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diff --git a/38315.txt b/38315.txt new file mode 100644 index 0000000..f6c3298 --- /dev/null +++ b/38315.txt @@ -0,0 +1,11553 @@ +The Project Gutenberg EBook of Artistic Anatomy of Animals, by Edouard Cuyer + +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: Artistic Anatomy of Animals + +Author: Edouard Cuyer + +Release Date: December 15, 2011 [EBook #38315] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK ARTISTIC ANATOMY OF ANIMALS *** + + + + +Produced by Chris Curnow, Harry Lame and the Online +Distributed Proofreading Team at https://www.pgdp.net (This +file was produced from images generously made available +by The Internet Archive) + + + + + + + + + + +--------------------------------------------------------------------+ + | TRANSCRIBER'S NOTES | + | | + | Transcription used in this e-text: | + | Texts in italics in the original work are transcribed between | + | underscores, as in _text_. | + | Bold-face text in the original work has been transcribed between | + | equal signs, as in =text=. | + | Small capitals have been transcribed as ALL CAPITALS. | + | The author sometimes uses a different typeface to describe a | + | shape, as the V in V-form. Where this different typeface is used,| + | this has been transcribed as [V]. | + | | + | More Transcriber's Notes will be found at the end of this text. | + +--------------------------------------------------------------------+ + + + + + THE + ARTISTIC ANATOMY OF ANIMALS + + + + + ARTISTIC + ANATOMY + OF ANIMALS + + BY EDOUARD CUYER, SUPPLEMENTARY + PROF OF ANATOMY AT THE SCHOOL OF + FINE ART PARIS, PROF OF ANATOMY + AT THE SCHOOL OF FINE ART ROUEN + + TRANSLATED & EDITED BY + GEORGE HAYWOOD + LECTURER ON ANATOMY AT THE ROYAL + COLLEGE OF ART SOUTH KENSINGTON + + [Illustration] + + LONDON + BAILLIERE, TINDALL & COX + 8 HENRIETTA ST COVENT GARDEN + + ANNO DOMINI + MDCCCCV + + ALL RIGHTS + RESVD + + + + +PREFACE + + +A few lines will suffice to explain why we have compiled the present +volume, to what wants it responds, and what its sphere of usefulness may +possibly embrace. + +In our teaching of plastic anatomy, especially at the Ecole des +Beaux-Arts--where, for the past nine years, we have had the very great +honour of supplementing the teaching of our distinguished master, +Mathias Duval, after having been prosector for his course of lectures +since 1881--it is our practice to give, as a complement to the study of +human anatomy, a certain number of lessons on the anatomy of those +animals which artists might be called on to represent. + +Now, we were given to understand that the subject treated in our +lectures interested our hearers, so much so that we were not surprised +to learn that a certain number repeatedly expressed a desire to see +these lectures united in book form. + +To us this idea was not new; for many years the work in question had +been in course of preparation, and we had collected materials for it, +with the object of filling up a void of which the existence was to be +regretted. But our many engagements prevented us from executing our +project as early as we would have wished. It is this work which we +publish to-day. + +[Illustration: FIG. I.--REPRODUCTION OF A SKETCH BY BARYE (COLLECTIONS +OF THE ANATOMICAL MUSEUM OF THE ECOLE DES BEAUX-ARTS--HUGUIER MUSEUM).] + +Putting aside for a moment the wish expressed by our hearers, we feel +ourselves in duty bound to inquire whether the utility of this +publication is self-evident. Let it be clearly understood that we wish +to express here our opinion on this subject, while putting aside every +personal sentiment of an author. + +No one now disputes the value of anatomical studies made in view of +carrying out the artistic representation of man. Nevertheless--for we +must provide against all contingencies--the conviction on this subject +may be more or less absolute; and yet it must possess this character in +an intense degree in order that these studies may be profitable, and +permit the attainment of the goal which is proposed in undertaking them. +It is in this way that we ever strive to train the students whose +studies we direct; not only to admit the value of these studies, but to +be materially and deeply convinced of the fact without any restriction. +Such is the sentiment which we endeavour to create and vigorously +encourage. And we may be permitted to add that we have often been +successful in this direction. + +Therefore it is that, at the beginning of our lectures, and in +anticipation of possible objections, we are accustomed to take up the +question of the utility of plastic anatomy. And in so doing, it is in +order to combat at the outset the idea--as mischievous as it is +false--which is sometimes imprudently enunciated, that the possession of +scientific knowledge is likely to tarnish the purity and freshness of +the impressions received by the artist, and to place shackles on the +emotional sincerity of their representation. + +[Illustration: FIG. II.--REPRODUCTION OF A SKETCH OF BARYE (COLLECTIONS +OF THE ANATOMICAL MUSEUM OF THE ECOLE DES BEAUX-ARTS--HUGUIER MUSEUM).] + +It is chiefly by employment of examples that we approach the subject. +These strike the imagination of the student more forcibly, and the +presentation of models of a certain choice, although rough in execution, +is, in our opinion, preferable to considerations of an order possibly +more exalted, but of a character less clearly practical. Let us, then, +ask the question: Those artists whose eminence nobody would dare to +question, did they study anatomy? If the answer be in the affirmative, +we surely cannot permit ourselves to believe that we can dispense with a +similar course. And, as proof of the studies of this class which the +masters have made, we may cite Raphael, Michelangelo, and, above all, +Leonardo da Vinci; and, of the moderns, Gericault. And we may more +clearly define these proofs by an examination of the reproductions of +their anatomical works, chosen from certain of their special +writings.[1] + + [1] Mathias Duval and A. Bical, 'L'anatomie des Maitres.' Thirty + plates reproduced from the originals of Leonardo da Vinci, + Michelangelo, Raphael, Gericault, etc., with letterpress and a + history of plastic anatomy, Paris, 1890. + + The manuscripts of Leonardo da Vinci of the Royal Library, + Windsor, 'Anatomy, Foliae A.,' published by Theodore Sabachnikoff, + with a French translation, written and annotated by Giovanni + Piumati, with an introduction by Mathias Duval. Edouard Rouveyre, + publisher, Paris, 1898. + + Mathias Duval and Edouard Cuyer, 'History of Plastic Anatomy: The + Masters, their Books, and Anatomical Figures' (Library of + Instruction of the School of Fine Arts), Paris, 1898. + +Accordingly, there is no scope for serious discussion, and it only +remains for us to enunciate the opinion that it is necessary that we +should imitate those masters, and, with a sense of respectful +discipline, follow their example. + +Here, with regard to the anatomy of animals, we pursue the same method, +and the example chosen shall be that of Barye. His talent is too far +above all criticism to allow that this example should be refused. The +admiration which the works of this great artist elicit is too +wide-spread for us to remain uninfluenced by the lessons furnished by +his studies. It is sufficient to see the sketches relating to these +studies, and his admirable casts from nature which form part of the +anatomical museum of the Ecole des Beaux-Arts, to be convinced that the +artistic temperament, of which Barye was one of the most brilliant +examples, has nothing to lose by its association with researches the +precision of which might seem likely to check its complete expansion. + +[Illustration: FIG. III.--REPRODUCTION OF A SKETCH OF BARYE (COLLECTIONS +OF THE ANATOMICAL MUSEUM OF THE ECOLE DES BEAUX-ARTS--HUGUIER MUSEUM).] + +In those sketches we find proofs of observation so scrupulous that we +cannot restrain our admiration for the man whose ardent imagination +was voluntarily subjected to the toil of study so profound. + +If the example of Barye, with whom we associate the names of other great +modern painters of animals, can determine the conviction which we seek +to produce, we shall be sincerely glad. To contribute to the propagation +of useful ideas, and to see them accepted, gives a feeling of +satisfaction far too legitimate for us to hesitate to say what we should +feel if our hope be realized in this instance. + +EDOUARD CUYER. + +[Illustration: FIG. IV.--REPRODUCTION OF A SKETCH OF BARYE (COLLECTIONS +OF ANATOMICAL MUSEUM OF THE SCHOOL OF FINE ARTS--HUGUIER MUSEUM).] + + + + +CONTENTS + + + INTRODUCTION + + PAGE + + GENERALITIES OF COMPARATIVE ANATOMY 1 + + + CHAPTER I + + OSTEOLOGY AND ARTHROLOGY: + + THE TRUNK 4 + THE POSTERIOR LIMBS 78 + THE POSTERIOR LIMBS IN SOME ANIMALS 90 + THE SKULL OF BIRDS 127 + + + CHAPTER II + + MYOLOGY: + + THE MUSCLES OF THE TRUNK 131 + MUSCLES OF THE ANTERIOR LIMBS 162 + MUSCLES OF THE POSTERIOR LIMBS 200 + MUSCLES OF THE HEAD 232 + + + CHAPTER III + + EPIDERMIC PRODUCTS OF THE EXTREMITIES OF THE FORE AND HIND LIMBS 247 + + + CHAPTER IV + + PROPORTIONS + + PROPORTIONS OF THE HEAD OF THE HORSE 273 + + + CHAPTER V + + THE PACES OF THE HORSE 282 + + + + +LIST OF ILLUSTRATIONS + + + FIG. PAGE + + 1. A HUMAN SKELETON IN THE ATTITUDE OF A QUADRUPED, TO GIVE A + GENERAL IDEA OF THE POSITION OF THE BONES IN OTHER + VERTEBRATES 5 + 2. SIZE OF THE ATLAS COMPARED WITH THE TRANSVERSE DIMENSIONS OF + THE CORRESPONDING PARTS OF THE SKULL IN MAN 7 + 3. SIZE OF THE ATLAS COMPARED WITH THE TRANSVERSE DIMENSIONS OF + THE CORRESPONDING REGIONS OF THE SKULL IN A DOG 8 + 4. LUMBAR VERTEBRAE OF A QUADRUPED (THE HORSE): SUPERIOR SURFACE 9 + 5. A TRANSVERSE SECTION OF THE THORAX OF A MAN PLACED + VERTICALLY--THAT IS TO SAY, IN THE DIRECTION WHICH IT WOULD + ASSUME IN A MAN PLACED IN THE ATTITUDE OF A QUADRUPED (A + DIAGRAMMATIC FIGURE) 13 + 6. A VERTICAL SECTION OF THE THORAX OF A QUADRUPED + (DIAGRAMMATIC) 14 + 7. STERNUM OF A BIRD (THE COCK): LEFT SIDE, EXTERNAL SURFACE 17 + 8. ANTERIOR LIMB OF THE BAT: LEFT SIDE, ANTERIOR SURFACE 20 + 9. ANTERIOR LIMB OF THE SEAL: LEFT SIDE, EXTERNAL SURFACE 21 + 10. SITUATION AND DIRECTION OF THE SCAPULA IN THE HUMAN BEING, + THE TRUNK BEING HORIZONTAL, AS IN QUADRUPEDS. VERTICAL AND + TRANSVERSE SECTION OF THE THORAX (DIAGRAMMATIC FIGURE) 22 + 11. POSITION AND DIRECTION OF THE SCAPULA IN QUADRUPEDS. + VERTICAL AND TRANSVERSE SECTION OF THE THORAX (DIAGRAMMATIC + FIGURE) 22 + 12. LEFT SCAPULA OF THE HUMAN BEING, POSTERIOR SURFACE, PLACED + IN THE POSITION WHICH IT WOULD OCCUPY IN THE SKELETON OF A + QUADRUPED 23 + 13. LEFT SCAPULA OF A HORSE: EXTERNAL SURFACE 23 + 14. VERTICAL AND TRANSVERSE SECTION, AT THE SITE OF THE + SHOULDERS, OF THE THORAX OF THE HORSE (DIAGRAMMATIC FIGURE) 24 + 15. VERTICAL AND TRANSVERSE SECTION, AT THE PLANE OF THE + SHOULDERS, OF THE THORAX OF THE DOG (DIAGRAMMATIC FIGURE) 24 + 16. LEFT CLAVICLE OF THE CAT: SUPERIOR SURFACE (NATURAL SIZE) 26 + 17. CLAVICLE OF THE DOG (NATURAL SIZE) 26 + 18. SKELETON OF THE SHOULDER OF A BIRD (VULTURE): ANTERO- + EXTERNAL VIEW OF THE LEFT SIDE 27 + 19. INFERIOR EXTREMITY OF THE LEFT HUMERUS OF A FELIDAE (LION) 31 + 20. INFERIOR EXTREMITY OF THE LEFT HUMAN HUMERUS, SHOWING THE + PRESENCE OF A SUPRATROCHLEAR PROCESS 31 + 21. SKELETON OF A BIRD (VULTURE): LEFT SURFACE 33 + 22. THE HUMAN HAND RESTING FOR ITS WHOLE EXTENT ON ITS PALMAR + SURFACE: LEFT SIDE, EXTERNAL SURFACE 35 + 23. THE HUMAN HAND RESTING ON ITS PHALANGES: LEFT SIDE, EXTERNAL + SURFACE 36 + 24. THE HUMAN HAND RESTING ON THE TIPS OF SOME OF ITS THIRD + PHALANGES: LEFT SIDE, EXTERNAL VIEW 36 + 25. SUPERIOR EXTREMITY OF THE BONES OF THE HUMAN FOREARM: LEFT + SIDE, SUPERIOR SURFACE 39 + 26. SUPERIOR EXTREMITY OF THE BONES OF THE FOREARM OF A DOG: + LEFT LIMB, SUPERIOR SURFACE 39 + 27. SUPERIOR EXTREMITY OF THE BONES OF THE FOREARM OF THE HORSE: + LEFT LIMB, SUPERIOR SURFACE 40 + 28. INFERIOR EXTREMITY OF THE BONES OF THE FOREARM OF A MAN: + LEFT SIDE, POSTERIOR SURFACE, POSITION OF SUPINATION 41 + 29. INFERIOR EXTREMITY OF THE BONES OF THE FOREARM OF A DOG: + LEFT SIDE, ANTERIOR SURFACE, NORMAL POSITION--THAT IS, THE + POSITION OF PRONATION 41 + 30. INFERIOR EXTREMITY OF THE BONE OF THE FOREARM OF THE HORSE: + LEFT SIDE, ANTERIOR SURFACE 42 + 31. SKELETON OF THE SUPERIOR LIMB OF A BIRD (VULTURE): LEFT + SIDE, EXTERNAL SURFACE 47 + 32. SUPERIOR LIMB OF THE HUMAN BEING, THE DIFFERENT SEGMENTS + BEING PLACED IN THE ATTITUDE WHICH THE CORRESPONDING PARTS + OCCUPY IN BIRDS: LEFT SIDE, EXTERNAL SURFACE 48 + 33. SKELETON OF THE BEAR: LEFT LATERAL SURFACE 50 + 34. SKELETON OF THE DOG: LEFT LATERAL SURFACE 52 + 35. SCAPULA OF THE DOG: LEFT SIDE, EXTERNAL SURFACE 53 + 36. LEFT SCAPULA OF THE CAT: EXTERNAL SURFACE 53 + 37. SKELETON OF THE FINGER OF A FELIDE (LION): LEFT SIDE, + INTERNAL SURFACE 57 + 38. SKELETON OF THE PIG: LEFT LATERAL SURFACE 58 + 39. SKELETON OF THE OX: LEFT LATERAL SURFACE 61 + 40. SKELETON OF THE HORSE: LEFT LATERAL SURFACE 64 + 41. FLEXION OF THE HUMERUS: RIGHT ANTERIOR LIMB OF THE HORSE, + EXTERNAL SURFACE (AFTER A CHROMOPHOTOGRAPHIC STUDY BY + PROFESSOR MAREY) 74 + 42. EXTENSION OF THE HUMERUS: RIGHT ANTERIOR LIMB OF THE HORSE, + EXTERNAL SURFACE (AFTER A CHROMOPHOTOGRAPHIC STUDY BY + PROFESSOR MAREY) 74 + 43. THE LEFT ILIAC BONE OF THE HUMAN BEING: EXTERNAL SURFACE, + PLACED IN THE POSITION WHICH IT WOULD OCCUPY IN THE SKELETON + OF A QUADRUPED 79 + 44. LEFT ILIAC BONE OF A QUADRUPED (HORSE): EXTERNAL SURFACE 79 + 45. PUBIC REGION OF THE PELVIS OF A MARSUPIAL (PHALANGER, FOX) 81 + 46. PELVIS OF A BIRD (THE COCK): EXTERNAL SURFACE, LEFT SIDE 82 + 47. POSTERIOR LIMB OF THE HORSE PLACED IN THE POSITION WHICH IT + SHOULD OCCUPY IF THE ANIMAL WERE A PLANTIGRADE: LEFT LIMB, + EXTERNAL SURFACE 89 + 48. SKELETON OF THE FOOT OF A BIRD (THE COCK): LEFT SIDE, + EXTERNAL SURFACE 90 + 49. PELVIS OF THE DOG, SEEN FROM ABOVE 91 + 50. PELVIS OF A FELIDE (LION), VIEWED FROM ABOVE 92 + 51. PELVIS OF THE OX: SUPERIOR SURFACE 95 + 52. TARSUS OF THE OX: POSTERIOR LEFT LIMB, ANTERO-EXTERNAL + SURFACE 97 + 53. PELVIS OF THE HORSE: SUPERIOR SURFACE 101 + 54. TARSUS OF THE HORSE: LEFT POSTERIOR LIMB, ANTERIOR SURFACE 104 + 55. EXTENSION OF THE LEG: RIGHT POSTERIOR LIMB OF THE HORSE, + EXTERNAL SURFACE (AFTER A CHRONOGRAPHIC STUDY BY PROFESSOR + MAREY) 107 + 56. HUMAN SKULL: MEASURE OF THE FACIAL ANGLE BY THE METHOD OF + CAMPER. ANGLE BAC = 80 deg. 110 + 57. SKULL OF THE HORSE: MEASURE OF THE FACIAL ANGLE BY THE + METHOD OF CAMPER. ANGLE BAC = 13 deg. 110 + 58. SKULL OF ONE OF THE FELIDAE (JAGUAR): LEFT LATERAL ASPECT 113 + 59. SKULL OF THE LION: LEFT LATERAL ASPECT 113 + 60. SKULL OF THE DOG: LEFT LATERAL ASPECT 115 + 61. SKULL OF THE PIG: LEFT LATERAL ASPECT 117 + 62. SKULL OF THE OX: LEFT LATERAL ASPECT 119 + 63. SKULL OF THE HORSE: LEFT LATERAL ASPECT 121 + 64. SKULL OF THE HARE: LEFT LATERAL ASPECT 123 + 65. SKULL OF THE COCK: LEFT LATERAL SURFACE 128 + 66. MYOLOGY OF THE HORSE: ANTERIOR ASPECT OF THE TRUNK 132 + 67. MYOLOGY OF THE HORSE: INFERIOR ASPECT OF THE TRUNK 135 + 68. MYOLOGY OF THE DOG: SUPERFICIAL LAYER OF MUSCLES 141 + 69. MYOLOGY OF THE OX: SUPERFICIAL LAYER OF MUSCLES 143 + 70. MYOLOGY OF THE HORSE: SUPERFICIAL LAYER OF MUSCLES 146 + 71. MYOLOGY OF THE HORSE: PANNICULUS MUSCLE OF THE TRUNK 148 + 72. MYOLOGY OF THE HORSE--SHOULDER AND ARM: LEFT SIDE, EXTERNAL + SURFACE 166 + 73. MYOLOGY OF THE DOG: LEFT ANTERIOR LIMB, EXTERNAL ASPECT 178 + 74. MYOLOGY OF THE OX: LEFT ANTERIOR LIMB, EXTERNAL ASPECT 180 + 75. MYOLOGY OF THE HORSE: LEFT ANTERIOR LIMB, EXTERNAL ASPECT 182 + 76. MYOLOGY OF THE DOG: LEFT ANTERIOR LIMB, INTERNAL ASPECT 190 + 77. MYOLOGY OF THE HORSE: ANTERIOR LIMB, LEFT SIDE, INTERNAL + ASPECT 192 + 78. LEFT ANTERIOR LIMB OF THE HORSE: INTERNAL ASPECT 194 + 