outgrowths from the jugals and postorbitals. Behind it is -bounded by a continuation of the post-temporal bar formed of the -squamosal and quadratojugal, and below by an =infratemporal arcade=, -which is chiefly composed of the quadratojugal and jugal. - -Below the post-temporal bar is a third vacuity, the =post-temporal -fossa= (fig. 52, D, 23), bounded above by the post-temporal bar and -below by the exoccipital and opisthotic. - -_Sphenodon_ and the Crocodilia are the only living reptiles with -complete supratemporal and infratemporal arcades, but they are both -present in the extinct Pterosauria and some Dinosauria. - -Supratemporal fossae, bounded below by supratemporal arcades, occur in -all reptiles except some Chelonia, the Ophidia, the Geckonidae among -Lacertilia, and the Pariasauria and others among Theromorpha; they are -specially large in _Nothosaurus_ among the Sauropterygia, _Dicynodon_ -among the Theromorpha, and many Crocodilia and Pterosauria. In some -Dinosaurs, such as _Ceratosaurus_, they are very small, while the -infratemporal fossae are correspondingly large. - -In _Elginia_[93] (Theromorpha) and some Chelonia, such as _Chelone_, -there are no fossae on the surface of the skull, a complete false roof -being developed; in other Chelonia, such as _Trionyx_, the true -cranium is freely visible, the only part of the false roof developed -being the infratemporal arcade. - -In many reptiles large =pre-orbital vacuities= occur; they are -specially large in the Pterosauria and in some of the Crocodilia and -Dinosauria (fig. 35, 3). In some Pterosauria they are confluent with -the orbits. - -The premaxillae are usually separate, but sometimes, as in some Ophidia -(fig. 51, 1), Chelonia, Lacertilia (Agamidae), and Dinosaurs -(Ceratopsia) they are united. In the Dinosaur _Hadrosaurus_ they are -exceedingly large and spatulate. In the Rhynchocephalian -_Hyperodapedon_ they are drawn out into a strongly curved beak. - -As regards the mandible, sometimes, as in most Rhynchocephalia, -Ophidia and Pythonomorpha, the rami have only a ligamental union; -sometimes, as in Crocodilia, the Rhynchosauridae and the majority of -Lacertilia, they are suturally united. In Chelonia (fig. 28, B, 12), -and apparently in Pterosauria, the two dentaries are completely fused -together. The sutures between the various bones of the lower jaw -usually persist, but in Ophidia those between the angular, -supra-angular, articular and coronoid are obliterated. There are -sometimes large vacuities in the mandible, as in Theromorpha, -Crocodilia, and some Dinosauria. In _Iguanodon_, _Polyonax_, -_Hypsilophodon_ and _Hadrosaurus_ among Dinosaurs the mandible has a -predentary or mento-meckelian bone which, in some cases at any rate, -was probably sheathed in a horny beak. - -The principal part of the auditory ossicular chain is formed by a -rod-like columella. The development of the hyoid apparatus varies, and -it often happens that the first branchial arch is better developed -than is the hyoid arch. In the Crocodilia and Chelonia there is a -large basilingual plate or body of the hyoid (fig. 53, 1); but while -in the Crocodilia the first branchial forms the only well-developed -arch, in the Chelonia the first and second branchials are both -strongly developed, and the hyoid is often fairly large. - - -THE RIBS. - -[Illustration FIG. 53. HYOIDS OF AN ALLIGATOR (_Caiman latirostris_) -(TO THE LEFT) AND OF A GREEN TURTLE (_Chelone midas_) (TO THE RIGHT) × -5/8. (Brit. Mus.) - -The cartilaginous portions are dotted. - - 1. basilingual plate or body of - the hyoid. - 2. hyoid arch. - 3. first branchial arch (anterior - cornu). - 4. second branchial arch (posterior - cornu).] - -Ribs are always present, and may be attached to any of the precaudal -vertebrae. In most reptiles the posterior cervical vertebrae bear -ribs, while the atlas and axis are ribless; in Crocodiles and Geckos, -however, ribs are borne even by the atlas and axis. On the other hand, -in the Chelonia none of the cervical vertebrae bear obvious ribs. In -the following groups the thoracic ribs have both capitula and -tubercula--Theromorpha, Ichthyosauria, Crocodilia, Dinosauria, -Pterosauria. In the other groups each rib articulates by a single -head, and the position of the facet is subject to a considerable -amount of variation, thus in the Squamata it lies on the centrum, and -in the Sauropterygia on the neural arch, while in the Chelonia the rib -articulates with the contiguous parts of two centra instead of -directly with one. - -In most reptiles a greater or smaller number of ribs are united -ventrally with a sternum; but in snakes a continuous series of similar -ribs, all articulating freely with the vertebral column, extends from -the third cervical vertebra to the end of the trunk. The number of -ribs connected with the sternum varies from three or four in Lizards -to eight or nine in Crocodiles. Those which reach the sternum are -nearly always divided into vertebral, sternal, and intermediate -portions, and as a rule only the vertebral portion is completely -ossified. In Crocodiles a number of sternal ribs are connected with a -cartilaginous arch, which is attached to the hind end of the sternum, -and represents the xiphisternum. The sacral ribs connecting the -vertebral column with the ilia are very distinct in Crocodiles; in -these animals and _Sphenodon_ the vertebral ribs have backwardly -projecting uncinate processes as in birds. - -In the curious arboreal lizard, _Draco volans_, the posterior ribs are -long and straight, and support a parachute-like expansion of the -integument used in its long flight-like leaps. In Chelonia the ribs -are generally combined with the carapace. - -In Ichthyosauria, Sauropterygia, Crocodilia and _Sphenodon_, abdominal -splint ribs occur; and probably all except the first of the paired -ossifications forming the plastron of Chelonia are of similar -character. Abdominal ribs have quite a different origin from true -ribs, for while true ribs are cartilage bones, abdominal ribs have no -cartilaginous precursors, but are simply the ossified tendons of the -rectus abdominalis muscle. - - -THE STERNUM. - -A sternum occurs in the following groups of reptiles: Rhynchocephalia, -nearly all Lacertilia, Pythonomorpha, Crocodilia, and Pterosauria, and -is generally more or less rhomboidal or shield-shaped. In Pterosauria -it is keeled and bears some resemblance to that of birds. It may have -been replaced by membrane bone. - -[Illustration FIG. 54. VENTRAL VIEW OF THE SHOULDER-GIRDLE OF STERNUM -OF A LIZARD (_Loemanctus longipes_) × 2. (After PARKER.) - - 1. interclavicle. - 2. clavicle. - 3. scapula. - 4. coracoid. - 5. precoracoidal process. - 6. glenoid cavity. - 7. sternum. - 8. xiphisternum. - 9. sternal rib.] - -The sternum is absent in Sauropterygia, Ichthyosauria, Chelonia, -Ophidia, and most of the snake-like Amphisbaenidae among Lacertilia; -while it is not well known in Theromorpha and Dinosauria. In the -Sauropod _Brontosaurus_, however, two rounded bones occur near the -base of the coracoids, and these probably represent ossified patches -in a sternum, which was mainly cartilaginous; similar structures occur -in _Iguanodon_. - -The sternum frequently remains wholly cartilaginous, especially in -Lacertilia; sometimes it becomes calcified, but true ossification does -not as a rule take place. - - -APPENDICULAR SKELETON. - - -THE PECTORAL GIRDLE. - -The pectoral girdle is well developed in all groups of reptiles except -the Ophidia, occurring even in the limbless Amphisbaenidae. It is very -solid in the Theromorpha. As a rule all three cartilage bones, -scapula, coracoid, and precoracoid are represented, and frequently -also the membrane bones,--clavicles, and interclavicle. - -The coracoids are generally flat expanded bones, which sometimes, as -in Sauropterygia and Ichthyosauria, meet in a ventral symphysis; -sometimes, as in Lacertilia, are united with the sides of the sternum. -In Chelonia neither the coracoids nor precoracoids meet one another, -but their free ends are connected by fibrocartilaginous bands. In -Lacertilia the coracoids are pierced by fenestrae. - -The precoracoid is generally represented, but the Theromorpha are the -only reptiles in which it is separately ossified; it forms a -well-marked process on the coracoid in Lacertilia (fig. 54, 5). It is -absent in Ichthyosauria, and Dinosauria, and probably in -Sauropterygia. In some Lacertilia and Chelonia the sternal ends of the -coracoids are unossified and form epicoracoids; in some Chelonia there -are also epiprecoracoids; but neither these nor the epicoracoids -overlap their fellows of the opposite side as they do in arciferous -Anura (see p. 185). In some Lacertilia with degenerate limbs the -pectoral girdle is also much reduced, in _Ophisaurus apus_ the ventral -borders of the coracoids are widely separated. - -A scapula is always present, and is generally expanded distally, but -in the Chelonia the distal end is cylindrical. In the Theromorpha it -has an acromial process with which the precoracoid articulates, and it -is very large in Dinosauria. In the Chelonia the scapula and -precoracoid are ossified continuously. Among the Pterosauria, -_Pteranodon_ has an unique pectoral girdle; the scapula and coracoid -are ankylosed and the scapula articulates with the neural spines of -several ankylosed vertebrae. - -Clavicles occur in some Theromorpha such as _Pariasaurus_, and also in -the Ichthyosauria, Sauropterygia, Rhynchocephalia, and most -Lacertilia. They are absent in the Pterosauria, the Chamaeleons among -Lacertilia, the Ophidia and the Crocodilia. They are wanting too in -the Chelonia, unless the first pair of ossifications in the plastron -are to be regarded as clavicles. In the Sauropterygia bones regarded -as the clavicles and interclavicle are generally well developed. The -unpaired ossification in the plastron of Chelonia is an interclavicle, -and a representative of the same bone occurs arising from the sternum -in Pterosauria. A well developed =T=-shaped interclavicle is found in -Ichthyosauria, Rhynchocephalia, Lacertilia, and some Theromorpha, such -as _Pariasaurus_. - - -THE LIMBS. - -In most reptiles there are two pairs of pentedactylate limbs provided -with claws, but in nearly all Ophidia and some Lacertilia -(_Amphisbaena_, _Lialis_, _Anguis_) the limbs have entirely -disappeared. In a few Ophidia such as _Python_ traces of the posterior -limbs occur, and in _Chirotes_ among the Amphisbaenidae there are -minute anterior limbs. The Lacertilians, _Chalcides_ (_Seps_) and -_Ophisaurus_ (_Bipes_, _Pseudopus_) have very small posterior limbs. - -The limbs are as a rule adapted for walking, but in Ichthyosauria, -Sauropterygia, Pythonomorpha and some Chelonia, they have the form of -swimming paddles, the relative size of the manus and pes being -increased, while that of the proximal and middle portions of the limbs -is reduced. This reduction is carried to its furthest extent in the -Ichthyosauria in which radius and ulna, tibia and fibula, have the -form of short polygonal bones similar to those constituting the manus -and pes. In the Pythonomorpha the reduction of the limb bones is not -quite so marked, in the Sauropterygia it is less, and still less in -the Chelonia. In the earlier Ichthyosauria too, the limb bones are not -so short as they are in the later forms. The Ichthyosaurian limb is -also remarkable, firstly for the fact that both humerus and femur are -terminated by concave articulating surfaces instead of by convex -condyles, and secondly for the great multiplication of the phalangeal -bones, each digit being sometimes composed of a series of over twenty. -Sometimes too the number of series is increased, either by the -bifurcation of some of the digits or by the development of marginal -bones. In the Sauropterygia the phalanges are likewise increased above -the normal but not so much as in Ichthyosauria. The humerus and femur -of Sauropterygia are noticeable for the enormous size of the terminal -epiphyses which form in each case by far the greater part of the bone. - - -THE ANTERIOR LIMB. - -The anterior limb is usually approximately equal in length to the -posterior, but in many Dinosauria it is considerably the shorter of -the two. The humerus is generally without distinct condyles, but they -are well developed in the Theromorpha, the Lacertilia and _Sphenodon_. - -In the Theromorpha, some Rhynchocephalia, and some Sauropterygia, such -as _Mesosaurus_, the humerus has an ent-epicondylar foramen; in -Lacertilia, Chelonia and some Dinosauria there is an ect-epicondylar -foramen or groove; _Sphenodon_ possesses both ent- and ect-epicondylar -foramina. The radius and ulna are always separate. In some Chelonia, -such as _Chelydra_, the carpus has a very simple arrangement, namely, -a proximal row of three bones, the radiale, intermedium and ulnare, -and a distal row of five carpalia, with one bone, the centrale, -between the two rows. Many reptiles have a carpus only slightly -different from this. Thus the carpus in _Sphenodon_ differs mainly in -having two centralia, that of most Lacertilia, in having the centrale -and intermedium fused. - -Crocodiles have a much reduced carpus with the radiale and ulnare -considerably elongated. The manus in Chamaeleons is curiously -modified, having the first three digits arranged in one group and -turned inwards, and the fourth and fifth in another group turned -outwards; carpalia 3 and 4 are united. - -In the Pterosauria the anterior limbs form wings, the phalanges of the -fifth digit being very greatly elongated to support the wing membrane. -The first digit is vestigial and the second, third, and fourth are -clawed. - - -THE PELVIC GIRDLE. - -The pelvic girdle is well developed in all reptiles which have -posterior limbs, but is absent or quite vestigial in Ophidia and those -Lacertilia which have no posterior limbs. The ilium and ischium agree -in their general characters throughout all the various groups of -reptiles, but that is not the case with the pubis. - -In many reptiles such as Chelonia, Ichthyosauria and Lacertilia the -ilia are small, more or less cylindrical bones either directed -backwards, or vertically placed as in the Chamaeleons. In the -Crocodilia they are larger and more expanded, while in Dinosauria and -Pterosauria they are greatly elongated both in front of, and behind, -the acetabulum. The ischia are generally strongly developed somewhat -square bones meeting in a ventral symphysis. In Dinosauria the ischium -(fig. 35, 9) is a much elongated and backwardly-directed bone, -bearing a forwardly projecting obturator process. In Pterosauria the -ischium is fused with the ilium, and in both pterosaurs and crocodiles -the ilium and ischium are the only bones taking part in the formation -of the acetabulum. In most Lacertilia there is an unpaired structure, -the _hypo-ischium_ or _os cloacae_ projecting back from the symphysis -ischii, which is usually separated from the symphysis pubis by a large -space, the _foramen cordiforme_. In some Lacertilia and Chelonia there -is a cartilaginous bar dividing the foramen cordiforme into two -obturator foramina; in many Chelonia this bar is ossified. Among -_Ophidia_, _Python_, _Tortrix_, _Typhlops_ and their allies have a -structure representing a vestigial ischio-pubis: but in most Ophidia -there is no trace of the pelvis. In some Theromorpha all the bones of -the pelvis are completely fused, forming an os innominatum as in -mammals; the pubes and ischia are so completely fused that sometimes -as in _Pariasaurus_ even the obturator foramina are closed. - -Concerning the reptilian pubis there are considerable difficulties. -Sometimes there is only a single pubic structure present, sometimes -there are two. The reptilian pubis is best understood by comparing the -arrangements met with in the various other groups with that in the -Orthopod Dinosaurs such as _Iguanodon_. In _Iguanodon_ the pubis -consists of two portions, viz. of a moderately broad pre-pubis -directed downwards and forwards, and of a narrow greatly elongated -post-pubis directed backwards parallel to the ischium. The pubis is -united to both ilium and ischium, the acetabulum has a large -unossified space, and neither pre-pubes nor post-pubes meet in ventral -symphyses. The arrangement bears a great resemblance to that of Ratite -birds. In Lacertilia, Chelonia, Rhynchocephalia and Ichthyosauria -together with Theropod and Sauropod Dinosaurs the pubis corresponds to -the pre-pubis of _Iguanodon_ and is a more or less cylindrical bone -expanded at both ends, meeting its fellow in a ventral symphysis. In -Chelonia and Lacertilia the pubis bears a lateral process which is -homologous with the post-pubis of Iguanodon. In Lacertilia and -sometimes in Chelonia there is a cartilaginous epipubis attached to -the anterior border of the pubic symphysis; this is well developed in -the Chamaeleons and Geckos. In Crocodilia there is, forming the -anterior and ventral portion of the acetabulum, a patch of cartilage -(fig. 49, 3) which is probably the true pubis homologous with that of -lizards and with the pre-pubis of _Iguanodon_. The large bone -generally called the pubis in Crocodiles is probably an epipubis. - - -THE POSTERIOR LIMB. - -The posterior limb is entirely absent in some Lacertilia and in most -Ophidia, though traces occur in _Python_, _Tortrix_ and _Typhlops_. In -the Ichthyosauria, Sauropterygia and Pythonomorpha the posterior limbs -form swimming paddles and have been already referred to. - -The arrangement of the proximal and middle segments of the limb is -fairly constant in all reptiles with limbs adapted for walking, and -the tibia and fibula are always separate. The pes is however subject -to a considerable amount of variation, especially as regards the -tarsus. In some Chelonia the tarsus like the carpus has an extremely -simple arrangement, consisting of a proximal row of three bones, the -tibiale, intermedium and fibulare, a centrale, and a distal row of -five tarsalia. In most living reptiles, however, the tibiale and -intermedium are as in mammals united, forming the astragalus. In -Crocodiles (fig. 48, B, 15) the centrale is also united with the -tibiale while the distal tarsalia are very slightly developed. The -calcaneum in Crocodiles is drawn out into a long process forming a -heel in a manner almost unique among Sauropsida. In _Sphenodon_ and -Lacertilia the tibia and fibula articulate with a single large bone -representing the whole proximal row of tarsalia. - -The pes is generally pentedactylate, but in some Crocodiles the fifth -digit is vestigial (fig. 48, B), and in some Dinosauria (fig. 35) -there are only three digits. The North American Dinosaurs present a -continuous series ranging from a pentedactylate plantigrade form like -_Morosaurus_, to such a form as _Hallopus_ with a highly digitigrade -and specialised pes reduced to three functional digits, and a -vestigial fifth metatarsal. The second, third and fourth metatarsals -in this form are nearly two-thirds as long as the femur, and the -calcaneum is drawn out into a heel much as it is in most mammals. - -In Lacertilia, Orthopoda and many Chelonia, the ankle joint comes to -lie between the proximal and distal row of tarsals as in birds. - - -FOOTNOTES: - -[91] See pp. 214 and 215. - -[92] These terms are defined on p. 199. - -[93] E.T. Newton, _Phil. Trans._ vol. CLXXXIV, B, p. 431 (1893). - - - - -CHAPTER XVII. - -CLASS. AVES[94]. - - -Birds form a large and extremely homogeneous class of the vertebrata, -and are readily distinguished from all other animals by the possession -of an epidermal exoskeleton having the form of feathers. Feathers -differ from hairs in the fact that they grow from papillae formed of -both the horny and the Malpighian layer of the epidermis, which -papillae at first project from the surface, and only subsequently -become imbedded in pits of the dermis. A dermal exoskeleton does not -occur in birds. - -The endoskeleton is characterised by its lightness, the large bones -being generally hollow; but the pneumaticity does not vary in -proportion to the power of flight. The cervical part of the vertebral -column is very long and flexible, while the post-cervical portion is -generally very rigid, owing to the fusion of many of the vertebrae, -especially in the lumbar and sacral regions. The vertebrae are -generally without epiphyses to their centra. The cervical vertebrae in -living forms have saddle-shaped articulating surfaces, and many of -them bear ribs. The thoracic ribs in almost all birds have large -uncinate processes. The sternum is very large, and the ribs are always -attached to its sides, not as in many reptiles to anybackwardly -projecting process or processes. The sternum ossifies from two or more -centres. - -The skull is extremely light, and its component bones show a great -tendency to fuse together completely. The facial part of the skull is -prolonged into a beak, chiefly formed of the premaxillae; this beak is -in all modern birds devoid of teeth, and is coated externally with a -horny epidermal sheath. The quadrate is large and freely movable. The -supratemporal arcade[1] is imperfect, while the infratemporal -arcade[95] is complete. There are no postorbital or postfrontal bones. -Neither parotic processes nor an interparietal foramen occur. There -are commonly large pre-orbital vacuities. The palatines and pterygoids -never form a secondary bony palate as in Crocodiles. Part of the floor -of the skull is formed by a wide _basitemporal_ (paired in the embryo) -which is continued in front as a long slender _rostrum_; these -structures have replaced the parasphenoid of Ichthyopsids. Cartilage -or bone is always developed in the sclerotic. The first branchial arch -is well developed, the hyoid arch but slightly. The coracoids are -large, and the clavicles are nearly always united forming the -_furcula_. There is no separate interclavicle and hardly any trace of -a precoracoid. - -The anterior limbs form wings, and the manus is in the adult always -much modified, never having more than three digits. The three bones of -the pelvis are, except in Archaeornithes, always ankylosed together in -the adult, and the ilium is greatly prolonged in front of the -acetabulum, which is perforated. The ilia are not connected with the -sacrum by ossified sacral ribs. The pubes and ischia are directed -backwards parallel to one another, and except in a very few forms -never meet their fellows in ventral symphyses. The fibula is generally -much reduced. The proximal tarsal bones are always ankylosed to the -tibia, and the distal tarsals to the metatarsals, so that the ankle -joint is _intertarsal_. The first metatarsal is nearly always free. -The pes never has more than four digits in the adult. - -The class Aves is most conveniently divided into two subclasses: 1. -Archaeornithes. 2. Neornithes. - - -Subclass I. ARCHAEORNITHES. - -The only form referred to this subclass of extinct birds is -_Archaeopteryx_[96], the earliest known bird. In this animal the -skeleton does not seem to be pneumatic. The cervical and trunk -vertebrae are generally thought to be flat, certainly their -articulating surfaces are not saddle-shaped. There is no long compound -sacrum as in modern birds. The tail is longer than the whole body, the -caudal vertebrae are twenty in number, they gradually taper as traced -away from the trunk, and each bears a pair of feathers. The posterior -caudal vertebrae are not united together to form a _pygostyle_. The -upper jaw bears thirteen pairs of conical teeth, planted in distinct -sockets in the maxillae and premaxillae, but the mandible has only three -pairs. The presence of these teeth forms the most essential difference -between the skull of _Archaeopteryx_ and that of modern birds, and the -fact that they occur on the premaxillae renders it improbable that a -horny beak was present. There is a ring of ossifications in the -sclerotic. The ribs do not show uncinate processes, and articulate -with the vertebrae by single heads not divided into capitula and -tubercula. Abdominal ribs appear to have been present. The furcula is -large, and the scapula has a well developed acromion. The sternum is -unknown. The radius and ulna are approximately equal in size. In the -manus the first, second and third digits[97] are present, each -terminated by a claw. The second digit is considerably the longest, -while the third includes four phalanges. The three bones of the pelvis -probably remained distinct throughout life. The tarsals are ankylosed -respectively to the tibia and metatarsals as in other birds. The -metatarsals are ankylosed together, and the pes has four digits. - - -_Subclass II._ NEORNITHES. - -To this subclass may be referred all known birds except -_Archaeopteryx_. They all agree in having a short tail whose component -vertebrae are commonly ankylosed together forming a pygostyle. The -three metacarpals do not all remain distinct. The bones of the pelvis -are ankylosed together, and to a large though variable number of -vertebrae. There are three orders, the Ratitae, Odontolcae, and -Carinatae. - - -_Order_ 1. RATITAE. - -The Ratitae differ from _Archaeopteryx_ and the great majority of -Carinatae in being flightless. The bones are generally not pneumatic, -containing marrow instead of air, in the Ostrich however they are very -pneumatic. The tail is short and the posterior caudal vertebrae are -generally ankylosed together forming a pygostyle. The pectoral girdle -has comparatively a much smaller size than in Carinatae, clavicles are -small or absent, and the scapula and coracoid lie nearly in the same -straight line. The ilium and ischium do not as in Carinatae unite -posteriorly, and enclose a foramen except in very old Rheas and Emeus. -The quadrate articulates with the cranium by a single head. The vomers -unite and form a broad plate, separating the palatines, pterygoids and -basisphenoidal rostrum. - -The anterior limbs are greatly reduced in size or even absent, while -the posterior limbs are greatly developed and adapted for running. The -tibia and fibula are quite distinct. - -Many ornithologists agree that the various forms grouped together as -Ratitae are not all very closely allied to one another, that they -resemble one another mainly in having lost the power of flight, and do -not form a natural group. - -The Ratitae include the following groups:-- - -_Æpyornithes_[98], huge extinct birds from Madagascar. - -_Apteryges_, including the Apteryx of New Zealand. - -_Dinornithes_[99], the Moas, huge extinct birds from New Zealand, and -some of the neighbouring islands. - -_Megistanes_, including the Cassowaries (_Casuarius_) of Australia, -New Guinea, and some of the neighbouring islands; and the Emeus -(_Dromaeus_) of Australia. - -_Rheornithes_, including the Rheas of S. America. - -_Struthiornithes_, including the Ostriches (_Struthio_) now living in -Africa, and found fossil in N. India and Samos. - - -_Order_ 2. ODONTOLCAE. - -This order includes only an extinct N. American bird -_Hesperornis_[100]. The jaws are provided with a series of sharp teeth -placed in continuous grooves, but the premaxillae are toothless, and -were probably sheathed in a horny beak. The rami of the mandible are -not ankylosed together in front. The skeleton is not pneumatic. The -cervical vertebrae have saddle-shaped articulating surfaces as in -ordinary birds, and the thoracic vertebrae are not ankylosed together. -The tail is comparatively long, and formed of twelve vertebrae with -only slight indications of a pygostyle. The ribs have uncinate -processes. The anterior limb is quite vestigial, being reduced to a -slender humerus. The posterior limb is very powerful and adapted for -swimming. - - -_Order_ 3. CARINATAE. - -This order includes the vast majority of living birds. The cervical -vertebrae have saddle-shaped articulating surfaces (except in the -Ichthyornithiformes). The posterior caudal vertebrae are ankylosed -forming a pygostyle. The quadrate articulates with the cranium by a -double head. In all except the Tinamidae the vomers are narrow behind -and not interposed between the palatines, pterygoids and -basisphenoidal rostrum. The sternum has a median keel, and the -anterior limbs are in the great majority of cases adapted for flight. -Clavicles are well developed, and the scapula and coracoid are nearly -at right angles to one another. The various groups into which the -Carinatae are divisible are shown in the table on pp. 40-42. Their -special characters will not be dealt with. - -[Illustration FIG. 55. _Gallus bankiva_ var. _domesticus_. THE LEFT -HALF OF THE SKELETON. The skull, vertebral column, and sternum are -bisected in the median plane. (After Marshall and Hurst.) - -A, acetabulum. B, cerebral fossa. CB, cerebellar fossa. CL, clavicle. -CO, coracoid. CR, cervical rib. C 1 = one, first cervical vertebra. -FE, femur. HC, ventral end of clavicle. HU, humerus. HY, hyoid. IF, -ilio-sciatic foramen. IL, ilium. IS, ischium. L, lachrymal. MC 3, -postaxial metacarpal. MN, mandible. MS, xiphoid processes. MT, -tarso-metatarsus. MT 1, first metatarsal. N, nasal. OP, optic foramen. -P, premaxillae. PB, pubis. PL, palatine. PY, pygostyle. R, radius. RC, -radial carpal. S, keel of sternum. SC, scapula. T, tibio-tarsus. TH 4, -fourth thoracic vertebra. U, ulna. UC, ulnar carpal. UP, uncinate -process. Z, infra-orbital bar. 1, 2, 3, 4, first, second, third and -fourth digits of pes. 3, pre-axial, 4, middle, and 5, postaxial digit -of manus.] - - -FOOTNOTES: - -[94] M. Fürbringer, _Untersuchungen zur Morphologie und Systematik der -Vögel_, I. and II. Amsterdam, 1888. Cf. H. Gadow, _Nature_, XXXIX. -1888, pp. 150 and 177. - -T.H. Huxley, "On the classification of birds." _P.Z.S._, London, 1867. - -E. Selenka and H. Gadow, _Vögel_ in Bronn's _Classen und Ordnungen des -Thierreichs_ 1869-1890. - -[95] See p. 283. - -[96] R. Owen, _Phil. Trans._, vol. CLIII., p. 33; 1863. T.H. Huxley, -_P. R.S._, vol. XVI., p. 243; 1868. C. Vogt, _Rev. Scient._, ser. 2, -tom. 9, p. 241; 1879. C.H. Hurst, _Nat. Sci._, vol. III., p. 275; -1893; vol. VI., pp. 112, 180, 244; 1895. W.P. Pycraft, _Nat. Sci._, -vol. V., pp. 350 and 437; 1894; and vol. VIII., p. 261; 1896. - -[97] According to Hurst the fourth and fifth digits are also present. - -[98] See C.W. Andrews, _P.Z.S._, 1894, p. 108. - -[99] See T.J. Parker, _Tr. Zool. Soc. London_, vol. XIII., pt. 2, -1895, and F.W. Hutton, several papers in _Tr. N. Zealand Inst._, 1893 -and 1895. - -[100] See O.C. Marsh. _Odontornithes. A monograph of the extinct -toothed birds of N. America._ New Haven, 1880. - - - - -CHAPTER XVIII. - -THE SKELETON OF THE WILD DUCK (_Anas boschas_). - - -I. EXOSKELETON. - -The exoskeleton of the Duck and indeed of all birds is entirely -epidermal in origin. Its most important part consists of =feathers=, -but it includes also the following horny structures:-- - -(_a_) =scales=, which cover the toes and tarso-metatarsus; - -(_b_) =claws=, which are attached to the distal phalanges of the toes -and of the pollex; - -(_c_) the wide =beak=, which sheaths both upper and lower jaws, and -whose edges are raised into lamellae, which act as strainers. - - -FEATHERS. - -A well developed feather, such as one of the large quill feathers of -the wing or tail, consists of the following parts: A main stem, the -=scapus=, which forms the axis running along the whole length of the -feather, and is divided into (1) a proximal hollow cylindrical -portion, the =calamus= or =quill=, and (2) a distal solid portion, the -=rachis= or =shaft=, which is square in section, flexible and grooved -along its ventral surface, and bears a number of lateral processes, -the =barbs=. The =calamus= which is partly imbedded in a pit in the -dermis, bears two holes: one, the =inferior umbilicus=, is at its -proximal end, and into it enters a vascular outgrowth from the dermis; -the other, the =superior umbilicus=, lies on the ventral surface at -the junction of the calamus and scapus. - -The =barbs= are a series of narrow elastic plates, attached by their -bases to the rachis, and with their edges looking upwards and -downwards. The barbs are connected together by a number of smaller -processes, the =barbules=, which interlock with one another by means -of hooklets, and bear the same relation to the barbs that the barbs do -to the rachis. The barbs and barbules, together with the rachis, -constitute the =vexillum= or =vane= of the feather. Any feather having -the above type of structure is called a =penna= or a =contour -feather=, from the fact that it helps to produce the contour of the -body. - - -VARIETIES OF FEATHERS. - -1. =Pennae.= There are two kinds of pennae or contour feathers. - -(_a_) The =quills=. These form the large feathers of the wing and -tail. They are divided into two groups, the =remiges=, or wing quills, -and the =rectrices=, or tail quills. - -The =remiges=[101] include three sets of feathers, the =primaries= or -=metacarpo-digitals=, which are attached to the bones of the manus, -the =secondaries= or =cubitals=, which are attached to the ulna, and -the =humerals=, which are attached to the humerus. - -The =primaries= differ from all the other quill feathers in having the -posterior half of the vane much wider than the anterior half. They are -ten in number, and of these six, the =metacarpal= quills (fig. 57, -14), are attached to the second and third metacarpals, one, the -=ad-digital= (fig. 57, 15), to the phalanx of the third digit, two, -the =mid-digitals= (fig. 57, 16), to the first phalanx of the second -digit, and two, the =pre-digitals= (fig. 51, 17), to the second -phalanx of the second digit. One of the pre-digitals is very small, -and is called the =remicle= (fig. 57, 11). - -[Illustration FIG. 56. THE WING OF A WILD DUCK (_Anas boschas_). - -The upper figure shows the dorsal side of a right wing, the lower -figure the ventral side of a left wing. × 1/3. (Brit. Mus.) - - 1. scapulars. - 2. tectrices marginales. - 3. tectrices minores. - 4. bastard wing. - 5. tectrices majores. - 6. metacarpo-digitals or primaries. - 7. tectrices mediae. - 8. cubitals or secondaries. - 9. pennae humerales. - 10. pennae axillares.] - -In addition, a group of three quill feathers is attached to the first -digit, constituting the =bastard wing= or =ala spuria= (fig. 56, 4). - -The =secondaries= or =cubitals= (fig. 56, 8) form a group of seventeen -feathers, attached to the ulna; they are shorter than the primaries, -and do not have the posterior half of the vane much wider than the -anterior half. - -The =humerals= (figs. 56, 9 and 57, 12) form a group of eight small -feathers, of varying length, attached to the anterior half of the -humerus. - -[Illustration FIG. 57. WINGS OF A WILD DUCK WITH THE COVERTS REMOVED -(_Anas boschas_). × 1/3. - -A. Right wing seen from the dorsal side. B. Left wing disarticulated -and seen from the ventral side. (Brit. Mus.) - - 1. humerus. - 2. radius. - 3. ulna. - 4. radial carpal. - 5. ulnar carpal. - 6. first phalanx of first digit. - 7. second metacarpal. - 8. third metacarpal. - 9. first phalanx of second digit. - 10. second phalanx of second digit. - 11. remicle. - 12. pennae humerales. - 13. cubitals or secondaries. - 14. metacarpal quills. - 15. ad-digital. - 16. mid-digitals. - 17. pre-digital.] - -(b) The =tectrices= or =coverts= are short feathers, which cover over -the quills of the rectrices and remiges, and clothe the body -generally. Their barbules are less developed than is the case with the -quill feathers, so that the barbs separate readily from one another, -especially at the base of the vane. The nomenclature of the various -patches of coverts on the wings is seen in fig. 56. A small patch of -backwardly-directed feathers surrounding the external auditory opening -are known as the =auriculars=. - -2. The =filoplumes= are rudimentary feathers, consisting of a minute -stem and slightly developed vane. They are left in the skin after the -other feathers have been removed. - -3. The =plumulae=, or down feathers, have the stem very slightly -developed, while the barbs are soft and free from one another. They -are distributed all over the body, not only among the contour -feathers, but also over the spaces (_apteria_) which bear no contour -feathers. - -In the young bird the rudiments of the new feathers are formed at the -bases of the embryonic down feathers, and as they grow they push them -out from the skin. The embryonic down feathers however remain attached -to the apices of the new feathers till these have reached a length of -about an inch; they are then shed. - - -II. ENDOSKELETON. - -As compared with that of the Turtle or Crocodile, the endoskeleton of -the Duck is characterised by: - -1. The great lightness of the bones, many of which contain air -cavities. - -2. The tendency to become ankylosed together shown by many of the -bones. - -3. The modification of the anterior limbs and girdle for the purpose -of flight. - - -1. THE AXIAL SKELETON. - -This, as in other vertebrates, is divisible into-- - - A. The vertebral column. - - B. The skull. - - C. The ribs and sternum. - - -A. THE VERTEBRAL COLUMN. - -The vertebral column of the duck, like that of the great majority of -birds, presents a number of well-marked characteristics, contrasting -strongly with those of the generality of higher vertebrates. The centra -are always without epiphyses. The neck is exceedingly long, about as -long as all the rest of the vertebral column put together, and is -remarkable for its flexibility. The trunk portion of the vertebral -column on the other hand is characterised by extreme rigidity, and -the marked tendency shown by the component vertebrae to fuse together -into one almost continuous mass. The most rigid part of the vertebral -column is that to which the pelvis is united, as no less than seventeen -vertebrae take part in the union. The tail of the duck, like that of -all living birds, is very short, and the posterior caudal vertebrae are -united together, forming the =pygostyle=. The vertebral column may be -divided into cervical, thoracic, lumbar, sacral, and caudal regions, -but the boundaries between the several regions are ill-defined. - - -THE CERVICAL VERTEBRAE. - -All the vertebrae anterior to the first one that bears a rib meeting -the sternum are regarded as cervical vertebrae. There are therefore -sixteen cervical vertebrae, the last two of which bear well developed -ribs. All are freely movable on one another. - -As a typical cervical vertebrae, any one from the fifth to the ninth -may be taken. The vertebra is rather elongated, and is very lightly -and strongly made, its most characteristic feature being the shape of -the articulating surfaces of the centra, which are generally described -as saddle-shaped. The anterior surface is convex from above downward, -and concave from side to side, while the posterior and more prominent -surface is concave from above downwards and convex from side to side. -The neural arch is low, and is drawn out into a slight blade-like -=neural spine=. Its base is deeply notched on both sides posteriorly -for the exit of the spinal nerves. Above these notches it is drawn out -into two rather prominent diverging processes, which bear the -=postzygapophyses=,--two flattened surfaces which look downwards and -outwards. The =transverse processes= form irregular outgrowths from -the anterior two-thirds of the sides of the vertebra; each projects -for a short distance downwards and outwards, and is terminated -posteriorly by a short backwardly-projecting spine. The transverse -processes are shown by development to ossify from separate centres, -and are therefore to be regarded as cervical ribs, and each is -perforated at its base by a canal for the passage of the vertebral -artery. Above the anterior end of the vertebrarterial canal are a pair -of thickened outgrowths, which bear upwardly and inwardly directed -=prezygapophyses=. Each transverse process is perforated near its -middle by a prominent foramen through which passes a vein which is -connected with the jugular vein. - -The third and fourth cervical vertebrae resemble the succeeding ones -in most respects, but have small =hypapophyses=, and the neural spines -are less blade-like. The posterior cervical vertebrae (tenth to -sixteenth) differ somewhat from the middle ones. They are shorter and -more massive, the neural arch is much shorter, being deeply notched in -the middle line in front and behind. The transverse processes arise -from the anterior half of the vertebra only, and in the eleventh -vertebra each is drawn out below into a pair of rather prominent -downwardly and inwardly directed processes. In the twelfth vertebra -these processes have almost coalesced, and in the thirteenth vertebra -they have coalesced completely, forming a prominent =hypapophysis=. In -the succeeding vertebrae this hypapophysis rapidly decreases in size. - -The fifteenth and sixteenth cervical vertebrae resemble the succeeding -thoracic vertebrae, having short thick centra and prominent squarely -truncated neural spines; the sides of the neural arches are very -deeply notched. The fifteenth vertebra has a short transverse process, -perforated by a wide vertebrarterial foramen, but this foramen is -absent in the sixteenth. The transverse processes of the fifteenth -vertebra bear two facets for the articulation of the capitulum and -tuberculum of the rib. The sixteenth vertebra has its tubercular facet -on the transverse process, but the capitular facet is borne on the -centrum. - -The second or =axis= vertebra is small, and has the centrum drawn out -into a comparatively very large hypapophysis. The posterior -articulating surface of the centrum is saddle-shaped, the anterior -nearly flat: above it the centrum is prolonged into the prominent -=odontoid process=, which is shown by development to be the detached -centrum of the atlas. The neural arch is deeply notched in the middle -line in front, and at the sides behind. It is drawn out posteriorly -into a wide massive outgrowth, which overhangs the third vertebra and -bears the downwardly-directed postzygapophyses. The prezygapophyses -are situated at the sides of the anterior end of the neural arch, and -look directly outwards. The transverse processes are very slightly -developed, and are pierced by the vertebrarterial canals. - -The =atlas= vertebra is a very slight ring-like structure, thickened -ventrally and bearing in front a prominent concave cavity for -articulation with the occipital condyle of the skull. Posteriorly it -bears a more or less flattened surface for articulation with the -centrum of the axis. It surrounds a large cavity partially divided -into a larger dorsal portion, which is the neural canal, and a smaller -ventral portion which lodges the odontoid process. The sides of the -atlas are pierced by the vertebrarterial canals, above which there are -two slight backwardly-projecting outgrowths bearing the -postzygapophyses on their inner faces. - - -THE THORACIC VERTEBRAE. - -The thoracic region includes all the vertebrae bearing free ribs, -except the first two, viz. those whose ribs do not reach the sternum. -There are seven thoracic vertebrae. The first four have centra with -saddle-shaped articulating surfaces, but are more or less firmly -united together by their neural spines; the last two are completely -ankylosed by their centra to the lumbar vertebrae. - -Each of the first five vertebrae has a prominent, vertical, abruptly -terminated neural spine, and straight transverse processes. The -zygapophyses and articulating surfaces at the ends of the centra are -well developed. The third, fourth, fifth, and sixth vertebrae have -very prominent hypapophyses. The articular facets for the ribs are -well marked, those for the tubercula lying at the free ends of the -transverse processes, and those for the capitula at the sides of the -anterior ends of the centra. The sixth and seventh thoracic vertebrae -are firmly fused by their centra and neural arches to one another and -to the lumbar vertebrae behind, and by their transverse processes to -the ilia. The sixth has its centrum terminated in front by a -saddle-shaped articulating surface, and bears a pair of prominent -prezygapophyses. Its transverse processes and centrum bear facets for -the tubercula and capitula of the ribs respectively. In the seventh -vertebra the tubercular facet is wanting. - - -THE SACRUM. - -[Illustration FIG. 58. A, DORSAL AND B, VENTRAL VIEW OF THE PELVIS AND -SACRUM OF A DUCK (_Anas boschas_). - - 1. ilium. - 2. ischium. - 3. pubis. - 4. pectineal process. - 5. lumbar vertebrae. - 6. true sacral vertebrae.] - -The =sacrum= generally consists of seventeen vertebrae fused with one -another and with the ilia. Their number may be reckoned from the -number of foramina for the exit of spinal nerves. The two most -anterior of these vertebrae bear ribs and have been already described -with the other thoracic vertebrae. Their neural spines and those of -the four succeeding vertebrae are fused together, forming a continuous -crest of bone completely united laterally with the ilia. The -transverse processes of all these six vertebrae are well developed, -but those of the posterior two (fig. 58, B, 5) are much the stoutest. -The next three vertebrae have broad centra, but their transverse -processes are very slightly developed and have no ventral elements. -These seven vertebrae belong to the =lumbar= series. The remaining -eight vertebrae have well-developed transverse processes, which in the -case of the first three or four are divisible into dorsal and ventral -elements. All the dorsal elements are united to form a pair of -flattened plates, partially separated by a series of foramina from a -median plate formed by the united neural arches. Laterally they are -continuous with the ischia. The first two of this series of vertebrae -are shown by their relation to the nerves to be the true =sacrals= -(fig. 58, B, 6), the remaining six belonging to the =caudal= series. - -Behind them come the six free caudal vertebrae, succeeded by a -terminal piece, the =pygostyle=, formed of a number of vertebrae fused -together; this bears the rectrices or tail quills. - -[Illustration FIG. 59. SKULL OF A DUCK (_Anas boschas_). × 1. - -A. Dorsal view of the cranium. B. Palatal view of the mandible. C. The -Hyoid. - -For numbers see Fig. 60.] - - -B. THE SKULL. - -[Illustration FIG. 60. A. Ventral view of the cranium of a Duck (_Anas -boschas_). B. Cranium and mandible seen from the left side. × 1. - - 1. maxillae. - 2. premaxillae. - 3. anterior nares. - 4. nasal process of premaxillae (fig. 59). - 5. nasal. - 6. frontal (fig. 59). - 7. lachrymal. - 8. postfrontal process. - 9. parietal (fig. 59). - 10. jugal. - 11. quadratojugal. - 12. quadrate. - 13. condyle of mandible. - 14. posterior articular process. - 15. dentary at symphysis. } - 16. basi-hyal. } (fig. - 17. uro-hyal. } 59). - 18. basibranchial. } - 19. vomer. - 20. palatine. - 21. pterygoid. - 22. anterior palatine foramen. - 23. basitemporal. - 24. foramen leading into tympanic cavity. - 25. bristle inserted into posterior opening of carotid canal. - 26. bristle inserted into posterior opening of Eustachian canal. - 27. bristle emerging through anterior opening of carotid canal. - Close by is seen the bristle emerging through the anterior - opening of the Eustachian canal. - 28. fenestral recess. - 29. maxillo-palatine. - 30. lambdoidal crest. - 31. rostrum. - -I. II. IV. V. IX. X. nerve foramina.] - -The skull of the duck, like that of birds in general, is characterised -(1) by its lightness, (2) by the contrast between the bones of the -cranium proper and those forming the rest of the skull, for the bones -forming the cranium proper are closely fused together, the sutures -between them being nearly all completely obliterated in the adult, -while the bones forming the face are loosely connected with the -cranium proper; (3) by the prolongation of the face into a long -toothless beak; (4) by the size of the orbits, and their position -entirely in front of the cranium, so that they are separated from one -another only by a thin interorbital septum. - -For purposes of description the skull may be divided into - - (1) The cranial portion. - (2) The facial portion. - (3) The mandible. - (4) The hyoid. - - -(1) THE CRANIAL PORTION. - -This is a rounded box expanded dorsally and posteriorly, but tapering -antero-ventrally. In the young skull the divisional lines between the -several bones can be easily seen, but in the adult they are quite -obliterated. - -(_a_) The _dorsal surface_ is rounded, expanded in front and behind, -but encroached upon in the middle by the cavities of the orbits. There -is a prominent divisional line in front, separating it from the facial -part of the skull. It is formed mainly by the _frontal_ (fig. 59, A, -6) and _parietal_ bones, but the frontals diverge a little anteriorly -and enclose between them the ends of the _nasal processes_ (fig. 59, -A, 4) of the _premaxillae_. Just in front of the orbit the outer -margins of the frontals are either notched or pierced by a pair of -foramina. - -(_b_) At the _posterior end_ of the cranium the most prominent feature -is the large, almost circular =foramen magnum=, through which the -spinal cord and brain communicate; this in young birds is seen to be -bounded by four distinct bones, dorsally by the =supra-occipital=, -ventrally by the =basi-occipital=, and laterally by the -=exoccipitals=. - -The =basi-occipital= forms the main part of a prominent convex knob, -the =occipital condyle=, with which the atlas articulates. The -occipital condyle is slightly notched above, and the ventral surface -of the cranium is deeply pitted just in front of it; the exoccipitals -also contribute slightly to its formation. Slightly in front of and -ventral to the foramen magnum is a small foramen through which the -hypoglossal nerve leaves the cranial cavity. - -The =supra-occipital= is separated from the parietal by a suture line -along which run a pair of prominent ridges, the =lambdoidal crests= -(fig. 60, B, 30). There are often a pair of prominent vacuities in the -supra-occipital dorsal to the foramen magnum. The =epi-otics= and -=opisthotics= become completely fused with the bones of the occipital -segment at a very early stage. - -(_c_) The _ventral surface_ of the cranium is wide behind, where it is -formed by a broad transverse membrane bone, the _basitemporal_ (fig. -60, A, 23), the sides of which are fused with the auditory capsules. -Slightly in front of and an eighth of an inch external to the -hypoglossal foramen the cranial wall is pierced by a pair of foramina -through which the tenth or pneumogastric nerves leave (fig. 60, A, X). -At the sides of the basitemporal are a pair of depressions, the -=tympanic recesses=, in each of which are three holes. Straight lines -joining these holes would form an isosceles triangle with its apex -directed forwards. Of the two holes at the base of the triangle, the -one nearer the middle line and leading into the cranial cavity, is for -the exit of the ninth or glossopharyngeal nerve (fig. 60, A, IX), it -lies just in front of the pneumogastric foramen. The more external -leads into the tympanic cavity, while the more anterior at the apex of -the triangle is the =posterior opening of the carotid canal= (fig. 60, -A, 25), which traverses the base of the cranium, and during life -lodges the carotid artery. - -The anterior end of the basitemporal is pierced near the middle line -by a pair of holes, the =anterior openings of the Eustachian canals=; -while just in front of these and a little further removed from the -middle line are the anterior openings of the =carotid canals=. -Bristles passed in through the posterior openings of the carotid -canals will emerge here (fig. 60, A, 27). In front of the basitemporal -the base of the cranium is formed by the =rostrum= (fig. 60, A, 31), -or thickened basal portion of the interorbital septum; this bears two -prominent surfaces with which the pterygoids articulate. In some kinds -of duck these surfaces are borne by well-marked basi-pterygoid -processes. - -(_d_) _The side of the cranium._ At the base of the posterior end is -seen the deep =tympanic cavity=. The dorsal part of this is divided by -a vertical partition into two halves; of these the more anterior is -the larger, and forms a deep funnel-shaped cavity, the =posterior -opening of the Eustachian canal= (fig. 60, B, 26). A bristle passed -into this opening emerges through the anterior opening of the -Eustachian canal. The more posterior of the two is the =fenestral -recess= (fig. 60, B, 28), and is in its turn divided by a slender -horizontal bar into a dorsal hole, the =fenestra ovalis=, and a -ventral hole, the =fenestra rotunda=. During life the fenestra ovalis -lodges the proximal end of the =columellar= chain. Lying at the outer -side and slightly dorsal to the tympanic cavity is a deep depression, -the =lateral tympanic recess=, and immediately in front of this is the -articular surface for the quadrate. The tympanic cavity is bounded -below by the basitemporal, posteriorly by the exoccipital, and above -by the _squamosal_, a membrane bone, which roofs over a good deal of -the side of the cranium, and bears ventrally a prominent surface with -which the quadrate articulates. Just in front of this is a large round -hole, the =trigeminal foramen= (fig. 60, B, V), behind which the -squamosal is drawn out into a short process. - -In front of the squamosal there is a prominent forwardly-projecting -=postfrontal process= (fig. 60, 8), which ossifies from a different -centre from that forming the squamosal, but in the adult is completely -fused with it. - -The =orbit= forms a large more or less hemispherical cavity which -lodges the eyeball. It is separated from its fellow of the opposite -side by an imperfect partition, the =interorbital septum=. In the -young skull it is seen to be bounded above by the frontal, with which -the _lachrymal_ (fig. 60, 7) is fused anteriorly, forming a large -backwardly-projecting process; while behind it is bounded by -the =alisphenoid=. The interorbital septum is formed by the -ossification and coalescence of the =mesethmoid= in front, with the -=orbitosphenoid= behind, and the =rostrum= below. The boundary of the -orbit below is very imperfect, the zygomatic arch being incomplete. - -The interorbital septum is pierced by the very prominent =optic -foramen= (fig. 60, B, 2), just behind which are the two much smaller -foramina for the exit of the oculomotor and pathetic (fig. 60, B, IV) -nerves, the more anterior being that for the oculomotor. - -Above and slightly in front of the optic foramen is a median opening, -the =olfactory foramen.= This leads into the cranial cavity behind, -and in front is continued forwards as a groove between the -interorbital septum and the frontal. - - -(2) THE FACIAL PART OF THE SKULL. - -This includes the olfactory capsule and associated bones, and the -upper jaw. - -The bones associated with the olfactory capsules are the _nasals_ and -_vomer_. The _nasals_ (figs. 59 and 60, 5) lie on the dorsal surface -immediately in front of the cranium, and are separated from one -another by the nasal processes of the premaxillae. Each is completely -fused in the adult with the corresponding maxillae and premaxillae, the -three bones together forming the boundary of the =anterior nares.= The -_vomer_ (fig. 60, 19) is unpaired and forms a small median vertical -plate lying ventral to the anterior continuation of the interorbital -septum. - -The bones of the upper jaw consist on each side of two slender arcades -which in front converge and are attached to the large beak, while -behind they diverge but are united by the =quadrate=. - -The =inner arcade= is formed by the pterygoid and palatine. The -_pterygoid_ (fig. 60, 21) is a short flattened bone, which articulates -behind with the quadrate, and on its inner side with a large flattened -surface borne by the rostrum, in front it meets the palatine, or -sometimes ends freely with a long antero-dorsally directed point. - -The _palatine_ (fig. 60, 20) is a slender irregular bone flattened -dorso-ventrally at its anterior end where it articulates with the -beak, and laterally behind. It gives off at its posterior end a -process, which is sometimes united with the vomer, sometimes projects -forwards, and meets its fellow dorsal to the vomer. In the large space -between it and the vomer is the opening of the =posterior nares=. - -The _premaxillae_ (figs. 59 and 60, 2) are very large, and form nearly -a third of the big shovel-shaped beak. They constitute the inner, and -part of the front boundary of the anterior nares, and send back a pair -of _nasal processes_ which partially separate the nasals from one -another. - -The =outer arcade= forms the slender =suborbital bar=, and consists -mainly of two rod-like bones, which in the adult are completely fused -together. The posterior of these is the _quadratojugal_ (figs. 59 and -60, 11) which articulates with the quadrate, the anterior is the small -and slender _jugal_ or _malar_ (figs. 59 and 60, 10). The extreme -anterior part of the bar is formed by the _maxillae_. The main part of -the maxillae however lies anterior to the suborbital bar, and extends -forwards along the side of the premaxillae forming all the lateral part -of the beak (figs. 59 and 60, 1); it also sends inwards a plate, the -=maxillo-palatine= (fig. 60, A, 29), which completely fuses with its -fellow in the middle line, and forms the posterior boundary of the -anterior palatine foramen. The term =desmognathous= describes the -condition of the skull in which the maxillo-palatines fuse with one -another in the middle line in this way. - -The =quadrate= (fig. 60, 12), which unites the two arcades behind, is -a stout irregular four-cornered bone forming the =suspensorium=. It -articulates by its dorso-posterior corner with the squamosal, and by -its antero-internal corner with the pterygoid. The middle of its -ventral surface forms a hemispherical knob with which the mandible -articulates, while its dorso-anterior border is drawn out into a long -point which extends towards the interorbital septum. - - -(3) THE MANDIBLE. - -The =mandible= or lower jaw consists of two =rami= which are flattened -and fused together in the middle line in front, while behind they -diverge from one another and articulate with the quadrates. - -Each ramus is composed of five bones fused together, one being a -cartilage bone, and the other four membrane bones. The =articular= is -the only cartilage bone of the mandible, it bears the double condyle -(figs. 59 and 60, 13) or concave articular surface for the quadrate, -and is drawn out behind into a large hooked =posterior articular -process=. The articular is also drawn out into a prominent process on -each side of the articular surface for the quadrate, and is marked by -a deep pit opening posteriorly. The articular is continuous in front -with =Meckel's cartilage= which forms the original cartilaginous bar -of the lower jaw, and is ensheathed by the membrane bones. Of these -the _supra-angular_ forms the upper part of the mandible in front of -the articular, its dorsal surface is drawn out into a small =coronoid -process=, its outer surface also bearing a prominent process. The -_angular_ is a small bone which underlies the articular and -supra-angular on the inner side of the jaw. The _dentary_ (fig. 59, -15) forms the anterior half of each ramus, and is the largest bone of -the mandible; it is fused with its fellow at the symphysis in front, -and extends back below the supra-angular. The _splenial_ is a small -bone lying along the middle half of the inner side of each ramus of -the mandible. - - -(4) THE HYOID. - -With the hyoid apparatus is included the =columella=. This forms a -minute rod of bone, one end of which is expanded and fits into the -fenestra ovalis, while the other end, terminated by a triradiate piece -of cartilage, is attached to the tympanic membrane. The structure is -as a whole homologous with the auditory ossicles of mammals and the -hyomandibular of fish. - -The =hyoid= consists of a median unpaired portion, formed of two -pieces of bone, the =basi-hyal= (fig. 59, C, 16) in front, and the -=uro-hyal= (fig. 59, C, 17) behind, the two being placed end to end -and terminated anteriorly by an unpaired cartilaginous plate, the =os -entoglossum.= At the posterior end there come off a pair of long -=posterior cornua=, each of which consists of two pieces, a longer -=basibranchial= (fig. 59, C, 18), and a shorter =cerato-branchial=. -For the homology of these parts see p. 336. - - -THE RIBS AND STERNUM. - -The last two cervical vertebrae bear long movable ribs which -articulate by distinct capitular and tubercular processes, but do not -meet the sternum. The thoracic ribs are eight in number, and each is -divisible into a =vertebral= and a =sternal= portion. The first five -thoracic ribs are flattened curved bars of bone, which articulate by a -prominent =capitulum= with the centrum of the corresponding vertebra, -and by a =tuberculum= with the transverse process. Projecting -backwards from each is a large hooked =uncinate process.= The last -three ribs which are without uncinate processes, become progressively -more slender, and in the eighth the tubercular processes are lost. - -The sternal portions of the ribs are imperfectly ossified pieces, -short and comparatively thick in the case of the anterior ribs, longer -and more slender in the case of the posterior ribs. - - -THE STERNUM[1]. - -The =sternum= or breast bone is exceedingly large in the Duck, as in -all birds, and projects back far beyond the thorax over much of the -anterior part of the abdomen. It is an irregularly oblong plate of -bone, abruptly truncated behind, somewhat concave dorsally, and drawn -out ventrally into a prominent keel, the =carina=, which projects for -some distance forwards beyond the body of the sternum, and tapers off -gradually behind. The point where the carina joins the body of the -sternum is at the anterior end drawn out into a small process, the -=rostrum=[102]. Just dorsolateral to this are a pair of deep grooves, -the =coracoid grooves=, with which the coracoids articulate. - -The sides of the sternum are drawn out in front into a pair of short -blunt =costal processes;= and just behind these are a series of seven -surfaces with which the ends of the sternal ribs articulate. -Immediately behind these surfaces the sides are produced into a pair -of long backwardly-projecting =xiphoid processes= which nearly meet -processes from the posterior end of the sternum. - - -2. THE APPENDICULAR SKELETON. - -This consists of the skeleton of the anterior and posterior limbs and -of their respective girdles. - - -A. THE PECTORAL GIRDLE[103]. - -The pectoral girdle in almost all birds is strongly constructed and -firmly united to the sternum. It consists of three bones, a dorsal -element, the =scapula=, a posterior ventral element, the =coracoid=, -and an anterior ventral element, the _clavicle_. - -The =scapula= forms a long curved flattened bone expanded at its -anterior end, where it meets the coracoid, and lying across the ribs -at its tapering posterior end. It helps to form the imperfect =glenoid -cavity=, with which the humerus articulates. The =coracoid=, a shorter -but stouter bone than the scapula, has its upper end or =head= -thickened and bears on its posterior border an irregular surface, with -part of which the scapula articulates, while the rest forms part of -the glenoid cavity. The inner border of the coracoid adjoining the -articular facet for the scapula is produced into a strong process -which helps to complete the =foramen triosseum=, a space lying between -the adjoining ends of the scapula and coracoid, through which the -tendon of the second pectoral muscle passes. The lower part of the -coracoid, which is much flattened and expanded, and abruptly truncated -posteriorly, articulates with the coracoid groove of the sternum. The -_clavicle_ is a thickened curved membrane bone, which is fused with -its fellow in the middle line below, the two forming the _furcula_ or -merrythought. Its dorsal end is drawn out into a process which -articulates with the coracoid. - - -THE ANTERIOR LIMB OR WING. - -This consists of three parts, a proximal part, the upper arm or -=brachium=, a middle part, the fore-arm or =antibrachium=, and a -distal part, the =manus=. When extended for flight the parts lie -almost in the same straight line, but when at rest they are folded on -one another in the form of a Z, the brachium and manus pointing -backwards, and the antibrachium forwards. When extended for flight the -surfaces and borders of the wing correspond in position with those of -the primitive vertebrate limb[104], the pre-axial border being -directed forwards and the postaxial backwards, while the dorsal and -ventral surfaces look respectively upwards and downwards. But when the -wing is at rest, the humerus as it extends backwards becomes slightly -rotated, so that its dorsal surface looks more inwards than upwards, -while the dorsal surface of the antibrachium looks partially outwards -and upwards, and that of the manus mainly outwards. - -The =brachium= or =upper arm= contains only a single bone, the -=humerus= (fig. 57, 1). This is a large nearly straight bone expanded -at both ends. The proximal end is specially expanded, forming two -=tuberosities=, and a large convex =head= articulating with the -glenoid cavity. The =pre-axial tuberosity= is the smaller of the two, -but is continued by a prominent =deltoid ridge=, which extends for a -very short distance down the shaft. The =postaxial tuberosity= is the -larger, and below it there is a very deep pit, the =pneumatic -foramen=, which leads into an air cavity in the shaft of the bone. The -shaft is long and straight, and at the distal end of the bone is the -=trochlea= with two convex surfaces, one pre-axial with which the -radius articulates, the other postaxial for the ulna. - -The =fore-arm= or =antibrachium= consists of two bones, the =radius= -and =ulna=. These are of nearly equal length, and are separated from -one another by a considerable space except at their terminations. - -The =radius= (fig. 57, 2), the pre-axial and smaller bone, is straight -and fairly stout; its proximal end articulates with the humerus by a -slightly cupped surface, while its distal end, which articulates with -the carpus, is convex and somewhat expanded. - -The =ulna= (fig. 57, 3) is longer, stouter, and slightly curved. Its -proximal end is expanded, forming two surfaces which articulate with -the trochlea of the humerus; behind them it is drawn out into a short -blunt =olecranon process=. Its distal end is less expanded, and -articulates with the carpus and also with the radius. - -The =Manus=. This includes the carpus or wrist, and the hand. - -The =Carpus=. While in the embryo the carpus consists of five -distinct elements arranged in a proximal row of two and a distal row -of three, in the adult only the proximal bones can be clearly -distinguished, the distal ones having become completely ankylosed with -the metacarpals to form the =carpo-metacarpus=. - -The two distinct carpal bones are the radial carpal and the ulnar -carpal. The radial carpal (fig. 57, 4) is a small somewhat cubical -bone, wedged in between the manus and the radius and ulna. The ulnar -carpal (fig. 57, 5) is a somewhat larger, more irregular bone, lying -adjacent to the end of the ulna. It is deeply notched to receive the -carpo-metacarpus. - -=The hand.= In the adult bird the hand is in a much modified -condition; only the first three digits are represented, and the -metacarpals are all fused with one another and with the distal -carpalia to form the =carpo-metacarpus=. - -The most prominent part of the carpo-metacarpus is formed by the -=second metacarpal= (fig. 57, 7), a stout, straight bone expanded at -both ends. The =third metacarpal= (fig. 57, 8) is a more slender -curved bone fused at both ends with the second metacarpal. The =first -metacarpal= forms simply a small projection on the radial side of the -proximal end of the second metacarpal. - -The =phalanges=. The first digit or =pollex= includes two phalanges, -the distal one being very small and bearing a claw. - -The second digit includes three phalanges, the proximal one being -somewhat flattened. The third digit has a single small phalanx. - - -THE PELVIC GIRDLE. - -The bones constituting the pelvic girdle are not only as in other -higher vertebrates ankylosed together forming the innominate bones, -but are also ankylosed with a series of some seventeen sacral and -pseudosacral vertebrae. The =acetabulum= (fig. 61, 5) with which the -head of the femur articulates is incompletely ossified. - -The =ilium= (figs. 58 and 61, 1) is the largest bone of the pelvis. It -forms a long flattened plate extending for a considerable distance -both in front of and behind the acetabulum, and is fused along its -whole length with the transverse processes and neural spines of the -sacral and pseudosacral vertebrae. It forms more than half the -acetabulum, above and behind which it is produced to form a process, -the =antitrochanter= (fig 61, 8), with which the great trochanter of -the femur articulates. - -[Illustration FIG. 61. LATERAL VIEW OF THE PELVIS AND SACRUM OF A DUCK -(_Anas boschas_) × 2/3. - - 1. ilium. - 2. ischium. - 3. pubis. - 4. pectineal process. - 5. acetabulum. - 6. ilio-sciatic foramen. - 7. fused vertebrae. - 8. antitrochanter.] - -The =ischium= (figs. 58 and 61, 2) is a flattened bone which forms -about one-third of the acetabulum, and lies ventral to the posterior -part of the ilium. Its anterior portion is separated from the ilium by -the large oval =ilio-sciatic foramen= (fig. 61, 6), while behind this -the two bones are completely fused. - -The =pubis= (figs. 58 and 61, 3) is a very long slender bar of bone -which forms only a very small part of the acetabulum and runs back -parallel to the ventral surface of the ischium with which it is -loosely connected at its posterior end. For the greater part of their -length the two bones are separated by the long narrow =obturator -foramen=. Behind the ischium the pubis is produced into a long curved -downwardly-projecting process, and in front of the acetabulum it bears -a short blunt =pectineal= or =pre-pubic process= (fig. 61, 4) probably -homologous with the pre-pubis of Orthopod Dinosaurs. The remainder of -the pubis is homologous with the post-pubis of Orthopod Dinosaurs. - - -THE POSTERIOR LIMB. - -The leg of the bird is somewhat differently constructed from that of -other vertebrates owing to the fact that there is no free tarsus, the -proximal tarsals having fused with the tibia, and the distal with the -metatarsals. - -The =thigh= consists of a single bone, the femur. The =femur= is a -comparatively short bone with a straight shaft and expanded ends. The -proximal end bears on its inner side a rounded =head=, which -articulates with the acetabulum. On its outer side is an irregular -outgrowth, the =great trochanter=, while between the two is the -surface which meets the antitrochanter of the ilium. The posterior end -also is expanded and marked by a wide groove which lodges the -=patella=. On each side of the groove is a strong =condylar ridge= for -articulation with the tibia. The external condyle is deeply grooved -behind for articulation with the fibula. - -The =crus= or =shin= consists of two separate bones, (1) the -=tibio-tarsus=, formed by the fusion of the tibia with the proximal -row of tarsals, and (2) the =fibula=. - -The =tibio-tarsus= is a thick straight bone nearly twice as long as -the femur. Both ends of the bone are considerably expanded. The -proximal end bears two slight depressions which articulate with the -condyles of the femur, and a third depression which partly lodges the -patella. The proximal end of the anterior or extensor surface is drawn -out into a very prominent =cnemial crest= which bends over towards the -postaxial side of the bone; a slight ridge is continued from it all -the way down the shaft. The proximal part of the shaft of the -tibio-tarsus bears a roughened ridge with which the fibula is closely -connected. The distal end is expanded and rotated outwardly and forms -a prominent pulley-like surface which articulates with the -tarso-metatarsus. - -The =fibula= is reduced to the proximal portion only, which is -expanded and articulates with a depression behind the external condyle -of the femur. The fibula further extends about a third of the way down -the shaft of the tibio-tarsus. The =patella= or =knee-cap= is a -sesamoid bone due to an ossification in the tendon of the extensor -muscles of the leg. - -The =ankle joint= lies between the proximal and distal tarsals which -as previously mentioned fuse respectively with the tibia and -metatarsus. - -The =Pes=. The pes includes four digits, and consists of the -tarso-metatarsus and the phalanges. The proximal tarsals which are -fused with the tibia also really belong to the pes. - -The =tarso-metatarsus= is a strong straight bone nearly as long as the -femur, and is formed by the fusion of the distal tarsals with the -second, third and fourth metatarsals. The proximal end of the bone is -expanded and bears two facets for articulation with the tibio-tarsus, -and near them on the posterior surface is a large roughened -projection. The lines of junction between the several metatarsals are -marked along the shaft by slight ridges. At the distal end of the bone -the three metatarsals diverge from one another and each bears a -prominent convex pulley-like surface. The =first metatarsal= is -reduced to the distal end, which tapers to a point proximally, and is -attached by ligaments near the distal end of the tarso-metatarsus. - -The =digits=. Four digits are present, each consisting of a metatarsal -(already described) and a certain number of phalanges, the terminal -one being in each case clawed. The first digit or =hallux= has two -phalanges, the second three, the third four, and the fourth five. - - -FOOTNOTES: - -[101] See R.S. Wray, _P.Z.S._, 1887, p. 343. - -[102] Often called the manubrium, but not homologous with the -manubrium of the mammalian sternum. - -[103] Cp. fig. 63. - -[104] See p. 28. - - - - -CHAPTER XIX. - -GENERAL ACCOUNT OF THE SKELETON IN BIRDS. - - -EXOSKELETON. - -The epidermal exoskeleton of birds is very greatly developed, feathers -constituting its most important part. - -Three kinds of feathers are found, viz. (_a_) _pennae_ including -quills and coverts, (_b_) down feathers or _plumulae_, and (_c_) -_filoplumes_ which are rudimentary feathers. The structure of the -different kinds of feathers is described on pp. 303-306. - -Sometimes a fourth class of feathers, the _semiplumae_, is recognised. -They have the stems of pennae, and the downy barbs and barbules of -plumulae. - -In most birds the pennae are not uniformly distributed over the whole -surface of the body, but are confined to certain tracts, the -=pterylae=; while the intervening spaces or =apteria= are either bare -or covered only with down feathers. In some birds, however, such as -the Ratitae and the Penguins, pennae are evenly distributed over the -whole body. - -In many birds the calamus or quill bears two vexilla or vanes, the -second of which, called the =aftershaft= or =hyporachis=, is generally -much the smaller, and is attached to the under surface of the main -vexillum. In the Moas, Emeu and Cassowary the two vexilla in the adult -bird are nearly equal in size; though in the nestling Emeu one is much -longer than the other. The aftershaft is very small in most Passeres -and gallinaceous birds, but is comparatively large in Parrots, Gulls, -Herons and most birds of prey. It is absent or extremely small in the -Ostrich, _Apteryx_, _Rhea_, Pigeons, Owls, Anseres, and others. - -The quill feathers include two groups, the =remiges= or wing quills, -and the =rectrices= or tail quills. In most birds the primary remiges, -or those which are attached to the bones of the manus, are ten or -eleven in number, and are set in grooves in the bones, being firmly -attached to them. In the Ostrich however the primaries are little -specialised in character and are as many as sixteen in number. They -are also less definitely attached to the bones; as their ends do not -lie in grooves in the bones, but project beyond them. - -The secondary quills or those attached to the ulna vary much in number -according to the length of the bone. The large dark quills in the -wings of Cassowaries are the secondaries. - -The wing of Penguins is very little differentiated. It is covered at -the margin by overlapping scales which gradually merge into scale-like -feathers at the proximal end. The wing of the Penguin has nothing -comparable to the remiges of other birds. - -In some birds, such as Herons (_Ardea_), there occur in places -plumulae of a peculiar kind, which grow persistently and whose summits -break off into fine powder as fast as they are formed. These feathers -are known as _powder-down_ feathers. They occur also in some Parrots -and are then scattered indiscriminately all over the body. - -Other exoskeletal structures besides feathers are commonly well -developed. Thus the extremities of the jaws are sheathed in horny -=beaks= whose form varies enormously according to the special mode of -life. - -In ducks and geese the beak with the exception of the anterior end is -soft, and its edges are raised into lamellae, while in the Mergansers -these lamellae become pointed processes supported by bony outgrowths. -These lamellae act as strainers. In Parrots and Hawks, on the other -hand, nearly the whole of the beak is hard. - -The toes and tarso-metatarsus are usually featherless and are covered -either with granular structures or with well-formed scales. The toes -are nearly always provided with =claws=, and these vary in correlation -with the character of the beak. Claws[105] also sometimes occur on the -manus. Thus _Archaeopteryx_ and some Ostriches and Rheas have claws on -all three digits. Most Ostriches and Rheas, and many Anseres and birds -of prey, have them on the first two digits, while the Secretary bird -(_Gypogeranus_) and many fowls, ducks, and birds of prey, especially -kestrels, have a claw only on the pollex. In the Cassowary, Emeu, -Apteryx and some Ostriches and Rheas only the second digit is clawed. - -Claws should not be confounded with =spurs=, which are conical horny -structures developed on bony outgrowths of the radial side of the -carpus, metacarpus, or metatarsus. They occur in a number of birds, -but are most commonly developed in gallinaceous birds, by which they -are used for fighting. A single spur occurs on the metacarpus in -_Megapodius_, in _Palamedea_, in _Parra jacana_ and in _Hoplopterus -spinosus_, the Spur-winged plover. The Derbian Screamer, _Chauna -derbiana_, has two metacarpal spurs, borne on the first and second -metacarpals. The Spur-winged goose, _Plectropterus gambensis_, has a -carpal spur borne on the radial carpal. Metatarsal spurs are quite -common. - -The male Solitaire (_Pezophaps_) has large bony excrescences on the -wrist which may, like spurs, have been sheathed in horn and used for -fighting. - -=Teeth= do not occur in any living birds, but conical teeth imbedded -in separate sockets are present in _Archaeopteryx_ and _Ichthyornis_, -while in _Hesperornis_ similar teeth occur implanted in continuous -grooves in the mandibles and maxillae, the premaxillae being toothless. - -Except that teeth are partly dermal in origin, a dermal exoskeleton is -quite unrepresented in birds. - - -ENDOSKELETON. - -Perhaps the most striking feature of the endoskeleton of birds is its -pneumaticity. In the embryo all the bones contain marrow, but as -growth proceeds this becomes replaced by air to a variable extent in -different forms. In all birds some part of the skeleton is pneumatic. -Many small birds and _Apteryx_ and Penguins among larger ones have air -only in the skull; in Pigeons air is present in all the bones except -the caudal vertebrae, the leg bones, and those of the antibrachium and -manus; in Hornbills every bone contains air. - -[Illustration FIG. 62. THIRD CERVICAL VERTEBRA OF AN OSTRICH -(_Struthio camelus_). × 1. A anterior, B posterior, C dorsal view (A -and B after MIVART). - - 1. neural spine. - 2. neural canal. - 3. prezygapophysis. - 4. postzygapophysis. - 5. posterior articular surface of centrum. - 6. anterior articular surface of centrum. - 7. vertebrarterial canal. - 8. hypapophysis.] - - -VERTEBRAL COLUMN. - -The vertebral column of birds is readily divisible into a very mobile -cervical region, and an extremely rigid post-cervical region. In most -birds the vertebral centra are without terminal epiphyses, but these -structures are found in Parrots. The cervical vertebrae are generally -large and vary in number from eight or nine to twenty-three in Swans. -Except in some extinct forms, such as _Ichthyornis_ and _Apatornis_, -in which they are biconcave, the centra are characterised by having -saddle-shaped articulating surfaces, which in front are concave from -side to side and slightly convex from above downwards, while -posteriorly they are convex from side to side and concave from above -downwards. The atlas is small and ring-like, and its centrum is fused -with the axis forming the odontoid process. Cervical ribs are often -well developed, and in some of the Ratitae they remain for a long time -distinct from the vertebrae. - -The thoracic vertebrae are distinguished from the cervical by the fact -that their true ribs are united to the sternum by means of sternal -ribs. This distinction, however, though convenient, is somewhat -arbitrary, as it has been shown that in the fowl and gannet, two pairs -of ribs which in the adult are free from the sternum, are connected -with it in the embryo. When, as in the Swans, the thoracic vertebrae -are not all fused together, they generally have saddle-shaped -articulating surfaces, but sometimes, as in the Penguins, Auks and -Plovers, the centra are convex in front and concave behind. The trunk -vertebrae generally have well-marked neural spines, while in the -Divers the anterior ones have peculiar bifurcating hypapophyses. - -The trunk vertebrae are not readily divisible into thoracic and -lumbar. There are two true sacral vertebrae, but as development -proceeds a number of other vertebrae become fused with the true -sacrals, the whole forming a large compound sacrum. These pseudosacral -vertebrae generally include the lumbar, and some of the thoracic and -caudal vertebrae. Sixteen to twenty vertebrae or even more may be -included in the compound sacrum, and sometimes the whole of the trunk -vertebrae are fused together. In _Archaeopteryx_ however but five -vertebrae take part in the formation of the sacrum. - -In _Archaeopteryx_ there are twenty long caudal vertebrae, of which -the last sixteen carry a pair of feathers apiece, but in all other -birds the tail is short and in the great majority of cases the -posterior vertebrae are fused together, forming the pygostyle. In the -Ratitae and Tinamidae a pygostyle is rarely or imperfectly developed. -In _Hesperornis_ there are twelve caudal vertebrae, six or seven of -which are united by their centra only, forming an imperfect pygostyle. - -The free caudal vertebrae are generally amphicoelous. - - -THE SKULL. - -The skull of all birds from _Archaeopteryx_ onwards is essentially -similar, differing from the skull of reptiles mainly in the extent to -which the cranium is arched, and its greater size in proportion to the -jaws. - -Most of the bones of the cranium are pneumatic, and all show a marked -tendency to fuse together, and have their outlines obliterated by the -disappearance of the sutures. The several bones remain longest -distinguishable in the Ratitae and to a less extent in the Penguins. -The orbits are very large and lie almost entirely in front of the -cranium; they are separated by an interorbital septum which is -sometimes, as in _Chauna_ and _Scythrops_, very complete, sometimes, -as in Hornbills and the Common Heron, very slightly developed. As a -general rule the sclerotic is cartilaginous. - -The anterior nares are almost always situated far back at the base of -the beak near the orbits, but in _Apteryx_ they are placed right at -its extremity. In _Phororhacos_ they are placed very high up on the -enormous beak and are not separated by any bony partition. - -The skull of Parrots has some peculiarities. In some Parrots the -lachrymal sends back a process which meets the postorbital process of -the frontal and completes the orbit. In most birds the upper beak is -immovably fixed, but in some it is attached to the cranium, only by -the nasals and by flexible processes of the premaxillae, so that by -this means a kind of elastic joint is established and the beak is able -to be moved on the cranium. In the Parrots and _Opisthocomus_ there is -a regular highly movable joint. - -In Cassowaries the fronto-nasal region of the skull is produced into -an enormous bony crest, and in Hornbills a somewhat similar structure -occurs. Although true teeth do not occur in any known bird except -_Archaeopteryx_, _Hesperornis_, and _Ichthyornis_, another extinct -bird, _Odontopteryx_, has the margins of both jaws provided with -forwardly-directed tooth-like serrations, formed of part of the actual -jawbone: a living hawk, _Harpagus_, too, has a deeply notched bill, to -which correspond serrations in the premaxillae. - -A basi-pterygoid process of the basisphenoid abuts against the -pterygoid in Ratitae and in Tinamous, plovers, fowls, pigeons, ducks -and geese among Carinatae, recalling the arrangement met with in many -reptiles. The squamosal is sometimes, as in the fowl, united with the -postorbital process of the frontal. In the Carinatae the quadrate -articulates with the cranium by a double convex surface, in the -Ratitae by a single one. The premaxillae are always comparatively large -bones, the maxillae on the contrary are small, but give rise to -important inwardly-projecting maxillo-palatine processes. - -The relations of the palatines, pterygoids, maxillae, and vomers vary -considerably, and on them Huxley has based a classification of -birds[106]. In the Ratitae and the Tinamous (Tinamidae), among -Carinatae the vomers unite and form a large broad bone, separating the -palatines and the pterygoids from the rostrum. Huxley uses the term -=Dromaeognathous= to describe this condition. In all other Carinatae -the vomers are narrow behind, and the palatines and pterygoids -converge posteriorly and articulate largely with the rostrum. Three -modifications of this condition are distinguished by Huxley, and -termed =Schizognathous=, =Ægithognathous=, and =Desmognathous=. - -In the =Schizognathae= the vomers coalesce and form a narrow elongated -bone, pointed in front, separating the maxillo-palatine processes of -the premaxillae. Waders, fowls, penguins, gulls, some falcons and -eagles, American vultures, some herons and many owls have the -Schizognathous arrangement. In pigeons and sandgrouse there is no -vomer, but the other bones have the Schizognathous arrangement. - -In the =Ægithognathae= the arrangement is the same as in the -Schizognathae, except that the vomers are truncated in front. -Passeres, swifts, woodpeckers, humming birds, rollers, hoopoes have -this arrangement. - -In the =Desmognathae= (fig. 60, A) the maxillo-palatine processes -approach one another in the middle line, and either unite with the -vomers, or unite with one another, hiding the vomers. Thus a more or -less complete bony roof is formed across the palate. The vomers in -Desmognathae are small or sometimes absent. Ducks, storks, most -herons, most birds of prey and owls, pelicans, cormorants, parrots, -and flamingoes are Desmognathous. - -The mandible, as in other Sauropsids, consists of a cartilage bone, -the articular, and a series of membrane bones, the dentary, splenial, -coronoid, angular, and supra-angular, developed round the unossified -Meckel's cartilage. The dentaries of the two rami are nearly always -fused together, but in _Ichthyornis_ and _Archaeopteryx_ the two rami -are but loosely united. There is often a fontanelle between the -dentary and the posterior bones, while the angle is sometimes, as in -the fowl, drawn out into a long curved process. - -The hyoid apparatus (fig. 59, C) consists of a median portion, and a -pair of cornua. The median portion is composed of three pieces placed -end to end, and called respectively the os entoglossum, the basi-hyal, -and the uro-hyal. The os entoglossum is shown by development to be -formed by the union of paired structures and is probably homologous -with the hyoid arch of fishes. The basi-hyal and the long cornua, each -of which is composed of two or three pieces placed end to end, are -homologous with the first branchial arch of fishes, while the uro-hyal -is probably homologous with the second branchial arch of fishes. In -Woodpeckers the cornua are enormously long, and curve over the skull, -extending as far forwards as the anterior nares. - - -RIBS AND STERNUM. - -Well-developed ribs are attached to the posterior cervical vertebrae -as well as to the thoracic vertebrae. The ribs generally have uncinate -processes and separate capitula and tubercula, but uncinate processes -are absent in _Chauna Palamedea_ and apparently in _Archaeopteryx_. - -The sternum (fig. 63) is greatly developed in all birds. In the -embryo[107] it is seen to be derived from the union of right and left -plates of cartilage, formed by the fusion of the ventral ends of the -ribs. In the Ratitae and a few Carinatae, such as _Stringops_, it is -flat, but in the great majority of birds it is keeled, though the -development of the keel varies greatly. It is large in the flightless -Penguins, which use their wings for swimming. Traces of an -interclavicle may occur in the embryo. - - -PECTORAL GIRDLE. - -[Illustration FIG. 63. SHOULDER-GIRDLE AND STERNUM OF - - A. BLACK VULTURE (_Vultur cinereus_) × 1/3. - B. PEACOCK (_Pavo cristatus_) × 3/8. - C. PELICAN (_Pelicanus conspicillatus_) × 1/3. (All Camb. Mus.) - - 1. carina of the sternum. - 2. coracoid. - 3. scapula. - 4. clavicle. - 5. costal process. - 6. surfaces for articulation with the sternal ribs. - 7. xiphoid processes. - 8. fontanelle.] - -The pectoral girdle is also strongly developed in all Carinatae, but -is much reduced in Ratitae. In some Moas the sternum has no facet for -the articulation of the coracoid, and the pectoral girdle appears to -have been entirely absent; it is extremely small also in _Apteryx_. -Clavicles are generally well developed in the Carinatae, and small -ones are found also in _Hesperornis_, and in Emeus and Cassowaries. In -the other living Ratitae and in _Stringops_ they are absent. In some -Parrots, Owls and Toucans they do not meet one another ventrally. -Clavicles are especially stout in some of the birds of prey. They do -not generally touch the sternum, but sometimes, as in the Pelican -(fig. 63, C), Adjutant and Frigate bird, they are fused with it. - -In all Ratitae the scapula and coracoid lie almost in the same -straight line with one another, in the Carinatae they are nearly at -right angles to one another. - - -ANTERIOR LIMB. - -In the wing of nearly all birds the ulna is thicker than the radius, -but in _Archaeopteryx_ the two bones are equal in size. In the wing of -_Archaeopteryx_ there are three long digits with distinct metacarpals. -In all other birds the digits are modified, the metacarpals being -commonly fused and the phalanges reduced in number. In _Palamedea_ and -some other birds the metacarpus bears a bony outgrowth, which when -sheathed in horn forms a spur. - -In most of the Ratitae and in the extinct Dodo (_Didus_) and Solitaire -(_Pezophaps_) the wing is very small, but the usual parts are -recognisable. In _Hesperornis_ apparently only the humerus is present; -in some Moas, in which the wing is imperfectly known, the presence of -the humerus is indicated by traces of a glenoid cavity. In most Moas -the wing is apparently completely absent. As compared with those in -other Ratitae, the wings of the Ostrich and Rhea are well developed. -In the Ostrich (fig. 64, B) and Rhea, as in nearly all Carinatae, the -manus has three digits, but in _Apteryx_ there is only a single digit, -the second. The Penguins (fig. 64, A) too among Carinatae have only -two digits, but in their case it is the pollex which is missing. In -the Ostrich the third digit has two phalanges, in all other living -birds it has only one phalanx. - - -PELVIC GIRDLE. - -[Illustration FIG. 64. BONES OF THE RIGHT WING OF - - A. A PENGUIN × 1/3. (Camb. Mus.) - B. OSTRICH (_Struthio camelus_) × 1/7. (Partly after PARKER.) - C. GANNET (_Sula alba_) × 1/3. (Camb. Mus.) - -In C the distal phalanges of the pollex and second digit have been -omitted. - - 1. humerus. - 2. radius. - 3. ulna. - 4. second metacarpal. - 5. third metacarpal. - 6. pollex. - 7. second digit. - 8. cuneiform. - 9. sesamoid bone.] - -Birds have a very large pelvis and its characters are constant -throughout almost the whole group. The ilium is very large, and is -united along its whole length with the sacral and pseudosacral -vertebrae. The ischium is broad and extends back parallel to the ilium -with which in most birds it fuses posteriorly, further forward the -ilio-sciatic foramen separates the two bones. In _Tinamus_, -_Hesperornis_, _Apteryx_ (fig. 65, B, 2), and _Struthio_, the ischia -are separate from the ilia along their whole length except at the -acetabulum; in _Phororhacos_, on the other hand, the two bones are -fused along almost their whole length. The bone usually called the -pubis in birds corresponds to the post-pubis of Dinosaurs and forms a -long slender rod (fig. 65, 3) lying parallel to the ischium. In many -birds the ischia and pubes are united at their distal ends. This is -the case in the Ostrich (fig. 65, D), in which the ilia and ischia are -widely separated. In many birds the pubis is drawn out in front into -the pectineal process, this is specially large in _Apteryx_ (fig. 65, -B, 5), and in the embryos of many birds. It is probably homologous -with the pre-pubis of Dinosaurs but in some birds is formed in part by -the ilium. The acetabulum in birds is always perforate. - -In _Rhea_ (fig. 65, C, 2) and probably in _Archaeopteryx_ a symphysis -ischii occurs, and in the ostrich alone among birds there is a -symphysis pubis. In _Archaeopteryx_ all three bones of the pelvis are -distinct, but they are imperfectly known. In Ichthyornis they are also -distinct, in all other known birds they are fused together to a -greater or less extent. - -[Illustration FIG. 65. PELVIC GIRDLE AND SACRUM OF - - A. CASSOWARY (_Casuarius galeatus_) × 1/8. - B. OWEN'S APTERYX (_A. oweni_) × 1/2. - C. BROAD BILLED RHEA (_R. macrorhyncha_) × 1/6. - D. OSTRICH (_Struthio camelus_) × 1/10. (All Camb. Mus.) - - 1. ilium. - 2. ischium. - 3. pubis. - 4. acetabulum. - 5. pectineal process.] - - -POSTERIOR LIMB. - -The tibia is always well developed and has a very strong cnemial -crest. The proximal tarsals are fused with its distal end, the whole -forming a compound bone, the tibio-tarsus. There is frequently an -oblique bar of bone crossing the anterior face of the tibio-tarsus at -the distal end, just above the articular surface of the -tarso-metatarsus, this is absent in Ostriches and _Æpyornis_. The -fibula though in the embryo and in _Archaeopteryx_ equal in length to -the tibia, is in the adult of other birds always imperfect, its -proximal end is often fused with the tibia, and its distal end is -commonly atrophied. In the Penguins however the distal end is -complete. The distal tarsals fuse with the second, third and fourth -metatarsals, forming a compound bone, the tarso-metatarsus. The first -metatarsal is nearly always free but occasionally as in _Phaëthon_ it -is fused with the others. No adult bird has more than four digits in -the pes. In the Penguins the metatarsals are separate, and in many -birds larger or smaller gaps exist between the fused metatarsals. In -most birds the third metatarsal is curved so as not to lie in the same -plane as the others, but in the Penguins they all three lie in the -same plane. The metatarsals are clearly separated in _Archaeopteryx_. -In Gallinaceous birds the tarso-metatarsus bears a bony outgrowth -which is sheathed in horn and forms a spur. - -In most birds the first four toes are present while the fifth is -always absent. The first toe commonly has two phalanges, the second -three, the third four, and the fourth five. In Swifts the third and -fourth toes have only three phalanges. Many birds, such as all Ratitae -except _Apteryx_, have only three toes, the hallux being absent; in -the Ostrich the second toe is also gone with the exception of a small -metatarsal, so that the foot retains only the third and fourth digits, -the third being much the larger of the two and bearing a claw, while -the fourth is clawless. - -In the Swifts, Cormorants, and Penguins, all four toes are directed -forwards. In most birds the hallux is directed backwards, and the -other toes forwards. In the Owls the fourth toe can be directed -backwards as well as the hallux, while in Parrots, Cuckoos, -Woodpeckers, and Toucans the fourth toe is permanently reversed. In -Trogons the second toe is reversed in addition to the hallux, but not -the fourth. - - -FOOTNOTES: - -[105] W.K. Parker, _Phil. Trans._ vol. 179, p. 385, 1888; and _Ibis_, -1888, p. 124. - -[106] See T.H. Huxley, "On the Classification of Birds," _P.Z.S._ -1867. - -[107] B. Lindsay, _P.Z.S._ 1885, p. 684. - - - - -CHAPTER XX. - -CLASS MAMMALIA. - - -The skeleton of the members of this class, the highest of the -vertebrata, has the following characteristics:-- - -Some part of the integument at some period of life is always provided -with hairs; these are epidermal structures arising from short papillae -of the Malpighian layer of the epidermis, which at once grow inwards -and become imbedded in pits of the dermis. Sometimes scales or spines -occur, and epidermal exoskeletal structures in the form of hoofs, -nails, claws and horns are also characteristic. As regards the -endoskeleton, the vertebral centra have terminal epiphyses except in -the Ornithodelphia and some Sirenia. In the skull the cranial region -is greatly developed as compared with that in lower vertebrates, and -whereas in many reptiles the true cranium is largely concealed by a -false roof, in mammals the only relic of this secondary roof is found -in the zygomatic arch, and postorbital bar. In the adult all the bones -except the mandible, hyoid, and auditory ossicles are firmly united -together. The basisphenoid is well ossified, and there is no -parasphenoid. The pro-otic ossifies, and unites with the epi-otic and -opisthotic before they coalesce with any other bones. - -The skull articulates with the vertebral column by means of two convex -occipital condyles formed mainly by the exoccipitals, and the mandible -articulates with the squamosal without the intervention of the -quadrate. The latter is much reduced, and is converted into the -tympanic ring, while the hyomandibular of fish is represented by the -auditory ossicles[108]. - -The teeth are always attached to the maxillae, premaxillae and -mandibles, never to any of the other bones. They are nearly always -implanted in distinct sockets, and are hardly ever ankylosed to the -bone. The teeth of mammals are generally markedly heterodont, four -forms, incisors, canines, premolars, and molars, being commonly -distinguishable. Some mammals are _monophyodont_, having only a single -set of teeth, but the great majority are _diphyodont_, having two -sets, a deciduous or milk dentition, and a permanent dentition. - -The _incisors_, the front teeth, are simple, one-rooted, adapted for -cutting, and are nearly always borne by the premaxillae. Next come the -_canines_, one on each side in each jaw. They are generally large -teeth adapted for tearing or holding, and get their name from the fact -that they are largely developed in the dog. The remaining teeth form -the grinding series, the more posterior of them being the _molars_, -which are not preceded by milk teeth[109]. Between the molars and the -canines are the _premolars_, which do as a rule have milk or deciduous -predecessors, though very frequently the first of them is without a -milk predecessor. - -In describing the dentition of any mammal, for the sake of brevity a -formula is generally made use of. Thus, the typical mammalian -dentition is expressed by the formula - - _i_ 3/3 _c_ 1/1 _pm_ 4/4 _m_ 3/3 = 11/11, - -giving twenty-two teeth on each side, or forty-four altogether[110]. -The incisors are represented by _i_, the canines by _c_, the premolars -by _p_ or _pm_, and the molars by _m_. The numbers above the lines -represent the teeth in the upper jaw, those below the lines the teeth -in the lower jaw. The milk dentition is expressed by a similar formula -with _d_ (deciduous) prefixed to the letter expressing the nature of -the tooth. - -The following terms are of frequent use as characterising certain -forms of the grinding surfaces of teeth, and it will be well to define -them at once. - -_Bunodont_ is a term applied to teeth with broad crowns raised into -rounded tubercles, e.g. the grinding teeth of Pigs and Hippopotami; - -_Bilophodont_ to teeth marked by a simple pair of transverse ridges, -with or without a third ridge running along the outer border of the -tooth at right angles to the other two, e.g. the grinding teeth of -_Lophiodon_, Kangaroo, Manatee, Tapir, _Dinotherium_; - -_Selenodont_ to teeth marked by crescentic ridges running from the -anterior towards the posterior end of the tooth, e.g. the grinding -teeth of the Ox and Sheep. - -Teeth whose crowns are low so that their whole structure is visible -from the grinding surface are called _brachydont_, while those with -higher crowns, in which the bases of the infoldings of enamel are -invisible from the grinding surface are said to be _hypsodont_. -Bunodont teeth are brachydont, the teeth of the Horse and Ox are -hypsodont. - -Passing now to the appendicular skeleton--the shoulder girdle differs -markedly from that of Sauropsids in the fact that the coracoid, except -in the Ornithodelphia, is greatly reduced, generally forming only a -small process on the scapula. In the pelvis the pubes meet in a -ventral symphysis, except in some Insectivora and Chiroptera. In many -mammals a fourth pelvic element, the _acetabular bone_, is -distinguishable. The ankle joint is _cruro-tarsal_, or situated -between the proximal tarsal bones and the tibia and fibula. Carpalia 4 -and 5 are united forming the _unciform_; and the ulnar sesamoid bone -or _pisiform_ is generally well developed. In the proximal row of -tarsal elements there are only two bones, the calcaneum and -astragalus. Of these the calcaneum is the fibulare, and the -astragalus is generally regarded as the tibiale and intermedium -fused[111]. - - -_Subclass I._ ORNITHODELPHIA OR PROTOTHERIA. - -This subclass contains only a single order, the Monotremata, and the -following characteristics are equally applicable to the subclass and -to the order. The vertebral centra have no epiphyses, and the odontoid -process remains for a long time free from the centrum of the second -vertebra. With the exception of the atlas of _Echidna_ the cervical -vertebrae are without zygapophyses. The cranial walls are smooth and -rounded, and the sutures between the several bones early become -completely obliterated as in birds. The mandible is a very slight -structure, with no ascending ramus, and with the coronoid process (see -p. 398) and angle rudimentary. The auditory ossicles show a low state -of development. The tubercula of the ribs articulate with the sides of -the centra of the thoracic vertebrae, not with the transverse -processes. Some of the cervical ribs remain for a long time separate -from the vertebrae. Well ossified sternal ribs occur. No true teeth -are present in the adult. The young _Ornithorhynchus_ has functional -molar teeth, but in the adult their place is taken by horny plates. In -the Echidnidae neither teeth nor horny plates occur. - -The coracoid (fig. 66, 3) is complete and well developed, and -articulates with the sternum. A precoracoid (epicoracoid) occurs in -front of the coracoid, and there is a large interclavicle (fig. 66, -6). The ridge on the scapula, corresponding to the spine of other -mammals, is situated on the anterior border instead of in the middle -of the outer surface. Epipubic bones are present. In the Echidnidae, -but not in _Ornithorhynchus_[112], the central portion of the -acetabulum is unossified as in birds. The humerus has a prominent -deltoid crest; its ends are much expanded, and the distal end is -pierced by an ent-epicondylar foramen. The fibula has a broad proximal -process resembling an olecranon. The limbs and their girdles bear a -striking resemblance to those of some Theromorphous reptiles. - -[Illustration FIG. 66. VENTRAL VIEW OF THE SHOULDER-GIRDLE AND STERNUM -OF A DUCKBILL (_Ornithorhynchus paradoxus_) × 3/4 (after PARKER). - - 1 and 2. scapula. - 3. coracoid. - 4. precoracoid (epicoracoid). - 5. glenoid cavity. - 6. interclavicle. - 7. clavicle. - 8. presternum. - 9. third segment of mesosternum. - 10. sternal rib. - 11. intermediate rib. - 12. vertebral rib.] - -The order Monotremata includes only two living families, the -Echidnidae and Ornithorhynchidae. - - -MESOZOIC MAMMALIA[113]. - -It will be well here to briefly refer to certain mammals of small -size, the remains of which have been found in deposits of Mesozoic -age. In the great majority of cases they are known only by the lower -jaw, or sometimes only by isolated teeth. A large number of them are -commonly grouped together as the Multituberculata, and are sometimes, -partly owing to the resemblance of their teeth to those of -_Ornithorhynchus_, placed with the Prototheria, sometimes between the -Prototheria and the Metatheria. They are characterised by having a -single pair of large incisors in the lower jaw, and one large with one -or two smaller incisors in each premaxillae. The lower canines are very -small or altogether wanting. The incisors are separated by a diastema -from the grinding teeth, which are sometimes (_Tritylodon_) -characterised by the possession of longitudinal rows of little -tubercles separated by grooves, sometimes by having the premolars -provided with high cutting edges, whose surfaces are obliquely -grooved. Some of the Mesozoic mammals found associated with the -Multituberculata, have however a dentition of an altogether different -type, with at least three lower incisors, well developed canines and -premolars, and numerous molars with peculiar three-cusped or -tritubercular grinding surfaces. These mammals, one of the best known -of which is _Phascolotherium_, are commonly separated from the -Multituberculata, and are divided by Osborn into two groups, one -allied to the Marsupials, and one to the Insectivores. The group -showing Marsupial affinities is further subdivided into carnivorous, -omnivorous, and herbivorous subgroups. The members of both groups -commonly have four premolars, and six to eight molars in each -mandibular ramus. - - -_Subclass II._ DIDELPHIA OR METATHERIA. - -This subclass, like the previous one, contains only a single order, -viz. the Marsupialia[114]; but the forms referable to it are far more -numerous than in the case of the Monotremata. - -The integument is always furry, and the teeth are always -differentiated into incisors, canines, premolars and molars. Except in -_Phascolomys_, the number of incisors in the upper and lower jaws is -never equal, and the number in the upper usually exceeds that in the -lower jaw. There is no such regular succession and displacement of -teeth as in most mammals. Sometimes the anterior teeth are diphyodont, -and as a general rule the tooth commonly regarded as the last premolar -is preceded by a milk tooth. The majority of the permanent teeth of -most Marsupials are regarded as belonging to the milk series for two -reasons, (1) they are developed from the more superficial tissues of -the jaws, (2) a second set, the permanent teeth, begin to develop as -outgrowths from them, but afterwards become aborted[115]. - -The odontoid process at an early stage becomes fused with the centrum -of the second cervical vertebra, and the number of thoraco-lumbar -vertebrae is always nineteen. The skull has several characteristic -features. The tympanic bone remains permanently distinct, and the -anterior boundary of the tympanic cavity is formed by the alisphenoid. -The carotid canal perforates the basisphenoid, and the lachrymal canal -opens either outside the orbit or at its margin. There are generally -large vacuities in the palate. The angle of the mandible is (except in -_Tarsipes_) more or less inflected; and as a rule the jugal furnishes -part of the articular surface for the mandible. There is no -precoracoid (epicoracoid) or interclavicle, and the coracoid is -reduced to form a mere process of the scapula, not coming near the -sternum. - -Epipubic, or so-called marsupial bones[116], nearly always occur, and -a fourth pelvic element, the acetabular bone, is frequently developed. -The fibula is always complete at its distal end, sometimes it is fused -with the tibia, but often it is not only free but is capable of a -rotatory movement on the tibia. This is the case in the families -Phascolomyidae, Didelphyidae, and Phalangeridae. - -The Marsupialia can be subdivided into two main groups, according to -the character of the teeth:-- - - -1. POLYPROTODONTIA. - -In this group the incisors are small, subequal and numerous, not less -than 4/3. The canines are larger than the incisors, and the molars -have sharp cusps. The members of this group are all more or less -carnivorous or insectivorous. The group includes the families -Didelphyidae, Dasyuridae, Peramelidae, and Notoryctidae[117]. - - -2. DIPROTODONTIA. - -In this group the incisors do not exceed 3/3, and are usually 3/1, -occasionally 1/1. The first upper and lower incisors are large and -cutting. The lower canines are always small or absent, and so in most -cases are the upper canines. The molars have bluntly tuberculated, or -transversely ridged crowns. The group includes the families -Phascolomyidae, Phalangeridae, Macropodidae, and Epanorthidae. - - -_Subclass III._ MONODELPHIA OR EUTHERIA. - -This great group includes all the Mammalia except the orders -Monotremata and Marsupialia. Coming to their general characteristics-- -as in the Didelphia the odontoid process and cervical ribs early -become fused with the centra which bear them, while the coracoid is -reduced so as to form a mere process on the scapula, and there is no -precoracoid (epicoracoid), such as is found in Ornithodelphia. -Clavicles may be present or absent; when fully developed they -articulate with the sternum, usually directly, but occasionally, as in -some Rodents and Insectivores, through the remains of the sternal end -of the precoracoid. There is never any interclavicle in the adult, -though sometimes traces of it occur during development. In the pelvis -the acetabula are imperforate; and well-developed epipubic bones are -never found in the adult, though traces of them occur in some -Carnivores and foetal Ungulates. - - -_Order 1._ EDENTATA[118]. - -Teeth are not, as the name of the order seems to imply, always -wanting; and sometimes they are very numerous. They are, however, -always imperfect, and, with very few exceptions, are homodont and -monophyodont. They have persistent pulps, and so grow indefinitely and -are never rooted. In all living forms they are without enamel, -consisting merely of dentine and cement, and are never found in the -front part of the mouth in the situation occupied by the incisors of -other mammals. These characters derived from the teeth are the only -ones common to the various members of the order, which includes the -living sloths, ant-eaters, armadillos, pangolins and aard-varks, -together with various extinct forms, chiefly found in beds of late -tertiary age in both North and South America, the best known being the -Megatheridae and Glyptodonts. - - -_Order 2._ SIRENIA[119]. - -The skeleton of these animals has a general fish-like form, in -correlation with their purely aquatic habits. The fore limbs have the -form of paddles, but the number of phalanges is not increased beyond -the normal. There are no external traces of hind limbs. - -The whole skeleton and especially the skull and ribs is remarkably -massive and heavy. The dentition varies; in the two living genera -_Manatus_ and _Halicore_, incisor and molar teeth are present, in one -extinct genus, _Rhytina_, teeth are entirely absent, while in another, -_Halitherium_, the dentition is more decidedly heterodont than in -living forms. In the two living genera the dentition is monophyodont, -but in _Halitherium_ the anterior grinding teeth are preceded by milk -teeth. The tongue and anterior part of the palate and lower jaw are -covered with roughened horny plates. The skull is noticeable for the -size and backward position of the anterior nares, also for the absence -or small size of the nasal bones. There is no union of certain of the -vertebrae to form a sacrum, and in living forms the centra are not -terminated by well-formed epiphyses[120]. - -The cervical vertebrae are much compressed, but they are never -ankylosed together. In _Manatus_ there are only six cervical -vertebrae. The caudal vertebrae have well-developed chevron bones. The -humerus is distinctly articulated to the radius and ulna, and these -two bones are about equally developed, and are often fused together. -There are no clavicles, and the pelvis is vestigial, consisting of a -pair of somewhat cylindrical bones suspended at some distance from the -vertebral column. In living forms there is no trace of a posterior -limb, but in _Halitherium_ there is a vestigial femur connected with -each half of the pelvis. - - -_Order 3._ CETACEA[121]. - -In these mammals the general form is more fish-like than is the case -even in the Sirenia. The skin is generally almost completely naked, -but hairs are sometimes present in the neighbourhood of the mouth, -especially in the foetus. In some Odontoceti vestiges of dermal -ossicles have been described, and in _Zeuglodon_ the back was probably -protected by dermal plates. The anterior limbs have the form of -flattened paddles, showing no trace of nails, the posterior limb bones -are quite vestigial or absent, and there is never any external sign of -the limb. Teeth are always present at some period of the life history, -but in the whalebone whales they are only present during foetal life, -their place in the adult animal being taken by horny plates of baleen. -In all living forms the teeth are simple and uniform structures -without enamel; they have single roots, and the alveoli in which they -are imbedded are often incompletely separated from one another. As in -some forms traces of a replacing dentition have been described, it has -been concluded that the functional teeth of Cetacea belong to the milk -dentition. - -The texture of the bones is spongy. The cervical vertebrae are very -short, and though originally seven in number, are in many forms -completely fused, forming one solid mass (fig. 67). The odontoid -process of the axis is short and blunt, or may be completely wanting. -The lumbar and caudal vertebrae are large and numerous, and as -zygapophyses are absent, are very freely movable on one another; -zygapophyses are also absent from the posterior thoracic vertebrae. -The lumbar vertebrae are sometimes more numerous than the thoracic. -The epiphyses are very distinct, and do not unite with the centra till -the animal is quite adult. None of the vertebrae are united to form a -sacrum, but the caudal vertebrae have large chevron bones. - -[Illustration FIG. 67. CERVICAL VERTEBRAE OF A CA'ING WHALE -(_Globicephalus melas_) × 1/4. (Camb. Mus.) - - 1. centrum of seventh cervical vertebra. - 2. neural arch of seventh cervical vertebra. - 3. transverse process of atlas. - 4. foramen for exit of first spinal nerve. - 5. transverse process of axis. - 6. fused neural spines of atlas and axis.] - -The skull is peculiarly modified; the bones forming the occipital -segment show a specially strong development, and the cranial cavity is -short, high, and almost spherical. The supra-occipital is very large -and rises up to meet the frontals, thus with the interparietal -completely separating the parietals from one another. - -The frontals are expanded, forming large bony plates, which roof over -the orbits. The zygomatic process of the squamosal is extremely large -and extends forwards to meet the supra-orbital process of the frontal; -the zygomatic process of the jugal is on the contrary very slender. -The face is drawn out into a long rostrum, formed of the maxillae and -premaxillae surrounding the vomer and the mesethmoid cartilage. The -maxillae are specially large, and extend backwards so as to partially -overlap the frontals. The nasals are always small, and the anterior -nares open upwards between the cranium and rostrum. The periotics are -loosely connected with the other bones of the skull and the tympanics -are commonly large and dense. The mandible has hardly any coronoid -process, and the condyles are at its posterior end. - -There are no clavicles, but the scapula and humerus are well -developed. The humerus moves freely in the glenoid cavity, but all the -other articulations of the anterior limb are imperfect; the various -bones have flattened ends, and are connected with one another by -fibrous tissue, which allows of hardly any movement. Frequently the -carpus is imperfectly ossified. - -The number of digits in the manus is generally five, sometimes four, -and when there are four digits it is the third and not the first that -is suppressed. The number of phalanges in the second and third digits -almost always exceeds that which is normal in mammals, and the -phalanges are also remarkable for having epiphyses at both ends. The -pelvis is represented by two small bones which lie suspended -horizontally at some distance below the vertebral column; in some -cases vestiges of the skeleton of the hind limb are attached to them. - -The Cetacea are divided into three suborders. - - -_Suborder_ (1). ARCHAEOCETI. - -The members of this group are extinct; they differ from all living -Cetacea in having the dentition heterodont and in the fact that the -back was probably protected by dermal plates. The skull is elongated -and depressed, and the brain cavity is very small. The temporal fossae -are large, and there is a strong sagittal crest. The nasals and -premaxillae are a good deal larger than they are in living Cetacea, and -the anterior nares are usually far forward. The cervical vertebrae are -not fused with one another, and the lumbar vertebrae are unusually -elongated. - -The limbs are very imperfectly known, but while the humerus is much -longer than in modern Cetaceans, it is nevertheless flattened -distally, indicating that the limb was paddle-like, and that there was -scarcely any free movement between the fore-arm and upper arm. - -The best known genus is _Zeuglodon_, which is found in beds of Eocene -age in various parts of Europe, and in Alabama. - - -_Suborder_ (2). MYSTACOCETI OR BALAENOIDEA. - -These are the Whalebone Whales or True Whales. - -Calcified teeth representing the milk dentition occur in the foetus, -but the teeth are never functional, and always disappear before the -close of foetal life. There is a definite though small olfactory -fossa. The palate is provided with plates of baleen or whalebone. The -skull is symmetrical, and is extremely large in proportion to the -body. The nasals are moderately well developed, and the maxillae do not -overlap the orbital processes of the frontals. The lachrymals are -small and distinct from the jugals. The tympanics are ankylosed to the -periotics, and the rami of the mandible do not meet in a true -symphysis. The ribs articulate only with the transverse processes, and -the capitula are absent or imperfectly developed. Only one pair of -ribs meets the sternum, which is composed of a single piece. - -The group includes among others the Right whale (_Balaena_), -Humpbacked whale (_Megaptera_), and Rorqual (_Balaenoptera_). - - -_Suborder_ (3). ODONTOCETI. - -Teeth always exist after birth and baleen is never present. The teeth -are generally numerous, but are sometimes few and deciduous; the -dentition is homodont (except in _Squalodon_). The dorsal surface of -the skull is somewhat asymmetrical, there is no trace of an olfactory -fossa, the nasals are quite rudimentary, and the hind ends of the -maxillae cover part of the frontals; in all these respects the skull -differs from that of the Mystacoceti. The lachrymal may either be -united to the jugal or may be large and distinct. The tympanic is not -ankylosed to the periotic. The rami of the mandible are nearly -straight and become united in a long symphysis. Some of the ribs have -well developed capitula articulating with the vertebral centra. The -sternum is almost always composed of several pieces as in other -mammals, and several pairs of ribs are connected with it. There are -always five digits to the manus, though the first and fifth are -usually very little developed. - -The suborder includes the Sperm Whale (_Physeter_), Narwhal -(_Monodon_), Dolphin (_Delphinus_), Porpoise (_Phocoena_), and many -other living forms as well as the extinct _Squalodon_ which differs -from the other members of the suborder in its heterodont dentition. - -_Order 4._ UNGULATA. - -This order includes a great and somewhat heterogeneous group of -animals, a large proportion of which are extinct. They all (except -certain extinct forms) agree in having the ends of the digits either -encased in hoofs or provided with broad flat nails. The teeth are -markedly heterodont and diphyodont, and the molars have broad crowns -with tuberculated or ridged surfaces. Clavicles are never present in -the adult except in a few generalised extinct forms such as -_Typotherium_, and it is only recently that vestigial clavicles have -been discovered in the embryo[122]. The scaphoid and lunar are always -distinct. - -The order Ungulata may be subdivided into two main groups, Ungulata -vera and Subungulata. - - -_Section I._ UNGULATA VERA[123]. - -The cervical vertebrae except the atlas are generally opisthocoelous. -The feet are never _plantigrade_[124]. In all the living and the great -majority of the extinct forms the digits do not exceed four, the first -being suppressed. In the carpus the os magnum articulates freely with -the scaphoid, and is separated from the cuneiform by the lunar and -unciform. In the tarsus the cuboid articulates with the astragalus as -well as with the calcaneum, and the proximal surface of the astragalus -is marked by a pulley-like groove. All the bones of the carpus and -tarsus strongly interlock. These characters with regard to the carpus -and tarsus do not hold in _Macrauchenia_ and its allies. The humerus -never has an ent-epicondylar foramen. - -The group is divided into two very distinct suborders:-- - - -_Suborder_ (1). ARTIODACTYLA. - -The Artiodactyla have a number of well marked characters, one of the -most obvious being the fact that many of the most characteristic forms -have large paired outgrowths on the frontal bones. These may be (1) -solid deciduous bony _antlers_, or (2) more or less hollow bony -outgrowths which are sheathed with permanently growing horn. - -The premolar and molar teeth are usually dissimilar, the premolars -being one-lobed and the molars two-lobed; the last lower molar of both -the milk and permanent dentitions is almost always three-lobed. - -The grinding surfaces of the molar teeth have a tendency to assume one -of two forms. In the Pigs and their allies the crowns are bunodont[1], -while in the more highly specialised Ruminants the crowns are -selenodont[125]. The nasals are not expanded posteriorly, and there is -no alisphenoid canal[126]. The thoraco-lumbar vertebrae are always -nineteen. The symphysis of the ischia and pubes is very elongated, and -the femur has no third trochanter. The limbs never have more than four -digits, and are symmetrical about a line drawn between the third and -fourth digits; the digits, on the other hand, are never symmetrical in -themselves. The astragalus has pulley-like surfaces both proximally -and distally, and articulates with the navicular and cuboid by two -nearly equal facets. The calcaneum articulates with the lower end of -the fibula when that bone is fully developed. - -In the Artiodactyla are included the following living groups:-- - -_a._ Suina. Pigs and Hippopotami. - -_b._ Tylopoda. Camels and Llamas. - -_c._ Tragulina. Chevrotains. - -_d._ Ruminantia or Pecora. Deer, giraffes, oxen, sheep and antelopes. - - -_Suborder_ (2). PERISSODACTYLA[127]. - -In this group there are never any bony outgrowths from the frontals. -The grinding teeth form a continuous series, the posterior premolars -resembling the molars in complexity, and the last lower molar -generally has no third lobe. The cervical vertebrae with the -exception of the atlas almost always have markedly opisthocoelous -centra, but in _Macrauchenia_ they are flat. The nasals are expanded -posteriorly, and an alisphenoid canal is present. The thoraco-lumbar -vertebrae are never less than twenty-two in number and are usually -twenty-three. The femur has a third trochanter (except in -_Chalicotherium_). The third digit of the manus and pes is symmetrical -in itself, and larger than the others, and in some cases the other -digits are quite vestigial. The number of the digits of the pes is -always odd. The astragalus is abruptly truncated distally, and the -facet by which it articulates with the cuboid, is much smaller than -that by which it articulates with the navicular. The calcaneum does -not articulate with the fibula, except in _Macrauchenia_. The group -includes many extinct forms, and the living families of the Tapirs, -Horses and Asses, and Rhinoceroses. - - -_Section II._ SUBUNGULATA. - -In this group is placed a heterogeneous collection of animals, the -great majority of which are extinct. There is really no characteristic -which is common to them all, and which serves to distinguish them as a -group from the Ungulata vera. But the most distinctive character -common to the greatest number of them is to be found in the carpus, -whose bones in most cases retain their primitive relation to one -another, the os magnum articulating with the lunar and sometimes just -meeting the cuneiform, but in living forms at any rate not -articulating with the scaphoid. The feet frequently have five -functional digits, and may be plantigrade. The proximal surface of the -astragalus is generally flattened instead of being pulley-like as in -Ungulata vera. - - -_Suborder_ (1). TOXODONTIA. - -This suborder includes some very aberrant extinct South American -ungulates, which have characters recalling the Proboscidea, both -groups of Ungulata vera, and the Rodentia. The limbs are -subplantigrade or digitigrade, and the digits are three, rarely five, -in number, the third being most developed. The carpus resembles that -of the Ungulata vera, in that the bones interlock and the magnum -articulates with the scaphoid. In the tarsus, however, the bones do -not interlock. The astragalus has a pulley-like proximal surface -(except in _Astrapotherium_, in which it is flat), and articulates -only with the navicular, not meeting the cuboid. The calcaneum has a -large facet for articulation with the fibula, as in Artiodactyla. -There is no alisphenoid canal, and the orbit is confluent with the -temporal fossa. Some of the forms (e.g. _Nesodon_) referred to this -group have the typical mammalian series of forty-four teeth, but in -others the canines are undeveloped. In _Toxodon_ all the cheek teeth -have persistent pulps, while in _Nesodon_ and _Astrapotherium_ they -are rooted. A clavicle is sometimes present (_Typotherium_), and the -femur sometimes has a third trochanter (_Typotherium_ and -_Astrapotherium_), sometimes is without one (_Toxodon_). - -The remains of these curious Ungulates have been found in beds of late -Tertiary age in South America. - - -_Suborder_ (2). CONDYLARTHRA[128]. - -This group includes some comparatively small extinct ungulates, which -are best known from the Lower Eocene of Wyoming, though their remains -have also been found in deposits of similar age in France and -Switzerland. Their characters are little specialised, and they show -relationship on the one hand to the Ungulata vera and on the other to -the Hyracoidea. They also have characters allying them to the -Carnivora. They generally have the typical mammalian series of -forty-four teeth, the molars being brachydont and generally bunodont. -The premolars are more simple than the molars. The limbs are -plantigrade, and have five digits with rather pointed ungual -phalanges. The os magnum, as in living Subungulates, articulates with -the lunar, not reaching the scaphoid. The astragalus has an elongated -neck, a pulley-like proximal and a convex distal articular surface, -and does not articulate with the cuboid. The humerus has an -ent-epicondylar foramen, and the femur has a third trochanter. The -best known genus is _Phenacodus_; it is perhaps the most primitive -ungulate whose skeleton is thoroughly well known, and is of special -interest from the fact that it is regarded as the lowest stage in the -evolutionary series of the horse. Its remains are found in the Lower -Eocene of Wyoming. - - -_Suborder_ (3). HYRACOIDEA[129]. - -This group of animals is very isolated, having no very close allies, -either living or extinct. The digits are provided with flat nails, -except the second digit of the pes, which is clawed. Canine teeth are -absent, and the dental formula is usually given as _i_ 1/2, _c_ 0/0, -_pm_ 4/4, _m_ 3/3. The upper incisors are long and curved, and have -persistent pulps as in Rodents; their terminations are, however, -pointed, not chisel-shaped, as in Rodents. The lower incisors have -pectinated edges. The grinding teeth have a pattern much like that in -_Rhinoceros_. In the skull (fig. 83) the postorbital processes of the -frontal and jugal almost or quite meet. The jugal forms part of the -glenoid cavity for articulation with the mandible, and also extends -forwards so as to meet the lachrymal. There is an alisphenoid canal. -There are as many as twenty-one or twenty-two thoracic vertebrae, and -the number of thoraco-lumbar vertebrae reaches twenty-eight or thirty. -There are no clavicles, and the scapula has no acromion; the coracoid -process is, however, well developed. The ulna is complete. In the -manus the second, third and fourth digits are approximately equal in -size, the fifth is smaller, and the first is vestigial. The femur has -a slight ridge representing the third trochanter. The fibula is -complete, but is generally fused with the tibia proximally. There is a -complicated articulation between the tibia and astragalus, which has a -pulley-like proximal surface. In the pes the three middle digits are -well developed, but there is no trace of a hallux, and the fifth digit -is represented only by a vestigial metatarsal. - -The only representatives of the suborder are some small animals -belonging to the genus _Procavia_ (_Hyrax_), which is found in Africa -and Syria; some of the species are by many authors placed in a -distinct genus _Dendrohyrax_. - - -_Suborder_ (4). AMBLYPODA[130]. - -This suborder includes a number of primitive extinct Ungulates, many -of which are of great size. Their most distinguishing characteristics -are afforded by the extremities. In the carpus the bones interlock a -little more than is the case in most Subungulata, and the corner of -the os magnum reaches the scaphoid, while the lunar articulates -partially with both magnum and unciform, instead of only with the -magnum. In the tarsus the cuboid articulates with both the calcaneum -and the astragalus, which is remarkably flat. The manus and pes are -short, nearly or quite plantigrade, and have the full number of -digits. The cranial cavity is singularly small. Canine teeth are -present in both jaws, and the grinding teeth have short crowns, marked -by =V=-shaped ridges. The pelvis is large, the ilia are placed -vertically, and the ischia do not take part in the ventral symphysis. - -The best known animals belonging to this suborder are the -Uintatheriidae (Dinocerata)[131], found in the Upper Eocene of -Wyoming. They are as large as elephants, and are characterised by the -long narrow skull drawn out into three pairs of rounded protuberances, -by the strong occipital crest, and by the very large upper canines. - - -_Suborder_ (5). PROBOSCIDEA. - -This suborder includes the largest of land mammals, the Elephants, and -certain of their extinct allies. The limbs are strong, and are -vertically placed; the proximal segment is the longest, and the manus -and pes are pentedactylate and subplantigrade. The digits are all -enclosed in a common integument, and each is provided with a broad -hoof. The vertebral centra are much flattened and compressed, -especially in the cervical region. The number of thoracic vertebrae is -very great, reaching twenty. The skull (figs. 96 and 97) is extremely -large, this being due to the great development of air cells, which -takes place in nearly all the bones of the adult skull. In the young -skull there are hardly any air cells, and the growth of the cranial -cavity does not by any means keep pace with the growth of the skull in -general. The supra-occipital is very large, and forms a considerable -part of the roof of the skull. The nasals and jugals are short, and -the premaxillae very large. The rami of the mandible meet in a long -symphysis, and the ascending portion is very high. Canine teeth are -absent, and the incisors have the form of ever-growing tusks composed -mainly of dentine; in living forms they are present in the upper jaw -only. The grinding teeth are large, and in living forms have a very -complex structure and mode of succession. In some of the extinct -forms, such as _Mastodon_ and especially _Dinotherium_, the teeth are -much more simple. In every case the teeth have the same general -structure, consisting of a series of ridges of dentine, coated with -enamel. In the more specialised forms the valleys between the ridges -are filled up with cement. The acromion of the scapula has a recurved -process, similar to that often found in rodents. Clavicles are absent. -The radius and ulna are not ankylosed, but are incapable of any -rotatory movement. All the bones of the extremities are very short and -thick; the scaphoid articulates regularly with the trapezoid and the -lunar with the magnum. The ilia are vertically placed, and are very -much expanded; the ischia and pubes are small, and form a short -symphysis. The femur has no third trochanter, and the tibia and fibula -are distinct. The fibula articulates with the calcaneum, and the -astragalus is very flat. - - * * * * * - -Here brief reference may be made to the TILLODONTIA[132], a group of -extinct mammals found in the Eocene beds of both Europe and North -America. They seem to connect together the Ungulata, Rodentia, and -Carnivora. - -The skull resembles that of bears, but the grinding teeth are of -Ungulate type, while the second incisors resemble those of rodents, -and have persistent pulps. The femur has a third trochanter, and the -feet resemble those of bears in being plantigrade and having pointed -ungual phalanges, differing, however, in having the scaphoid and lunar -distinct. - - -_Order 5._ RODENTIA. - -The Rodents form a very large and well-defined group of mammals easily -distinguishable by their peculiar dentition. Canines are absent, and -the incisors are very large and curved, growing from persistent pulps. -They are rectangular in section and are much more thickly coated with -enamel on their anterior face than elsewhere; consequently, as they -wear down they acquire and retain a chisel-shaped (scalpriform) edge. -There is never more than one pair of incisors in the mandible, and -except in the Hares and Rabbits, there is similarly only a single pair -in the upper jaw. These animals are, too, the only rodents which have -well developed deciduous incisors. There is always a long diastema -separating the incisors from the grinding teeth. The grinding teeth, -which are arranged in a continuous series, vary in number from two to -six in the upper jaw, and from two to five in the lower jaw. The -number of premolars is always below the normal, often they are -altogether wanting, but generally they are 1/1. Sometimes the grinding -teeth form roots, sometimes they grow persistently. - -The premaxillae are always large, and the orbits always communicate -freely with the temporal fossae. The condyle of the mandible is -elongated from before backwards, and owing to the absence of a -postglenoid process to the squamosal, a backward and forward motion of -the jaw can take place. The zygomatic arch is complete, but the jugal -is short and only forms the middle of it. The palate is small, being -sometimes, as in the hares, narrowed from before backwards, sometimes -as in the mole-rats (Bathyerginae) narrowed transversely. - -The thoraco-lumbar vertebrae are usually nineteen in number. Clavicles -are generally present, and the acromion of the scapula is commonly -very long. The feet are as a rule plantigrade, and provided with five -clawed digits. - -There are two main groups of Rodentia; the Duplicidentata, or Hares -and Rabbits, which have two pairs of upper incisors, whose enamel -extends round to the posterior surface; and the Simplicidentata, in -which there is only a single pair of upper incisors, whose enamel is -confined to the anterior surface. This group includes all the Rodents -except the Hares and Rabbits. - - -_Order 6._ CARNIVORA. - -The living Carnivora form a natural and well-marked group, but as is -the case with so many other groups of animals, when their extinct -allies are included, it becomes impossible to readily define them. - -The manus and pes never have less than four well-developed digits, and -these are nearly always provided with more or less pointed nails, -generally with definite claws. The hallux and pollex are never -opposable. The dentition is diphyodont and markedly heterodont. The -teeth are always rooted, except in the case of the canines of the -Walrus. The incisors are generally 3/3, and are comparatively small, -while the canines are large, pointed, and slightly recurved. The cheek -teeth are variable, and are generally more or less compressed and -pointed; sometimes their crowns are flattened and tuberculated, but -they are never divided into lobes by deep infoldings of enamel. The -squamosal is drawn out into a postglenoid process, and the mandible -has a large coronoid process. The condyle of the mandible is -transversely elongated, and the glenoid fossa is very deep; in -consequence of this arrangement the mandible can perform an up and -down movement only, any rotatory or back and fore movement being -impossible. The jugal is large, and the zygomatic arch generally -strong, while the orbit and temporal fossa are in most cases -completely confluent. The scapula has a large spine. The clavicle is -never complete and is often absent, this forming an important -distinction between the skeleton of a Carnivore and of any Insectivore -except _Potamogale_. The humerus often has an ent-epicondylar foramen, -and the radius and ulna, tibia and fibula are always separate. The -manus is often capable of the movements of pronation and supination, -and the scaphoid, lunar and centrale are in living forms always united -together. - -The order Carnivora includes three suborders. - - -_Suborder_ (1). CREODONTA[133]. - -This suborder contains a number of extinct Carnivora, which present -very generalised characters. - -The cranial cavity is very small; and the fourth upper premolar and -first lower molar are not differentiated as carnassial teeth[134], as -they are in modern Carnivora. The Creodonta also differ from modern -Carnivora in the fact that the scaphoid and lunar are usually -separate, and that the femur has a third trochanter. The feet are -plantigrade. - -They resemble the Condylarthra, another very generalised group, in -having an ent-epicondylar foramen. - -They occurred throughout the Tertiary period in both Europe and North -America, and have also been found in India. One of the best known -genera is _Hyaenodon_. - - -_Suborder_ (2). CARNIVORA VERA or FISSIPEDIA. - -The skeleton is mainly adapted for a terrestrial mode of life, and the -hind limbs have the normal mammalian position. In almost every case -the number of incisors is 3/3. Each jaw always has one specially -modified _carnassial_ or sectorial tooth which bites like a scissors -blade against a corresponding tooth in the other jaw. In front of it -the teeth are always more or less pointed, while behind it they are -more or less broadened and tuberculated. In the manus the first digit, -and in the pes the first and fifth digits are never longer than the -rest, and the digits of both limbs are almost invariably clawed. Some -forms are plantigrade, some digitigrade, some subplantigrade. The -group includes all the ordinary terrestrial Carnivora, and is divided -into three sections:-- - -Æluroidea[135], including the cats, civets, hyaenas, and allied forms. - -Cynoidea, including the dog tribe. - -Arctoidea, including the bears, raccoons, weasels, and allied forms. - - -_Suborder_ (3). PINNIPEDIA[136]. - -In this suborder the limbs are greatly modified and adapted for a more -or less purely aquatic life, the proximal and middle segments of the -limbs are shortened, while the distal segment, especially in the leg, -is much elongated and expanded. There are always five well-developed -digits to each limb, and in the pes the first and fifth digits are -generally larger than the others. The digits generally bear straight -nails instead of claws, but even nails are sometimes absent. There is -no carnassial tooth, and the teeth in other ways differ considerably -from those of Carnivora vera. The incisors are always fewer than 3/3; -while the cheek teeth generally consist of four premolars and one -molar, all of very uniform character, being compressed with conical -crowns, and never more than two roots. - -The suborder includes three families--Otariidae (Eared Seals), -Trichechidae (Walrus), and Phocidae (Seals). - - -_Order 7._ INSECTIVORA[137]. - -This order contains a large number of small generally terrestrial -mammals. The limbs are plantigrade or subplantigrade, and are -generally pentedactylate. All the digits are armed with claws, and the -pollex and hallux are not opposable. The teeth are diphyodont, -heterodont, and rooted. The cheek teeth have tuberculated crowns, and -there are never less than two pairs of incisors in the mandible; often -the incisors, canines, and premolars are not clearly differentiated -from one another, and special carnassial teeth are never found. The -cranial cavity is small, and the facial part of the skull is generally -much developed; often the zygomatic arch is incomplete. Clavicles are -well developed (except in _Potamogale_), and the humerus generally has -an ent-epicondylar foramen. The femur frequently has a ridge -representing the third trochanter. There are two suborders: - - -_Suborder_ (1). DERMOPTERA. - -This suborder includes only a very aberrant arboreal genus -_Galeopithecus_, remarkable for its greatly elongated limb bones, and -peculiar dentition. The incisors of the lower jaw are deeply -pectinated or divided by several vertical fissures, the canines and -outer upper incisors have two roots. Ossified inter centra occur in -the thoraco-lumbar region of the vertebral column. - - -_Suborder_ (2). INSECTIVORA VERA. - -This suborder includes all the ordinary Insectivora, such as moles, -shrews and hedgehogs. The upper and lower incisors are conical, not -pectinated. - - -_Order 8._ CHIROPTERA[138]. - -This order is perhaps the best marked and most easily defined of all -the orders of mammals. The anterior limbs form true wings and the -whole skeleton is modified in relation to flight. - -The anterior limbs are vastly larger than the posterior; for all the -bones except the carpals are much elongated, and this applies -specially to the phalanges of all the digits except the pollex. - -The pollex is clawed and so is sometimes the second digit; the other -digits of the manus are without nails or claws. The teeth are -divisible into the four usual types and the series never exceeds _i_ -2/3 _c_ 1/1 _pm_ 3/3 _m_ 3/3 × 2, total 38. The milk teeth are quite -unlike the permanent teeth. The orbit is not divided by bone from the -temporal fossa. The vertebral column is short, and in old animals the -trunk vertebrae have a tendency to become partially fused together. -The cervical vertebrae are remarkably wide, and the development of -spinous processes is everywhere slight. The presternum has a prominent -keel for the attachment of the pectoral muscles. The clavicles are -very long and strong, and the scapula has a long spine and coracoid -process. The ulna is vestigial, consisting only of a proximal end -ankylosed to the radius. All the carpals of the proximal row--the -scaphoid, lunar and cuneiform--are united, forming a single bone. The -pelvis is very weak and narrow, and only in the Rhinolophidae do the -pubes meet in a symphysis. The anterior caudal vertebrae are -frequently united to the ischia. The fibula is generally vestigial, -and the knee joint is directed backwards instead of forwards. The pes -has five slender clawed digits, and the calcaneum is often drawn out -into a spur which helps to support the membrane connecting the hind -limbs with the tail. - -There are two suborders of Chiroptera: - -1. The MEGACHIROPTERA or Flying foxes, which almost always have smooth -crowns to the molar teeth, and the second digit of the manus clawed. - -2. The MICROCHIROPTERA including all the ordinary bats which have -cusped molar teeth, and the second digit of the manus clawless. - - -_Order 9._ PRIMATES. - -The dentition is diphyodont and heterodont, the incisors generally -number 2/2, and the molars, except in the Hapalidae (Marmosets), are -3/3. The cheek teeth are adapted for grinding, and the molars are more -complex than the premolars. A process from the jugal meets the -postorbital process of the frontal completing the postorbital bar. - -The clavicle is well developed, and the radius and ulna are never -united. The scaphoid and lunar of the carpus, and commonly also the -centrale, remain distinct from one another. As a rule both manus and -pes have five digits, but the pollex may be vestigial. The pollex is -opposable to the other digits, and so is the hallux except in Man; the -digits are almost always provided with flat nails. The humerus has no -ent-epicondylar foramen and the femur has no third trochanter. - -The order Primates is divisible into two suborders: - - -_Suborder_ (1). LEMUROIDEA. - -The skull has the orbit communicating freely with the temporal fossa -beneath the postorbital bar (except in _Tarsius_). The lachrymal -foramen is external to the margin of the orbit. Both pollex and hallux -are well developed. In the pes the second digit is terminated by a -long pointed claw, and so is also the third in _Tarsius_. The lumbar -region of the vertebral column is long, sometimes including as many as -nine vertebrae. Besides the Lemurs the group includes the aberrant -_Tarsius_ and _Chiromys_. - - -_Suborder_ (2). ANTHROPOIDEA. - -The skull has the orbit almost completely shut off from the temporal -fossa, and the lachrymal foramen is situated within the orbit. The -pollex is sometimes vestigial or absent. The second digit of the pes -has a flattened nail except in the Hapalidae, in which all the digits -of the pes except the hallux are clawed. - -The Anthropoidea are divided into five families: - -1. Hapalidae or Marmosets. - -2. Cebidae or American Monkeys. - -3. Cercopithecidae or Old World Monkeys. - -4. Simiidae or Anthropoid Apes. - -5. Hominidae or Men. - - -FOOTNOTES: - -[108] This is Gadow's view; according to Huxley the quadrate forms the -malleus; according to Baur it forms the zygomatic process of the -squamosal, and according to Broom the interarticular mandibular -cartilage. - -[109] According to Leche, _Morphol. Jahrb._ XIX. p. 502, the molar -teeth belong morphologically to the first series, i.e. they are milk -teeth without vertical successors. - -[110] The researches of Bateson, _P.Z.S._ 1892, p. 102, have shown -that cases of individual variation in the number of teeth are common. - -[111] Baur, however, suggests (_Anat. Anz._ vol. IV. 1889), that a -tibial sesamoid found in _Procavia_, many rodents, edentates and -_Ornithorhynchus_ is a vestigial tibiale, and that the astragalus is -the intermedium. - -[112] This perforation of the acetabulum in _Echidna_ is a secondary -character occurring late in development, and consequently is not of -phylogenetic importance. - -[113] See R. Owen, "Monograph of the Fossil Mammalia of the Mesozoic -Formation," _Pal. Soc. Mon._ 1871. - -H.F. Osborn, "Structure and Affinities of Mesozoic Mammals," _J. of -Philad. Acad._ 1888, vol. IX. - -O.C. Marsh, "Jurassic Mammals," _Amer. J. Sci._ 1878 _et seq._ - -[114] See Oldfield Thomas, _Brit. Mus. Cat. of Marsupialia and -Monotremata_ (1888). - -[115] W. Kükenthal, _Anat. Anz._ VI. p. 364, 1891. C. Röse, _Anat. -Anz._ VII. p. 639. - -[116] These bones however have no connection with the marsupium, being -nearly equally developed in both male and female. They are simply -sesamoid bones forming ossifications in the inner tendon of the -external oblique muscle, and are developed as supports for the -abdominal wall. Very similar structures have been independently -developed in various Amphibians, Reptiles and monodelphian Mammals. -See W. Leche, _Biol. Fören._ III. p. 120. - -[117] See H. Gadow, _P.Z.S._ 1892, p. 361. - -[118] See W.H. Flower, "On the Mutual Affinities of the Animals -composing the order Edentata," _P.Z.S._ 1882, p. 358. For the fossil -Edentates of N. America see E. Cope, _Amer. Natural._ 1889; for those -of S. America see various papers by F. Ameghino, H. Burmeister and R. -Owen. Also T.H. Huxley, "On the Osteology of Glyptodon," _Phil. -Trans._ 1865. - -[119] See J.F. Brandt, _Symbolae Sirenologicae_, St Petersburg, 1846, -1861, 1868. - -[120] Epiphyses are fully developed in _Halitherium_, and traces occur -in _Manatus_. - -[121] See P.J. van Beneden and P. Gervais, _Ostéographie des Cétacés_, -1869-80. - -[122] H. Wincza, _Morphol. Jahrb._ XVI., p. 647. - -[123] See M. Pavlow, "Études sur l'histoire paléontologique des -Ongulés." _Bull. Soc. Moscou_, 1887--1890. - -[124] In a _plantigrade_ animal the whole of the foot is placed on the -ground in walking. A _digitigrade_ animal places only its toes on the -ground. An intermediate condition is distinguished by the term -_subplantigrade_. - -[125] See p. 345. - -[126] See p. 401. - -[127] See E.D. Cope, "The Perissodactyla," _Amer. Natural._, 1887. - -[128] See E.D. Cope, "The Condylarthra," _Amer. Natural._, 1884, and -"Synopsis of the Vertebrates of the Puerco series," _Tr. Amer. Phil. -Soc._, 1888. O.C. Marsh, "A new order of extinct Eocene Mammals -(Mesodactyla)," _Amer. J. Sci._, 1892. - -[129] See O. Thomas, "On the species of Hyracoidea," _P.Z.S._, 1892, -p. 50. - -[130] See E.D. Cope, "The Amblypoda," _Amer. Natural._, 1884 and 1885. - -[131] See O.C. Marsh, "The Dinocerata," _U.S. Geol. Survey_, 1884, -vol. X. - -[132] See O.C. Marsh, _Amer. J. Sci._, 1875 and 1876. - -[133] E.D. Cope, "The Creodonta," _Amer. Natural._, 1884. W.B. Scott, -"Revision of the N. American Creodonta," _P. Ac. Philad._, 1892. - -[134] See next paragraph. - -[135] St G. Mivart, _The Cat_, London, 1881. - -[136] St G. Mivart, _P.Z.S._, 1885. - -[137] St G. Mivart, "On the Osteology of Insectivora," _J. Anat. -Physiol. norm. path._, 1867 and 1868, and _P.Z.S._, 1871. G.E. Dobson, -_Monograph of the Insectivora_, London, 1882--90. - -[138] See G.E. Dobson, _Brit. Mus. Catalogue of Chiroptera_, 1878. See -also other papers by the same author and by Oldfield Thomas. - - - - -CHAPTER XXI. - -THE SKELETON OF THE DOG[139] (_Canis familiaris_). - - -I. EXOSKELETON. - -The exoskeleton of the dog includes three sets of structures: 1. -hairs, 2. claws, 3. teeth. =Hairs= and =claws= are epidermal -exoskeletal structures, while =teeth= are partly of dermal, and partly -of epidermal origin. - -1. =Hairs= are delicate epidermal structures which grow imbedded in -little pits or follicles in the dermis. Specially large hairs forming -the =vibrissae= or =whiskers= grow attached to the upper lip. - -2. =Claws= are horny epidermal sheaths, one of which fits on to the -pointed distal phalanx of each digit. They are sharply curved -structures, and being in the dog non-retractile, their points are -commonly much blunted by friction with the ground. The claws of the -pollex, and of the hallux when it is present, however do not meet the -ground, and therefore remain comparatively sharp. - -3. =Teeth=[140]. Although as regards their mode of origin, teeth are -purely exoskeletal or tegumentary structures, they become so -intimately connected with the skull that they appear to belong to the -endoskeleton. - -Each tooth, as has been already described, consists of three distinct -tissues, dentine and cement of dermal origin, and enamel of epidermal -origin. - -[Illustration FIG. 68. DENTITION OF A DOG (_Canis familiaris_) × 1/2. -(Camb. Mus.) - - _i_ 2. second incisor. - _c._ canine. - _pm_ 1, _pm_ 4. first and fourth premolars. - _m_ 1. first molar.] - -The teeth of the dog (fig. 68) form a regular series arranged along -the margins of both upper and lower jaws, and imbedded in pits or -=alveoli= of the maxillae, premaxillae, and mandibles. They are all -fixed in the bone by tapering roots, and none of them grow from -persistent pulps. - -They are divisible into four distinct groups, the =incisors=, -=canines=, =premolars= and =molars=. There are three incisors, one -canine and four premolars on each side of each jaw. But while there -are three molars on each side of the lower jaw, the last is wanting in -the upper jaw. The dentition of the dog may then be represented by the -formula - - _i_ 3/3 _c_ 1/1 _pm_ 4/4 _m_ 2/3 × 2 = 42. - -In each jaw there is one large specially modified tooth called the -=carnassial=, the teeth in front of this are more or less pointed and -compressed, while those behind it are more or less flattened and -tuberculated. - -=Teeth of the upper jaw.