79. LEFT ANTERIOR LIMB OF THE HORSE: EXTERNAL ASPECT 196 + 80. LEFT ANTERIOR LIMB OF THE HORSE: EXTERNAL ASPECT 196 + 81. DIAGRAM OF THE POSTERIOR PART OF A TRANSVERSE SECTION + PASSING THROUGH THE MIDDLE OF THE LEFT FORE-LIMB OF THE DOG: + SURFACE OF THE INFERIOR SEGMENT OF THE SECTION 198 + 82. DIAGRAM OF A HORIZONTAL SECTION OF THE MIDDLE OF THE FOREARM + OF THE LEFT LEG OF THE HORSE: SURFACE OF THE INTERIOR + SEGMENT OF THE SECTION 198 + 83. MYOLOGY OF THE HORSE: THE ANTERIOR TIBIAL MUSCLE (FLEXOR OF + THE METATARSUS), LEFT LEG, ANTERIOR VIEW 214 + 84. MYOLOGY OF THE DOG: LEFT HIND-LIMB, EXTERNAL ASPECT 216 + 85. MYOLOGY OF THE OX: LEFT LEG, EXTERNAL ASPECT 218 + 86. MYOLOGY OF THE HORSE: LEFT HIND-LIMB, EXTERNAL ASPECT 220 + 87. MYOLOGY OF THE DOG: LEFT HIND-LIMB, INTERNAL ASPECT 222 + 88. MYOLOGY OF THE HORSE: LEFT HIND-LEG, INTERNAL ASPECT 223 + 89. MYOLOGY OF THE DOG: MASTICATORY MUSCLES (A DEEPER DISSECTION + THAN THAT SHOWN IN FIG. 90) 233 + 90. MYOLOGY OF THE DOG: MUSCLES OF THE HEAD 235 + 91. MYOLOGY OF THE OX: MUSCLES OF THE HEAD 237 + 92. MYOLOGY OF THE HORSE: MUSCLES OF THE HEAD 239 + 93. CLAW OF THE DOG: INFERIOR SURFACE 249 + 94. LEFT HAND OF THE DOG: INFERIOR SURFACE, PLANTAR TUBERCLES 249 + 95. VERTICAL ANTERO-POSTERIOR SECTION OF THE FOOT OF A HORSE 250 + 96. THIRD PHALANX OF THE HORSE: LEFT ANTERIOR LIMB, EXTERNAL + SURFACE 251 + 97. LEFT ANTERIOR FOOT OF THE HORSE: ANTERIOR ASPECT 253 + 98. LEFT ANTERIOR FOOT OF THE HORSE: EXTERNAL ASPECT 254 + 99. VERTICAL AND TRANSVERSE SECTION OF A LEFT HUMAN FOOT: + OUTLINE OF THE SURFACE OF THE POSTERIOR SEGMENT OF THIS + SECTION (DIAGRAMMATIC FIGURE) 255 + 100. INFERIOR SURFACE OF A FORE-HOOF OF THE HORSE: LEFT SIDE 256 + 101. THIRD PHALANX OF THE HORSE: LEFT ANTERIOR LIMB, INFERIOR + VIEW 257 + 102. THIRD PHALANX OF THE HORSE: LEFT POSTERIOR LIMB, INFERIOR + VIEW 257 + 103. INFERIOR SURFACE OF A HIND-HOOF OF A HORSE: LEFT SIDE 258 + 104. LEFT POSTERIOR FOOT OF A HORSE: EXTERNAL ASPECT 259 + 105. FOOT OF THE OX: LEFT SIDE, ANTERO-EXTERNAL VIEW 260 + 106. THE PROPORTIONS OF THE HORSE (AFTER BOURGELAT) 265 + 107. PROPORTIONS OF THE HORSE (AFTER COLONEL DUHOUSSET) 270 + 108. PROPORTIONS OF THE HEAD OF THE HORSE, VIEWED IN PROFILE + (AFTER COLONEL DUHOUSSET) 274 + 109. THE SAME DESIGN AS THAT OF FIG. 108, ON WHICH WE HAVE + INDICATED, BY SIMILAR LINES, THE PRINCIPAL CORRESPONDING + MEASUREMENTS 275 + 110. PROPORTIONS OF THE HEAD OF THE HORSE, SEEN FROM THE FRONT + (AFTER COLONEL DUHOUSSET) 276 + 111. THE SAME FIGURE AS FIG. 110, ON WHICH WE HAVE MARKED, BY + SIMILAR LINES, THE PRINCIPAL MEASUREMENTS WHICH CORRESPOND + THERETO 277 + 112. HORSE OF WHICH THE LENGTH CONTAINS MORE THAN TWO AND A HALF + TIMES THAT OF THE HEAD, AND OF WHICH THIS DIMENSION (A, B) + EXCEEDS THE HEIGHT 279 + 113. HORSE OF WHICH THE LENGTH CONTAINS MORE THAN TWO AND A HALF + TIMES THAT OF THE HEAD, AND OF WHICH THIS DIMENSION (A, B) + EXCEEDS THE HEIGHT 280 + 114. HORSE OF WHICH THE LENGTH CONTAINS MORE THAN TWO AND A HALF + TIMES THAT OF THE HEAD, AND OF WHICH THIS DIMENSION (A, B) + IS INFERIOR TO THE HEIGHT 281 + 115. EXPERIMENTAL SHOES, INTENDED TO RECORD THE PRESSURE OF THE + FOOT ON THE GROUND 284 + 116. RUNNER FURNISHED WITH THE EXPLORATORY AND REGISTERING + APPARATUS OF THE VARIOUS PACES 285 + 117. TRACING OF THE RUNNING OF A MAN (AFTER PROFESSOR MAREY) 286 + 118. NOTATION OF A TRACING OF THE RUNNING OF A MAN (AFTER + PROFESSOR MAREY) 287 + 119. NOTATION OF VARIOUS MODES OF PROGRESSION OF A MAN (AFTER + PROFESSOR MAREY) 287 + 120. SWING OF THE RAISED ANTERIOR LIMB (AFTER G. COLIN) 289 + 121. SWING OF THE ANTERIOR LIMB ON THE POINT OF PRESSURE (AFTER + G. COLIN) 290 + 122. POSTERIOR LIMB, GIVING THE IMPULSE (AFTER G. COLIN) 291 + 123. NOTATION OF THE AMBLING GAIT IN THE HORSE (AFTER PROFESSOR + MAREY) 292 + 124. THE AMBLE: RIGHT LATERAL PRESSURE 293 + 125. NOTATION OF THE GAIT OF THE TROT IN A HORSE (AFTER PROFESSOR + MAREY) 294 + 126. THE TROT: RIGHT DIAGONAL PRESSURE 295 + 127. THE TROT: TIME OF SUSPENSION 295 + 128. NOTATION OF THE PACE OF STEPPING IN THE HORSE (AFTER + PROFESSOR MAREY) 296 + 129. THE STEP: RIGHT LATERAL PRESSURE 297 + 130. THE STEP: RIGHT DIAGONAL PRESSURE 297 + 131. THE GALLOP: FIRST PERIOD 298 + 132. THE GALLOP: SECOND PERIOD 298 + 133. THE GALLOP: THIRD PERIOD 299 + 134. THE GALLOP: TIME OF SUSPENSION 299 + 135. NOTATION OF THE GALLOP DIVIDED INTO THREE PERIODS OF TIME + (AFTER PROFESSOR MAREY) 300 + 136. NOTATION OF THE GALLOP OF FOUR PERIODS IN THE HORSE (AFTER + PROFESSOR MAREY) 300 + 137. LEAP OF THE HARE (AFTER G. COLIN) 301 + 138. THE LEAP 302 + 139. THE LEAP 302 + 140. THE LEAP 303 + 141. THE LEAP 303 + 142. THE LEAP 305 + 143. THE LEAP 305 + + + + +THE ARTISTIC ANATOMY OF ANIMALS + + + + +INTRODUCTION + +GENERALITIES OF COMPARATIVE ANATOMY + + +Of the animals by which we are surrounded, there are some which, +occupying a place in our lives by reason of their natural endowments, +are frequently represented in the works of artists--either as +accompanying man in his work or in his amusements, or as intended to +occupy the whole interest of the composition. + +The necessity of knowing, from an artistic point of view, the structure +of the human body makes clear the importance we attach, from the same +point of view, to the study of the anatomy of animals--that is, the +study of comparative anatomy. The name employed to designate this branch +of anatomy shows that the object of this science is the study of the +relative position and form which each region presents in all organized +beings, taking for comparison the corresponding regions in man. The head +in animals compared with the human head; the trunk and limbs compared to +the trunk and limbs of the human being--this is the analysis we +undertake, and the plan of the subject we are about to commence. + +Our intention being, as we have just said, the comparison of the +structure of animals with that of man, should we describe the anatomy of +the human being in the pages which follow? We do not think so. Plastic +human anatomy having been previously studied in special works,[2] we +take it for granted that these have been studied before undertaking the +subject of comparative anatomy. We will therefore not occupy time with +the elementary facts relative to the skeleton and the superficial layer +of muscles. We will not dilate on the division of the bones into long, +short, large, single, paired, etc. All these preliminary elements we +shall suppose to have been already studied. + + [2] Mathias Duval, 'Precis of Anatomy for the Use of Artists': Paris, + 1881. 'Artistic Anatomy of the Human Body,' third edition, plates + by Dr. Fau, text with figures by Edouard Cuyer: Paris, 1896. + 'Artistic Anatomy of Man,' by J. C. L. Sparkes, second edition, + text with 50 plates: Bailliere, Tindall and Cox, London, 1900. + +This being granted, it is, nevertheless, necessary to take a rapid +bird's-eye view of organized beings, and to recall the terms used in +their classification. + +Animals are primarily classed in great divisions, based on the general +characters which differentiate them most. These divisions, or +_branches_, allow of their being so grouped that in each of them we find +united the individuals whose general structure is uniform; and under the +name of vertebrates are included man and the animals with which our +studies will be occupied. The vertebrates, as the name indicates, are +recognised by the presence of an interior skeleton formed by a central +axis, the vertebral column, round which the other parts of the skeleton +are arranged. + +The vertebrate branch is divided into classes: fishes, amphibians or +batrachians, reptiles, birds, and mammals. + +The mammals--from the Latin _mamma_, a breast--are characterized by the +presence of breasts designed for the alimentation of their young. Their +bodies are covered with hair, hence the name _piliferes_ proposed by +Blainville; and, notwithstanding that in some individuals the hairs are +few, the character is sufficient to distinguish them from all other +vertebrates. + +We find united in this class animals which, at first, seem out of place, +such as the whale and the bat; and, from their external appearance +alone, the former would appear to belong to the fishes, and the latter +to birds. Yet, on studying their structure, we find that, not only do +these animals merit a place in the class which they occupy, because they +possess the distinctive characters of mammals; but, still further, their +internal structure is analogous to that of man and of the other +individuals of this class. + +Notwithstanding this similarity of structure, the whale is not without +some points of difference from its neighbours the horse and the dog; +therefore, in order to place each of these animals in a position +suitable to it, mammals are divided into secondary groups called +_orders_. The first of these orders includes, under the name _primates_, +man and apes. The latter contain animals which approach birds in certain +characters of their organism, forming a link between the latter and +mammals. + +We find, in studying the regions of the body in some of the vertebrates, +that, while they present differences from the corresponding regions of +the human body, they also offer most striking analogies. We can, for +example, recognise the upper limb of man in the anterior one of +quadrupeds, in the wing of the bat, in the paddle of the seal, etc. It +is, so to speak, those variations of a great plan which give such a +charm to the study of comparative anatomy. + +The division of classes into orders, which we have just mentioned, +being still too general, it was found necessary to establish +subdivisions--more and more specialized--to which the names _families_, +_genera_, _species_, and _varieties_ were given. + + + + +CHAPTER I + +OSTEOLOGY AND ARTHROLOGY + + +THE TRUNK + +The Vertebral Column + +We commence the study of the skeleton with a description of the trunk. + +The trunk being, in quadrupeds, horizontal in direction (Fig. 1), the +two regions of which it consists occupy, for this reason, the following +positions: the thorax occupies the anterior part, the abdomen is placed +behind it; the vertebral column is horizontal, and is situated at the +superior aspect of the trunk; it projects beyond the latter: anteriorly, +to articulate with the skull; and, posteriorly, to form the skeleton of +the tail, or caudal appendix. + +The number of the vertebrae is not the same in all mammalia. Of the +several regions of the vertebral column, the cervical shows the greatest +uniformity in the number of the vertebrae of which it consists, with but +two exceptions (eight or nine in the three-toed sloth, and six in the +manatee); we always find seven cervical vertebrae, whatever the length of +the neck of the animal. There are no more than seven vertebrae in the +long neck of the giraffe, but they are very long ones; and not less than +seven in the very short neck of the dolphin, in which they are reduced +to mere plates of bone not thicker than sheets of cardboard. If the +cervical region presents uniformity in the number of its bones, it is +not so with the other regions of the column. + +The following table shows their classification in some animals: + +VERTEBRAE. + + +------------+-----------+---------+---------+ + | | Cervical. | Dorsal. | Lumbar. | + +------------+-----------+---------+---------+ + | Bear | 7 | 14 | 6 | + | Dog | 7 | 13 | 7 | + | Cat | 7 | 13 | 7 | + | Rabbit | 7 | 12 | 7 | + | Pig | 7 | 14 | 6 or 7 | + | Horse | 7 | 18 | 6 or 5 | + | Ass | 7 | 18 | 5 | + | Camel | 7 | 12 | 7 | + | Giraffe | 7 | 14 | 5 | + | Ox | 7 | 13 | 6 | + | Sheep | 7 | 13 | 6 | + +------------+-----------+---------+---------+ + +[Illustration: FIG. 1.--A HUMAN SKELETON IN THE ATTITUDE OF A QUADRUPED. +TO GIVE A GENERAL IDEA OF THE POSITION OF THE BONES IN OTHER +VERTEBRATES.] + +It is worthy of notice that in birds the number of the cervical vertebrae +is not constant, as in mammals; they are more numerous than the dorsal. +These latter are almost always joined to one another by a fusion of +their spinous processes; the two or three last vertebrae are similarly +united to the iliac bones, between which they are fixed. The dorsal +vertebrae thus form one piece, which gives solidity to the trunk, and +provides a base of support to the wings, for the movements of flying. +There are, so to speak, no lumbar vertebrae, the bones of that region, +which cannot be differentiated from the sacrum, having coalesced with +the bones of the pelvis. + +VERTEBRAE. + + +------------------+-----------+---------+ + | | Cervical. | Dorsal. | + +------------------+-----------+---------+ + | Vulture | 15 | 7 | + | Eagle | 13 | 9 | + | Cock | 14 | 7 | + | Ostrich | 18 | 9 | + | Swan | 23 | 10 | + | Goose | 18 | 9 | + | Duck | 15 | 9 | + +------------------+-----------+---------+ + +In reptiles, the relation between the number of the cervical vertebrae +and that of the dorsal is very variable; some serpents are devoid of +cervical vertebrae, having only dorsal ones--that is, vertebrae carrying +well-developed ribs. + +VERTEBRAE. + + +-------------------+-----------+---------+---------+ + | | Cervical. | Dorsal. | Lumbar. | + +-------------------+-----------+---------+---------+ + | Crocodile | 7 | 14 | 3 | + | Caiman | 7 | 12 | 5 | + | Boa | 3 | 248 | 0 | + | Python | 0 | 320 | 0 | + | Viper | 2 | 145 | 0 | + +-------------------+-----------+---------+---------+ + +Regarding the direction of the vertebral column in animals, in which the +trunk is not vertical, it is evident that the spinous processes point +upward, and that in comparing them with those of man they must be +arranged so that the superior surface of the human vertebra will +correspond to the anterior surface of that of the quadruped. Of the +cervical vertebrae, the atlas and axis call for special notice. Apropos +of the atlas, we find that it, in the human being, is narrower than the +corresponding parts of the skull, and is therefore hidden under the base +of the cranium (Fig. 2); in quadrupeds its width is equal to that of the +skull, and sometimes exceeds, because of the great development of its +wing-shaped transverse processes, that of the neighbouring parts of the +head (Fig. 3). On this account those transverse processes often project +under the skin of the lateral surfaces of the upper part of the neck. + +[Illustration: FIG. 2.--SIZE OF THE ATLAS COMPARED WITH THE TRANSVERSE +DIMENSIONS OF THE CORRESPONDING PARTS OF THE SKULL IN MAN. + +1, Atlas; 2, mastoid process; 3, external occipital protuberance; 4, +inferior maxilla.] + +The axis is furnished on its anterior surface with the odontoid process, +which articulates with the anterior (or inferior) arch of the atlas, +according to the direction of the neck. The spinous process, flattened +from without inwards, is more or less pointed; it is elongated from +before backwards, so as partly to overlap the atlas and the third +cervical vertebra. + +We find that this process overlaps less and less the neighbouring +vertebrae when we examine in succession the bear, the cat, the dog, the +ox, and the horse. With regard to the other vertebrae of this region, +they diminish in width from the second to the seventh; and, in some +animals, the anterior surface of the body presents a tubercle which +articulates with a cavity hollowed in the posterior surface of that of +the vertebra before it; this feature dwindles away in the dorsal and +lumbar regions. + +The spinous process, slightly developed in the third cervical vertebra, +gradually increases in size to the seventh, the spinous process of +which, long and pointed, well deserves the name of _the prominent_ which +is bestowed on it; but it should not be forgotten that the spinous +process of the axis is equally developed. + +[Illustration: FIG. 3.--SIZE OF THE ATLAS COMPARED WITH THE TRANSVERSE +DIMENSIONS OF THE CORRESPONDING REGIONS OF THE SKULL IN A DOG. + +1, Atlas; 2, zygomatic arch; 3, external occipital protuberance; 4, +inferior maxilla.] + +On the inferior surface of the body of each of the vertebrae is found a +prominent crest, especially well marked at the posterior part; this +crest is but slightly developed in the bear and in the cat tribe, and is +not found in swine. + +The transverse processes of the cervical vertebrae, from their relation +to the trachea, are known as the _tracheal processes_. + +The most marked characteristic of the dorsal vertebrae is furnished by +the spinous processes. They are long and narrow. As a rule, the spinous +processes of the foremost dorsal vertebrae are the most developed and +are directed obliquely upwards and backwards. As we approach the last +vertebrae of this region, the processes become shorter and tend to become +vertical, and the last ones are even, in some cases, directed upwards +and forwards; this disposition is well marked in the dog and the cat. In +the cetaceans, on the contrary, the length of the spinous processes +increases from the first to the last. + +[Illustration: FIG. 4.--LUMBAR VERTEBRAE OF A QUADRUPED (THE HORSE): +SUPERIOR SURFACE. + +1, Spinous process; 2, anterior articular process and transverse process +of the first lumbar vertebra of the left side; 3, costiform process.] + +In the horse the spinous processes of the first dorsal vertebrae produce +the prominence at the anterior limit of the trunk, where the mane ends, +which is known as the _withers_. + +The lumbar vertebrae are thicker than the preceding; they are known by +their short and latterly-flattened spinous processes, and still more +readily by their transverse processes, which, as they are evidently +atrophied ribs, it is more accurate to denominate costiform processes +(Fig. 4). These are long, flattened from above downwards, and directed +outwards and forwards. + +The true transverse processes are represented by tubercles situated on +the superior borders of the articular processes of each of the vertebrae +of the lumbar region. Apropos of these different osseous processes, we +are reminded that they are also present in the human skeleton. + +In the horse the costiform processes of the fifth and sixth lumbar +vertebrae articulate, and are sometimes ankylosed, one with the other; +the terminal ones articulate with the base of the sacrum. Sometimes the +processes of the fourth and fifth are thus related; this is the case in +the figure (4) given; here the costiform processes of the fourth and +fifth vertebrae articulate, and the two terminal ones have coalesced. + +In the ox, the same processes are more developed than in the horse; +their summits elevating the skin, produce, especially in animals which +have not much flesh, prominences which limit the flanks in the superior +aspect. The costiform processes of the last lumbar vertebrae are separate +from each other; those of the latter are not in contact with the sacrum. + +=The Sacrum.=[3]--This bone, single and median, is formed by the mutual +coalescence of several vertebrae, which vary in number according to the +species observed. + + [3] In human anatomy, the sacrum and the coccyx are studied as part of + the pelvis; we, therefore, in the study of the artistic anatomy of + man, study these bones with the bones of the lower limbs. Here we + do not follow this plan. In animals the sacrum and the coccyx, as + a matter of fact, clearly continue the superior border of the + skeleton of the trunk; hence we study them with the vertebral + column. + +_Vertebrae Constituting the Sacrum._--Bears, 5; dogs, 3; cats, 3; +rabbits, 4; swine, 4; horses, 5; camels, 4; oxen, 5; sheep, 4. + +The sacrum is situated between the two iliac bones; with which it +articulates, and contributes to the formation of the pelvis. It is +obliquely placed, from before backwards, and from below upwards; +immediately behind the lumbar section of the vertebral column; and is +continued by the coccygeal vertebrae, which form the skeleton of the +tail. + +It is triangular in outline, and is generally more narrow in proportion +than in the human being. All things considered, it is more large and +massive, and of greater density, in species which sometimes assume the +upright posture, rather than in those which cannot assume that +attitude; for example, the sacrum of the ape, of the bear, of the dog, +and of the opossum are proportionately larger than those of the +horse.[4] + + [4] This is particularly striking only in those portions of the sacrum + that are not in relation with the other bones of the pelvis. We + think that the general form of this bone depends on the mode of + its connexions with the iliac bones and the extent of the + articular surfaces by which it is in contact with the latter. + +Its superior surface presents a crest, formed by the fusion of the +spinous processes of the vertebrae which form it. In certain species +these processes are attached only by their bases, and are separated from +each other superiorly. In the pig they are wholly wanting. + +=The Coccygeal Vertebrae.=--These vertebrae, few in number (and sometimes +ankylosed) in the human being, form in the latter a small series, the +coccyx; which is inclined forwards, that is to say, towards the interior +of the pelvis. In quadrupeds, on the contrary, their number is large; +they are not ankylosed, and they form the skeleton of the caudal +appendix. + +The first coccygeal vertebrae--that is, those which are next the +sacrum--present characters which are common to those of other regions: +they have a body, a foramen, and processes. As we trace them backwards, +these characters become gradually effaced; and they become little more +than small osseous cylinders simply expanded at their extremities. + + +Direction and Form of the Spinal Column + +The curves of the vertebral column are, in quadrupeds, slightly +different from those which characterize the human spine. First, instead +of their being, as in the latter, curves in the antero-posterior aspect, +because of the general attitude of the body, they are turned in the +supero-inferior direction. + +The cervical region is not a single curve, as in the human being. It +presents two: one superior, with its convexity looking upwards; the +other inferior, the convexity of which is turned downwards. This +arrangement reminds one of that of a console. + +The dorsal and lumbar regions are placed in a single curved line, more +or less concave downwards; so that in the lumbar region there is no +curve analogous to that which exists in man; a form which, in the +latter, is due to the biped attitude--that is to say, the vertical +position of the trunk. Briefly, there is in quadrupeds one dorso-lumbar +curve; and not both a dorsal and a lumbar, with convexities in opposite +directions. + +At the extremity of the dorso-lumbar region is the sacrum and the caudal +appendix, which describe a curve of which the concavity is directed +downwards and forwards. + +It is necessary to point out that it is not the curves of the three +anterior portions of the spinal column which determine the form of the +superior border of the neck and shoulders, and of the same part of the +trunk. For the first portion, there is a ligament which surmounts the +cervical region, and substitutes its modelling influence for that of the +vertebrae. It is the _superior cervical ligament_, which arises from the +spinous process of the first cervical vertebrae, and is inserted into the +external occipital protuberance on the upper part of the posterior +surface of the skull. The summits of the spinous processes of the +vertebrae alone give form to the superior median border of the trunk. In +this connection we here repeat that it is not the general curvature of +the vertebral column which produces the withers, but the great length of +the spinous process of the first vertebrae of the dorsal region. + + +The Thorax + +The dorsal vertebrae form the posterior limit in man, and superior in +quadrupeds, of the region of the trunk known as the _thorax_. A single +bone, the sternum, is situated at the aspect opposite; the ribs bound +the thorax on its sides. + +In its general outlines the thorax in quadrupeds resembles that +of man--that is to say, that, as in the latter, the anterior +portion--superior in the human being--is narrower than the part +opposite. But the progressive widening takes place in a more regular and +continuous fashion, so that it presents a more definitely conical +outline. This purely conical form is nevertheless found in the human +species, but only during infancy; the inferior portion of the thoracic +cage being then widely expanded, because of the development of the +abdominal viscera, which at that period are relatively large. + +But the proportionate measurements of the thorax are different. Indeed, +we may recall that in man the thorax is flattened from before backwards, +so that the distance between the sternum and the vertebral column is +shorter than the distance from the rib of one side to the corresponding +one of the opposite side (Fig. 5). In animals, on the contrary, it is +flattened laterally. Its vertical diameter--measured from the sternum to +the vertebral column--is greater than the transverse measurement (Fig. +6). + +[Illustration: FIG. 5.--A TRANSVERSE SECTION OF THE THORAX OF A MAN +PLACED VERTICALLY--THAT IS TO SAY, IN THE DIRECTION WHICH IT WOULD +ASSUME IN A MAN PLACED IN THE ATTITUDE OF A QUADRUPED (A DIAGRAMMATIC +FIGURE). + +1, Dorsal vertebra; 2, sternal region; 3, costal region of one side; 3', +costal region of the other side.] + +From this results a peculiar arrangement of the muscles that we are able +to bring directly into prominence, which presents points of interest +from the point of view of the contraction of the subcutaneous layer. +Indeed, in man the region occupied by the pectorals is very broad; it is +a wide surface turned directly forward. In quadrupeds, this region of +the pectorals is narrowed. It is not spread out, as in the preceding +instances; and the appearance it presents is explained by the fact that +the thorax is compressed laterally. If we examine the thorax on one of +its lateral surfaces, the muscles, on the contrary, are more extended. +We see the contour of the vertebral column, and the median part of the +abdomen; and, especially in the horse, between the great dorsal and the +great oblique of the abdomen, we find a large space, in which the ribs, +with the intercostals which join them, are uncovered; the muscles in +question separate the one from the other, under the influence, it would +seem, of the great dimensions of the lateral wall of the thorax. + +[Illustration: FIG. 6.--A VERTICAL SECTION OF THE THORAX OF A QUADRUPED +(DIAGRAMMATIC). + +1, Fifth dorsal vertebra; 2, sternal region; 3, costal region of one +side; 3', costal region of the opposite side.] + +=The Sternum.=--The sternum is, in quadrupeds, directed obliquely +downwards and backwards; its form varies in different species. In the +carnivora, it consists of eight bones, irregularly cylindrical in form, +being slightly flattened from within outwards, and thickened at their +extremities. They remain separate, and this contributes elasticity and +flexibility to the thorax. The first nine costal cartilages articulate +directly with the sternum. The first of these cartilages articulates +with a nodule situated a little above the middle of the first bone of +the sternum. + +In the horse the sternum is flattened laterally in its anterior portion, +and from above downwards in its posterior half. The six bones which +form the sternum are connected by cartilage. The keel-shaped piece, +situated in front of the sternum, is also cartilaginous. This process, +but slightly marked posteriorly, becomes more and more prominent in +front, and terminates at its anterior extremity by a prolongation, +slightly curved backwards, which projects for some centimetres beyond +the cavity in which the first costal cartilage is received. This process +is known as the _tracheal process_, or _rostral cartilage_. The +posterior extremity of the sternum, flattened from above downwards, ends +in a cartilaginous plate; concave superiorly, and convex inferiorly: +this is the abdominal prolongation, or _xiphoid appendix_. + +In the ox, the sternum is formed of two distinct bones, which are united +by an articulation. One, the anterior, is short, and forms the first +portion of the sternum; it is slightly flattened from side to side, and +vertical in direction. The other, the posterior, is longer, and is +formed by the fusion of several small bones; it is placed horizontally, +and is flattened from above downwards. At the level of articulation of +these two portions, and because of their different directions, the bone +is bent. This bend occurs at the point of articulation of the second +costal cartilage. On the superior border of the anterior segment the +cartilage of the first rib is articulated. The xiphoid appendix, which +is cartilaginous, is attached to the extremity of a long process of the +last bone of the sternum. + +The shape of the anterior extremity of the sternum is influenced by the +presence or absence of clavicles. We have seen that in some quadrupeds +the clavicles are wanting. In the first case, this extremity is large, +and approaches in shape to the corresponding part of the human sternum, +which is so clearly designed to give a point of support to the anterior +bone of the shoulder. In the second, on the contrary, this extremity is +narrow. + +The sternum in birds is very different from that in mammalia, which we +have been studying. It varies greatly in extent and shape, under the +influence of certain conditions. To understand the cause of these +variations it is necessary to remember that in man (as, indeed, in other +animals; but the example of man, for that which follows, will be more +striking, on account of the mobility of his upper limbs) the sternum +gives origin to the pectoral muscles, and that these muscles are +inserted into other parts of the thoracic limbs, designed by their +contraction to draw the arms downwards, forwards, and inwards--that is, +when these are in a state of abduction and in a horizontal direction, +they draw them towards the anterior surface of the thorax and downwards. +Now, this movement is similar to that made by birds during flight. It is +necessary to add that, in the latter case, the more the displacement of +the upper limbs has of force and extent, the more the pectoral muscles +are developed. + +For these reasons, birds, in which, during flight, the movements of the +thoracic limbs--the wings--are necessarily energetic, present a great +development of the pectoral muscles; having consequently, because an +extent of surface for the origin of the muscles commensurate with their +development is necessary, a very large and peculiarly shaped sternum +(Figs. 18, 6; and 21, 6). Indeed, not only is the sternum large, but, +further, in order to form a deeper surface, proportionately adapted to +the muscles which arise from and cover it, its anterior surface +presents, in the median line, a prominent crest known as the _keel_. +This prominence forms two lateral fossae. We cite as examples, the +sternum of the eagle, the vulture, the falcon, and the hawk. + +All birds are not, however, equally adapted to flight, for in the +domestic cock, which flies but a short distance, and badly, the sternum +is less developed (Fig. 7); it is also diminished by slots, which +diminish its surface. These slots, two on each side, are called from +their position the internal and external slots. They are bounded by +narrow, elongated, bony processes, an internal and an external; the +expanded lower extremity of the latter overlaps the last inferior ribs +(see p. 19). The part of the external border which surmounts this +external process is hollowed out into grooves, which receive the +inferior ribs, and terminates superiorly in an osseous projection known +as _the costal prominence_. + +In the ostrich, the cassowary, and the apteryx, which run, but do not +fly, the sternum has the form of a plate of bone slightly convex, but +without a keel. + +[Illustration: FIG. 7.