= - -The first and second =incisors= are small teeth with long conical -roots and somewhat chisel-shaped crowns. Surrounding the base of the -crown there is a rather prominent ridge, terminated laterally by a -pair of small cusps. This ridge, the =cingulum=, serves to protect the -edge of the gums from injury by the hard parts of food. The third -incisor is a good deal like the others but larger, and has the -cingulum well developed though not terminated by lateral cusps. All -the incisors are borne by the premaxillae, the remaining teeth by the -maxillae. - -The =canine= is a large pointed tooth, slightly recurved and with a -long tapering root. - -The =premolars= are four in number, and in all the cingulum is fairly -well seen. The first is a very small tooth with a single tapering -root, the second and third are larger and have two roots, while the -fourth, the =carnassial=, is much the largest and has three roots. -Each of the second, third and fourth premolars has a stout blade, the -middle portion of which is drawn out into a prominent cone; the -posterior part of the fourth premolar forms a compressed ridge, and -at the antero-internal edge of the tooth there is a small inner -tubercle. - -The two =molar= teeth are of very unequal size. The first, which has -two anterior roots and one posterior, is wider than it is long, its -outer portion being produced into two prominent cusps, while its inner -portion is depressed. The second molar is a small tooth resembling the -first in its general appearance, but with much smaller outer cusps. - -=Teeth of the lower jaw.= - -The three =incisors= of the lower jaw have much the same character as -the first two of the upper jaw; while the =canine= is identical in -character with that of the upper jaw. - -The four =premolars= gradually increase in size from the first to the -last, but none are very large. The first premolar is a single-rooted -tooth resembling that of the upper jaw; the second, third and fourth -are two-rooted, like the second and third of the upper jaw, which they -closely resemble in other respects. - -The first =molar= forms the =carnassial= (fig. 84, V), and with the -exception of the canine, is much the largest tooth of the lower jaw; -it is a two-rooted tooth, with a long compressed bilobed blade, and a -posterior tuberculated talon or heel. The second molar is much -smaller, though likewise two-rooted, while the third molar is very -small and has only a single root. All the teeth except the molars are -preceded in the young animal by temporary =milk teeth=. These milk -teeth, though smaller, are very similar to the permanent teeth by -which they are ultimately replaced. - - -II. ENDOSKELETON. - -1. THE AXIAL SKELETON. - -This includes the vertebral column, the skull, and the ribs and -sternum. - - -A. THE VERTEBRAL COLUMN. - -This consists of a series of about forty vertebrae arranged in -succession so that their centra form a continuous rod, and their -neural arches a continuous tube, surrounding a cavity, the =neural -canal=. - -The vertebrae may be readily divided into five groups:-- - -1. The =cervical= or neck vertebrae. - -2. The =thoracic= or chest vertebrae which bear ribs. - -3. The =lumbar= vertebrae which are large and ribless. - -4. The =sacral= vertebrae which are fused with one another and united -with the pelvis. - -5. The =caudal= or tail vertebrae which are small. - -Except in the sacral region the vertebrae are movably articulated to -one another, while their centra are separated from one another by -cartilaginous =intervertebral discs=. - - -GENERAL CHARACTERS OF A VERTEBRA. - -Take as a type the =fourth lumbar vertebra=. It may be compared to a -short tube whose inner surface is smooth and regular, and whose outer -surface is thickened and drawn out in a variety of ways. The basal -part of the vertebra is the =centrum= or body which forms the -thickened floor of the neural canal. Its two ends are slightly convex -and are formed by the =epiphyses=, two thin plates of bone which are -at first altogether distinct from the main part of the centrum, but -fuse with it as the animal grows older; its sides are drawn out into a -pair of strong =transverse processes=, which project forwards, -outwards, and slightly downwards. The =neural arch= forms the sides -and roof of the neural canal, and at each end just above the centrum -bears a pair of =intervertebral notches= for the passage of the spinal -nerves, the posterior notches being considerably deeper than the -anterior. The neural arch is drawn out into a series of processes. -Arising from the centre of the dorsal surface is a prominent median -=neural spine= or =spinous process=, which projects upwards and -slightly forwards; its anterior edge is vertical, while its posterior -edge slopes gradually. At the two ends of the neural arch arise the -two pairs of =zygapophyses= or articulating surfaces, which -interlock with those of the adjacent vertebrae. The anterior or -=prezygapophyses= look inwards, and are large and concave; they are -borne upon a pair of large blunt outgrowths of the neural arch, the -=metapophyses=. The posterior or =postzygapophyses= are slightly -convex and look outwards and downwards; they are borne upon backwardly -projecting outgrowths of the neural arch. Lastly there are a pair of -minute projections arising from the posterior end of the neural arch, -below the postzygapophyses. These are the =anapophyses=. In young -individuals the development of all the processes of the various -vertebrae is less marked, and the epiphyses are obviously distinct. - -[Illustration FIG. 69. A, ATLAS AND B, AXIS VERTEBRA OF A DOG (_Canis -familiaris_) (after VON ZITTEL). - - 1. transverse process of atlas. - 2. vertebrarterial canal. - 3. foramen for exit of spinal nerve. - 4. neural spine. - 5. odontoid process. - 6. anterior articulating surface of centrum. - 7. centrum. - 8. transverse process of axis. - 9. postzygapophysis.] - - -THE CERVICAL VERTEBRAE. - -These are seven in number, as in almost all mammals. They are -characterised by the fact that they have small ribs fused with them, -forming transverse processes perforated by canals through which the -vertebral arteries run. - -The first, or =atlas= vertebra (fig. 69, A), differs much from all the -others; it is drawn out into a pair of wide wing-like transverse -processes (fig. 69, A, 1), and forms a ring surrounding a large -cavity. This cavity is during life divided into two parts by a -transverse ligament; the upper cavity is the true neural canal, while -the lower lodges the =odontoid process= of the second vertebra, which -is the detached centrum of the atlas. The neural arch is broad and -regular; it has no spinous process, and is perforated in front by a -pair of foramina for the passage of the first spinal nerves. The -mid-ventral portion of the atlas is rather thick, and bears a minute -backwardly-projecting hypapophysis. The bases of the broad transverse -processes are perforated by the =vertebrarterial canals= (fig. 69, A, -2). The atlas bears at each end a pair of large articulating surfaces; -those at the anterior end articulate with the condyles of the skull, -and are very deeply concave; those at the posterior end for -articulation with the axis, are nearly as large, but are flattened. -The atlas ossifies from three centres, one forming the mid-ventral -portion, the others the two halves of the remainder. - -The second, or =axis= vertebra (fig. 69, B), also differs much from -the other cervicals. The long and broad centrum has a very flat dorsal -surface, and is produced in front into the conical =odontoid process= -(fig. 69, B, 5), and bears a pair of very large convex outwardly -directed surfaces for articulation with the atlas. At its posterior -end it is drawn out into a pair of small backwardly-directed spines, -the transverse processes; these are perforated at their bases by the -vertebrarterial canals. The neural arch is deeply notched in front and -behind for the passage of the spinal nerves, and is drawn out above -into a very long compressed neural spine (fig. 69, B, 4), which -projects a long way forwards, and behind becomes bifid and thickened, -bearing a pair of flat downwardly directed postzygapophyses. In the -young animal the odontoid process is readily seen to ossify from a -centre anterior to that forming the anterior epiphysis of the axis. - -The remaining five cervical vertebrae, the third to the seventh -inclusive, have rather flattened wide centra, obliquely truncated at -either end. The neural spine progressively increases in size as the -vertebrae are followed back. The transverse processes vary -considerably; those of the third are divided into a thicker -backwardly-, and a more slender forwardly-projecting portion; those of -the fourth and fifth mainly extend downwards, and that of the sixth is -divided into a horizontal portion and a downwardly-projecting -=inferior lamella=. All the cervical vertebrae except the seventh have -the bases of the transverse processes perforated by the -vertebrarterial canals. The prezygapophyses in each case look upwards -and slightly inwards, while the postzygapophyses look downwards and -slightly outwards. - - -THE THORACIC VERTEBRAE. - -The =thoracic vertebrae= are twelve or thirteen in number, and all -bear movably articulated ribs. As a group they are characterised by -their comparative shortness, and in the case of the first eight or -nine by the great length of the backwardly-sloping neural spine. The -posterior thoracic vertebrae approach in character the succeeding -lumbar vertebrae. - -As type of the anterior thoracic vertebrae, take any one between the -second and sixth inclusive. The centrum is short, and has its -terminations vertically truncated. At the top of the centrum, at both -anterior and posterior ends on each side, is a demi-facet (fig. 70, A, -4), which, together with that on the adjacent vertebra, forms an -articulating surface for the capitulum of the rib. The neural arch is -small and deeply notched behind for the passage of the spinal nerve. -It is drawn out above into a very long neural spine (fig. 70, A, 1), -whose base extends back over the succeeding vertebra and bears the -downwardly-directed postzygapophyses (fig. 70, A, 6). The summit of -the neural arch is deeply notched in front, and on each side of the -notch are the prezygapophyses, which look almost vertically upwards. -The transverse processes are short and blunt, and are flattened below -(fig. 70, A, 3) for the articulation of the tubercula of the ribs. - -[Illustration FIG. 70. A, SECOND THORACIC, AND B, SECOND LUMBAR -VERTEBRA OF A DOG (_Canis familiaris_) SEEN FROM THE RIGHT SIDE (after -VON ZITTEL). - - 1. neural spine. - 2. centrum. - 3. transverse process bearing in A the facet for articulation with - the tuberculum of the rib. - 4. facet for articulation with the capitulum of the rib. - 5. metapophysis. - 6. postzygapophysis.] - -The posterior three or four thoracic vertebrae differ much from the -others. The centra are longer, the neural spines short and not -directed backwards, the articular facets for the heads of the ribs are -confined to the anterior end of the centrum of each vertebra, not -overlapping on to the preceding vertebra. The transverse processes are -small and irregular, and metapophyses and anapophyses are developed. -The prezygapophyses also look more inwards, and the postzygapophyses -more outwards than in the more typical thoracic vertebrae. - - -THE LUMBAR VERTEBRAE. - -The =lumbar vertebrae= are seven in number, and their general -characteristics have been already described. As a group they are -characterised by their large size, and the great development of the -transverse processes, metapophyses and neural spines. - - -THE SACRAL VERTEBRAE. - -Three vertebrae are commonly found fused together, forming the -=sacrum=; the divisions between the three being indicated by the -foramina for the exit of the spinal nerves. - -Of these three vertebrae, the first is much the largest, and is firmly -united to the ilium on each side by a structure formed by the -transverse processes and expanded ribs. In the adult this structure -forms one continuous mass, but in the young animal a ventral portion -formed by the rib is clearly distinguishable from a dorsal portion -formed by the transverse process. All three have low neural spines. -The anterior sacral vertebra bears a large pair of prezygapophyses, -while the posterior one bears a small pair of postzygapophyses. - - -THE CAUDAL VERTEBRAE. - -The =caudal vertebrae= are about nineteen in number. The earlier ones -have well-developed neural arches, transverse processes, and -zygapophyses, but as the vertebrae are followed back they gradually -lose all their processes, and the neural arch as well, becoming at -about the thirteenth from the end reduced to simple cylindrical -centra. - - -B. THE SKULL. - -The =skull= consists of the following three parts: (_a_) the cranium, -with which are included the skeletal supports of the various special -sense organs, and the bones of the face and upper jaw; (_b_) the lower -jaw or mandible, which is movably articulated to the cranium, and -(_c_) the hyoid. - - -(_a_) THE CRANIUM. - -The cranium is a compact bony box, forming the anterior expanded -portion of the axial skeleton. It has a longitudinal axis, the -=craniofacial= axis around which the various parts are arranged, and -this axis is a direct continuation of that of the vertebral column. -Similarly the cavity of the cranium is a direct continuation of the -spinal canal. The posterior part of the craniofacial axis, which has -relations only with the cranium, is called the =basicranial axis=. - -In the dog as in the other types previously described, the skull in -its earliest stages is cartilaginous, containing no bone. In the -adult, however, the cartilage is to a great extent replaced by bone, -and in addition to this cartilage bone, membrane bone is largely -developed, and intimately united with the cartilage bone to form one -complete whole. - -In the description of the dog's skeleton, as in those of the previous -types, the names of the membrane bones are printed in italics, while -those of the cartilage bones are printed in thick type. - -Most of the numerous foramina perforating the skull walls will be -described after the bones have been dealt with. - -For purposes of description the cranium may be further subdivided -into:-- - -1. The cranium proper or brain case. - -2. The sense capsules. - -3. The upper jaw. - - -1. THE CRANIUM PROPER OR BRAIN CASE. - -Taking the membrane and cartilage bones together, they are seen to be -more or less arranged in three segments, which however must not be -regarded as homologous with the segments forming the vertebral column. - -[Illustration FIG. 71. DIAGRAM OF THE RELATIONS OF THE PRINCIPAL BONES -IN THE MAMMALIAN SKULL (modified after FLOWER). - -Cartilage is dotted. Cartilage bones are marked by dots and dashes, -membrane bones are left white. - - 1. basi-occipital. - 2. exoccipital. - 3. supra-occipital. - 4. basisphenoid. - 5. alisphenoid. - 6. parietal. - 7. presphenoid. - 8. orbitosphenoid. - 9. frontal. - 10. periotic, immediately below which is the tympanic. - 11. lachrymal. - 12. ethmo-turbinal. - 13. maxillo-turbinal. - 14. nasal. - 15. mesethmoid. - 16. vomer. - 17. pterygoid. - 18. palatine. - 19. maxillae. - 20. premaxillae. - 21. squamosal. - 22. mandible. - 23. tympano-hyal. - 24. stylo-hyal. - 25. epi-hyal. - 26. basi-hyal. Between this and the epi-hyal is the cerato-hyal. - 27. thyro-hyal. - 28. jugal. - -Nerve exits are indicated by Roman numerals.] - -The =occipital segment= is the most posterior of the three, and -consists of four cartilage bones, which in the adult are commonly -completely fused together. They surround the great =foramen magnum= -(fig. 75, 2) through which the brain and spinal cord communicate. -Forming the lower margin of the foramen magnum is a large flat -unpaired bone, the =basi-occipital= (fig. 75, 5). Above this on each -side are the =exoccipitals=, whose sides are drawn out into a pair of -downwardly-directed =paroccipital processes=, which are applied to the -tympanic bullae[141]. The inner side of each exoccipital is converted -into the large rounded =occipital condyle= (fig. 72, 13) by which the -skull articulates with the atlas vertebra. The dorsal boundary of the -foramen magnum is formed by a large unpaired flat bone, the -=supra-occipital= (figs. 72 and 75, 1), which is continuous with a -small bone, the _interparietal_, prolonged forwards between the -parietal bones of the next segment. - -In old animals the interparietal forms the hind part of a prominent -ridge running along the mid-dorsal surface of the skull and called the -=sagittal crest=, while the junction line of the occipital and -parietal segments forms a prominent =occipital crest=. - -The plane in which the bones of the occipital segment lie is called -the occipital plane; the angle that it makes with the basicranial axis -varies much in different mammals. - -The =parietal segment= consists of both cartilage and membrane bones. -It is formed of five bones, which are in contact with those of the -occipital segment on the dorsal and ventral surfaces, while laterally -they are separated by the interposition of the auditory bones, and to -some extent of the squamosal. The =basisphenoid= (fig. 75, 6), an -unpaired bone forming the ventral member of this segment, is the -direct continuation of the basi-occipital. It tapers anteriorly, but -is rather deep vertically, its upper or dorsal surface bearing a -depression, the =sella turcica=, which lodges the pituitary body of -the brain. From the sides of the basisphenoid arise the =alisphenoids= -(fig. 75, 11) a pair of bones of irregular shape generally described -as wing-like; each gives off from its lower surface a =pterygoid -plate=, which is united in front with the palatine, and below with the -pterygoid. The alisphenoids are united above with a pair of large -nearly square bones, the _parietals_ (fig. 73, 2), which meet one -another in the mid-dorsal line. The line of junction is frequently -drawn out into a strong ridge, which forms the anterior part of the -=sagittal crest=. - -[Illustration FIG. 72. VERTICAL LONGITUDINAL SECTION TAKEN A LITTLE TO -THE LEFT OF THE MIDDLE LINE THROUGH THE SKULL OF A DOG (_Canis -familiaris_) × 3/5. (Camb. Mus.) - - 1. supra-occipital. - 2. interparietal. - 3. parietal. - 4. frontal. - 5. cribriform plate. - 6. nasal. - 7. mesethmoid. - 8. maxillae. - 9. vomer. - 10. ethmo-turbinal. - 11. maxillo-turbinal. - 12. premaxillae. - 13. occipital condyle. - 14. basi-occipital. - 15. tympanic bulla. - 16. basisphenoid. - 17. pterygoid. - 18. palatine. - 19. alisphenoid. - 20. internal auditory meatus. - 21. tentorium. - 22. foramen lacerum posterius. - 23. floccular fossa. - 24. coronoid process. - 25. condyle. - 26. angle. - 27. mandibular symphysis. - 28. inferior dental foramen. - 29. stylo-hyal. - 30. epi-hyal. - 31. cerato-hyal. - 32. basi-hyal. - 33. thyro-hyal. - XII. condylar foramen.] - -The =frontal segment=, which surrounds the anterior part of the brain, -is closely connected along almost its whole posterior border with the -parietal segment. - -Its base is formed by the =presphenoid= (fig. 75, 12), a very deep -unpaired bone, narrow and compressed ventrally, and with an irregular -dorsal surface. The presphenoid is continuous with a second pair of -wing-like bones, the =orbitosphenoids=. Each orbitosphenoid meets the -alisphenoid behind, but the relations of the parts in this region are -somewhat obscured by a number of large foramina piercing the bones, -and also by an irregular vacuity, the =foramen lacerum anterius= or -=sphenoidal fissure=, which lies between the orbitosphenoid and -alisphenoid, separating the lateral parts of the parietal and frontal -segments, in the same way as the space occupied by the auditory bones -separates the lateral parts of the occipital and parietal segments. -The orbitosphenoids pass obliquely forwards and upwards, and are -united above with a second pair of large membrane bones, the -_frontals_ (fig. 73, 3). The outer side of each frontal is drawn out -into a rather prominent rounded =postorbital process= (fig. 73, 10), -from which a ridge converges backwards to meet the sagittal crest. The -anterior part of the frontal is produced to form the long nasal -process, which is wedged in between the nasal and maxillae. - -[Illustration FIG. 73. DORSAL VIEW OF THE CRANIUM OF A DOG (_Canis -familiaris_) × 2/3. - - 1. supra-occipital. - 2. parietal. - 3. frontal. - 4. nasal. - 5. maxillae (facial portion). - 6. premaxillae. - 7. squamosal. - 8. jugal. - 10. postorbital process of frontal. - 11. infra-orbital foramen. - 12. anterior palatine foramen. - 13. lachrymal foramen. - _i_ 1. first incisor. - _c._ canine. - _pm_ 4. fourth premolar.] - -The cranial cavity is continuous in front with the =nasal= or -=olfactory cavities=, but the passage is partially closed by a screen -of bone, the =cribriform plate= (fig. 72, 5), which is placed -obliquely across the anterior end of the cranial cavity, and is -perforated by a number of holes through which the olfactory nerves -pass. The plane of the cribriform plate is called the =ethmoidal -plane=, and as was the case also with the occipital plane, the angle -that it makes with the basicranial axis varies much in different -mammals, and is of importance. The =olfactory fossa= in which lie the -olfactory lobes of the brain, is partially separated from the -=cerebral fossa=, or cavity occupied by the cerebral hemispheres, by -ridges on the orbitosphenoids and frontals. The presphenoid is -connected in front with a vertical plate formed partly of bone, partly -of unossified cartilage; this plate, the =mesethmoid= (fig. 72, 7), -separates the two olfactory cavities which lodge the olfactory organs. -Its anterior end always remains unossified, and forms the septal -cartilage of the nose. - -The brain case may then, to use the words of Sir W.H. Flower, be -described as a tube dilated in the middle and composed of three bony -rings or segments, with an aperture at each end, and a fissure or -space at the sides between each of them. - - -2. THE SENSE CAPSULES. - -Each of the three special sense organs, of hearing, of sight, and of -smell, is in the embryo provided with a cartilaginous or membranous -protecting capsule; and two of these, the auditory and olfactory -capsules, become afterwards more or less ossified, and intimately -related to the cranium proper. - - -(1) =Bones in relation to the Auditory capsules.= - -These bones lie on each side wedged into the vacuity between the -lateral parts of the occipital and parietal segments; they are three -in number, the =periotic=, the _tympanic_ and the _squamosal_. - -The =periotic= is the most important of them, as it replaces the -cartilaginous auditory capsule of the embryo, and encloses the -essential organ of hearing. It commences to ossify from three centres -corresponding to the pro-otic, epi-otic and opisthotic of lower -skulls, such as those of the Turtle and Crocodile. - -These ossifications however very early combine to form a single bone, -the =periotic=, which nevertheless consists of two portions, the -=petrous= and the =mastoid=, differing considerably from one another. - -[Illustration FIG. 74. DIAGRAM OF THE MAMMALIAN TYMPANIC CAVITY AND -ASSOCIATED PARTS (modified from LLOYD MORGAN). - - 1. external auditory meatus. - 2. tympanic membrane. - 3. malleus. - 4. incus. - 5. lenticular. - 6. stapes. - 7. fenestra ovalis. - 8. fenestra rotunda. - 9. Eustachian tube. - 10. cavity occupied by the cochlea. - 11. cavity occupied by the membranous labyrinth.] - -The =petrous portion= lies dorsally and anteriorly, and is much the -more important of the two, as it encloses the essential part of the -auditory organ. It forms an irregular mass of hard dense bone, -projecting into the cranial cavity, and does not appear on the -external surface at all. The =mastoid portion= lies ventrally and -posteriorly, is smaller, and formed of less dense bone than is the -petrous portion, from which it differs also in the fact that it -appears on the surface of the skull, just external to the exoccipital. -The petrous portion bears a ridge, which together with a ridge on the -supra-occipital, and the =tentorium= (fig. 72, 21), a transverse fold -of the dura mater[142], separates the large cerebral fossa from the -=cerebellar fossa=, which is much smaller than the cerebral fossa and -lies behind and partly beneath it. The plane of the tentorium is -called the =tentorial plane=, and the angles that it makes with the -basicranial axis and with the occipital and ethmoidal planes vary much -in different mammals. - -The periotic has its inner surface marked by important depressions, -while both inner and outer surfaces are pierced by foramina. At about -the middle of its inner surface are seen two deep pits, one lying -immediately above the other. Of these the more ventral is a foramen, -the =internal auditory meatus= (fig. 72, 20), through which the VIIth -(facial) and VIIIth (auditory) nerves leave the cranial cavity, the -facial nerve passing through the bone and afterwards leaving the skull -by the =stylomastoid foramen= (fig. 75, VII), while the auditory -passes to the inner ear. The more dorsal of the two pits is not a -foramen but the =floccular fossa= (fig. 72, 23) which lodges the -floccular lobe of the cerebellum. In some skulls another wide and -shallow but fairly prominent depression is seen dorsal to and slightly -behind the floccular fossa, this also lodges part of the cerebellum. -Behind the internal auditory meatus, between the periotic and -exoccipital is seen the internal opening of the =foramen lacerum -posterius= (fig. 72, 22). The shape of this opening varies. The -ventro-anterior border of the periotic is marked by a deep notch, the -sides of which sometimes unite, converting it into a foramen. - -On the outer side of the periotic, and clearly seen only after the -removal of the tympanic, are two holes, the =fenestra ovalis= and the -=fenestra rotunda=. - -The _tympanic_ (figs. 72, 15 and 75, 4) is a greatly expanded -boat-shaped bone, which forms the auditory bulla and lies immediately -ventral to the periotic; it is separated from the periotic by the -=tympanic cavity= into which the fenestra rotunda and the fenestra -ovalis open. - -There are several other openings into the tympanic cavity. - -(_a_) On the external surface is a large oval opening, the =external -auditory meatus= bounded by a thickened rim. - -(_b_) Into the outer and anterior part of the cavity the outer end of -the =Eustachian tube= opens; while the inner end passes through a -foramen (fig. 75, 22) just external to the foramen lacerum medium, on -its way to open into the pharynx. - -(_c_) The internal carotid artery also enters the tympanic cavity by a -canal which commences in the foramen lacerum posterius, and passes -forwards to open on the inner side of the bulla. The artery then -passes forwards, and barely appearing on the ventral surface of the -cranium, enters the brain cavity through the foramen lacerum medium -(fig. 75, 9). - -Immediately behind the tympanic, between it and the mastoid process of -the periotic and the paroccipital process of the exoccipital is the -=stylomastoid foramen= (fig. 75, VIII). - -Within the tympanic cavity are four small bones, the =auditory -ossicles= (cp. fig. 74), called respectively the =malleus=, =incus=, -=lenticular= and =stapes=; these together form a chain extending from -the fenestra ovalis to the tympanic membrane. - -The =malleus= has a somewhat rounded head (fig. 100, B, 1) which -articulates with the incus, while the other end of the bone is drawn -out into a long process, the =manubrium=, which lies in relation to -the tympanic membrane. The head is also more or less connected by a -thin plate of bone, the =lamella=, to another outgrowth, the -=processus longus=. The =incus= (fig. 100, B, 3) is somewhat -anvil-shaped, and is drawn out into a process which is connected with -the =lenticular=, a nodule of bone interposed between the incus and -the stapes, with which it early becomes united. The =stapes= (fig. -100, B, 2) is stirrup-shaped, consisting of a basal portion from which -arise two =crura=, which meet and enclose a space, the =canal=. - -The _squamosal_ (fig. 73, 7) is a large bone occupying much of the -side wall of the cranial cavity, and articulating above with the -parietal, and behind with the supra-occipital, while in front it -overlaps the frontal and alisphenoid. But though it occupies so large -a space on the outer wall, it forms very little of the internal wall -of the skull, but is really like a bony plate attached to the outer -surface of the cranial wall. The squamosal is drawn out into a strong -forwardly-directed =zygomatic process= which meets the jugal or malar. -The ventral side of the zygomatic process is hollowed out, forming the -=glenoid fossa= (fig. 75, 8), a smooth laterally elongated surface -with which the lower jaw articulates, while the hinder edge of the -glenoid fossa is drawn out into a rounded =postglenoid process= (fig. -75, 23). The articulation is such as to allow but little lateral play -of the lower jaw. - - -(2) =Bones in relation to the Optic capsules.= - -The only bone developed in relation to the optic capsule on each side -is the _lachrymal_. This is a small membrane bone lying between the -frontal and palatine behind, and the maxillae and jugal in front. It is -perforated by a prominent =lachrymal foramen= (fig. 73, 13) which -opens within the orbit. - - -(3) =Bones in relation to the Olfactory capsules.= - -In connection with the =olfactory capsules=, five pairs of bones are -developed, two pairs being membrane bones, and three pairs cartilage -bones. - -Of membrane bones, the _nasals_ (fig. 73, 4) are a pair of long narrow -bones, lying closely side by side, and forming the main part of the -roof of the olfactory chamber. Their posterior ends overlap the -frontals, and the outer margin of each is in contact with the nasal -process of the frontal, and with the maxillae and premaxillae. - -Lying immediately ventral to the nasals, and on each side of the -perpendicular mesethmoid, are the =ethmoid= or =turbinal= bones, -which have a curious character, being formed of a number of delicate -plates intimately folded on one another. The posterior pair of these -bones, the =ethmo-turbinals= (fig. 72, 10), are the larger, and form a -mass of intricately folded lamellae attached behind to the cribriform -plate, and passing laterally into two thin plates of bone, which abut -on the maxillae. The uppermost lamella of each ethmo-turbinal is larger -than the others and more distinct. It is sometimes distinguished as -the =naso-turbinal=, and forms an imperfect lower boundary to a canal, -which is bounded above by the nasals. In front of and somewhat below -the ethmo-turbinals, lie another pair of bones of similar character, -the =maxillo-turbinals= (fig. 72, 11). - -The last bone to be mentioned in connection with the olfactory -capsules is a membrane bone, the _vomer_ (fig. 72, 9). This is a -slender vertically-placed bone, whose anterior part lies between the -maxillo-turbinals, while behind it extends beyond the mesethmoid, so -as to underlie the anterior part of the presphenoid. The anterior part -of the vomer forms a kind of trough, while further back in the region -of the ethmo-turbinals it sends out a pair of strong lateral plates, -each of which, passing below the ethmo-turbinal, joins the side wall -of the nasal cavity, and forms a partition dividing the nasal cavity -into a lower =narial passage= and an upper =olfactory chamber=. - - -THE JAWS. - -In the embryo both upper and lower jaws are formed of cartilaginous -bars, but in the adult not only has the cartilage entirely -disappeared, but even cartilage bone is absent, the jaws being formed -of membrane bone. - - -3. THE UPPER JAW. - -[Illustration FIG. 75. VENTRAL VIEW OF THE CRANIUM OF A DOG (_Canis -familiaris_) × 3/5. (Camb. Mus.) - - 1. supra-occipital. - 2. foramen magnum. - 3. occipital condyle. - 4. tympanic bulla. - 5. basi-occipital. - 6. basisphenoid. - 7. external auditory meatus. - 8. glenoid fossa. - 9. foramen lacerum medium and anterior opening of carotid canal. - 10. postglenoid foramen. - 11. alisphenoid. - 12. presphenoid. - 13. vomer. - 14. jugal. - 15. pterygoid. - 16. palatal process of palatine. - 17. maxillae (palatal portion). - 18. posterior palatine foramina. - 19. anterior palatine foramen. - 20. premaxillae. - 21. alisphenoid canal. - 22. Eustachian foramen. - 23. postglenoid process of squamosal. - II. optic foramen. - III, IV, V{1}, VI. foramen lacerum anterius. - V{2}. foramen rotundum. - V{3}. foramen ovale. - VII. stylomastoid foramen. - IX, X, XI. foramen lacerum posterius. - XII. condylar foramen. - _i_ 2. second incisor. - _c._ canine. - _pm_ 1, _pm_ 4. first and fourth premolars. - _m_ 1. first molar.] - -The bones of the upper jaw are closely connected with those of the -cranium proper and olfactory capsules. The most posterior of them is -the _pterygoid_ (fig. 75, 15), a thin vertically placed plate of bone, -which articulates above with the basisphenoid, the presphenoid, and -the strong pterygoid process of the alisphenoid. The ventral end of -the pterygoid is drawn out into a small backwardly-projecting =hamular -process=. In front the pterygoid articulates with the _palatine_, a -much larger bone, consisting of (1) a vertical portion, which passes -up to meet the orbitosphenoid and frontal, and sends inwards a plate -which meets the presphenoid and vomer, forming much of the roof of the -posterior part of the narial passage; and (2) a strong horizontal -portion, the =palatal process= (fig. 75, 16), which passes inwards and -meets its fellow in the middle line, forming the posterior part of the -bridge of bone supporting the hard palate. The palatal process is -continuous in front, with a large bone, the _maxillae_, which, like -the palatine, consists of vertical and horizontal portions. The -vertical, or =facial portion= (fig. 73, 5), is the largest, and -constitutes the main part of the side of the face in front of the -orbit, forming also the chief part of the outer wall of the nasal -cavity. It is continuous in front with the premaxillae, above with the -nasal and frontal, and behind with the lachrymal, jugal, and palatine. -The horizontal, or =palatal portion= (fig. 75, 17), forms the anterior -part of the bony plate supporting the hard palate, and meets its -fellow in a long straight symphysis. The junction line between the -palatal and facial portions is called the =alveolar border=, and -along it are attached the canine, premolar, and molar teeth. - -The anterior part of the upper jaw on each side is formed by a small -bone, the _premaxillae_, which bears the incisor teeth. It, like the -maxillae, has a palatal portion (fig. 75, 20), which meets its fellow -in the middle line, and an ascending portion, which passes backwards -as the =nasal process=, tapering regularly and lying between the nasal -and the maxillae. The two premaxillae form the outer and lower borders -of the anterior nares. The last bone to be mentioned in connection -with the upper jaw and face is the _jugal_ or _malar_ (figs. 73, 8, -and 75, 14), a strong bone which forms the anterior half of the -zygomatic arch. It is firmly united in front to the maxillae, and -behind meets the zygomatic process of the squamosal, being drawn out -dorsally into a short =postorbital process= at the point of meeting. -This process lies immediately below the postorbital process of the -frontal, and if the two met, as they do in some mammals, they would -partially shut off the orbit from a larger posterior cavity, the -=temporal fossa=. In the living animal a ligament unites the two -postorbital processes. - - -(_b_) THE LOWER JAW OR MANDIBLE. - -This consists of two elongated symmetrical halves, the =rami=, which -are united to one another at the median symphysis in front, while -behind they diverge considerably, and each articulates with the -glenoid surface of the corresponding squamosal. In young animals the -rami are united at the symphysis by fibrous tissue, but in old animals -they sometimes become fused together. The upper or alveolar border -bears the teeth, and behind them is drawn out into a high laterally -compressed =coronoid process= (fig. 72, 24), which is hollowed on its -outer surface. Immediately behind the coronoid process is the -transversely elongated =condyle= (fig. 72, 25), which fits into the -glenoid cavity in such a way as to allow free up and down movement of -the jaw, with but little rolling motion. The posterior end of the jaw -below the condyle forms a short rounded process, the =angle= (fig. -72, 26). Two prominent foramina are to be seen in the lower jaw. These -are firstly the =inferior dental foramen= (fig. 72, 28), which lies on -the inner surface below the coronoid process; through it an artery and -a branch of the fifth nerve enter to supply the teeth, and secondly -the =mental foramen=, which lies on the outer side near the anterior -end, and through which a branch of the same nerve emerges. - - -(_c_) THE HYOID. - -The =Hyoid= of the dog consists of a transverse median piece, the -=basi-hyal=[1] (fig. 72, 32), from which arise two pairs of =cornua=. -The =anterior cornu= is much the longer of the two, and consists -principally of three short separate ossifications, placed end to end -and called respectively the =cerato-hyal=[143], =epi-hyal=, and -=stylo-hyal=. All of them are short rods of bone, contracted in the -middle, and expanded at the ends, where they are tipped with -cartilage. The cerato-hyal (fig. 72, 31) lies next to the basi hyal. -The stylo-hyal is terminated by a much smaller bone, the -=tympano-hyal=, which lies in a canal between the tympanic and -periotic, and is ankylosed to the periotic just to the anterior and -inner side of the stylomastoid foramen. - -The =posterior cornu= of the hyoid is much smaller than the anterior; -it consists of a short bone, the =thyro-hyal= (fig. 72, 33), which -connects the basi-hyal with the thyroid cartilage of the larynx. - -FORAMINA OF THE SKULL. - -The foramina, or apertures perforating the walls of the skull, are -very numerous, and may either be due to holes actually penetrating the -bone, or may be small vacuities between the margins of two elsewhere -contiguous bones. - -They may be divided into two groups, the first including - -I. The holes through which the =twelve cranial nerves= leave the -cranial cavity. - -_a._ The most anterior of these nerves, the olfactory, leaves the -skull by a number of small holes piercing the =cribriform plate= (fig. -72, 5). - -_b._ The second, or optic, passes out by a large hole, the =optic -foramen= (fig. 75, II) piercing the orbitosphenoid. The optic foramen -is the most anterior of the three prominent holes seen within and -immediately behind the orbit. - -_c._ The third, fourth, and sixth nerves, i.e. those supplying the eye -muscles, and with them the first or ophthalmic branch of the large -fifth or trigeminal nerve, pass out by a large hole, the =foramen -lacerum anterius= (fig. 75, III, IV, V{1}, VI), which, as has been -already mentioned, lies between the orbitosphenoid and alisphenoid. - -_d._ Immediately behind the foramen lacerum anterius, the alisphenoid -is perforated by a prominent round hole, the =foramen rotundum= (fig. -75, V{2}), through which the second branch of the trigeminal nerve -passes out. - -_e._ A quarter of an inch further back there is another prominent -hole, the =foramen ovale= (fig. 75, V{3}), through which the third -branch of the trigeminal nerve leaves the cranium. - -_f._ The seventh or facial nerve, as already mentioned, leaves the -cranial cavity and enters the auditory capsule, through an opening in -the periotic called the =internal auditory meatus=, while it finally -leaves the skull by the =stylomastoid foramen= (fig. 75, VII), which -lies between the tympanic bulla, the paroccipital process, and the -mastoid portion of the periotic. - -_g._ The eighth or auditory nerve on leaving the cranial cavity, -passes with the facial straight into the auditory capsule through the -=internal auditory meatus= (fig. 72, 20). It is then distributed to -the organ of hearing. - -_h._ The ninth, tenth and eleventh nerves leave the skull through the -=foramen lacerum posterius= (fig. 75, IX, X, XI), a large space lying -between the auditory bones and the exoccipital. - -_i._ Finally, the twelfth nerve, the hypoglossal, passes out through -the prominent =condylar foramen= (fig. 75, XII), which perforates the -exoccipital just behind the foramen lacerum posterius. - - -II. OTHER OPENINGS IN THE SKULL. - -_a._ The =anterior narial opening= lies at the anterior end of the -skull, and is bounded by the premaxillae and nasals. In the natural -condition it is divided into two by a vertical partition, formed by -the =narial septum=, the anterior unossified part of the mesethmoid. - -_b._ Penetrating the middle of the maxillae at the side of the face is -the rather large =infra-orbital foramen= (fig. 73, 11), through which -part of the second branch of the trigeminal nerve passes out from the -orbit to the side of the face. - -_c._ Several foramina are seen perforating the anterior part of the -orbit. The most dorsal of these, perforating the lachrymal bone, is -the =lachrymal foramen= (fig. 73, 13). Lying below and slightly -external to this is a large foramen, through which part of the second -branch of the trigeminal enters on its way to the infra-orbital -foramen and so to the side of the face. Lastly, lying below these, and -perforating the palatine, are two closely apposed foramina, the -=internal orbital foramina=, through which part of the first or -ophthalmic branch of the trigeminal nerve leaves the orbit, passing -into the nasal cavity. - -_d._ The anterior part of the palate between the premaxillae and the -maxillae is perforated by a pair of long closely apposed apertures, the -=anterior palatine foramina= (fig. 75, 19). They transmit part of the -trigeminal nerve. - -_e._ Towards the posterior part of the palate are two pairs of small -=posterior palatine foramina= (fig. 75, 18). These perforate the -palatine and transmit branches of the trigeminal nerve and certain -blood-vessels. - -_f._ The =posterior narial opening= is bounded chiefly by the -palatines. - -_g._ The =alisphenoid canal= (fig. 75, 21) is a short canal -penetrating the base of the alisphenoid bone, and transmitting the -external carotid artery. It lies between the foramen rotundum and the -foramen ovale. - -_h._ Between the auditory bulla and the foramen ovale are seen two -openings. The more external of these is the opening of the =Eustachian -canal= (fig. 75, 22), which communicates with the tympanic cavity. The -more internal is the =foramen lacerum medium= (fig. 75, 9), through -which the internal carotid enters the cranial cavity. - -_i._ The =external auditory aperture= (fig. 75, 7) is a large opening -with rough edges at the outer side of the tympanic bulla. - -_j._ Between it and the glenoid surface of the squamosal is the -=postglenoid= foramen (fig. 75, 10) through which a vein passes out. - -_k._ Lastly, there is the great =foramen magnum= (fig. 75, 2), between -the occipital condyles. Through it the brain and spinal cord -communicate. - - -C. THE RIBS AND STERNUM. - -[Illustration FIG. 76. STERNUM AND STERNAL RIBS OF A DOG (_Canis -familiaris_) × 1/2. - - 1. presternum. - 2. first sternebra of mesosternum. - 3. last sternebra of mesosternum. - 4. xiphisternum. The flattened cartilaginous plate terminating the - xiphisternum is not shown. - 5. first sternal rib.] - -These, together with the thoracic vertebrae, form the skeletal -framework of the thorax. Each rib is a curved rod, which at its dorsal -end is movably articulated to the vertebra, and at its ventral end is -either connected with the sternum, or ends freely. In the dog there -are thirteen pairs of ribs, nine pairs of which are directly connected -with the sternum, while the remaining four end freely and are known as -=floating ribs=. Each rib is obviously divided into two parts, a -dorsal or =vertebral part=, and a ventral or =sternal part=. The -vertebral portion, which forms about two-thirds of the whole rib, is a -flattened, regularly curved rod, completely ossified. Its dorsal end -is rounded, forming the =head= or =capitulum=, which articulates with -a concave surface furnished partly by the corresponding vertebra and -partly by the vertebra next in front. The last three or four however -articulate with one vertebra only. A short way behind the capitulum on -the dorsal side of the rib is a rounded outgrowth, the =tubercle= or -=tuberculum=, by means of which the rib articulates with the -transverse process. The portion of the rib between the head and the -tubercle is known as the =neck=. The =sternal portion= of the rib -(fig. 76) is a short bar of calcified or imperfectly ossified -cartilage, about one-third of the length of the corresponding bony -portion. The anterior sternal ribs are somewhat more cartilaginous -than the posterior ones. The vertebral portions increase in length -from the first which is very stout, and has the capitulum and -tuberculum very distinct, to about the eighth or ninth; afterwards -they gradually diminish in size. The first nine to eleven have the -capitula and tubercula separate, afterwards they gradually merge -together. - - -THE STERNUM. - -This is an elongated cylindrical structure lying in the mid-ventral -wall of the thorax, and is divided into eight segments or -=sternebrae=. The anterior segment, the =presternum= (fig. 76, 1) or -=manubrium sterni= is expanded in front; the next six segments, which, -together form the =mesosternum= are elongated, somewhat contracted in -the middle and expanded at the ends. The last segment or -=xiphisternum= (fig. 76, 4) is long and narrow, and terminates in a -flattened expanded plate of cartilage. The first pair of sternal ribs -articulate with the sides of the presternum, and the remaining pairs -between the successive sternebrae. Between the last sternebra and the -xiphisternum two pairs articulate. Development shows that the sternum -is formed by the union in the middle line of two lateral portions; -this can be well seen in the presternum and xiphisternum of the puppy, -but no traces of this median division remain in the adult dog. - - -2. THE APPENDICULAR SKELETON. - -The appendicular skeleton consists of the bones of the anterior and -posterior limbs, and of their respective supports, the pectoral and -pelvic girdles. - - -THE PECTORAL GIRDLE. - -The =pectoral girdle= lies external to the ribs, and has no bony -attachment to the axial skeleton. In almost all Mammalia it is, as -compared with that in Sauropsids, very incomplete; and in the dog it -is even more reduced than in the majority of Mammalia. The dorsal -portion or =scapula= is well developed, but the ventral portion is -almost entirely absent. - -The =scapula= is somewhat triangular in shape, the apex being -directed downwards and forwards, and being expanded to form the -shallow =glenoid cavity= with which the head of the humerus -articulates. The inner surface of the scapula is nearly flat, while -the outer is drawn out into a very prominent ridge, the =spine=, -which, arising gradually near the dorsal end, runs downwards, dividing -the surface into two nearly equal parts, the =prescapular= and -=postscapular fossae=, and ends in a short blunt process, the -=acromion=. The anterior border of the scapula is somewhat curved, and -is called the =coracoid border=; it is terminated ventrally by a -slight blunt swelling, the =coracoid process=, which ossifies from a -different centre from the rest of the scapula, and is probably the -sole representative of the =coracoid=. The dorsal or =suprascapular -border= of the scapula is rounded, while the posterior or =glenoid -border= is nearly straight. The clavicle[144] or collar bone, which in -a large proportion of mammals is well seen, in the dog is very -imperfectly developed; it is short and broad, and is suspended in the -muscles, not reaching either the scapula or sternum. - - -THE ANTERIOR LIMB. - -The anterior limb of the dog is divisible into the usual three -portions, the =brachium= or =upper arm=, the =antibrachium= or -=fore-arm=, and the =manus= or =wrist= and =hand=. - -The =brachium= or =upper arm= includes only a single bone, the -=humerus=. - -The =humerus= is a stout elongated bone, articulating by its large -proximal =head= (fig. 77, 1) with the glenoid cavity of the scapula, -and at its distal end by the =trochlea= with the bones of the -fore-arm. The head passes on its inner side into an area roughened for -the attachment of muscles and called the =lesser tuberosity= (fig. 77, -2); while in front it is divided by the shallow =bicipital groove= -from a large roughened area, the =greater tuberosity= (fig. 77, 3), -which is continued as a slight roughened ridge, extending about -one-third of the way down the outer side of the shaft. This ridge, -which in many animals is much more strongly developed than it is in -the dog, is called the =deltoid ridge=. The =trochlea= (fig. 77, 5) at -the distal end of the bone is a pulley-like surface, elevated at the -sides and grooved in the middle. It articulates with the radius and -ulna of the fore-arm. On each side of it are slight roughened -projections, the =internal= and =external condyles= (fig. 77, 7). In -the cat and many other animals there's a foramen, the =ent-epicondylar -foramen= above the internal condyle, but in the dog this is not -developed. Passing up the shaft from the external condyle is a slight -ridge, the =supinator= or =ectocondylar ridge=; this is better -developed in many mammals. Immediately above the trochlea in front and -behind are the deep =supra-trochlear fossae=, which communicate with -one another through the =supra-trochlear foramen= (fig. 77, 8). The -posterior of these, the =olecranon fossa=, is much the deeper, and -receives the olecranon process of the ulna when the arm is extended. -The head and tuberosities of the humerus ossify from one centre, the -shaft from a second, and the trochlea and condyles from a third. - -The =fore-arm= or =antibrachium= contains two bones, the =radius= and -=ulna=; they are immovably articulated with one another, but not -fused. The pre-axial bone, the =radius= (fig. 77, B), which lies more -or less in front of the ulna, is external to the ulna at its proximal -end, and at its distal end is internal to that bone. It articulates -with the external portion of the trochlea, while the ulna articulates -with the internal portion. It is a straight bone with its distal end -slightly larger than its proximal end. The proximal end articulates -with the trochlea, the distal end with the bones of the carpus. - -[Illustration FIG. 77. BONES OF THE LEFT UPPER ARM AND FORE-ARM OF A -DOG (_Canis familiaris_) × 1/2. - -A, humerus (seen from the posterior side); B, radius, C, ulna, both -seen from the anterior side. - - 1. head. - 2. lesser tuberosity. - 3. greater tuberosity. - 4. shaft of the humerus. - 5. trochlea. - 6. internal condyle. - 7. external condyle. - 8. supra-trochlear foramen. - 9. proximal end of the radius. - 10. shaft of the radius. - 11. olecranon. - 12. surface for articulation with the trochlea. - 13. surface for articulation with the radius. - 14. distal end of the ulna.] - -The postaxial bone, the =ulna= (fig. 77, C), has the proximal end much -enlarged, forming the =olecranon= (fig. 77, 11), and tapers gradually -to the distal end. Near its proximal end the ulna is marked by a deep -=sigmoid notch=, which bears on its inner side a concave surface -(fig. 77, 12) for articulation with the trochlea. The pointed proximal -end of the sigmoid notch is called the =coronoid process=. Somewhat -in front of and below the sigmoid notch is a smaller hollow (fig. 77, -13), with which the radius articulates. - -In the young animal the ends of both radius and ulna are seen to -ossify from centres different from those forming the shafts. The -epiphyses forming both ends of the radius, and the distal end of the -ulna are large, while that at the proximal end of the ulna is small, -and forms only the end of the olecranon. - -The =Manus= is divided into - -_a._ The =carpus= or =wrist=, formed of a group of small bones. - -_b._ The =hand=, which includes firstly some elongated bones, the -=metacarpals=, forming what corresponds to the palm of the hand, and -secondly the phalanges, which form the =fingers=. - -The =Carpus= or =wrist=. The carpus of the dog consists of seven small -bones, arranged in a proximal row of three, and a distal row of four. -It differs much from the simpler type met with in the newt. The -largest bone of the proximal row is the =scapho-lunar= (fig. 80, 1), -formed by the fused =scaphoid= (radiale), =lunar= (intermedium), and -=centrale=; it has a large convex proximal surface for articulation -with the radius, and articulates distally with the trapezium, -trapezoid, and magnum, and internally with the cuneiform. The -=cuneiform= (ulnare) (fig. 80, 2) has a posterior rounded surface -articulating with the ulna; it articulates in front with the unciform, -and internally with the =pisiform= (fig. 80, 7), which is a -comparatively large sesamoid bone on the ulnar side of the carpus. -Frequently also there is a small sesamoid bone on the radial side of -the carpus. The =trapezium= (carpale 1), =trapezoid= (carpale 2), and -=magnum= (carpale 3) (fig. 80, 5) are all small bones, and support -respectively the first, second, and third metacarpals. The =unciform= -(carpalia 4 and 5) (fig. 80, 6) is larger, and supports the fourth and -fifth metacarpals. - -The hand has five =digits=, each consisting of an elongated -=metacarpal=, followed by =phalanges=, the last of which, the =ungual -phalanx=, is pointed and curved, and bears the claw. Each of the -metacarpals is seen in the young animal to have its distal end formed -by a prominent epiphysis, and each of the phalanges, except those -bearing the claws, has a similar epiphysis at its proximal end. - -The =pollex= (fig. 80, A, I ) is far shorter than the other digits, -and normally does not touch the ground in walking. It has only two -phalanges, while each of the other digits has three. A pair of small -sesamoid bones are developed on the ventral or flexor side of the -metacarpo-phalangeal articulations of all the digits except the -pollex. Frequently similar sesamoid bones occur also on the dorsal -side of the phalangeal articulations. - - -THE PELVIC GIRDLE. - -The =pelvic girdle= consists of two halves, which lie nearly parallel -to the vertebral column. - -Each half is firmly united to its fellow in a ventral symphysis -behind, and is in front expanded and united to the sacrum. Each half -or =innominate bone= is seen in the young animal to consist of four -distinct parts, the =ilium= or dorsal element, the =pubis= or anterior -ventral element, the =ischium= or posterior ventral element, and a -small fourth part, the =acetabular= or =cotyloid= bone, wedged in -between the three others. These parts, though all distinct in the -young animal, are in the adult so completely fused that their -respective boundaries cannot be distinguished. At about the middle of -the outer surface of the innominate bone is a very deep cavity, the -=acetabulum= (fig. 78, A, 1) with which the head of the femur -articulates; all the bones except the pubis take part in its -formation. - -The =ilium= is a rather long bone, expanded in front and contracted -behind; it forms about half the acetabulum. On its inner or =sacral -surface= (fig. 78, 4) is a large roughened patch for articulation -with the sacrum; its outer or =gluteal surface= is concave. The -posterior part of the bone is flattened below, forming the narrow -=iliac surface= (fig. 78, A, 5). - -[Illustration FIG. 78. RIGHT INNOMINATE BONE, A, OF A FULL-GROWN -TERRIER, B, OF A COLLIE PUPPY. × 1. - -A is seen from the ventral side, B from the inner or sacral side. - - 1. acetabulum. - 2. thyroid foramen. - 3. supra-iliac border of ilium. - 4. sacral surface. - 5. iliac surface. - 6. acetabular border. - 7. pubic border. - 8. ischial border. - 9. ischium. - 10. tuberosity of ischium. - 11. ischial symphysis. - 12. pubis. - 13. pubic symphysis. - 14. cotyloid or acetabular bone.] - -The =ischium= (fig. 78, 9) is a wide flattened bone forming the -posterior part of the innominate bone. It meets the pubis ventrally, -but is separated from it for the greater part of its length by the -large =obturator= or =thyroid foramen= (fig. 78, 2). At its posterior -end externally it bears a rather prominent roughened =ischial -tuberosity= (fig. 78, A, 10). The ischium meets its fellow in a -ventral symphysis, and forms about one-third of the acetabulum. - -[Illustration FIG. 79. FRONT VIEW OF THE LEFT LEG BONES OF A DOG -(_Canis familiaris_) × 1/2. - -A femur, B tibia, C fibula, D patella. - - 1. head of femur. - 2. neck. - 3. great trochanter. - 4. shaft. - 5. external condyle. - 6. internal condyle. - 7. fabella. - 8. cnemial crest.] - -The =pubis= (fig. 78, 12) is smaller than either the ischium or ilium; -it does not take part in the formation of the acetabulum, and like the -ischium, meets its fellow in a ventral symphysis. The =acetabular -bone= (fig, 78, B, 14) is small and triangular, and is wedged in -between the other three. It forms about one-sixth of the acetabulum. - - -THE POSTERIOR LIMB. - -The =posterior limb=, like the anterior, is divisible into three -parts; these are the =thigh=, the =crus= or =shin=, and the =pes=. - -The =thigh= contains only a single bone, the =femur=. - -The =femur= is a long straight bone with a nearly smooth shaft and -expanded ends. The proximal end bears on its inner side the large -rounded =head= (fig. 79, A, 1) which articulates with the acetabulum. -External to the head and divided from it by a deep pit is a large -rough outgrowth, the =great trochanter= (fig. 79, 3). The deep pit is -the =trochanteric= or =digital fossa=. On the inner side below the -head is a smaller roughened surface, the =lesser trochanter=. The -lower or distal end of the bone bears two prominent rounded surfaces, -the =condyles=, which articulate with the tibia. They are separated -from one another by the deep =intercondylar notch=, which is continued -above and in front as a shallow groove, lodging a large sesamoid bone, -the =patella= or =knee-cap=. At the back of the knee-joint are a pair -of smaller sesamoids, the =fabellae= (fig. 79, 7). - -In the young animal there are three epiphyses to the shaft of the -femur, one forming the head, one the great trochanter, and one the -distal end. - -The =crus= or =shin= contains two bones, the =tibia= and =fibula=. The -=tibia= is a fairly thick straight bone, expanded at both ends, -especially at the head or proximal end. The proximal end is triangular -in cross section, and bears two facets for articulation with the -condyles of the femur. The anterior surface of the proximal end of the -tibia is marked by the strong =cnemial crest= (fig. 79, 8), which runs -some way down the shaft. The distal end of the tibia articulates with -the astragalus by an irregular, somewhat square surface. - -The shaft of the tibia ossifies from one centre, the distal end from a -second, and the proximal end from two more. - -[Illustration FIG. 80. A, RIGHT MANUS, B, RIGHT PES OF A DOG (_Canis -familiaris_) × 1/2 (after VON ZITTEL). - - 1. bone representing the fused scaphoid, lunar and centrale. - 2. cuneiform. - 3. trapezium. - 4. trapezoid. - 5. magnum. - 6. unciform. - 7. pisiform. - 8. first metacarpal. - 9. fifth metacarpal. - 10. astragalus. - 11. calcaneum. - 12. navicular. - 13. middle cuneiform. - 14. external cuneiform. - 15. cuboid. - 16. first metatarsal. - -The digits are numbered with Roman numerals.] - -The =fibula= (fig. 79, C) is a distinct but very slender bone, -somewhat expanded at both ends. It lies external to the tibia and -articulates by its proximal end with the head of the tibia, and by its -distal end with the calcaneum. Its shaft and proximal end ossify from -one centre, and its distal end from a second. - - -The =Pes=. - -The structure of the =pes= corresponds closely with that of the manus. -It is divided into:-- - -_a._ The =tarsus= or =ankle= formed of a group of small bones. - -_b._ The =foot=, which includes, firstly, some elongated bones, the -=metatarsals=, forming what corresponds to the sole of the foot, and -secondly the =phalanges=, which form the toes. - -The =Tarsus=. The tarsus of the dog consists of seven bones arranged -in two rows, of two and four respectively, with a =centrale= between -them. The two bones of the proximal row are the =astragalus= and -=calcaneum=. - -The =astragalus= (fig. 80, 10) corresponds to the fused =tibiale= and -=intermedium= of the typical tarsus. Its proximal end is much wider -than its distal end, and forms a large rounded =condyle= articulating -with the tibia, while its posterior end meets the navicular. It lies -to the dorsal side of the foot. - -The =calcaneum= (fibulare) (fig. 80, 11), the thickest bone in the -pes, lies somewhat behind, and to the outer side of the astragalus. It -articulates with the astragalus and fibula, and is drawn out behind -into a long rounded process, which forms the heel, and is in the young -animal terminated by an epiphysis. Between the proximal and distal -rows of tarsals is the =navicular= (centrale) (fig. 80, 12), a -somewhat flattened and square bone articulating with the astragalus. - -The distal row of tarsals consists of four bones. The =internal -cuneiform= (tarsale 1) is a smooth flattened bone lying to the inner -side of the foot; it articulates with the first metatarsal and with -the navicular. The =middle cuneiform= (tarsale 2) (fig. 80, 13) is a -still smaller bone, lying external to the internal cuneiform. It -articulates with the second metatarsal and with the navicular. The -=external cuneiform= (tarsale 3) (fig. 80, 14) is a larger, somewhat -square bone lying external to the middle cuneiform. It articulates -with the third metatarsal and with the navicular. The =cuboid= -(tarsalia 4 and 5) (fig. 80, 15) is a considerably larger bone lying -to the outer side of the foot. It articulates with the fourth and -fifth metatarsals and with the calcaneum. - -The pes has sometimes five digits, sometimes four, the hallux being -absent. Even when present the =hallux= (fig. 80, =B, I=) is commonly -much reduced, and may be quite vestigial, and represented only by a -small nodular metatarsal. - -Each of the other digits consists of a long metatarsal, which in the -young animal has a prominent epiphysis at its distal end, and of three -phalanges. The proximal and middle phalanges have epiphyses at their -proximal ends, while the distal phalanx is without epiphyses and is -claw-shaped. - - -FOOTNOTES: - -[139] W. Ellenberger and H. Baum, _Anatomie des Hundes_, Berlin, 1891. - -[140] T.H. Huxley, "Dental and cranial characters of the Canidae," -_P.Z.S._ 1880. - -[141] See p. 392. - -[142] The dura mater is a membrane which lines the cranial cavity and -is formed of tough connective tissue. - -[143] These are not strictly homologous with the basi-hyal and -cerato-hyal of the Dogfish. - -[144] See note to p. 25. - - - - -CHAPTER XXII. - -GENERAL ACCOUNT OF THE SKELETON IN MAMMALIA. - - -THE EXOSKELETON AND VERTEBRAL COLUMN. - - -EPIDERMAL EXOSKELETON. - -=Hair=, which forms the characteristic Mammalian exoskeleton, varies -much in different animals, and in different parts of the same animal. -A large proportion of mammals have the surface fairly uniformly -covered with hair of one kind only. In some forms however there are -two kinds of hair, a longer and stiffer kind alone appearing on the -surface, and a shorter and softer kind forming the under fur. In most -mammals hairs of a special character occur in certain regions, such as -above the eyes, on the margins of the eyelids, and on the lips and -cheeks, here forming the vibrissae or whiskers. - -Sometimes as in _Hippopotamus_, _Orycteropus_ and the Sirenia, the -hair, though scattered over the whole surface, is extremely scanty, -while in the Cetacea it is limited to a few bristles in the -neighbourhood of the mouth, or may even be absent altogether in the -adult. In most mammals the hairs are shed and renewed at intervals, -sometimes twice a year, before and after the winter. The vibrissae or -large hairs which occur in many animals upon the upper lip, and the -mane and tail of Equidae are probably persistent. - -In the hedgehogs, porcupines and _Echidna_ certain of the hairs are -modified and greatly enlarged, forming stiff spines. Similar spines -occur in the young of _Centetes_, and in _Acanthomys_ among the -Muridae. - -Several other forms of epidermal exoskeleton are met with in mammals, -including:-- - -(_a_) =Scales=. These overlie the bony scutes of armadillos and occur -covering the tail in several groups of mammals, such as beavers and -rats. In the Manidae the body is covered by flat scales which overlap. - -(_b_) The =horns= of Bovine Ruminants. These, which must on no account -be confused with antlers, are hollow cases of hardened epidermis -fitting on to bony outgrowths of the frontals. In almost every case -they are unbranched structures growing continuously throughout life, -and are very rarely shed entire. In the Prongbuck _Antilocapra_ -however they are bifurcated and are periodically shed. Horns are -nearly always limited to a single pair, but the four-horned antelope -_Tetraceros_ has two pairs, the anterior pair being the smaller. - -(_c_) The =horns of Rhinoceroses=. These are conical structures -composed of a solid mass of hardened epidermal cells growing from a -cluster of long dermal papillae. From each papilla there grows a fibre -which resembles a thick hair, and cementing the whole together are -cells which grow from the interspaces between the papillae. These -fibres differ from true hairs in not being developed in pits in the -dermis. Rhinoceros horns may be either one or two in number, and are -borne on the fronto-nasal region of the skull. They vary much in -length, the longest recorded having the enormous length of fifty-seven -inches. - -(_d_) _Nails_, _hoofs_ and =claws=. In almost all mammals except the -Cetacea, these are found terminating the digits of both limbs. =Nails= -are more or less flattened structures, =claws= are pointed and -somewhat curved. In most mammals the nails tend to surround the ends -of the digits much more than they do in man. Sometimes the nail of one -digit differs from that of all the others; thus the second digit of -the pes in the Hyracoidea and Lemuroidea is terminated by a long claw, -the other digits having flat nails. In the Felidae the claws are -retractile, the ungual phalanx with claw attached folding back when -the animal is at rest into a sheath, above, or by the side of the -middle phalanx. In the Sloths and Bats enormously developed claws -occur, forming hooks by which the animals suspend themselves. In -_Notoryctes_ the third and fourth digits of the manus bear claws of -great size; similar claws occur in _Chrysochloris_, being correlated -in each case with fossorial habits. The nail at its maximum -development entirely surrounds the terminal phalanx of the digit to -which it is attached, and is then called a =hoof=. Hoofs are specially -characteristic of the Ungulata. - -(_e_) =Spurs= and =beaks= are structures which are hardly represented -among mammals, while so characteristic of birds. They are however both -found in the Monotremata. In both _Echidna_ and _Ornithorhynchus_ the -male has a peculiar hollow horny spur borne on a sesamoid bone -articulated to the tibia. The jaws in _Ornithorhynchus_ are cased in -horny beaks similar to those of birds, and are provided with horny -pads which act as teeth. - -(_f_) =Horny plates= of a ridged or roughened character occur upon the -anterior portion of the palate, and of the mandibular symphysis in all -three genera of recent Sirenia; also upon the toothless anterior -portion of the palate in Ruminants. - -(_g_) The =baleen of whales= also belongs to the epidermal -exoskeleton. It consists of a number of flattened horny plates -arranged in a double series along the palate. The plates are somewhat -triangular in form and have their bases attached to the palate at -right angles to its long axis, while their apices hang downwards into -the mouth cavity. The outer edge of each plate is hard and smooth, -while the inner edge and apex fray out into long fibres which look -like hair. At the inner edge of each principal plate are subsidiary -smaller plates. The plates are formed of a number of fibres each -developed round a dermal papilla in the same way as are the fibres -forming the horns of _Rhinoceros_. Baleen and Rhinoceros horn likewise -agree in that the fibres are bound together by less hardened -epithelial cells, which readily wear away and allow the harder fibres -to fray out. The greatest development of baleen occurs in the Northern -Right whale, _Balaena mysticetus_, in which the plates number three -hundred and eighty or more on each side, and reach a length of ten or -twelve feet near the middle of the series. - - -DERMAL EXOSKELETON. - -Mammals show two principal kinds of exoskeletal structures which are -entirely or partially dermal in origin, viz. the bony scutes of -armadillos, and teeth. - -The =bony scutes of armadillos= are quadrate or polygonal in shape and -are in general aggregated together, forming several shields protecting -various regions of the body. The head is generally protected by a -_cephalic_ shield, the anterior part of the body by a _scapular_, and -the posterior by a _pelvic_ shield. The tail is also generally encased -in bony rings, and scutes are irregularly scattered over the surface -of the limbs. The mid-body region is protected by a varying number of -bands of scutes united by soft skin, so as to allow of movement. -Corresponding to each dermal scute is an epidermal plate. In -_Chlamydophorus_ the scutes are mainly confined to the posterior -region where they form a strong vertically-placed shield which -coalesces with the pelvis. The anterior part of the body is mainly -covered by horny epidermal plates with very little ossification -beneath. In the gigantic extinct Glyptodonts the body is covered with -a solid carapace formed by the union of an immense number of plates, -and there are no movable rings. The top of the head is defended by a -similar plate, the tail is generally encased in an unjointed bony -tube, and there is commonly a ventral plastron. - -In _Phocaena phocaenoides_ the occurrence of vestigial dermal ossicles -has been described, and in _Zeuglodon_ the back was probably protected -by dermal plates. - -TEETH[145]. - -Teeth are well developed in the vast majority of mammalia, and are of -the greatest morphological and systematic importance, many extinct -forms being known only by their teeth. Mammalian teeth differ from -those of lower animals in various well-marked respects. (1) They are -attached only to the maxillae, premaxillae and mandible, never to the -palatines, pterygoids or other bones. (2) They frequently have more -than one root. (3) They are always, except in some Odontoceti, placed -in distinct sockets. (4) They are hardly ever ankylosed to the bone. -(5) They are in most cases markedly heterodont. (6) They are commonly -developed in two sets, the milk dentition and permanent dentition. - -It sometimes happens that teeth after being formed are reabsorbed -without ever cutting the gum. This is the case, for instance, with the -upper incisors of Ruminants. - -The form of mammalian teeth varies much, some are simple conical -structures comparable to those of most reptiles, and these may either -have persistent pulps, as in the case of the upper canines of the -Walrus and the tusks of Elephants, or may be rooted as in most canine -teeth. Some teeth have chisel-shaped edges, and this may be their -original form, as in the human incisors, or may, as in those of -Rodents, be brought about by the more rapid wearing away of the -posterior edge, the anterior edge being hardened by a layer of enamel. -Then, again, the crown may, as in the majority of grinding teeth, be -more or less flattened. The various terms used in describing some of -the forms of the surface of grinding teeth are defined on page 345. - -[Illustration FIG. 81. SKULL OF A YOUNG INDIAN RHINOCEROS (_R. -unicornis_), SHOWING THE CHANGE OF THE DENTITION × 1/7. (Brit. Mus.) - - 1. nasal. - 2. frontal. - 3. parietal. - 4. zygomatic process of squamosal. - 5. jugal. - _mI{1}._ milk incisor. - _mc._ milk canine. - _mpm{1}._ milk premolar. - _I{1}._ first incisor. - _c._ canine. - _pm{2}_, _pm{3}_, _pm{4}_. 2nd, 3rd and 4th premolars. - _m{1}_, _m{2}_. first and second molars.] - -The teeth of the Aard Varks are compound, and differ completely from -those of all other mammals (see p. 425). - -As a rule, the higher the general organisation of an animal the -better are its milk teeth developed, and the more do they form a -reproduction on a small scale of the permanent set. This fact is well -seen in the Primates, Carnivora and Ungulata. The method of notation -by which the dentition of any mammal can be briefly expressed as a -formula has been already described. The regular mammalian arrangement -of teeth for each side is expressed by the formula - - _i_ 3/3 _c_ 1/1 _pm_ 4/4 _m_ 3/3 × 2; total, 44. - -MONOTREMATA. In _Echidna_ teeth are quite absent. In the young -_Ornithorhynchus_[146] functional molar teeth of a multi-tubercular -type resembling those of some Mesozoic mammalia are present, but in -the adult they disappear, their office being discharged by horny -plates. - -MARSUPIALIA[147] have a heterodont dentition, which has generally been -regarded as almost monophyodont, the only tooth which has an obvious -deciduous predecessor being the last premolar. The researches of -Röse[148] and Kükenthal[149] tend to show that the teeth of Marsupials -are developed in the same way as in other mammals, and are diphyodont. -In the case of the premolars, teeth which are homologous with the -permanent teeth of other mammals begin to develop as lateral -outgrowths from the milk teeth, but afterwards become absorbed, so -that the teeth which actually persist belong to the milk series. The -last premolar, however, does as a rule develop and replace its milk -predecessor; sometimes, however, as in _Didelphys_, it takes its place -among the milk molars without replacing one of them. - -The types of dentition characteristic of the different groups of -placental mammals may mostly be paralleled among the Marsupials. Thus -among the polyprotodont forms the Didelphyidae or opossums, and some -of the Dasyuridae, such as _Sarcophilus_ and _Thylacinus_, have a -typical carnivorous dentition with small incisors, large canines, and -molars with pointed compressed crowns. The dental formula of -_Thylacinus_, is _i_ 4/3 _c_ 1/1 _pm_ 3/3 _m_ 4/4, total 46. - -In _Myrmecobius_ five or six molar teeth occur on each side, and the -total number of teeth reaches fifty-two or fifty-six. The teeth bear -rows of tubercles, and resemble those of the Multituberculate mesozoic -Mammals[150], more than do those of any other living form. Calcified -teeth have recently been described[151] in _Myrmecobius_ earlier than -the functional or milk set. This would relegate the milk teeth of -mammals in general to a second series, and the permanent teeth to a -third. In _Notoryctes_ the dental formula[152] is given as _i_ 3/2 _c_ -1/1 _pm_ 2/3 _m_ 4/4, total 40. The canines are small, and the -anterior molars have strongly developed cusps, and much resemble those -of _Chrysochloris_ (Insectivora). - -Among the diprotodont types the Phascolomyidae, or Wombats, have a -dentition recalling that of the Rodents. All the teeth grow from -persistent pulps, and the incisors have enamel only on the anterior -surface as in Rodents. The dental formula is _i_ 1/1 _c_ 0/0 _pm_ 1/1 -_m_ 4/4, total 24. There are indications of a vestigial second pair of -incisors. - -The Macropodidae, or Kangaroos, have a herbivorous dentition with the -formula _i_ 3/1 _c_ (0--1)/0 _pm_ 2/2 _m_ 4/4. The incisors are sharp -and cutting, and are separated by a long diastema or gap from the -molars, which have their crowns marked by ridges or cusps. There are -indications of several vestigial incisors. - -_Coenolestes_, a remarkable form recently described from America, -belongs to the diprotodont section, and is the only living member of -the section known outside the Australian region[153]. An exceptional -dentition is seen in the case of the extinct _Thylacoleo_, in which -the functional teeth are reduced to two pairs; one pair of large -cutting incisors and one of compressed sharp-edged premolars. - -EDENTATA. Some Edentata, viz. the ant-eaters (Myrmecophagidae) are, as -far as is known, absolutely toothless at all stages of their -existence; being the only mammals except _Echidna_ in which no tooth -germs have been discovered; others, viz. the Manidae, though showing -foetal tooth germs, are quite toothless in post-foetal life; others, -viz. some of the armadillos, have the largest number of teeth met with -in land mammals. The teeth are homodont except in the Aard Varks, and -grow from persistent pulps. In the sloths (Bradypodidae) and the -Megatheriidae, there are five pairs of teeth in the upper and four in -the lower jaw. The teeth of sloths consist of a central axis of -vasodentine, surrounded firstly by a thin coating of hard dentine, and -secondly by a thick coating of cement. - -In no living Edentate have the teeth any enamel; it has, however, been -described as occurring in certain early Megatheroid forms from S. -America[154], and an enamel organ has also been discovered in an -embryo _Dasypus_[155]. In the Armadillos (Dasypodidae) the number of -teeth varies from 8/8 or 7/7 in _Tatusia_, to upwards of 25/25 in -_Priodon_, which therefore may have upwards of a hundred teeth, the -largest number met with in any land mammal. In _Tatusia_ all the teeth -except the last are preceded by two-rooted milk teeth. The Aard Varks -are diphyodont, and milk teeth are also known in a species of -_Dasypus_, but with these exceptions Edentates are, as far as is -known, monophyodont. In _Glyptodon_ the teeth are almost divided into -three lobes by two deep grooves on each side. - -The Aard Varks (Orycteropodidae) are quite exceptional as regards -their teeth, which are cylindrical in shape, and are made up of a -number of elongated denticles fused together. Each denticle contains a -pulp cavity from which a number of minute tubes radiate outwards. -These teeth are diphyodont and somewhat heterodont, eight to ten pairs -occur in the upper jaw and eight in the lower, but they are not all in -place at one time. The last three teeth in each jaw are not preceded -by milk teeth[156]. - -SIRENIA. The teeth of Sirenia show several very distinct types, the -least modified being that of the extinct Halitheriidae, which have -large incisors in the upper jaw, and five or six pairs of tuberculated -grinding teeth in each jaw, the anterior ones being preceded by milk -teeth. - -In both the living genera the dentition is monophyodont. In _Manatus_ -the dentition is _i_ 2/2 _pm_ and _m_ 11/11. The incisors are -vestigial, and disappear before maturity. The grinding teeth have -square enamelled crowns marked by transverse tuberculated ridges. They -are not all present in the jaw at the same time. In _Halicore_ the -upper jaw bears a pair of straight tusklike incisors; in the male -these have persistent pulps and project out of the mouth; in the -female they soon cease to grow and are never cut. They are separated -by a long diastema from the grinding teeth which have tuberculated -crowns and are 5/5 or 6/6 in number, but are not all in place at once. -Several other pairs of slender teeth occur in the young animal, but -are absorbed or fall out before maturity. In _Rhytina_ teeth are -altogether absent. - - -CETACEA. - -_ARCHAEOCETI._ _Zeuglodon_ has the following dentition, _i_ 3/3 _c_ -1/1 _pm_ and _m_ 5/5, total 36. The incisors and canines are simple -and conical; the cheek teeth are compressed and have serrated cutting -edges like those in some seals. - -In the _MYSTACOCETI_, or whalebone whales, calcified tooth germs -probably belonging to the milk dentition are present in the embryo, -but they are never functional, and are altogether absent in the adult. -The anterior of these germs are simple, the posterior ones are -originally complex, but subsequently split up into simple teeth like -those of the anterior part of the jaw. Hence according to Kükenthal, -who described these structures, the Cetacean dentition was originally -heterodont. - -In the living _ODONTOCETI_ the dentition is homodont and monophyodont. -In some cases traces occur of a replacing dentition which never comes -to maturity, and renders it probable that the functional teeth of the -Odontoceti are really homologous with the milk teeth of other mammals. -Some of the dolphins afford the apparently simplest type of mammalian -dentition known. The teeth are all simple, conical, slightly recurved -structures, with simple tapering roots and without enamel. The -dentition is typically _piscivorous_, being adapted for seizing active -slippery animals such as fish. The prey is then swallowed entire -without mastication. Sometimes the teeth are excessively numerous, -reaching two hundred or more (fifty to sixty on each side of each jaw) -in _Pontoporia_. This multiplication of teeth is regarded by Kükenthal -as due to the division into three parts of numbers of trilobed teeth -similar to those of some seals. - -In the Sperm whale, _Physeter_, the lower jaw bears a series of twenty -to twenty-five stout conical recurved teeth, while in the upper jaw -the teeth are vestigial and remain imbedded in the gum. An extinct -form, _Physodon_, from the Pliocene of Europe and Patagonia is allied -to the Sperm whale, but has teeth in both jaws. In the Grampus _Orca_, -the teeth number about 12/12, and are very large and strong. In some -forms the teeth are very much reduced in number; thus in _Mesoplodon_ -the dentition consists simply of a pair of conical teeth borne in the -mandible. In the Narwhal _Monodon_ the dentition is practically -reduced to a single pair of teeth, which lie horizontally in the -maxillae, and in the female normally remain permanently in the alveoli. -In the male the right tooth remains rudimentary, while the left is -developed into an enormous cylindrical tusk marked by a spiral groove. -Occasionally both teeth develop into tusks, and there is reason for -thinking that two-tusked individuals are generally or always female. -In the extinct _Squalodon_ the dentition is decidedly heterodont, and -the molars have two roots. The dental formula is - - _i_ 3/3 _c_ 1/1 _pm_ 4/4 _m_ 7/7, total 60. - -It is probable that the homodont condition of modern Odontoceti is not -primitive, but due to retrogressive evolution. - - -UNGULATA. - -Just as in the Cetacea a piscivorous dentition is most typically -developed, so the Ungulata are, as a group, the most characteristic -representatives of a _herbivorous_ dentition in its various forms. - - -UNGULATA VERA. - -_ARTIODACTYLA_. As regards the living forms, the Artiodactyla can be -readily divided into two groups, namely those with bunodont and those -with selenodont teeth. It has, however, been shown that selenodont -teeth always pass through an embryonic bunodont stage[157]. The -bunodont type is best seen in Pigs and Hippopotami and such extinct -forms as _Hyotherium_. In _Hippopotamus_ the dental formula is _i_ -(2-3)/(1-3) _c_ 1/1 _pm_ 4/4 _m_ 3/3. - -The incisors and canines of _Hippopotamus_ are very large and grow -continuously. The genus _Sus_, which affords a good instance of an -_omnivorous_ type of dentition, has the regular unmodified Mammalian -dental formula _i_ 3/3 _c_ 1/1 _pm_ 4/4 _m_ 3/3, total 44. The -canines, specially in the male, are large and have persistent pulps, -and the upper canines do not have the usual downward direction but -pass outwards and upwards. In the Wart Hog, _Phacochaerus_, they are -enormously large, but a still more extraordinary development of teeth -is found in _Babirussa_. In the male _Babirussa_ the canines, which -are without enamel, are long, curved and grow continuously. Those of -the upper jaw never enter the mouth, but pierce the skin of the face -and curve backwards over the forehead. The dental formula of -_Babirussa_ is _i_ 2/3 _c_ 1/1 _pm_ 2/2 _m_ 3/3, total 34. - -The Wart Hog has a very anomalous dentition, for as age advances all -the teeth except the canines and last molars show signs of -disappearing; both pairs of persisting teeth are however very large. - -Various extinct Ungulata such as _Anoplotherium_ have teeth which are -intermediate in character between the bunodont and selenodont types. -_Anoplotherium_ has the regular mammalian series of forty-four teeth. -The crowns of all the teeth are equal in height, and there is no -diastema--an arrangement found in no living mammal but man. - -We come now to the selenodont Artiodactyla. - -The Tylopoda--camels (Camelidae) and Llamas (Aucheniidae) when young -have the full number of incisors, but in the adult the two upper -middle ones are lost. The molars are typically selenodont and -hypsodont[158]. In the Camel the dental formula is _i_ 1/3 _c_ 1/1 -_pm_ 3/2 _m_ 3/3, total 34. The upper incisors, canines and first -premolars of the Camel are very small teeth, and the first premolar -is separated by a long diastema from the others. - -The Tragulina or Chevrotains have no upper incisors, while the canines -are largely developed, especially in the male. - -The Ruminantia or Pecora are very uniform as regards their dentition. -The upper incisors are always absent, for though their germs are -developed they are reabsorbed without ever becoming visible, and as a -rule the upper canines are absent too, while the lower canines are -incisiform. The grinding teeth are typically selenodont, and in the -lower jaw form a continuous series separated by a wide diastema from -the canines. The dental formula is usually - - _i_ 0/3 _c_ 0-1/1 _pm_ 3/3 _m_ 3/3. - -The canines are largely developed in the male Muskdeer (_Moschus_) and -in _Hydropotes_. - -_PERISSODACTYLA_. The premolars and molars have a very similar -structure and form a continuous series of large square teeth with -complex crowns. The crowns are always constructed on some modification -of the bilophodont[159] plan, as is easily seen in the case of the -forms with brachydont teeth, but in animals like the Horse, in which -the teeth are very hypsodont, this arrangement is hard to trace. All -four premolars in the upper jaw are preceded by milk teeth, while in -Artiodactyla the first has no milk predecessors. - -In the Tapiridae the grinding teeth are brachydont and the lower ones -are typically bilophodont. The last two upper molars have the -transverse ridges united by an outer longitudinal ridge. The dentition -is _i_ 3/3 _c_ 1/1 _pm_ 4/3 _m_ 3/3, total 42. - -In some of the extinct Perissodactyles such as _Lophiodon_[160], the -dentition is brachydont and bilophodont, the grinding teeth in general -resembling the posterior upper molars of the Tapir. The same type of -brachydont tooth is seen in _Palaeotherium_ but the transverse ridges -are crescentic instead of straight, and are separated from one another -by shallow valleys without cement. Some of the Palaeotheridae have the -regular series of forty-four teeth. - -A complete series of forms is known showing how from the simple -brachydont teeth of the Palaeotheridae, were derived the complicated -hypsodont teeth of the Equidae. The increase in depth of the tooth was -accompanied by increase in the depth and complexity of the enamel -infoldings, and of the cement filling them. - -Both upper and lower grinding teeth of the Equidae are much -complicated by enamel infoldings, but their derivation from the -bilophodont type can still be recognised. The diastema in front of the -premolars is longer in the living Equidae than in their extinct -allies. In the adult horse the dental formula is _i_ 3/3 _c_ 1/1 _pm_ -3/3 _m_ 3/3, total 40, with often a vestigial first upper premolar -(fig. 82, _pm_ 1). The last molar is not more complex than the others, -and in the female the canine is quite vestigial. The incisors are -large and adapted for cutting and have the enamel curiously folded in -forming a deep pit. The milk dentition is _di_ 3/3 _dc_ 0/0 _dpm_ 3/3, -total 24. The last milk premolar is not more complex than the premolar -that succeeds it. The horse affords an excellent instance of a -typically _herbivorous_ type of dentition, the cutting incisors, -reduced canines and series of large square flat-crowned grinding teeth -being most characteristic. - -In _Rhinoceros_ the grinding teeth are much like those of _Lophiodon_, -having an outer longitudinal ridge from which two crescentic -transverse ridges diverge. The upper premolars are as complex as the -molars, and there are no canines; in some species incisors also are -absent. The dental formula is - - _i_ (0--2)/(0--1) _c_ 0/(0--1) _pm_ 4/4 _m_ 3/3. - -[Illustration FIG. 82. PALATAL ASPECT OF THE CRANIUM AND MANDIBLE OF A -DONKEY (_Equus asinus_) × 1/5. (Camb. Mus.) - - 1. supra-occipital. - 2. occipital condyle. - 3. basi-occipital. - 4. vacuity representing the confluent foramen lacerum posterius - and foramen lacerum medium. - 5. auditory bulla. - 6. glenoid surface. - 7. vomer. - _i_ 1, _i_ 3. first and third incisors. - _c._ canine. - _pm_ 1, _pm_ 2. first and second premolars. - _m_ 1. first molar.] - -Among the Titanotheriidae _Palaeosyops_[161] has very brachydont teeth -whose crowns have been described as _buno-selenodont_, the inner pair -of columns being bunodont, the outer, selenodont. Similar grinding -teeth occur in _Chalicotherium_. Some of the Titanotheriidae have the -regular mammalian series of forty-four teeth. - - -SUBUNGULATA. - -_TOXODONTIA._ _Nesodon_ has the regular dental formula; its grinding -teeth are rooted and the upper ones resemble those of Rhinoceros. The -second upper and third lower incisors form ever-growing tusks. There -is a marked difference between the deciduous and permanent dentition. -_Astrapotherium_ likewise has large rooted cheek teeth of a -rhinocerotic type, and each jaw bears a pair of permanently growing -tusks, those of the lower jaw being the canines. The dental formula is - - _i_ 1/3 _c_ 0/1 _pm_ 2/1 _m_ 3/3, total 28. - -In _Toxodon_ the upper incisors and molars are large and curved and -all the teeth have persistent pulps. In _Typotherium_ there are no -tusks, but the upper incisors are chisel-like, recalling those of -Rodents. - -The _CONDYLARTHRA_ have brachydont, generally bunodont teeth, with the -premolars simpler than the molars. They generally have the regular -dental formula. - -_HYRACOIDEA._ The dental formula of _Procavia_ is usually given as _i_ -1/2 _c_ 0/0 _pm_ 4/4 _m_ 3/3, total 34; in young individuals however -there occur a second pair of upper incisors which early fall out. The -upper incisors resemble those of Rodents in being long and curved and -growing from persistent pulps. They are however triangular in -transverse section, not rectangular, having two antero-lateral faces -covered with enamel and a posterior face without enamel. Their -terminations are pointed, not chisel-shaped as in Rodents. The lower -incisors (fig. 83, _i_ 1) are pectinate or partially divided by -vertical fissures, and the grinding teeth are of the rhinocerotic -type. - -[Illustration FIG. 83. SKULL OF _Procavia (Dendrohyrax) dorsalis_ × -2/3. (Camb. Mus.) - - 1. nasal. - 2. parietal. - 3. external auditory meatus. - 4. paroccipital process of the exoccipital. - 5. jugal. - 6. lachrymal foramen. - _i_ 1. first incisor.] - -_AMBLYPODA._ Two of the best known forms belonging to this extinct -group differ much as regards dentition. For while _Coryphodon_ has the -regular dental formula, and the canines of both jaws of moderate size, -in _Uintatherium_ the dentition is very specialised, there are no -upper incisors, and the upper canines form a pair of enormous tusks. -The grinding teeth form a continuous series marked by =V=-shaped ridges -and the dental formula is _i_ 0/3 _c_ 1/1 _pm_ 3/3 _m_ 3/3 total 34. - -_PROBOSCIDEA._ The incisors are composed entirely of dentine and have -the form of conical tusks projecting greatly from the mouth. In -living forms they are confined to the upper jaw, in some species of -the extinct _Mastodon_ however they occur in the lower jaw also. In -_Dinotherium_ they are probably absent from the upper jaw, but form a -pair of downwardly and backwardly-directed tusks growing from the -elongated symphysis of the mandible. - -The grinding teeth in the various Proboscidea show a very remarkable -series of modifications. In _Dinotherium_ they are bilophodont or else -are marked by three straight transverse ridges. The dental formula is -_i_ 0?/1 _c_ 0/0 _pm_ 2/2 _m_ 3/3, and the teeth have the normal -method of succession. In _Mastodon_ as in _Dinotherium_ the grinding -teeth are marked by transverse ridges, but the ridges are subdivided -into conical or mammillary cusps, and similar cusps often occur -between the ridges. These cusps are covered with very thick enamel and -the spaces between them are not filled up with cement. There are six -of these grinding teeth for each side of each jaw but only three are -in place at once. The first three are milk teeth as they may be -succeeded vertically by others. - -In the true Elephants the number and depth of the enamel folds is much -increased, and the spaces between the folds are filled up with cement. -A very complete series of extinct forms is known with teeth -intermediate in character between those of _Mastodon_ and those of the -Mammoth and living elephants. The dental formula of _Elephas_ is - - _di_ 1/0 _i_ 1/0 _c_ 0/0 _dm_ 3--4/3--4 _m_ 3/3. - -Sir W.H. Flower describes[162] the mode of succession of teeth in -Elephants as follows: "As regards the mode of succession that of -modern Elephants is as before mentioned very peculiar. During the -complete lifetime of the animal there are but six molar teeth on each -side of each jaw with occasionally a rudimentary one in front, -completing the typical number of seven. The last three represent the -true molars of ordinary mammals, those in front appear to be milk -molars which are never replaced by permanent successors, but the whole -series gradually moves forwards in the jaw, and the teeth become worn -away and their remnants cast out in front while development of others -proceeds behind. The individual teeth are so large and the processes -of growth and destruction by wear take place so slowly, that not more -than one or portions of two teeth are ever in place and in use on each -side of each jaw at one time, and the whole series of changes -coincides with the usual duration of the animal's life. On the other -hand the _Dinotherium_, the opposite extreme of the Proboscidean -series, has the whole of the molar teeth in place and use at one time, -and the milk molars are vertically displaced by premolars in the -ordinary fashion. Among Mastodons transitional forms occur in the mode -of succession as well as in structure, many species showing a vertical -displacement of one or more of the milk molars, and the same has been -observed in one extinct species of Elephant (_E. planifrons_) as -regards the posterior of these teeth." - -In the TILLODONTIA the grinding teeth are of Ungulate type, while the -second incisors are large and grow from persistent pulps, so as to -resemble those of Rodents. - -RODENTIA have a most characteristic and very constant dentition, the -common dental formula being - - _i_ 1/1 _c_ 0/0 _pm_ (0--1)/(0--1) _m_ 3/3, total 18 or 20. - -The incisors always have chisel-like edges and persistent pulps, and -are separated by a wide diastema from the premolars. Canines are -always absent, and there are generally three grinding teeth not -preceded by milk teeth; their surface may be grooved, or may be -bunodont. Teeth are most numerous in the Duplicidentata (Hares and -Rabbits), in which the formula is _i_ 2/1 _c_ 0/0 _pm_ 3/2 _m_ 3/3, -total 28, and fewest in Hydromys and certain other forms, in which -the formula is _i_ 1/1 _c_ 0/0 _pm_ 0/0 _m_ 2/2, total 12. The hares -and rabbits are the only rodents which have well developed deciduous -incisors, though a vestigial milk incisor has been described in the -Mouse (_Mus musculus_). The last upper molar of _Hydrochaerus_ is very -complicated, its structure approaching that of the teeth of Elephants. - -[Illustration FIG. 84. CARNASSIAL OR SECTORIAL TEETH OF CARNIVORA -(from FLOWER). - -_Upper sectorial teeth_ of I. _Felis_, II. _Canis_, III. _Ursus_. 1. -anterior, 2. middle, 3. posterior cusp of blade, 4. inner lobe -supported on distinct root, 5. inner lobe posterior in position and -without distinct root, characteristic of the Ursidae. - -_Lower sectorial teeth._ 1. _Felis_, 2. _Canis_, 3. _Herpestes_. 1. -anterior, 2. posterior lobe of blade, 3. inner tubercle, 4. heel.] - -CARNIVORA have the teeth rooted and markedly diphyodont and -heterodont. The canines are greatly developed, and the incisors are -small. - -In _CARNIVORA VERA_ the incisors are almost always 3/3. The fourth -upper premolar and first lower molar are differentiated as carnassial -teeth (see p. 436), and retain fundamentally the same characters -throughout the suborder. The upper carnassial (fig. 84, I. II. III.) -consists of a more or less compressed, commonly trilobed blade borne -on two roots, with an inner tubercle borne on a third root. The lower -carnassial has only two roots; its crown consists of a bilobed blade -with generally an inner cusp, and a heel or talon (fig. 84, 4) behind -the blade. - -The most thoroughly carnivorous type of dentition is seen in the -Æluroidea, and especially in the cat tribe (Felidae). In the genus -_Felis_ the dental formula is _i_ 3/3 _c_ 1/1 _pm_ 3/2 _m_ 1/1, total -30. The incisors are very small, so as not to interfere with the -action of the large canines, the lower carnassial is reduced to simply -the bilobed blade (fig. 84, IV), and the cheek teeth are greatly -subordinated to the carnassial. The extinct _Machaerodus_ has the -upper canines comparable in size to those of the Walrus. - -The Civets and Hyaenas have a dentition allying them closely to the -cats. The hyaena-like _Proteles_ has, however, the grinding teeth -greatly reduced. - -In the Cynoidea[163] the general dentition is _i_ 3/3 _c_ 1/1 _pm_ 4/4 -_m_ 2/3, total 42. This differs from the regular mammalian dentition -only in the absence of the last upper molar. The upper carnassial -tooth (fig. 84, II.) consists of a larger middle and smaller posterior -lobe with hardly any trace of an anterior lobe. The lower carnassial -(fig. 84, V.) is typical, consisting of a bilobed blade with inner -cusp and posterior talon. - -The dentition of the Cynoidea is most closely linked with that of the -Arctoidea by means of fossil forms. - -[Illustration FIG. 85. MANDIBLE OF ISABELLINE BEAR (_Ursus -isabellinus_) × 1/2. (Camb. Mus.) - - 1. condyle. - 2. coronoid process. - _i_ 1. first incisor. - _c._ canine. - _pm_ 1, _pm_ 2. first and second premolars. - _m_ 1. first molar. The dotted - line is pointing to the posterior - half of the tooth. - This specimen has only - three premolars, there - should be four.] - -In the Arctoidea the dentition is not so typically carnivorous as in -the Æluroidea and Cynoidea. In the bears, Ursidae, the molars have -broad flat tuberculated crowns (fig. 85). The dental formula in -_Ursus_ is _i_ 3/3 _c_ 1/1 _pm_ 4/4 _m_ 2/3, total 42. The upper -carnassial (fig. 84, III.) differs from that of the Æluroidea and -Cynoidea in having no inner lobe supported on a third root. In the -large group of Mustelidae there are generally two molars in the lower -and one in the upper jaw. The grinding teeth commonly have large, -flattened, more or less tuberculated crowns, and the upper molar may -be as large or much smaller than the carnassial. - -In the _CREODONTA_ there are no specially differentiated carnassial -teeth. - -[Illustration FIG. 86. LEFT MANDIBULAR RAMUS OF THE SEA LEOPARD -(_Ogmorhinus leptonyx_) WITH THE ROOTS OF THE TEETH EXPOSED × 1/3. -(Camb. Mus.) - - 1. condyle. - 2. coronoid process. - _i_ 3. third incisor. - _c._ canine. - _pm_ 1, _pm_ 4. first and fourth premolars. - _m._ molar.] - -In the _PINNIPEDIA_ the dentition differs considerably from that of -the Carnivora vera. The milk dentition is always vestigial, and the -teeth are frequently absorbed before birth. There are four premolars -and one molar, forming an uniform series of cheek teeth, all of which -except in the Walrus have compressed and pointed, never flattened, -crowns. There is no special carnassial tooth, and the incisors are -always fewer than 3/3. In _Otaria_ the dentition is - - _i_ 3/2 _c_ 1/1 _pm_ 4/4 _m_ 1 or 2/1, total 34 or 36. - -In the Walrus the upper canines form immense tusks. The other teeth -are all small and one-rooted, and the molars have flat crowns. In the -true seals the dentition is strikingly piscivorous, the cheek teeth -often having accessory cusps (fig. 86). - -The INSECTIVORA are diphyodont and heterodont, having well-developed -rooted teeth. The canines are usually weak, the incisors pointed, and -those of the two jaws often meet like a pair of forceps. The crowns of -the molars are characteristically studded with short cusps. Some -genera, such as _Gymnura_ and the mole, _Talpa_, have the regular -mammalian dentition. In the hedgehog, _Erinaceus_, the dentition is - - _i_ 3/2 _c_ 1/1 _pm_ 3/2 _m_ 3/3, total 36. - -In the genus _Sorex_ (Shrews) the teeth differ in the following two -marked respects from those of most other Monodelphia, (1) they are -monophyodont, (2) the lower incisors sometimes become fused to the -jaws. Most Insectivora have square molar teeth, but in _Potamogale_, -_Chrysochloris_, _Solenodon_ and the Centetidae the molar teeth are -triangular in section. Four molars occur in _Centetes_. - -In the aberrant genus _Galeopithecus_ the dentition is _i_ 2/3 _c_ 1/1 -_pm_ 2/2 _m_ 3/3, total 34. The upper incisors are placed at some -distance from the anterior end of the jaw, and the outer upper -incisors and canines of both jaws have two roots,--a very unusual -character. The lower incisors are deeply grooved or pectinated in the -same way as are the lower incisors of _Procavia_. The upper incisors -and canines of both jaws bear many cusps, and are very similar in -appearance to the cheek teeth of some Seals. - -The dentition of the CHIROPTERA is diphyodont and heterodont, and the -dental formula never exceeds - - _i_ 2/3 _c_ 1/1 pm 3/3 _m_ 3/3, total 38. - -The milk teeth are very slender and have sharp recurved cusps; they -are quite unlike the permanent teeth. The permanent teeth are of two -types. In the Insectivorous forms the molar teeth are cusped, and -resemble those of Insectivora. In the blood-sucking Vampire bat -_Desmodus_, the teeth are peculiarly modified; the canines and the -single pair of upper incisors are much enlarged and exceedingly sharp, -while all the other teeth are much reduced in size. - -In the Frugivorous bats the molar teeth have nearly always smooth -crowns. The dental formula in the chief genus _Pteropus_ is _i_ 2/2 -_c_ 1/1 _pm_ 3/3 _m_ 2/3, total 34. - -The PRIMATES have a diphyodont and heterodont dentition, generally of -an omnivorous type, with cheek teeth adapted for grinding. The -incisors are generally 2/2, and the molars, except in the Hapalidae, -are 3/3. In the Lemurs the upper canines are large, and the lower -incisors slender and directed almost horizontally forwards. The Aye -Aye, _Chiromys_, has the following singular dentition: _i_ 1/1 _c_ 0/0 -_pm_ 1/0 _m_ 3/3, total 18. The incisors much resemble those of -rodents having persistent pulps, and enamel only on the anterior face. - -In Man and in the Anthropoid and Old World Apes the dental formula is -always _i_ 2/2 _c_ 1/1 _pm_ 2/2 _m_ 3/3, total 32. - -In the Cebidae there is an extra premolar in each jaw bringing the -number up to 36. In the Hapalidae, as in the Cebidae, there is a third -premolar, but the molars are reduced to 2/2. Man is the only Primate -that has the teeth arranged in a continuous series. In all the others -there is a gap or diastema of larger or smaller size between the -incisors and canines. In all except man also the canines are enlarged, -especially in the males. - -The Exoskeletal structures of mammals may be summarised in the -following table: - - I. _Epidermal exoskeletal structures._ - - 1. Hairs (_a_) ordinary hair, - (_b_) vibrissae and bristles, - (_c_) spines of hedgehog, porcupine, _Echidna_, - _Centetes_, _Acanthomys_. - 2. Scales { of Manidae, - { on tails of rats, beavers, &c. - 3. Horns of Rhinoceros. - 4. Horns of Bovine Ruminants. - 5. Nails, claws, hoofs. - 6. Spurs of male _Ornithorhynchus_ and _Echidna_. - 7. Horny beak and teeth of _Ornithorhynchus_. - 8. Horny pads on jaws of Sirenians and Ruminants. - 9. Baleen of whales. - 10. Enamel of teeth. - - II. _Dermal exoskeletal structures._ - - 1. Dentine and cement of teeth. - 2. Bony scutes of Armadillos. - - -ENDOSKELETON. - -VERTEBRAL COLUMN. - -CERVICAL VERTEBRAE. - -The cervical vertebrae of all mammals have certain characters in -common. However long the neck may be, the number of cervical -vertebrae, with very few exceptions, is seven. Movable ribs are -generally absent, and if present are small and do not reach the -sternum. The transverse processes are generally wide but not long, and -are perforated near the base by the vertebrarterial canals, through -which the vertebral arteries pass; they generally bear downwardly -directed inferior lamellae which are sometimes as in the seventh human -cervical seen to ossify from centres distinct from those forming the -rest of the transverse process, and are really of the nature of ribs. -The atlas and axis always differ much from the other vertebrae. - -We may pass now to the special characters of the cervical vertebrae in -the different groups. In MONOTREMES and MARSUPIALS the number of -cervical vertebrae is always seven. With the exception of the atlas of -_Echidna_ the cervical vertebrae of Monotremes are without -zygapophyses. In Monotremes the transverse processes ossify from -centres distinct from that forming the body, and remain suturally -connected with the rest of the vertebra until the adult condition is -reached. The method of the ossification of the atlas in Marsupials -varies considerably, thus in some forms such as the Wombats -(_Phascolomys_) there is an unossified gap in the middle of the -inferior arch of the atlas, which may remain permanently open; in -_Thylacinus_ this gap is filled up by a distinct heart-shaped piece of -bone, while in _Didelphys_ and _Perameles_ the atlas is ossified below -in the same way as in other mammals. In _Notoryctes_ the second to -sixth cervical vertebrae are ankylosed together. - -The cervical vertebrae of the EDENTATA have some remarkable -peculiarities. In the three-fingered Sloth, _Bradypus_, there are nine -cervical vertebrae, all except the last of which have their transverse -processes perforated by the vertebrarterial canals. In a two-fingered -sloth, _Choloepus hoffmanni_, there are only six cervical vertebrae. -In the Megatheriidae, Anteaters (Myrmecophagidae), Pangolins -(Manidae), and Aard Varks (Orycteropodidae), the cervical vertebrae -are normal, but in the Armadillos (Dasypodidae), and still more in the -Glyptodonts, several of them are commonly fused together. The fusion -affects not only the centra, but also the neural arches, so that the -neural canals form a continuous tube. - -In the Glyptodonts there is a complex joint at the base of the neck to -allow the partial retraction of the head within the carapace. This -arrangement recalls that in Tortoises. - -As a rule the SIRENIA possess seven short cervical vertebrae, not -fused together and not presenting any marked peculiarities. In -_Manatus_ however there are only six cervical vertebrae and they are -very variable. - -[Illustration FIG. 87. CERVICAL VERTEBRAE OF A YOUNG FIN WHALE -(_Balaenoptera musculus_) × 1/10. (Camb. Mus.) - - 1. surface on the atlas for articulation - with the occipital condyle of the skull. - 2. foramen for exit of the first spinal nerve. - 3. upper transverse process. - 4. lower transverse process. - -In the fresh specimen these two transverse processes are united by -cartilage, in adult individuals the whole transverse process is -ossified. - - 5. epiphyses of centrum. - 6. neural spine.] - -In the CETACEA there are invariably seven cervical vertebrae, but they -are always very short and are frequently even before birth fused -together by their centra into one continuous mass (see fig. 67). -Sometimes the last one or two are free. In the Rorquals -(_Balaenoptera_) however, the cervical vertebrae are quite separate -and distinct (fig. 87), and in the fluviatile Odontoceti, -_Platanista_, _Inia_, and _Pontoporia_, and also in _Beluga_ and -_Monodon_, though very short they are free. In _Physeter_ the first -vertebra is free while the others are fused. An odontoid process is -not commonly present even in Cetaceans with free cervical vertebrae, -but a very short one occurs in the Rorquals. The cervical vertebrae of -Rorquals give off on each side two transverse processes (fig. 87, 3 -and 4) which enclose between them a wide space. These processes are -not completely ossified till the animal is adult. - -[Illustration FIG. 88. ATLAS (B) AND AXIS (A) VERTEBRAE OF AN OX (_Bos -taurus_) × 1/4. (Camb. Mus.) - - 1. neural canal. - 2. transverse process. - 3. surfaces for articulation with the occipital condyles of the skull. - 4. spout-like odontoid process. - 5. hypapophysis. - 6. anterior opening of the vertebrarterial canal. - 7. foramen for the exit of the second spinal nerve. - 8. neural spine. - 9. postzygapophysis.] - -In all UNGULATA the number of cervical vertebrae is seven. Among the -Artiodactyla two forms of the odontoid process of the axis occurs; in -the Suina and Tragulina it is conical, in the Ruminantia and Tylopoda -it is spout-like (fig. 88, 4). The atlas in the Suina and to a less -extent in the Ruminantia has long flattened transverse processes, and -the remaining cervical vertebrae are opisthocoelous. Those of the -Giraffe and Llama (fig. 103) are noticeable for their great length. In -the Tylopoda the posterior half of the vertebrarterial canal is -confluent with the neural canal. - -The Perissodactyla have remarkably opisthocoelous cervical vertebrae. -Those of _Macrauchenia_ have the posterior half of the vertebrarterial -canal confluent with the neural canal as in Tylopoda. In the -Proboscidea they are short flattened discs slightly opisthocoelous; -the axis and seventh vertebra and to a less extent the sixth have high -neural spines. - -In the RODENTIA the atlas generally has broad wing-like transverse -processes, and the axis a large and long neural spine, while the -odontoid process is much developed. In the Jerboas (_Dipus_) all the -cervical vertebrae except the atlas are fused together, a condition -recalling that in armadillos. - -In the CARNIVORA the wings of the atlas are well developed (fig. 69, -A, 1), and it is deeply cupped for articulation with the condyles of -the skull. The axis has a long odontoid process and a high compressed -neural spine (fig. 69, B, 4). The third to sixth cervical vertebrae -have large transverse processes with prominent perforated inferior -lamellae, whose ventral margins in the third and fourth vertebrae -diverge as they pass backwards, while in the fifth they are parallel -and in the sixth convergent. The transverse processes of the seventh -vertebra have no inferior lamellae and are not perforated. -Metapophyses are often developed. - -In the INSECTIVORA the cervical vertebrae vary considerably. The -neural spines except in the case of the axis are generally very small -and in the Shrews and Moles the neural arches are exceedingly slender. - -In the CHIROPTERA all the cervical vertebrae are broad and short with -slender neural arches. - -PRIMATES. In Man the cervical vertebrae have short blunt transverse -processes and small often bifid neural spines. The neural and -vertebrarterial canals are large. The atlas forms a ring surrounding a -large cavity, and has a very slender inferior arch and small -transverse processes. Traces of a pro-atlas have been described in -_Macacus_ and _Cynocephalus_. The axis has a prominent spine and -odontoid process and short transverse processes. In most Primates the -cervical vertebrae are very similar to those of man, but the inferior -lamellae of the transverse processes are better developed. In the -Anthropoid Apes the neural spines are as a rule much elongated. - - -THORACO-LUMBAR, OR TRUNK VERTEBRAE. - -In the MONOTREMATA there are nineteen thoraco-lumbar vertebrae, -sixteen (_Echidna_) or seventeen (_Ornithorhynchus_) of which bear -ribs. The transverse processes are very short and do not articulate -with the ribs, which are united to the centra only. - -In the MARSUPIALIA there are always nineteen thoraco-lumbar vertebrae, -thirteen of which generally bear ribs. The lumbar vertebrae frequently -have large metapophyses and anapophyses, these being specially well -seen in the Kangaroos and Koala (_Phascolarctus_). - -The EDENTATA are very variable as regards their trunk vertebrae. The -two genera of Sloths differ much as regards the number, for while -_Bradypus_ has only nineteen, fifteen or sixteen of which bear ribs, -_Choloepus_ has twenty-seven, twenty-four of which are thoracic, and -bear ribs. In _Bradypus_ a small outgrowth from the transverse process -articulates with the neural arch of the succeeding vertebra. In both -genera the neural spines are all directed backwards. - -In the Megatheriidae as in the sloths the neural spines are all -directed backwards, and in the lumbar region additional articulating -surfaces occur, better developed than are those in _Bradypus_. - -In the ant-eaters (Myrmecophagidae) there are seventeen or eighteen -thoraco-lumbar vertebrae, all of which except two or three bear ribs. -The posterior thoracic and anterior lumbar vertebrae articulate in a -very complex fashion, second, third, and fourth pairs of zygapophyses -being progressively developed in addition to the ordinary ones, as the -vertebrae are followed back. - -In the Armadillos the lumbar vertebrae have long metapophyses which -project upwards and forwards and help to support the carapace. In -_Glyptodon_ almost all the thoraco-lumbar vertebrae are completely -ankylosed together. - -In the Manidae there are no additional zygapophyses but the normal -ones of the lumbar and posterior thoracic regions are very much -developed, the postzygapophyses being semi-cylindrical and fitting -into the deep prezygapophyses of the succeeding vertebra. - -In the SIRENIA the number of lumbar vertebrae is very small; in the -dugong there are nineteen thoracic and four lumbar, and in the manatee -seventeen thoracic and two lumbar. - -In the CETACEA the number of thoracic vertebrae varies from nine in -_Hyperoödon_ to fifteen or sixteen in _Balaenoptera_, and the number -of lumbar vertebrae from three in _Inia_ to twenty-four or more in -_Delphinus_. The lumbar vertebrae are often very loosely articulated -together and the zygapophyses sometimes as in the Dolphins are placed -high up on the neural spines. The centra are large, short in the -anterior region but becoming longer behind. The epiphyses are -prominent, and so are the neural spines and to a less extent the -metapophyses. The transverse processes are well developed, anteriorly -they arise high up on the neural arch, but when the vertebral column -is followed back they come gradually to be placed lower down, till in -the lumbar region they project from the middle of the centra. This can -be well traced in the Porpoise (_Phocaena_). In the Physeteridae the -transverse processes of the anterior thoracic vertebrae are similar to -those of most Cetacea, but when followed back, instead of shifting -their position on the vertebrae, they gradually disappear, and other -processes gradually arise from the point where the capitulum of the -rib articulates. - -UNGULATA. In the Ungulata vera the thoraco-lumbar vertebrae are -slightly opisthocoelous. The anterior thoracic vertebrae commonly have -exceedingly high backwardly-projecting neural spines (fig. 89, 1); but -those of the lumbar and posterior thoracic vertebrae often point -somewhat forwards so that the spines all converge somewhat to a point -called the _centre of motion_ (cp. fig. 101). In the Artiodactyla -there are always nineteen thoraco-lumbar vertebrae, and in the -Perissodactyla twenty-three. - -_Procavia_ sometimes has thirty thoraco-lumbar vertebrae, a greater -number than occurs in any other terrestrial mammal; twenty-two of -these are thoracic and eight lumbar. In _Phenacodus_ the convergence -of the neural spines to a centre of motion is well seen. - -[Illustration FIG. 89. FIRST AND SECOND THORACIC VERTEBRAE OF AN OX -(_Bos taurus_) × 1/3. (Camb. Mus.) - - 1. neural spine. - 2. neural canal. - 3. prezygapophysis. - 4. facet for articulation with the tuberculum of the rib. - 5. facet for articulation with the capitulum of the rib. - 6. postzygapophysis. - 7. foramen for exit of spinal nerve.] - -In the Proboscidea there are twenty-three thoraco-lumbar vertebrae, of -which nineteen or twenty bear ribs. - -In the RODENTIA there are generally nineteen thoraco-lumbar vertebrae -but occasionally the number rises as high as twenty-five. In the Hares -(Leporidae) the number is nineteen, twelve or thirteen of which are -thoracic. The anterior thoracic vertebrae have short centra and high -backwardly-directed neural spines, the lumbar vertebrae have large -forwardly-and downwardly-directed transverse processes with expanded -ends. Metapophyses, anapophyses and hypapophyses are all present. In -the Agouti (_Dasyprocta_) the convergence of the neural spines to a -centre of motion is very strongly marked. - -In the CARNIVORA the trunk vertebrae are nearly always twenty or -twenty-one in number; in the genera _Felis_ and _Canis_ thirteen of -these are thoracic and seven lumbar. The anterior thoracic vertebrae -have long backwardly-projecting neural spines, while the posterior -thoracic and lumbar vertebrae have shorter and thicker neural spines -which project slightly forwards. In the Pinnipedia there is no change -in the direction of the neural spines, and anapophyses are but little -developed. - -In the INSECTIVORA the number of trunk vertebrae varies much from -nineteen--thirteen thoracic and six lumbar--in _Tupaia_, to -twenty-four--nineteen thoracic and five lumbar--in _Centetes_. The -development of the various processes varies in accordance with the -habits of the animals, being great in the active forms, slight in the -slowly moving or burrowing forms. In _Talpa_ and _Galeopithecus_ the -intervertebral discs of the thoraco-lumbar region instead of being -cartilaginous have ossified forming inter centra, a condition met with -in very few mammals. - -In the CHIROPTERA there are seventeen or eighteen thoraco-lumbar -vertebrae, eleven to fourteen of which may bear ribs. The development -of processes is slight. - -Among PRIMATES the number of trunk vertebrae is generally nineteen, of -which twelve to fourteen bear ribs; in man and the Gorilla and -Chimpanzee the number is, however, seventeen, and in the Orang -(_Simia_) sixteen. In some of the Lemuroidea there are as many as -twenty-three or twenty-four. In most cases the neural spines converge -more or less to a centre of motion, and this is especially marked in -some of the Lemurs; it does not occur in man and the anthropoid apes. - - -SACRAL AND CAUDAL VERTEBRAE. - -At the posterior end of the trunk in all mammals a certain number of -vertebrae are found fused together forming the sacrum. But of these -only two or three answer to the definition of true sacral vertebrae in -being united to the ilia by small ribs. The others which belong to the -caudal series may be called pseudosacral vertebrae. In different -individuals of the same species it sometimes happens that different -vertebrae are attached to the pelvis and form the sacrum. Sometimes -even different vertebrae are attached to the pelvis at successive -periods in the life history of the individual. This is owing to a -shifting of the pelvis and has been especially well seen in man. In -young human embryos the pelvis is at a certain stage attached to -vertebra 30, but as development goes on it becomes progressively -attached to the twenty-ninth, twenty-eighth, twenty-seventh, -twenty-sixth and twenty-fifth vertebrae. As the attachment to these -anterior vertebrae is gained, the attachment to the posterior ones -becomes lost, so that in the adult the pelvis is generally attached to -vertebrae 25 and 26. But there are no absolutely pre-determined sacral -vertebrae, as sometimes the pelvis does not reach vertebra 25, -remaining attached to vertebrae 26 and 27; sometimes it becomes -attached even to vertebra 24. This shifting of the pelvis is seen in -_Choloepus_ in a more marked degree even than in man. - -Of the MONOTREMATA, _Ornithorhynchus_ has two sacral vertebrae -ankylosed together, while _Echidna_ has three or four[164]. - -In MARSUPIALIA as a rule only one vertebra is directly united to the -ilia, but one or two more are commonly fused to the first. In the -Wombats there may be as many as four or five vertebrae fused together -in the sacral region. In _Notoryctes_ there is extensive fusion in the -sacral region, six vertebrae, owing mainly to the great development of -their metapophyses, being united with one another, and with the ilia, -and the greater part of the ischia. - -In most EDENTATA there is an extensive fusion of vertebrae in the -sacral region. This is especially marked in the Armadillos and -Megatheriidae, and to a less extent in the Sloths and Aard Varks. - -In the SIRENIA the vestigial pelvis is attached by ligament to the -transverse processes of a single vertebra, which hence may be regarded -as sacral. - -In CETACEA there is no sacrum, the vestigial pelvis not being -connected with the vertebral column. - -In most UNGULATA the sacrum consists of one large vertebra united to -the ilia, and having a varying number of smaller vertebrae fused with -it behind. - -The same arrangement obtains in most RODENTIA, but in the Beavers -(Castoridae) all the fused vertebrae are of much the same size, the -posterior ones having long transverse processes which nearly meet the -ilia. - -In CARNIVORA there may be two sacral vertebrae as in the Hyaena, three -as in the Dog, four or five as in Bears and Seals. - -In INSECTIVORA from three to five are united, while in many CHIROPTERA -all the sacral and caudal vertebrae have coalesced. Among PRIMATES, in -Man and Anthropoid Apes there are usually five fused vertebrae forming -the sacrum, but of these only two or three are connected to the ilia -by ribs. In most of the other Anthropoidea there are two or three -fused vertebrae, and in the Lemuroidea two to five. - -FREE CAUDAL VERTEBRAE. The free caudal vertebrae vary greatly in -number and character. When the tail is well developed, the anterior -vertebrae are comparatively short and broad, with well-developed -neural arches and zygapophyses; but as the tail is followed back, the -centra gradually lengthen and become cylindrical, and at the same time -the neural arches and all the processes gradually become reduced and -disappear, so that the last few vertebrae consist of simple rod-like -centra. Chevron bones are frequently well-developed. - -Of the MONOTREMES _Echidna_ has twelve caudal vertebrae, two of which -bear irregular chevron bones. In _Ornithorhynchus_ there are twenty or -twenty-one caudal vertebrae with well-developed hypapophyses, but no -chevron bones. - -In MARSUPIALS there is great diversity as regards the tail. In the -Wombat and Koala the tail is small and without chevron bones. In most -other Marsupials it is very long, having sometimes as many as -thirty-five vertebrae in the prehensile-tailed opossums. In the -Kangaroos the tail is very large and stout. Chevron bones are almost -always present, and in _Notoryctes_ are large and expanded. - -Most EDENTATES have large tails with well-developed chevron bones. The -length of the tail varies greatly from the rudimentary condition in -Sloths to that in the Pangolins, one of which has forty-six to -forty-nine caudal vertebrae--the largest number in any known mammal. -Chevron bones are much developed, sometimes they are Y-shaped, -sometimes as in _Priodon_, they have strong diverging processes. The -caudal vertebrae of Glyptodonts, though enclosed in a continuous bony -sheath, have not become ankylosed together. - -The SIRENIA have numerous caudal vertebrae with wide transverse -processes. In the CETACEA also the tail is much developed, and the -anterior vertebrae have large chevron bones and prominent straight -transverse processes; the posterior caudal vertebrae, which in life -are enclosed in the horizontally expanded tail fin, are without -transverse processes. - -In UNGULATA the tail is simple, formed of short cylindrical vertebrae, -which in living forms are never provided with chevron bones. The -number of caudal vertebrae varies from four, sometimes met with in -_Procavia_, to thirty-one in the Elephant. The tail is exceedingly -long in _Anoplotherium_ and in _Phenacodus_, in which there are thirty -caudal vertebrae. - -In RODENTIA the tail is variable. In the Hares, Guinea pig (_Cavia_) -and _Capybara_ it is very small, in _Pedetes_ and the Beaver it is -very long and has well-developed chevron bones. - -Most of the CARNIVORA except the Bears and Seals have very long tails, -the greatest number of vertebrae, thirty-six, being met with in -_Paradoxurus_. Bears have only eight to ten caudal vertebrae. Chevron -bones are not often much developed. - -In INSECTIVORA the tail is very variable as regards length, the number -of vertebrae varying from eight in _Centetes_ to forty-three in -_Microgale_. - -In CHIROPTERA the tail is sometimes quite rudimentary, and as in -_Pteropus_, composed of a few coalesced vertebrae, sometimes it is -formed of a large number of slender vertebrae. - -In PRIMATES also the tail is very variable. In Man all the four caudal -vertebrae are rudimentary and are fused together, forming the -_coccyx_. In the Anthropoid apes, too, there are only four or five -caudal vertebrae. In many monkeys of both the eastern and western -hemispheres the tail is very long, having thirty-three vertebrae in -_Ateles_, in which genus it is also prehensile. Chevron bones are -present in all Primates with well-developed tails. In the Lemuroidea -the number of caudal vertebrae varies from seven to twenty-nine. - - -FOOTNOTES: - -[145] See W.H. Flower, "Remarks on the homologies and notation of the -teeth in Mammalia," _J. Anat. and Physiol. norm. path._, Vol. III., p. -262; R. Owen, _Odontography_, London, 1840--45; C.S. Tomes, _Manual of -Dental Anatomy_, London, 1876. See also H.F. Osborn, "Recent -researches on succession of teeth in Mammals," _Amer. Natural._, -XXVII., p. 493, and "Rise of Mammalia in N. America," _Stud. Biol. -Lab. Columb. Coll._, Zool. I., no. 2. - -[146] See E.B. Poulton, _P.R.S._, Feb. 1888, and _Quart. J. Micr. -Sci._, Vol. XXIX. 1889; also Oldfield Thomas, _P.R.S._, XLVI. (1889). - -[147] W.H. Flower, _Phil. Trans._, vol. 156, pp. 631--641, 1867; also -Oldfield Thomas, _Phil. Trans._, pp. 443--462, 1887. - -[148] C. Röse, _Anat. Anz._ VII., p. 639. - -[149] W. Kükenthal, _Anat. Anz._ VI., p. 364. - -[150] See p. 348. - -[151] W. Leche, _Morph. Jahrb._ XX., pp. 113--142 (1893). - -[152] E.C. Stirling, _P.Z.S._ 1891, p. 327. - -[153] O. Thomas, _P.Z.S._, 1895, p. 870. - -[154] F. Ameghino, _Bull. Ac. Argen._ XII. p. 437. According to H. -Burmeister, _Annal. Mus. Buenos Aires_, III. 401 (1891), enamel does -not occur, osteodentine having been mistaken for it. - -[155] E. Ballowitz, _Arch. Mikr. Anat._ XL. p. 133. - -[156] See Oldfield Thomas, _P.R.S._, vol. XLVII., p. 246 (1890). - -[157] J. Taeker, "_Fur Kenntniss der Odontogenese bei Ungulaten_." -Dorpat, 1892. - -[158] See p. 345. - -[159] See p. 345. - -[160] According to H.F. Osborn, _Amer. Natural._, XXVI. p. 763, a -number of not very closely allied forms have been included under -_Lophiodon_. - -[161] C. Earle, _J. Ac. Philad._, vol. IX., 1892, p. 267. - -[162] _Encyclopaedia Britannica_, article _Mammalia_, p. 424. - -[163] See T.H. Huxley, "The dental and cranial characters of the -Canidae," _P.Z.S._, 1880, p. 238. - -[164] G.B. Howes, _Journ. of Anat. and Phys._ XXVII., p. 544. - - - - -CHAPTER XXIII. - -GENERAL ACCOUNT OF THE SKELETON IN MAMMALIA (CONTINUED). - - -THE SKULL AND APPENDICULAR SKELETON. - - -THE SKULL. - -MONOTREMATA. In both genera the cranium is thin-walled, has a fairly -large cavity, and is very smooth and rounded externally. The sutures -between many of the bones early become obliterated in a manner -comparable to that in birds, and the facial portion of the skull is -much prolonged. - -In _Echidna_ the face is drawn out into a gradually tapering rostrum, -formed mainly by the premaxillae, maxillae and nasals. The zygomatic -arch is very weak, and the palate extends very far back. The tympanic -forms a slender ring. The mandible is extremely slight, with no -ascending portion, and but slight traces of the coronoid process and -angle. The hyoid has a wide basi-hyal and stout thyro-hyals, while the -anterior cornua are slender, and include ossified epi-hyals and -cerato-hyals. - -In _Ornithorhynchus_ the zygomatic arch is much stouter than in -_Echidna_. The face is produced into a wide beak, mainly supported by -the premaxillae, between whose diverging anterior ends there is a -dumb-bell-shaped bone. The maxillae are flattened below, and each -bears a large horny tooth, which meets a corresponding structure borne -on a surface near the middle of the mandible. The mandible is -considerably stouter than in _Echidna_, but the angle and coronoid -process are but little developed. The infra-orbital foramen and the -inferior dental and mental foramina of the mandible are all very -large. - -[Illustration FIG. 90. HALF FRONT VIEW[165] OF THE SKULLS OF A -TASMANIAN WOLF (_Thylacinus cynocephalus_) (to the left) × 3/8; AND OF -A HAIRY-NOSED WOMBAT (_Phascolomys latifrons_) (to the right) × 3/8. -(Camb. Mus.) - - 1. premaxillae. - 2. nasal. - 3. frontal. - 4. infra-orbital foramen. - 5. lachrymal. - 6. jugal. - 7. coronoid process of the mandible. - 8. lachrymal foramen. - i. 1. first upper incisor. - C. canine.] - -MARSUPIALIA. The skulls of the various types of the Marsupials -frequently bear a strong superficial resemblance to those of some of -the different groups of placental mammals. Thus the skull of the -Dasyuridae resembles that of the Carnivora, the resemblance being most -marked between the skulls of _Thylacinus_ and the dog. The skull of -_Notoryctes_ is strongly suggestive of that of an Insectivore, and -that of other Marsupials such as the wombat, recalls equally the -characteristic features of a Rodent's skull. But, however much they -may differ from one another, the skulls of all Marsupials agree in the -following respects. (1) The brain cavity, and especially the cerebral -fossa, has a very small comparative size. (2) The nasals are always -large, and the mesethmoid is extensively ossified, and terminated by a -prominent vertical edge. (3) Processes from the jugal and frontal in -living forms never meet and enclose the orbit, but the zygomatic arch -is always complete. (4) The jugal always extends back to form part of -the glenoid fossa. (5) The lachrymal canal opens either external to or -upon the margin of the orbit, and the nasal processes of the -premaxillae never quite reach the frontals. (6) The posterior part of -the palate is commonly pierced by large oval vacuities. (7) The -tympanic is small and never fused to the bones of the cranium. (8) The -carotid canal perforates the basisphenoid and not the tympanic bulla. -(9) The optic foramen and sphenoidal fissure are confluent. (10) In -every case except _Tarsipes_ the angle of the mandible is more or less -inflected. - -The skull of the extinct _Thylacoleo_ differs from that of all other -Marsupials in the fact that the postorbital bar is complete. The hyoid -is constructed on much the same plan in all Marsupials. It consists of -a small basi-hyal, a pair of broad cerato-hyals, and a pair of strong -thyro-hyals. The epi-hyals and stylo-hyals are generally unossified. - -EDENTATA. In Sloths (Bradypodidae) the sutures become early -obliterated, the cranial portion of the skull is rather high, and the -facial portion very short. The lachrymal is very small, and its canal -opens outside the orbit. The zygomatic arch is incomplete, and the -jugal (fig. 91, 5) is curiously forked, but in a manner differing in -the two genera. The premaxillae are very small,--in _Bradypus_ quite -vestigial. The mandible is well developed, the angle being specially -marked in _Bradypus_. In _Choloepus_ the symphysial part is drawn out -in a somewhat spout-like manner (fig. 91, 6). In both genera the -thyro-hyals are ankylosed with the basi-hyal. - -[Illustration FIG. 91. SKULL OF A TWO-FINGERED SLOTH (_Choloepus -didactylus_) × 1/2. (Camb. Mus.) - - 1. anterior nares. - 2. postorbital process of the frontal. - 3. coronoid process. - 4. angle of the mandible. - 5. jugal. - 6. spout-like prolongation of the mandible.] - -In _Megatherium_ the general appearance of the skull is distinctly -sloth-like, but the facial portion is more elongated, partly owing to -the development of a prenasal bone, and the zygomatic arch is -complete. The mandible is very deep in the middle, and is drawn out -into a long spout-like process in front. - -Anteaters (Myrmecophagidae) have a much modified skull, and this is -especially the case in the Great Anteater, _Myrmecophaga_. The skull -is smooth and evenly-rounded, in these respects recalling that of -_Echidna_, but it is longer and tapers much more gradually than in -_Echidna_. The occipital condyles are remarkably large. The premaxillae -are small, and the long rostrum is chiefly composed of the maxillae and -nasals with the mesethmoid and vomer. The zygomatic arch is -incomplete, and there is no trace of a separation between the orbit -and the temporal fossa. The palate is much elongated, the pterygoids -meeting in the middle line just like the palatines. The mandible is -very long and slender, there being no definite coronoid process, and a -short and slight symphysis. The hyoid arch is noticeable for the -length of the anterior cornu. - -In the Armadillos (Dasypodidae) the skull varies a good deal in shape, -but the facial portion is always tapering and depressed. The zygomatic -arch is complete. In _Dasypus_ and _Chlamydophorus_ the tympanic bulla -is well ossified. - -In the Glyptodontidae the skull is very short and deep; the zygomatic -arch is complete, and has a long downwardly projecting maxillary -process. The mandible is massive, and has a very high ascending -portion. - -In the Manidae the skull is smooth and rounded, the zygomatic arch is -incomplete, and the orbit is inconspicuous. The palate is long and -narrow, but the pterygoids do not take part in its formation. The -mandible is slightly developed and has no angle or coronoid process. - -In _Orycteropus_ the zygomatic arch is complete, and there is a small -postorbital process to the frontal. The mandible is well-developed, -having a coronoid process and definite ascending portion, and the -hyoid is well ossified. - -SIRENIA. The skull, and especially the brain case of all Sirenia, is -remarkable for the general density of the component bones, which, -though often very thick, are