--STERNUM OF A BIRD (THE COCK): LEFT SIDE, +EXTERNAL SURFACE. + +1, Keel; 2, internal slot; 3, external slot; 4, internal process; 5, +external process; 6, inferior ribs; 7, costal process; 8, surface for +articulation with the coracoid bone.] + +The shape of the sternum, correlated to the faculty of flight (or of +swimming; apropos of which we may cite the penguin, of which the +rudimentary wings resemble fins, and perform their functions only), or +the absence of this faculty, has furnished the division of birds into +two groups. In one are included, under the name _Carinates_ (_carina_, +keel), those in which the sternum is provided with a keel; in the other +division are those in which the sternum is not furnished with one. These +latter, on account of their unique mode of progression, are more nearly +allied to the mammals. + +The keel is developed in flying mammals (bats). + +=Ribs and Costal Cartilages.=--There are on each side of the thorax as +many ribs as there are dorsal vertebrae. In animals, as in man, the ribs +which articulate with the sternum by their cartilages are called _true_, +or _sternal_ ribs; those whose cartilages do not articulate with the +sternum are called _false_, or _asternal_. The longer ribs are those +situated in the middle region of the thorax. + +The ribs are directed obliquely downwards and backwards, and this +obliquity is more marked in the posterior ones than in the anterior. +They are, however, less oblique than in the human being; what proves +this is that the first rib in man is oblique, while in quadrupeds it is +vertical. + +The curvature of the ribs is less pronounced in quadrupeds than in the +human being, but this is not equal in all animals. The ribs of the bear +are more curved than those of the dog; the latter has ribs more curved +than those of the horse. + +Each rib, at its vertebral extremity, presents, from within outwards, a +wedge-shaped head for articulation with two dorsal vertebrae, a neck, and +a tuberosity. External to the tubercle are found some rough impressions, +for muscular attachments, which correspond to the angle of the human +rib. + +In the following table, we give the number and classification of the +ribs of some animals: + +NUMBER OF THE RIBS ON EACH SIDE OF THE THORAX. + + Sternal. Asternal. + Bear 14 divided into 9 and 5 + Dog 13 " " 9 " 4 + Cat 13 " " 9 " 4 + Rabbit 12 " " 7 " 5 + Pig 14 " " 7 " 7 + Horse 18 " " 8 " 10 + Camel 12 " " 8 " 4 + Ox 13 " " 8 " 5 + Sheep 13 " " 8 " 5 + +The costal cartilages, by which the first ribs are united to the sternum +(sternal ribs), whilst the latter are united one to the other without +being directly connected with the sternum (asternal ribs), are, as a +rule, in quadrupeds, directed obliquely downwards, forwards, and +inwards; each forms, with the rib to which it belongs, an obtuse angle +more or less open anteriorly. Their length is proportionate to that of +the ribs. The cartilages, which are continued from the asternal ribs, +unite and form the borders, directed obliquely downwards and forwards, +of the fossa which is found at the inferior and posterior part of the +thorax, and which forms the lateral limits of the epigastric region. In +the dog and cat the ribs are thick and almost cylindrical; the costal +cartilages are thicker at the margin of the sternum than at their costal +extremity. In the ox, the ribs are flattened laterally and are very +broad, the more so as we examine a portion further from the vertebral +column. From the second to the twelfth they are quadrangular in the +superior fourth, and thicker than in the rest of their extent. The first +costal cartilage is vertical; the following ones are progressively more +oblique in a direction downwards and forwards. The four or five +cartilages which succeed the first unite with slight obliquity to the +sternum; their union with that bone gives the impression of a very +strong, well-knit apparatus. The costal cartilages which unite with the +sternum are flattened laterally in the portions next the ribs, and +flattened from front to back in the rest of their extent. + +In the horse the ribs increase in length from the first to the ninth; +they are flattened from without inwards, and increase in width from the +first to the sixth or seventh, and the following ones become narrower. +The costal cartilages, from the second to the eighth, are, as in the ox, +at first flattened laterally, near the ribs; while near the sternum they +are flattened from front to back. + +In birds, the ribs are each furnished with a flat process (Fig. 18, 10), +which springs from the posterior border, is directed backwards, and +overlaps the external surface of the succeeding rib. These processes are +not found, as a rule, on the first or last ribs. + +As for the costal cartilages, they are, as a rule, ossified, and receive +the name of inferior ribs (Fig. 18, 11), united to the preceding +(superior ribs; Fig. 18, 9) by articulation; by the other extremity they +are joined to the sternum; the first superior ribs generally want them. +Sometimes the last inferior rib becomes connected with the one that +precedes it, not articulating with the sternum; and thus recalls the +relations of the asternal ribs which we have noticed in our study of the +mammals. + +In the bat, as in birds, the costal cartilages are ossified. + + +THE ANTERIOR LIMBS[5] + + [5] Consult Figs. 21, 33, 34, 38, 39, 46. + +The anterior limbs, homologous to the upper limbs in man, are formed, as +in the latter, of four segments: the shoulder, the arm, the forearm, and +the hand. These limbs, considered in the vertebral series, present +themselves under very different aspects, which are determined by the +functions they are called upon to perform. + +They constitute the forepaw in terrestrial mammals; in aerial +vertebrates they form wings; in aqueous mammals they act as paddles. In +whatever series we study them, we can readily find the relationship of +the different parts; it is very easy to recognise the same bones in the +upper limbs of the human being, the wings of the bat (Fig. 8) and of +birds (Fig. 21), and in the anterior paddles of the seal (Fig. 9) and of +the dolphin. + +[Illustration: FIG. 8.--ANTERIOR LIMB OF THE BAT: LEFT SIDE, ANTERIOR +SURFACE. + +1, Clavicle; 2, scapula; 3, humerus; 4, radius; 5, cubitus; 6, carpus; +7, thumb; 8, metacarpus; 9, phalanges.] + +In quadrupeds, the shoulder and arm are hidden, the latter more or less +completely, in the muscular mass which binds it to the lateral wall of +the trunk; so that the anterior limbs only present; free from the trunk: +the elbow, forearm, and hand. + + +The Shoulder + +In some vertebrates, the shoulder is formed of two bones--the scapula +and clavicle; in others of only one bone--the scapula; the clavicle in +this case does not exist. + +=The Scapula or Omoplate.=--The scapula is situated on the lateral +surface of the thorax, and is directed obliquely, from above downwards +and from behind forwards. + +We must first recall, so as to be able to make a comparison, that in man +this bone is placed at the posterior surface of the thoracic cage; so +that if we look at the human thorax on one of its lateral aspects we see +chiefly the external border of the scapula; it is the external surface +(homologous to the posterior surface of the human scapula) which we see +in its full extent when we look on the same surface of the thorax in +quadrupeds. + +[Illustration: FIG. 9.--ANTERIOR LIMB OF THE SEAL: LEFT SIDE, EXTERNAL +SURFACE. + +1, Scapula; 2, humerus; 3, radius; 4, ulna; 5, carpus; 6, metacarpus; 7, +phalanges of the fingers.] + +To sum up, if we fancy the human being in the position of the quadruped, +the scapula will have its surfaces almost parallel to the ground (Fig. +10); while in quadrupeds, the surfaces are situated in a plane which is +almost perpendicular to the ground (Fig. 11). This position of the +scapula in an almost vertical plane is designed to give the necessary +point of support to the osseous columns that form the skeleton of the +other portions of the anterior limbs. + +Because of this position of the scapula (Figs. 12 and 13), the spinal +border is superior, the cervical, anterior, and the axillary, posterior. +In direct contrast to what obtains in the human scapula, the spinal +border is the shortest of the three; except in the bat, and the +majority of the cetaceans. + +[Illustration: FIG. 10.--SITUATION AND DIRECTION OF THE SCAPULA IN THE +HUMAN BEING, THE TRUNK BEING HORIZONTAL, AS IN QUADRUPEDS. VERTICAL AND +TRANSVERSE SECTION OF THE THORAX (DIAGRAMMATIC FIGURE). + +1, Contour of the thorax; 2, 2, the scapula.] + +[Illustration: FIG. 11.--POSITION AND DIRECTION OF THE SCAPULA IN +QUADRUPEDS. VERTICAL AND TRANSVERSE SECTION OF THE THORAX (DIAGRAMMATIC +FIGURE). + +1, Contour of the thorax; 2, 2, the scapula.] + +In certain animals (in the ungulates [_hoofed_[6]]--pigs, oxen, sheep, +horses) the superior, or spinal, border of the scapula is surmounted by +a cartilage called _the cartilage of prolongation_. + + [6] For the definition of the word _hoofed_, see p. 37. + +This is the cause why the border to which it is fixed is so slightly +noticeable under the skin in these animals; indeed, in the upper part, +the bone and cartilage are not distinguishable in the contour of the +corresponding region of the back; being applied to the lateral surfaces +of the spinous processes, the prominence formed by the extremities of +which is directly continuous with the plane of the scapula (Fig. 16). + +[Illustration: FIG. 12.--LEFT SCAPULA OF THE HUMAN BEING, POSTERIOR +SURFACE, PLACED IN THE POSITION WHICH IT WOULD OCCUPY IN THE SKELETON OF +A QUADRUPED. + +1, Cervical border; 2, spinal border; 3, axillary border; 4, +supraspinous fossa; 5, subspinous fossa; 6, scapular spine; 7, glenoid +cavity; 8, coracoid process; 9, acromion process.] + +[Illustration: FIG. 13.--LEFT SCAPULA OF A HORSE: EXTERNAL SURFACE. + +1, Cervical border; 2, spinal border--the scapula here represented, +being from a hoofed animal, has a cartilage of extension attached to its +spinal border; 3, axillary border; 4, supraspinous fossa; 5, subspinous +fossa; 6, spine of the scapula; 7, glenoid cavity; 8, coracoid process. +The scapula of the horse has no acromion process, but it is easy, if we +compare the human scapula, to judge of the position which this process +would occupy if it were present.] + +In quadrupeds whose scapula, on the contrary, is wanting in the +cartilage of prolongation (in the _clawed_,[7] such as the cat and dog), +the superior border of the scapula is visible, especially when the +animal is resting on its fore-limbs, particularly when it crouches; at +such a time the skin is markedly raised by that border; and the spinous +processes of the vertebrae, beyond which it projects, occupy the bottom +of a fossa (Fig. 15). The internal surface of the scapula is turned +towards the ribs; it is known, as in man (in whom this surface is +anterior), as the subscapular fossa. + + [7] For the definition of this word, see p. 37. + +[Illustration: FIG. 14.--VERTICAL AND TRANSVERSE SECTION, AT THE SITE OF +THE SHOULDERS, OF THE THORAX OF THE HORSE (DIAGRAMMATIC FIGURE). + +1, Outline of the thorax at the level of the third dorsal vertebra; 2, +2, scapula; 3, spinal border of the scapula; 4, cartilage of +prolongation; 5, contour of the skin.] + +[Illustration: FIG. 15.--VERTICAL AND TRANSVERSE SECTION, AT THE PLANE +OF THE SHOULDERS, OF THE THORAX OF A DOG (DIAGRAMMATIC FIGURE). + +1, Outline of the thorax at the level of the third dorsal vertebra; 2, +2, scapula; 3, spinal border of the scapula; 4, contour of the skin.] + +Its external surface is divided into two parts by the spine of the +scapula; which, in some animals, terminates inferiorly in a flat and +clearly distinct process, the homologue of the acromion process of the +human scapula. The two regions separated by the spine are known as the +supraspinous fossa and the infraspinous fossa. The supraspinous fossa is +anterior to the spine, and the infraspinous is posterior to it. The +surfaces of the scapula are, in quadrupeds, flatter than in the human +being, and in particular the subscapular fossa, which is also less +concave. Some authors attribute this to the lesser curvature of the ribs +in quadrupeds. A few words will suffice to prove that there must be +another reason. The scapula is not in immediate contact with the ribs; +the subscapular fossa is not moulded on them. Besides, the form of the +scapula is, as in other parts of the skeleton, dependent on the +disposition of muscles, and the development of these latter is +correlated to the extent and energy of the movements which the +individual is able or required to execute. But the movements which +those muscles produce (more especially the rotation of the humerus) are, +in quadrupeds, less extensive than in the human being; and, +consequently, the muscles which produce them are, proportionally, less +strongly developed. The inferior angle (superior and external in man), +situated at the junction of the cervical and axillary borders, presents +the glenoid cavity, which, looking downwards, receives the articular +surface of the superior extremity of the bone of the arm--that is to +say, the head of the humerus. Above this cavity, on the lower part of +the cervical border, is situated a tubercle which reminds us of the +coracoid process of the human scapula. The region occupied by the +glenoid cavity is separated from the body of the bone by a +constriction--the neck of the scapula. + +In birds the scapula is elongated in a direction parallel to the +vertebral column, and very narrow in the opposite (Fig. 18): it is also +flat, and has no spine. Its coracoid process is represented by a +peculiar bone--the coracoidean or coracoid bone--which we shall describe +later on when we come to the study of the clavicle and of the anterior +region of the shoulder (see p. 26). + +=The Clavicle.=--The clavicle is found only in the human being, and in +animals whose anterior limbs, possessing great freedom of movement in +all directions, require that the scapula should possess a point of +support which, while affording this, can be displaced with it, or draw +it in certain directions. Now, this point of support is furnished by the +clavicle. + +In animals possessed of hoofs (ungulates), such as the sheep, ox, and +horse, the clavicle does not exist. Indeed, in them the freedom of +movement of the anterior limbs is limited; they move by projection in +the forward and backward directions only; they merely fulfil the +functions of giving support to and carrying about the body. The clavicle +is rudimentary in the cat and the dog; in the cat it is a small, +elongated bone (Fig. 16), 2 centimetres in length, thin and curved, +connected with the sternum and the scapula by ligamentous bundles. In +the dog it is represented by a small osseous plate only (Fig. 17), +which is not connected with any of the neighbouring bones. + +It is on the deep surface of a muscle which passes from the head and +neck to the humerus (mastoido-humeral, a muscle common to the arm, neck, +and head) in which this rudimentary bone is found to be developed. + +The clavicle exists in perfect state in mammals which use their limbs +for digging, grasping, or flying; the insectivora (hedgehog, mole) and +some rodents (squirrel, woodchuck) are provided with it. + +The cheiroptera (bats) possess an extremely well-developed clavicle, on +account of the varied movements which their thoracic limbs execute. + +[Illustration: FIG. 16.