without air sinuses. It is noticeable -also for the roughness of the bones, and the irregular manner in which -they are united together. - -[Illustration FIG. 92. LATERAL VIEW OF THE SKULL OF _Rhytina stelleri_ -× 1/8. (Brit. Mus.) - - 1. frontal. - 2. parietal. - 3. zygomatic process of the squamosal. - 4. squamosal. - 5. exoccipital. - 6. occipital condyle. - 7. pterygoid process of the alisphenoid. - 8. jugal. - 9. premaxillae. - 10. angle of the mandible. - 11. maxillae.] - -The cranial cavity is decidedly small, the reduction being specially -noticeable in the cerebral fossa, which is not much larger than the -cerebellar fossa. The foramen magnum is large, and the dorsal surface -of the cranium narrow. The zygomatic arch is very strongly developed, -the squamosal (fig. 92, 4) being especially prominent, and being drawn -out not only into the zygomatic process, but also into a large -post-tympanic process which articulates with the exoccipital. At the -side of the skull between the squamosal, supra-occipital and -exoccipital, there is a wide vacuity in the cranial wall, partially -filled up by the very large periotic, which is ankylosed to the -tympanic, but is not united to any other bones of the skull. The -foramen lacerum medium is confluent with the foramen lacerum anterius, -and the two together form an enormous vacuity on the floor of the -skull, bounded chiefly by the exoccipital, basi-occipital, alisphenoid -and squamosal. The jugal (fig. 92, 8) is large and in _Manatus_ sends -up a strong process, which nearly or quite meets the postorbital -process of the frontal, completing the orbit. In the other Sirenia the -orbit is completely confluent with the very large temporal fossa. The -lachrymal in _Manatus_ is very small, but is larger in _Halicore_. The -premaxillae (fig. 92, 9) are large, but smaller in _Manatus_ than in -the other genera, in all of which they are curiously bent down in -front. Their upper margin forms the anterior border of a very large -aperture lying high on the roof of the skull and extending back for a -considerable distance. This aperture is formed by the union of the two -anterior nares. The nasals are quite vestigial or absent, and the -narial aperture is bounded above by the frontals; in its floor are -seen the slender vomer and large mesethmoid. The palate is long and -narrow, and formed mainly by the maxillae; behind it there is a large -irregular process formed by the union of the palatine, pterygoid, and -pterygoid plate of the alisphenoid. The mandible is very massive and -has a very high ascending portion, a rounded angle (fig. 92, 10), and -a prominent coronoid process; the two rami are firmly ankylosed -together. The hyoid consists principally of the broad flat basi-hyal; -the anterior cornua are but slightly ossified, while the thyro-hyals -are not ossified at all. - -CETACEA. The skull in all Cetacea, especially in the Odontoceti, is a -good deal modified from the ordinary mammalian type. - -In the _ARCHAEOCETI_ this modification is less marked than in either -of the other suborders. The nasals and premaxillae are a good deal -larger than they are in living forms, and the anterior nares are -placed further forward. The maxillae do not extend back over the -frontals, and there is a well-marked sagittal crest. - -In the _MYSTACOCETI_ the skull is always quite bilaterally -symmetrical, and is not so much modified from the ordinary mammalian -type as in the Odontoceti. The parietals are not, as in the -Odontoceti, separated by a wide interparietal, but meet; they are, -however, hidden under the very large supra-occipital. The nasals are -developed to a certain extent, and the nares, though placed very far -back and near the top of the head, terminate forwardly-directed narial -passages. Turbinal bones are also developed to some extent; this fact, -and the occurrence of a definite though small olfactory fossa -constituting important distinctions from the Odontoceti. The maxillae -are large, but do not extend back to cover the frontals as in the -Odontoceti. The zygomatic process of the squamosal is very large. The -mandibular rami are not compressed, but are rounded and arched -outwards, and never meet in a long symphysis. - -_ODONTOCETI._ The skull departs widely from the ordinary mammalian -type. The following description will apply to any of the following -genera of the Delphinidae, _Phocaena_, _Globicephalus_, -_Lagenorhynchus_, _Delphinus_, _Tursiops_, _Prodelphinus_, _Sotalia_. - -The upper surface of the skull is more or less asymmetrical. The -cerebral cavity is high, short and broad; and formed mainly by the -cerebral fossa, the olfactory fossa being entirely absent. The -supra-occipital (fig. 93, 3) is very large, and forms much of the -posterior part of the roof of the skull. It has the interparietal -(fig. 93, 7) fused with it, and completely separates the two -parietals. The frontal (fig. 93, 10) is large and laterally expanded, -forming the roof of the orbit, but is almost completely covered by an -extension of the maxillae. The zygomatic arch is very slender, and is -mainly formed by a rod-like process from the jugal (fig. 93, 15), the -zygomatic process of the squamosal being short and stout. - -The nasal passages are peculiarly modified, instead of passing -horizontally forwards above the roof of the mouth, they pass upwards -and even somewhat backwards towards the top of the skull (fig. 93, -23). They are bounded laterally by two processes from the premaxillae, -the left of which is shorter than the right. The nasal cavities are -narrow and without turbinals and the nasals (fig. 93, 19) are almost -as much reduced as in Sirenia. - -[Illustration FIG. 93. A, LATERAL VIEW, AND B, LONGITUDINAL SECTION OF -THE SKULL OF A YOUNG CA'ING WHALE (_Globicephalus melas_) × 1/6. -(Brit. Mus.) - - 1. basi-occipital. - 2. exoccipital. - 3. supra-occipital. - 4. basisphenoid. - 5. alisphenoid. - 6. parietal. - 7. interparietal. - 8. presphenoid. - 9. orbitosphenoid. - 10. frontal. - 11. mesethmoid. - 12. tympanic. - 13. periotic. - 14. squamosal. - 15. jugal. - 16. vomer. - 17. palatine. - 18. pterygoid. - 19. nasal. - 20. maxillae. - 21. premaxillae. - 22. mandible. - 23. anterior nares.] - -In front of the nasal openings the face is prolonged as a narrow beak -or rostrum of varying length, formed by the maxillae and premaxillae -surrounding the vomer and large mesethmoid (fig. 93, 11), which sends -forwards a long partially cartilaginous process, and is fused behind -with the presphenoid (fig. 93, 8). The basi-occipital (fig. 93, 1) too -is fused with the basisphenoid. The foramen rotundum is confluent with -the sphenoidal fissure, and the foramen ovale with the foramen lacerum -medium and the foramen lacerum posterius. The palate is mainly formed -by the maxillae; the premaxillae and palatines (fig. 93, 17), though -both meet in symphyses, forming very little of it. The pterygoids vary -in size in the different genera, sometimes as in _Lagenorhynchus_ and -_Delphinus_ meeting in the middle line, sometimes as in _Phocaena_ and -_Globicephalus_ (fig. 93, 18) being widely separated. The tympanic and -periotic are not fused together, and the periotic has generally no -bony union with the rest of the skull. The mandible is rather slightly -developed, with the rami straight, compressed and tapering to the -anterior end. The condyle is not raised at all above the edge of the -ramus; the angle is rounded and the coronoid process is very small. -_Platanista_ has a curiously modified skull; the rostrum and mandible -are exceedingly long and narrow, and arising from the maxillae are two -great plates of bone which nearly meet above. - -In the Physeteridae the skull is raised into a very prominent crest at -the vertex behind the nares. In front of this in _Hyperoödon_ a pair -of ridges occur, formed by outgrowths from the maxillae. In the old -male these ridges reach an enormous size and almost meet in the middle -line. In _Physeter_, the Sperm whale, these ridges are not developed; -the maxillae and premaxillae unite with the other bones of the crest -enclosing an enormous half basin-shaped cavity, at the base of which -are the very asymmetrical anterior narial apertures. - -In all living Cetacea the hyoid has the same general shape, consisting -firstly of a crescentic bone formed by the fusion of the thyro-hyals -with the basi-hyal, and secondly of the anterior cornu formed -principally by the strong stylo-hyal. - -UNGULATA. None of the distinctive characters separating the Ungulata -from the other groups of mammals are drawn from the skull. But in the -Ungulata vera as opposed to the Subungulata a distinguishing feature -is found in the fact that the lachrymal and jugal form a considerable -part of the side of the face, and that the jugal always forms the -anterior part of the zygomatic arch, the maxillae taking no part in it. - - -UNGULATA VERA. - -_ARTIODACTYLA._ The skull in Artiodactyla differs from that in -Perissodactyla in the fact that the posterior end of the nasal is not -expanded and there is no alisphenoid canal. - -The skulls in the different groups of Artiodactyla differ considerably -from one another. - -[Illustration FIG. 94. A, CRANIUM AND B, MANDIBLE OF A PIG (_Sus -scrofa_) × 1/5. (Camb. Mus.) - - 1. jugal. - 2. postorbital process of the frontal. - 3. zygomatic process of the squamosal. - 4. supra-occipital. - 5. glenoid cavity. - 6. occipital condyle. - 7. foramen magnum. - 8. paroccipital process of the exoccipital. - 9. tympanic bulla. - 10. pterygoid. - 11. anterior palatine foramen. - 12. palatal plate of maxillae. - 13. coronoid process. - 14. mandibular condyle. - _i_ 1, _i_ 2, _i_ 3. first, second, and third incisors. - _c._ canine. - _pm_ 1, _pm_ 2, _pm_ 3, _pm_ 4. first, second, third, and fourth - premolars. - _m_ 1, _m_ 2, _m_ 3. first, second, and third molars.] - -The skull of the Pig[166] will be described as illustrative of the -skull in the Suina. In the Pig as in most Artiodactyla the face is -bent sharply down on the basicranial axis, the commencement of the -vomer being situated below the mesethmoid instead of in front of it as -in most skulls. The occipital region of the skull is small, and the -line of junction of the supra-occipital and parietals is raised into a -prominent occipital crest. The parietal completely fuses at an early -stage with its fellow, and the exoccipital is drawn out into a long -paroccipital process (fig. 94, A, 8). The frontal is large and broad -and drawn out into a small postorbital process. The lachrymal too is -large and takes a considerable part in forming the side of the face in -front of the orbit, as does also the jugal, though to a less extent. -The face is long and tapers much anteriorly. The nasals are long and -narrow, as are the nasal processes of the premaxillae, which do not -however reach the frontals. A prenasal ossicle is developed in front -of the mesethmoid. The palate is long and narrow, the pterygoid (fig. -94, A, 10) is small, but the pterygoid process of the alisphenoid is -prominent. The squamosal is small and has the tympanic fused with it; -the tympanic is dilated below, forming a bulla (fig. 94, A, 9) filled -with cancellous bone, and above forms the floor of a long -upwardly-directed auditory meatus. The mandible has a high ascending -portion and a small coronoid process (fig. 94, B, 13). The hyoid -differs from that of most Ungulates, the stylo-hyal being very -imperfectly ossified. - -[Illustration FIG. 95. MANDIBLE OF A HIPPOPOTAMUS (_H. amphibius_) × -1/7. (Camb. Mus.) - -The second incisor of the left side is missing and the crowns of the -grinding teeth are much worn. - - 1. condyle. - 2. coronoid process. - 3. mental foramina. - _i_ 1, _i_ 2. first and second incisors. - _c._ canine. - _pm_ 3. third premolar. - _m_ 1, _m_ 3. first and third molar.] - -In _Hippopotamus_ the skull though essentially like that of the pig is -much modified in detail. The brain cavity is very small, while the -jaws are immensely developed. The face contracts in front of the -orbits and then expands again greatly, to lodge the enormous incisor -and canine teeth. The postorbital bar is complete or nearly so, and -the orbits project curiously outwards and slightly upwards; the -lachrymal is thin and much dilated. The squamosal is drawn out into a -postglenoid process, and the hamular process of the pterygoid is -prominent. The tympanic bulla is filled with cancellous bone. The -mandible is enormously large, the symphysis is long, the angle much -expanded and drawn out into a process which projects outwards and -forwards. - -Among extinct forms related to the Suina, _Cyclopidius_ is noticeable -for having large vacuities in the lachrymo-nasal region, while -_Cotylops_ has the postorbital bar complete; both these forms are from -the North American Miocene. - -In the Tylopoda and Tragulina the skull resembles in most respects -that of the Ruminants, shortly to be described; but it is allied to -that of the Suina in having the tympanic bulla filled with cancellous -bone. The tympanic bulla is better developed in the Tragulina than in -most Ungulates. - -Among Ruminants, the Bovidae, that large group including the Oxen, -Sheep, and Antelopes, as a rule have the face bent on the basicranial -axis much as in the Suina. The parietals are generally small and early -coalesce, the frontals are large and are usually drawn out into horn -cores, which are however absent in the skulls of some domestic -varieties of sheep and oxen, and also in some of the earlier extinct -forms of Bovidae. These horn cores are formed internally of cancellous -bone, and on them the true epidermal horns are borne. In young animals -there is a distinct interparietal, but this early fuses with the -supra-occipital, and in the oxen also with the parietals. The -occipital crest is generally well marked, but in the genus _Bos_ -becomes merged in a very prominent straight ridge running between the -two horn cores; this ridge, which contains air cells communicating -with those in the horn cores, is not nearly so well marked in _Bison_. -There is often, as in _Gazella_, a vacuity on the side of the face -between the nasal, frontal, lachrymal, and maxillae, but this is not -found in oxen or sheep. The premaxillae are small, the nasals are long -and pointed, and the turbinals are much developed. The Saiga antelope -has a curiously specialised skull; the nasals are absent or have -coalesced with the frontals and the anterior nares are enormously -large. In all Ruminants the lachrymal is large and forms a -considerable part of the side of the face; it often bears a -considerable depression, the _suborbital_ or _lachrymal fossa_, well -seen in most of the smaller antelopes. The postorbital bar is -complete, and the orbit is prominent and nearly circular. The -palatines and pterygoids are moderately large, and the pterygoids have -a backwardly-projecting hamular process. The squamosal is small, but -has a postglenoid process. The tympanic is not fused to the periotic -and has a small bulla not filled with cancellous bone. There is a -large paroccipital process to the exoccipital and the mandible has a -long slender coronoid process. - -In the Cervidae and Giraffidae the face is not bent down on the -basicranial axis as it is in the Bovidae. The frontals are drawn out, -not into permanent horn cores as in the Bovidae, but into short -outgrowths, the pedicels, upon which in the Cervidae long antlers are -annually developed. These _antlers_ are outgrowths of bone, and are -covered during development by vascular integument, which dries up and -peels off when growth is complete. Every year they are detached, by a -process of absorption at the base, and shed. They may occur in both -sexes, as in the Reindeer, but as a rule they are found only in the -male. They are generally more or less branched, and are sometimes of -enormous size and weight, as in the extinct _Cervus megaceros_. In -young animals they are always simple, but become annually more and -more complicated as the animal grows older. - -In the Giraffe the frontals bear a small pair of bony cores, which are -at first distinct, but subsequently become fused to the skull. In the -allied _Sivatherium_, a very large form from the Indian Pliocene, the -skull bears two pairs of bony outgrowths, a pair of short conical -outgrowths above the orbits, and a pair of large expanded outgrowths -on the occiput. - -The opening of the lachrymal canal is commonly double and the -lachrymal fossa is large in the Cervidae and the Giraffidae except -_Sivatherium_. The vacuity between the frontal, lachrymal, maxillae, -and nasal is specially large. - -The hyoid of Ruminants is noticeable for the development of the -anterior cornua, which include stout and short cerato-hyals and -epi-hyals, long and strong stylo-hyals and large tympano-hyals which -are more or less imbedded in the tympanics. - -_PERISSODACTYLA._ In the skull of Perissodactyles an alisphenoid canal -is found and the nasals are expanded behind. Among the living animals -belonging to this group the skull least modified from the ordinary -type is that in _Rhinoceros_. In this form the skull is considerably -elongated, the facial portion being very large. The occipital region -is elevated, but the cranial cavity is small, the boundary line -between the occipital and parietal regions being drawn out into a -prominent crest, which is occupied by air cells. There is no -postorbital process to the frontal, and the orbit is completely -confluent with the temporal fossa. The nasals are fused together and -are very strongly developed, extending far forwards, sometimes -considerably beyond the premaxillae. In some extinct species, such as -_Elasmotherium_ and the Tichorhine Rhinoceros, _R. antiquitatis_, the -mesethmoid is ossified as far forwards as the end of the nasals. The -nasals are arched and bear one or two roughened surfaces to which the -great nasal horns are attached. The premaxillae are very small and the -pterygoids are slender. The palate is long, narrow, and deeply -excavated behind. The postglenoid process of the squamosal is well -developed, and generally longer than the paroccipital process of the -exoccipital. The tympanic and periotic are both small and are fused -together. The condyle of the mandible is very wide, the angle rounded, -and the coronoid process moderately developed. - -In the Titanotheriidae, a family of extinct Perissodactyla from the -Miocene of North America, the occipital region is much elevated, as is -also the fronto-nasal region, the nasals (perhaps only in the male) -bearing a pair of blunt bony outgrowths. Between these two elevated -regions the skull is much depressed. The cranial cavity is very small, -the orbit confluent with the temporal fossa, and the zygomatic arch -massive. - -In _Tapirus_ the orbit and temporal fossa are confluent. The nasals -are small, wide behind and pointed in front, and are supported by the -mesethmoid; the anterior nares are exceedingly large and their lateral -boundaries are entirely formed by the maxillae. The postglenoid and -post-tympanic processes of the squamosal are large. The periotic is -not fused to the squamosal or to the small tympanic. The mandible is -large and has the angle much developed and somewhat inflected. - -_Palaeotherium_, which lived in early Tertiary times, has a skull much -like that of the Tapir, especially as regards the nasal bones. - -In the Horse and its allies (Equidae) the facial portion of the skull -is very large as compared with the cranial portion, the nasals and -nasal cavities being specially large. In the living species of the -genus _Equus_ there is no fossa between the maxillae and lachrymal, but -it occurs in some extinct species. The lachrymal and jugal form a -considerable part of the side of the face; and the orbit though small -is complete and prominent. The postorbital bar is formed by a strong -outgrowth from the frontal, which unites with a forward extension of -the squamosal. The squamosal may extend forwards and form part of the -wall of the orbit, a very unusual feature, as in most mammals the -squamosal stops before the postorbital bar. The palate is narrow and -excavated behind as in _Rhinoceros_; the palatines take very little -part in its formation. The glenoid surface for the articulation of the -mandible is very wide. The squamosal gives rise to small postglenoid -and post-tympanic processes, and the exoccipital to a large -paroccipital process. The tympanic and periotic are ankylosed -together, but not to any other bones. - -In the SUBUNGULATA, the lachrymal and jugal do not form any -considerable part of the side of the face, and the maxillae commonly -takes part in the formation of the zygomatic arch. - -_TOXODONTIA._ The skull in the Toxodontia shows several Artiodactyloid -features, while the manus and pes are of a more Perissodactyloid type. -The Artiodactyloid features are (1) the absence of an alisphenoid -canal, (2) the fact that the palate is not excavated behind, and that -the palatines form a considerable part of it, and (3) the fusion of -the tympanic to the squamosal and exoccipital, forming the floor of an -upwardly directed auditory meatus. The frontal has a fairly well -developed postorbital process, but the orbit is confluent with the -temporal fossa. The premaxillae is well developed, as is the -paroccipital process of the exoccipital, especially in _Typotherium_. -The mandible has a rounded angle and a coronoid process of moderate -size. In _Typotherium_ the ascending portion is very massive. - -_CONDYLARTHRA._ As far as is known the skull of these generalised -Ungulates is depressed, and is frequently marked by a strong sagittal -crest. The cranial cavity is small, the cerebral fossa in _Phenacodus_ -being exceptionally small. The orbit is completely confluent with the -temporal fossa. - -_HYRACOIDEA._ The skull of _Procavia_ resembles that of -Perissodactyles more than that of any other Ungulates, but differs -strongly in the comparatively small size of its facial portion. The -posterior portion of the cranium is rather high, the occipital plane -being nearly vertical. There is a small interparietal. The nasals are -wide behind, and the zygomatic arch is strongly developed, its most -anterior part being formed by the maxillae. The jugal and parietal give -rise to postorbital processes which sometimes meet, but as a rule the -orbit is confluent with the temporal fossa; it is very uncommon for -the parietal to give rise to a postorbital process, and even in -_Procavia_ the frontal often forms part of the process. The -alisphenoid canal, and postglenoid and paroccipital processes are well -developed. The tympanic bulla is large and the periotic and tympanic -are fused together, but not as a rule to the squamosal. The ascending -portion of the mandible is very high and broad, the angle rounded and -the coronoid process moderate in size. The hyoid is singular, there is -a large flat basi-hyal prolonged laterally into two broad flattened -thyro-hyals. Articulating with its anterior end are two large -triangular cerato-hyals, which are drawn out into two processes -meeting in the middle line. - -_AMBLYPODA._ In the Uintatheriidae (Dinocerata) the skull has a very -remarkable character, being long and narrow and drawn out into three -pairs of rounded protuberances, a small pair on the nasals, a larger -pair on the maxillae in front of the orbits, and the largest pair on -the parietals. The cranial cavity, and especially the cerebral fossa, -is extraordinarily small. The orbit is not divided behind from the -temporal fossa. The mandible has a prominent angle, and a long curved -coronoid process; its symphysial portion bears a curious flattened -outgrowth to protect the great upper canines. - -In _Coryphodon_ the skull is of a more normal character, being without -the conspicuous protuberances. The cranial cavity though very small is -not so small as in _Uintatherium_. - -[Illustration FIG. 96. SKULL OF A YOUNG INDIAN ELEPHANT (_Elephas -indicus_), SEEN FROM THE RIGHT SIDE, THE ROOTS OF THE TEETH HAVE BEEN -EXPOSED. × 1/8. (Camb. Mus.) - - 1. exoccipital. - 2. parietal. - 3. frontal. - 4. squamosal. - 5. jugal. - 6. premaxillae. - 7. maxillae. - 9. supra-occipital. - 13. basi-occipital. - 14. postorbital process of the frontal. - 15. lachrymal. - 16. pterygoid process of the alisphenoid. - _i_ 1. incisor. - _mm_ 3., _mm_ 4. third and fourth milk molars. - _m_ 1. first molar.] - -_PROBOSCIDEA._ The character of the skull in the young elephant -differs much from that in the old animal. In very young individuals -the skull is of a normal character, and the cranial cavity is -distinctly large in proportion to the bulk of the skull. But as the -animal gets older, while its brain does not grow much, the size of its -trunk and especially of its tusks increases greatly; and consequently -the skull wall is required to be of very great superficial extent in -order to afford space for the attachment of the muscles necessary for -the support of these heavy weights. This increase in superficial -extent is brought about without much increase in weight of bone by the -development of an enormous number of air cells in nearly all the bones -of the skull; sometimes, as in the case of the frontal, separating the -inner wall of the bone from the outer, by as much as a foot. This -development of air cells is accompanied by the obliteration of the -sutures between the various bones. The most noticeable point with -regard to the cranial cavity is the comparatively large size of the -olfactory fossa. The supra-occipital (figs. 96 and 97, 9) is -large--exceedingly large in the adult skull; the parietals (figs. 96 -and 97, 2) are also very large. The frontals send out small -postorbital processes, but these do not meet processes from the small -jugal, which forms only the middle part of the slender zygomatic -arch, the anterior part being formed by the maxillae. The lachrymal -(fig. 96, 15) is small and lies almost entirely inside the orbit. The -anterior narial aperture (fig. 97, 8) is wide and directed upwards, -opening high on the anterior surface of the skull. It is bounded above -by the short thick nasals and below by the premaxillae. The narial -passage is freely open, maxillo-turbinals not being developed. The -palatine is well developed, the pterygoid is small and early fuses -with the pterygoid process of the alisphenoid. The tympanic is united -with the periotic but not with the squamosal, and forms a large -auditory bulla. There are no paroccipital or postglenoid processes. -The exoccipital is not perforated by the condylar foramen,--a very -exceptional condition. - -[Illustration FIG. 97. LONGITUDINAL SECTION TAKEN RATHER TO THE RIGHT -OF THE MIDDLE LINE OF THE SKULL OF A YOUNG INDIAN ELEPHANT (_E. -Indicus_) × 1/8. (Camb. Mus.) - - 8. anterior nares. - 10. periotic. - 11. palatine. - 12. pterygoid. - 17. nasal. - -Other numbers as in Fig. 96.] - -The mandible has a high ascending portion, is rounded off below and -has no angle. The symphysial portion is long, narrow, and spout-like, -and the coronoid process is small. The thyro-hyals are ankylosed with -the basi-hyal, which is connected with the large forked stylo-hyals by -ligament only. - -RODENTIA. The cranial cavity is depressed, elongated, and rather -small, and the cerebral fossa lies entirely in front of the cerebellar -fossa. The occipital plane is vertical or directed somewhat backwards, -and the supra-occipital does not form much of the roof of the cranium. -The paroccipital processes of the exoccipitals are generally of -moderate size; in the Capybara (_Hydrochaerus_), however, they are -very long, and are laterally compressed and directed forwards. The -parietals are small, and often become completely fused together; there -is sometimes a small interparietal. The frontals in most genera have -no trace of a postorbital process; in Squirrels, Marmots and Hares, -however, one occurs, but in no case does it meet a corresponding -process from the zygomatic arch, so the orbit and temporal fossa are -completely confluent. In Hares the postorbital process of the frontal -is much flattened, and has an irregular margin. The temporal fossa is -always small, and in _Lophiomys_ is arched over by plates arising -respectively from the parietal and jugal; a secondary roof is thus -partially developed in a manner unique among mammals, but carried to a -great extent in many Chelonia. The nasal bones and cavities are large, -attaining their maximum development in the Porcupines (fig. 98, 1). -The premaxillae is always very large, and sends back a long process -which meets the frontal. The vomer is occasionally found persisting in -two separate halves, a feature recalling the arrangement in -Sauropsids. In many Rodents there is an enormous vacuity at the base -of the maxillary portion of the zygomatic arch. It is sometimes as -large as the orbit, and attains its maximum development in the -Capybara and other Hystricomorpha; in the Marmots, Beavers, and -Squirrels (Sciuromorpha), and in the Hares it is undeveloped. In -_Lagostomus_ the maxillae bears an upwardly directed plate of bone, -shutting off from this vacuity a space which is the true infra-orbital -foramen. - -[Illustration FIG. 98. HALF FRONT VIEW OF THE SKULL OF A PORCUPINE -(_Hystrix cristata_) × 1/2. (Camb. Mus.) - - 1. nasal. - 2. maxillo-turbinals. - 3. infra-orbital vacuity. - 4. maxillae. - 5. premaxillae. - 6. jugal. - _i_ 1. upper incisor.] - -The zygomatic arch is always complete, and in many cases the jugal -extends back to form part at least of the glenoid surface for -articulation with the mandible. In _Coelogenys_ the jugal and -maxillary portion of the zygomatic arch is greatly expanded and -roughened, and the maxillary portion encloses a large cavity. The -palate in Rodents is narrow, and the space between the incisor and -molar teeth passes imperceptibly into the sides of the face. The -anterior palatine foramina form long, rather narrow slits in this -region. The bony palate between the grinding teeth is sometimes as in -the Hares very short, sometimes as in the Capybara very long. The -maxillae extends back beneath the orbit to unite with the squamosal. -The pterygoid is always small, but sometimes has a well-marked hamular -process which in _Hystrix_, _Lagostomus_, and some other genera unites -with the tympanic bulla. The periotic is large, and fused with the -tympanic, which forms a prominent bulla, and is generally drawn out -into a tubular meatus. The bulla attains its maximum development in -_Chinchilla_ and _Dipus_. - -The mandible is narrow and rounded in front, the two halves meeting in -a long symphysis. The angle is generally drawn out into a long -backwardly-projecting process, which is often pointed and directed -upwards. In the Hares the angle is rounded. The coronoid process is -never large. - -There are a number of points in which the skull of the Duplicidentata -(Hares and Rabbits) differs from that of other Rodents. (_a_) The -sutures between the basi-occipital and basisphenoid, and between the -basisphenoid and presphenoid remain open throughout life. (_b_) Much -of the maxillae forming the side of the face in front of the orbit is -fenestrated. (_c_) The optic foramina are united to form a single -hole, much as in birds. (_d_) The coronoid process is slightly -differentiated from the ascending portion of the mandible. The first -two of these points have been thought to indicate degradation of the -hares and rabbits as compared with higher mammals. - -CARNIVORA[167]. It is characteristic of the skull in Carnivora that -the glenoid fossa is deep, and the postglenoid process (fig. 75, 23) -well developed. The condyle of the mandible is much elongated -transversely. The orbit and temporal fossa in the great majority of -forms communicate freely, the postorbital bar being incomplete. - -_CARNIVORA VERA._ The axis of the facial portion of the skull is a -direct continuation of that of the cranial portion. The cranial -cavity though rather depressed is large, and generally long, though in -Cats it is comparatively short and wide. The occipital plane is nearly -vertical, and the exoccipitals are developed into fairly prominent -paroccipital processes. The interparietal is commonly distinct, and -the parietals unite in a long sagittal suture, which is often -developed into a crest. The nasals (fig. 73, 4) are well developed, -especially in Cats, and the nasal processes of the premaxillae do not -nearly reach the frontals. A considerable part of the palate is formed -by the palatine, and the maxillary portion is pierced by rather long -anterior palatine foramina. The pterygoid has a hamular process. The -zygomatic arch is strong, especially in Cats. Postorbital processes -are developed on the frontal (fig. 73, 10) and jugal, but never form a -complete postorbital bar. A carotid canal is well seen in the Ursidae, -and to a less extent in the Felidae; in the Canidae there is an -alisphenoid canal (fig. 75, 21). - -The auditory bulla differs a good deal in the different groups. In the -Bears (Ursidae) it is not much inflated, and is most prominent along -its inner border; it is not closely connected with the paroccipital -process. In the Cats it is very prominent, and its cavity is almost -divided by a septum into two parts, the inner of which contains the -auditory ossicles. The paroccipital process is closely applied to the -bulla. In the Dogs the bulla is intermediate in character between that -of the Cats and that of the Bears; it is partially divided by a -septum, and is moderately expanded. - -The mandible is well developed with a prominent angle (fig. 72, 26), -and a large coronoid process. The hyoid consists of a broad basi-hyal, -a long many-jointed anterior cornu and short thyro-hyals (fig. 72, -33). - -The skull in the _CREODONTA_ is in most respects allied to that of the -Canidae, but presents some ursine affinities. The tympanic bulla is -fairly prominent, but has no well-developed septum. The cranial cavity -is very small and narrow, the zygomatic arch standing away from it. -The temporal fossa is of great size. - -In the _PINNIPEDIA_ the cranial cavity is large and rounded. The skull -is much compressed in the interorbital region, and in correlation with -this compression the ethmo-turbinals are little developed, while the -maxillo-turbinals are large. The orbit is large, and the temporal -fossa smaller than in the Carnivora vera. In the Walrus (_Trichechus_) -the anterior part of the face is distorted by the development of the -huge canines. The Otariidae have an alisphenoid canal. The tympanic -bulla is small in _Otaria_, large in the Phocidae, and flattened in -the Walrus. The hyoid is similar to that in Carnivora vera. - -INSECTIVORA. The skull varies much in the different members of the -order Insectivora, but the following points of agreement are found. -The cranial cavity is of small size, and is never much elevated. The -facial part of the skull is generally considerably elongated, and the -nasals and premaxillae are well developed. The zygomatic arch is -usually slender or incomplete, and the coronoid process and angle of -the mandible are commonly prominent. - -In some Insectivora, such as _Galeopithecus_, _Tupaia_, and -_Macroscelides_, the skull shows a higher type of structure than is -met with in most members of the order. In these genera the cranial -cavity is comparatively large, and the occipital plane is nearly -vertical. The zygomatic arch is fairly strong, and the frontal and -jugal give rise to postorbital processes which nearly or quite -(_Tupaia_) meet. The tympanic bulla is well developed, and produced -into a tubular auditory meatus, this being specially well marked in -_Macroscelides_. - -In the other Insectivora the cranial cavity is of smaller comparative -size, and the orbit and temporal fossa are completely confluent, often -without any trace of a postorbital bar. The occipital plane commonly -slopes forwards. In the Hedgehogs (Erinaceidae) and Centetidae the -tympanic is very slightly developed, forming a small ring. The -zygomatic arch of Hedgehogs and _Gymnura_ is very slender, the jugal -being but little developed and the squamosal and maxillae meeting one -another; in the Centetidae the jugal is absent and the arch is -incomplete. - -The Moles (Talpidae) have an elongated, depressed and rounded skull -with a very slender zygomatic arch formed by the squamosal and -maxillae. The nasals are fused together, and the mesethmoid is ossified -very far forwards. In the Shrews (Soricidae) there is no zygomatic -arch; the tympanic is ring-like, and the angle of the mandible is very -prominent. The hyoid has a transversely extended basi-hyal, a long -anterior cornu with three ossifications, and thyro-hyals which are -sometimes fused to the basi-hyal. - -CHIROPTERA. In the frugivorous Flying Foxes (Pteropidae) the skull is -elongated, and the cranial cavity is large and arched, though -considerably contracted in front. There are commonly strong sagittal -and supra-orbital crests. The parietals take a great part in the -formation of the walls of the cranial cavity, the supra-occipital and -frontals being small. The frontal is drawn out into a long postorbital -process, but the zygomatic arch, which is slender, and formed mainly -by the squamosal and maxillae, gives rise to only a small postorbital -process, so that the orbit and temporal fossa are confluent. There is -no alisphenoid canal, and the tympanics are very slightly connected -with the rest of the skull. The mandible has a large coronoid process, -a rounded angle, and a transversely expanded condyle. - -In Insectivorous Bats the skull is generally shorter and broader than -in the Pteropidae. The cranial cavity is large and rounded, and has -thin smooth walls. The zygomatic arch is slender, and postorbital -processes are not generally well developed. The premaxillae is -generally small, sometimes absent. The tympanics are ring-like and are -not connected with the surrounding bones. The angle of the mandible is -distinct. The hyoid in most respects resembles that of the -Insectivora. - -PRIMATES. The characters of the skull differ greatly in the two -suborders of Primates, the Anthropoidea and the Lemuroidea. - -In the _LEMUROIDEA_ the general relative proportions of the cranium -and face are much as in most lower mammals, and the occipital plane -forms nearly a right angle with the basicranial axis. The postorbital -processes of the frontals are commonly continued as a pair of ridges -crossing the roof of the cranium and meeting the occipital crest. -Though the postorbital bar is complete, the orbit and temporal fossa -communicate freely below it. The lachrymal canal opens outside the -orbit, and the lachrymal forms a considerable part of the side of the -face. The tympanic is developed into a large bulla. The hyoid -apparatus much resembles that of the Dog. - -In the _ANTHROPOIDEA_ the skull differs greatly from that in the -Lemuroidea. The cranial portion of the skull is very large as compared -with the facial portion, though the comparative development varies, -some monkeys, such as the baboons (Cynocephali) having the facial -portion relatively large. The comparative size of the jaws does not -vary inversely with the general development of the animal, some of the -Cercopithecidae having comparatively larger jaws than some of the -Cebidae. The great size of the cranial part of the skull is mainly due -to the immense development of the cerebral fossa, which commonly -completely overlaps the olfactory fossa in front, and the cerebellar -fossa behind. This development also has the effect of making the -ethmoidal and occipital planes lie, not at right angles to the -basicranial axis, but almost in the same straight line with it. This -is, however, not always the case, as the Howling Monkey (_Mycetes_) -and also some of the very highest monkeys, the Gibbons (_Hylobates_), -have the occipital plane nearly vertical to the basicranial axis. In -adult Man the basi-occipital, exoccipitals and supra-occipital -coalesce, forming the so-called occipital bone; while the -basisphenoid, presphenoid, alisphenoids, orbitosphenoids and -pterygoids form the sphenoid bone. The roof of the skull is partly -formed by the large supra-occipital and frontals, but mainly by the -parietals (fig. 99, 1), which in Man are of enormous extent. - -[Illustration FIG. 99. HALF FRONT VIEW OF THE SKULLS, _A_ OF AN OLD, -_B_ OF A YOUNG GORILLA (_Gorilla savagei_) × 1/4. (Camb. Mus.) - - 1. parietal. - 2. sagittal crest. - 3. frontal. - 4. supra-orbital ridge. - 5. squamosal. - 6. maxillae. - 7. external auditory meatus.] - -In Man and in most monkeys, at any rate when young (fig. 99, B), the -roof of the skull is smooth and rounded, but in many forms, such as -the Baboons, in the adult the supra-orbital and occipital ridges are -much developed. In the Gorilla this is also the case with the sagittal -crest (fig. 99, A, 2). The bones of the upper surface of the cranium -interlock with wavy outlines. The nasals vary much in length, being -much shorter in man than in most monkeys; they commonly become early -fused together, as do also the frontals. The vomer is well developed, -and the ethmo-turbinal always forms part of the boundary of the orbit. -There are frequently, as in many Lemuroidea, a pair of more or less -well-marked ridges, crossing the roof of the skull from the -postorbital processes of the frontals to the occipital crest. The -orbit is completely encircled by bone, and the alisphenoid assists the -jugal and frontal in shutting it off from the temporal fossa, leaving -however a communication between the two as the sphenomaxillary -fissure. In most cases the frontals meet one another in the middle -line between the mesethmoid and orbitosphenoid, but in Man, Simia, and -some Cebidae this does not take place. In nearly all Cebidae the -parietal and jugal meet one another, separating the frontal and -alisphenoid on the skull wall; in Man and all Old World monkeys, on -the other hand, the alisphenoid and frontal meet and separate the -jugal and parietal. The premaxillae nearly always send back processes -which meet the nasals. The palate is rather short and both the -palatine and the premaxillae take a considerable part in its formation. -The pterygoid plate of the alisphenoid is decidedly large, and there -is no alisphenoid canal. There is never any great development either -of the paroccipital process of the exoccipital, or of the postglenoid -process of the squamosal. The periotic and tympanic are always fused -together; in Cebidae they form a small bulla, but a bulla is not -developed in any Old World forms. The periotic is large, especially -the mastoid portion, which forms a distinct portion of the skull wall -between the squamosal and exoccipital. In Man and still more in Old -World monkeys, the external auditory meatus is drawn out into a -definite tube, whose lower wall is formed by the tympanic; in the -Cebidae the tympanic is ring-like. The perforation of the periotic by -the carotid canal is always conspicuous. - -The mandible is rather short and broad, and the angle formed by the -meeting of the two rami is more obtuse than in most mammals. The -coronoid process is fairly well developed, and the angle is more or -less rounded. In most Primates the condyle is considerably widened, -but this is not the case in Man. In _Mycetes_ the mandible is very -large, its ascending portions being specially developed. The hyoid of -Primates is remarkable for the large expanded basi-hyal, which is -generally concave above and convex below. The anterior cornu is never -well ossified, but the thyro-hyal is always strong. In _Mycetes_ the -basi-hyal is enormously large, forming a somewhat globular thin-walled -capsule. - - -AUDITORY OSSICLES. - -[Illustration FIG. 100. MALLEUS, STAPES AND INCUS OF _A._ MAN. _B._ -DOG. _C._ RABBIT. (After DORAN) x 1. - - 1. head of malleus. - 2. canal of stapes. - 3. incus. - 4. processus longus (or gracilis). - 5. manubrium of malleus. - 6. processus brevis. - 7. lamella.] - -There are in mammals four auditory ossicles forming a chain extending -from the fenestra ovalis to the tympanic membrane. Three of these, the -=malleus=, =incus= and =stapes=, are always distinct, while the -fourth, the =lenticular=, is smaller than the others and is sometimes -not distinct. The names are derived from human anatomy and indicate in -the case of the first three a more or less fanciful resemblance -respectively to a hammer, an anvil and a stirrup. The ossicles are -homologous as a whole to the hyomandibular of fishes and to the -columellar chain of Sauropsids and Amphibians. The malleus is -homologous to the extra-columella of Crocodiles and the stapes to the -columella. The =malleus= when typically developed consists of a -rounded _head_ (fig. 100, 1) which bears a surface articulating with -the incus, and a short _neck_ continued into a process, the -_manubrium_ (fig. 100, 5), which comes into relation with the tympanic -membrane. From the junction of the neck and manubrium two processes -are given off, a _processus longus_ or _gracilis_ (fig. 100, 4), which -in the embryo is continuous with Meckel's cartilage, and a _processus -brevis_ (fig. 100, 6). The =incus= generally consists of a more or -less anvil-shaped portion which articulates with the malleus, and of a -process which is connected with the stapes by the small =lenticular=. -The =stapes= is generally stirrup shaped, consisting of a basal -portion from which arise two _crura_ separated by a space the canal -through which a branch of the pharyngeal artery runs The lenticular is -frequently cartilaginous and sometimes is not developed at all. - -The above is the arrangement of the auditory ossicles met with in the -higher Mammalia, but in the lower Mammalia the characters approach -more nearly to those met with in Sauropsids. - -In MONOTREMES the ossicles, though distinctly mammalian in character, -show a very low type of development. The incus is articulated, or -often fused, with an outgrowth from the head of the malleus. The -stapes is very much like a reptilian columella, having a single crus -with no perforation. - -In MARSUPIALS the ossicles are of a low type, but not so low as the -rest of the skeleton might have led one to expect, and all or almost -all the points showing a low grade of development may be paralleled -among the Monodelphia. The lowest Marsupials as regards the ossicles -are the Peramelidae, whose ossicles are of a frail papery consistence. -The Didelphyidae on the other hand have the most highly developed -ossicles, the malleus much resembling that of many Insectivores, and -the stapes having two definite crura separated by a canal. - -In EDENTATES the character of the ossicles varies much. In Sloths the -stapes approaches that of Sauropsids in its narrowness and the slight -trace of a canal; this character is however still more marked in -_Manis_, whose stapes is as Sauropsidan as that of Monotremes, and -consists of a nearly circular basal plate bearing a column which does -not show any sign of division into crura. The stapes of other -Edentates, such as ant-eaters, aard varks, and most armadillos, is of -a high type and has well-developed crura. _Priodon_ has a lower type -of stapes than _Dasypus_ and _Tatusia_. - -The ossicles of the SIRENIA differ widely from those of all other -mammals in their great density and clumsy form. - -In CETACEA the ossicles are solid, though not so solid as in Sirenia, -and their details vary much. The malleus is always firmly fused to the -tympanic by means of the processus longus, and the manubrium is very -little if at all developed. The incus has the stapedial end greatly -developed, and the stapes has very thick crura with hardly any canal. -The ossicles of the Mystacoceti are apparently less specialised than -are those of the Odontoceti. - -The auditory ossicles of the UNGULATA do not present any characters -common to all the members of the group. - -Among Ruminants they are chiefly remarkable for the development of a -broad lamellar expansion between the head and the processus longus of -the malleus. In some cases the malleus of the foetus differs -strikingly from that of the adult. Among Perissodactyla the Rhinoceros -and Tapir have the malleus of a low type, recalling those of -Marsupials; while in the Horse the head is well developed, and the -malleus is of a higher type. - -The ossicles of _Procavia_, which recall those of the Equidae, are -chiefly remarkable for the small size of the body of the incus. In -Elephants the ossicles are large and massive. - -In the RODENTIA (fig. 100, C) the malleus is generally characterised -by a very broad manubrium. In many genera such as _Bathyergus_, and -most of the Hystricomorpha such as _Hystrix_, _Chinchilla_ and -_Dasyprocta_, the malleus and incus are ankylosed together. - -CARNIVORA. In Carnivora vera the most striking feature of the malleus -is the occurrence of a broad lamellar expansion between the head and -neck and the processus longus. This however does not occur in some -Viverridae. In the Carnivora vera the incus and stapes are small as -compared with the malleus, but in the Pinnipedia they are large. In -the Pinnipedia the auditory ossicles have a very dense consistence, -and except in the Otariidae are very large. The stapes frequently has -no canal, or only a very small one. - -In INSECTIVORA the characters of the auditory ossicles are very -diverse. Many forms such as shrews, moles, hedgehogs, and the -Centetidae have a low type of malleus resembling that of Edentates. -_Chrysochloris_ has very extraordinary auditory ossicles. The head of -the malleus is drawn out into a great club-shaped process, the incus -is long and narrow, and differs much from the ordinary type. - -In CHIROPTERA the ossicles and especially the malleus much resemble -those of shrews. The stapes is always normal in character, never -becoming at all columelliform. - -PRIMATES. In Man and the Anthropoid Apes the malleus has a rounded -head, a short neck, and the manubrium, a processus longus and a -processus brevis. The incus consists of an anvil-shaped portion from -which arises a long tapering process. The stapes has diverging crura -and consequently a wide canal. The crura in other monkeys do not -diverge so much as in man and anthropoid apes. The New World monkeys -have no neck to the malleus. - - -THE STERNUM[168]. - -In MONOTREMES and most MARSUPIALS the sternum does not present any -characters of special importance. The presternum is strongly keeled in -_Notoryctes_. - -The sternum in EDENTATES is very variable: in the Sloths it is very -long, the mesosternum of _Choloepus_ having twelve segments. In the -ant-eaters and armadillos the presternum is broad and sometimes as in -_Priodon_ strongly keeled. In _Manis macrura_ the xiphisternum is -drawn out into a pair of cartilaginous processes about nine inches -long. - -In the SIRENIA the sternum is simple and elongated, and of fairly -equal width throughout, in the adult it shows no sign of segmentation. -Its origin from the union of two lateral portions can be well seen in -_Manatus_. - -Two distinct types of sternum are met with in the CETACEA. In the -Odontoceti the sternum consists of a broad presternum followed by -three or four mesosternal segments, but with no xiphisternum. -Indications of the original median fissure can be traced, and are very -evident in _Hyperoödon_. In the Mystacoceti, on the other hand, the -sternum consists simply of a broad flattened presternum which is -sometimes more or less heart-shaped, sometimes cross-shaped. Only a -single pair of ribs are united to it. - -The sternum in UNGULATA is generally long and narrow and formed of six -or generally seven segments. The presternum is as a rule small and -compressed, often much keeled, especially in the horse and tapir. The -segments of the mesosternum gradually widen as followed back and the -xiphisternum is often terminated by a cartilaginous plate. - -In the RODENTIA the sternum is long and narrow and generally has a -large presternum, and a xiphisternum terminated by a broad -cartilaginous plate. - -In the CARNIVORA, too, the sternum (fig. 76) is long and narrow and -formed of eight or nine pieces, all of nearly the same size. The -xiphisternum generally ends in an expanded plate of cartilage. - -In INSECTIVORA the sternum is well developed but variable. The -presternum is commonly large and is sometimes as in the Hedgehog -(_Erinaceus_) bilobed in front, sometimes as in the Shrew (_Sorex_) -trilobed. It is especially large in the Mole (_Talpa_) and is expanded -laterally and keeled below. - -In the CHIROPTERA the presternum is strongly keeled and so is -sometimes the mesosternum. - -Among PRIMATES, in Man and the Anthropoid Apes the sternum is rather -broad and flattened; the mesosternum consists of four segments which -are commonly fused together and the xiphisternum is imperfectly -ossified. - - -THE RIBS. - -Free ribs are borne as a rule only by the thoracic vertebrae; ribs may -be found in other regions, especially the cervical and sacral, but -these are almost always ankylosed to the vertebrae. As a general rule -the first thoracic rib joins the presternum, while the succeeding ones -are attached between the several segments of the mesosternum. Some of -the posterior ribs frequently do not reach the sternum; they may then -be attached by fibrous tissue to the ribs in front, or may end freely -(_floating ribs_). There are generally thirteen pairs of ribs, and in -no case do they have uncinate processes. - -In MONOTREMES (fig. 102, B) each rib is divided not into two but into -three parts, an intermediate portion being interposed between the -vertebral and sternal parts. The sternal ribs are well ossified, and -some are very broad and flat. The intermediate portions are -unossified, those of the anterior ribs are short and narrow, but they -become longer and wider further back. - -In MARSUPIALS there are almost always thirteen pairs of ribs, whose -sternal portions are very imperfectly ossified. _Notoryctes_ has -fourteen pairs of ribs, eight of which are floating: the first rib is -very stout, and is abruptly bent on itself to join the sternum. It has -no distinct sternal portion. All the other ribs are slender. - -Of the EDENTATES the Sloths have very numerous ribs; twenty-four pairs -occur in _Choloepus_, and half of these reach the sternum. In the -Armadillos there are only ten or twelve pairs of ribs, but the sternal -portions are very strongly ossified. The first rib is remarkably broad -and flat, and is not divisible into vertebral and sternal portions. - -In the SIRENIA there are a very large number of ribs noticeable for -their great thickness and solidity, but not more than three are -attached to the sternum. - -CETACEA. In the Whalebone whales the ribs are remarkable for their -very loose connection both with the vertebral column and with the -sternum. The capitula are scarcely developed, and the attachment of -the tubercula to the transverse processes is loose. The first rib is -the only one connected with the sternum. In the Toothed whales the -anterior ribs have capitula articulating with the centra, as well as -tubercula articulating with the transverse processes; in the posterior -ones, however, only the tubercula remain. Seven pairs of well-ossified -sternal ribs generally meet the sternum. In the Physeteridae most of -the ribs are connected to the vertebrae by both capitula and -tubercula. - -In the UNGULATA the ribs are generally broad and flattened, and this -is especially the case in the genera _Bos_ and _Bubalus_ (fig. 101, -6). The anterior ribs are short and nearly straight, and sternal ribs -are well developed. The Artiodactyla have twelve to fifteen pairs of -ribs, the Perissodactyla eighteen or nineteen, and _Procavia_ twenty -to twenty-two. The Elephant has nineteen to twenty-one pairs, seven of -which may be floating ribs. - -[Illustration FIG. 101. SKELETON OF A CAPE BUFFALO (_Bubalus caffer_). -The left scapula is omitted for the sake of clearness × 1/17. (Brit. -Mus.) - - 1. premaxillae. - 2. nasal. - 3. orbit. - 4. neural spine of first thoracic vertebra. - 5. scapula. - 6. rib. - 7. femur. - 8. patella. - 9. tibia. - 10. metatarsals. - 11. radius. - 12. metacarpals.] - -In the RODENTIA there are generally thirteen pairs of ribs, which do -not present any marked peculiarities. - -The CARNIVORA have thirteen to fifteen pairs of ribs, whose vertebral -portions are slender, nearly straight and subcylindrical, while their -sternal portions are long and imperfectly ossified (fig. 76, 5). There -is nothing that calls for special remark about the ribs, in either -INSECTIVORA or CHIROPTERA. - -PRIMATES. In Man and the Orang (_Simia_) there are generally twelve -pairs of ribs; in the Gorilla and Chimpanzee (_Anthropopithecus_), and -Gibbons (_Hylobates_), there are thirteen, in the Cebidae twelve to -fifteen, and in the Lemuroidea twelve to seventeen pairs. The first -vertebral rib is shorter than the others, and the sternal ribs -generally remain cartilaginous throughout life, though in man the -first may ossify. - - -APPENDICULAR SKELETON. - - -THE PECTORAL GIRDLE. - -By far the most primitive type of the pectoral or shoulder girdle is -found in the MONOTREMATA. The scapula (fig. 102, A, 1) is long and -recurved, and has only two surfaces, one corresponding to the -prescapular[1] fossa, the other to the postscapular[1] and -subscapular[169] fossae. The coracoid is a short bone attached above -to the scapula and below to the presternum; it forms a large part of -the glenoid cavity. In front of the coracoid there is a fairly large -flattened epicoracoid (fig. 102, 6); there is also a large =T=-shaped -interclavicle (fig. 102, 4), which is expanded behind and rests on the -presternum. The clavicles rest on and are firmly united to the -anterior border of the interclavicle. This shoulder girdle differs -greatly from that of any other mammals, and recalls that of some -Lacertilia. - -[Illustration FIG. 102. _A_, SIDE VIEW, _B_, DORSAL VIEW OF THE -SHOULDER GIRDLE AND PART OR THE STERNUM OF THE SPINY ANTEATER -(_Echidna aculeata_) × 1. (After PARKER.) - - 1. scapula. - 2. suprascapula. - 3. clavicle. - 4. interclavicle. - 5. coracoid. - 6. epicoracoid. - 7. glenoid cavity. - 8. presternum. - 9. second sternal rib. - 10. second vertebral rib.] - -In MARSUPIALS, as in all mammals except the Monotremes, the shoulder -girdle is much reduced; there are no epicoracoids and interclavicle, -and the coracoid forms simply a small process on the scapula, -ossifying from a centre separate from that giving rise to the rest of -the bone. The scapula has a long acromion, and a clavicle is always -present except in _Perameles_. Unossified remains of the precoracoids -are found at either end of the clavicle. The scapula of _Notoryctes_ -has a very high overhanging spine, and there is a second strong ridge -running along the proximal part of the glenoid border. - -The shoulder girdle of the EDENTATA shows some very curious -variations. In _Orycteropus_ the scapula is of very normal form and -the clavicle is well developed. In the Pangolins and Anteaters the -scapula is very broad and rounded; there is no clavicle in the -Pangolins, and generally only a vestigial one in Anteaters. In -Armadillos, Sloths, and Megatheriidae, the acromion is very long and -the clavicle is well developed. In the Sloths, _Megatherium_, and -_Myrmecophaga_, a connection is formed between the coracoid, which is -unusually large, and the coracoid border of the scapula, converting -the coraco-scapula notch into a foramen. In _Bradypus_ the clavicle is -very small, and is attached to the coracoid, which sometimes forms a -distinct bone[170]. - -In the SIRENIA the scapula is somewhat narrow and curved backwards: -the spine, acromion, and coracoid process are moderately developed, -and there is no clavicle. - -CETACEA. In nearly all the Odontoceti the scapula is broad and -somewhat fan-shaped; the prescapular fossa is much reduced, and the -acromion and coracoid process form flattened processes, extending -forwards nearly parallel to one another. Some of the Mystacoceti, such -as _Balaenoptera_, have a broad, fan-shaped scapula, with a long -acromion and coracoid process, extending parallel to one another. -Others, such as _Balaena_, have a higher and narrower scapula, with a -smaller coracoid process. - -In UNGULATA the scapula is always high and rather narrow, and neither -acromion nor coracoid process is ever much developed. In no adult -Ungulate except _Typotherium_ is there any trace of a clavicle, but a -vestigial clavicle has been described in early embryos of sheep[171]. - -[Illustration FIG. 103. SKELETON OF A LLAMA (_Auchenia glama_) × 1/18. -(Brit. Mus.) - - 1. hyoid. - 2. atlas vertebra. - 3. seventh cervical vertebra. - 4. scapula. - 5. imperfectly ossified suprascapula. - 6. olecranon process of ulna. - 7. metacarpals. - 8. ilium. - 9. patella. - 10. calcaneum.] - -UNGULATA VERA. In the Ruminantia the suprascapular region (fig. 103, -5) is very imperfectly ossified, and when this is removed the upper -border of the scapula is very straight (fig. 101, 5). The spine is -prominent, and generally has a fairly well-marked acromion. In -_Hippopotamus_ the acromion is fairly prominent, but in the other -Suina, though the spine is prominent, the acromion is not developed. -The Perissodactyla have no acromion, but while the Equidae and -_Hyracotherium_ have the scapula long and slender, with the spine very -slightly developed, the other living Perissodactyla have the spine -prominent and strongly bent back at about the middle of its length. - -SUBUNGULATA. _Typotherium_ (Toxodontia) differs from all other known -Ungulates in having well-developed clavicles; its scapula has a strong -backwardly-projecting process, much like that in _Rhinoceros_. - -_Phenacodus_ (Condylarthra), has a curiously rounded scapula, with the -coracoid and suprascapular borders passing imperceptibly into one -another. The scapula resembles that of a carnivore more than does that -of any existing Ungulate. - -_Procavia_ has a triangular scapula with a prominent spine and no -acromion; there is a large unossified suprascapular region. - -The scapula in the Proboscidea has a large rounded suprascapular -border and a narrow, slightly concave glenoid border. The spine is -large, and has a prominent process projecting backwards from about its -middle. The spine lies towards the front end of the scapula, so that -the postscapular fossa is much larger than the prescapular fossa. - -In RODENTIA the shoulder girdle is of a rather primitive type. The -scapula is generally high and narrow, somewhat as in Ruminantia; it -differs, however, from the Ruminant scapula in having a high acromion, -which is often, as in the Hares and Rabbits, terminated by a long -metacromion. The development of the clavicle varies, and sometimes it -is altogether absent. It is frequently connected by cartilaginous -bands or ligaments (fig. 104, 7 and 9), on the one hand with the -scapula, and on the other with the sternum. These unossified bands are -remains of the precoracoid. Epicoracoidal vestiges of the sternal ends -of the coracoids (fig. 104, 11) are also often present. - -In the CARNIVORA VERA the scapula is large, and generally has rather -rounded borders. The spine and acromion are well developed, and the -prescapular and postscapular fossae are nearly equal in size. The -coracoid is very small, and the clavicle is never completely -developed, being often absent, as in the Bears and most of their -allies. In the Seals (Phocidae) the scapula is elongated and curved -backwards, and has a very concave glenoid border. In the Eared Seals -(Otariidae) the scapula is proportionally much larger and wider, the -prescapular fossa being specially large, and being traversed by a -ridge, which converges to meet the spine. - -[Illustration FIG. 104. DORSAL VIEW OF THE STERNUM AND RIGHT HALF OF -THE SHOULDER-GIRDLE OF _Mus sylvaticus_ × 4. (After PARKER.) - - 1. postscapular fossa. - 2. prescapular fossa. - 3. spine. - 4. suprascapular border unossified. - 5. coracoid process. - 6. acromion. - 7. cartilaginous vestige of precoracoid at scapular end of clavicle. - 8. clavicle. - 9. cartilaginous vestige of precoracoid at sternal end of clavicle. - 10. omosternum. - 11. epicoracoid. - 12. presternum. - 13. first segment of mesosternum. - 14. xiphisternum. - 15. cartilaginous termination of xiphisternum. - 16. 2nd sternal rib. - 17. 