--LEFT CLAVICLE OF THE CAT: SUPERIOR SURFACE +(NATURAL SIZE). + +1, Internal extremity; 2, external extremity.] + +[Illustration: FIG. 17.--CLAVICLE OF THE DOG (NATURAL SIZE).] + +This formation of the shoulder which favours flight in the bat is even +more remarkable in birds. In these latter (Fig. 18) the clavicles, fused +together by their lower extremities, form one bone, having the shape of +the letter V or U, which is known as the _fourchette_; this bone, acting +as a true spring, keeps the shoulders apart, and prevents their +approximation during the energetic movements which flight necessitates. + +In birds whose power of flight is strong, the two limbs of this bone are +widely separated and thick, and the fourchette is U-shaped. Those whose +flight is awkward and but slightly energetic have the limbs of the +fourchette slender; they unite at a more acute angle, and the bone is V +shaped. + +Furthermore, a bone named the _coracoid_ joins the scapula to the +sternum; this bone, often fused with the scapula, where it contributes +to the formation of the glenoid cavity, represents in birds the coracoid +process of the human scapula. If we fancy this process directed +inwards, and sufficiently lengthened to join the sternum, we shall have +an idea of the disposition of the bone we are now discussing, and the +reasons for which the name has been chosen by which it is designated. +The coracoid bone, like the fourchette which it reinforces, offers to +the wings a degree of support proportionate to the efforts developed by +those limbs; for this reason it is thick and solid in birds of powerful +flight. + +[Illustration: FIG. 18.--SKELETON OF THE SHOULDER OF A BIRD (VULTURE): +ANTERO-EXTERNAL VIEW OF THE LEFT SIDE. + +1, Left clavicle; 2, inferior portion of the right clavicle, forming by +its ankylosis with that of the other side the fourchette; 3, coracoid +bone; 4, scapula; 5, articular surface for humerus; 6, superior half of +the sternum; 7, keel of sternum; 8, spinous process of the dorsal +vertebrae; 9, superior ribs; 10, process of one of these ribs; 11, +inferior ribs.] + +The superior extremity of each branch of the fourchette, at the level of +its junction with the coracoid and the scapula, bounds, with these +latter, a foramen which gives passage to the tendon of the elevator +muscle of the wing, or small pectoral. The importance of the fourchette +being, as we have seen, in proportion to the movements of flying, it is +easy to understand that the bone is not found in the ostrich. + + +The Arm + +A single bone, the humerus, forms the skeleton of this portion of the +thoracic limb. + +=The Humerus.=--The bone of the arm is, in quadrupeds, inclined from +above downwards and from before backwards. + +It is, with relation to other regions, short in proportion as the +metacarpus is elongated, and as the number of digits is lessened. In the +horse, for example, whose metacarpus is long, and in which but one digit +is apparent, the humerus is very short. The slight development in length +of the humerus explains its close application to the side of the animal +as far as the elbow. + +In animals in which the humerus is longer, the bone is slightly free, as +well as the elbow, at its inferior extremity. Later on we will return to +the consideration of this peculiarity and of the proportions of the +humerus, after we have studied the other parts of the fore-limbs. + +The humerus in quadrupeds is inflected like the letter S; in man this +general form is less accentuated, the humerus being almost straight. On +its body, which appears twisted on its own axis, we find the +musculo-spiral groove,[8] which crosses the external surface, and is +very deep in some animals. Above this groove, and on the external +surface, there exists a rough surface which is the impression of the +deltoid. In some species this rugosity is very prominent, and is called +_the tuberosity of the deltoid_; it is prolonged downwards by a border +which forms the anterior crest of the musculo-spiral groove and limits +this latter in front. The external border of the bone, or posterior +crest of the groove, limits it behind. + + [8] It would be going outside our province to discuss whether the + humerus is really twisted on its axis. This question, often + discussed, has been solved in some recent works in the following + manner: the humerus has undergone torsion at the level of its + superior extremity, and not at the level of its body; this does + not authorize us further to accord any definite sense to the + denomination 'groove of torsion' (musculo-spiral groove). That + which we must especially remember in connection with this fact, + is, as we shall afterwards see, the difference of direction which + the articular head presents according as the torsion has been more + or less considerable: because this is established, according to + the same order, in man and in quadrupeds. + +The superior extremity is enlarged, and remarkable in three portions +which it presents; these are: an articular surface and two tuberosities. + +The articular surface, or head of the humerus, smooth and round, is in +contact with the glenoid cavity of the scapula. This head in the human +skeleton is directed upwards and inwards; in quadrupeds its direction is +upwards and backwards. The inferior extremity, having in both one and +the other its long axis directed transversely, and the point of the +elbow looking backwards in all, the result is that the head of the +humerus is not situated vertically above the same regions; in the first, +it is almost directly above the internal part of this extremity; in the +latter, it is situated above its posterior surface, or the point of the +elbow in the complete skeleton. This difference of direction is +correlated with the position of the scapula, the glenoid cavity of +which, as we have already seen, is in man turned outwards, whereas in +quadrupeds it looks downwards. In the latter case the scapula +consequently rests on the head of the humerus; and this position is most +favourable for the performance of the functions which the anterior limbs +have to fulfil in these latter. + +Of the tuberosities of the head of the humerus, one is situated on the +external aspect--it is the great tuberosity, or _trochiter_; the other +is placed internally--it is the small tuberosity, or _trochin_. The +great tuberosity is divided into three parts--summit, convexity, and +crest; these different parts give insertion to the muscles of the +shoulder. We recollect that the facets (anterior, middle, and posterior) +of the great tuberosity of the humerus in man give attachment to the +muscles of the same region. The head of the humerus in the human body +projects above the tuberosities. We shall see afterwards, when dealing +with some special quadrupeds, that in some of these, on the other hand, +the tuberosities are on a higher level than the articular head of the +bone. Between the two tuberosities is the bicipital groove. + +In man, the superior extremity of the humerus, although covered by the +deltoid, reveals its presence by elevating the corresponding portion of +the latter. In quadrupeds, the anterior part of this extremity, although +similarly covered by muscular bundles, produces a prominence under the +skin. This prominence is situated at the summit of the angle formed by +the opposing directions of the scapula and the bone of the arm, and +constitutes what is known by the name of the _point of the shoulder_, or +of the _point of the arm_. + +The inferior extremity, transversely enlarged, presents an undulating +articular surface, which reminds us of the trochlea and the condyle of +the human humerus; on which, however, the condyle is more sharply +defined from the trochlea. + +In the human skeleton, the internal lip of the trochlea descends lower +than the external; and also lower than the condyle. In the bear, the +cat, and the dog, it is the same. In the ox and the sheep, the condyle +is lower than the trochlea, but only very little lower. In the horse the +arrangement is still the same, but a little more accentuated. + +On the lateral parts of this extremity we find: internally, a +prominence, the epitrochlea; and, externally, another, the epicondyle. +It is from this latter that the crest arises, which, passing upwards, +forms the posterior limit of the groove of torsion. + +The two prominences, which we have just described from a general point +of view, present special arrangements which it is necessary to point +out. When we examine the form of the outline of the inferior extremity +of the humerus in man, the bear, the cat, the dog, the ox, and the +horse, we find in following this order that the extremity tends to +become narrow transversely, and that the epicondyle and the epitrochlea +are less and less prominent on the external and internal aspects +respectively. These two processes, indeed, project backwards; the +epitrochlea always remaining more developed than the epicondyle. Because +of this projection backwards, the cavity situated on the posterior +surface of the inferior extremity, the olecranon fossa, is very deep, +more so than in the humerus of man. Its borders being thus formed by the +two processes, are very prominent. In front we find the coronoid fossa, +which is less deep than that of which we have just spoken. + +There exists in some mammals an osseous canal, situated above the +epitrochlea, and known as the _supratrochlear canal_ (Fig. 19). It is +bounded by a plate of bone which at its middle portion is detached from +the shaft of the humerus, and blends with the latter at both its +extremities. The brachial artery and median nerve pass through the +foramen. + +[Illustration: FIG. 19.--INFERIOR EXTREMITY OF THE LEFT HUMERUS OF A +FELIDE (LION). + +1, Epitrochlea; 2, supra-epitrochlear foramen.] + +[Illustration: FIG. 20.--INFERIOR EXTREMITY OF THE LEFT HUMAN HUMERUS, +SHOWING THE PRESENCE OF A SUPRATROCHLEAR PROCESS. + +1, Epitrochlea; 2, supra-epitrochlear process.] + +A similar condition is sometimes found, as an abnormality, in +man, which presents itself under the following aspect (Fig. +20): an osseous prominence more or less long, in the shape of a +crochet-needle--supra-epitrochlear process--situated 5 or 6 centimetres +above the epitrochlea; the summit of this process gives attachment to a +fibrous band, which is inserted by its other end into the epitrochlea +and the internal intermuscular aponeurosis. The fibro-osseous ring thus +formed gives passage to the brachial artery and the median nerve, or in +case of a premature division of this artery to the ulnar branch of the +same.[9] + + [9] For further details of this anomaly, see Testut, 'The Epitrochlear + Process in Man' (_International Journal of Anatomy and + Physiology_, 1889); A. Nicolas, 'New Studies on the Supratrochlear + Process in Man' (_Review of Biology of the North of France_, t. + iii., 1890-1891). + +There is also found in some mammals a perforation of the thin plate of +bone which, in others, separates the olecranon fossa from the coronoid. +This perforation is sometimes found as an abnormality in the human +humerus. + +As does the sternum and the skeleton of the shoulder, the humerus of +birds presents differences correlated to the functions which the +thoracic limbs are destined to fulfil. Lying on the side of the thorax, +directed obliquely downwards and backwards (Fig. 21), it is +proportionately longer in individuals of powerful flight than in those +which fly less or not at all. In the vulture it projects beyond the +posterior part of the pelvis; in the cock it does not even reach the +anterior border of the same. To these differences in length are added +differences in volume and in the development of the processes which +serve for muscular attachment, which are more considerable in birds of +powerful flight. + +The humerus is so placed that the radial border, external in man and +quadrupeds, looks upwards, with the result that the surface of the bone +of the arm, which in these latter is anterior, in the former looks +outwards. The humeral head, which is turned forwards and a little +inwards, is convex and elongated in the vertical direction. Behind and +above this head is found a crest for the insertion of muscles. It is the +same for the region below, where there is a tuberosity whose inferior +surface presents a pretty large opening which looks inwards to a fossa +from the floor of which a number of minute openings communicate with the +interior of the bone. This is the pneumatic foramen of the humerus. + +It is of interest to remember in connection with this subject that in +birds, in keeping with the conditions of flight, every system of organs +is adapted to diminish the weight of the body. We particularly draw +attention to the osseous framework, the structure of which is such that +the weight of the animal is greatly lessened. This condition is secured +by the pneumaticity. The bone consists of a cover of compact tissue, +which, instead of enclosing marrow, is hollowed out by cavities which +contain air, and communicate with special pouches, the air-sacs, which +are appendages of the lungs.[10] + + [10] The presence of air in the bones does not seem to be always + associated with the power of flight; as a matter of fact, we find + air spaces in the bones of some birds which do not fly (E. J. + Marey, 'The Flight of Birds,' Paris, 1890, p. 51). + +[Illustration: FIG. 21.--SKELETON OF A BIRD (VULTURE): LEFT SURFACE. + +1, Cranium; 2, face; 3, cervical vertebrae; 4, spinous processes of the +dorsal vertebrae; 5, coccygeal vertebrae; 6, sternum; 7, keel; 8, superior +ribs; 9, inferior ribs; 10, clavicle; 11, coracoid bone (for the details +of the skeleton of the shoulder, see Fig. 18); 12, humerus; 13, radius; +14, ulna; 15, carpus; 16, hand (for details of the skeleton of this +region, see Fig. 31); 17, ilium; 18, ischium; 19, pubis (for the details +of the pelvis, see Fig. 46); 20, femur; 21, tibia; 22, fibula; 23, +osseous nodule, which some anatomists think represents the calcaneum; it +is the sole vestige of the tarsus; 24, metatarsus; 25, foot; 26, first +toe (for the details of the skeleton of the foot, see Fig. 48).] + +The antibrachial extremity of the humerus is flattened from without +inwards. It terminates in two articular surfaces, which articulate with +the radius and ulna. + +The olecranon process of the ulna being slightly developed, it follows +that the olecranon fossa is not large; neither is the coronoid. + + +General View of the Form of the Forearm and Hand + +We now proceed to the study of the two regions of the fore-limbs which +present the greatest variety in regard to the number of bones and also +in regard to form and proportions. These two regions are the forearm and +the hand. + +It is first of all necessary to say that in man, when the fore-limb +hangs beside the body, and the dorsum of the hand looks backwards, the +two bones of the forearm are parallel, and that this position is known +by the name of _supination_. It is also necessary to remember that there +is another attitude, in which the radius, crossing the ulna, and +carrying the hand with it, displaces the latter in such a way that the +palmar surface looks backwards. This second position is known as +_pronation_. + +Let us now suppose that a man wishes to walk in the attitude of a +quadruped. It will be necessary, in order that his upper limbs, being +for the moment anterior ones, may act as members of support, to place +the forearm in pronation, in order that, as is more normal, the hands +may rest on the ground by their palmar surfaces. In this position the +radius, being rotated on its own axis at its upper extremity and around +the ulna in the rest of its extent, shall have its inferior extremity +situated on the inner side of the corresponding extremity of the latter. + +Such is the situation of the bones of the forearm and the attitude of +the hand in quadrupeds. In short, quadrupeds have their anterior members +in the position of pronation. + +The individual whom we have just supposed placed in the attitude of a +quadruped would be able to maintain this position by pressing on the +ground more or less extensive portions of his hands; the whole palm of +the hand may be applied to the ground (Fig. 22); or the fingers +only--that is to say, the phalanges (Fig. 23); or the extremities of +the fingers only--that is to say, the third phalanges (Fig. 24). This +last position, which is certainly difficult to maintain, should here be +regarded rather as theoretical. + +We shall meet with each of these modes of support in certain groups of +animals. Thus, the bear, badger, and the majority of rodents, have the +paws applied to the ground by the whole extent of the palmar surface of +the hand, from the wrist to the tips of the fingers. They are therefore +called plantigrade, from the analogy, in this case, of the palm of the +hand to the plantar surface, or sole of the foot. + +[Illustration: FIG. 22.--THE HUMAN HAND RESTING FOR ITS WHOLE EXTENT ON +ITS PALMAR SURFACE: LEFT SIDE, EXTERNAL SURFACE.] + +In others, such as the lion, tiger, panther, cat, wolf, and fox, the +support is made no longer on the whole extent of the palmar surface, but +on the corresponding surface of the fingers only--the metacarpus is +turned back, and, consequently, the wrist--that is to say, the +carpus--is removed from the ground. These are the digitigrades. + +Lastly, the ruminants (sheep, oxen, deer, etc.), and also the pig, ass, +and horse, rest on the third phalanx only. In them not only is the +metacarpus turned back, but also the two first phalanges. The wrist is +very far removed from the ground. In these animals, the third phalanx is +enclosed in a case of horn, a nail (the hoof), and because the support +of the limb is on that nail, the name of unguligrades has been given +them. Nevertheless, as the point of support is on the third phalanx, +which is also known by the name of phalangette, we are of opinion that, +in order to specify definitely, although they walk on their fingers, as +do the digitigrades, the support is provided not by the whole extent of +those appendages, they might receive the name of phalangettigrades. + +[Illustration: FIG. 23.--THE HUMAN HAND RESTING ON ITS PHALANGES: LEFT +SIDE, EXTERNAL SURFACE.] + +[Illustration: FIG. 24.--THE HUMAN HAND RESTING ON THE TIPS OF SOME OF +ITS THIRD PHALANGES: LEFT SIDE, EXTERNAL VIEW.] + +It is necessary among the ruminants to make an exception of the camel +and the llama, which are digitigrades. + +Just in proportion as the hand is raised from the ground, as we have +just seen in passing from the plantigrades to the digitigrades and +unguligrades, the number of bones of that region diminishes, the bones +of the forearm coalesce, and the ulna tends to disappear; the hand +becomes less and less suitable for grasping, climbing, or digging, so as +to form an organ exclusively adapted for walking and supporting the +body. + +Thus, the bear (plantigrade) has five digits, and the power of +performing the movements of supination and pronation. Indeed, we know +with what facility this animal is able to move his paws in every +direction, and climb a tree by grasping it with his fore-limbs. It is +well known, however, that no animal except the ape can perform the +movements of rotation of the radius around the ulna with the same +facility as man; and that none possesses the same degree of suppleness, +extent, and variety of movements of the forearm and hand. + +In the digitigrades there is one finger which is but slightly developed, +and which is always removed from the ground--that is, the thumb: there +is also a little less mobility of the radius around the ulna. + +In the ungulates the limbs are simply required to perform the movements +of walking, and form veritable columns of support, which become the more +solid as they are less divided. The bones of the forearm are fused +together; there is therefore no possibility of rotation of the radius +around the ulna. The metacarpus is reduced to a single piece, which in +the horse constitutes what is known as the _canon_. The number of digits +becomes diminished, so that in ruminants there are not more than two, +and in the horse but one. We should, however, add that, up to the +present, we have taken into account only perfect digits, those that rest +on the ground. We shall see further on that there exist supplementary +digits, but that they are only slightly developed, and are represented +in some cases by mere osseous spurs; it is this fact that has permitted +us to ignore them in the general study which we have just made. + +Because, as we have already said, the unguligrades have the inferior +extremity of the digit encased in a horny sheath, which forms the hoof +of the horse and the corresponding structures (_onglons_) in the ox, +those animals have been placed in a special group, which is based on +that peculiarity--that is, the group of ungulate mammals. + +The plantigrades and digitigrades, of which the paws have their surfaces +of support strengthened by an epidermic sole and fatty pads, have the +free extremities of the third phalanges covered on their dorsal surface +by nails or claws; hence they are named _unguiculate_ mammals. + +The bat and birds have the bones of the forearm so arranged that the +radius cannot rotate around the ulna. This is necessary in order that +during flight, when the wing is being lowered, the radius and hand shall +not be able to turn; for, if such rotation took place, each stroke of +the wing would place it in a vertical position, which would occasion a +loss of resistance incompatible with the effect to be obtained. + + +The Forearm + +The skeleton of the forearm in quadrupeds is vertical in direction; +consequently, it forms with the arm an angle open anteriorly; this is +well seen on examining the lateral surface. If we examine it on its +anterior surface, we find a slight obliquity directed downwards and +inwards. In animals in which the bones of the forearm are separate--that +is to say, susceptible of supination and pronation--we find a more close +resemblance to those of the human skeleton. The ulna, the superior +extremity of which always projects beyond that of the radius, has a +shaft which gradually narrows from above downwards. Its inferior +extremity is terminated by a round head in those animals in which the +ulna is fully developed; in others, as it is atrophied, it ends in a +thin, long process. + +The ulna presents at its superior extremity a posterior process, the +olecranon, which forms the point of the elbow. We find on the anterior +surface of the same, another process, the coronoid. + +It is necessary to dwell on the relations of these parts. In man the +head of the radius is situated at the anterior part of the external +surface of the superior extremity of the ulna (Fig. 25); indeed, the +small sigmoid cavity with which the head articulates is situated on the +outer side of the coronoid process, and this apophysis is placed in +front. In the plantigrades and digitigrades the head of the radius is +placed still more forward, so much so that it is situated almost in +front of the superior extremity of the ulna (Fig. 26). In the +unguligrades it is placed directly in front of this latter (Fig. 27). + +Further, the displacement of the radius is made at the expense of the +superior extremity of the neighbouring bone; the radius appears to +appropriate more and more the parts which in man belong exclusively to +the ulna--for example, the coronoid process. In the plantigrades and the +digitigrades half of the process still belongs to the ulna and the +remainder to the radius. In the ungulates--the horse, for example--the +coronoid process belongs to the radius; the ulna, situated behind the +latter, is correspondingly diminished in size. + +[Illustration: FIG. 25.--SUPERIOR EXTREMITY OF THE BONES OF THE HUMAN +FOREARM: LEFT SIDE, SUPERIOR SURFACE. + +1, Radius; 2, ulna; 3, olecranon process; 4, coronoid process.] + +[Illustration: FIG. 26.--SUPERIOR EXTREMITY OF THE BONES OF THE FOREARM +OF THE DOG: LEFT LIMB, SUPERIOR SURFACE. + +1, Radius; 2, ulna; 3, olecranon process; 4, coronoid process.] + +In brief, when we study this region of the skeleton in plantigrades, +then in digitigrades, and finally in unguligrades, we find a kind of +progressive absorption of one of the two bones (ulna) by the other +(radius), which thus becomes the more developed. + +It is easy to explain this partial disappearance of the ulna. When the +forearm is capable of performing the movements of pronation and +supination, the ulna is completely developed, for it is in its small +sigmoid cavity that the head of the radius revolves, and it is around +its inferior extremity, the head, that the corresponding extremity of +the radius turns. But when the movements of rotation of the forearm do +not exist, the inferior extremity of the ulna becomes functionally +useless and disappears. As to its role in the movements of the region of +the wrist, that is nil, for we may remember--we will observe it again +when we come to treat of the articulations--that the hand articulates +with the radius alone (radio-carpal articulation); this is the reason +that, when the forearm possesses the fullest mobility, the hand follows +the movements which that bone makes around the ulna. + +[Illustration: FIG. 27.--SUPERIOR EXTREMITY OF THE BONES OF THE FOREARM +OF THE HORSE: LEFT LIMB, SUPERIOR SURFACE. + +1, Radius; 2, ulna; 3, olecranon process; 4, coronoid process.] + +It is not so with the articulation at the elbow-joint; there it is the +ulna, which, with the humerus, forms the essential parts (humero-ulnar +articulation); its olecranon process limits the movement of extension +of the forearm. It is for this reason that, even in those quadrupeds in +which the ulna is atrophied, the olecranon process presents a relatively +considerable degree of development. + +[Illustration: FIG. 28.--INFERIOR EXTREMITY OF THE BONES OF THE FOREARM +OF A MAN: LEFT SIDE, POSTERIOR SURFACE, POSITION OF SUPINATION. + +1, Radius; 2, ulna; A, groove for the long abductor and short extensor +muscles of the thumb; B, groove for the radial muscles; C, groove for +the long extensor of the thumb; D, groove for the special extensor of +the index finger and of the common extensor of the fingers; E, groove +for the proper extensor of the little finger; F, groove for the +posterior ulna.] + +[Illustration: FIG. 29.--INFERIOR EXTREMITY OF THE BONES OF THE FOREARM +OF THE DOG: LEFT SIDE, ANTERIOR SURFACE, NORMAL POSITION--THAT IS, THE +POSITION OF PRONATION. + +1, Radius; 2, ulna; A, groove for the long abductor and for the short +extensor of the thumb; B, groove for the radials; D, groove for the long +extensor of the thumb, the special extensor of the index-finger, and the +common extensor of the fingers; E, groove for the special extensor of +the little finger.] + +We know that on the posterior surface of the inferior extremity of the +bones of the human forearm are grooves in which pass the tendons of the +posterior and external muscles which, belonging to this region, are +directed for insertion towards the hand. + +In animals, because of the movement of rotation of the radius, the +surface of this bone, which is anterior, corresponds to the posterior +surface of the same in man. (To possess a clear conception of this, it +is necessary to remember that, in this latter, the bones of the forearm +are always described as in the position of supination; they are thus +represented in Fig. 28. The direction of the surfaces of the radius is +the reverse of that in animals, since the latter have the radius always +in a state of pronation.) + +Consequently it is on the anterior surface of the bone that we find the +grooves concerning which it is necessary to give some details. Regarding +them in passing from the radius towards the ulna, those grooves give +passage to the tendons of the muscles whose names occupy the columns on +p. 43. The letters which are referred to each serve to define their +order, and to facilitate reference to Figs. 28, 29, and 30. + +[Illustration: FIG. 30.--INFERIOR EXTREMITY OF THE BONE OF THE FOREARM +OF THE HORSE: LEFT SIDE, ANTERIOR SURFACE. + +1, Radius; A, groove for the long abductor and the short extensor of the +thumb; B, groove for the radials; D, groove for the common extensor of +the digits; E, groove for the special extensor of the little finger.] + +We should mention that the groove E is situated, both in man and in the +dog, at the level of the inferior radio-ulnar articulation; but that in +the horse, as the ulna does not exist at that level, the groove is +situated on the external surface of the inferior extremity of the +radius. It is necessary to add that, in some horses, the ulna is, +nevertheless, represented in this region by a tongue-like process of +bone; and in such cases the groove is situated in front of this process, +at the level of the line of coalescence, which there represents the +articulation. + + -----------------------+-----------------------+----------------------- + MAN. | DOG. | HORSE. + -----------------------+-----------------------+----------------------- + A. Long abductor of the|A. Long abductor of the|A. _Oblique extensor of + of the thumb, and | thumb and short | the metacarpus_, the + short extensor of | extensor of the | homologue of the + the thumb. | thumb united as one | long abductor of the + | muscle, _the oblique| thumb and the short + | extensor of the | extensor of the + | metacarpus_.[11] | thumb, united as one + | | muscle. + | | + B. First and second |B. The two radials |B. The radials + external radials | blended superiorly, | represented by a + (_extensor carpi | distinct inferiorly;| single muscle, _the + radialis longior_ | this is _the | anterior extensor of + and _brevior_). | anterior extensor of| the metacarpus_. + | the metacarpus_. | + | | + C. Long extensor of the|C. Long extensor of the|C. The long extensor of + thumb. | thumb and special | the thumb and the + | extensor of the | special extensor of + | index finger united | the index are + | superiorly. These | absent. + | muscles pass in the | + | following groove. | + | | + D. Special extensor of |D. Common extensor of |D. _Anterior extensor + the index finger and| the digits and the | of the phalanges_, + the common extensor | two preceding | the homologue of the + of the fingers. | muscles. | common extensor of + | | the digits. + | | + E. Special extensor of |E. _Extensor of the |E. Lateral extensor of + the little finger. | third, fourth, and | the phalanges, the + | fifth digits_, or | homologue of the + | _the lateral | special extensor of + | extensor of the | the little finger. + | digits_, the | + | homologue of the | + | special extensor of | + | the little finger. | + | | + F. The posterior ulnar |There does not exist on the forearm a groove + (_extensor carpi |for the posterior ulnar muscle, or _external + ulnaris_). |flexor of the metacarpus_. + -----------------------+----------------------------------------------- + + [11] The words printed in italics are the names used in veterinary + anatomy. + +It is also useful to note, with reference to the groove F, in which +passes, in man, the tendon of the posterior ulnar muscle, that, when the +forearm is in pronation, the radius alone being displaced, we can only +see this groove on the surface which looks backwards; and that it is +then separated from the groove which contains the tendon of the special +extensor of the little finger by an interval equal to the thickness of +the head of the ulna.