1st vertebral rib.] - -In the INSECTIVORA the shoulder girdle is well developed and, as in -Rodents, remains are met with of various parts not generally seen in -mammals. In the Shrews the scapula is long and narrow, and has a -well-marked spine, whose end bifurcates, forming the acromion and -metacromion. The clavicle is long and slender, and is connected with -the sternum and acromion by vestiges of the precoracoid. Considerable -remains of the sternal end of the coracoid are also found. In -_Potamogale_, however, there are no clavicles. In the Mole the -shoulder girdle is greatly developed, and of very remarkable form. The -scapula is high and very narrow, with the spine and acromion very -little developed. The other shoulder girdle element is an irregular -bone, which articulates with the humerus and presternum, and is -connected by ligaments with the scapula. This bone appears to -represent both the coracoid and the clavicle, being formed partly of -cartilage bone, partly of membrane bone. - -In the CHIROPTERA the scapula is large and oval, and has a moderately -high spine and a large acromion. The coracoid process is well -developed and is often forked. The clavicles are also well developed, -and vestiges of the precoracoid and of the sternal end of the coracoid -are often found. - -In PRIMATES the clavicle and coracoid process are always well -developed. In Man and the Gorilla the scapula has a long straight -suprascapular border, a well-developed coracoid process and spine, and -a large curved acromion. Vestiges of the precoracoid occur at each end -of the clavicle. The shape of the scapula varies much in the lower -Primates. - - -THE UPPER ARM AND FORE-ARM. - -In the MONOTREMATA the humerus is short, very broad at each end and -contracted in the middle. The radius and ulna are stout and of nearly -equal size, while the ulna has a greatly expanded olecranon. - -In the MARSUPIALIA the humerus is generally a strong bone, broad at -the distal end and having well marked deltoid and supinator ridges, -which are specially large in _Notoryctes_. An ent-epicondylar or -supracondylar foramen (fig. 105, 5) is almost always present except in -_Notoryctes_. The radius and ulna are always distinct and well -developed, and a certain amount of rotation can take place between -them. The ulna of _Notoryctes_ has an enormous hooked olecranon which -causes the bone to be nearly twice as long as the radius. - -[Illustration FIG. 105. ANTERIOR SURFACE OF THE RIGHT HUMERUS OF A -WOMBAT (_Phascolomys latifrons_). (After OWEN.) - - 1. head. - 2. greater tuberosity. - 3. lesser tuberosity. - 4. deltoid ridge. - 5. ent-epicondylar (supracondylar) foramen. - 6. supinator ridge. - 7. external condyle. - 8. internal condyle. - 9. articular surface for radius. - 10. articular surface for ulna.] - -EDENTATA. The Sloths have long slender arm bones; the humerus is -nearly smooth and has a very large ent-epicondylar foramen in -_Choloepus_, but not in _Bradypus_. The radius and ulna can be -rotated on one another to a considerable extent. The humerus in all -other Edentates is very strong and has the points for the attachment -of muscles much developed, especially in the Armadillos and -Megatheriidae. An ent-epicondylar foramen is found in all living -forms. The radius and ulna are well developed, but are not capable of -much rotation. - -In the SIRENIA the humerus is well developed and of a normal -character. It is expanded at each end and has a prominent internal -condyle, a small olecranon fossa, and no ent-epicondylar foramen. In -the Dugong and _Rhytina_ there is a bicipital groove and the -tuberosities are distinct, but in the Manatee there is no bicipital -groove, and the tuberosities coalesce. The radius and ulna are about -equally developed and ankylosed together at both ends. - -In the CETACEA the arm bones are very short and thick. The humerus has -a globular head, and a distal end terminated by two equal flattened -surfaces to which the radius and ulna are united. There is no -bicipital groove, and the tuberosities coalesce. The radius and ulna -are flat expanded bones fixed parallel to one another, but the ulna -has a definite olecranon. Scarcely any movement can take place between -them and the humerus, and in old animals the three bones are often -ankylosed together. - -In the UNGULATA VERA the humerus is stout and rather short. The great -tuberosity is always large and often overhangs the bicipital groove, -it is especially large in _Titanotherium_ (_Brontops_). There is never -an ent-epicondylar foramen. The radius is always large at both ends, -but the condition of the ulna is very variable. Sometimes, as in -_Tapirus_, _Rhinoceros_, _Macrauchenia_, Suina and Tragulina, the ulna -is well developed, and quite distinct from the radius; but in most -forms, although complete, it is much reduced distally, and is fused to -the radius. Sometimes, as in the Horse and Giraffe, it is reduced to -the olecranon and to a very slender descending process which does not -nearly reach the carpus. In the Tylopoda, though the ulna is complete -and its distal end is often distinct, it has coalesced with the radius -throughout its whole length; the olecranon is generally very large. - -SUBUNGULATA. In the large Condylarthra the humerus has an -ent-epicondylar foramen, and the radius and ulna are stout bones -nearly equal in size. - -In _Procavia_ the humerus is rather long, and has a very prominent -greater tuberosity, and a large supra-trochlear fossa, but no -ent-epicondylar foramen. - -In the Proboscidea the humerus is marked by a greatly developed -supinator ridge, and is very long, longer than the radius and ulna. -The ulna has a remarkable development, having its distal end larger -than that of the radius, it has also a larger articular surface for -the humerus than has the radius. - -In RODENTIA the humerus varies much in its development according to -the animal's mode of life. In the Hares it is long and straight, with -a small distal end, and a slight deltoid ridge. In the Beaver on the -other hand the deltoid and supinator ridges are considerably -developed. There is generally a large supra-trochlear fossa, but no -ent-epicondylar foramen. - -CARNIVORA. In the Carnivora vera the humerus has large tuberosities, a -prominent deltoid ridge and a deep olecranon fossa. The shaft is -generally curved, and an ent-epicondylar foramen is often found, -though not in the Canidae, Hyaenidae, and Ursidae. The radius and ulna -are never united. The radius (fig. 77, B) has a very similar -development throughout its whole length, while the ulna has a large -olecranon (fig. 77, C, 11) and a shaft tapering somewhat towards the -distal end. - -In the Pinnipedia the arm bones are very strongly developed. The -humerus has a very prominent deltoid ridge, and the proximal end of -the ulna and distal end of the radius are much expanded. - -In the INSECTIVORA the arm bones are well developed, and the radius -and ulna, though sometimes united, are generally distinct; as a rule -there is an ent-epicondylar foramen, but this is absent in the -Hedgehog. The Mole has an extraordinary humerus, very short and -curved, and much flattened and expanded at both ends. It articulates -both with the scapula and coraco-clavicle. The ulna has a greatly -developed olecranon. - -In the CHIROPTERA both humerus and radius are exceedingly long and -slender; the ulna is reduced to little more than the proximal end and -is fused to the radius. There is no ent-epicondylar foramen. - -All PRIMATES have the power of pronation and supination of the -fore-arm, by the rotation of the distal end of the radius round that -of the ulna. - -In Man and the Anthropoid Apes the humerus is long and straight, and -has a globular head; neither of the tuberosities, nor the deltoid nor -supinator ridges are much developed. The olecranon fossa is deep and -there is no ent-epicondylar foramen. The radius is curved and has a -narrow proximal, and expanded distal end, the ulna is straighter than -the radius and has the distal end much smaller than the proximal; the -olecranon is not much developed. - -In the lower Primates, although the radius and ulna are always quite -separate, the power of pronation and supination is not nearly so great -as in the higher forms. In most of the Cebidae and Lemurs an -ent-epicondylar foramen occurs. - - -THE MANUS. - -The Manus is divisible into two parts, viz. the carpus or wrist, and -the hand which is composed of the metacarpals and phalanges. The -carpal bones are always modified from their primitive arrangement, -sometimes more, sometimes less. One modification however is always -found in mammals, viz. the union of carpalia, 4 and 5 to form the -_unciform_ bone. Two sesamoid bones are commonly developed, one on -each side of the carpus, the _pisiform_ or one on the ulnar side being -much the larger and more constant: it has been suggested that these -represent respectively vestiges of a prepollex and a post-minimus -digit[172]. - -One or more of the five digits commonly present may be lost, and -sometimes all are lost except the third. The terminal or ungual -phalanges of the digits are commonly specially modified to support -nails, claws, or hoofs. There are as a rule two small sesamoid bones -developed on the ventral or flexor side of the metacarpo-phalangeal -articulations, and sometimes similar bones occur on the dorsal or -extensor side. - -MONOTREMATA. In _Echidna_ the carpus is broad, the scaphoid and lunar -are united and there is no centrale. The pisiform is large and several -other sesamoid bones occur. Each of the five digits is terminated by a -large ungual phalanx. In _Ornithorhynchus_ the manus is more slender, -but the general arrangement is the same as in _Echidna_. - -MARSUPIALIA. The carpus has no centrale and the lunar is generally -small or absent. Five digits are almost always present. In _Choeropus_ -however the only two functional digits are the second and third, which -have very long closely apposed metacarpals; the fourth digit is -vestigial, but has the normal number of phalanges, while the first and -fifth are absent. The manus in _Notoryctes_ is extraordinarily -modified, the scaphoid and all the distal carpalia are apparently -fused, the first, second, and fifth digits are very small, the third -and fourth, though having only one phalanx apiece, bear each an -enormous claw. Lying on and obscuring the ventral surface of the manus -is a large bone, probably a sesamoid. - -Among the EDENTATA there is a great diversity in the structure of the -manus, the centrale is however always wanting, and except in _Manis_ -the scaphoid and lunar are distinct. In the Sloths the manus is very -long, narrow, and curved, and terminated by two or three long hooked -claws, borne by the second and third, or the second, third and fourth -digits. The fifth digit is absent, and the fourth is represented only -by a small metacarpal. In the Anteaters the third digit is greatly -developed and bears a long hooked claw. In _Myrmecophaga_ all five -digits are fairly well though irregularly developed, in _Cycloturus_ -the first, fourth, and fifth, are vestigial. In the Armadillos the -manus is broad, and has strongly developed ungual phalanges. The -digits, though almost always five in number, vary much in their -relative arrangement. In _Dasypus_ they are regular, but are -remarkably irregular in Priodon. The pollex is absent in Glyptodonts -and in _Megatherium._ In _Megatherium_ the fifth digit is clawless -while the second, third, and fourth bear enormous claws. In the -Manidae the scaphoid and lunar are united; five digits are present, -the third and fourth being very large, and all being terminated by -deeply cleft ungual phalanges. In _Orycteropus_ the pollex is absent, -while the other digits are terminated by pointed ungual phalanges. - -In SIRENIA the general structure of the manus is quite of the ordinary -mammalian type. In _Manatus_ most of the bones of the carpus are -distinct, but in _Halicore_ many, especially those of the distal row, -have coalesced. The digits are always five in number and have the -normal number of flattened phalanges. - -In the CETACEA, on the other hand, the manus is much modified by the -fact that the number of phalanges may be greatly increased above the -normal number of three, thirteen or fourteen sometimes occurring in -each digit. These are believed to be duplicated epiphyses. In the -Mystacoceti the manus remains largely cartilaginous, in the Odontoceti -it is better ossified, and the phalanges commonly have epiphyses at -both ends. In _Physeter_ the carpal bones also have epiphyses. The -carpus generally consists of six bones arranged in two rows of three -each. Five digits are generally present, but sometimes as in -_Balaenoptera musculus_, there are four, the third being suppressed. -Their relative development varies much. The Sperm Whale which till -recently was placed in the entrance hall of the Natural History Museum -at South Kensington has one phalanx to the first digit, four to the -second, five to the third, four to the fourth, and three to the fifth. -Generally the manus is short and broad, but sometimes, as in -_Globicephalus_, it is much elongated owing to the great development -of the second and third digits. - -UNGULATA[173]. The manus of the members of this great order is of very -great classificatory and morphological importance. All the members -agree in having the scaphoid and lunar distinct, and in almost every -case the ends of the digits are either encased in hoofs or provided -with broad flat nails. It is by means of characters derived from the -manus and pes that the group is subdivided into the Ungulata vera and -the Subungulata. - -In the UNGULATA VERA the manus is never plantigrade, and there are not -more than four digits, the pollex being almost always completely -suppressed: in _Cotylops_ among extinct Artiodactyla however a -vestigial pollex is found. The centrale is absent, and the magnum -articulates freely with the scaphoid, and is separated from the -cuneiform by the unciform and lunar. All the bones of the carpus -interlock strongly, and the axis of the third digit passes through the -magnum and between the scaphoid and lunar. - -There is a very strong distinction between the manus of the suborders -Artiodactyla and Perissodactyla. In the Artiodactyla the axis of the -manus passes between the third and fourth digits, which are almost -equally developed and, except in the Hippopotami and some extinct -forms such as _Anoplotherium_, have their ungual phalanges flattened -on their contiguous surfaces. - -In all _ARTIODACTYLA_ the third and fourth digits are large, but a -gradual reduction in the second and fifth can be well traced. Thus in -the Suina the second and fifth digits, though smaller than the third -and fourth, are well developed and all four metacarpals are distinct. -In the Tragulina too all four metacarpals are developed, and in -_Dorcatherium_ the third and fourth commonly remain distinct as in the -Suina. In the other Artiodactyla however the third and fourth -metacarpals are almost always united, though indications of their -separate origin remain. In some Ruminantia, such as many Deer, the -second and fifth digits are reduced to minute splint bones attached to -the proximal end of the fused third and fourth metacarpals, and to -small hoof-bearing phalanges, sometimes attached to splint-like distal -vestiges of the metacarpals, sometimes altogether unconnected with any -other skeletal structures. In some other Ruminants, such as the Sheep -and Oxen, the only remnants of the second and fifth digits are nodules -of bone supporting the hoofs, and in others, such as the Giraffe, -_Anoplotherium commune_, some Antelopes and the Tylopoda, all traces -of these digits have disappeared. The Camels differ from all living -Ungulata vera in not having the distal phalanges completely encased in -hoofs, and from all except the Hippopotami in placing a considerable -amount of the manus on the ground in walking. - -[Illustration FIG. 106. MANUS OF PERISSODACTYLES. - -_A._ LEFT MANUS OF _Tapirus_. (After VON ZITTEL.) - -_B._ RIGHT MANUS OF _Titanotherium_. (After MARSH.) - -_C._ LEFT MANUS OF _Chalicotherium gigantium_. (After GERVAIS.) - - 1. scaphoid. - 2. lunar. - 3. cuneiform. - 4. trapezoid. - 5. magnum. - 6. unciform. - 7. trapezium. - II, III, IV, V. second, third, fourth and fifth digits.] - -While the manus of the Artiodactyla is symmetrical about a line drawn -between the third and fourth digits, that of the _PERISSODACTYLA_ is -symmetrical about a line drawn through the middle of the third digit, -which is larger than the others and has its ungual phalanx evenly -rounded and symmetrical in itself. The most reduced manus in the whole -of the mammalia is found in the Horse and its allies, in which the -third digit, terminated by a very wide ungual phalanx, is the only one -functional. Small splint bones representing the second and fourth -metacarpals are attached to the upper part of the third metacarpal. In -_Hipparion_[174] and other early horse-like animals the second and -fourth digits, though very small and functionless, are complete and -are terminated by small hoofs. In _Rhinoceros_ the second and fourth -digits are equally developed and nearly as large as the third, and -reach the ground in walking, a vestige of the fifth is also present. -In the Tapir (fig. 106, A) and _Hyracotherium_ the fifth digit is -fully developed but is scarcely functional. In _Titanotherium_ -(_Brontops_) (fig. 106, B) it is nearly as well developed as any of -the others, and there is little or no difference between the relative -development of the third and fourth digits. - -The Chalicotheriidae[175], though distinctly Perissodactyles in -various respects such as their cervical vertebrae and teeth, differ -not only from all other Perissodactyles, but from almost all other -Ungulates, in the very abnormal character of their manus. For while -the carpus and metacarpus are like those of ordinary Perissodactyles, -the phalanges resemble those of Edentates, each second phalanx having -a strongly developed trochlea, and each distal one being curved, -pointed and deeply cleft at its termination (fig. 106, C). - -The Macraucheniidae, while agreeing with Perissodactyles in having -only three digits, with the limb symmetrical about a line drawn -through the middle of the third, have a carpus which approaches -closely to the subungulate condition, the magnum articulating -regularly with the lunar, and only to a slight extent with the -scaphoid. - -In the SUBUNGULATA the manus sometimes has five functional digits, and -a considerable part of it rests on the ground in walking. The bones of -the carpus retain their primitive relation to one another, the magnum -articulating with the lunar, but not with the scaphoid. This character -does not however hold in the Toxodontia, for in most of the animals -belonging to this group the magnum does articulate with the scaphoid. -The corner of the scaphoid just reaches the magnum also in Amblypoda. - -As far as is known the _TOXODONTIA_ generally have three, sometimes -five digits to the manus, and the third is symmetrical in itself--a -Perissodactyloid feature. - -In _Phenacodus_ (fig. 107, B) (_CONDYLARTHRA_) all five digits are -well developed, the pollex being the smallest. The carpal bones retain -their primitive arrangement, the magnum articulating with the lunar -and not with the scaphoid. There is no separate centrale. - -[Illustration FIG. 107. LEFT MANUS OF - -_A. Coryphodon hamatus._ (After MARSH.) × 1/5. - -_B. Phenacodus primaevus._ (After COPE.) × 1/3. - -_C. Procavia (Dendrohyrax) arboreus._ (After VON ZITTEL.) × 6/7. - - 1. scaphoid. - 2. lunar. - 3. cuneiform. - 4. trapezium. - 5. trapezoid. - 6. magnum. - 7. unciform. - 8. centrale. - 9. pisiform. - I, II, III, IV, V. first, second, third, fourth and fifth digits - respectively.] - -In the _HYRACOIDEA_ (fig. 107, C) the manus is very similar to that in -_Phenacodus_, but a centrale is present and the pollex is much -reduced. - -The manus of the _AMBLYPODA_, such as _Coryphodon_ (fig. 107, A) and -_Uintatherium_, is short and broad, with five well developed digits -and large carpal bones. The carpals however interlock to a slight -extent, and the corner of the magnum reaches the scaphoid. - -In the _PROBOSCIDEA_ the manus is very short and broad, with large -somewhat cubical carpals which articulate by very flat surfaces and do -not interlock at all. All five digits are present, and none of them -are much reduced in size. The manus in Proboscidea and in _Coryphodon_ -is subplantigrade. - -In the Tillodontia the manus is plantigrade and has pointed ungual -phalanges, in this respect approaching the Carnivora. It differs -however from that of all living Carnivora in having the scaphoid and -lunar distinct. - -In RODENTIA the manus nearly always has five digits with the normal -number of phalanges: the pollex may however be very small as in the -Rabbit, or absent as sometimes in the Capybara. The scaphoid and lunar -are generally united, and a centrale may be present or absent. In -_Pedetes caffer_ the radial sesamoid is double and the distal bone -bears a nail-like horny covering. In _Bathyergus_ the pisiform is -double. It is upon these facts that the contention for the former -existence of prehallux and post-minimus digits has partly been based. - -In living CARNIVORA the scaphoid, lunar and centrale are always -united, forming a single bone. All five digits are present, but as a -rule in Carnivora vera the pollex is small, and in _Hyaena_ is -represented only by a small metacarpal. Sometimes, as in Cats and -Dogs, the manus is digitigrade, sometimes, as in Bears, plantigrade. -The ungual phalanges are large and pointed, and in forms like the -Cats, whose claws are retractile, they can be folded back into a deep -hollow on the ulnar side of the middle phalanx; a small radial -sesamoid is often present. - -In Pinnipedia the manus is large and flat and the digits are -terminated by ungual phalanges which are blunt (sea lions and walrus), -or slightly curved and pointed (seals). The pollex is nearly or quite -as long as the second digit, and as a rule the digits then -successively diminish in size. - -The Creodonta differ from living Carnivora in the fact that the -scaphoid and lunar are usually separate. - -In INSECTIVORA the scaphoid and lunar are sometimes united, sometimes -separate, and a separate centrale is usually present. There are -generally five digits, but sometimes the pollex is absent. In the Mole -the manus is greatly developed and considerably modified. It is very -wide, its breadth being increased by the great development of the -radial sesamoid which is very large and sickle-shaped. The ungual -phalanges are also large and are cleft at their extremities. - -In the CHIROPTERA the manus is greatly modified for the purpose of -flight. The pollex is short and is armed with a rather large curved -claw, the other digits are enormously elongated, the elongation in the -case of the Insectivorous bats being mainly due to the metacarpals, -and in the Frugivorous bats to the phalanges. In the Frugivorous bats -the second digit is clawed as well as the pollex, in other bats this -claw is always absent, and so is often the ungual phalanx, the middle -phalanx then tapering gradually to its termination. - -In PRIMATES as a rule the manus is moderately short and wide. The -carpus has the scaphoid and lunar distinct, and generally also the -centrale; sometimes however, as in Man, the Gorilla, Chimpanzee, and -some Lemurs, the centrale has apparently fused with the scaphoid. -There are almost always five well-developed digits, but in the genera -_Colobus_ and _Ateles_ the pollex is vestigial. - -The magnum in man is the largest bone of the carpus. The pisiform also -is well developed, but there is no radial sesamoid. In Man, the -Gorilla, Chimpanzee, and Orang, the carpus articulates only with the -radius, in most Primates it articulates also with the ulna. The third -digit of the Aye-Aye (_Chiromys_) is remarkable for its extreme -slenderness. - - -THE PELVIC GIRDLE. - -The pelvic girdle in all mammals except the Sirenia and Cetacea -consists of two halves, usually united with one another at the -symphysis in the mid-ventral line, and connected near their upper -ends, with the sacral vertebrae. Each half forms one of the -_innominate_ bones, and includes at least three separate elements, a -dorsal bone, the ilium, and two ventral bones, the ischium and pubis. -Very often a fourth pelvic element, the acetabular or cotyloid bone, -occurs. - -In the MONOTREMATA the pelvis is short and broad, and the pubes and -ischia meet in a long symphysis. The acetabulum is perforated in -_Echidna_ as in birds, but not in _Ornithorhynchus_. A pair of -elongated slender bones project forwards from the edge of the pubes -near the symphysis; these are sesamoid bones formed by ossifications -in the tendons of the external oblique abdominal muscles, and are -generally called _marsupial bones_. - -In the MARSUPIALIA the ilia are generally very simple, straight, and -narrow, while the pubes and ischia are well developed and meet in a -long symphysis. Marsupial bones are nearly always prominent, but are -not developed in _Thylacinus_ or _Notoryctes_. The ischium often has a -well-marked tuberosity and in Kangaroos the pubis bears a prominent -pectineal process on its anterior border close to the acetabulum. The -pelvis in _Notoryctes_ differs much from that in all other Marsupials, -the ilium and ischium being ankylosed with six vertebrae in a manner -comparable to that of many Edentates. - -In the EDENTATA the pelvis is generally well developed, but the -symphysis is very short. In the Sloths the pelvis is rather weak and -slender, the obturator foramina are very large and the ischia do not -meet in a symphysis. In the Megatheriidae the pelvis is exceedingly -wide and massive, and is firmly ankylosed with a number of vertebrae. -In the Armadillos, Glyptodonts, Anteaters, and Pangolins it is much -developed and firmly united to the vertebral column by both the ilia -and the ischia. In _Orycteropus_ however the ischium does not become -united to the vertebral column, and the pubis generally has a strongly -developed pectineal process. - -In the SIRENIA the pelvis is quite vestigial. In the Dugong it -consists on each side of two slender bones, one of which represents -the ilium and the other the ischium and pubis; the two bones are -placed end to end and are commonly fused together. The ilium is -attached by ligament to the transverse process of one of the -vertebrae. In the Manatee each half of the pelvis is represented by a -triangular bone connected by ligaments with its fellow and with the -vertebral column. In neither Manatee nor Dugong is there any trace of -an acetabulum but one can be made out in _Halitherium_. - -In the CETACEA the pelvis is even more vestigial than in the Sirenia, -consisting simply of a pair of small straight bones which probably -represent the ischia, and lie parallel to and below the vertebral -column at the point where the development of chevron bones commences. - -In UNGULATA VERA the pelvis is generally rather long and narrow. The -ilium is flattened and expanded in front (fig. 103, 8), but becomes -much narrower and more cylindrical before reaching the acetabulum. -Both pubis and ischium contribute to the symphysis which is often very -long. The ischia are large and have prominent tuberosities, especially -in Artiodactyles. In most Ruminantia there is a deep depression, the -supra-acetabular fossa above the acetabulum, but this is not found in -the Suina or Tylopoda. - -SUBUNGULATA. In _Procavia_ the pelvis is long and narrow, and bears -resemblance to that in Artiodactyles. - -The Proboscidea have a very large pelvis set nearly at right angles to -the vertebral column; the ilium is very wide, having expanded iliac[1] -and gluteal[1] surfaces, and a narrow sacral[176] surface. The pubes -and ischia are rather small, but both meet their fellows in the -symphysis. _Uintatherium_ (suborder Amblypoda) also has a large and -vertically placed pelvis (fig. 108) with a much expanded ilium. The -pelvis however differs from that of the Proboscidea in the fact that -the ischia do not meet in a ventral symphysis. - -In many RODENTIA the ilia have their gluteal, iliac, and sacral -surfaces of nearly equal extent; in the Hares, however, the gluteal -and iliac surfaces are confluent. The pubes and ischia are always well -developed and sometimes, as in the Hares, the acetabular bone also. In -these animals the pubis does not take part in the formation of the -acetabulum, and the ischium bears on its outer side a well-marked -ischial tuberosity. - -In the CARNIVORA the pelvis is long and narrow. The iliac surfaces -(fig. 78, A, 5) are very small and the sacral large; the crest or -supra-iliac border is formed by the union of the sacral and gluteal -surfaces. The symphysis is long and includes part of both pubis and -ischium. The ischial tuberosity (fig. 78, A, 10) is often well marked, -and sometimes as in _Viverra_ the acetabular bone is distinct. In the -Pinnipedia the pelvic symphysis is little developed, or sometimes not -developed at all, and the obturator foramina are remarkably large. - -In some INSECTIVORA such as _Galeopithecus_, there is a long pelvic -symphysis, in others such as _Erinaceus_ and _Centetes_, it is very -short, in others again such as _Talpa_ and _Sorex_, there is no pelvic -symphysis. The acetabular bone is exceptionally large in _Talpa_ and -_Sorex_. - -In CHIROPTERA the pelvis is small and narrow, and in the great -majority of cases the two halves do not meet in a ventral symphysis. -The pubis has a strongly developed pectineal process, which -occasionally unites with a process from the ilium enclosing a large -pre-acetabular foramen. - -PRIMATES. In Man and the Anthropoid Apes the pelvis is very large and -wide, and the ilium has much expanded iliac and gluteal surfaces. The -symphysis is rather short and formed by the pubis alone. The -acetabulum is deep and the obturator foramen large, and there is -frequently a well-marked ischial tuberosity. In the lower Anthropoidea -the ilium is long and narrow and has a small iliac surface. The -ischial tuberosities are large in the old world monkeys. - -[Illustration FIG. 108. LEFT ANTERIOR AND POSTERIOR LIMB AND LIMB -GIRDLE OF _Uintatherium mirabile_. The anterior limb is to the left, -the posterior to the right × 1/10. (From casts, Brit. Mus.) - - 1. ilium. - 2. head of femur. - 3. great trochanter. - 4. patella. - 5. fibula. - 6. tibia. - 7. second digit of pes. - 8. ungual phalanx of fifth digit of pes. - 9. calcaneum. - 10. postscapular fossa. - 11. prescapular fossa. - 12. coracoid process. - 13. humerus. - 14. radius. - 15. ulna. - 17. unciform. - 18. cuneiform. - 20. lunar. - 21. first metacarpal. - 22. fifth metacarpal.] - - -THE THIGH AND SHIN. - -In the MONOTREMATA the femur is short, rather narrow in the middle, -and expanded at each end. The great and lesser trochanters are large -and about equally developed, but there is no third trochanter. The -fibula is very large and is expanded at its proximal end, forming a -flattened plate much resembling an olecranon. The patella is well -developed. - -In the MARSUPIALIA there is no third trochanter to the femur, the -fibula is well developed but not the patella as a general rule. -_Notoryctes_ has a femur with a prominent ridge extending some little -way down the shaft from the great trochanter; the tibia has a -remarkably developed crest, and the fibula has its proximal end much -expanded and perforated; there is an irregularly shaped patella -closely connected with the proximal end of the tibia. - -EDENTATA. In the Sloths the leg bones are all long and slender. The -femur has no third trochanter, and the fibula is complete and nearly -equal in size to the tibia. In the Megatheriidae the leg bones are -extraordinarily massive, the circumference of the shaft of the femur -in _Megatherium_ equalling or exceeding the length of the bone. There -is no third trochanter in _Megatherium_. In most of the remaining -Edentata the leg bones are strongly developed. The femur in the -Armadillos and Aard Varks has a strong third trochanter, and the -tibia and fibula are both large and are commonly ankylosed together at -either end. The limb bones are very massive also in the Glyptodonts. - -SIRENIA. In no living Sirenian is there any trace of a hind limb, but -in _Halitherium_ a vestigial femur is found, which articulates with -the pelvis by a definite acetabulum. - -[Illustration FIG. 109. LEFT FEMUR OF AN OX (_Bos taurus_) (to the -left) AND OF A SUMATRAN RHINOCEROS (_R. sumatrensis_) (to the right). -× 1/6. (Camb. Mus.) - - 1. head. - 2. great trochanter. - 3. lesser trochanter. - 4. third trochanter. - 5. shaft. - 6. condyles.] - -In the Mystacoceti among the CETACEA small nodules of bone or -cartilage occur connected with the vestigial pelvis, and may represent -the femur and tibia. No trace of the skeleton of the hind limb is -known in the Odontoceti. - -In the UNGULATA VERA the femur is noticeable for the size of the great -trochanter (fig. 109, 2); there is no definitely constricted neck -separating the head from the rest of the bone, and the lesser -trochanter (fig. 109, 3) is not very prominent. All Perissodactyles -except the Chalicotheriidae show a strongly marked third trochanter, -but this is absent in all known Artiodactyles. The development of the -fibula in general corresponds to that of the ulna. In _Rhinoceros_, -_Macrauchenia_, _Tapirus_ and the Suina it is distinct and fairly well -developed; in the Tragulina on the other hand it is vestigial, being -reduced to the proximal end only. In the Ruminantia and Tylopoda also, -it is much reduced forming merely a small bone attached to the distal -end of the tibia, sometimes, as in the Red deer a slender vestige of -the proximal end also is preserved quite detached from the distal -portion; in the Horse this proximal portion is all that there is found -of the fibula. The progressive diminution of the fibula can be well -seen in the series of forms that are regarded as the ancestors of the -Horse. The patella of the Ungulata vera is well ossified, but -fabellae[177] are not usually found. - -SUBUNGULATA. Of the Toxodontia, _Toxodon_ has no third trochanter -while _Typotherium_ and _Astrapotherium_ have one. In the Condylarthra -the femur has well-marked lesser and third trochanters, and the fibula -and patella are well developed. In the Hyracoidea there is a slight -ridge on the femur in the place of the third trochanter, the fibula is -complete, but is generally fused to the tibia at its proximal end. - -Of the Amblypoda, _Coryphodon_ has a third trochanter, but -_Uintatherium_ has none; in this respect, in the vertical position and -general appearance (fig. 108) of the limb, and in the articulation of -the fibula with the calcaneum, the leg of _Uintatherium_ closely -approaches that of the Proboscidea. - -In the Proboscidea the femur is very long and straight, the -development of trochanters is slight, and the fibula though slender is -complete and articulates with the calcaneum. - -A third trochanter is found in the Tillodontia. - -In RODENTIA the femur is variable, the great trochanter is generally -large and so sometimes is the third as in the Hares. In most Rodents -as in the Beaver the fibula is distinct, sometimes as in the Hares it -is united distally with the tibia. The patella is well developed, and -so too are the fabellae as a general rule. - -CARNIVORA. In the Carnivora vera the femur (fig. 79, A) is generally -rather straight and slender, and has a very distinct head. The fibula -(fig. 79, C) is always distinct and there is generally a considerable -interval between it and the tibia. Fabellae (fig. 79, 7) are commonly -present. - -In the Pinnipedia the femur is short, broad and flattened, having a -prominent great trochanter. The fibula is nearly as large as the -tibia, and the two bones are generally ankylosed together at their -proximal ends. - -The Creodonta differ from all living Carnivores in having a femur with -a third trochanter. - -In the INSECTIVORA a third trochanter is sometimes developed. The -fibula is sometimes distinct, sometimes fused distally with the tibia, -thus differing from that of a Carnivore. - -In CHIROPTERA the femur is straight, slender and rather short, with a -small but well-developed head. The fibula may be well developed or -quite vestigial or absent. Owing to the connection of the hind limb -with the wing membrane the knee joint is directed backwards. - -In PRIMATES the femur is rather long and slender, having a nearly -spherical head and large great trochanter. The tibia and fibula are -always distinct and well developed. Fabellae are not found in the -highest forms but are generally present in the others. - - -THE PES. - -The skeleton of the pes is in most respects a counterpart of that of -the manus. Just as in the manus if one digit is absent it is the -pollex, so in the pes it is the hallux. But while in the manus the -third digit is always well developed, however much the limb may be -modified, in the pes any of the digits may be lost. In all mammals the -tibiale and intermedium fuse to form the _astragalus_, and the fourth -and fifth tarsalia to form the _cuboid_. Sesamoid bones are -considerably developed. In almost every case the phalanges and first -metatarsal have epiphyses only on their proximal ends, while the -remaining four metatarsals have epiphyses only on their distal ends. - -In the MONOTREMATA all the usual tarsal bones are distinct, and the -five digits have the normal number of phalanges. Several sesamoid -bones are developed, the most important one, found only in the male, -being articulated to the tibia and bearing the curious horny spur. The -ungual phalanges of the pes like those of the manus, are deeply cleft -at their extremities. In the Echidnidae the pes is turned outwards and -backwards in walking. - -In the MARSUPIALIA the pes is subject to great modifications, but in -every case the seven usual tarsal bones are distinct. In the -Didelphyidae the foot is broad, all five digits are well developed, -and the hallux is opposable to the others. In the Dasyuridae the foot -is narrow, and the hallux may be very small, or as in _Thylacinus_ -completely absent. In _Notoryctes_ the pes is much less abnormal than -the manus, and all five digits have the usual number of phalanges. The -fifth metatarsal has a curious projecting process, and there is a -large sesamoid above the hallux. In the Wombats (Phascolomyidae) the -foot is short and broad, the digits are all distinct, and the hallux -is divaricated from the others. - -In the remaining marsupials the second and third metacarpals and -digits are very slender, and are enclosed within a common integument. -This condition is known as _syndactylism_, and its effect is to -produce the appearance of one toe with two claws. In the Kangaroos -(Macropodidae) the pes is very long and narrow, owing to the -elongation of the metacarpals. The fourth digit is greatly developed, -the fifth moderately so, while the hallux is absent, and the second -and third digits are very small. The Peramelidae have the foot -constructed on the same plan as in the Kangaroos, and in one genus -_Choeropus_ the same type of foot is carried to a greater extreme than -even in the Kangaroos. Thus the fourth digit is enormously developed, -the second and third are small, and the fifth smaller still, while the -hallux is absent. In the Phalangers and Koalas though the second and -third toes are very slender, the hallux is well developed and -opposable. - -EDENTATA. In the Sloths the pes much resembles the manus, being long -and narrow, but in both genera the second, third and fourth digits are -well developed. Most of the other Edentates have a but little modified -pes with the normal number of tarsal bones and the complete series of -digits. In _Cycloturus_ however the hallux is vestigial and it is -absent in Glyptodonts. _Megatherium_ has a greatly modified pes, the -hallux is absent, and the second digit vestigial, while the third is -very large, having an enormous ungual phalanx. The calcaneum too is -abnormally large. - -No trace of the pes occurs in either SIRENIA or CETACEA. - -In the UNGULATA the pes like the manus is subject to much variation -and is of great morphological importance. - -In the UNGULATA VERA the pes is never plantigrade and never has more -than four digits, the hallux being absent. The cuboid always -articulates with the astragalus, and the tarsal bones strongly -interlock. As was the case also with the manus, the pes is formed on -two well-marked types characteristic respectively of the Artiodactyla -and Perissodactyla. - -_ARTIODACTYLA._ Just as in the manus, the third and fourth digits are -well and subequally developed; their ungual phalanges have the -contiguous sides flat, and the axis of the limb passes between them, -and between the cuboid and navicular. The astragalus has both the -proximal and distal surfaces pulley-like, and articulates with the -navicular and cuboid by two facets of nearly equal size. The calcaneum -articulates with the lower end of the fibula if that bone is fully -developed. - -In the Suina four toes are developed, and though in the Peccaries the -third and fourth metatarsals are united, they are all distinct in most -members of the group, as are all the tarsal bones. In the Hippopotami -the four digits are of approximately equal size, and the middle ones -do not have the contiguous faces of their ungual phalanges flattened. - -In the Tragulina the cuboid, navicular, and two outer cuneiforms are -united forming a single bone; all four metatarsals are complete and -the two middle ones are united. In the Tylopoda and _Anoplotherium -commune_ only the third and fourth digits are developed, their -metatarsals are free distally, but are elsewhere united. In the -Ruminantia the cuboid and navicular are always united and so are the -second and third cuneiforms, while in _Cervulus_ all four bones are -united together. The third and fourth metatarsals in Ruminants are -always united in the same way as are the third and fourth metacarpals, -while the second and fifth are always wanting. In Deer the second and -fifth digits are usually each represented by three small phalanges, -but in the Giraffe and most Bovidae the bones of these digits are -wanting. - -[Illustration - - FIG. 110. _A._ LEFT PES OF A TAPIR (_Tapirus americanus_). × 1/6. - _B._ RIGHT PES OF A RHINOCEROS (_R. sumatrensis_). × 1/8. - _C._ (CAST OF) RIGHT PES OF _Hipparion gracile_. × 1/7. - _D._ RIGHT PES OF A HORSE (_Equus caballus_). × 1/10. (All Camb. Mus.) - - 1. calcaneum. - 2. astragalus. - 3. navicular. - 4. cuboid. - 5. external cuneiform. - 6. middle cuneiform. - 7. internal cuneiform.] - -In the _PERISSODACTYLA_ the pes like the manus is symmetrical about a -line drawn through the third digit; this line when continued passes -through the external cuneiform, navicular and astragalus. The -astragalus has its distal portion abruptly truncated, and the facet by -which it articulates with the cuboid is much smaller than that by -which it articulates with the navicular. The calcaneum does not -articulate with the fibula. The tarsus in _Macrauchenia_ like the -carpus differs from that of other Perissodactyles and resembles that -of Subungulates in having the bones arranged in lines with little or -no interlocking. The calcaneum resembles that of Artiodactyles in -having a small facet for articulation with the fibula. _Tapirus_ (fig. -110, A), _Rhinoceros_ (fig. 110, B) and _Titanotherium_ have a short -and broad foot with the usual tarsal bones and three well-developed -digits,--a number never exceeded by any Perissodactyle. From this -tridactylate limb a series of stages is exhibited by various extinct -forms leading gradually to the condition met with in the Horse (fig. -110, D) in which the third toe is greatly developed, while the second -and fourth are reduced to slender metatarsals attached to the proximal -half of the third metatarsal. - -In _Chalicotherium_ and _Agriochoerus_ the pes has the same abnormal -characters as the manus, the digits being clawed and the ungual -phalanges in _Chalicotherium_ deeply cleft. - -In the SUBUNGULATA the pes is sometimes plantigrade and -pentedactylate, the cuboid sometimes does not articulate with the -astragalus, and the tarsal bones sometimes do not interlock. - -In _Typotherium_ (_TOXODONTIA_) the hallux is absent and the other -four digits are well developed; in _Toxodon_ and _Nesodon_ the pes is -tridactylate. The tarsal bones have the regular Subungulate -arrangement, the cuboid not articulating with the astragalus. The -calcaneum articulates with the fibula as in Artiodactyles. The -astragalus in most forms, but not in _Astrapotherium_, resembles that -of the Ungulata vera in having a grooved proximal surface. - -In _Phenacodus_ (_CONDYLARTHRA_) the tarsus is very little modified, -five digits are present, the first and fifth being small and not -reaching the ground. - -In _Procavia_ only the three middle digits are present with a vestige -of the fifth metacarpal. - -In the _AMBLYPODA_ the pes (fig. 108) is very short and broad, all -five digits are functional, and at any rate in _Coryphodon_ -plantigrade, the hallux being the smallest. The astragalus is very -flat, and the tarsals interlock to a slight extent, the cuboid -articulating with both calcaneum and astragalus. - -The pes in the _PROBOSCIDEA_ much resembles that in the Amblypoda, but -differs in that the astragalus does not articulate with the cuboid, -the tarsals not interlocking at all. - -In the RODENTIA the structure of the foot is very variable. In Beavers -the foot is very large, all five digits being well developed; the -fifth metatarsal articulates with the outer side of the fourth -metatarsal, and not with the cuboid, and there is a large sesamoid -bone on the tibial side of the tarsus. In the Rats, Porcupines and -Squirrels, there are five digits, in the Hares only four, and in the -Capybara and some of its allies only three. In the Jerboa (_Dipus_) a -curious condition of the pes is met with, as it consists of three very -long metatarsals fused together and bearing three short toes, each -formed of three phalanges. _Lophiomys_ differs from all other Rodents -in having the hallux opposable. - -CARNIVORA. In the Carnivora vera the pes is regular and shows little -deviation from the normal condition. All the usual tarsal bones are -present, but sometimes as in the Dogs, Cats, and Hyaenas, the hallux -is vestigial. Sometimes as in the Bears the pes is plantigrade, -sometimes as in the Cats and Dogs it is digitigrade. In this respect -and in the character of the ungual phalanges, the pes closely -corresponds with the manus. In the Sea Otter (_Latax_) the foot is -large and flattened and approaches in character that of the -Pinnipedia. - -In the Pinnipedia the pes differs much from that in the Carnivora -vera. In the Seals in which the foot cannot be used for walking, and -is habitually directed backwards, the first and fifth digits are much -longer and stouter than any of the others. In the Sea Lions which can -use the pes for walking, the digits are all of nearly the same length, -and in the Walrus the fifth is somewhat the longest. - -In the INSECTIVORA the pes is almost always normal, and provided with -five digits. - -In the CHIROPTERA the pes is pentedactylate, and the digits are -terminated by long curved ungual phalanges. In some genera the toes -have only two phalanges. The calcaneum is sometimes produced into a -long slender process which helps to support the membrane between the -leg and the tail. - -Among the PRIMATES Man has the simplest form of pes. In Man all five -digits are well developed, the hallux being considerably the largest. -Sesamoid bones occur only under the metatarso-phalangeal joint of the -hallux. - -In the other Primates the internal cuneiform has a saddle-shaped -articulating surface for the hallux, which is obliquely directed to -the side of the foot and opposable to the other digits. Two sesamoid -bones are usually developed below each metatarso-phalangeal joint, and -one below the cuboid. The second digit in Lemurs, and all except the -hallux in _Chiromys_ have pointed ungual phalanges; in all other cases -the ungual phalanges are flat. In some of the Lemuroidea, especially -_Tarsius_, the tarsus is curiously modified by the elongation of the -calcaneum and navicular. - - -FOOTNOTES: - -[165] The figure was drawn from a photograph and the size of the jaws -relatively to the cranium is exaggerated. - -[166] See W.K. Parker, "On the Structure and Development of the Skull -in the Pig." _Phil. Trans._ pp. 289-336, 1874. - -[167] See W.H. Flower, "On the value of the characters of the base of -the cranium in the classification of the order Carnivora." _P.Z.S._ -1869, p. 5. - -[168] See W.K. Parker, _Monograph of the shoulder-girdle and sternum -of the Vertebrata_, _Ray Soc._ 1868. - -[169] See p. 405. - -[170] See E. Lydekker, _P.Z.S._ 1895, p. 172. - -[171] See H. Wincza, _Morph. Jahr._ XVI. p. 647, 1890. - -[172] See K. Bardeleben, _P.Z.S._, 1889, p. 259. - -[173] See E. Cope, "The origin of the foot structures of Ungulata," -_Journ. of Philad. Acad._ 1874. H.F. Osborn, "The evolution of the -Ungulate foot," _T. Amer. Phil. Soc._ 1889. - -[174] See O.C. Marsh, various papers including "Fossil horses in -America," _Amer. Natural._ 1874; "Polydactyl horses," _Amer. J. Sci._ -1879 and 1892. M. Pavlow, "Le développement des Equidés," _Bul. Soc. -Moscou_, 1887, and subsequent papers in the same. Osborn and Wortman, -"On the Perissodactyls of the White River beds," _Bull. Amer. Mus._ -Dec. 23rd, 1895. - -[175] See H.F. Osborn, _Chalicotherium and Macrotherium, Amer. -Natural._ 1889--91--92. - -[176] See p. 409. - -[177] See p. 412. - - - - -LIST OF AUTHORS REFERRED TO. - - - Abbott, E.C., 112 - - Ameghino, F., 351, 424 - - Andrews, C.W., 299 - - - Balfour, F.M., 16 - - Ballowitz, E., 424 - - Bardeleben, K., 504 - - Bateson, W., 50, 344 - - Baum, H., 374 - - Baur, G., 27, 189, 190, 344, 346 - - Beneden, P.J. van, 353 - - Benham, W.B., 51 - - Bettany, G.T., 16, 87, 154 - - Boulenger, G.A., 169 - - Brandt, J.F., 352 - - Bridge, T.W., 123 - - Brühl, C.B., 210 - - Burmeister, H., 351, 424 - - - Cope, E.D., 135, 199, 204, 351, 359, 361, 363, 368 - - Credner, H., 135 - - - Dean, B., 63, 104 - - Dobson, G.E., 369, 370 - - - Earle, C., 432 - - Ecker, A., 151 - - Ellenberger, W., 374 - - - Flower, W.H., 28, 42, 351, 420, 422, 434 - - Fritsch, A., 135 - - Fürbringer, M., 295 - - - Gadow, H., 40, 112, 190, 295, 343, 350 - - Gegenbaur, C., 127 - - Gervais, P., 353 - - Günther, A.C.L.G., 70, 104 - - - Haslam, G., 151 - - Hasse, C., 112, 113 - - Haswell, W.A., 127 - - Hertwig, O., 169 - - Hoffmann, C.K., 190, 202, 210 - - Howes, G.B., 164, 451 - - Hubrecht, A.A.W., 104 - - Hulke, J.W., 192, 204 - - Hurst, C.H., 71, 297 - - Hutton, F.W., 299 - - Huxley, T.H., 11, 13, 133, 135, 191, 210, 295, 297, 334, 343, 351, - 374, 437 - - - Kirkaldy, J.W., 51 - - Klein, E., 11 - - Kölliker, A., 9 - - Kükenthal, W., 349, 422 - - - Lankester, E. Ray, 51 - - Leche, W., 344, 423 - - Lindsay, B., 336 - - Lydekker, R., 36, 42, 190, 195, 495 - - - Macbride, E.W., 50 - - Marsh, O.C., 204, 209, 299, 348, 361, 364, 365, 508 - - Marshall, A.M., 71, 151 - - Masterman, A.T., 51 - - Meyer, H. v., 135 - - Miall, L.C., 135, 243 - - Mivart, St G., 369 - - Morgan, C. Lloyd, 11 - - - Newton, E.T., 283 - - - Osborn, H.F., 348, 420, 429, 508 - - Owen, R., 191, 204, 210, 297, 348, 351, 420 - - - Parker, T.J., 83, 96, 299 - - Parker, W.K., 16, 24, 53, 87, 154, 173, 200, 243, 465, 489 - - Pavlow, M., 358, 508 - - Pollard, H.B., 119 - - Poulton, E.B., 422 - - Pycraft, W.P., 297 - - - Ridewood, W.G., 106, 164 - - Röse, C., 422 - - - Sagemehl, M., 104 - - Schäfer, E., 11 - - Scott, W.B., 368 - - Seeley, H.G., 191, 212 - - Selenka, E., 40, 295 - - Shufeldt, R., 123 - - Smith, E. Noble, 11 - - Stirling, E.C., 423 - - Swirski, G., 103 - - - Taeker, J., 427 - - Thomas, O., 349, 362, 370, 422, 424, 425 - - Tomes, C.S., 420 - - Traquair, R.H., 55, 58 - - - Vogt, C., 297 - - - Wiedersheim, R., 25, 134, 136 - - Wincza, H., 358, 495 - - Woodward, A. Smith, 34, 54, 58, 62, 127, 210 - - Wortman, J.L., 508 - - Wray, R.S., 303 - - - Zittel, K.A. v., 36, 205, 212 - - - - -INDEX. - - - Every reference is to the page: words in italics are names of - genera or species; figures in italics indicate that the - reference relates to systematic position; figures in thick type - refer to an illustration; _f._ = and in following page or - pages; _n._ = note. - - - Aard Vark, _44_, _352_; - femur, 517; - sacrum, 452; - teeth, 425; - see _Orycteropus_ - - Aard wolf, _48_; - see _Proteles_ - - Abdominal ribs, crocodile, 260; - reptiles, 286 - - Abdominal shield, turtle, 215 - - _Acanthias_, _32_; - calcification of vertebrae, 114; - pectoral fins, 130 - - _Acanthodes_, _32_, _64_ - - Acanthodii, _32_; - general characters, 64; - spines, 106 - - _Acanthomys_, _47_; - spines, 417 - - Acanthopterygii, _34_ - - Accipitres, _41_ - - Acetabular bone, 25, 513; - dog, 409 f.; - frog, 165 - - Acetabulum, 25; - crocodile, 266; - dog, 409; - duck, 324; - frog, 165; - newt, 149; - turtle, 235 - - _Acipenser_, _32_, 117; - exoskeleton, 67; - distribution, 66; - pectoral fins, 131; - plates, 104; - skull, 121, =122=; - spinal column, 112 - - Acipenseridae, _32_ - - Acrodont, defined, 199; - teeth of reptiles, 273 - - _Acrodus_, _32_; - teeth, 109 - - Acromion, dog, 405 - - _Actinotrocha_, _30_; - organ regarded as double notochord, 51 - - Ad-digital quill, duck, 303 - - Adjutant, _41_; - clavicles, 338 - - Ægithognathous, 335 - - Æluroidea, _48_, _369_; - teeth, 437 - - Æpyornis, _40_; - tibio-tarsus, 341 - - Æpyornithes, _40_, _299_ - - Aftershaft, 328 - - _Agama_, _38_; - teeth, 273 - - Agamidae, _38_; - premaxillae, 284 - - Aglossa, _36_ - - Agouti, _48_; - see _Dasyprocta_ - - Agriochoeridae, _45_ - - _Agriochoerus_, _45_; - pes, 525 - - Ala spuria, duck, 304 - - Alcidae, _42_; - see Auks - - Alisphenoid, 19; - crocodile, 247; - duck, 317; - dog, 386 - - _Alligator_, _39_, _210_, _212_; - hyoid, =285=; - limbs, =264=; - pectoral girdle, =262=; - pelvis and sacrum, =267=; - scutes, 271; - skull, =245=, =248=, =253= - - Alligatoridae, 39 - - _Alytes_, _36_; - fronto-parietal fontanelle, 179; - vertebrae, 172 - - Amblypoda, _47_; - general characters, 363; - manus, 510; - pes, 525; - skull, 473; - teeth, 433; - thigh and shin, 519 - - _Amblystoma_, _35_; - skull, 175 - - American monkeys, _373_; - see _Cebidae_ - - American vultures, _41_; - vomers, 335 - - _Amia_, _33_; - distribution, 66; - exoskeleton, 67; - pectoral fin, 131; - scales, 105; - skull, 123; - tail, 115, 117; - vertebrae, 114 - - Amiidae, _33_ - - _Ammocoetes_, _31_, _55_ - - Amphibia, _35_; - anterior limb, 185; - exoskeleton, 168; - general characters, 133; - hyoid apparatus, 180; - pectoral girdle, 184; - pelvic girdle, 187; - posterior limb, 188; - ribs, 182; - skull, 173; - sternum, 182; - teeth, 169; - vertebral column, 170 - - Amphicoelous, defined, 14 - - _Amphioxus_, _30_; - skeleton, 51 f.; - spinal column, 112 - - _Amphisbaena_, _38_, 272; - loss of limbs, 289 - - Amphisbaenidae, _38_, _200_; - pectoral girdle, 288; - skull, 277; - vertebral column, 275 - - Amphitheriidae, _43_ - - _Amphiuma_, _35_, _135_; - manus, 187; - pes, 188; - skull, 174 - - Amphiumidae, _35_ - - Anacanthini, _33_ - - Anal shield, turtle, 215 - - _Anas_, _41_; - _A. boschas_, see Duck - - Ankylosis, defined, 12 - - Angel fish, _32_ - - Angler, attachment of teeth, 107 - - Anguidae, _38_ - - _Anguilla_, _33_; - see Eel - - _Anguis_, _38_; - loss of limbs, 289; - scutes, 271 - - Angular, 22; - cod, 100; - crocodile, 258; - duck, 319; - salmon, 94; - turtle, 231 - - Angulo-splenial, frog, 161 - - Ankle joint, duck, 327; - reptiles, 294 - - Anomodontia, _36_ - - Anoplotheriidae, _45_ - - _Anoplotherium_, _45_; - manus, 506; - pes, 523; - tail, 454; - teeth, 428 - - _Anser_, _41_ - - Anseres, _41_; - aftershaft, 329; - claws, 330 - - Anseriformes, _41_ - - Anteaters, _352_; - absence of teeth, 424; - manus, 505; - pectoral girdle, 495; - pelvis, 513; - skull, 458; - thoraco-lumbar vertebrae, 447; - Spiny --, _43_; - Great and Two-toed --, _44_ - - Antelope, _359_; - manus, 507; - Four-horned A., _46_ - - Anterior limb, 26; - Amphibia, 185; - birds, 338; - crocodile, 263; - dog, 405; - duck, 322; - frog, 164; - newt, 147; - reptiles, 290; - turtle, 232 - - Anthropoid apes, _373_; - arm-bones, 503; - pelvis, 515 - - Anthropoidea, 49; - general characters, 372; - sacrum, 452; - skull, 482; - teeth, 441 - - _Anthropopithecus_, _49_; - ribs, 493 - - Antiarcha, _31_; - general characters, 55 - - Antibrachium, see fore-arm - - _Antilocapra_, _46_; - horns, 417 - - Antilocapridae, _46_ - - Antitrochanter, duck, 325 - - Antlers, 8, 358; - Cervidae, 469 - - Antorbital process, 18 - - Anura, _36_; - general characters, 136; - hyoid apparatus, 180; - pelvis, 187; - posterior limb, 188; - skull, 179; - sternum, 182; - vertebrae, 172 - - _Apatornis_, _40_; - vertebrae, 332 - - Apteria, 328 - - Apteryges, _40_ - - _Apteryx_, _40_, _299_; - aftershaft, 329; - anterior nares, 333; - claws, 330; - foot, 342; - manus, 338; - pectineal process, 341; - pectoral girdle, 338; - pneumaticity of skeleton, 331; - _A. oweni_, pelvic girdle and sacrum, =340= - - Aqueductus vestibuli, dogfish, 74 - - Arcade: - infratemporal--, crocodile, 255; - _Sphenodon_, 283; - inner --, duck, 318; - outer --, duck, 318; - supratemporal --, crocodile, 257; - reptiles, 281 - - Archaeoceti, _44_; - general characters, 356; - skull, 461; - teeth, 426 - - _Archaeopteryx_, _40_, _297_; - claws, 330; - fibula, 341; - mandible, 335; - metatarsals, 342; - pelvis, 341; - ribs, 336; - sacrum, 333; - skull, 333; - tail, 333; - teeth, 330; - wing, 338 - - Archaeornithes, _40_; - characters, 297 - - _Archegosaurus_, _35_, _136_; - palatines, 177 - - Archipterygium, _Ceratodus_, 127; - Ichthyotomi, 62 - - Arcifera, _36_, 185 - - Arctoidea, _48_, 369; - teeth, 438 - - _Ardea_, _41_; - see Heron - - Ardeae, _41_ - - Arm, see fore-arm and upper arm - - Armadillo, _44_, _352_; - cervical vertebrae, 443; - femur, 517; - humerus, 501; - lumbar vertebrae, 447; - manus, 505; - pectoral girdle, 495; - pelvis, 513; - ribs, 491; - sacrum, 452; - scales, 417; - scutes, 419; - skull, 459; - teeth, 424 - - Armour plates, 8 - - Arthrodira, _34_; - characters, 70 - - Articular, 22; - cod, 100; - crocodile, 258; - duck, 319; - newt, 144; - salmon, 94; - turtle, 231 - - Artiodactyla, _45_; - characters, 358; - manus, 506; - odontoid process, 445; - pes, 522; - ribs, 491; - skull, 465; - teeth, 427; - thoraco-lumbar vertebrae, 448 - - Asses, _360_ - - _Asterolepis_, _31_, _55_ - - Asterospondyli, 114 - - Astragalus, 27; - crocodile, 268; - dog, 414; - mammals, 521 - - Astrapotheriidae, _46_ - - _Astrapotherium_, _46_, 361; - dental formula, 432; - femur, 519; - pes, 525 - - _Ateles_, _49_; - pollex, 512; - tail, 454 - - Atlantosauridae, _38_ - - Atlas, 15; - crocodile, 240; - dog, =379=, 380; - duck, 309; - ox, =445=; - turtle, 219 - - Attachment of teeth, 4; - in fish, 107 - - _Auchenia_, _45_; - see Llama - - Auditory aperture or meatus: - external --, crocodile, 250; - dog, 402; - turtle, 228; - internal --, crocodile, 246, 251; - dog, 392; - turtle, 228 - - Auditory capsule, 20; - cod, 96; - crocodile, 250; - dog, 390; - dogfish, 74; - frog, 156; - newt, 143; - turtle, 227 - - Auditory ossicles, crocodile, 251; - dog, 393; - duck, 320; - mammals, 485 f.; - turtle, 228 - - Auks, _42_; - thoracic vertebrae, 332 - - Autostylic, 61, 119 - - Aves, _40_; - characters, 295; - see Birds - - Axial skeletal rods, 50 - - Axial skeleton, crocodile, 239; - cod, 83; - dog, 377; - dogfish, 72; - duck, 307; - frog, 152; - newt, 138; - turtle, 218 - - Axis vertebra, crocodile, 241; - dog, 380; - duck, 309; - turtle, 220 - - Axolotl, _35_; - see _Siredon_ - - Aye Aye, _49_; - see _Chiromys_ - - - _Babirussa_, _45_; - dental formula, 428 - - Baboon, _49_; - see _Cynocephalus_ - - _Balanoglossus_, _30_, 50 - - _Balaena_, _44_, _357_; - scapula, 495; - _B. mysticetus_ baleen, 419 - - Balaenidae, _44_ - - Balaenoidea, _44_; - general characters, 356 - - _Balaenoptera_, _44_, 357; - manus, 506; - thoracic vertebrae, 448; - scapula, 495; - _B. musculus_, cervical vertebrae, =444= - - Baleen, 3, 418 - - _Balistes_, _33_; - teeth, 111 - - Balistidae, _33_ - - Ball and socket joints, 13 - - Bandicoot, _43_ - - Barb, 302 - - Barbule, 303 - - Barramunda, _34_; - see _Ceratodus_ - - Basalia, dogfish, 79 - - Basibranchial, dogfish, 78; - cod, 101; - duck, 320; - newt, 145; - salmon, 95 - - Basi-branchiostegal, cod, 101; - salmon, 95 - - Basicranial axis, 19; - dog, 384 - - Basidorsalia, dogfish, 72 - - Basi-hyal, dogfish, 78; - dog, 399; - duck, 320 - - Basilar plate, 17 - - Basilingual plate, Anura, 180; - crocodile, 259; - frog, 161; - turtle, 231 - - Basi-occipital, 19; - crocodile, 246; - cod, 97; - dog, 386; - duck, 315; - salmon, 89; - turtle, 224 - - Basipterygium, cod, 103; - dogfish, 82 - - Basisphenoid, 19; - crocodile, 247; - dog, 386; - salmon, 91; - turtle, 225 - - Bastard wing, duck, 304 - - Bathyerginae, palate, 366 - - _Bathyergus_, _47_; - auditory ossicles, 488; - manus, 511 - - Batoidei, _32_, 64 - - _Batrachoseps_, _35_; - teeth, 169 - - Bats, claws, 418; - Horseshoe bats, _49_; - see Chiroptera - - _Bdellostoma_, _31_, _55_; - teeth, 57 - - Beak, 3; - birds, 329; - duck, 302; - _Siren_, 168; - tadpoles of Anura, 168; - turtle, 215 - - Bears, _48_, _369_; - manus, 511; - pes, 526; - sacral vertebrae, 452; - skull, 479; - Isabelline -- mandible, =438= - - Beaver, _47_; - fibula, 520; - humerus, 502; - pes, 526; - sacrum, 452; - tail, 454 - - _Belodon_, _39_, 211; - frontals, 277; - palate, 281; - vertebrae, 275 - - Bichir, _33_; - see _Polypterus_ - - Bicipital groove, dog, 405 - - Bilophodont, defined, 345; - teeth of Tapiridae, 429 - - _Bipes_, _38_; - limbs, 289 - - Birds, anterior limb, 338; - endoskeleton, 331 f.; - exoskeleton, 328 f.; - general characters, 295; - hyoid, 336; - pectoral girdle, 336; - pelvic girdle, 339; - posterior limb, 341; - ribs, 336; - skull, 333; - sternum, 336; - teeth, 330; - vertebral, 332 - - _Bison_, _46_; - occipital crest, 468 - - Blind snake, _38_; - see _Typhlops_ - - Blind worm, _38_; - see _Anguis_ - - Boidae, _38_ - - _Bombinator_, _36_; - vertebrae, 172 - - Bone, development of, 10 f. - - Bone cells, 10 - - Bony Ganoids, fins, 105; - pelvic fin, 132; - ribs, 126; - skull, 123; - vertebral column, 114; - see _Holostei_ - - Border: - alveolar --, of dog's jaw, 398; - coracoid, glenoid, and suprascapular -- of dog's scapula, 405 - - _Bos_, _46_; - occipital crest, 468; - ribs, 491; - see Ox - - Bottlenose, _44_; - see _Hyperoödon_ - - Bovidae, _46_; - pes, 523; - skull, 468 - - Bow-fin, _33_; - see _Amia_ - - Brachial ossicles, cod, 103 - - Brachium; see upper arm - - Brachydont, defined, 345; - teeth of Ungulates, 429 f. - - _Brachycephalus_, _36_; - bony plates of, 168 - - Brain case, crocodile, 245; - dog, 384; - duck, 314; - frog, 154; - newt, 140; - turtle, 224 - - Bradypodidae, _43_; - see Sloths - - _Bradypus_, _43_; - cervical vertebrae, 443; - pectoral girdle, 495; - skull, 457; - thoraco-lumbar vertebrae, 447 - - Branchial arches, Amphibia, 180 f.; - cod, 101; - dogfish, 78; - fish, 120 f.; - newt, 145; - salmon, 95; - -- basket, Marsipobranchii, 38; - -- skeleton, _Amphioxus_, 52; - Balanoglossus, 50 - - _Branchiosaurus_, _35_; - branchial arches, 180 - - Branchiostegal rays, cod, 100 - - _Brontops_, _46_; - see _Titanotherium_ - - _Brontosaurus_, _38_, _207_; - sternum, 288 - - _Bubalus_, _46_; - ribs, 491; - see Buffalo - - Buccal skeleton, _Amphioxus_, 52 - - _Buceros_, _42_; - see Hornbill - - Buckler, of Labyrinthodonts, 168, 184 - - Buffalo, _46_; - Cape --, skeleton of, =492= - - _Bufo_, _36_; - hyoid, 182; - jaws, 169; - _B. viridis_, carpus, 186 - - Bufonidae, _36_ - - Bunodont, defined, 345; - teeth of Ungulata, 427 f. - - Buno-selenodont, defined, 432 - - - Caeciliidae, _35_ - - _Caiman_, _39_; - _C. latirostris_ hyoid, =285=, - limbs, =264=, - lateral view of skull, =248=, - palatal view of cranium and mandible, =245=, - longitudinal section of skull, =253=, - pectoral girdle, =262=, - pelvic girdle and sacrum, =267=; - _C. sclerops_, scutes, 271 - - Ca'ing whale, _45_; - see _Globicephalus_ - - _Calamoichthys_, _33_; - distribution, 66 - - Calamus, 302 - - Calcaneum, 27; - crocodile, 268; - dog, 414 - - Calcar, of frog, 167 - - _Callorhynchus_, _32_, _66_; - teeth, 110 - - Camel, _45_, _359_; - manus, 507; - teeth, 428 - - Camelidae, _45_ - - _Camelus_, _45_; - see Camel - - Camptosauridae, _39_ - - Canal: - alisphenoid --, dog, 402; - carotid --, duck, 315; - Eustachian --, crocodile, 247; - dog, 402; - duck, 316; - interorbital --, dogfish, 76 - - Canaliculi, 10 - - Canidae, _48_; - humerus, 502; - skull, 479; - see Dog - - Canine, 344; - dog, 376 f. - - _Canis_, _48_; - thoraco-lumbar vertebrae, 450; - see Dog - - _Capitosaurus_, _35_; - skull, =176= - - Capybara, _48_; - manus, 511; - pes, 526; - skull, 476; - tail, 454 - - Carapace, Chelonia, 271; - _Dermochelys_, 272; - Glyptodonts, 419; - Green turtle, 215; - Loggerhead turtle, =216= - - Carcharidae, _32_ - - Carina sterni, duck, 321 - - Carinatae, _40_; - general characters, 300; - quadrate, 334 - - Carnassial teeth, 368; - carnivora, =436=; - dog, 376 f. - - Carnivora, _48_; - arm bones, 502; - auditory ossicles, 488; - cervical vertebrae, 446; - general characters, 367; - manus, 511; - pelvis, 515; - pes, 526; - ribs, 493; - sacral vertebrae, 452; - skull, 478; - sternum, 490; - tail, 454; - teeth, 437; - thigh and shin, 520; - thoraco-lumbar vertebrae, 450 - - Carnivora vera, _48_; - general characters, 368; - scapula, 497 - - Carp, _33_; - pharyngeal teeth, 111 - - Carpo-metacarpus, duck, 324 - - Carpus, 26; - crocodile, 265; - dog, 408; - duck, 323; - frog, 164; - newt, 147; - turtle, 233 - - Cartilage, structure of, 10 - - Cartilaginous ganoids, cranium, 121; - pelvic fin, 132; - spinal column, 112; - see Chondrostei - - Cassowary, _40_, _299_; - aftershaft, 328; - bony crest, 334; - claws, 330; - pelvic girdle and sacrum, =340=; - secondaries, 329 - - _Castor_, _47_; - see Beaver - - Castoridae, _47_ - - _Casuarius_, _40_; - see Cassowary - - Cataphracti, _34_ - - Cat, _48_, _369_; - hallux, 526; - manus, 511; - skull, 479 - - Cat-fish, _33_ - - Cathartae, _41_ - - _Cathartes_, _41_; - see American vulture - - Caudal fin, Cetacea, 453; - fish, 116; - -- vertebrae, crocodile, 243; - cod, 85; - dog, 383; - duck, 312; - general characters, 16; - newt, 140; - turtle, 222 - - _Cavia_, _48_; - tail, 454 - - Caviidae, _48_ - - Cebidae, _49_, _373_; - ribs, 493; - skull, 484; - teeth, 441 - - _Coenolestes_, _43_, 424 - - Cement, 5 - - _Centetes_, _49_; - caudal vertebrae, 454; - pelvic symphysis, 515; - spines, 417; - teeth, 440; - thoraco-lumbar vertebrae, 450 - - Centetidae, _49_; - auditory ossicles, 488; - skull, 480 - - Centrale, 27; - see Carpus and Tarsus - - Centre of motion, 448 - - Centrum, 14 - - _Cephalaspis_, _31_, _55_ - - Cephalic shield, armadillos, 419 - - _Cephalochordata_, _30_, 51 - - _Cephalodiscus_, _30_, 50 - - _Ceratodus_, _34_, _70_; - branchial arches, 124; - cranium, =125=; - skeleton, =128=; - skull, 117, 124; - spinal column, 113; - teeth, 111 - - Cerato-branchial, cod, 101; - dogfish, 78; - duck, 320; - salmon, 95 - - Cerato-hyal, 23; - cod, 100; - dog, 399; - dogfish, 78; - salmon, 95 - - _Ceratophrys_, _36_; - bony plates of, 168; - teeth, 170 - - _Ceratops_, _39_; - see _Polyonax_ - - Ceratopsia, _39_; - characters, 209; - premaxillae, 284 - - Ceratopsidae, _39_ - - _Ceratosaurus_, _38_, 208; - supratemporal fossae, 283; - _C. nasicornis_, skeleton, =206= - - Cercopithecidae, _49_, _373_ - - Cervical ribs, crocodile, 260; - reptiles, 285 - - Cervical vertebrae, crocodile, 239; - dog, 380; - duck, 307; - general characters, 15; - mammals, 442; - turtle, 219 - - Cervidae, _46_; - skull, 469 - - _Cervulus_, _46_; - pes, 523 - - _Cervus_, 46; - _C. megaceros_, antlers, 469 - - _Cestracion 32_; - calcification of vertebrae 114; - external branchial arches 121; - pectoral fin 130; - skull =118=; - suspensorium 119; - teeth 109; - vertebral column 114 - - Cestraciontidae _32_ - - Cetacea _44_, 522; - arm bones 501; - auditory ossicles 487; - caudal vertebrae 453; - cervical vertebrae 444; - characters 353; - exoskeleton 416 f.; - hind limb 518; - manus 505; - pectoral girdle 495; - pelvis 514; - position of limbs 28; - ribs 491; - skull 461 f.; - sternum 489; - teeth 426; - thoraco-lumbar vertebrae 448 - - Cetiosauridae _38_ - - _Chalcides_ _38_; - limbs 289 - - Chalicotheriidae _46_; - femur 519; - manus 509 - - _Chalicotherium_ _46_; - femur 360; - pes =508=, 525; - teeth 432 - - _Chamaeleon_ _38_, 199 f.; - epipubis 293; - ilia 291; - manus 291; - skull 278 - - Chamaeleonidae _38_ - - Charadriidae _42_ - - Charadriiformes _42_ - - _Chauna_ _41_; - interorbital septum 333; - ribs 336; - _C. derbiana_, spurs 330 - - _Chelone_ _37_, _194_; - plastron 271, =218=; - see Turtle - - Chelonia _37_; - beaks 271; - carapace 271; - general characters 193; - humerus 290; - limbs 290; - palate 281; - pectoral girdle 288; - pelvic girdle 291; - skull 277 f.; - tarsus 293; - vertebrae 275 f. - - Chelonidae _37_ - - Chelydae _37_ - - _Chelydra_ _37_; - carpus 26, 291 - - Chelydridae _37_ - - _Chelys_ _37_, _195_ - - Chersidae _37_ - - Chevron bones 16; - crocodile 243; - mammals 453 f.; - reptiles 276 - - Chevrotain _45_, _359_; - teeth 429 - - _Chimaera_ _32,_ _66_; - attachment of fins 130; - pelvic girdle 127; - skull =65=; - teeth 110 - - Chimaeridae _32_ - - Chimaeroidei, general characters 65 - - Chimpanzee _49_; - carpus 512; - ribs 493; - thoraco-lumbar vertebrae 450 - - _Chinchilla_ _47_; - auditory ossicles 488 - - Chinchillidae _47_ - - Chiromyidae _49_ - - _Chiromys_ _49,_ _372_; - manus 512; - pes 527; - teeth 441 - - Chiroptera _49_; - auditory ossicles 488; - arm bones 503; - cervical vertebrae 446; - general characters 370; - manus 512; - pelvis 515; - pes 527; - sacrum 452; - shoulder girdle 499; - skull 481; - sternum 490; - tail 454; - teeth 440; - thigh and shin 520; - thoraco-lumbar vertebrae 450 - - _Chirotes_ _38_; - limbs 289 - - _Chlamydophorus_ _44,_ _272_; - scutes 419; - skull 459 - - _Chlamydoselache_ _31_; - branchial arches 121 - - _Choeropus_ _43_; - manus 504; - pes 522 - - _Choloepus_ _43_; - ribs 491; - shifting of pelvis 451; - skull =458=; - sternum 489; - thoraco-lumbar vertebrae 447; - _C. hoffmanni_ cervical vertebrae 443 - - Chondrocranium, salmon 87 - - Chondroid tissue, _Balanoglossus_ 50 - - Chondrostei _32_; - fins 105; - general characters 67; - teeth 110; - see Cartilaginous ganoids - - Chordal sheath, _Amphioxus_ 52 - - Chrysochloridae _49_ - - _Chrysochloris_ _49_; - auditory ossicles 488; - claws 418; - teeth 440 - - _Ciconia_ _41_; - see Stork - - Ciconiiformes _41_ - - Cingulum 376 - - Civet _48,_ _369_; - teeth 437 - - _Cladoselache_ _31,_ _63_; fin 129 - - Clasper 132; - dogfish 82 - - Clavicle 25; - birds 338; - cod 102; - duck 322; - dog 405; - fish 126; - frog 163; - mammals 494 f.; - reptiles 289 - - Claws 3; - birds 330; - crocodile 237; - dog 374; - duck 302; - mammals 417; - turtle 215 - - Clupeidae, _33_ - - _Clupeus_, _33_ - - Cnemial crest, dog, 412; - duck, 326 - - _Coccosteus_, _34_, _70_ - - Coccyx, man, 454 - - Cochliodontidae, _31_ - - _Cochliodus_, _31_; - dental plates, 109 - - Cod, _33_; - appendicular skeleton, 101 f.; - cranium, 96; - mandibular and hyoid arches, =99=; - median fins, 86; - pectoral girdle and fin, =102=; - ribs, 86; - skull, 96 f.; - vertebral column, 83 f. - - _Coelogenys_, _48_; - zygomatic arch, 477 - - _Coenolestes_, _43_, 424 - - Coffer-fish, _33_; - see, _Ostracion_ - - _Colobus_, _49_; - pollex, 512 - - Colubridae, _38_ - - Columbae, _42_ - - Columbidae, _42_ - - Columella, crocodile, 251; - duck, 320; - frog, 157; - turtle, 228 - - Columella cranii, 200 n; - see epipterygoid - - Colymbi, _40_ - - Colymbiformes, _40_ - - Compsognathidae, _38_ - - _Compsognathus_, _38_, 208 - - Condylar ridge, duck, 326 - - Condyle of humerus, dog, 406; - of mandible, dog, 398 - - Condylarthra, _47_; - femur, 519; - general characters, 361; - manus, 509; - skull, 472; - teeth, 432 - - Contour feather, duck, 303 - - Copula, 23 - - _Coracias_, _42_; - see Roller - - Coraciae, _42_ - - Coraciiformes, _42_ - - Coracoid, 25; - cod, 103; - crocodile, 263; - duck, 322; - frog, 163; - Monotremata, 493; - newt, 147; - reptiles, 288; - turtle, 232 - - Coracoid groove, duck, 321 - - Cormorant, _41_; - foot, 342; - skull, 335 - - Cornu, see hyoid - - Cornua trabeculae, 18 - - _Coryphodon_, _47_; - femur, 519; - manus, 510; - pes, 525; - skull, 473; - teeth, 433; - _C. hamatus_, manus, =510= - - Coryphodontidae, _47_ - - Costal plate, turtle, 215; - -- process, duck, 321; - -- shield, turtle, 214 - - Cotyloid bone, 25, 513; - see Acetabular bone - - Cotylopidae, _45_ - - _Cotylops_, _45_; - pollex, 506; - skull, 468 - - Coverts, 306, 328 - - Cranium, 18; - cod, 96 f.; - crocodile, 244 f.; - development of, 16 f.; - dog, 384 f.; - dogfish, 73 f.; - duck, 314; - frog, 154 f.; - newt, 140 f.; - turtle, 222 f. - - Cranio-facial axis, dog, 384 - - Creodonta, _48_; - carpus, 512; - femur, 520; - general characters, 368; - skull, 479; - teeth, 439 - - Cribriform plate, dog, 388, 400 - - Crocodile, _210_, _212_; - anterior limb, 263; - exoskeleton, 237; - pectoral girdle, 262; - pelvic girdle, 266; - posterior limb, 268; - ribs and sternum, 259; - skeleton, 237 f.; - skull, 243 f.; - tarsus, 293; - teeth, 238; - vacuities in surface of cranium, 256; - vertebral column, 239 - - Crocodilia, _39_; - general characters of, 210; - palate, 281; - skull, 277 f.; - succession of teeth, 274; - teeth, 273 - - Crocodilidae, _39_ - - _Crocodilus_, _39_; - _C. palustris_, sternum and associated bones, =261=; - late thoracic and first sacral vertebrae, =242=; - _C. vulgaris_, cervical vertebrae, =239= - - Crossopterygii, _33_; - general characters, 68 - - Crotalidae, _38_ - - _Crotalus_, _38_; - jaws 280; - see Rattlesnake - - Crows, _42_ - - Crura of stapes, dog, 393 - - Cruro-tarsal, ankle joint, 345 - - Crus, 26; - crocodile, 268; - dog, 412; - duck, 326; - frog, 166; - newt, 149; - turtle, 235 - - Crusta petrosa, 5 - - _Cryptobranchus_, _35_, 135; - skull, 175; - _C. lateralis_, sacral vertebrae, 171 - - Cryptodira, _37_; - characters, 194 - - Ctenoid scales, 8, 60, 105 - - Cubitals, 303 f. - - Cuboid, 27; - dog, 415 - - Cuckoo, foot, 342 - - Cuculi, _42_ - - Cuculiformes, _42_ - - Cuneiform bones, 27; - dog, 414 f. - - _Cyclodus_, _38_; - see _Tiliqua_ - - Cycloid scales, 8, 60, 105; - cod, 83 - - _Cyclopidius_, _45_; - skull, 468 - - Cyclospondyli, 114 - - Cyclostomata, _31_; - general characters, 53 - - _Cycloturus_, _44_; - hallux, 522; - manus, 505 - - _Cygnus_, _41_; - see Swan - - _Cynocephalus_, _49_; - cervical vertebrae, 446; - skull, 482 - - Cynoidea, _48_, _369_; - dental formula, 437 - - _Cynognathus_, _36_; - occipital condyle, 277; - teeth, 273 - - Cyprinidae, _33_ - - _Cyprinus_, _33_; - see Carp - - Cypseli, _42_ - - Cypselidae, _42_; - see Swifts - - Cystignathidae, _36_ - - - _Dactylopterus_, _34_; - pectoral fins, 131 - - Dasypodidae, _44_ - - _Dasyprocta_, _48_; - auditory ossicles, 488; - thoraco-lumbar vertebrae, 450 - - Dasyproctidae, _48_ - - _Dasypus_, _44_; - manus, 505; - skull, 459; - stapes, 487; - teeth, 424 - - Dasyuridae, _43_, _350_; - dentition, 423; - pes, 521; - skull, 456 - - Deer, _359_; - manus, 507; - pes, 523; - Chinese water --, _46_, - see _Hydropotes_; - Musk --, _46_, - see _Moschus_; - Red -- fibula, 519 - - Delphinidae, _45_ - - _Delphinus_, _45_, 357; - lumbar vertebrae, 448; - skull, 462 f. - - Deltoid ridge, crocodile, 263; - dog, 406; - frog, 164 - - _Dendrohyrax_, 363 - - Dental formula, regular, 344, 422; - Anthropoidea, 441; - _Astrapotherium_, 432; - _Babirussa_, 428; - Camel, 428; - _Chiromys_, 441; - Chiroptera (many), 440; - Cynoidea, 437; - _Dinotherium_, 434; - Dog, 376; - Duplicidentata, 435; - _Elephas_, 434; - _Erinaceus_, 440; - _Felis_, 437; - _Galeopithecus_, 440; - _Hippopotamus_, 427; - Horse, 430; - _Hydromys_, 436; - Hyracoidea, 362; - Macropodidae, 423; - _Manatus_, 425; - _Notoryctes_, 423; - _Otaria_, 439; - _Procavia_, 432; - _Pteropus_, 441; - Rodentia (most), 435; - Ruminantia, 429; - _Squalodon_, 427; - _Sus_, 428; - Tapiridae, 429; - _Thylacinus_, 423; - _Uintatherium_, 433; - _Ursus_, 439; - _Zeuglodon_, 426 - - Dentary, 22; - crocodile, 258; - cod, 100; - duck, 320; - frog, 161; - newt, 144; - salmon, 94; - turtle, 230 - - Dentine, 5 - - Derbian Screamer, spurs, 330 - - Dermal exoskeleton, crocodile, 237; - fish, 105; - mammals, 419; - reptiles, 271; - turtle, 215 - - Dermo-supra-occipital, Labyrinthodontia, 177; - _Polypterus_, 122 - - Dermochelydidae, _37_ - - _Dermochelys_, _37_, _194_, 214, 270; - carapace and plastron, 272 - - Dermoptera, _48_; - general characters, 370 - - Derotremata, _35_ - - _Desmodus_, _49_; - teeth, 441 - - Desmognathous, 319, 335 - - Development of bone, 10; - of cranium, 16; - of teeth, 7 - - _Dicynodon_, _36_, _192_; - beak, 271; - supratemporal fossa, 283; - teeth, 273 - - Didelphia, _43_; - general characters, 349 - - Didelphyidae, _43_, _350_; - auditory ossicles, 486; - pes, 521; - teeth, 423 - - _Didelphys_, _43_; - atlas, 443; - teeth, 422 - - _Didus_, _42_; - see Dodo - - Digitigrade, defined, 358 n. - - Digits, _26_; - see Manus and Pes - - _Dimetrodon_, _36_; - thoracic vertebrae, 276 - - _Dinichthys_, _34_, _70_ - - Dinocerata, 364; - see Uintatheriidae - - Dinornithes, _40_, _299_; - see Moas - - Dinosauria, _38_; - general characters, 204; - humerus, 290; - ischium, 291; - pectoral girdle, 288; - pes, 293; - pre-orbital vacuity, 284; - ribs, 285; - vertebrae, 275 f. - - Dinotheriidae, _47_ - - _Dinotherium_, _47_, 365; - dental formula, 434; - teeth, 345 - - _Diodon_, _33_; - beaks, 111; - _D. hystrix_, scales, 105 - - Diphycercal tail, 60, 116 - - Diphyodont, defined, 7, 344 - - _Diplacanthus_, _32_, _64_ - - Dipneumona, _34_ - - Dipnoi, _34_; - general characters, 69; - pelvic fins, 131; - skull, 124; - spinal column, 113; - tail, 116; - teeth, 111 - - Dipodidae, _47_ - - Diprotodont, 423 - - Diprotodontia, _43_; - characters, 350 - - Dipteridae, _34_, _70_; - cranium, 124; - tail, 117; - teeth, 111 - - _Dipus_, _47_; - cervical vertebrae, 446; - pes, 526 - - Discoglossidae, _36_ - - _Discoglossus_, _36_; - ribs, 182; - vertebrae, 172 - - Distal, defined, 23 n. - - Divers, _40_; - thoracic vertebrae, 332 - - _Docidophryne_, _36_; - shoulder girdle and sternum, =183= - - Dodo, _42_; - wing, 338 - - Dog, _48_; - arm bones, =407=; - anterior limb, 405; - atlas and axis, =379=; - cranium, 384, =389=, =396=; - dentition, =375=; - innominate bone, =410=; - leg bones, =411=; - manus, 408, =413=, 511; - pectoral girdle, 404; - pelvic girdle, 409; - pes, =413=, 414; - posterior limb, 412; - ribs, 402; - second lumbar vertebra, =382=; - second thoracic vertebra, =382=; - skull, 383, =387=; - sternum, =403=, 404; - vertebral column, 378 - - Dogfish, _64_; - cranium, 73; - exoskeleton, 71; - median fins, 79; - pectoral girdle and fin, 79; - pelvic girdle, 81; - pelvic fin, 81; - ribs, 73; - skull, 73, =75=; - vertebral column, 72; - visceral skeleton, 77; - Spotted and Spiny --, _32_ - - Dolphin, _45_, _357_; - lumbar vertebrae, 448; - Gangetic --, _45_, - see _Platanista_ - - Donkey, skull, =431= - - _Dorcatherium_, _45_; - manus, 507 - - Dorsal vertebra, 16 - - Dorsal shield, crocodile, 238 - - Down feathers, 306 - - _Draco_, _38_; - ribs, 286 - - Dromaeognathous, 335 - - _Dromaeus_, _40_, _299_; - see Emeu - - Duck, _41_, 334; - beak, 329; - claws, 330; - cranium, =313=; - exoskeleton, 302; - pectoral girdle, 321; - pelvic girdle, 324, =311=, =325=; - pes, 327; - posterior limb, 326; - ribs, 320; - skull, 312, =312=, =313=; - sternum, 321; - vertebral column, 307; - wing, 322, =304=, =305= - - Duckbill, _43_; - see _Ornithorhynchus_ - - Dugong, _44_; - humerus, 501; - pelvis, 514; - thoraco-lumbar vertebrae, 448; - see _Halicore_ - - Duplicidentata, _48_, 366; - dental formula, 435; - skull, 478 - - - Eagles, 335 - - Eared Seals, _369_; - scapula, 498; - see Otariidae - - _Echidna_, _43_; - caudal vertebrae, 453; - manus, 504; - pelvis, 513; - sacral vertebrae, 451; - shoulder-girdle and sternum, =494=; - skull, 455; - spines, 417; - spur, 418; - thoraco-lumbar vertebrae, 447 - - Echidnidae, _43_; - pes, 521 - - Ectethmoid, 21 n. - - Ectocondylar ridge, dog, 406 - - Edentata, _43_; - auditory ossicles, 487; - arm bones, 500; - caudal vertebrae, 453; - cervical vertebrae, 443; - manus, 504; - pectoral girdle, 495; - pes, 522; - pelvis, 513; - ribs, 491; - sacrum, 452; - skull, 457; - sternum, 489; - teeth, 424; - thigh and shin, 517; - thoraco-lumbar vertebrae, 447 - - Eel, _33_; - scales, 105 - - Elasmobranchii, _31_; - cranium, 118 f.; - clasper, 132; - general characters, 61; - pelvic fins, 131; - ribs, 125; - teeth, 109; - vertebral column, 113 f.; - visceral arches, 120 - - _Elasmotherium_, _46_; - mesethmoid, 470 - - Elephant, _47_; - auditory ossicles, 487; - caudal vertebrae, 453; - ribs, 491; - skull, 473 f., =474= and =475=; - tusks, 420; - see also Proboscidea - - Elephantidae, _47_ - - _Elephas_, _47_, _364_; - dental formula, 434; - _E. planifrons_, 435; - see Elephant - - _Elginia_, _36_; - skull, 191, 283 - - Embolomerous, 172 - - Emeu, _40_, _299_; - aftershaft, 328; - claws, 330 - - Enamel, 4; - -- cap, 7; - -- organ, 7 - - Endochondral ossification, 11 - - Endoskeleton, Amphibia, 170; - birds, 331 f.; - cod, 83 f.; - crocodile 239, f.; - dog, 377 f.; - dogfish, 71 f.; - duck, 306 f.; - fish, 112 f.; - frog, 151 f.; - mammals, 442 f.; - newt, 138 f.; - reptiles, 275 f.; - turtle, 218 f. - - Engystomatidae, _36_ - - Entoplastron, turtle, 217 - - Epanorthidae, _43_, _350_ - - Epi-branchial, cod, 101; - dogfish, 78; - salmon, 94 - - Epicoracoid, 25; - frog, 163; - turtle, 232; - Monotremes, 493; - vestiges of in Rodentia, 497 - - _Epicrium_, _35_; - orbit, 179 - - Epidermal exoskeleton, birds, 328; - crocodile, 237; - dog, 374; - duck, 302; - mammals, 416; - reptiles, 270; - turtle, 214 - - Epi-hyal, cod, 100; - dog, 399; - salmon, 94 - - Epi-otic, 20; - cod, 96; - crocodile, 250; - Labyrinthodontia, 177; - reptiles, 278; - salmon, 89; - turtle, 227 - - Epiphysis, 11 - - Epiplastron, turtle, 217 - - Epiprecoracoid, Amphibia, 184; - turtle, 232 - - Epipterygoid, Lacertilia, 200; - reptiles, 278 - - Epipubis, crocodile, 267; - newt, 149; - turtle, 235 - - Episternum, 217; - frog, 163 - - Equidae, _46_; - mane, 416; - scapula, 496; - skull, 471 - - _Equus_, _46_; - see Horse - - Erinaceidae, _49_ - - _Erinaceus_, _49_; - dental formula, 440; - pelvic symphysis, 515; - presternum, 490; - see Hedgehog - - Esocidae, _33_ - - Esox, _33_; - attachment of teeth, 107 - - Ethmoid, 394; - see median ethmoid - - Ethmoidal plane, 390; - -- region, 21 - - Ethmo-palatine ligament, dogfish, 77 - - Ethmo-turbinal, dog, 395 - - _Euchirosaurus_, _35_; - vertebrae, 171 - - Eustachian canal, see Canal - - Eusuchia, _39_; - general characters, 212 - - Eutheria, _43_; - general characters, 351 - - _Exocaetus_, _33_; - pectoral fins, 131 - - Exoccipital, 19; - cod, 97; - crocodile, 246; - dog, 386; - duck, 314; - frog, 154; - newt, 141; - salmon, 89; - turtle, 224 - - Exoskeleton, 2; - Amphibia, 168; - birds, 328; - crocodile, 237; - dog, 374; - dogfish, 71; - duck, 302; - fish, 104; - ganoids, 66; - mammals, 442; - reptiles, 270; - turtle, 214 - - Extensor side, defined, 29 - - Extra-branchial, dogfish, 79 - - Extra-columella, crocodile, 251; - turtle, 228 - - - Fabella, dog, 412 - - _Falco_, _41_ - - Falcon _41_, 335 - - Falconiformes, _41_ - - Feathers, 3, 328; - duck, 302 - - Felidae, _48_; - claws, 418 - - _Felis_, _48_; - dental formula, 437; - thoraco-lumbar vertebrae, 450 - - Femoral shield, turtle, 215 - - Femur, 26; - crocodile, 268; - dog, 412; - duck, 326; - frog, 166; - mammals, 517 f.; - newt, 149; - ox and rhinoceros, =518=; - turtle, 235 - - Fenestra ovalis, crocodile, 250 f.; - dog, 392; - duck, 316; - frog, 157; - turtle, 228; - -- rotunda, dog, 392; - duck, 316 - - Fenestral recess, duck, 316 - - Fibula, 26; - crocodile, 268; - dog, 412; - duck, 327; - frog, 166; - newt, 149; - turtle, 235 - - Fibulare, 27; - see Tarsus - - File-fish, _33_; - see _Balistes_ - - Filoplume, 306 - - Finches, _42_ - - Fins, fish, 115; - caudal --, Cetacea, 453; - cod, 87; - fish, 116; - Ichthyosauria, 195; - median --, cod, 86; - dogfish, 79; - pectoral --, cod, 103; - dogfish, 79; - pelvic --, cod, 103; - dogfish, 81 - - Fin-rays, 105, 115; - cod, 83, 103; - dogfish, 79 - - Firmisternia, _36_, 185 - - Fish, appendicular skeleton, 126; - endoskeleton, 112 f.; - exoskeleton, 104; - general characters, 60 f.; - paired fins, 127 f.; - ribs, 125 f.; - skull, 117 f.; - spinal column, 112 f.; - teeth, 106 f. - - Fissipedia, _48_; - general characters, 368 - - Flamingo, 335 - - Flexor side, defined, 29 - - Floating ribs, dog, 402; - mammals, 490 - - Flower, Sir W.H., on succession of teeth in elephants, 434 - - Flying-fish, _33_; - -- fox, _49_, _371_, - skull, 481, - see _Pteropus_; - -- gurnard, _34_, - see _Dactylopterus_; - -- lemur, _48_, - see _Galeopithecus_; - -- lizard, _38_, - see _Draco_ - - Fontanelle, salmon, 89; - anterior --, dogfish, 74; - frog, 154; - posterior --, frog, 154 - - Foot, crocodile, 269; - dog, 414; - frog, 167; - newt, 149 f.; - turtle, 236 - - Foramen: - anterior palatine --, dog, 401; - condylar --, dog, 401; - -- cordiforme, reptiles, 292; - ect-epicondylar --, _Sphenodon_, 290; - ent-epicondylar --, 191 n.; - Carnivora vera, 502; - Cebidae, 503; - _Choloepus_, 500; - Condylarthra, 362, 502; - Creodonta, 368; - Insectivora, 503; - Lemurs, 503; - Marsupials, 500; - reptiles, 290; - external mandibular --, crocodile, 258; - inferior dental --, dog, 399; - infra-orbital --, dog, 401; - Rodents, 477; - ilio-sciatic --, duck, 325; - internal mandibular --, crocodile, 258; - internal orbital --, dog, 401; - interparietal --, Labyrinthodontia, 173, 177; - reptiles, 277; - -- lacerum anterius, dog, 388, 400; - -- lacerum medium, dog, 402; - -- lacerum posterius, dog, 392, 401; - lachrymal --, dog, 394, 401; - -- magnum, cod, 97; - crocodile, 257; - dog, 386, 402; - dogfish, 76; - duck, 314; - frog, 154; - newt, 141; - salmon, 89; - turtle, 224; - mental --, dog, 399; - obturator --, duck, 326; - dog, 410; - ophthalmic --, dogfish, 74; - optic --, dog, 400; - dogfish, 74; - orbitonasal --, dogfish, 74; - -- ovale, crocodile, 249; - dog, 400; - pneumatic --, duck, 323; - pneumogastric --, dogfish, 76; - posterior palatine --, dog, 401; - postglenoid --, dog, 402; - pre-acetabular --, Chiroptera, 515; - -- rotundum, dog, 400; - stylomastoid --, dog, 392 f., 400; - thyroid --, dog, 410; - trigeminal --, duck, 316; - -- triosseum, duck, 322 - - Fore-arm, 26; - crocodile, 265; - dog, 406; - duck, 323; - frog, 164; - newt, 147; - turtle, 233 - - Fossa: - cerebellar --, dog, 392; - cerebral --, dog, 392; - digital --, dog, 412; - floccular --, dog, 392; - infratemporal --, see lateral temporal --; - lachrymal --, Ruminants, 469; - lateral temporal --, crocodile, 257; - _Sphenodon_, 283; - olecranon --, dog, 406; - prescapular --, dog, 405; - postscapular --, dog, 405; - post-temporal --, _Sphenodon_, 283; - pterygoid --, crocodile, 257; - suborbital --, Ruminants, 469; - supra-acetabular --, Ruminants, 514; - supratemporal --, crocodile, 249, 256; - reptiles, 283; - supra-trochlear --, dog, 406; - temporal --, dog, 398; - trochanteric --, dog, 412 - - Fowl, _41_, 335; - claws, 330; - skeleton, =301= - - Fox, _48_ - - Frigate bird, _41_; - clavicles, 338 - - Frog, anterior limb, 164; - cranium, =155=, =157=; - hyoid apparatus, 161; - pelvic girdle, 165; - posterior limb, 166; - shoulder-girdle and sternum, =183=; - skull, 154 f., =155=, =159=; - teeth, 151; - vertebral column, 152; - Common --, Edible --, Fire-bellied --, Green-tree --, - Horned --, Midwife --, Painted -- and Toad --, _36_; - - Frontal, 19; - cod, 96; - crocodile, 249; - dog, 388; - duck, 314; - newt, 141; - salmon, 91; - turtle, 225; - -- segment, crocodile, 249; - dog, 388; - turtle, 225 - - Fronto-parietal, frog, 156 - - Frugivorous bats, manus 512; - see Pteropidae - - Fulcra 67; - _Polypterus_ 106 - - Furcula 296; duck 322 - - - Gadidae _33_ - - _Gadus_ _33_; - see Cod - - Galeopithecidae _48_ - - _Galeopithecus_ _48_, _370_; - dental formula 440; - inter centra 450; - pelvic symphysis 515; - skull 480 - - _Galesaurus_ _36_, _192_; teeth 273 - - _Galeus_, _32_; - occipital joint 118 - - Galli _41_ - - Galliformes _41_ - - _Gallus_ _41_; - _G. bankiva_ skeleton =301= - - Gannet, _41_; wing =339= - - Ganoid scales 8, 60, 104 - - Ganoidei _32_; - general characters and distribution 66; - pectoral girdle 126; - pelvic fins 132; - teeth 110; - skull 121 f.; - spinal column 112 and 114 - - Garialidae _39_ - - _Garialis_ _39_, _212_ - - Garial 210 - - Gar pike 33; - see _Lepidosteus_ - - _Gavialis_ _39_ - - _Gazella_ _46_ - - Gazelle _46_; - skull 468 - - Geckonidae _37_; - see Gecko - - Gecko _37_; - epipubis 293; - parietals 277; - supratemporal fossa 283; - vertebrae 275 - - Gibbon _49_; - ribs 493; - skull 482 - - Gill-rays, dogfish 78; - salmon 95 - - _Giraffa_ _46_ - - Giraffe _46_, _359_; - cervical vertebrae 445; - manus 507; - pes 523; - ulna 501 - - Giraffidae _46_; skull 469 - - Girdle bone, frog 156 - - Glenoid cavity 25; - crocodile 263; - dog 405; - duck 322; - frog 162; - newt 146; - turtle 232; - --fossa, dog 394 - - Globe-fish _33_ - - _Globicephalus_ _45_; - cervical vertebrae 354; - manus 506; - skull 463 - - Gluteal surface of ilium, dog 410 - - _Glyptodon_ _44_; - carapace 419; - cervical vertebrae 443; - caudal vertebrae 453; - manus 505; - pelvis 513; - pes 522; - teeth 425; - thoraco-lumbar vertebrae 447 - - Glyptodontidae _44_, _352_; - skull 459; - see also _Glyptodon_ - - Gnathostomata _31_, _59_ - - Golden mole _49_; - see Chrysochloris - - Goniopholidae _39_ - - _Goniopholis_ _39_; - vertebrae 275 - - Goose 334; - beak 329; - Spur-winged--41 - - _Gorilla_ _49_; - carpus 512; - ribs 493; - scapula 499; - skull =483=; - thoraco-lumbar vertebrae 450 - - Gruidae _41_; - see Cranes - - Gruiformes _41_ - - Guinea-pig _48_; - tail 454 - - Gular shield, turtle 215 - - Gulls _42_, 335; - aftershaft 328 - - Gymnodontidae _33_; - beaks 111 - - Gymnophiona _35_; - branchial arches 180; - general characters 136; - ribs 182; - scales 168; - skull 177; - teeth 169; - vertebrae 172 - - _Gymnura_ _49_; - teeth 440; - zygomatic arch 481 - - _Gypogeranus_ _41_; - claws 330 - - _Gyrinophilus_ _35_; - vertebral column 171 - - - Haddock _33_ - - Hadrosauridae _39_ - - _Hadrosaurus_ _39_; - skull 284 - - Hag or hag-fish _31_, 54 f. - - Hair 3; - dog 374; - mammals 416 - - _Halicore_ _44_, _352_; - manus 505; - skull 460; - teeth 425; - see Dugong - - Halicoridae _44_ - - Halitheriidae _44_ - - _Halitherium_ _44_, 352; - femur 518; - pelvis 514; - teeth 425 - - Hallux 26; - dog 415; - duck 327; - frog 167 - - Hamular process, dog 397 - - Hand, crocodile 266; - dog 408 f.; - duck 324; - frog 165; - newt 147; - turtle 233 - - _Hapale_ _49_ - - Hapalidae _49_, 372 f.; - teeth 441 - - Hare _48_, 366; - acetabular bone 515; - dental formula 435; - femur 520; - humerus 502; - pelvis 515; - scapula 497; - skull 476; - tail 454; - thoraco-lumbar vertebrae 449; - Cape jumping --, _47_; - see _Pedetes_ - - _Harpagus_, _41_; - serrated beak, 334 - - _Harriotta_, _32_, _66_ - - _Hatteria_, _37_, _197_; - see _Sphenodon_ - - Haversian canals, 10; - -- system, 10 - - Hawks, beak of, 330 - - Hedgehog, _49_, _370_; - auditory ossicles, 488; - humerus, 503; - presternum, 490; - skull, 480; - spines, 417; - see _Erinaceus_ - - Hemichordata, _30_, _50_ - - _Heptanchus_, _31_; - branchial arches, 63, =120=; - vertebrae, 114 - - Herbivorous dentition, 427, 430 - - Heron, _41_, 335; - interorbital septum, 333; - powder down feathers, 329 - - Herring, _33_ - - _Hesperornis_, _40_, _299_; - caudal vertebrae, 333; - clavicles, 338; - teeth, 330; - wing, 338 - - Heterocercal tail, 60, 116 - - Heterodont, 7 - - Heterostraci, _31_; - general character, 54 - - _Hexanchus_, _31_; - branchial arches, 63, 121 - - Hinge joint, 13 - - _Hipparion_, _46_; - manus, 508; - pes, =524= - - Hippopotamidae, _45_ - - _Hippopotamus_, _45_, _359_; - dental formula, 427; - hair, 416; - mandible, 467; - manus, 506; - pes, 523; - scapula, 496; - skull, 467; - teeth, 345 - - Hoatzin, _41_; - see _Opisthocomus_ - - Holocephali, _32_, 65, 104; - clasper, 132; - spinal column, 113; - tail, 116; - teeth, 109 - - Holoptychiidae, _33_ - - _Holoptychius_, _33_; - scales, 105 - - Holostei, _33_; - general characters, 68; - teeth, 110; - see Bony Ganoids - - Hominidae, _49_, _373_ - - _Homo_, _49_; - see Man - - Homocercal tail, 60, 69, 117; - codfish, 87 - - Homodont, defined, 7 - - Hoofs, 3, 418 - - Hoopoe, _42_, 335 - - _Hoplopterus_, spur, 330 - - Hornbill, _42_, 331; - bony crest, 334; - interorbital septum, 333 - - Horns, 3, 417 - - Horny plates on palate, 418; - -- teeth, Lampreys, 4; - Myxinoids, 57; - _Ornithorhynchus_, 4 - - Horse, _46_, _360_; - fibula, 519; - malleus, 487; - manus, 507; - pes, =524=; - skull, 471; - teeth, 345, 430; - ulna, 501 - - Howling monkey, _49_; - see _Mycetes_ - - Humerals, duck, 303 f. - - Humeral shield, turtle, 215 - - Humerus, 26; - crocodile, 263; - dog, 405; - duck, 323; - frog, 164; - newt, 147; - turtle, 232; - wombat, =500= - - Humming-birds, _42_, 335 - - Humpbacked whale, _44_, _357_ - - _Hyaena_, _48_, _369_; - hallux, 526; - pollex, 511; - sacral vertebrae, 452; - teeth, 437 - - Hyaenidae, _48_; - humerus, 502 - - _Hyaenodon_, _48_, _368_ - - Hyaenodontidae, _48_ - - Hyaline cartilage, 10 - - _Hydrochaerus_, _48_; - teeth, 437; - see Capybara - - _Hydromys_, _47_; - dental formula, 436 - - Hydrophidae, _38_; - scales, 270 - - _Hydropotes_, _46_; - canines, 429 - - _Hyla_, _36_; - fronto-parietal fontanelle, 179; - sternum, 184 - - Hylidae, _36_ - - _Hylobates_, _49_; - ribs, 493; - skull, 482 - - Hyoid, 21; - alligator, =285=; - Amphibia, 180; - birds, 336; - cod, 100; - crocodile, 259; - dogfish, 77; - dog, 399; - duck, 320; - frog, 161; - newt, 144; - reptiles, 284; - salmon, 94; - turtle, 231, =285= - - Hyomandibular, 23; - cod, 100; - dogfish, 78; - salmon, 94 - - _Hyomoschus_, _45_ - - Hyoplastron, turtle, 217 - - Hyostylic, 61, 119 - - _Hyotherium_, _45_; - teeth, 427 - - _Hyperodapedon_, _37_, _198_; - premaxillae, 284 - - _Hyperoödon_, _44_; - skull, 464; - sternum, 489; - thoracic vertebrae, 448 - - Hypo-branchial, cod, 101; - dogfish, 78 - - Hypo-hyal, cod, 100; - salmon, 95 - - Hypo-ischium, Lacertilia, 292 - - Hypoplastron, turtle, 217 - - Hyporachis, 328 - - _Hypsilophodon_, _39_; - predentary bone, 284 - - Hypsodont, defined, 345, 429 - - Hypural bone, cod, 85 - - Hyracidae, _47_ - - Hyracoidea, _47_; - femur, 519; - general characters, 362; - manus, 510; - nails, 418; - skull, 472; - teeth, 432 - - _Hyracotherium_, _46_; - manus, 508; - scapula, 496 - - _Hyrax_, _47_, _363_; - see _Procavia_ - - Hystricidae, _47_ - - Hystricomorpha, _47_; - auditory ossicles, 488 - - _Hystrix_, _47_; - auditory ossicles, 488; - see Porcupine - - - Ichthyodorulites, 106 - - Ichthyoidea, _35_; - general characters, 134 - - Ichthyopsida, _31_; - general characters, 59 - - Ichthyopterygium, 130 - - _Ichthyornis_, _40_; - mandible, 335; - pelvis, 341; - teeth, 330; - vertebrae, 332 - - Ichthyornithiformes, _40_, 300 - - Ichthyosauria, _37_; - general characters, 195; - ribs, 285 - - Ichthyosauridae, _37_ - - _Ichthyosaurus_, _37_, _197_; - limbs, 290; - palatines, 281; - pectoral girdle, 288; - position of limbs, 28; - skull, =196=; - teeth, 273; - vertebral column, 275 - - Ichthyotomi, _31_; - general characters, 62; - fins, 130 f.; - tail, 116 - - _Iguana_, _38_; - teeth, 273 - - Iguanidae, _38_; - zygosphenes, 200, 276 - - _Iguanodon_, _39_, 208 f.; - jaws, 292; - predentary, 284; - sternum, 288; - teeth, 272 f.; - vertebrae, 275 - - Iguanodontidae, _39_ - - Iliac surface of ilium, dog, 410 - - Ilium, 25; - crocodile, 266; - dog, 409; - duck, 325; - frog, 165; - mammals, 513 f.; - newt, 149; - reptiles, 291; - turtle, 235 - - Incisors, dog, 376 f.; - mammals, 344 - - Incus, dog, 393; - man, dog and rabbit, =485= - - Infra-marginal shield, turtle, 215 - - Infra-pharyngeal bone, cod, 101 - - _Inia_, _45_; - cervical vertebrae, 444; - lumbar vertebrae, 448 - - Innominate bone, dog, 409; - mammals, 513 - - Insectivora, _48_; - arm bones, 503; - auditory ossicles, 488; - cervical vertebrae, 446; - general characters, 369 f.; - manus, 512; - pelvis, 515; - pes, 527; - sacrum, 452; - shoulder-girdle, 499; - skull, 480; - sternum, 490; - tail, 454; - teeth, 440; - thigh and shin, 520; - thoraco-lumbar vertebrae, 450 - - Insectivora vera, _49_; - general characters, 370 - - inter centra, 15; - _Galeopithecus_, 370; - Ichthyosauria, 195; - Labyrinthodontia, 172; - _Sphenodon_, 198; - _Talpa_, 450 - - Interclavicle, 25; - crocodile, 263; - Monotremata, 494; - reptiles, 289 - - Intercondylar notch, dog, 412 - - Intergular shield, turtle, 215 - - Interhyal, cod, 100 - - Intermedium, 27; - see Carpus and Tarsus - - Intermuscular bones, cod, 86 - - Internasal septum, dogfish, 76 - - Interorbital septum, birds, 333; - crocodile, 247; - duck, 317; - reptiles, 277 - - Interspinous bones, cod, 86 - - Intertarsal ankle joint, 190 - - Intervertebral discs, 15, 378 - - Ischial tuberosity, dog, 411 - - Ischium, 25; - crocodile, 266; - dog, 410; - duck, 325; - frog, 165; - newt, 149; - turtle, 235 - - _Ischyodus_, _32_, _66_ - - Ivory, 5 - - - Jacana, _42_; - see _Parra_ - - _Jacare_, _39_; - scutes, 271 - - Jaws, 21; - cod, 98 f.; - crocodile, 252 f.; - dog, 395 f.; - dogfish, 77; - duck, 317 f.; - frog, 158 f.; - newt, 143 f.; - salmon, 93 f.; - turtle, 229 f. - - Jerboa, _47_; - cervical vertebrae, 446; - pes, 526 - - Joints, kinds of, 13 - - Jugal, 22; - crocodile, 255; - dog, 398; - duck, 318; - turtle, 229 - - Jugulares, 132 - - - Kangaroo, _43_; - dental formula, 423; - lumbar vertebrae, 447; - pectineal process, 513; - pes, 522; - tail, 453; - teeth, 345 - - Kestrel, claws, 330 - - Killer, _45_; - see _Orca_ - - Kiwi, _40_; - see _Apteryx_ - - Knee-cap, see patella - - Koala, _43_; - lumbar vertebrae, 447; - pes, 522; - tail, 453 - - Kükenthal, W., on teeth of Cetacea, 426; - on teeth of Marsupials, 422 - - - Labial cartilage, dogfish, 77; - _Squatina_, 119 - - Labridae, _33_ - - _Labrus_, _33_; - see Wrasse - - Labyrinthodontia, _35_; - buckler, 168; - general characters, 135; - interparietal foramen, 173; - pelvis, 187; - ribs, 182; - skull, 176; - teeth, 169 - - Lacertilia, _37_; - general characters, 199; - pectoral girdle, 288; - skull, 277; - vertebrae, 275 - - Lachrymal, 20; - cod, 97; - crocodile, 251; - dog, 394; - duck, 317; - salmon, 93 - - Lacunae, 10 - - _Lagenorhynchus_, _45_; - skull, 462 - - _Lagostomus_, _47_; - maxillae, 477 - - Lambdoidal crest, duck, 315 - - Lamella of malleus, dog, 393 - - Lamnidae, _32_ - - Lamprey, _31_, 55 f. - - Lancelet, _30_; - see _Amphioxus_ - - Laridae, _42_; - see Gulls - - Larks, _42_ - - Larvacea, _30_; - notochord, 51 - - _Latax_, _48_; - pes, 526 - - Lateral ethmoid, 21; - cod, 97; - salmon, 89 f. - - Leathery turtle, _37_; - see _Dermochelys_ - - Lemuroidea, _49_; - caudal vertebrae, 454; - general characters, 372; - nails, 418; - ribs, 493; - sacrum, 452; - skull, 482; - thoraco-lumbar vertebrae, 450; - see Lemurs - - Lemurs, carpus, 512; - pes, 527; - teeth, 441; - see Lemuroidea - - Lenticular, 485; - dog, 393 - - _Lepidosiren_, _34_, _70_; - branchial arches, 125; - fins, 130 - - Lepidosteidae, _33_ - - _Lepidosteus_, _33_; - attachment of teeth, 108; - distribution, 66; - pectoral fins, 131; - scales, 67, 104; - skull, 123; - tail, 117; - vertebrae, 68 - - _Lepidotus_, _33_; - teeth, 110 - - Leporidae, _48_ - - Lepospondyli, _35_ - - _Lepus_, _48_; - see Hare - - _Leptoptilus_, _41_; - see Adjutant - - _Lialis_, _37_, 289 - - Limbs, general account, 26; - modifications in position of, 28; - reptiles, 289 - - Llama, _45_, 359; - cervical vertebrae, 445; - skeleton, =496=; - teeth, 428 - - Limicolae, _42_ - - Lingual apparatus, lampreys, 58; - myxinoids, 57 - - Lion, _48_ - - _Loemanctus longipes_, shoulder girdle and sternum, =287= - - Loggerhead turtle, carapace, =216= - - _Lophiodon_, _46_; - teeth, 345, 429 - - Lophiodontidae, _46_ - - Lophiomyidae, _47_ - - _Lophiomys_, _47_; - pes, 526; - skull, 476 - - _Lophius_, attachment of teeth, 107 - - Lower jaw, see Mandible - - Lumbar vertebrae, 16; - crocodile, 242; - dog, 378 f.; - duck, 311 - - Lunar, 27; - dog, 408 - - - _Macacus_, _49_; - cervical vertebrae, 446 - - _Machaerodus_, _48_; - upper canines, 437 - - _Macrauchenia_, _46_, 358; - calcaneum, 360; - cervical vertebrae, 445; - fibula, 519; - tarsus, 523; - ulna, 501 - - Macraucheniidae, _46_, 509 - - Macropodidae, _43_, _350_; - dental formula, 423; - pes, 522 - - _Macropus_, _43_; - see Kangaroo - - Macroscelidae, _49_ - - _Macroscelides_, _49_; - skull, 480 - - Magnum, 27; - see Carpus - - Malar, 22; - see jugal - - Malleus, dog, 393; - man, dog and rabbit, =485= - - Mammalia, _42_; - auditory ossicles, 485; - cervical vertebrae, 442; - exoskeleton, 416; - general characters, 343; - manus, 503; - Mesozoic --, 348; - pectoral girdle, 493; - pelvic girdle, 512; - pes, 521; - ribs, 490; - sacral and caudal vertebrae, 451; - skull, 455; - sternum, 489; - thigh and shin, 517; - thoraco-lumbar vertebrae, 447 - - Man, _49_; - arm bones, 503; - auditory ossicles, 488; - caudal vertebrae, 454; - cervical vertebrae 446; - pelvis, 515; - pes, 527; - ribs, 493; - scapula, 499; - skull, 483; - sternum, 490; - teeth, 441 - - Manatee, _44_; - see _Manatus_ - - Manatidae, _44_ - - _Manatus_, _44_; - cervical vertebrae, 444; - dental formula, 425; - humerus, 501; - manus, 505; - pelvis, 514; - skull, 460; - sternum, 489; - teeth, 345; - thoraco-lumbar vertebrae, 448 - - Mandible, birds, 335; - cod, 100; - crocodile, 258; - dog, 398; - duck, 319; - frog, 160; - Hippopotamus, =467=; - Isabelline bear, =438=; - newt, 144; - salmon, 94; - turtle, 230 - - Manidae, _44_; - see _Manis_ - - _Manis_, _44_; - auditory ossicles, 487; - manus, 504; - scales, 3, 417; - skull, 459; - _M. macrura_ xiphisternum, 489; - see Pangolin - - Manubrium of malleus 486; - dog, 393; - -- sterni, dog 404 - - Manus, 26; - crocodile, 265; - dog, 408, =413=; - duck, 323; - frog, 164; - mammalia, 503; - newt, 147; - Perissodactyles, =508=; - turtle, 233 - - Marginal plate, turtle 216; - -- ray, 131; - -- shield, turtle, 214 - - Marmoset, _49_, 372 f. - - Marmot, frontals, 476 - - Marsipobranchii, _31_, _53_; - spinal column, 56 - - Marsupial bones, 513 - - Marsupial mole, 43; - see _Notoryctes_ - - Marsupialia, _43_; - arm bones, 499; - auditory ossicles, 486; - cervical vertebrae, 443; - caudal vertebrae, 453; - general characters, 349; - manus, 504; - pectoral girdle, 494; - pelvis, 513; - pes, 521; - ribs, 491; - sacral vertebrae, 451; - skull, 456; - teeth, 422; - thigh and shin, 517; - thoraco-lumbar vertebrae, 447 - - _Mastodon_, _47_, _365_; - teeth, 434 - - _Mastodonsaurus_, _35_, _136_; - pelvis, 187 - - Mastoid portion of periotic, dog, 391 - - Maxilla, 22; - cod, 98; - crocodile, 254; - dog, 397; - duck, 318; - frog, 159; - newt, 144; - turtle, 229 - - Maxillo-mandibular arch, 21 - - Maxillo-palatine, duck, 318 - - Maxillo-turbinal, dog, 395 - - Meatus, external auditory --, crocodile, 250; - dog, 393; - turtle, 228; - internal auditory --, crocodile, 251; - dog, 392, 400; - turtle, 228 - - Meckel's cartilage, 22; - cod, 100; - dogfish, 77; - salmon, 94 - - Median ethmoid, 21; - cod, 98; - Gymnophiona, 179; - salmon, 91; - -- fin, Amphibia, 52; - cod, 86; - dogfish, 79 - - Megachiroptera, _49_; - general characters, 371 - - _Megalobatrachus_, _35_, _135_; - carpus, 186; - skull, 175 - - Megalosauridae, _38_ - - _Megalosaurus_, _38_, _208_ - - _Megapodius_, spur, 330 - - _Megaptera_, _44_, _357_ - - Megatheriidae, _44_, 352; - humerus, 501; - leg bones, 517; - pelvis, 513; - sacrum, 452; - teeth, 424; - thoraco-lumbar vertebrae, 447 - - _Megatherium_, _44_; - femur, 517; - manus, 505; - pectoral girdle, 495; - pes, 522; - skull, 458 - - Megistanes, _40_, _299_ - - Membranous cranium, 17 - - Menobranchidae, _35_ - - _Menobranchus_, _35_, _135_; - carpus, 185; - pes, 188; - skull, 174; - teeth, 169 - - _Menopoma_, _35_; - see _Cryptobranchus_ - - Mento-meckelian, 22; - frog, 161; - reptiles, 284 - - Merganser, _41_; - beak, 329 - - _Mergus_, _41_ - - Merrythought, duck, 322 - - Mesethmoid, 20; - dog, 390; - duck, 317 - - _Mesoplodon_, _44_; - teeth, 427 - - Mesopterygium, 79 - - Mesosauridae, _37_ - - _Mesosaurus_, _37_ - - Mesosternum, dog, 404 - - Metacarpal quill, duck, 303 - - Metacarpo-digital, duck, 303 - - Metacarpus, 26; - see Manus - - Metacromion, hares and rabbits, 497 - - Meta-pterygium, 79 - - Metatarsus 26; - see Pes - - Metatheria, _43_; - general characters, 349 - - _Metriorhynchus_, _39_, 278 - - Microchiroptera, _49_; - general characters, 371 - - _Microgale_, _49_; - caudal vertebrae, 454 - - Mid-digital quill, duck, 303 - - Milk-teeth, 344; - dog, 377; - horse, 430 - - Moa, _40_, _299_; - aftershaft, 328; - pectoral girdle, 336; - wing, 338 - - Molar teeth, 344; - dog, 376 f. - - Mole, _49_, _370_; - auditory ossicles, 488; - cervical vertebrae, 446; - humerus, 503; - manus, 512; - presternum, 490; - shoulder girdle, 499; - skull, 481; - teeth, 440; - Golden --, _49_; - see _Chrysochloris_; - Marsupial --, _43_; - see _Notoryctes_ - - _Molge_, _35_, _135_; - see Newt - - Monitor, _38_; - see _Varanus_ - - Monkey, _49_, _373_; - see under Primates - - Monodelphia, _43_; - characters of, 351 - - _Monodon_, _45_, _357_; - see Narwhal - - Monophyodont, defined, 7, 344 - - Monopneumona, _34_ - - Monotremata, _42_; - arm bones, 499; - auditory ossicles, 486; - caudal vertebrae, 453; - cervical vertebrae, 443; - general characters, 346; - manus, 504; - pectoral girdle, 493; - pelvis, 513; - pes, 521; - ribs, 490; - sacral vertebrae, 451; - skull, 455; - sternum, 489; - teeth, 422; - thigh and shin, 517; - thoraco-lumbar vertebrae, 447 - - _Morosaurus_, _38_, _207_; - pes, 294 - - _Mosasaurus_, _38_, _204_ - - _Moschus_, _46_; - canines, 429 - - Mouse, _47_; - teeth, 437; - see _Mus_ - - Mud-fish, _34_ - - Multituberculata, _43_, _348_ - - Muntjac, _46_; - see _Cervulus_ - - Muraenidae, _33_ - - Muridae _47_ - - _Mus_, _47_; - _M. musculus_, teeth, 437; - _M. sylvaticus_, sternum and shoulder girdle, 498 - - Musk deer, _46_; - canines, 429 - - Mustelidae, _48_; - teeth 439 - - _Mycetes_, 49; - hyoid, 485; - mandible, 484; - skull, 482 - - Myliobatidae, _32_; - teeth, 109 - - Myomorpha, _47_ - - _Myrmecobius_, teeth, 423 - - _Myrmecophaga_, _44_; - manus 505; - pectoral girdle, 495; - skull, 458 - - Myrmecophagidae, _44_, 424; - see Anteaters - - Mystacoceti, _44_; - general characters, 356; - hind limb, 518; - manus, 505; - pectoral girdle, 495; - skull, 461; - teeth, 426 - - _Myxine_, _31_, 55; - fins, 115; - notochordal sheath, 9 - - Myxinoidei, _31_, 55 - - - Nails, 3; - Amphibia, 168; - mammals, 417 - - Nares: - anterior --, crocodile, 252, 257; - dog, 401; - duck, 317; - newt, 143; - turtle, 225, 229; - posterior --, crocodile, 257; - dog, 402; - duck, 318; - frog, 158; - newt, 143; - turtle, 230 - - Narial cavity, salmon, 89; - -- passage, crocodile, 254; - dog, 395; - -- septum, dog, 401 - - Narwhal, _45_, _357_; - teeth, 427 - - Nasal 21; - crocodile, 252; - dog, 394; - duck, 317; - frog, 158; - newt, 143; - turtle, 228; - -- capsule, 20; - cod, 97; - crocodile, 252; - dog, 394; - dogfish, 74; - frog, 158; - newt, 143; - turtle, 228; - -- cavity, dog, 388; - -- fossae, salmon, 89; - -- horns, rhinoceros, 3 - - Navicular, 27; - dog, 414 - - Neornithes, _40_; - general characters, 298 - - _Nesodon_, _46_, _361_; - pes, 525; - teeth, 432 - - Nesodontidae, _46_ - - Neural arch, 14; - -- plate, turtle, 215; - -- spine, 14 - - Neuromere, defined, 112 - - Newt, _35_; - anterior limb, 147; - hyoid apparatus or visceral arches, 144, =181=; - pelvic girdle, 149; - ribs, 145; - shoulder girdle, =146=; - skull, 140; - sternum, 145; - vertebral column, 138 - - Notidanidae, _31_; - calcification of vertebrae, 114; - pectoral fins, 130; - vertebral column, 113; - visceral arches, 63, 119 f. - - Notochord, _Amphioxus_ 52; - Balanoglossus, 50; - dogfish, 72; - Tunicates, 51 - - _Nothosaurus_, _37_, _193_; - supratemporal fossae, 283 - - Nothosauridae, _37_ - - _Notoryctes_, _43_; - arm bones, 500; - caudal vertebrae, 453; - cervical vertebrae, 443; - claws, 418; - dental formula, 423; - manus, 504; - pelvis, 513; - pectoral girdle, 494; - pes, 521; - ribs, 491; - sacrum, 452; - skull, 457; - sternum, 489; - thigh and shin, 517 - - Notoryctidae, _43_, _350_ - - Nuchal plate, turtle, 215; - -- shield, crocodile, 238; - turtle, 214 - - _Nyrania_, _35_; - palatines, 177 - - - Occipital condyle, crocodile, 246; - dog, 386; - duck, 315; - frog, 154; - turtle, 224; - -- crest, dog, 386; - -- segment, crocodile, 246; - dog, 384; - turtle, 224 - - _Odontaspis_, _32_; - succession of teeth, =107= - - Odontoblast, 7 - - Odontoceti, _44_; - general characters, 357; - manus, 505; - pectoral girdle, 495; - skull, 462; - sternum, 489; - teeth, 426 - - Odontolcae, _40_; - general characters, 299 - - _Odontopteryx_, _40_; - jaws, 334 - - _Ogmorhinus_, _48_; - mandibular ramus, =439= - - Olecranon process, dog, 406; - duck, 323; - frog, 164 - - Olfactory capsule, see nasal capsule; - -- cavity, dog, 388; - -- chamber, dog, 395; - -- fossa, dog, 390 - - Olm, _35_ - - _Omosaurus_, exoskeleton, 272 - - Omosternum, frog, 163 - - _Onychodactylus_, _35_; - nails, 168 - - Operculum, cod, 101; - salmon, 95 - - Ophidia, _38_; - general characters, 202; - jaw bones, 280; - scales, 270; - skull, 277 f.; - vertebral column, 275 - - _Ophisaurus_, _38_; - limbs, 289; - pectoral girdle, 289 - - Opisthocoelous, defined, 14 - - _Opisthocomus_, 41; - skull, 334 - - Opisthotic, 20; - cod, 96; - crocodile, 250; - salmon, 89 f.; - turtle, 227 - - Opossum, _43_; - caudal vertebrae, 453; - teeth, 423 - - Optic capsule, 20; - crocodile, 251; - dog, 394; - turtle, 228 - - Orang, _49_; - carpus, 512; - ribs, 493; - thoraco-lumbar vertebrae, 450 - - Orbit, crocodile, 257; - dogfish, 74; - duck, 317 - - Orbital ring, cod, 97; - salmon, 93 - - Orbitosphenoid, 19; - dog, 388; - duck, 317; - newt, 141 - - _Orca_, _45_; - teeth, 427 - - _Oreodon_, _45_; - see _Cotylops_ - - Ornithodelphia, _42_; - general characters, 346 - - Ornithosauria, _212_ - - Ornithorhynchidae, _43_ - - _Ornithorhynchus_, _43_; - beak, 3, 418; - caudal vertebrae, 453; - manus, 504; - pelvis, 513; - sacral vertebrae, 451; - shoulder girdle, =347=; - skull, 455; - spur, 418; - tarsus, 27 n.; - teeth, 4, 346, 422; - thoraco-lumbar vertebrae, 447 - - Ornithopoda, _39_; - general characters, 209 - - Orthopoda, _39_; - general characters, 208; - pubes, 292 - - Orycteropodidae, _44_; - teeth 425 - - _Orycteropus_, _44_; - hair, 416; - manus, 505; - pectoral girdle, 495; - pelvis, 513; - skull, 459; - see Aard Vark - - Osborn, H.F., on Mesozoic Mammals, 348 - - Os entoglossum, duck, 320 - - Osteoblast, 11 - - Osteoclast, 11 - - Osteodentine, 108 - - Osteostraci, _31_; - general characters, 54 - - _Ostracion_, _33_, 69; - plates, 105 - - Ostracionidae, _33_ - - Ostracodermi, _31_; - general characters, 54 - - Ostrich, _40_, _299_; - aftershaft, 329; - cervical vertebrae, =331=; - claws, 330; - foot, 342; - manus, 338; - pelvic girdle and sacrum, =340=; - pubis, 341; - tibio-tarsus, 341; - wing, =339= - - _Otaria_, _48_; - dentition, 439; - tympanic bulla, 480 - - Otariidae, _48_, _369_; - auditory ossicles, 488; - scapula, 498; - skull, 480 - - Owen's apteryx, pelvic girdle and sacrum, =340= - - Owen's chameleon, epidermal horns, 271 - - Owls, _42_, 335; - aftershaft, 329; - foot, 342 - - Owl-parrot, _42_; - see _Stringops_ - - Ox, _46_, 359; - atlas and axis, =445=; - three cervical vertebrae, =15=; - femur, =518=; - manus, 507; - teeth, 345; - two thoracic vertebrae, =449= - - - Paca, _48_ - - Paired fins, 127 - - Palaeoniscidae, _32_ - - _Palaeoniscus_, _32_; - scales, 67 - - Palaeospondylidae, _31_ - - _Palaeospondylus_, _31_, 58 - - _Palaeosyops_, _46_; - teeth, 432 - - Palaeotheriidae, _46_ - - _Palaeotherium_, 46; - skull, 471; - teeth, 430 - - _Palamedea_, _41_; - spur, 330, 338 - - Palamedeae, _41_ - - Palate, reptiles, 280 f. - - Palatine, cod, 98; - crocodile, 254; - dog, 397; - duck, 318; - frog, 160; - salmon, 93; - turtle, 230 - - Palato-pterygo-quadrate bar, 22; - dogfish, 77; - fish, 120 f.; - salmon, 93 - - Palm civet, _48_ - - Pangolin, _44_; - pectoral girdle, 495; - pelvis, 513; - caudal vertebrae, 453; - see _Manis_ - - Parachordals, 17 - - _Paradoxurus_, _48_; - tail, 454 - - Parasphenoid, 21; - cod, 97; - frog, 156; - newt, 141; - reptiles, 278; - salmon, 93 - - Parasuchia, _39_; - general characters, 211 - - Parethmoid, 21 n. - - Pariasauria, _36_ - - _Pariasaurus_, _36_, _192_; - pectoral girdle, 289; - pelvis, 292; - supratemporal fossa, 283; - teeth, 273 - - Parietal, 19; - cod, 96; - crocodile, 247; - dog, 386; - duck, 314; - newt, 141; - salmon, 91; - turtle, 225; - -- segment, crocodile, 247; - dog, 386; - turtle, 225 - - Paroccipital process, dog, 386 - - _Parra_, _42_; - spur, 330 - - Parrots, 335; - aftershaft, 328; - beak, 330; - epiphyses of centra, 332; - foot, 342; - powder-down feathers, 329; - skull, 334 - - Parrot fish, _33_; - see _Scarus_ - - Passeres, aftershaft, 328 - - Passeriformes, _42_ - - Patella, dog, 412; - duck, 327 - - _Pavo_, _41_; - _P. cristatus_, shoulder girdle and sternum, =337= - - Peacock, _41_; - see _Pavo_ - - Peccary, pes, 523 - - Pecora, _46_, _359_; - teeth, 429 - - Pectinated incisors, _Galeopithecus_, 370, 440; - _Procavia_, 362 - - Pectineal process, duck, 326 - - Pectoral fins, cod, 103; - dogfish, 79; - -- girdle, 24; - Amphibia, 184; - birds, 336; - cod, 101; - crocodile, 262; - dog, 404; - dogfish, 79; - duck, 321; - fish, 126; - frog, 162; - mammalia, 493; - newt, 145; - reptiles, 288; - turtle, 231; - -- shield, turtle, 215 - - _Pedetes_, _47_; - manus, 511; - tail, 454 - - Pelican, _41_, 335; - clavicles, 338 - - _Pelicanus_, _41_; - _P. conspicillatus_ shoulder girdle and sternum, =337= - - _Pelobates_, _36_; - vertebrae, 172; - _P. cultripes_ teeth, 169 - - Pelobatidae, _36_ - - Pelvic fins, cod, 103; - dogfish, 82; - fish, 131; - -- girdle, 25; - Amphibia, 187; - birds, 339; - crocodile, 266; - dog, 409; - dogfish, 81; - duck, 324; - fish, 127; - frog, 165; - mammals, 512; - newt, 149; - Ratitae, =340=; - Reptilia, 291; - turtle, 235 - - Penguin, _40_; - distribution of feathers, 328; - fibula, 341; - foot, 342; - manus, 338; - metatarsus, 342; - pneumaticity of skeleton, 331; - skull, 333; - sternum, 336; - thoracic vertebrae, 332; - wing, 329, =339= - - Penna, duck, 303 - - Pentedactylate, defined, 26 - - _Perameles_, _43_; - atlas, 443; - pectoral girdle, 494 - - Peramelidae, _43_, _350_; - auditory ossicles, 486; - pes, 522 - - _Perca_, _34_ - - Perch, _34_; - pelvic fin, 132; - urostyle, 117 - - Percidae, _34_ - - Perennibranchiata, _35_; - characters, 135 - - Perichondrium, 10 - - Perichordal sheath, 16 - - Periosteal ossification, 10 - - Periosteum, 10 - - Periotic, dog, 390; - -- capsule, see Auditory capsule - - Perissodactyla, _46_; - cervical vertebrae, 445; - general characters, 359; - manus, 507; - pes, 523; - ribs, 491; - scapula, 496; - skull, 470; - teeth, 429; - thoraco-lumbar vertebrae, 448 - - Persistent pulps, 5 - - Pes, 26; - crocodile, 268; - dog, =413=, 414; - duck, 327; - frog, 166; - mammals, 521; - reptiles, 293; - turtle, 236; - of Tapir, Rhinoceros, _Hipparion_ and Horse, =524= - - _Petromyzon_, _31_, 55 f.; - notochordal sheath, 9 - - Petromyzontidae, _31_, 55 - - Petrous portion of periotic, dog, 391 - - _Pezophaps_, _42_; - see Solitaire - - _Phacochaerus_, _45_; - teeth, 428 - - _Phaëthon_, _41_; - metatarsals, 342 - - _Phalacrocorax_, _41_ - - Phalangeridae, _43_, 350 - - Phalanges, 26; - see Manus and Pes - - Phaneroglossa, _36_ - - Pharyngo-branchial, cod, 101; - dogfish, 78; - salmon, 95 - - Pharyngognathi, _33_ - - _Phascolarctus_, _43_; - see Koala - - Phascolomyidae, _43_, _350_ - - _Phascolomys_, _43_, 349; - see Wombat - - _Phascolotherium_, _43_, 348 - - Phenacodontidae, _47_ - - _Phenacodus_, _47_, _362_; - caudal vertebrae, 454; - manus, =510=; - pes, 525; - scapula, 497; - skull, 472; - thoraco-lumbar vertebrae, 449 - - _Phocaena_, _45_, _357_; - skull, 462; - thoraco-lumbar vertebrae, 448; - _P. phocaenoides_, ossicles, 420 - - Phocidae, _48_, _369_; - scapula, 497; - tympanic bulla, 480 - - _Phoronis_, _30_, 50 f. - - _Phororhacos_, _41_; - anterior nares, 333; - ischia, 341 - - _Physeter_, _44_; - cervical vertebrae, 444; - manus, 505; - skull, 464; - teeth, 426 - - Physeteridae, _44_; - ribs, 491; - thoraco-lumbar vertebrae, 448 - - _Physodon_, _44_; - teeth, 426 - - Physodontidae, _44_ - - Physostomi, _33_ - - Phytosauridae, _39_ - - _Phytosaurus_, _39_; - see _Belodon_ - - Pici, _42_ - - _Picus_, _42_; - see Woodpecker - - Pig, _45_, _359_; - skull, 465 f., =466=; - teeth, 345, 427 - - Pigeons, _42_, 334 f.; - aftershaft, 329; - pneumaticity of skeleton, 331 - - Pike, _33_; - pelvic fin, 132; - teeth, 107, 110 - - Pinnipedia, _48_; - arm bones, 502; - auditory ossicles, 488; - general characters, 369; - manus, 511; - pelvis, 515; - pes, 526; - skull, 480; - teeth, 439; - thigh and shin, 520; - thoraco-lumbar vertebrae, 450 - - _Pipa_, _36_; - hyoid apparatus, 182; - jaws, 169; - skull, 180; - sternum, 184; - vertebrae, 172 - - Pipidae, _36_ - - Pisces, _31_; - general characters, 60 - - Piscivorous dentition, 426, 440 - - Pisiform, 345, 504; - crocodile, 265; - dog, 408; - turtle, 233 - - Pituitary fossa, crocodile, 247; - -- space, 17 - - Placodontia, _36_ - - _Placodus_, _36_, _192_; - teeth 273 - - Placoid scale, 4, 60, 104 - - Plantigrade, defined, 358 n. - - Plastron, _Dermochelys_, 272; - _Chelone midas_, 217, =218=, 271 - - Platanistidae, _45_ - - _Platanista_, _45_; - cervical vertebrae, 444; - skull, 464 - - Plectognathi, _33_; - vertebrae, 115 - - _Plectropterus_, _41_; - _P. gambensis_, spur, 330 - - Plesiosauridae, _37_; - limbs, 193; - parasphenoid, 192; - skull, 278 - - _Plesiosaurus_, _37_, _193_; - position of limbs, 28 - - Pleuracanthidae, _63_; - fins, 115 - - Pleurodira, _37_; - general characters, 195 - - Pleurodont, 159, 199, 273 - - Pleuronectidae, _33_ - - Pleuropterygii, _31_, 63 - - _Pliosaurus_, _37_, _193_ - - Plovers, _42_, 334; - thoracic vertebrae, 332 - - Pneumaticity of bird's skeleton, 331 - - _Polacanthus_, _39_; - exoskeleton, 272 - - Pollex, 26; - see Manus - - _Polyodon_, _32_, 104; - distribution, 66; - pectoral fins, 131; - skull, 122; - spinal column, 112; - teeth, 110 - - Polyodontidae, _32_ - - _Polyonax_, _39_, _209_; - beak, 271; - frontals, 277; - jaw, 274; - predentary, 284 - - Polyprotodont, 423 - - Polyprotodontia, _43_; - general characters, 350 - - Polypteridae, _33_ - - _Polypterus_, _33_, _68_; - distribution, 66; - exoskeleton, 67; - pectoral fins, 131; - pelvic fins, 132; - pelvis, 127; - scales, 104; - skull, 122; - tail, 116 - - _Pontoporia_, _45_; - cervical vertebrae, 444; - teeth, 426 - - Porcupine, _47_; - pes, 526; - skull, 476, =477=; - spines, 417 - - Porpoise, _45_, _357_; - thoraco-lumbar vertebrae, 448 - - Postaxial, 28 - - Posterior cornu, duck, 320; - turtle, 231; - -- limb, 26; - Amphibia, 188; - birds, 341; - dog, 412; - duck, 326; - frog, 166; - newt, 149, =148=; - reptiles, 293; - turtle, 235, =234= - - Postfrontal, 21; - crocodile, 250; - turtle, 225 - - Postorbital bar, crocodile, 250, 255 f.; - _Hatteria_, 283; - -- groove, dogfish, 76 - - Post-temporal, cod, 102; - reptiles, 283; - -- bar, crocodile, 256; - _Hatteria_, 283 - - _Potamogale_, _49_, 367, 370; - shoulder girdle, 499; - teeth, 440 - - Potamogalidae, _49_ - - Powder-down feathers, 329 - - Pre-axial, 28 - - Precoracoid, 25; - frog, 163; - newt, 147; - reptiles, 288; - turtle, 232 - - Predentary, reptiles, 284 - - Predigital quill, duck, 303 - - Prefrontal, 21; - crocodile, 249; - reptiles, 278; - turtle, 225 - - Prefronto-lachrymal, newt, 141 - - Prehallux, frog, 167 f. - - Premaxilla, 22; - cod, 98; - crocodile, 252; - dog, 398; - duck, 314, 318; - frog, 158; - newt, 143; - salmon, 94; - turtle, 230 - - Premolar, dog, 370, 377; - mammals, 344 - - Prenasal process, frog, 158 - - Pre-orbital vacuity, reptiles, 283 - - Presphenoid, 19; - dog, 388 - - Prespiracular ligament, dogfish, 77 - - Presternum, dog, 404 - - Primaries, duck, 303 - - Primates, _49_; - arm bones, 503; - auditory ossicles, 488; - cervical vertebrae, 446; - general characters, 372; - manus, 512; - pelvis, 515; - pes, 527; - ribs, 493; - sacrum, 452; - shoulder girdle, 499; - skull, 482 f.; - sternum, 490; - tail, 454; - teeth, 441; - thigh and shin, 520; - thoraco-lumbar vertebrae, 450 - - _Priodon_, _44_; - caudal vertebrae, 453; - manus, 505; - stapes, 487; - sternum, 489; - teeth, 424 - - Pristidae, _32_ - - _Pristis_, _32_; - snout or rostrum, 109, 119 - - Proboscidea, _47_; - arm bones, 502; - cervical vertebrae, 445; - general characters, 364; - femur, 519; - manus, 511; - pelvis, 514; - pes, 526; - scapula, 497; - skull, 473; - teeth, 433; - thoraco-lumbar vertebrae, 449 - - _Procavia_, _47_, _363_; - auditory ossicles, 487; - caudal vertebrae, 453; - dental formula, 432; - humerus, 502; - manus, 510; - pelvis, 514; - pes, 525; - ribs, 491; - scapula, 497; - skull, 433, 472; - tarsus, 27; - thoraco-lumbar vertebrae, 449 - - Process, alinasal --, frog, 158; - basi-pterygoid --, birds, 334; - coracoid --, dog, 405; - coronoid -- (of mandible), dog, 398; - duck, 319; - coronoid -- (of ulna), dog, 408; - pectineal --, duck, 326; - postfrontal --, duck, 316; - postglenoid --, dog, 394; - postorbital -- (of frontal), dog, 388; - postorbital -- (of jugal), dog, 398; - posterior articular --, duck, 319; - zygomatic --, dog, 394 - - Processus brevis, 486; - -- gracilis, 486; - -- longus, 486; - dog, 393 - - Procoelous, defined, 14 - - _Prodelphinus_, _45_; - skull, 462 - - Proganosauria, _37_ - - Prone position, 29 - - Prongbuck, _46_; - horns, 417 - - Pro-otic, 20; - frog, 157; - turtle, 227 - - Pro-pterygium, dogfish, 79 - - Proteidae, _35_ - - _Proteles_, _48_; - teeth, 437 - - Protelidae, _48_ - - Proterosauridae, _37_ - - _Proterosaurus_, _37_; - teeth, 198, 274; - vertebrae, 197 - - _Proteus_, _35_, 135, 182; - branchial arches, 180; - digits, 187; - pes, 188; - skull, 174 - - _Protopterus_, _34_, _70_, 117; - branchial arches, 121, 124; - fins, 130; - skull, 124; - vestigial gill on pectoral girdle, 129 - - Prototheria, _42_; - general characters, 346 - - Proximal, defined, 23 n. - - _Psephurus_, distribution, 66 - - _Pseudopus_, _38_; - limbs, 289 - - Psittaci, _42_; - see Parrots - - _Pteranodon_, _39_, _274_; - pectoral girdle, 289 - - Pteranodontidae, _39_ - - _Pteraspis_, _31_, _54_ - - _Pterichthys_, _31_, _55_ - - _Pterocles_, _42_; - see Sandgrouse - - Pteroclidae, _42_ - - Pterodactylidae, _39_ - - _Pterodactylus_, _39_, 213 - - Pteropidae, _49_; - skull, 481 - - _Pteropus_, _49_; - dental formula, 441; - tail, 454 - - Pterosauria, _39_; - general characters, 212; - ischia, 292; - limbs, 291; - pre-orbital vacuity, 284; - ribs, 285; - sternum, 287; - vertebrae, 275 f. - - Pterotic, 20; - cod, 96; - salmon, 90 f. - - Pterygoid, cod, 98; - crocodile, 255; - dog, 397; - duck, 318; - frog, 160; - newt, 144; - salmon, 93; - turtle, 230; - -- fossa, crocodile, 255; - -- plate, dog, 388 - - Pterylae, 328 - - Pubis, 25; - crocodile, 266 f.; - duck, 325; - dog, 411; - frog, 165; - newt, 149; - reptiles, 292; - turtle, 235 - - Pygal plate, turtle, 217; - -- shield, turtle, 214 - - Pygopodidae, _37_ - - Pygostyle, duck, 307, 312 - - _Python_, _38_; - ischio-pubis, 292; - jaws, 280; - vestiges of limbs, 289, 293 - - Pythonomorpha, _38_; - general characters, 204; - limbs, 290; - teeth, 273 - - - Quadrate, 22; - cod, 98; - crocodile, 255; - duck, 319; - frog, 160; - newt, 144; - salmon, 93; - turtle, 229 - - Quadratojugal, 22; - crocodile, 255; - duck, 318; - frog, 160; - turtle, 229 - - Quill, duck, 302 - - - Rabbit, _48_, 366; - pollex, 511 - - Raccoon, 369 - - Rachis, duck, 302 - - Rachitomous, defined, 171 - - Radiale, 27; - see Carpus - - Radialia, 115; - dogfish, 79 f. - - Radio-ulna, frog, 164 - - Radius, 26; - crocodile, 265; - dog, 406; - duck, 323; - newt, 147; - turtle, 233 - - _Raia_, _32_; - calcification of vertebrae, 114 - - Raiidae, _32_ - - _Rana_, _36_; - see Frog - - Ranidae, _36_; - shoulder girdle, 185 - - Rat, pes, 526 - - Ratitae, 40; - caudal vertebrae, 333; - clavicles, 338; - foot, 342; - general characters, 298; - skull, 333; - sternum, 336; - vomers, 334; - wing, 338 - - Rattlesnake, _38_; - rattle, 3, 270 - - Ray, pectoral fin, 130; - Eagle --, Electric -- and Sting --, _32_ - - Rectrices, 303, 329 - - Reed-fish, _33_ - - Reindeer, antlers, 469 - - Remicle, duck, 304 - - Remiges, 303, 329 - - Reptiles, anterior limb, 290; - exoskeleton, 270; - fossae in skull, 281; - pectoral girdle, 288; - pelvic girdle, 291; - posterior limb, 293; - ribs, 285; - skull, 276; - sternum, 287; - teeth, 272; - vertebral column, 275 - - Reptilia, _36_; - general characters, 190; - see Reptiles - - _Rhabdopleura_, _30_, 50 - - _Rhamphastos_, _42_; - see Toucan - - Rhamphorhynchidae, _39_ - - _Rhamphorhynchus_, _39_, 213, 274 - - _Rhea_, _40_; - aftershaft, 329; - claws, 330; - ischia, 341; - manus, 338; - _R. macrorhyncha_, pelvic girdle and sacrum, =340= - - Rheornithes, _40_ - - _Rhina_, _32_; - see _Squatina_ - - Rhinal process, frog, 158 - - _Rhinoceros_, _46_, 360, 419; - femur, =518=; - fibula, 519; - malleus, 487; - manus, 508; - nasal horns, 3, 417; - pes, 525; - skull, =421=, 470; - teeth, 430; - ulna, 501; - _R. antiquitatis_, 470 - - Rhinocerotidae, _46_ - - Rhinolophidae, _49_ - - Rhiptoglossa, _38_ - - Rhizodontidae, _33_ - - _Rhizodus_, _33_; - teeth, 110 - - Rhynchocephalia, _37_; - general characters, 197; - humerus, 290; - teeth, 273 f.; - vertebrae, 275 - - Rhynchosauridae, _37_; - maxillae, 198 - - _Rhytina_, _44_, 352, 425; - humerus, 501; - skull, =460= - - Rhytinidae, _44_ - - Ribs, 23; - Amphibia, 182; - birds, 336; - cod, 86; - crocodile, 259; - dog, 402; - dogfish, 73; - duck, 320; - fish, 125; - frog, 153; - mammalia, 490; - newt, 145; - reptiles, 285 - - Ridge, supra-orbital and suborbital, dogfish, 74 - - Rodentia, _47_; - auditory ossicles, 488; - cervical vertebrae, 446; - dental formula, 435; - general characters, 365; - pelvis, 515; - pes, 526; - humerus, 502; - manus, 511; - ribs, 493; - sacrum, 452; - shoulder girdle, 497; - skull, 476; - sternum, 489; - tail, 454; - teeth, 421; - thigh and shin, 520; - thoraco-lumbar vertebrae, 449 - - Roller, _42_, 335 - - Rooted teeth, defined, 5 - - Rorqual, _44_, 357; - cervical vertebrae, 444 - - Rostrum, crocodile, 247; - dogfish, 74; - duck, 316; - _Pristis_, 119; - -- of sternum, duck, 321 - - Röse, C., on teeth of Marsupials, 422 - - Ruminantia, _46_, _359_; - auditory ossicles, 487; - fibula, 519; - horny plates on palate, 418; - hyoid, 470; - manus, 507; - odontoid process, 445; - pes, 523; - scapula, 495; - teeth, 420, 429 - - - Sabre-toothed lion, _48_; - see _Machaerodus_ - - Sacral ribs, crocodile, 243; - -- surface of ilium, dog, 409; - -- vertebrae, 16; - crocodile, 243; - dog, 383; - duck, 312; - frog, 153; - newt, 140; - turtle, 222 - - Sacrum, duck, 310; - see Sacral vertebrae - - Sagittal crest, dog, 386 - - _Saiga_, skull, 468 - - Salamander, _35_ - - _Salamandra_, _35_, _135_; - antibrachium and manus of larva, =186=; - manus of larva, 185; - tarsus, 27 - - Salamandrina, _35_, _135_; - skull, 175; - sternum, 182 - - _Salmo_, _33_ - - Salmon, _33_; - branchial arches, 95; - chondrocranium, 87; - opercular bones, 95; - pectoral fins, 131; - skull, 87 - - Salmonidae, _33_ - - Sandgrouse, _42_, 335 - - _Sarcophilus_, _43_; - teeth, 423 - - Sauropoda, _38_; - general characters, 205; - teeth, 273; - vertebrae, 276 - - Sauropsida, _36_; - general characters, 189 - - Sauropterygia, _37_; - general characters, 192; - limbs, 290; - palate, 281; - pectoral girdle, 288; - vertebrae, 276 - - Saw-fish, _32_; - see _Pristis_ - - Scales, cod, 83; - crocodile, 237; - ctenoid, 8; - cycloid, 8; - duck, 302; - ganoid, 8; - Gymnophiona, 168; - mammals, 417 - - Scale-foot, 37 - - Scalpriform, 366 - - _Scaphirhynchus_, _32_, _104_; - distribution, 66; - exoskeleton, 67; - spinal column, 112 - - Scaphoid, 27; - mammals, 504 f. - - Scapho-lunar, dog, 408 - - Scapula, 25; - cod, 103; - crocodile, 263; - dog, 404; - duck, 322; - frog, 162; - newt, 146; - turtle, 232 - - Scapular shield, armadillo, 419 - - Scapus, duck, 302 - - _Scarus_, _33_; - beaks, 111 - - Scelidosauridae, _39_ - - Schizognathous, defined, 335 - - Scincidae, _38_ - - _Scincus_, _38_; - scutes, 271 - - Sciuromorpha, _47_ - - Sclerotic, turtle, 228 - - Screamer, _41_; - spurs, 330 - - Scutes, armadillos, 419; - crocodile, 237; - reptiles, 271 - - Scylliidae, _32_ - - _Scyllium_, _32_; - calcification of vertebrae, 114; - pectoral fins, 130; - suspensorium, 119; - see Dogfish - - _Scymnus_, _32_, _118_; - calcification of vertebrae, 114; - mandibular arch, 120; - pectoral fins, 130 - - _Scythrops_, _42_; - interorbital septum, 333 - - Sea leopard, _48_; - see _Ogmorhinus_; - -- lion, _48_; - manus, 511; - pes, 526; - position of limbs, 29; - -- otter, _48_; - pes, 526 - - Seal, _369_; - manus, 511; - pes, 526; - sacral vertebrae, 452; - scapula, 497 - - Secondaries, duck, 303 f. - - Secretary-bird, _41_; - claws, 330 - - Selachii, _31_; - general characters, 63; - teeth, 108 - - Selenodont, defined, 345, 428 - - Sella turcica, crocodile, 247; - dog, 386 - - Semionotidae, _33_ - - Semiplumae, 328 - - Sense capsules, see Auditory, Nasal and Optic capsule - - _Seps_, 38; - limbs, 289 - - Shagreen, 61 - - Shaft of feather, 302 - - Shark, 64; - Frill-gilled --, _31_; - see _Chlamydoselache_; - Port Jackson --, _32_; - see _Cestracion_ - - Sheep, _359_; - manus, 507; - teeth, 345 - - Shields of turtle, 214 - - Shin, 26; - see Crus - - Shoulder girdle, see Pectoral girdle - - Shrew, _49_, _370_; - auditory ossicles, 488; - cervical vertebrae, 446; - presternum, 490; - skull, 481; teeth, 440 - - Sigmoid notch, dog, 406 - - Siluridae, _33_; - plates, 105 - - _Simia_, _49_; - ribs, 493; - skull, 484; - thoraco-lumbar vertebrae, 450 - - Simiidae, _49_, _373_ - - Simplicidentata, _47_, 366 - - _Siphonops_, _35_; - _S. annulatus_, skull, =178= - - _Siredon_, _35_; - skull, 175; - teeth, 169; - visceral arches, =181= - - _Siren_, _35_, _135_, 188; - beaks, 168; - branchial arches, 180; - digits, 187; - skull, 174; - teeth, 169 - - Sirenia, _44_, 522; - arm bones, 501; - caudal vertebrae, 453; - cervical vertebrae, 443; - general characters, 352; - hair, 416; - horny plates, 418; - manus, 505; - pectoral girdle, 495; - pelvis, 514; - ribs, 491; - skull, 459; - sternum, 489; - teeth, 425; - thoraco-lumbar vertebrae, 448 - - Sirenidae, _35_ - - Sirenoidei, _34_; - general characters, 70 - - _Sivatherium_, _46_; - skull, 469 - - Skate, _32_ - - Skeletogenous layer, 14, 16; - _Amphioxus_, 52, 112 - - Skeleton, defined, 1; - Cape Buffalo, =492=; - _Ceratodus_, =128=; - cod, 83 f.; - crocodile, 237 f.; - dog, 374 f.; - duck, 302 f.; - frog, 151 f.; - llama, =496=; - newt, 138 f.; - turtle, 214 f. - - Skink, _38_; - see _Tiliqua_ - - Skull, 16 f.; - Amphibia, 173 f.; - Anura, 179 f.; - birds, 333 f.; - cod, 96 f.; - crocodile, 243 f.; - diagram of Mammalian, 385; - Dipnoi, 124; - dog, 383 f.; - dogfish, 73 f.; - donkey, =431=; - duck, 312 f.; - fish, 117; - frog, 154 f., =159=; - _Globicephalus_, =463=; - Gymnophiona, 177; - Indian elephant, =474=; - Mammalia, 455; - Marsipobranchii, 57; - pig, =466=; - _Procavia_, =433=; - reptiles, 276 f.; - Rhinoceros, =421=; - _Rhytina_, =460=; - sloth, =458=; - Tasmanian wolf, =456=; - Teleostei, 124; - turtle, 222 f.; - wombat, =456= - - Sloth, _43_, _352_; - auditory ossicles, 487; - arm bones, 500; - claws, 418; - leg bones, 517; - manus, 505; - pectoral girdle, 495; - pelvis, 513; - pes, 522; - ribs, 491; - sacrum, 452; - skull, 457; - sternum, 489; - teeth, 424; - thoraco-lumbar vertebrae, 447 - - Snake, _38_; - see Ophidia - - Sole, _33_ - - _Solea_, _33_ - - _Solenodon_, _49_; - teeth, 440 - - Solenodontidae, _49_ - - Solitaire, _42_, _330_; - wing, 338; - wrist, 330 - - _Sorex_, _49_; - pelvis, 515; - see Shrew - - Soricidae, _49_; - skull, 481 - - Spalacidae, _47_ - - _Spatularia_, _32_; - distribution, 66 - - _Spelerpes_, _35_; - branchial arches, 180; - ribs, 182; - _S. belli_ teeth, 169 - - Sperm whale, _44_, _357_; - see _Physeter_ - - _Sphargis_, _37_; - see _Dermochelys_ - - Sphenethmoid, frog, 156 - - Sphenisci, _40_; - see Penguins - - Sphenisciformes, _40_ - - _Sphenodon_, _37_, 197 f.; - carpus, 291; - cervical vertebrae, 275; - fossae in skull, 281; - humerus, 290; - interparietal foramen, 277; - ribs, 286; - skull, =282=; - tarsus, 293; - teeth, 274 - - Sphenodontidae, _37_ - - Sphenoidal fissure, dog, 388 - - Sphenotic, 20; - cod, 97; - salmon, 89 - - Spider monkey, _49_; - see _Ateles_ - - Spinacidae, _32_ - - Spinal column, 13; - Dipnoi, 113; - fish, 112; - Holocephali, 113; - Marsipobranchii, 56 - - Spines, Elasmobranchs, 61; - mammals, 417 - - Spiny ant-eater, _43_; - see _Echidna_; - -- mouse, 47; - see _Acanthomys_ - - Splenial, 22; - crocodile, 258; - duck, 320; - turtle, 231 - - Spurs, birds, 330; - Monotremata, 418 - - Spur-winged goose, 330; - -- plover, 330 - - Squalidae _31_, _64_ - - _Squalodon_, _45_, _357_; - dental formula, 427 - - Squalodontidae, _45_ - - Squamata, _37_; - general characters, 198; - position of teeth, 272; - skull, 278 - - Squamosal, 21; - crocodile, 256; - dog, 394; - duck, 316; - frog, 160; - newt, 144; - turtle, 229 - - _Squatina_, _32_; - calcification of vertebrae, 114; - labial cartilages, 119; - tail, 63; - vertebral column, 114 - - Squatinidae, _32_ - - Squirrels, frontals, 476; - pes, 526 - - Stapes, dog, 393; - frog, 157; - man, dog, rabbit, =485=; - newt, 141 - - Steganopodes, _41_ - - Stegosauria, _39_; - general characters, 209 - - Stegosauridae, _39_ - - _Stegosaurus_, _39_, _208_ f.; - exoskeleton, 272 - - Steller's sea-cow, _44_; - see _Rhytina_ - - Stereornithes, _41_ - - Stereospondyli, _35_ - - Sternal ribs, crocodile, 259; - dog, 402; - duck, 320; - mammals, 490 f. - - Sternebra, dog, 404 - - Sternum, 24; - Amphibia, 182; - birds, 336; - crocodile, 260, =261=; - dog, =403=; - duck, 321; - frog, 163; - Mammalia, 489; - newt, 145; - reptiles, 287 - - Stork, 335; - White --, _41_ - - Striges, _42_; - see Owls - - _Stringops_, _42_; - sternum, 336 - - _Struthio_, _40_, _299_; - see Ostrich - - Struthiornithes, _40_, _299_ - - Sturgeon, _32_; - see _Acipenser_ - - Stylo-hyal, dog, 399 - - Suborbital bar, duck, 318; - -- ridge, dogfish, 76 - - Subplantigrade, defined, 358 n. - - Subungulata, _46_; - arm bones, 502; - general characters, 360; - manus, 509; - pelvis, 514; - pes, 525; - shoulder girdle, 497; - skull, 471; - teeth, 432; - thigh and shin, 519 - - Suidae, _45_ - - Suina, _45_, 358 f.; - fibula, 519; - manus, 507; - odontoid process, 445; - pelvis, 514; - pes, 523; - ulna, 501 - - Sula, _41_; - see Gannet - - Supinator ridge, dog, 406 - - Supine position, defined, 29 - - Supra-angular, 22; - crocodile, 258; - duck, 319; - turtle, 230 f. - - Supracaudal shield, turtle, 214 - - Supraclavicle, cod, 102 - - Supra-occipital, 19; - crocodile, 247; - dog, 386; - duck, 315; - turtle, 224 - - Supra-orbital, 20; - crocodile, 251 - - Suprapharyngeal bone, cod, 101 - - Suprascapula, crocodile, 263; - frog, 162 - - Supratemporal arcade, crocodile, 256; - reptiles, 281 - - Surinam toad, _36_; - see _Pipa_ - - Sus, _45_; - dental formula, 428; - see Pig - - Suspensorium, Amphibia, 173; - dogfish, 78; - duck, 319; - frog, 160; - newt, 144; - Pisces, 61 - - Sutures, 12 - - Swan, _41_; - cervical and thoracic vertebrae, 332 - - Swift, _42_, 335; - foot, 342 - - Symplectic, cod, 100; - salmon, 94 - - - Tails, fish, 60 - - Talpa, _49_; - pelvis, 515; - see Mole - - Talpidae, _49_ - - Tapir, _46_, 360; - malleus, 487; - pes, =524=, 525; - teeth, 345; - see _Tapirus_ - - Tapiridae, _46_; - dental formula, 429 - - _Tapirus_, _46_; - fibula, 519; - manus, =508=; - skull, 471; - see Tapir - - Tarsier, _49_ - - Tarsiidae, _49_ - - _Tarsipes_, _43_, 349; - mandible, 457 - - _Tarsius_, _49_, 372; - pes, 527 - - Tarso-metatarsus, duck, 327 - - Tarsus, 26 f.; - crocodile, 268; - dog, 414; - frog, 166; - newt, 150; - turtle, 236 - - Tasmanian devil, _43_; - see _Sarcophilus_; - -- wolf, _43_; - see _Thylacinus_ - - _Tatusia_, _44_; - stapes, 487; - teeth, 424 - - Tectospondyli, 114 - - Tectrices, duck, 306 - - Teeth, =6=; - Amphibia, 169; - birds, 330; - cod, 83; - crocodile, 238; - development, 7; - dog, 374 f.; - fish, 106 f.; - frog, 158 f.; - horses, 5; - mammals, 344, 420 f.; - pharyngeal, 8; - reptiles, 272 f.; - structure, 4; - succession, 7 - - Teleosauridae, _39_ - - _Teleosaurus_, _39_; - palate, 281; - scutes, 271; - vertebrae, 275 - - Teleostei, _33_; - general characters, 69; - ribs, 126; - skull, 124; - tail, 117; - teeth, 110; - vertebral column, 115 - - Temnospondyli, _35_ - - Tenrec, _49_; - see _Centetes_ - - Tentorium, dog, 392 - - Terrapin, _37_ - - _Testudo_, _37_, _194_ - - _Tetraceros_, _46_; - horns, 417 - - _Thalassochelys_, carapace, =216= - - Thecodont, defined, 273 - - Theriodontia, _36_ - - Theromorpha, _36_; - general characters, 191; - humerus, 290; - pectoral girdle, 288; - ribs, 285; - skull, 278; - teeth, 273; - vertebral column, 275 f. - - Theropoda, _38_; - general characters, 207; - teeth, 273 - - Thoracic ribs, crocodile, 259; - see Ribs; - -- vertebrae, 16; - crocodile, 241, =242=; - dog, 381, =382=; - duck, 310; - turtle, 221 - - Thoraco-lumbar vertebrae, mammals, 447 f. - - Thornback skate, 104 - - _Thylacinus_, _43_; - atlas, 443; - dental formula, 423; - pelvis, 513; - pes, 521; - skull, =456= - - _Thylacoleo_, _43_; - skull, 457 - - Thyro-hyal, dog, 399 - - Tibia, 26; - crocodile, 268; - dog, 412; - newt, 149; - turtle, 235 - - Tibiale 27; - see Tarsus - - Tibio-fibula, frog, 166 - - Tibio-tarsus, duck, 326 - - Tichorhine Rhinoceros, 470 - - Tiger, _48_ - - _Tiliqua_, _38_; - scutes, 200, 271 - - Tillodontia _47_, 365; - femur, 520; - manus, 511; - teeth, 435 - - Tinamidae 300; - caudal vertebrae, 333; - vomers, 334 - - Tinamiformes, _41_ - - _Tinamus_, _41_; - ischia, 341 - - Titanotheriidae, _46_; - skull, 470; - teeth, 432 - - _Titanotherium_, _46_; - humerus, 501; - manus, =508=; - pes, 525 - - Toad, _36_; - shoulder girdle, 185 - - Tope, _32_ - - Torpedinidae, _32_ - - _Torpedo_, _32_, 104 - - Tortoise, _37_; - position of limbs, 28 - - _Tortrix_, ischio-pubis, 292; - traces of posterior limb, 293 - - Toucan, _42_; - foot, 342 - - _Toxodon_, _46_, 361; - femur, 519; - pes, 525; - teeth, 432 - - Toxodontia, _46_; - general characters, 361; - manus, 509; - skull, 472; - teeth, 432 - - Toxodontidae, _46_ - - Trabeculae 11; - -- cranii, 17 - - Tragulidae, _45_ - - Tragulina, _45_, 359; - fibula, 519; - manus, 507; - odontoid process, 445; - pes, 523; - skull, 468; - teeth, 429; - ulna, 501 - - Transpalatine, crocodile, 255; - reptiles, 278 - - Trapezium, 27; - dog, 408 - - Trapezoid, 27; - dog, 408 - - Trichechidae, _48_, 369 - - _Trichechus_, _48_; - see Walrus - - Trionychia, _37_; - general characters, 194 - - Trionychidae, _37_ - - _Trionyx_, _37_, 193 f.; - exoskeleton, 214, 270; - skull, 283; - vestiges of teeth, 274 - - _Trissolepis_, _32_; - scales, 104 - - _Tritylodon_, _43_; - teeth, 348 - - Trochanter, dog 412; - duck, 326 - - Trochilidae, _42_; - see Humming-birds - - Trochlea, crocodile, 263; - dog, 405 f.; - duck, 323; - turtle, 232 - - Trogon, _42_; - foot, 342 - - Trogonidae, _42_ - - _Tropidonotus_, _38_; - jaws, 280; - skull, =279= - - Trunk vertebrae, cod, 84; - see thoracic and lumbar vertebrae - - _Trygon_, _32_; - calcification of vertebrae, 114; - caudal spine, 106 - - Trygonidae, _32_ - - Tuberosities of humerus, dog, 405; - of ischium, dog, 411 - - Tunicata, _30_, 51 - - _Tupaia_, skull, 480; - thoraco-lumbar vertebrae, 450 - - Turbinals, dog, 395 - - _Tursiops_, _45_; - skull, 462 - - Turtle, _37_; - anterior limb, 232, =234=; - cranium, 222 f., =226=; - hyoid, 231, =285=; - mandible, 230; - pectoral girdle, 231; - pelvic girdle, 235; - pes, 236; - plastron, 217, =218=; - posterior limb, =234=, 235; - sense capsules, 227; - skull, 222; - vertebral column, 219; - Leathery --, see _Dermochelys_; - Snapping --, see _Trionyx_ - - Tylopoda, _45_, 359; - fibula, 519; - manus, 507; - odontoid process, 445; - pelvis, 514; - pes, 523; - skull, 468; - teeth, 428; - ulna, 502 - - Tympanic, dog, 392; - -- cavity, crocodile, 250; - diagram of mammalian, =391=; - dog, 393; - duck, 315 f.; - turtle, 228; - -- recess, duck, 315 - - Tympano-hyal, dog, 399 - - Typhlopidae, _38_; - scales, 270; - skull, 278 - - _Typhlops_, _38_; - ischio-pubis, 292; - traces of posterior limb, 293 - - Typotheriidae, _46_ - - _Typotherium_, _46_, 358, 361; - clavicle, 495, 497; - femur, 519; - pes, 525; - skull, 472; - teeth, 432 - - - _Udenodon_, _36_, _192_; - beak, 271 - - Uintatheriidae, _47_; - skull, 364 - - _Uintatherium_, _47_; - dental formula, 433; - leg, 519; - limbs and limb girdles, =516=; - manus, 510; - pelvis, 514; - skull, 473 - - Ulna, 26; - crocodile, 265; - dog, 406; - duck, 323; - frog, 164; - newt, 147; - turtle, 233 - - Ulnare, 27; - see Carpus - - Umbilicus, inferior and superior, duck, 303 - - Uncinate process, 190; - crocodile, 259; - duck, 320 - - Unciform, 27, 345, 504; - dog, 408 - - Ungulata, _45_; - auditory ossicles, 487; - caudal vertebrae, 453; - cervical vertebrae, 445; - general characters, 357; - manus, 506; - pectoral girdle, 495; - pes, 522; - ribs, 491; - sacrum, 452; - skull, 464 f.; - sternum, 489; - teeth, 427 f.; - thoraco-lumbar vertebrae, 448 - - Ungulata vera, _45_; - arm bones, 501; - general characters, 358; - manus, 506; - pelvis, 514; - thigh and shin, 519 - - Upper arm, 26; - crocodile, 263; - dog, 405; - duck, 323; - frog, 164; - newt, 147; - turtle, 232 - - _Upupa_, _42_; - see Hoopoe - - Urochordata, _30_, 51 - - Urodela, _35_; - general characters, 134; - pelvis, 187; - ribs, 182; - skull, 174 - - Urohyal, cod, 101; - duck, 320 - - Urostyle, Anura 172; - cod, 85; - frog, 153; - Teleostei, 117 - - Ursidae, _48_; - humerus, 502 - - _Ursus_, _48_; - dental formula, 439; - see Bears - - - Vacuities, anterior palatine --, crocodile, 252, 258; - -- in reptilian skull, 281; - posterior palatine --, crocodile, 254, 257; - pre-orbital --, reptiles, 283 f. - - Vampire, _49_; - teeth, 441 - - Vane, of feather, 303 - - Varanidae, _38_ - - _Varanus_, _38_; - shoulder girdle, =202=; - skull, =201= - - Vasodentine, 108, 272 - - Vertebral column, 14; - Amphibia, 170; - birds, 332; - cod, 83; - crocodile, 239; - dog, 378; - duck, 307; - Elasmobranchs, 113; - frog, 152; - mammals, 442; - newt, 138; - turtle, 219; - -- ribs, crocodile, 259; - dog, 402; - duck, 320; - -- shield, turtle, 214 - - Vertebrata, general characters, 53 - - Vexillum, of feather, 303 - - Vibrissae, dog, 374 - - Viscacha, _47_ - - Visceral skeleton, 21; - dogfish, 77; - Elasmobranchs, 119 f. - - _Viverra_, _48_; - acetabular bone, 515 - - Viverridae, _48_ - - Vomer, 21; - cod, 98; - crocodile, 252; - dog, 395; - duck, 317; - frog, 158; - salmon, 93; - turtle, 229 - - Vomero-palatine, newt, 143 - - _Vultur_, _41_ - - Vulture, _41_; - Black --, shoulder girdle and sternum, =337= - - - Waders, 335 - - Walrus, _48_, 367, 369; - canines, 420; - manus, 511; - pes, 526; - position of limbs, 29; - skull, 480; - teeth, 440 - - Warblers, _42_ - - Wart hog, _45_; - teeth, 428 - - Weasel, _369_ - - Whale, baleen, 3, 418; - Ca'ing --, _45_, - see _Globicephalus_; - Humpbacked --, _44_, 357; - Right --, _44_, 357; - Sperm --, _44_, 357, - see _Physeter_; - True or Whalebone --, 356 - - Whiting, _33_ - - Wild duck, _41_; - see Duck - - Wing, duck, 322; - Gannet, Ostrich, and Penguin, =339= - - Wolf, _48_ - - Wombat, _43_; - atlas, 443; - pes, 521; - sacrum, 451; - skull, =456=; - tail, 453; - teeth, 423 - - Woodpecker, _42_, 335; - foot, 342; - hyoid, 336 - - Wrasse, _33_; - teeth, 111 - - - _Xenacanthus_, _31_; - pectoral fins, 130 - - Xenopidae, _36_ - - _Xenopus_, _36_; - branchial arches, 182; - nails, 168; - pelvis, 188; - ribs, 182 - - Xiphiplastron, turtle, 217 - - Xiphisternal horn, crocodile, 260 - - Xiphisternum, dog, 404; - frog, 163 - - Xiphoid process, duck, 321 - - - _Zeuglodon_, _44_, 353, 356; - dental formula, 426; - dermal plates, 420 - - Zeuglodontidae, _44_ - - Zygantra, defined, 199 n.; - reptiles, 276 - - Zygapophyses, cod, 84; - crocodile, 240 f.; - dog, 379 f.; - duck, 308 f.; - frog, 152 f.; - newt, 139; - turtle, 219 f. - - Zygosphene, defined, 199 n.; 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Reynolds @@ -147,46 +147,7 @@ div.tnotes { </style> </head> <body> - - -<pre> - -The Project Gutenberg EBook of The Vertebrate Skeleton, by Sidney H. Reynolds - -This eBook is for the use of anyone anywhere at no cost and with -almost no restrictions whatsoever. You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org - - -Title: The Vertebrate Skeleton - -Author: Sidney H. Reynolds - -Release Date: August 9, 2013 [EBook #43431] - -Language: English - -Character set encoding: ISO-8859-1 - -*** START OF THIS PROJECT GUTENBERG EBOOK THE VERTEBRATE SKELETON *** - - - - -Produced by Chris Curnow, Mark Young and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - - -</pre> - - +<div>*** START OF THE PROJECT GUTENBERG EBOOK 43431 ***</div> <div class="tnotes covernote"> <p class="noin">Transcriber's Note</p> @@ -2465,7 +2426,7 @@ archipterygia (see p. 127).</p></blockquote><p><span class="pagenum"><a name="Pa <li><span style="margin-left: 1em;">Subgroup Steganopodes. Sula—gannet.</span></li> <li><span style="margin-left: 11.3em;">Pelicanus—pelican.</span></li> -<li><span style="margin-left: 11.3em;">Phaëthon—frigate bird.</span></li> +<li><span style="margin-left: 11.3em;">Phaëthon—frigate bird.</span></li> <li><span style="margin-left: 11.3em;">Phalacrocorax—cormorant.</span></li> <li><span style="margin-left: 1em;">Subgroup Ardeae. Ardea—heron</span></li> @@ -2658,7 +2619,7 @@ archipterygia (see p. 127).</p></blockquote><p><span class="pagenum"><a name="Pa <li><span style="margin-left: 4em;">Suborder (3)</span>. <span class="smcap">Odontoceti.</span></li> <li>Family <b>Physeteridae</b>. Physeter—sperm whale.</li> -<li><span style="margin-left: 14em;">Hyperoödon—bottlenose.</span></li> +<li><span style="margin-left: 14em;">Hyperoödon—bottlenose.</span></li> <li><span style="margin-left: 14em;">Ziphius.</span></li> <li><span style="margin-left: 14em;">Mesoplodon.</span></li> @@ -3012,7 +2973,7 @@ the notochord is lost in the adult.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_068.jpg" width="800" height="169" alt="" title="" /> -<div class="caption"><a class="smcap">Fig. 3. Diagram of the skeleton of</a><i> Amphioxus lanceolatus</i> × 3<br /> +<div class="caption"><a class="smcap">Fig. 3. Diagram of the skeleton of</a><i> Amphioxus lanceolatus</i> × 3<br /> (after a drawing in the Index collection at the Brit. Mus.).<br /> <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. skeleton of dorsal fin.</td><td align="left">5. branchial skeleton.</td></tr> @@ -3196,7 +3157,7 @@ Ammocoete.<span class="pagenum"><a name="Page_56" id="Page_56">[56]</a></span></ <div class="figcenter" style="width: 800px;"> <img src="images/i_073.jpg" width="800" height="399" alt="" title="" /> <div class="caption"><a class="smcap">Fig. 4. A, dorsal; B, lateral and C, ventral view of the<br /> -skull of</a> <i>Petromyzon marinus</i> × 1 (after <a class="smcap">Parker</a>).<br /> +skull of</a> <i>Petromyzon marinus</i> × 1 (after <a class="smcap">Parker</a>).<br /> <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. horny teeth.</td><td align="left">8. lateral distal mandibular.</td></tr> @@ -3957,7 +3918,7 @@ enters the orbit (fig. 6, 9).<span class="pagenum"><a name="Page_76" id="Page_76 <div class="figcenter" style="width: 800px;"> <img src="images/i_092.jpg" width="800" height="358" alt="" title="" /> <div class="caption"><a class="smcap">Fig. 6. Lateral view of the skull of a Dogfish</a> (<i>Scyllium<br /> -canicula</i>) × 2/3.<br /> +canicula</i>) × 2/3.<br /> <table border="0" width="100%" cellpadding="0" cellspacing="0" summary=""> <tr><td align="left">1. nasal capsule.</td><td align="left">10. ethmo-palatine ligament.</td></tr> @@ -4128,7 +4089,7 @@ distally.</p> <div class="figcenter" style="width: 691px;"> <img src="images/i_097.jpg" width="691" height="600" alt="" title="" /> <div class="caption"><a class="smcap">Fig. 7. Semidorsal view of the pectoral girdle and fins<br /> -of a Dogfish</a> (<i>Scyllium canicula</i>) × 2/3.<br /> +of a Dogfish</a> (<i>Scyllium canicula</i>) × 2/3.<br /> The gaps between the radiale are blackened. <table border="0" width="100%" cellpadding="1" cellspacing="1" summary=""> @@ -4789,7 +4750,7 @@ Dogfish.</p> <div class="figcenter" style="width: 797px;"> <img src="images/i_116.jpg" width="797" height="600" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 12. Mandibular and hyoid arches of a Cod</span> (<i>Gadus<br /> -morrhua</i>) × ½ (Brit. Mus.). +morrhua</i>) × ½ (Brit. Mus.). <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. palatine.</td><td align="left">9. articular.</td></tr> @@ -4895,7 +4856,7 @@ greatly developed, and the cartilage bones, the <b>scapula</b> and <div class="figcenter" style="width: 600px;"> <img src="images/i_119.jpg" width="600" height="622" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 13. The right half of the pectoral girdle and right<br /> -pectoral fin of a Cod</span> (<i>Gadus morrhua</i>) × ½ (Brit. Mus.). +pectoral fin of a Cod</span> (<i>Gadus morrhua</i>) × ½ (Brit. Mus.). <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. post-temporal.</td><td align="left">5. scapula.</td></tr> @@ -5109,7 +5070,7 @@ closely allied to bone.</p> <div class="figcenter" style="width: 722px;"> <img src="images/i_125.jpg" width="722" height="600" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 15. Part of the lower jaw of a Shark</span> (<i>Galeus</i>)<br /> -(from <span class="smcap">Owen</span> after <span class="smcap">André</span>). +(from <span class="smcap">Owen</span> after <span class="smcap">André</span>). <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. teeth in use.</td><td align="left">a Sting-ray (<i>Trygon</i>) which has</td></tr> @@ -5468,8 +5429,8 @@ are still distinguishable.</p> <div class="figcenter" style="width: 600px;"><span class="pagenum"><a name="Page_118" id="Page_118">[118]</a></span> <img src="images/i_135.jpg" width="600" height="759" alt="" title="" /> -<div class="caption"><span class="smcap">Fig. 16.</span> A. <span class="smcap">Skull of</span> <i>Notidanus</i> × ½ (Brit. Mus.). B. <span class="smcap">Skull of</span><br /> -<i>Cestracion</i> × 1/3 (after <span class="smcap">Gegenbaur</span>). In neither case are the<br /> +<div class="caption"><span class="smcap">Fig. 16.</span> A. <span class="smcap">Skull of</span> <i>Notidanus</i> × ½ (Brit. Mus.). B. <span class="smcap">Skull of</span><br /> +<i>Cestracion</i> × 1/3 (after <span class="smcap">Gegenbaur</span>). In neither case are the<br /> branchial arches shown. <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> @@ -5714,7 +5675,7 @@ branchial arches bear gill rakers.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_142.jpg" width="800" height="485" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 19. Dorsal (to the left) and ventral (to the right) views -of the cranium of</span> <i>Ceratodus miolepis</i> (after <span class="smcap">Günther</span>). +of the cranium of</span> <i>Ceratodus miolepis</i> (after <span class="smcap">Günther</span>). <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. cartilaginous part of the</td><td align="left">7. pre-opercular (squamosal).</td></tr> @@ -5811,7 +5772,7 @@ fin-rays.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_145.jpg" width="800" height="190" alt="" title="" /> -<div class="caption"><span class="smcap">Fig. 20. Lateral view of the skeleton of</span> <i>Ceratodus miolepis</i> (after <span class="smcap">Günther</span>). +<div class="caption"><span class="smcap">Fig. 20. Lateral view of the skeleton of</span> <i>Ceratodus miolepis</i> (after <span class="smcap">Günther</span>). <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. ethmoid.</td><td align="left">9. pectoral girdle.</td></tr> @@ -6288,7 +6249,7 @@ connect the frontals with the maxillae.<span class="pagenum"><a name="Page_142" <div class="figcenter" style="width: 600px;"> <img src="images/i_159.jpg" width="600" height="616" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 21. A dorsal, B ventral, and C lateral views of the skull<br /> -of a Newt</span> (<i>Molge cristata</i>) × 2½ (after <span class="smcap">Parker</span>).<br /> +of a Newt</span> (<i>Molge cristata</i>) × 2½ (after <span class="smcap">Parker</span>).<br /> The cartilage is dotted, the cartilage bones are marked with dots and<br /> dashes, the membrane bones are left white. @@ -6440,7 +6401,7 @@ a posterior part, the <b>coracoid</b>.<span class="pagenum"><a name="Page_146" i <div class="figcenter" style="width: 399px;"> <img src="images/i_163.jpg" width="399" height="800" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 22. A ventral, and B lateral view of the shoulder girdle -and sternum of an old male Crested Newt</span> (<i>Molge cristata</i>) × 3 +and sternum of an old male Crested Newt</span> (<i>Molge cristata</i>) × 3 (after <span class="smcap">Parker</span>). <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> @@ -6509,7 +6470,7 @@ the frog probably being the one that is absent.