[12] When the forearm is supinated, the two grooves +are found, on the other hand, one beside the other: and the tendons +which they contain are very naturally in contact. + + [12] Edouard Cuyer, 'Shape of the Region of the Wrist in Supination + and Pronation' (_Bulletin de la Societe d'Anthropologie_, Paris, + 1888). + +In birds the forearm is flexed on the arm, and the latter being directed +downwards and backwards, the former is, consequently, directed upwards +and forwards. Further, because of the position of the humerus, which, as +we mentioned on p. 32, has its inferior extremity so turned that the +surface which is anterior in man becomes external, the radius, instead +of being outside the ulna, is placed above it. This latter is larger +than the radius, but its olecranon process is very slightly developed. + + +The Hand + +The hand in animals, as in man, is formed of three parts--the carpus, +metacarpus, and fingers. In man, the forearm and the hand being +described in the position of supination; the bones of the carpus are +named in passing from the most external to the most internal--that is to +say, from that which corresponds to the radial side of the forearm to +that which corresponds to the ulnar side. In animals in which, as we +know, but it is not unprofitable to repeat, the hand is in pronation, +the radial side of the forearm being placed inside, we enumerate the +carpal bones in counting the most internal as the first; this is the +only method which permits us, in taking our point of departure from the +human skeleton as our standard, to recognise the homologies of the bones +of the carpal region. + +These bones, eight in number, are arranged in two transverse rows, of +which one, the first, is superior or antibrachial; the other, the +second, is inferior or metacarpal. Each of these rows contains four +bones. Considered in the order we have indicated above--that is to say, +proceeding from the radial to the ulnar side--they are thus named: +scaphoid, semilunar, cuneiform, and pisiform, in the first row; +trapezium, trapezoid, os magnum, and unciform, in the second. The number +of these bones is not the same in all animals on account of the +coalescence or absence of some. In each row the bones are placed side by +side, with the exception of the pisiform, which being placed on the +palmar surface of the cuneiform, produces a small projection in man, but +a very pronounced one in quadrupeds. + +The pisiform is called the _hooked bone_ in some veterinary anatomies. +If we consider the hook which it forms, we may recognise that the name +is appropriate; but from the point of view of comparison with the human +carpus, the name is unfortunate, for it creates confusion between the +true pisiform (the fourth bone in the upper row), and the last bone in +the lower row, which is the veritable unciform bone. We do not here seek +for similarity of form, but homology of regions; and it is only by using +the same names to denote the same things that we can succeed in +determining such homology. + +Taken as a whole, the bones of the carpus form a mass which, by its +superior border, articulates with the bones of the forearm, and by its +inferior border is in relation with the metacarpal region. Its dorsal +surface (anterior in quadrupeds) is slightly convex; its palmar surface +(posterior in quadrupeds) is excavated, and forms a groove in which pass +the tendons of the flexors of the fingers. This last, in man, has the +appearance of a gutter, because of the prominences caused by the +projection of the internal and external bones beyond their fellows. + +In quadrupeds the palmar groove is especially determined by the pisiform +bone, of which we have just mentioned the great development. + +The region occupied by the carpus, in the unguligrades, is known as the +_knee_; it would have been more appropriately named had it been called +the _wrist_. + +The number of the metacarpal bones in mammals never exceeds five, but it +often falls below it; the same is true for the digits. The first are +generally equal in number to the latter; an exception is met with in +ruminants, whose two metacarpals coalescing soon after birth, form but +one bone; this, the _canon_ bone, articulates with two digits. + +The number of metacarpals and digits diminishes in proportion as the +limbs cease to be organs of prehension, and become more exclusively +organs of support and locomotion. + +The number of phalanges is two for the thumb and three for each of the +other digits; except in the cetaceans, in which they are more numerous. + +In the bat, the metacarpals and phalanges are very long, and form the +skeleton of the wing; these phalanges are not furnished with nails; the +thumb, which is very short, is alone provided with one (Fig. 8). + +With regard to the relative dimensions of the bones of the metacarpus, +it is necessary to remember that, in the human being, the second +metacarpal is the longest; then, in the order of decrease, come the +third, fourth, fifth, and first. In quadrupeds we shall also find +differences in length (see the chapter relating to the anterior limbs in +certain animals), but the order of decrease is not always that which we +have just mentioned. + +In man the articular surface, situated at the inferior extremity of each +of the metacarpals, is rounded, and is called the head. This allows the +first phalanx, which is in relation with that surface, to be displaced +in every direction; indeed, this phalanx can not only be flexed and +extended, but it can also be moved laterally; this latter movement +allows of the fingers being separated and drawn together. + +In quadrupeds which can only perform the movements of flexion and +extension of the digits--for example, the horse--the inferior extremity +of the metacarpal has not a rounded head of a regular outline; it is +marked by a prominent median crest, directed from before backwards, so +that the articular surfaces, which fit more exactly, form a sort of +hinge which allows of backward and forward movements only, and permits +no lateral displacement. In man, at the level of the inferior extremity +of the first metacarpal, in the vicinity of the articulation of this +bone with the first phalanx of the thumb, we find two sesamoid +bones--small bones developed in the fibrous tissue which surrounds the +articulation. We also meet with such structures, but more rarely, at the +level of the corresponding articulation of the index and auricular +digits; and, more rarely still, at those of the middle and ring fingers. +In quadrupeds, these bones are normally developed, and we shall see +afterwards that in some animals, as they reach a considerable size, they +are able to influence the external outlines; we shall see this, for +example, in the horse. + +The hand, in birds, is directed obliquely downwards and backwards (Fig. +31). For the better understanding of its position in relation to the +forearm, we should remember that this latter, as we have described (p. +44), directed obliquely upwards and forwards, has the radius placed +above the ulna; the hand being oblique in the opposite direction and +placed under the forearm is, by this arrangement, inclined towards the +ulnar border of the latter. + +[Illustration: FIG. 31.--SKELETON OF THE SUPERIOR LIMB OF A BIRD +(VULTURE): LEFT SIDE, EXTERNAL SURFACE. + +1, Humerus; 2, radius; 3, ulna; 4, radial bone of the carpus; 5, ulnar +bone of the carpus; 6, first metacarpal; 7, second metacarpal; 8, third +metacarpal; 9, first digit, the homologue of the thumb; 10, first +phalanx of the second digit; 11, second phalanx of the second digit; 12, +third digit.] + +For the rest, in order to be able to distinguish readily the +corresponding parts in the hand of a bird and that of a man, we merely +have to place the human forearm obliquely, in a direction upwards and +forwards (Fig. 32), the radius being above; this position we can obtain +by semi-pronation; then, to incline strongly the hand downwards and +backwards, moving the ulnar border of the hand towards the ulna; the +thumb is then anterior, the little finger posterior, and the palm of the +hand is turned towards the trunk. + +The carpus in birds is formed by two bones only, with which the skeleton +of the forearm articulates. That which is in contact with the radius is +called the _radial bone of the carpus_; and that with which the ulna +articulates is named the _ulnar bone_. + +[Illustration: FIG. 32.--SUPERIOR LIMB OF THE HUMAN BEING, THE DIFFERENT +SEGMENTS BEING PLACED IN THE ATTITUDE WHICH THE CORRESPONDING PARTS +OCCUPY IN BIRDS: LEFT SIDE, EXTERNAL SURFACE.] + +The metacarpus is formed of three bones; the first, which is very short, +is fused at its superior extremity with the adjoining one; this latter +and the third, both longer than the first, but of unequal size, are +fused at their extremities. The metacarpal, which articulates with the +radial bone of the carpus, is larger than the one which is in line with +the ulna. To the metacarpus succeed three digits, of which the central +is the longest, and is formed of two phalanges; the other two are formed +each by a small, stylet-shaped bone. The middle finger, situated on the +prolongation of the metacarpal, which articulates with the radial bone +of the carpus, has its first phalanx large and flattened transversely; +this phalanx seems to have been formed by the union of two bones of +unequal development; the second phalanx is styloid in form. As to the +other two fingers, they are placed, one in front and the other behind; +the first, which articulates with the short metacarpal, fused at its +upper end with the principal bone of the metacarpus, in position +represents the thumb. The other, which is the third finger, articulates +with the inferior extremity of the thinnest bone of the metacarpus; it +is sometimes closely united to the corresponding border of the first +phalanx of the large--that is to say, of the median--digit. + + +The Anterior Limbs in Certain Animals + +=Plantigrades=: =Bear= (Fig. 33).--The scapula of the bear approaches in +shape to a trapezium, of which the angles have been rounded off. The +anterior border (cervical) is strongly convex in the part next the +glenoid cavity. The junction of the superior (spinal) and the cervical +border forms almost a right angle, the summit of which corresponds to +the origin of the spine. At its posterior angle there is a prominence, +directed downwards, the surface of which is hollowed and is separated +from the infraspinous fossa by a crest, so that at this level a third +fossa is added to the infraspinous one. The neck of the scapula is but +slightly marked. The acromion is prominent, and projects a little beyond +the glenoid cavity. + +The clavicle is rudimentary, but, as an example of the complete +development of this bone in plantigrade quadrupeds, we may cite the +marmoset. + +The humerus is furnished at its superior extremity with a large +tuberosity, wide, and situated in front of the head of the bone; the +effect of this is that the bicipital groove is internal. As in man, the +great tuberosity does not reach so high as the humeral head, but it +approaches more nearly to that level. The deltoid impression is very +extensive, and descends pretty far down on the body of the bone. The +epitrochlea is prominent; the epicondyle is surmounted by a well-marked +crest, curved and flexuous in outline. + +[Illustration: FIG. 33.--SKELETON OF THE BEAR: LEFT LATERAL SURFACE. + +1. Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical vertebra; 6, +first dorsal vertebra; 7, fourteenth and last dorsal vertebra; 8, lumbar +vertebrae; 9, sacrum; 10, coccygeal vertebrae; 11, sternum; 12, ninth and +last sternal rib; 13, costal cartilages; 14, acromion process; 15, third +fossa on the external surface of the scapula; 16, great tuberosity of +the humerus; 17, musculo-spiral groove; 18, epicondyle; 19, radius; 20, +ulna; 21, olecranon process; 22, carpus; 23, pisiform; 24, metacarpus; +25, phalanges; 26, ilium, external fossa; 27, pubis; 28, tuberosity of +the ischium; 29, obturator foramen; 30, great trochanter of the femur; +31, condyles of the femur; 32, patella, or knee-cap; 33, anterior +tuberosity of the tibia; 34, fibula; 35, tarsus; 36, calcaneum, or +heel-bone; 37, metatarsus; 38, phalanges.] + +The articular surface, which is in contact with the radius, is not a +regularly formed condyle; it is a little flattened on its anterior +surface, and presents at this level a slight depression which +corresponds to a small eminence on the anterior aspect of the superior +extremity of the radius. The surface which articulates with the ulna, +viewed on its anterior aspect, has the shape of a slightly-marked +trochlea; except at the level of the internal lip, which, as in man, +descends lower than the surface for articulation with the radius +(condyle). Behind, the trochlea is more clearly defined. + +The bear possesses a considerable power of rotation of the radius; the +bones of the forearm are joined only at their extremities, while in the +remainder of their extent they are widely separated. The ulna terminates +below in a head and a styloid process; these articulate with the two +last bones of the first row of the carpus--viz., the cuneiform and +pisiform. The bones of the carpus are seven in number, the scaphoid and +the semilunar being fused together. + +The metacarpals, five in number, differ very little from one another in +regard to length, though they increase in size from the first to the +fifth; this may be demonstrated by looking at the palmar surface of the +hand. It is the reverse of that which we find in man, for the fifth +metacarpal is the thickest of all, and the first is the most slender. + +At the level of each metacarpo-phalangeal articulation are two sesamoid +bones. + +The third digit is the longest. The terminal phalanges present two very +different portions: one, the anterior, is curved and pointed; it serves +to support the nail, whose shape it assumes; the other, posterior, forms +a sort of sheath into which the base of the nail is received. + +The inferior portion of the posterior surface of this latter part +articulates with the second phalanx in the case of each of the last four +digits, but with the first phalanx in the case of the thumb. + +[Illustration: FIG. 34.--SKELETON OF THE DOG: LEFT LATERAL SURFACE. + +1, Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical vertebra; 6, +thirteenth and last dorsal vertebra; 7, lumbar vertebrae; 8, sacrum; 9, +coccygeal vertebrae; 10, anterior extremity of the sternum; 11, xiphoid +appendix; 12, ninth and last sternal rib; 13, costal cartilages; 14, +spinal border of the scapula; 15, supraspinous fossa of the scapula; 16, +infraspinous fossa of the scapula; 17, great tuberosity of the humerus; +18, deltoid impression; 19, musculo-spiral groove; 20, olecranon +process; 21, radius; 22, carpus; 23, pisiform; 24, metacarpus; 25, +sesamoid bones; 26, phalanges; 27, ilium, iliac crest; 28, pubis; 29, +tuberosity of the ischium; 30, great trochanter of the femur; 31, +patella, or knee-cap; 32, anterior tuberosity of the tibia; 33, fibula; +34, tarsus; 35, calcaneum, or heel-bone; 36, metatarsus; 37, sesamoid +bones; 38, phalanges.] + +[Illustration: FIG. 35.--SCAPULA OF THE DOG: LEFT SIDE, EXTERNAL +SURFACE. + +1, Posterior or axillary border; 2, superior or spinal border; 3, +anterior or cervical border; 4, spine of scapula; 5, coracoid process; +AA', length of spinal border.] + +[Illustration: FIG. 36.--LEFT SCAPULA OF THE CAT: EXTERNAL SURFACE. + +1, Posterior or axillary border; 2, superior or spinal border; 3, +anterior or cervical border; 4, spine of the scapula; 5, coracoid +process; AA', length of the spinal border.] + +=Digitigrades=: =Cat=, =Dog= (Fig. 34).