</p> <div class="figcenter" style="width: 738px;"> <img src="images/i_165.jpg" width="738" height="600" alt="" title="" /> <div class="caption"> <span class="smcap">Fig. 23. A right posterior, and B right anterior limb of a Newt</span> -× 1½ (<i>Molge cristata</i>). +× 1½ (<i>Molge cristata</i>). <table border="0" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. femur.</td><td align="left">10. humerus.</td></tr> @@ -6774,7 +6735,7 @@ exoccipitals.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_172.jpg" width="800" height="473" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 24. A dorsal, and B ventral views of the cranium of a -Common Frog</span> (<i>Rana temporaria</i>) × 2 (after <span class="smcap">Parker</span>). +Common Frog</span> (<i>Rana temporaria</i>) × 2 (after <span class="smcap">Parker</span>). In this and the next two figs. cartilage is dotted, cartilage bones are marked with dots and dashes, membrane bones are left white. @@ -6844,7 +6805,7 @@ closely united to the cranium.</p> <img src="images/i_174.jpg" width="800" height="444" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 25. A dorsal and B ventral view of the cranium of a common Frog</span> (<i>Rana temporaria</i>) from which the membrane bones have -mostly been removed. × 2 (after <span class="smcap">Parker</span>). +mostly been removed. × 2 (after <span class="smcap">Parker</span>). <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. sphenethmoid.</td><td align="left">8. pro-otic.</td></tr> @@ -6920,7 +6881,7 @@ a short process which projects upwards and meets the nasal.</p> <div class="figcenter" style="width: 600px;"> <img src="images/i_176.jpg" width="600" height="643" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 26.</span> <span class="smcap">A, Lateral view of the skull</span>, <span class="smcap">B, Posterior view of the -cranium of a Common Frog</span> (<i>Rana temporaria</i>) × 2 (after <span class="smcap">Parker</span>). +cranium of a Common Frog</span> (<i>Rana temporaria</i>) × 2 (after <span class="smcap">Parker</span>). <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. sphenethmoid.</td><td align="left">14. mento-meckelian.</td></tr> @@ -7565,7 +7526,7 @@ definite tympanic cavity.</p> <div class="figcenter" style="width: 600px;"> <img src="images/i_193.jpg" width="600" height="775" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 27. Dorsal view of the skull of a Labyrinthodont</span> (<i>Capitosaurus -nasutus</i>) × 1/9 (from <span class="smcap">von Zittel</span>). +nasutus</i>) × 1/9 (from <span class="smcap">von Zittel</span>). <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. premaxillae.</td><td align="left">12. postorbital.</td></tr> @@ -8440,7 +8401,7 @@ present, but are absent in the Chamaeleons.<span class="pagenum"><a name="Page_2 <div class="figcenter" style="width: 600px;"> <img src="images/i_218.jpg" width="600" height="756" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 33. A, Lateral view, and B, longitudinal section of the skull -of a Lizard</span> (<i>Varanus varius</i>). × 3/5. (Brit. Mus.) +of a Lizard</span> (<i>Varanus varius</i>). × 3/5. (Brit. Mus.) <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. premaxillae.</td><td align="left">16. transpalatine.</td></tr> @@ -8468,7 +8429,7 @@ of a Lizard</span> (<i>Varanus varius</i>). × 3/5. (Brit. Mus.) <div class="figcenter" style="width: 600px;"> <img src="images/i_219.jpg" width="600" height="625" alt="" title="" /> -<div class="caption"><span class="smcap">Fig. 34.</span> <span class="smcap">Lateral view of the shoulder-girdle of</span> <i>Varanus.</i> × 3/5. +<div class="caption"><span class="smcap">Fig. 34.</span> <span class="smcap">Lateral view of the shoulder-girdle of</span> <i>Varanus.</i> × 3/5. (Brit. Mus.). <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> @@ -8601,7 +8562,7 @@ and some of them are borne by the premaxillae.<span class="pagenum"><a name="Pag <div class="figcenter" style="width: 800px;"> <img src="images/i_223.jpg" width="800" height="540" alt="" title="" /> -<div class="caption"><span class="smcap">Fig. 35. Restored skeleton of</span> <i>Ceratosaurus nasicornis</i>. × 1/30. (After Marsh.) +<div class="caption"><span class="smcap">Fig. 35. Restored skeleton of</span> <i>Ceratosaurus nasicornis</i>. × 1/30. (After Marsh.) <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. anterior nares.</td><td align="left">5. scapula.</td></tr> @@ -9002,7 +8963,7 @@ Crocodiles.</p> <div class="figcenter" style="width: 600px;"> <img src="images/i_235.jpg" width="600" height="655" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 37. The Plastron of a Green Turtle</span> (<i>Chelone midas</i>). -× 1/7. (Camb. Mus.) +× 1/7. (Camb. Mus.) <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. epiplastron (clavicle).</td><td align="left">4. hypoplastron.</td></tr> @@ -9192,7 +9153,7 @@ of the neural canal of the vertebrae.<span class="pagenum"><a name="Page_223" id <div class="figcenter" style="width: 460px;"> <img src="images/i_240.jpg" width="460" height="800" alt="" title="" /> -<div class="caption"><span class="smcap">Fig. 38. The skull of the Green Turtle</span> (<i>Chelone midas</i>). × ½. +<div class="caption"><span class="smcap">Fig. 38. The skull of the Green Turtle</span> (<i>Chelone midas</i>). × ½. <span class="smcap">A, posterior half, B, anterior half.</span> (Brit. Mus.) <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> @@ -9302,7 +9263,7 @@ part in the bounding of the orbits.<span class="pagenum"><a name="Page_226" id=" <div class="figcenter" style="width: 800px;"> <img src="images/i_243.jpg" width="800" height="414" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 39. Longitudinal vertical section through the Cranium of a Green Turtle</span> -(<i>Chelone midas</i>). × 2/3. (Camb. Mus.) +(<i>Chelone midas</i>). × 2/3. (Camb. Mus.) <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. parietal.</td><td align="left">10. palatine.</td><td align="left">17. jugal.</td></tr> @@ -9552,7 +9513,7 @@ end it is closely united with the precoracoid, the two bones ossifying continuously. It tapers away distally, and is directed dorsalwards towards the carapace.</p> -<p>The <b>precoracoid</b> forms an angle of about 130° with the +<p>The <b>precoracoid</b> forms an angle of about 130° with the scapula, with which it is completely fused at its proximal end. Its distal end is somewhat expanded and flattened, and is terminated by a fibrocartilaginous <b>epiprecoracoid</b> which @@ -9632,8 +9593,8 @@ or less pointed.</p> <div class="figcenter" style="width: 600px;"> <img src="images/i_251.jpg" width="600" height="698" alt="" title="" /> <div class="caption"><span class="smcap">Fig.</span> 40. A. <span class="smcap">Anterior limb of a young Hawksbill Turtle</span> (<i>Chelone -imbricata</i>) × ¼ (Brit. Mus.). B. <span class="smcap">Posterior limb of a large Green -Turtle</span> (<i>Chelone midas</i>) × 1/8 (Camb. Mus.). +imbricata</i>) × ¼ (Brit. Mus.). B. <span class="smcap">Posterior limb of a large Green +Turtle</span> (<i>Chelone midas</i>) × 1/8 (Camb. Mus.). <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. humerus.</td><td align="left">12. femur.</td></tr> @@ -9938,7 +9899,7 @@ are just like the third.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_259.jpg" width="800" height="405" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 42. Anterior view of A, a late thoracic and B, the first sacral -vertebra of a young Crocodile</span> (<i>C. palustris</i>). × 1/3. +vertebra of a young Crocodile</span> (<i>C. palustris</i>). × 1/3. <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. neural spine.</td><td align="left">4. sacral rib.</td></tr> @@ -10051,7 +10012,7 @@ organs;</p> <div class="figcenter" style="width: 668px;"> <img src="images/i_262.jpg" width="668" height="600" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 43. Palatal aspect A, of the cranium, B, of the mandible of -an Alligator</span> (<i>Caiman latirostris</i>). × 1/3. (Brit. Mus.) +an Alligator</span> (<i>Caiman latirostris</i>). × 1/3. (Brit. Mus.) <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. premaxillae.</td><td align="left">12. quadratojugal.</td></tr> @@ -10144,7 +10105,7 @@ articulates with the <b>alisphenoids</b>.</p> <div class="figcenter" style="width: 800px;"><span class="pagenum"><a name="Page_248" id="Page_248">[248]</a></span> <img src="images/i_265.jpg" width="800" height="445" alt="" title="" /> -<div class="caption"><span class="smcap">Fig. 44. Lateral view of the skull of an Alligator</span> (<i>Caiman latirostris</i>). × 1/3. (Brit. Mus.) +<div class="caption"><span class="smcap">Fig. 44. Lateral view of the skull of an Alligator</span> (<i>Caiman latirostris</i>). × 1/3. (Brit. Mus.) <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. premaxillae.</td><td align="left">9. palatine.</td><td align="left">16. external auditory</td><td align="left">22. angular.</td></tr> @@ -10326,7 +10287,7 @@ occur between the maxillary and mandibular teeth.<span class="pagenum"><a name=" <div class="figcenter" style="width: 800px;"> <img src="images/i_270.jpg" width="800" height="461" alt="" title="" /> -<div class="caption"><span class="smcap">Fig. 45. Longitudinal section through the skull of an Alligator</span> (<i>Caiman latirostris</i>). × 1/3. (Brit. Mus.) +<div class="caption"><span class="smcap">Fig. 45. Longitudinal section through the skull of an Alligator</span> (<i>Caiman latirostris</i>). × 1/3. (Brit. Mus.) <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. premaxillae.</td><td align="left">for the trigeminal nerve.</td><td align="left">16. maxillae.</td><td align="left">25. squamosal.</td></tr> @@ -10621,7 +10582,7 @@ pair of long <b>xiphisternal horns</b> (fig. 46, 5).<span class="pagenum"><a nam <div class="figcenter" style="width: 408px;"> <img src="images/i_278.jpg" width="408" height="800" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 46. Sternum and Associated Membrane bones of a Crocodile</span> -(<i>C. palustris</i>) × 1/3. (Brit. Mus.)<br /> +(<i>C. palustris</i>) × 1/3. (Brit. Mus.)<br /> The last pair of abdominal ribs which are united with the epipubes by<br /> a plate of cartilage have been omitted. @@ -10653,7 +10614,7 @@ their respective girdles.</p> <div class="figcenter" style="width: 600px;"> <img src="images/i_279.jpg" width="600" height="645" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 47. Left half of the pectoral girdle of an Alligator</span> (<i>Caiman -latirostris</i>) × 2/3. (Brit. Mus.) +latirostris</i>) × 2/3. (Brit. Mus.) <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. scapula.</td><td align="left">3. interclavicle.</td></tr> @@ -10712,7 +10673,7 @@ bones of the fore-arm, the radius and ulna.<span class="pagenum"><a name="Page_2 <div class="caption"><span class="smcap">Fig. 48.</span> <span class="smcap">A, right anterior, and B, right posterior limb of a young Alligator</span> (<i>Caiman latirostris</i>). (Brit. Mus.)<br /> -<span style="margin-left: 3em;">A × ½. </span><span style="margin-left: 2em;">B × about 1/3.</span> +<span style="margin-left: 3em;">A × ½. </span><span style="margin-left: 2em;">B × about 1/3.</span> <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. humerus.</td><td align="left">10. proximal phalanx of second</td></tr> @@ -10819,7 +10780,7 @@ between the anterior parts of the ilium and ischium.</p> <div class="figcenter" style="width: 600px;"> <img src="images/i_284.jpg" width="600" height="636" alt="" title="" /> -<div class="caption"><span class="smcap">Fig. 49. Pelvis and sacrum of an Alligator</span> (<i>Caiman latirostris</i>) × ½.<br /> +<div class="caption"><span class="smcap">Fig. 49. Pelvis and sacrum of an Alligator</span> (<i>Caiman latirostris</i>) × ½.<br /> (Brit. Mus.) <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> @@ -11077,7 +11038,7 @@ seen in the Crocodilia.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_291.jpg" width="800" height="284" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 50. Preparation of part of the right mandibular ramus of</span> -<i>Crocodilus palustris</i> × ½. (Brit. Mus.) +<i>Crocodilus palustris</i> × ½. (Brit. Mus.) <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. tooth in use.</td><td align="left">3. symphysial surface of the</td></tr> @@ -11467,7 +11428,7 @@ hyoid is often fairly large.<span class="pagenum"><a name="Page_285" id="Page_28 <div class="figcenter" style="width: 747px;"> <img src="images/i_302.jpg" width="747" height="600" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 53. Hyoids of an Alligator</span> (<i>Caiman latirostris</i>) (<span class="smcap">to the left</span>) -<span class="smcap">and of a Green Turtle</span> (<i>Chelone midas</i>) (<span class="smcap">to the right</span>) × 5/8. +<span class="smcap">and of a Green Turtle</span> (<i>Chelone midas</i>) (<span class="smcap">to the right</span>) × 5/8. (Brit. Mus.)<br /> The cartilaginous portions are dotted. @@ -11538,7 +11499,7 @@ membrane bone.</p> <img src="images/i_304.jpg" width="440" height="800" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 54. Ventral view of the shoulder-girdle <ins class="edcorr" title="Errata: p. 287, description of figure, for shoulder-girdle of sternum read shoulder-girdle and sternum.">and</ins> sternum of a -Lizard</span> (<i>Loemanctus longipes</i>) × 2. (After <span class="smcap">Parker</span>.) +Lizard</span> (<i>Loemanctus longipes</i>) × 2. (After <span class="smcap">Parker</span>.) <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. interclavicle.</td><td align="left">6. glenoid cavity.</td></tr> @@ -12103,7 +12064,7 @@ of the pre-digitals is very small, and is called the <b>remicle</b> <div class="caption"><span class="smcap">Fig. 56. The wing of a Wild Duck</span> (<i>Anas boschas</i>). <p class="cen">The upper figure shows the dorsal side of a right wing, the lower figure</p> -<p class="cen">the ventral side of a left wing. × 1/3. (Brit. Mus.)</p> +<p class="cen">the ventral side of a left wing. × 1/3. (Brit. Mus.)</p> <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. scapulars.</td><td align="left">6. metacarpo-digitals or</td></tr> @@ -12130,7 +12091,7 @@ half of the humerus.</p> <div class="figcenter" style="width: 735px;"> <img src="images/i_322.jpg" width="735" height="600" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 57. Wings of a Wild Duck with the coverts removed</span> -(<i>Anas boschas</i>). × 1/3.<br /> +(<i>Anas boschas</i>). × 1/3.<br /> <p>A. Right wing seen from the dorsal side. B. Left wing disarticulated</p> <p class="cen">and seen from the ventral side. (Brit. Mus.)</p> @@ -12388,7 +12349,7 @@ vertebrae fused together; this bears the rectrices or tail quills.</p> <div class="figcenter" style="width: 600px;"> <img src="images/i_329.jpg" width="600" height="639" alt="" title="" /> -<div class="caption"><span class="smcap">Fig. 59. Skull of a Duck</span> (<i>Anas boschas</i>). × 1. +<div class="caption"><span class="smcap">Fig. 59. Skull of a Duck</span> (<i>Anas boschas</i>). × 1. <p>A. Dorsal view of the cranium. <span style="margin-left: 2em;">B. Palatal view of the mandible.</span></p> <p class="cen">C. The Hyoid.</p> @@ -12403,7 +12364,7 @@ vertebrae fused together; this bears the rectrices or tail quills.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_330.jpg" width="800" height="595" alt="" title="" /> <div class="caption"><p><span class="smcap">Fig. 60.</span> A. Ventral view of the cranium of a Duck (<i>Anas boschas</i>).</p> -<p><span style="margin-left: 2em;">B. Cranium and mandible seen from the left side. × 1.</span></p> +<p><span style="margin-left: 2em;">B. Cranium and mandible seen from the left side. × 1.</span></p> <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. maxillae.</td><td align="left">22. anterior palatine foramen.</td></tr> @@ -12886,7 +12847,7 @@ femur articulates.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_342.jpg" width="800" height="478" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 61. Lateral view of the pelvis and sacrum of a Duck</span> (<i>Anas -boschas</i>) × 2/3. +boschas</i>) × 2/3. <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. ilium.</td><td align="left">5. acetabulum.</td></tr> @@ -13123,7 +13084,7 @@ and manus; in Hornbills every bone contains air.</p> <div class="figcenter" style="width: 616px;"> <img src="images/i_348.jpg" width="616" height="600" alt="" title="" /> <div class="caption"><p><span class="smcap">Fig. 62. Third Cervical Vertebra of an Ostrich</span> (<i>Struthio camelus</i>).</p> -<p>× 1. A anterior, B posterior, C dorsal view (A and B after <span class="smcap">Mivart</span>).</p> +<p>× 1. A anterior, B posterior, C dorsal view (A and B after <span class="smcap">Mivart</span>).</p> <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. neural spine.</td><td align="left">6. anterior articular surface of</td></tr> @@ -13330,9 +13291,9 @@ embryo.</p> <img src="images/i_354.jpg" width="600" height="725" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 63. Shoulder-girdle and sternum of</span></p> -<p>A. <span class="smcap">Black Vulture</span> (<i>Vultur cinereus</i>) × 1/3.</p> -<p>B. <span class="smcap">Peacock</span> (<i>Pavo cristatus</i>) × 3/8.</p> -<p>C. <span class="smcap">Pelican</span> (<i>Pelicanus conspicillatus</i>) × 1/3. (All Camb. Mus.)</p> +<p>A. <span class="smcap">Black Vulture</span> (<i>Vultur cinereus</i>) × 1/3.</p> +<p>B. <span class="smcap">Peacock</span> (<i>Pavo cristatus</i>) × 3/8.</p> +<p>C. <span class="smcap">Pelican</span> (<i>Pelicanus conspicillatus</i>) × 1/3. (All Camb. Mus.)</p> <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. carina of the sternum.</td><td align="left">6. surfaces for articulation with</td></tr> @@ -13393,9 +13354,9 @@ phalanges, in all other living birds it has only one phalanx.<span class="pagenu <img src="images/i_356.jpg" width="650" height="600" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 64. Bones of the right wing of</span></p> -<p>A. <span class="smcap">A Penguin</span> × 1/3. (Camb. Mus.)</p> -<p>B. <span class="smcap">Ostrich</span> (<i>Struthio camelus</i>) × 1/7. (Partly after <span class="smcap">Parker</span>.)</p> -<p>C. <span class="smcap">Gannet</span> (<i>Sula alba</i>) × 1/3. (Camb. Mus.)</p> +<p>A. <span class="smcap">A Penguin</span> × 1/3. (Camb. Mus.)</p> +<p>B. <span class="smcap">Ostrich</span> (<i>Struthio camelus</i>) × 1/7. (Partly after <span class="smcap">Parker</span>.)</p> +<p>C. <span class="smcap">Gannet</span> (<i>Sula alba</i>) × 1/3. (Camb. Mus.)</p> <p>In C the distal phalanges of the pollex and second digit have been omitted.</p> @@ -13437,10 +13398,10 @@ the ilium. The acetabulum in birds is always perforate.</p> <img src="images/i_357.jpg" width="469" height="800" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 65. Pelvic girdle and sacrum of</span></p> -<p>A. <span class="smcap">Cassowary</span> (<i>Casuarius galeatus</i>) × 1/8.</p> -<p>B. <span class="smcap">Owen's Apteryx</span> (<i>A. oweni</i>) × ½.</p> -<p>C. <span class="smcap">Broad billed Rhea</span> (<i>R. macrorhyncha</i>) × 1/6.</p> -<p>D. <span class="smcap">Ostrich</span> (<i>Struthio camelus</i>) × 1/10. (All Camb. Mus.)</p> +<p>A. <span class="smcap">Cassowary</span> (<i>Casuarius galeatus</i>) × 1/8.</p> +<p>B. <span class="smcap">Owen's Apteryx</span> (<i>A. oweni</i>) × ½.</p> +<p>C. <span class="smcap">Broad billed Rhea</span> (<i>R. macrorhyncha</i>) × 1/6.</p> +<p>D. <span class="smcap">Ostrich</span> (<i>Struthio camelus</i>) × 1/10. (All Camb. Mus.)</p> <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. ilium.</td><td align="left">4. acetabulum.</td></tr> @@ -13472,7 +13433,7 @@ atrophied. In the Penguins however the distal end is complete. The distal tarsals fuse with the second, third and fourth<span class="pagenum"><a name="Page_342" id="Page_342">[342]</a></span> metatarsals, forming a compound bone, the tarso-metatarsus. The first metatarsal is nearly always free but occasionally -as in <i>Phaëthon</i> it is fused with the others. No adult bird +as in <i>Phaëthon</i> it is fused with the others. No adult bird has more than four digits in the pes. In the Penguins the metatarsals are separate, and in many birds larger or smaller gaps exist between the fused metatarsals. In most birds @@ -13658,7 +13619,7 @@ resemblance to those of some Theromorphous reptiles.</p> <div class="figcenter" style="width: 523px;"> <img src="images/i_364.jpg" width="523" height="800" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 66. Ventral view of the shoulder-girdle and sternum of -a Duckbill</span> (<i>Ornithorhynchus paradoxus</i>) × ¾ (after <span class="smcap">Parker</span>). +a Duckbill</span> (<i>Ornithorhynchus paradoxus</i>) × ¾ (after <span class="smcap">Parker</span>). <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1 and 2. scapula.</td><td align="left">8. presternum.</td></tr> @@ -13890,7 +13851,7 @@ bones.</p> <div class="figcenter" style="width: 663px;"> <img src="images/i_371.jpg" width="663" height="600" alt="" title="" /> <div class="caption"><span class="smcap">Fig. 67. Cervical vertebrae of a Ca'ing Whale</span> (<i>Globicephalus -melas</i>) × ¼. (Camb. Mus.) +melas</i>) × ¼. (Camb. Mus.) <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. centrum of seventh cervical</td><td align="left">4. foramen for exit of first spinal</td></tr> @@ -14509,7 +14470,7 @@ the pollex.</p> <p>The pollex is clawed and so is sometimes the second digit; the other digits of the manus are without nails or claws. The teeth are divisible into the four usual types and the series -never exceeds <i>i</i> <sup>2</sup>/<sub>3</sub> <i>c</i> <sup>1</sup>/<sub>1 </sub> <i>pm</i> <sup>3</sup>/<sub>3</sub> <i>m</i> <sup>3</sup>/<sub>3</sub> × 2, total 38. The milk +never exceeds <i>i</i> <sup>2</sup>/<sub>3</sub> <i>c</i> <sup>1</sup>/<sub>1 </sub> <i>pm</i> <sup>3</sup>/<sub>3</sub> <i>m</i> <sup>3</sup>/<sub>3</sub> × 2, total 38. The milk teeth are quite unlike the permanent teeth. The orbit is not divided by bone from the temporal fossa. The vertebral column is short, and in old animals the trunk vertebrae @@ -14641,7 +14602,7 @@ enamel of epidermal origin.</p> <div class="figcenter" style="width: 574px;"> <img src="images/i_392.jpg" width="574" height="800" alt="" title="" /> -<div class="caption"><span class="smcap">Fig. 68. Dentition of a Dog</span> (<i>Canis familiaris</i>) × ½. (Camb. Mus.) +<div class="caption"><span class="smcap">Fig. 68. Dentition of a Dog</span> (<i>Canis familiaris</i>) × ½. (Camb. Mus.) <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left"><i>i</i> 2. second incisor.</td><td align="left"><i>pm</i> 1, <i>pm</i> 4. first and fourth</td></tr> @@ -14662,7 +14623,7 @@ But while there are three molars on each side of the lower jaw, the last is wanting in the upper jaw. The dentition of the dog may then be represented by the formula</p> -<p class="cen"><i>i</i> <sup>3</sup>/<sub>3</sub> <i>c</i> <sup>1</sup>/<sub>1</sub> <i>pm</i> <sup>4</sup>/<sub>4</sub> <i>m</i> <sup>2</sup>/<sub>3</sub> × 2 = 42.</p> +<p class="cen"><i>i</i> <sup>3</sup>/<sub>3</sub> <i>c</i> <sup>1</sup>/<sub>1</sub> <i>pm</i> <sup>4</sup>/<sub>4</sub> <i>m</i> <sup>2</sup>/<sub>3</sub> × 2 = 42.</p> <p>In each jaw there is one large specially modified tooth @@ -15093,7 +15054,7 @@ ridge, which forms the anterior part of the <b>sagittal crest</b>.</p> <img src="images/i_404.jpg" width="800" height="566" alt="" title="" /> <div class="caption"><p><span class="smcap">Fig. 72. Vertical longitudinal section taken a little to the left of the middle line through the skull of a Dog</span> (<i>Canis familiaris</i>) -× <sup>3</sup>/<sub>5</sub>. (Camb. Mus.)</p> +× <sup>3</sup>/<sub>5</sub>. (Camb. Mus.)</p> <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. supra-occipital.</td><td align="left">18. palatine.</td></tr> @@ -15144,7 +15105,7 @@ and maxillae.</p> <div class="figcenter" style="width: 485px;"><span class="pagenum"><a name="Page_389" id="Page_389">[389]</a></span> <img src="images/i_406.jpg" width="485" height="800" alt="" title="" /> <div class="caption"><p><span class="smcap">Fig. 73. Dorsal view of the cranium of a Dog</span></p> -<p class="cen">(<i>Canis familiaris</i>) × <sup>2</sup>/<sub>3</sub>.</p> +<p class="cen">(<i>Canis familiaris</i>) × <sup>2</sup>/<sub>3</sub>.</p> <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. supra-occipital.</td><td align="left">10. postorbital process of frontal.</td></tr> @@ -15393,7 +15354,7 @@ jaws being formed of membrane bone.</p> <div class="figcenter" style="width: 400px;"><span class="pagenum"><a name="Page_396" id="Page_396">[396]</a></span> <img src="images/i_413.jpg" width="480" height="800" alt="" title="" /> <div class="caption"><p><span class="smcap">Fig. 75. Ventral view of the cranium of a Dog</span></p> -<p class="cen">(<i>Canis familiaris</i>) × <sup>3</sup>/<sub>5</sub>. (Camb. Mus.)</p> +<p class="cen">(<i>Canis familiaris</i>) × <sup>3</sup>/<sub>5</sub>. (Camb. Mus.)</p> <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. supra-occipital.</td><td align="left">17. maxillae (palatal portion).</td></tr> @@ -15677,7 +15638,7 @@ afterwards they gradually merge together.</p> <div class="figcenter" style="width: 514px;"><a name="Page_403" id="Page_403"></a> <img src="images/i_420.jpg" width="514" height="800" alt="" title="" /> -<div class="caption"><span class="smcap">Fig. 76. Sternum and sternal ribs of a Dog</span> (<i>Canis familiaris</i>) × ½. +<div class="caption"><span class="smcap">Fig. 76. Sternum and sternal ribs of a Dog</span> (<i>Canis familiaris</i>) × ½. <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. presternum.</td><td align="left">4. xiphisternum. The flattened</td></tr> @@ -15809,7 +15770,7 @@ with which the radius articulates.</p> <div class="figcenter" style="width: 505px;"><a name="Page_407" id="Page_407"></a> <img src="images/i_424.jpg" width="505" height="800" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 77. Bones of the left upper arm and fore-arm of a Dog</span></p> -<p class="cen">(<i>Canis familiaris</i>) × ½.</p> +<p class="cen">(<i>Canis familiaris</i>) × ½.</p> <p class="cen">A, humerus (seen from the posterior side); B, radius, C, ulna, both seen</p> <p class="cen">from the anterior side.</p> @@ -15908,7 +15869,7 @@ below, forming the narrow <b>iliac surface</b> (fig. 78, A, 5).</p> <div class="figcenter" style="width: 600px;"> <img src="images/i_427.jpg" width="600" height="643" alt="" title="" /> <div class="caption"><p><span class="smcap">Fig. 78. Right innominate bone, A, of a full-grown Terrier, B, of</span></p> -<p class="cen"><span class="smcap">a Collie Puppy.</span> × 1.</p> +<p class="cen"><span class="smcap">a Collie Puppy.</span> × 1.</p> <p class="cen">A is seen from the ventral side, B from the inner or sacral side.</p> @@ -15934,7 +15895,7 @@ forms about one-third of the acetabulum.</p> <div class="figcenter" style="width: 466px;"> <img src="images/i_428.jpg" width="466" height="800" alt="" title="" /> <div class="caption"><p><span class="smcap">Fig. 79. Front view of the left leg bones of a Dog</span> </p> -<p class="cen">(<i>Canis familiaris</i>) × ½.</p> +<p class="cen">(<i>Canis familiaris</i>) × ½.</p> <p class="cen">A femur, B tibia, C fibula, D patella.</p> @@ -15996,7 +15957,7 @@ from a second, and the proximal end from two more.</p> <div class="figcenter" style="width: 447px;"> <img src="images/i_430.jpg" width="447" height="800" alt="" title="" /> <div class="caption"><p><span class="smcap">Fig. 80. A, right manus, B, right pes of a Dog</span> </p> -<p class="cen">(<i>Canis familiaris</i>) × ½ (after <span class="smcap">von Zittel</span>).</p> +<p class="cen">(<i>Canis familiaris</i>) × ½ (after <span class="smcap">von Zittel</span>).</p> <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. bone representing the fused</td><td align="left">9. fifth metacarpal.</td></tr> @@ -16273,7 +16234,7 @@ are defined on page 345.</p> <div class="figcenter" style="width: 763px;"> <img src="images/i_438.jpg" width="763" height="600" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 81. Skull of a young Indian Rhinoceros</span> (<i>R. unicornis</i>),</p> -<p class="cen"><span class="smcap">SHOWING THE CHANGE OF THE DENTITION</span> × 1/7. (Brit. Mus.)</p> +<p class="cen"><span class="smcap">SHOWING THE CHANGE OF THE DENTITION</span> × 1/7. (Brit. Mus.)</p> <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. nasal.</td><td align="left"><i>mc.</i> milk canine.</td></tr> @@ -16297,7 +16258,7 @@ mammal can be briefly expressed as a formula has been already described. The regular mammalian arrangement of teeth for each side is expressed by the formula</p> -<p class="cen"><i>i</i> <sup>3</sup>/<sub>3</sub> <i>c</i> <sup>1</sup>/<sub>1</sub> <i>pm</i> <sup>4</sup>/<sub>4</sub> <i>m</i> <sup>3</sup>/<sub>3</sub> × 2; total, 44.</p> +<p class="cen"><i>i</i> <sup>3</sup>/<sub>3</sub> <i>c</i> <sup>1</sup>/<sub>1</sub> <i>pm</i> <sup>4</sup>/<sub>4</sub> <i>m</i> <sup>3</sup>/<sub>3</sub> × 2; total, 44.</p> <p><span class="smcap">Monotremata.</span> In <i>Echidna</i> teeth are quite absent. In the young <i>Ornithorhynchus</i><a name="FNanchor_146_146" id="FNanchor_146_146"></a><a href="#Footnote_146_146" class="fnanchor">[146]</a> functional molar teeth of a multi-tubercular @@ -16308,7 +16269,7 @@ discharged by horny plates.</p> <p><span class="smcap">Marsupialia</span><a name="FNanchor_147_147" id="FNanchor_147_147"></a><a href="#Footnote_147_147" class="fnanchor">[147]</a> have a heterodont dentition, which has generally been regarded as almost monophyodont, the only tooth which has an obvious deciduous predecessor being the -last premolar. The researches of Röse<a name="FNanchor_148_148" id="FNanchor_148_148"></a><a href="#Footnote_148_148" class="fnanchor">[148]</a> and Kükenthal<a name="FNanchor_149_149" id="FNanchor_149_149"></a><a href="#Footnote_149_149" class="fnanchor">[149]</a> tend +last premolar. The researches of Röse<a name="FNanchor_148_148" id="FNanchor_148_148"></a><a href="#Footnote_148_148" class="fnanchor">[148]</a> and Kükenthal<a name="FNanchor_149_149" id="FNanchor_149_149"></a><a href="#Footnote_149_149" class="fnanchor">[149]</a> tend to show that the teeth of Marsupials are developed in the same way as in other mammals, and are diphyodont. In the case of the premolars, teeth which are homologous with @@ -16436,7 +16397,7 @@ in the embryo, but they are never functional, and are altogether absent in the adult. The anterior of these germs are simple, the posterior ones are originally complex, but subsequently split up into simple teeth like those of the -anterior part of the jaw. Hence according to Kükenthal, +anterior part of the jaw. Hence according to Kükenthal, who described these structures, the Cetacean dentition was originally heterodont.</p> @@ -16453,7 +16414,7 @@ for seizing active slippery animals such as fish. The prey is then swallowed entire without mastication. Sometimes the teeth are excessively numerous, reaching two hundred or more (fifty to sixty on each side of each jaw) in <i>Pontoporia</i>. This -multiplication of teeth is regarded by Kükenthal as due to the +multiplication of teeth is regarded by Kükenthal as due to the division into three parts of numbers of trilobed teeth similar to those of some seals.</p> @@ -16615,7 +16576,7 @@ species incisors also are absent. The dental formula is</p> <div class="figcenter" style="width: 600px;"><span class="pagenum"><a name="Page_432" id="Page_432">[432]</a></span> <img src="images/i_448.jpg" width="600" height="698" alt="" title="" /> <div class="caption"><p><span class="smcap">Fig. 82. Palatal aspect of the cranium and mandible of a -Donkey</span> (<i>Equus asinus</i>) × <sup>1</sup>/<sub>5</sub>. (Camb. Mus.)</p> +Donkey</span> (<i>Equus asinus</i>) × <sup>1</sup>/<sub>5</sub>. (Camb. Mus.)</p> <table border="0" width="100%" cellpadding="1" cellspacing="0" summary=""> <tr><td align="left">1. supra-occipital.</td><td align="left">6. glenoid surface.</td></tr> @@ -16674,7 +16635,7 @@ fissures, and the grinding teeth are of the rhinocerotic type.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_450.jpg" width="800" height="560" alt="" title="" /> -<div class="caption"><span class="smcap">Fig. 83. Skull of</span> <i>Procavia (Dendrohyrax) dorsalis</i> × <sup>2</sup>/<sub>3</sub>. (Camb. Mus.) +<div class="caption"><span class="smcap">Fig. 83. Skull of</span> <i>Procavia (Dendrohyrax) dorsalis</i> × <sup>2</sup>/<sub>3</sub>. (Camb. Mus.) <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. nasal.</td><td align="left">5. jugal.</td></tr> @@ -16831,7 +16792,7 @@ that of the Arctoidea by means of fossil forms.</p> <div class="figcenter" style="width: 527px;"> <img src="images/i_455.jpg" width="527" height="800" alt="" title="" /> -<div class="caption"><p class="cen"><span class="smcap">Fig. 85. Mandible of Isabelline Bear</span> (<i>Ursus isabellinus</i>) × ½.</p> +<div class="caption"><p class="cen"><span class="smcap">Fig. 85. Mandible of Isabelline Bear</span> (<i>Ursus isabellinus</i>) × ½.</p> <p class="cen">(Camb. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. condyle.</td><td align="left"><i>m</i> 1. first molar. The dotted</td></tr> @@ -16860,7 +16821,7 @@ carnassial teeth.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_456.jpg" width="800" height="284" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 86. Left mandibular ramus of the Sea Leopard</span> (<i>Ogmorhinus leptonyx</i>)</p> -<p class="cen"><span class="smcap">WITH THE ROOTS OF THE TEETH EXPOSED</span> × <sup>1</sup>/<sub>3</sub>. (Camb. Mus.)</p> +<p class="cen"><span class="smcap">WITH THE ROOTS OF THE TEETH EXPOSED</span> × <sup>1</sup>/<sub>3</sub>. (Camb. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. condyle.</td><td align="left"><i>pm</i> 1, <i>pm</i> 4. first and fourth</td></tr> <tr><td align="left">2. coronoid process.</td><td align="left">premolars.</td></tr> @@ -17046,7 +17007,7 @@ they are very variable.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_461.jpg" width="800" height="408" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 87. Cervical vertebrae of a young Fin Whale</span></p> -<p class="cen">(<i>Balaenoptera musculus</i>) × <sup>1</sup>/<sub>10</sub>. (Camb. Mus.)</p> +<p class="cen">(<i>Balaenoptera musculus</i>) × <sup>1</sup>/<sub>10</sub>. (Camb. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. surface on the atlas for articulation</td><td align="left"><span style="margin-left: 2.2em;">In the fresh specimen these two</span></td></tr> <tr><td align="left">with the occipital condyle</td><td align="left">transverse processes are united by</td></tr> @@ -17076,7 +17037,7 @@ completely ossified till the animal is adult.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_462.jpg" width="800" height="334" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 88. Atlas (B) and axis (A) vertebrae of an Ox</span></p> -<p class="cen">(<i>Bos taurus</i>) × ¼. (Camb. Mus.)</p> +<p class="cen">(<i>Bos taurus</i>) × ¼. (Camb. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. neural canal.</td><td align="left">6. anterior opening of the</td></tr> <tr><td align="left">2. transverse process.</td><td align="left">vertebrarterial canal.</td></tr> @@ -17195,7 +17156,7 @@ small; in the dugong there are nineteen thoracic and four lumbar, and in the manatee seventeen thoracic and two lumbar.</p> <p>In the <span class="smcap">Cetacea</span> the number of thoracic vertebrae varies from -nine in <i>Hyperoödon</i> to fifteen or sixteen in <i>Balaenoptera</i>, and +nine in <i>Hyperoödon</i> to fifteen or sixteen in <i>Balaenoptera</i>, and the number of lumbar vertebrae from three in <i>Inia</i> to twenty-four or more in <i>Delphinus</i>. The lumbar vertebrae are often very loosely articulated together and the zygapophyses sometimes @@ -17234,7 +17195,7 @@ motion is well seen.</p> <div class="figcenter" style="width: 610px;"> <img src="images/i_466.jpg" width="610" height="600" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 89. First and second thoracic vertebrae of an Ox</span></p> -<p class="cen">(<i>Bos taurus</i>) × <sup>1</sup>/<sub>3</sub>. (Camb. Mus.)</p> +<p class="cen">(<i>Bos taurus</i>) × <sup>1</sup>/<sub>3</sub>. (Camb. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. neural spine.</td><td align="left">5. facet for articulation with the</td></tr> <tr><td align="left">2. neural canal.</td><td align="left">capitulum of the rib.</td></tr> @@ -17483,9 +17444,9 @@ dental and mental foramina of the mandible are all very large.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_473.jpg" width="800" height="363" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 90. Half front view<a name="FNanchor_165_165" id="FNanchor_165_165"></a><a href="#Footnote_165_165" class="fnanchor">[165]</a> of the skulls of a Tasmanian Wolf</span></p> -<p class="cen">(<i>Thylacinus cynocephalus</i>) (to the left) × <sup>3</sup>/<sub>8</sub>; <span class="smcap">and of a </span></p> +<p class="cen">(<i>Thylacinus cynocephalus</i>) (to the left) × <sup>3</sup>/<sub>8</sub>; <span class="smcap">and of a </span></p> <p class="cen"><span class="smcap">hairy-nosed Wombat</span></p> -<p class="cen">(<i>Phascolomys latifrons</i>) (to the right) × <sup>3</sup>/<sub>8</sub>. (Camb. Mus.)</p> +<p class="cen">(<i>Phascolomys latifrons</i>) (to the right) × <sup>3</sup>/<sub>8</sub>. (Camb. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. premaxillae.</td><td align="left">7. coronoid process of the</td></tr> <tr><td align="left">2. nasal.</td><td align="left">mandible.</td></tr> @@ -17544,7 +17505,7 @@ are ankylosed with the basi-hyal.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_475.jpg" width="800" height="589" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 91. Skull of a two-fingered Sloth</span></p> -<p class="cen"><i>(Choloepus didactylus</i>) × ½. (Camb. Mus.)</p> +<p class="cen"><i>(Choloepus didactylus</i>) × ½. (Camb. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. anterior nares.</td><td align="left">4. angle of the mandible.</td></tr> <tr><td align="left">2. postorbital process of the</td><td align="left">5. jugal.</td></tr> @@ -17603,7 +17564,7 @@ irregular manner in which they are united together.</p> <div class="figcenter" style="width: 800px;"><a name="Page_460" id="Page_460"></a> <img src="images/i_477.jpg" width="800" height="506" alt="" title="" /> -<div class="caption"><p class="cen"><span class="smcap">Fig. 92. Lateral view of the skull of</span> <i>Rhytina stelleri</i> × <sup>1</sup>/<sub>8</sub>.</p> +<div class="caption"><p class="cen"><span class="smcap">Fig. 92. Lateral view of the skull of</span> <i>Rhytina stelleri</i> × <sup>1</sup>/<sub>8</sub>.</p> <p class="cen">(Brit. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. frontal.</td><td align="left">7. pterygoid process of the</td></tr> @@ -17713,7 +17674,7 @@ much reduced as in Sirenia.</p> <div class="figcenter" style="width: 600px;"><span class="pagenum"><a name="Page_463" id="Page_463">[463]</a></span> <img src="images/i_480.jpg" width="600" height="716" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 93. A, Lateral view, and B, Longitudinal section of the skull</span></p> -<p class="cen"><span class="smcap">of a young Ca'ing Whale</span> (<i>Globicephalus melas</i>) × <sup>1</sup>/<sub>6</sub>. (Brit. Mus.)</p> +<p class="cen"><span class="smcap">of a young Ca'ing Whale</span> (<i>Globicephalus melas</i>) × <sup>1</sup>/<sub>6</sub>. (Brit. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. basi-occipital.</td><td align="left">13. periotic.</td></tr> <tr><td align="left">2. exoccipital.</td><td align="left">14. squamosal.</td></tr> @@ -17756,7 +17717,7 @@ are two great plates of bone which nearly meet above.</p> <p>In the Physeteridae the skull is raised into a very prominent crest at the vertex behind the nares. In front of this -in <i>Hyperoödon</i> a pair of ridges occur, formed by outgrowths +in <i>Hyperoödon</i> a pair of ridges occur, formed by outgrowths from the maxillae. In the old male these ridges reach an enormous size and almost meet in the middle line. In <i>Physeter</i>, the Sperm whale, these ridges are not developed; the @@ -17789,7 +17750,7 @@ considerably from one another.</p> <div class="figcenter" style="width: 600px;"><span class="pagenum"><a name="Page_466" id="Page_466">[466]</a></span> <img src="images/i_483.jpg" width="600" height="720" alt="" title="" /> -<div class="caption"><p class="cen"><span class="smcap">Fig. 94. A, Cranium and B, mandible of a Pig</span> (<i>Sus scrofa</i>) × <sup>1</sup>/<sub>5</sub>.</p> +<div class="caption"><p class="cen"><span class="smcap">Fig. 94. A, Cranium and B, mandible of a Pig</span> (<i>Sus scrofa</i>) × <sup>1</sup>/<sub>5</sub>.</p> <p class="cen">(Camb. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. jugal.</td><td align="left">11. anterior palatine foramen.</td></tr> @@ -17836,7 +17797,7 @@ being very imperfectly ossified.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_484.jpg" width="800" height="500" alt="" title="" /> -<div class="caption"><p class="cen"><span class="smcap">Fig. 95. Mandible of a Hippopotamus</span> (<i>H. amphibius</i>) × <sup>1</sup>/<sub>7</sub>.</p> +<div class="caption"><p class="cen"><span class="smcap">Fig. 95. Mandible of a Hippopotamus</span> (<i>H. amphibius</i>) × <sup>1</sup>/<sub>7</sub>.</p> <p class="cen">(Camb. Mus.)</p> <p>The second incisor of the left side is missing and the crowns of the @@ -18072,7 +18033,7 @@ cavity though very small is not so small as in <i>Uintatherium</i>.</p> <div class="figcenter" style="width: 663px;"><a name="Page_474" id="Page_474"></a> <img src="images/i_491.jpg" width="663" height="600" alt="" title="" /> <div class="caption"><p class="noin"><span class="smcap">Fig. 96. Skull of a young Indian Elephant</span> (<i>Elephas indicus</i>), <span class="smcap">SEEN</span></p> -<p class="cen"><span class="smcap">from the right side, the roots of the teeth have been exposed.</span> × <sup>1</sup>/<sub>8</sub>. (Camb. Mus.).</p> +<p class="cen"><span class="smcap">from the right side, the roots of the teeth have been exposed.</span> × <sup>1</sup>/<sub>8</sub>. (Camb. Mus.).</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. exoccipital.</td><td align="left">14. postorbital process of the</td></tr> <tr><td align="left">2. parietal.</td><td align="left">frontal.</td></tr> @@ -18126,7 +18087,7 @@ very exceptional condition.</p> <img src="images/i_492.jpg" width="605" height="600" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 97. Longitudinal section taken rather to the right of the middle line of the skull of a young Indian Elephant</span> (<i>E. -Indicus</i>) × <sup>1</sup>/<sub>8</sub>. (Camb. Mus.)</p> +Indicus</i>) × <sup>1</sup>/<sub>8</sub>. (Camb. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">8. anterior nares.</td><td align="left">12. pterygoid.</td></tr> <tr><td align="left">10. periotic.</td><td align="left">17. nasal.</td></tr> @@ -18176,7 +18137,7 @@ which is the true infra-orbital foramen.</p> <div class="figcenter" style="width: 600px;"> <img src="images/i_494.jpg" width="600" height="652" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 98. Half front view of the skull of a Porcupine</span></p> -<p class="cen">(<i>Hystrix cristata</i>) × ½. (Camb. Mus.)</p> +<p class="cen">(<i>Hystrix cristata</i>) × ½. (Camb. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. nasal.</td><td align="left">5. premaxillae.</td></tr> <tr><td align="left">2. maxillo-turbinals.</td><td align="left">6. jugal.</td></tr> @@ -18391,7 +18352,7 @@ parietals (fig. 99, 1), which in Man are of enormous extent.</p> <div class="figcenter" style="width: 800px;"> <img src="images/i_500.jpg" width="800" height="482" alt="" title="" /> <div class="caption"><p><span class="smcap">Fig. 99. Half front view of the skulls, <i>A</i> of an old, <i>B</i> of a</span></p> -<p class="cen"><span class="smcap">young Gorilla</span> (<i>Gorilla savagei</i>) × ¼. (Camb. Mus.)</p> +<p class="cen"><span class="smcap">young Gorilla</span> (<i>Gorilla savagei</i>) × ¼. (Camb. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. parietal.</td><td align="left">5. squamosal.</td></tr> <tr><td align="left">2. sagittal crest.</td><td align="left">6. maxillae.</td></tr> @@ -18616,7 +18577,7 @@ portions can be well seen in <i>Manatus</i>.</p> In the Odontoceti the sternum consists of a broad presternum followed by three or four mesosternal segments, but with no xiphisternum. Indications of the original median fissure can -be traced, and are very evident in <i>Hyperoödon</i>. In the +be traced, and are very evident in <i>Hyperoödon</i>. In the Mystacoceti, on the other hand, the sternum consists simply of a broad flattened presternum which is sometimes more or less heart-shaped, sometimes cross-shaped. Only a single pair @@ -18718,7 +18679,7 @@ ribs.<span class="pagenum"><a name="Page_492" id="Page_492">[492]</a></span></p> <div class="figcenter" style="width: 800px;"><a name="Page_493" id="Page_493"></a> <img src="images/i_509.jpg" width="800" height="531" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 101. Skeleton of a Cape Buffalo</span> (<i>Bubalus caffer</i>).</p> -<p>The left scapula is omitted for the sake of clearness × <sup>1</sup>/<sub>17</sub>. (Brit. Mus.)</p> +<p>The left scapula is omitted for the sake of clearness × <sup>1</sup>/<sub>17</sub>. (Brit. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. premaxillae.</td><td align="left">7. femur.</td></tr> <tr><td align="left">2. nasal.</td><td align="left">8. patella.</td></tr> @@ -18771,7 +18732,7 @@ that of any other mammals, and recalls that of some Lacertilia.</p> <img src="images/i_511.jpg" width="800" height="505" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 102. <i>A</i>, Side view, <i>B</i>, Dorsal view of the shoulder girdle and</span></p> <p class="cen"><span class="smcap">part or the sternum of the Spiny Anteater</span> (<i>Echidna aculeata</i>)</p> -<p class="cen">× 1. (After <span class="smcap">Parker</span>.)</p> +<p class="cen">× 1. (After <span class="smcap">Parker</span>.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. scapula.</td><td align="left">6. epicoracoid.</td></tr> <tr><td align="left">2. suprascapula.</td><td align="left">7. glenoid cavity.</td></tr> @@ -18827,7 +18788,7 @@ in early embryos of sheep<a name="FNanchor_171_171" id="FNanchor_171_171"></a><a <div class="figcenter" style="width: 684px;"><a name="Page_496" id="Page_496"></a> <img src="images/i_513.jpg" width="684" height="600" alt="" title="" /> -<div class="caption"><p class="cen"><span class="smcap">Fig. 103. Skeleton of a Llama</span> (<i>Auchenia glama</i>) × <sup>1</sup>/<sub>18</sub>.</p> +<div class="caption"><p class="cen"><span class="smcap">Fig. 103. Skeleton of a Llama</span> (<i>Auchenia glama</i>) × <sup>1</sup>/<sub>18</sub>.</p> <p class="cen">(Brit. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. hyoid.</td><td align="left">6. olecranon process of ulna.</td></tr> @@ -18901,7 +18862,7 @@ ridge, which converges to meet the spine.</p> <div class="figcenter" style="width: 600px;"> <img src="images/i_515.jpg" width="600" height="662" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 104. Dorsal view of the sternum and right half of the</span></p> -<p class="cen"><span class="smcap">shoulder-girdle of</span> <i>Mus sylvaticus</i> × 4. (After <span class="smcap">Parker</span>.)</p> +<p class="cen"><span class="smcap">shoulder-girdle of</span> <i>Mus sylvaticus</i> × 4. (After <span class="smcap">Parker</span>.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. postscapular fossa.</td><td align="left">precoracoid at sternal end of</td></tr> <tr><td align="left">2. prescapular fossa.</td><td align="left">clavicle.</td></tr> @@ -19322,11 +19283,11 @@ separate centrale.</p> <img src="images/i_527.jpg" width="800" height="491" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 107. Left manus of</span></p> -<p class="cen"><i>A. Coryphodon hamatus.</i> (After <span class="smcap">Marsh</span>.) × <sup>1</sup>/<sub>5</sub>.</p> +<p class="cen"><i>A. Coryphodon hamatus.</i> (After <span class="smcap">Marsh</span>.) × <sup>1</sup>/<sub>5</sub>.</p> -<p class="cen"><i>B. Phenacodus primaevus.</i> (After <span class="smcap">Cope</span>.) × <sup>1</sup>/<sub>3</sub>.</p> +<p class="cen"><i>B. Phenacodus primaevus.</i> (After <span class="smcap">Cope</span>.) × <sup>1</sup>/<sub>3</sub>.</p> -<p class="cen"><i>C. Procavia (Dendrohyrax) arboreus.</i> (After <span class="smcap">von Zittel</span>.) × <sup>6</sup>/<sub>7</sub>.</p> +<p class="cen"><i>C. Procavia (Dendrohyrax) arboreus.</i> (After <span class="smcap">von Zittel</span>.) × <sup>6</sup>/<sub>7</sub>.</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. scaphoid.</td><td align="left">7. unciform.</td></tr> <tr><td align="left">2. lunar.</td><td align="left">8. centrale.</td></tr> @@ -19547,7 +19508,7 @@ are large in the old world monkeys.</p> <img src="images/i_533.jpg" width="514" height="800" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 108. Left anterior and posterior limb and limb girdle of</span></p> <p class="cen"><i>Uintatherium mirabile</i>. The anterior limb is to the left, the posterior</p> -<p class="cen">to the right × <sup>1</sup>/<sub>10</sub>. (From casts, Brit. Mus.)</p> +<p class="cen">to the right × <sup>1</sup>/<sub>10</sub>. (From casts, Brit. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. ilium.</td><td align="left">11. prescapular fossa.</td></tr> <tr><td align="left">2. head of femur.</td><td align="left">12. coracoid process.</td></tr> @@ -19600,7 +19561,7 @@ which articulates with the pelvis by a definite acetabulum.</p> <div class="figcenter" style="width: 600px;"> <img src="images/i_535.jpg" width="600" height="755" alt="" title="" /> <div class="caption"><p class="cen"><span class="smcap">Fig. 109. Left femur of an Ox</span> (<i>Bos taurus</i>) (to the left) <span class="smcap">and of</span></p> -<p class="cen"><span class="smcap">a Sumatran Rhinoceros</span> (<i>R. sumatrensis</i>) (to the right). × <sup>1</sup>/<sub>6</sub>.</p> +<p class="cen"><span class="smcap">a Sumatran Rhinoceros</span> (<i>R. sumatrensis</i>) (to the right). × <sup>1</sup>/<sub>6</sub>.</p> <p class="cen">(Camb. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. head.</td><td align="left">4. third trochanter.</td></tr> @@ -19802,10 +19763,10 @@ Bovidae the bones of these digits are wanting.</p> <div class="figcenter" style="width: 349px;"> <img src="images/i_541.jpg" width="349" height="800" alt="" title="" /> -<div class="caption"><p class="cen"><span class="smcap">Fig. 110.</span> <i>A.</i> <span class="smcap">Left pes of a Tapir</span> (<i>Tapirus americanus</i>). × <sup>1</sup>/<sub>6</sub>.</p> -<p class="cen"><i>B.</i> <span class="smcap">Right pes of a Rhinoceros</span> (<i>R. sumatrensis</i>). × <sup>1</sup>/<sub>8</sub>.</p> -<p class="cen"><i>C.</i> <span class="smcap">(Cast of) right pes of</span> <i>Hipparion gracile</i>. × <sup>1</sup>/<sub>7</sub>.</p> -<p class="cen"><i>D.</i> <span class="smcap">Right pes of a Horse</span> (<i>Equus caballus</i>). × <sup>1</sup>/<sub>10</sub>. (All Camb. Mus.)</p> +<div class="caption"><p class="cen"><span class="smcap">Fig. 110.</span> <i>A.</i> <span class="smcap">Left pes of a Tapir</span> (<i>Tapirus americanus</i>). × <sup>1</sup>/<sub>6</sub>.</p> +<p class="cen"><i>B.</i> <span class="smcap">Right pes of a Rhinoceros</span> (<i>R. sumatrensis</i>). × <sup>1</sup>/<sub>8</sub>.</p> +<p class="cen"><i>C.</i> <span class="smcap">(Cast of) right pes of</span> <i>Hipparion gracile</i>. × <sup>1</sup>/<sub>7</sub>.</p> +<p class="cen"><i>D.</i> <span class="smcap">Right pes of a Horse</span> (<i>Equus caballus</i>). × <sup>1</sup>/<sub>10</sub>. (All Camb. Mus.)</p> <table border="0" width="100%" cellpadding="4" cellspacing="0" summary=""> <tr><td align="left">1. calcaneum.</td><td align="left">5. external cuneiform.</td></tr> <tr><td align="left">2. astragalus.</td><td align="left">6. middle cuneiform.</td></tr> @@ -19965,7 +19926,7 @@ elongation of the calcaneum and navicular.</p> <li>Bridge, T.W., <a href="#Page_123">123</a></li> -<li>Brühl, C.B., <a href="#Page_210">210</a></li> +<li>Brühl, C.B., <a href="#Page_210">210</a></li> <li>Burmeister, H., <a href="#Page_351">351</a>, <a href="#Page_424">424</a></li> @@ -19991,7 +19952,7 @@ elongation of the calcaneum and navicular.</p> <li>Fritsch, A., <a href="#Page_135">135</a></li> -<li>Fürbringer, M., <a href="#Page_295">295</a></li> +<li>Fürbringer, M., <a href="#Page_295">295</a></li> <li>Gadow, H., <a href="#Page_40">40</a>, <a href="#Page_112">112</a>, <a href="#Page_190">190</a>, <a href="#Page_295">295</a>, <a href="#Page_343">343</a>, <a href="#Page_350">350</a></li> @@ -20000,7 +19961,7 @@ elongation of the calcaneum and navicular.</p> <li>Gervais, P., <a href="#Page_353">353</a></li> -<li>Günther, A.C.L.G., <a href="#Page_70">70</a>, <a href="#Page_104">104</a></li> +<li>Günther, A.C.L.G., <a href="#Page_70">70</a>, <a href="#Page_104">104</a></li> <li>Haslam, G., <a href="#Page_151">151</a></li> @@ -20030,9 +19991,9 @@ elongation of the calcaneum and navicular.</p> <li>Klein, E., <a href="#Page_11">11</a></li> -<li>Kölliker, A., <a href="#Page_9">9</a></li> +<li>Kölliker, A., <a href="#Page_9">9</a></li> -<li>Kükenthal, W., <a href="#Page_349">349</a>, <a href="#Page_422">422</a></li> +<li>Kükenthal, W., <a href="#Page_349">349</a>, <a href="#Page_422">422</a></li> <li>Lankester, E. Ray, <a href="#Page_51">51</a></li> @@ -20085,12 +20046,12 @@ Pycraft, W.P., <a href="#Page_297">297</a></li> <li>Ridewood, W.G., <a href="#Page_106">106</a>, <a href="#Page_164">164</a></li> -<li>Röse, C., <a href="#Page_422">422</a></li> +<li>Röse, C., <a href="#Page_422">422</a></li> <li>Sagemehl, M., <a href="#Page_104">104</a></li> -<li>Schäfer, E., <a href="#Page_11">11</a></li> +<li>Schäfer, E., <a href="#Page_11">11</a></li> <li>Scott, W.B., <a href="#Page_368">368</a></li> @@ -20839,7 +20800,7 @@ Bats, claws, <a href="#Page_418">418</a>;</li> <li class="subitem">see Ox</li> <li>Bottlenose, <i><a href="#Page_44">44</a></i>;</li> -<li class="subitem">see <i>Hyperoödon</i></li> +<li class="subitem">see <i>Hyperoödon</i></li> <li>Bovidae, <i><a href="#Page_46">46</a></i>;</li> <li class="subitem">pes, <a href="#Page_523">523</a>;</li> @@ -22915,7 +22876,7 @@ Cape jumping —, <i><a href="#Page_47">47</a></i>;</li> <li><i>Hyperodapedon</i>, <i><a href="#Page_37">37</a></i>, <i><a href="#Page_198">198</a></i>;</li> <li class="subitem">premaxillae, <a href="#Page_284">284</a></li> -<li><i>Hyperoödon</i>, <i><a href="#Page_44">44</a></i>;</li> +<li><i>Hyperoödon</i>, <i><a href="#Page_44">44</a></i>;</li> <li class="subitem">skull, <a href="#Page_464">464</a>;</li> <li class="subitem">sternum, <a href="#Page_489">489</a>;</li> <li class="subitem">thoracic vertebrae, <a href="#Page_448">448</a></li> @@ -23174,7 +23135,7 @@ Joints, kinds of, <a href="#Page_13">13</a></li> <li class="subitem">pes, <a href="#Page_522">522</a>;</li> <li class="subitem">tail, <a href="#Page_453">453</a></li> -<li>Kükenthal, W., on teeth of Cetacea, <a href="#Page_426">426</a>;</li> +<li>Kükenthal, W., on teeth of Cetacea, <a href="#Page_426">426</a>;</li> <li class="subitem">on teeth of Marsupials, <a href="#Page_422">422</a></li> @@ -24342,7 +24303,7 @@ Penguin, <i><a href="#Page_40">40</a></i>;</li> <li><i>Phacochaerus</i>, <i><a href="#Page_45">45</a></i>;</li> <li class="subitem">teeth, <a href="#Page_428">428</a></li> -<li><i>Phaëthon</i>, <i><a href="#Page_41">41</a></i>;</li> +<li><i>Phaëthon</i>, <i><a href="#Page_41">41</a></i>;</li> <li class="subitem">metatarsals, <a href="#Page_342">342</a></li> <li><i>Phalacrocorax</i>, <i><a href="#Page_41">41</a></i></li> @@ -25067,7 +25028,7 @@ Rat, pes, <a href="#Page_526">526</a></li> <li class="subitem"><i>Pristis</i>, <a href="#Page_119">119</a>;</li> <li class="subitem">— of sternum, duck, <a href="#Page_321">321</a></li> -<li>Röse, C., on teeth of Marsupials, <a href="#Page_422">422</a></li> +<li>Röse, C., on teeth of Marsupials, <a href="#Page_422">422</a></li> <li>Ruminantia, <i><a href="#Page_46">46</a></i>, <i><a href="#Page_359">359</a></i>;</li> <li class="subitem">auditory ossicles, <a href="#Page_487">487</a>;</li> @@ -26379,16 +26340,16 @@ ably worked out, and on the whole, well written.</p> <span style="margin-left: 1em;">By </span><span class="smcap">A.C. Seward</span>, M.A., F.R.S., Fellow of Emmanuel College.<br /> <span style="margin-left: 1em;">In 2 vols. Demy 8vo. Vol. I. 12<i>s.</i> [Vol. II. <i>In the Press.</i>]</span></p> -<p><i>Revue Scientifique.</i> Nous ne pouvons entrer dans le détail; mais il est -évident que M. Seward, praticien distingué lui-même, est très au courant +<p><i>Revue Scientifique.</i> Nous ne pouvons entrer dans le détail; mais il est +évident que M. Seward, praticien distingué lui-même, est très au courant des travaux des autres, il les cite et utilise abondamment; et ceci est fait -pour inspirer confiance. Au total, son œuvre est appuyée sur des bases -solides, et elle restera sans doute longtemps le bréviaire, le manuel de ceux -qui veulent, non pas seulement s'initier à la paléobotanique, mais retrouver -les renseignements qui sont épars dans des centaines de monographies qu'on -a souvent peine à se procurer. Le livre de M. Seward fait partie des +pour inspirer confiance. Au total, son œuvre est appuyée sur des bases +solides, et elle restera sans doute longtemps le bréviaire, le manuel de ceux +qui veulent, non pas seulement s'initier à la paléobotanique, mais retrouver +les renseignements qui sont épars dans des centaines de monographies qu'on +a souvent peine à se procurer. Le livre de M. Seward fait partie des <i>Cambridge Natural Science Manuals</i>, et il est digne de cette collection, qui -est elle-même digne du foyer scientifique universellement réputé, où il a vu +est elle-même digne du foyer scientifique universellement réputé, où il a vu le jour.</p> <p><i>Guardian.</i> We have already alluded to the spirit of caution which @@ -26513,12 +26474,12 @@ in origin.</p></div> <div class="footnote"><p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3]</span></a> See also p. 71.</p></div> -<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4]</span></a> It is usual to regard the clavicle as a membrane bone, but Kölliker has +<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4]</span></a> It is usual to regard the clavicle as a membrane bone, but Kölliker has shown that in rabbit embryos of about the 17th day it is cartilaginous.</p></div> <div class="footnote"><p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5]</span></a> In compiling these paragraphs on Histology, free use has been made of Klein and Noble Smith's <i>Atlas of Histology</i>, the small Histologies of -Klein and Schäfer, Huxley's <i>Elementary Physiology</i>, and Lloyd Morgan's +Klein and Schäfer, Huxley's <i>Elementary Physiology</i>, and Lloyd Morgan's <i>Animal Biology</i>.</p></div> <div class="footnote"><p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span class="label">[6]</span></a> See Huxley's <i>Elementary Physiology</i>, Revised edition, London, 1886, p. @@ -26544,7 +26505,7 @@ Soc. London, 1868.</p></div> <div class="footnote"><p><a name="Footnote_12_12" id="Footnote_12_12"></a><a href="#FNanchor_12_12"><span class="label">[12]</span></a> See R. Wiedersheim, <i>Zeitschr. wiss. Zool.</i> vol. <span class="smcap">LIII.</span> suppl. p. 43, 1892.</p></div> -<div class="footnote"><p><a name="Footnote_13_13" id="Footnote_13_13"></a><a href="#FNanchor_13_13"><span class="label">[13]</span></a> G. Baur, <i>Beiträge zur Morphogenie des Carpus und Tarsus der +<div class="footnote"><p><a name="Footnote_13_13" id="Footnote_13_13"></a><a href="#FNanchor_13_13"><span class="label">[13]</span></a> G. Baur, <i>Beiträge zur Morphogenie des Carpus und Tarsus der Vertebraten</i>, Theil 1. Batrachia. Jena, 1888, and <i>Amer. Natural.</i>, vol. <span class="smcap">XIX.</span> 1885 (several papers).</p></div> @@ -26560,7 +26521,7 @@ that of von Zittel has been followed.</p></div> <div class="footnote"><p><a name="Footnote_17_17" id="Footnote_17_17"></a><a href="#FNanchor_17_17"><span class="label">[17]</span></a> This classification of birds is essentially that of Gadow and Selenka in Bronn's <i>Classen und Ordnungen des Thierreichs</i>, Band <span class="smcap">vi</span>., Abth. <span class="smcap">iv.</span>, -Vögel. Leipzig, 1891.</p></div> +Vögel. Leipzig, 1891.</p></div> <div class="footnote"><p><a name="Footnote_18_18" id="Footnote_18_18"></a><a href="#FNanchor_18_18"><span class="label">[18]</span></a> The classification adopted is almost entirely that given in Flower and Lydekker's <i>Mammals Living and Extinct</i>. London, 1891.</p></div> @@ -26607,7 +26568,7 @@ Soc. Edinb.</i> vol. <span class="smcap">XII.</span> 1892-93, pp. 87-94, and 312 <div class="footnote"><p><a name="Footnote_32_32" id="Footnote_32_32"></a><a href="#FNanchor_32_32"><span class="label">[32]</span></a> See B. Dean, <i>J. Morphol.</i> vol. <span class="smcap">IX.</span> pp. 87-114, 1894, and <i>Nat. Sci.</i> vol. <span class="smcap">VIII.</span> p. 245, 1896.</p></div> -<div class="footnote"><p><a name="Footnote_33_33" id="Footnote_33_33"></a><a href="#FNanchor_33_33"><span class="label">[33]</span></a> A. Günther, <i>Phil. Trans.</i> vol. 161, Part <span class="smcap">II.</span> 1871, p. 511. T.H. +<div class="footnote"><p><a name="Footnote_33_33" id="Footnote_33_33"></a><a href="#FNanchor_33_33"><span class="label">[33]</span></a> A. Günther, <i>Phil. Trans.</i> vol. 161, Part <span class="smcap">II.</span> 1871, p. 511. T.H. Huxley, "On Ceratodus and the classification of fishes," <i>P.Z.S.</i> 1876, p. 24.</p></div> @@ -26626,7 +26587,7 @@ Hechtes</i>, Dorpat, 1880, the true coracoid is aborted, and the so-called coracoid of Teleosteans is really the precoracoid.</p></div> <div class="footnote"><p><a name="Footnote_39_39" id="Footnote_39_39"></a><a href="#FNanchor_39_39"><span class="label">[39]</span></a> The following general works on fishes may be referred to: Bashford -Dean, <i>Fishes, Living and Fossil</i>, New York, 1895. A. Günther, <i>An +Dean, <i>Fishes, Living and Fossil</i>, New York, 1895. A. Günther, <i>An Introduction to the Study of Fishes</i>, Edinburgh, 1880. A.A.W. Hubrecht and M. Sagemehl, <i>Fische</i> in Bronn's <i>Classen und Ordnungen des Thierreichs</i>, Band <span class="smcap">VI.</span> Leipzig, 1876.</p></div> @@ -26639,8 +26600,8 @@ references are there given to the literature of the subject.</p></div> <div class="footnote"><p><a name="Footnote_42_42" id="Footnote_42_42"></a><a href="#FNanchor_42_42"><span class="label">[42]</span></a> C. Hasse, <i>Zeitschr. wiss. Zool.</i> <span class="smcap">LVII.</span> 1893, p. 76.</p></div> -<div class="footnote"><p><a name="Footnote_43_43" id="Footnote_43_43"></a><a href="#FNanchor_43_43"><span class="label">[43]</span></a> C. Hasse, <i>Das natürliche System der Elasmobranchier auf Grundlage des -Baues und der Entwickelung ihrer Wirbelsäule</i>, Jena, 1879 and 1885, and +<div class="footnote"><p><a name="Footnote_43_43" id="Footnote_43_43"></a><a href="#FNanchor_43_43"><span class="label">[43]</span></a> C. Hasse, <i>Das natürliche System der Elasmobranchier auf Grundlage des +Baues und der Entwickelung ihrer Wirbelsäule</i>, Jena, 1879 and 1885, and "Die fossilen Wirbel, Morph. Studien <span class="smcap">I.-IV.</span>," <i>Morphol. Jahrb. Bd.</i> <span class="smcap">II.</span>, <span class="smcap">III.</span> and <span class="smcap">IV.</span> 1876-78.</p></div> @@ -26733,7 +26694,7 @@ there given.</p></div> <div class="footnote"><p><a name="Footnote_74_74" id="Footnote_74_74"></a><a href="#FNanchor_74_74"><span class="label">[74]</span></a> The exact position of the suture between the prefrontal and postfrontal is not known.</p></div> -<div class="footnote"><p><a name="Footnote_75_75" id="Footnote_75_75"></a><a href="#FNanchor_75_75"><span class="label">[75]</span></a> A. Günther, On the Anatomy of Hatteria, <i>Phil. Trans</i>, vol. 157, 1867, +<div class="footnote"><p><a name="Footnote_75_75" id="Footnote_75_75"></a><a href="#FNanchor_75_75"><span class="label">[75]</span></a> A. Günther, On the Anatomy of Hatteria, <i>Phil. Trans</i>, vol. 157, 1867, p. 595.</p></div> <div class="footnote"><p><a name="Footnote_76_76" id="Footnote_76_76"></a><a href="#FNanchor_76_76"><span class="label">[76]</span></a> <b>Zygosphenes</b> are extra articulating surfaces borne upon the anterior @@ -26770,7 +26731,7 @@ the main those given by von Zittel.</p></div> <div class="footnote"><p><a name="Footnote_86_86" id="Footnote_86_86"></a><a href="#FNanchor_86_86"><span class="label">[86]</span></a> See O.C. Marsh, <i>Amer. J. Sci.</i> (3), vol. 48, 1894, p. 85.</p></div> -<div class="footnote"><p><a name="Footnote_87_87" id="Footnote_87_87"></a><a href="#FNanchor_87_87"><span class="label">[87]</span></a> See C.B. Brühl, <i>Das Skelet der Krokodiliden</i>, Wien, +<div class="footnote"><p><a name="Footnote_87_87" id="Footnote_87_87"></a><a href="#FNanchor_87_87"><span class="label">[87]</span></a> See C.B. Brühl, <i>Das Skelet der Krokodiliden</i>, Wien, 1862. C.K. Hoffmann in Bronn's <i>Klassen und Ordnungen des Thierreichs</i>, Bd. <span class="smcap">VI.</span> Abth. <span class="smcap">III.</span> 1881-85. T.H. Huxley, <i>Proc. Linn. Soc.</i> (Zoology) 1860 vol. <span class="smcap">IV.</span> p. 1. R. Owen, <i>History of British fossil Reptiles</i>. <i>Crocodilia</i> @@ -26796,13 +26757,13 @@ Parker, <i>Tr. Z.S.</i>, vol. <span class="smcap">XI.</span> 1885, p. 263.</p></ <div class="footnote"><p><a name="Footnote_93_93" id="Footnote_93_93"></a><a href="#FNanchor_93_93"><span class="label">[93]</span></a> E.T. Newton, <i>Phil. Trans.</i> vol. <span class="smcap">CLXXXIV</span>, <span class="smcap">B</span>, p. 431 (1893).</p></div> -<div class="footnote"><p><a name="Footnote_94_94" id="Footnote_94_94"></a><a href="#FNanchor_94_94"><span class="label">[94]</span></a> M. Fürbringer, <i>Untersuchungen zur Morphologie und Systematik der -Vögel</i>, I. and II. Amsterdam, 1888. Cf. H. Gadow, <i>Nature</i>, <span class="smcap">XXXIX</span>. 1888, +<div class="footnote"><p><a name="Footnote_94_94" id="Footnote_94_94"></a><a href="#FNanchor_94_94"><span class="label">[94]</span></a> M. Fürbringer, <i>Untersuchungen zur Morphologie und Systematik der +Vögel</i>, I. and II. Amsterdam, 1888. Cf. H. Gadow, <i>Nature</i>, <span class="smcap">XXXIX</span>. 1888, pp. 150 and 177. </p><p> T.H. Huxley, "On the classification of birds." <i>P.Z.S.</i>, London, 1867. </p><p> -E. Selenka and H. Gadow, <i>Vögel</i> in Bronn's <i>Classen und Ordnungen des +E. Selenka and H. Gadow, <i>Vögel</i> in Bronn's <i>Classen und Ordnungen des Thierreichs</i> 1869-1890.</p></div> <div class="footnote"><p><a name="Footnote_95_95" id="Footnote_95_95"></a><a href="#FNanchor_95_95"><span class="label">[95]</span></a> See p. 283.</p></div> @@ -26869,7 +26830,7 @@ O.C. Marsh, "Jurassic Mammals," <i>Amer. J. Sci.</i> 1878 <i>et seq.</i></p></di <div class="footnote"><p><a name="Footnote_114_114" id="Footnote_114_114"></a><a href="#FNanchor_114_114"><span class="label">[114]</span></a> See Oldfield Thomas, <i>Brit. Mus. Cat. of Marsupialia and Monotremata</i> (1888).</p></div> -<div class="footnote"><p><a name="Footnote_115_115" id="Footnote_115_115"></a><a href="#FNanchor_115_115"><span class="label">[115]</span></a> W. Kükenthal, <i>Anat. Anz.</i> <span class="smcap">VI.</span> p. 364, 1891. C. Röse, <i>Anat. Anz.</i> +<div class="footnote"><p><a name="Footnote_115_115" id="Footnote_115_115"></a><a href="#FNanchor_115_115"><span class="label">[115]</span></a> W. Kükenthal, <i>Anat. Anz.</i> <span class="smcap">VI.</span> p. 364, 1891. C. Röse, <i>Anat. Anz.</i> <span class="smcap">VII.</span> p. 639.</p></div> <div class="footnote"><p><a name="Footnote_116_116" id="Footnote_116_116"></a><a href="#FNanchor_116_116"><span class="label">[116]</span></a> These bones however have no connection with the marsupium, being @@ -26877,7 +26838,7 @@ nearly equally developed in both male and female. They are simply sesamoid bones forming ossifications in the inner tendon of the external oblique muscle, and are developed as supports for the abdominal wall. Very similar structures have been independently developed in various Amphibians, -Reptiles and monodelphian Mammals. See W. Leche, <i>Biol. Fören.</i> +Reptiles and monodelphian Mammals. See W. Leche, <i>Biol. Fören.</i> <span class="smcap">III.</span> p. 120.</p></div> <div class="footnote"><p><a name="Footnote_117_117" id="Footnote_117_117"></a><a href="#FNanchor_117_117"><span class="label">[117]</span></a> See H. Gadow, <i>P.Z.S.</i> 1892, p. 361.</p></div> @@ -26894,12 +26855,12 @@ Huxley, "On the Osteology of Glyptodon," <i>Phil. Trans.</i> 1865.</p></div> <div class="footnote"><p><a name="Footnote_120_120" id="Footnote_120_120"></a><a href="#FNanchor_120_120"><span class="label">[120]</span></a> Epiphyses are fully developed in <i>Halitherium</i>, and traces occur in <i>Manatus</i>.</p></div> -<div class="footnote"><p><a name="Footnote_121_121" id="Footnote_121_121"></a><a href="#FNanchor_121_121"><span class="label">[121]</span></a> See P.J. van Beneden and P. Gervais, <i>Ostéographie des Cétacés</i>, +<div class="footnote"><p><a name="Footnote_121_121" id="Footnote_121_121"></a><a href="#FNanchor_121_121"><span class="label">[121]</span></a> See P.J. van Beneden and P. Gervais, <i>Ostéographie des Cétacés</i>, 1869-80.</p></div> <div class="footnote"><p><a name="Footnote_122_122" id="Footnote_122_122"></a><a href="#FNanchor_122_122"><span class="label">[122]</span></a> H. Wincza, <i>Morphol. Jahrb.</i> <span class="smcap">XVI.</span>, p. 647.</p></div> -<div class="footnote"><p><a name="Footnote_123_123" id="Footnote_123_123"></a><a href="#FNanchor_123_123"><span class="label">[123]</span></a> See M. Pavlow, "Études sur l'histoire paléontologique des Ongulés." +<div class="footnote"><p><a name="Footnote_123_123" id="Footnote_123_123"></a><a href="#FNanchor_123_123"><span class="label">[123]</span></a> See M. Pavlow, "Études sur l'histoire paléontologique des Ongulés." <i>Bull. Soc. Moscou</i>, 1887—1890.</p></div> <div class="footnote"><p><a name="Footnote_124_124" id="Footnote_124_124"></a><a href="#FNanchor_124_124"><span class="label">[124]</span></a> In a <i>plantigrade</i> animal the whole of the foot is placed on the @@ -26972,9 +26933,9 @@ Vol. <span class="smcap">XXIX.</span> 1889; also Oldfield Thomas, <i>P.R.S.</i>, <div class="footnote"><p><a name="Footnote_147_147" id="Footnote_147_147"></a><a href="#FNanchor_147_147"><span class="label">[147]</span></a> W.H. Flower, <i>Phil. Trans.</i>, vol. 156, pp. 631—641, 1867; also Oldfield Thomas, <i>Phil. Trans.</i>, pp. 443—462, 1887.</p></div> -<div class="footnote"><p><a name="Footnote_148_148" id="Footnote_148_148"></a><a href="#FNanchor_148_148"><span class="label">[148]</span></a> C. Röse, <i>Anat. Anz.</i> <span class="smcap">VII.</span>, p. 639.</p></div> +<div class="footnote"><p><a name="Footnote_148_148" id="Footnote_148_148"></a><a href="#FNanchor_148_148"><span class="label">[148]</span></a> C. Röse, <i>Anat. Anz.</i> <span class="smcap">VII.</span>, p. 639.</p></div> -<div class="footnote"><p><a name="Footnote_149_149" id="Footnote_149_149"></a><a href="#FNanchor_149_149"><span class="label">[149]</span></a> W. Kükenthal, <i>Anat. Anz.</i> <span class="smcap">VI.</span>, p. 364.</p></div> +<div class="footnote"><p><a name="Footnote_149_149" id="Footnote_149_149"></a><a href="#FNanchor_149_149"><span class="label">[149]</span></a> W. Kükenthal, <i>Anat. Anz.</i> <span class="smcap">VI.</span>, p. 364.</p></div> <div class="footnote"><p><a name="Footnote_150_150" id="Footnote_150_150"></a><a href="#FNanchor_150_150"><span class="label">[150]</span></a> See p. 348.</p></div> @@ -27038,7 +26999,7 @@ of Philad. Acad.</i> 1874. H.F. Osborn, "The evolution of the Ungulate foot," <div class="footnote"><p><a name="Footnote_174_174" id="Footnote_174_174"></a><a href="#FNanchor_174_174"><span class="label">[174]</span></a> See O.C. Marsh, various papers including "Fossil horses in America," <i>Amer. Natural.</i> 1874; "Polydactyl horses," <i>Amer. J. Sci.</i> 1879 and 1892. -M. Pavlow, "Le développement des Equidés," <i>Bul. Soc. Moscou</i>, 1887, and +M. Pavlow, "Le développement des Equidés," <i>Bul. Soc. Moscou</i>, 1887, and subsequent papers in the same. Osborn and Wortman, "On the Perissodactyls of the White River beds," <i>Bull. Amer. Mus.</i> Dec. 23rd, 1895.</p></div> @@ -27070,382 +27031,6 @@ will be displayed.</p> </div> - - - - - - - -<pre> - - - - - -End of Project Gutenberg's The Vertebrate Skeleton, by Sidney H. 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