--In these animals the anterior +(cervical) border of the scapula is convex; the posterior (axillary) +border is straight or slightly concave. The supraspinous and +infraspinous fossae are of equal extent (Figs. 35 and 36). The neck is +short. The spine of the scapula becomes more and more prominent towards +its inferior extremity, where it ends in a twisted and inflexed portion, +which represents the acromion process; this process terminates at the +level of the glenoid cavity. The coracoid process is represented by a +small tubercle, slightly curved inwards; this tubercle is situated +above the glenoid cavity, at the inferior part of the cervical border. + +In the dog, the posterior angle, formed by the junction of the axillary +and the superior (spinal) borders, is obtuse; the spine rises +perpendicularly from the surface of the bone. The width of the scapula, +measured at the level of the spinal border (from A to A', Fig. 35), +equals about half the length of the spine. We must, however, make an +exception for the turnspit dog, in which the superior border equals +three-fourths of that length. The scapula is, in this case, of a more +compact type; it is broader, but shorter. In the cat, the anterior +outline of the scapula, formed by the union of the cervical border and +the corresponding half of the spinal, is more convex; the posterior +angle is not obtuse, as in the dog. The spine is bent slightly downwards +and backwards; before terminating in the acromion process it presents a +triangular projection, the apex of which is directed downwards. The +tubercle which represents the coracoid process is curved inwards more +strongly than that of the dog, thus resembling more closely the +appearance of this process in the human being. + +All proportions considered, the scapula of the cat is broader than that +of the dog; its width, measured along the length of its spinal border +(from A to A', Fig. 36), equals three-fourths of the length of the +spine. + +The clavicle is rudimentary; it is, however, better developed in the cat +than in the dog. The clavicle of the cat is represented by a small, +elongated bone, curved in outline, the convexity being turned forward; +it is united to the acromion and the sternum by ligamentous fibres; that +of the dog is merely a scale-like osseous plate situated on the +posterior surface of a muscle of this region (see Figs. 16 and 17). + +The humerus is long and twisted in the shape of an S. The inferior +articular surface has the form of a simple pulley, for the condyle is +very slightly marked. The internal part of this articular surface +descends lower than the external; this condition resembles that found in +the human being, where the inner lip of the trochlea is lower than the +condyle. + +In the dog, the olecranon fossa communicates with the coronoid by an +opening. + +In the cat, there is a supra-epitrochlear canal (see Fig. 19), but no +olecranon perforation. + +The bones of the forearm articulate at their extremities. The body of +the radius is united to the body of the ulna by a short, thick, +interosseous ligament; the fibres of this ligament, though short, do not +prevent the production of some movements at the articulations of the +bones. + +The radius so crosses the ulna that above, it is in front and external +to the latter, while below, it is internal. This bone is flattened from +front to back, and slightly convex anteriorly. Its superior extremity is +formed, externally, of a portion which represents the head of the radius +in man; internally, by another portion which represents half of the +coronoid process of the ulna, which, in the human being, belongs +exclusively to the latter (see p. 39, the encroachment of the radius on +the ulna). This extremity is surrounded with a vertical articular +surface which is placed in contact with a small cavity which is hollowed +out on the ulna (the lesser sigmoid cavity); and presents at its +superior aspect a surface which articulates with the inferior extremity +of the humerus. The shaft of the bone has on its internal border +rugosities analogous to the imprint of the pronator radii teres of the +human skeleton; these rugosities, indeed, give insertion to a muscle of +the same function, and bearing the same name. The inferior extremity, +broader than the superior, is hollowed on its external aspect by a small +cavity which receives the inferior extremity of the ulna; its inferior +surface (concave) articulates with the carpus; its anterior surface (the +homologue of the posterior surface of the corresponding extremity of the +human radius) presents grooves which serve for the passage of the +tendons of the muscles which pass from the forearm to the back of the +hand. (For the names of the muscles whose tendons pass in these grooves, +see Fig. 29.) + +The ulna is furnished at its superior extremity with an olecranon +process, which is more prominent than that of the human ulna; this +process is compressed laterally, and its internal surface is hollowed; +there we also find a great sigmoid cavity, and a coronoid process +situated at the internal part of the anterior surface, a process which, +as we have previously shown, it shares with the radius. + +The shaft of the bone, prismatic and triangular, diminishes in thickness +as it approaches the lower extremity, which articulates with the +corresponding extremity of the radius. In the dog, the ulna terminates +inferiorly in a blunt point, without enlargement, analogous to the head +of the human ulna; in the cat, by a head which is prolonged into a +styloid process, by which it articulates with a portion of the carpus. + +The carpus consists of seven bones--three in the superior row and four +in the inferior. In the superior row the scaphoid and semilunar bones +are fused together. The pisiform is elongated and expanded at its two +extremities; it forms a prominence which, directed backwards, projects +beyond the level of the other bones of this region. + +The metacarpal bones are five in number; they are enumerated from within +outwards; they articulate with the carpus and with each other. The +inferior extremity of each metacarpal bone presents the form of a +condyle in front; and is divided behind so as to form two lateral +condyles, which are separated by a median crest; on these posterior +condyles are applied two small sesamoid bones. The metacarpal bone of +the thumb is very short; the third and fourth are the longest. The +metacarpus, as a whole, is directed vertically. + +The phalanges are three in number for each finger, except the thumb, +which has but two. The first phalanx, directed almost horizontally +forwards, is the longest; the second is directed downwards and forwards; +the third consists of two portions: a posterior part, which forms a sort +of sheath into which the base of the nail is received; and an anterior, +conical in form, and curved in crochet shape, which forms a support for +the nail (Fig. 37). + +The third and fourth digits are the longest; the second and fifth are of +equal length; the thumb is the shortest; it does not touch the ground, +and does not even reach the articulation of the metacarpal bone and +first phalanx of the second finger. + +In the cat, the metacarpal bone of the thumb, although shorter than any +of the others, is quite as thick. The third digit is a little longer +than either the second or fourth. In animals of this genus, the claws, +in the condition of repose, are retracted, and removed from the ground; +this prevents their being worn, and thus preserves their sharpness. At +such times the third phalanx is received into a groove which is found on +the external surface of the second phalanx. In the dog, the claws are +not tractile. + +[Illustration: FIG. 37.--SKELETON OF THE FINGER OF A FELIDE (LION): LEFT +SIDE, INTERNAL SURFACE. + +1, Metacarpus; 2, sesamoid bones; 3, first phalanx; 4, second phalanx; +5, third phalanx; 6, gutter for the reception of the base of the nail; +7, prominent osseous crest formed to lodge in the concavity of the +nail.] + +[Illustration: FIG. 38.--SKELETON OF THE PIG: LEFT LATERAL SURFACE. + +1, Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical vertebra; 6, +first dorsal vertebra; 7, fourteenth and last dorsal vertebra; 8, lumbar +vertebrae; 9, sacrum; 10, coccygeal vertebrae; 11, anterior extremity of +the sternum; 12, xiphoid appendix; 13, seventh and last sternal rib; 14, +costal cartilage; 15, cartilage of prolongation of the scapula; 16, +great tuberosity of the humerus; 17, olecranon process; 18, radius; 19, +ulna; 20, pisiform; 21, metacarpus; 22, phalanges of the two great toes; +23, phalanges of the external toe; 24, ilium; 25, pubis; 26, tuberosity +of the ischium; 27, great trochanter; 28, knee-cap; 29, anterior +tuberosity of the tibia; 30, fibula; 31, tarsus; 32, calcaneum; 33, +metatarsus; 34, phalanges of the two great toes; 35, phalanges of the +external toe.] + +=Unguligrades=: =Pig= (Fig. 38).--The scapula is markedly narrowed in +the region above the glenoid cavity. The spine is atrophied at both its +extremities, so that at its inferior part we do not find the acromion +process. In its middle portion the spine is prominent, and presents a +triangular process which turns backwards, overlapping a part of the +infraspinous fossa; this latter is much larger than the supraspinous. +The spinal border is surmounted by the cartilage of prolongation, the +superior margin of which is convex; this cartilage extends posteriorly +beyond the posterior (axillary) border of the bone. + +The small tuberosity of the superior extremity of the humerus is but +slightly developed; the great tuberosity, on the contrary, is very +large. The bicipital groove is situated internal to this. The deltoid +impression is scarcely marked. + +The forearm is short, directed obliquely downwards and inwards, thus +forming with the hand an angle, of which the apex is directed inwards. +The two bones of the forearm are strongly bound to one another by an +interosseous ligament, which is formed of very short fibres. The radius +appropriates, at its superior extremity, the coronoid process of the +ulna. The latter is, notwithstanding, well developed in the rest of its +extent; it has a flattened shaft which almost completely overlaps the +posterior surface of the radius; its inferior extremity reaches to the +carpus. + +The carpus is formed of eight bones--four in the superior row, and four +in the inferior. The third bone of the superior row (cuneiform) is more +in contact with the ulna than with the radius. + +There are but four metacarpal bones; there is no metacarpal of the +thumb. The two median metacarpal bones are the longest; they are those +which correspond to the digits which alone touch the ground. The +internal digit and the external one are thin and short; they are +functionless, as a rule, taking no part in supporting the limbs on the +ground. Notwithstanding this, they are formed, as the other digits, of a +number of phalanges, which give them the semblance of perfect digits. +(We shall soon see that in certain animals there exist digits which, +being incomplete with regard to the numbers of their constituent bones, +more accurately merit the name of imperfect digits.) + +The third phalanges are each enclosed in a horny hoof, to which the name +of _onglon_ has been given. + +We have already drawn attention to the smaller lateral digits, and +noted the general fact that they do not come in contact with the ground. +It is necessary to modify this statement by adding that under certain +conditions they give a slight amount of support; for example, when the +individual is the subject of excessive obesity, the limbs yield under +the weight, and the nails of the lateral digits may touch the ground. + +A similar fact may be noticed in pigs of ordinary bulk at the moment +when, during walking, each of the fore-limbs commences to bear the +weight--that is to say, when it is directed obliquely downwards and +forwards; then all the digits are in contact with the ground. + +=Unguligrades (Ungulates)=: =Sheep=, =Ox= (Fig. 39).--The scapula, which +is of elongated form, is very narrow in the vicinity of the glenoid +cavity. The spine, which becomes more and more salient towards its +inferior part, terminates abruptly in a border, which, forming an acute +angle with the crest, produces a projection which represents the +acromion process--a very rudimentary acromion, for it does not reach the +level of the glenoid cavity. The supraspinous fossa is much smaller than +the infraspinous; it hardly equals one-third the extent of the latter. +The anterior border, thin and convex in its superior portion, is concave +in the rest of its extent; the posterior border is thick and slightly +concave; the spinal border is surmounted by the cartilage of +prolongation. In the ox the spine of the scapula, in its middle portion, +is flexed a little backwards on the infraspinous fossa. + +[Illustration: FIG. 39.--SKELETON OF THE OX: LEFT LATERAL SURFACE. + +1, Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical vertebra; 6, +first dorsal vertebra; 7, thirteenth and last dorsal vertebra; 8, lumbar +vertebrae; 9, sacrum; 10, coccygeal vertebrae; 11, sternum; 12, xiphoid +appendix; 13, eighth and last sternal rib; 14, costal cartilages; 15, +spine of scapula; 16, cartilage of prolongation of the scapula; 17, +great tuberosity of the humerus; 18, musculo-spiral groove; 19, +olecranon process; 20, radius; 21, carpus; 22, pisiform; 23, metacarpus; +24, rudimentary metacarpal; 25, sesamoid bones; 26, first phalanges; 27, +second phalanges; 28, third phalanges; 29, anterior iliac spine; 30, +pubis; 31, tuberosity of the ischium; 32, great trochanter; 33, +supracondyloid fossa of the femur; 34, patella, or knee-cap; 35, +anterior tuberosity of the tibia; 36, fibula; 37, coronoid tarsal bone; +38, tarsus; 39, calcaneum; 40, metatarsus; 41, rudimentary metatarsus; +42, sesamoid bones; 43, first phalanges; 44, second phalanges; 45, third +phalanges.] + +The great tuberosity of the humerus is highly developed; its summit, +very prominent, is flexed over the bicipital groove; a prominence of the +small tuberosity also bends over the groove, with the result that at +this level the latter is converted into a sort of canal. At the inferior +extremity the condyle, although not large, is recognisable; for it is +separated from the trochlea by a depression in form of a groove. In +contrast to the condition found in man, the condyle descends to a level +a little below that of the internal lip of the trochlea. (For the +arrangement of the epicondyle and the epitrochlea, see p. 30.) In the +sheep, the deltoid impression is but slightly marked; in the ox, it is +more evident. + +The forearm is directed obliquely downwards and inwards, so as to form, +with the hand, an angle of which the apex is internal; this angular +outline of the _knee_ (wrist) is so characteristic of ruminants that the +corresponding region of the horse, when salient inwards, receives the +name of _ox-knee_. The radius bears the coronoid process, and the larger +part of the articular surface which comes in contact with the inferior +extremity of the humerus; the condyle and the trochlea articulate with +the radius in front; while behind, the trochlea articulates with that +part of the sigmoid cavity which belongs to the ulna. The posterior +surface of the shaft of the radius is flattened; its anterior surface is +slightly convex. The inferior extremity articulates with the carpus by a +surface which is directed obliquely downwards and inwards. The shaft of +the ulna is very slender, and fused in its middle third with the body of +the radius; it terminates below, at the level of the external part of +the inferior extremity of the radius, by a slightly expanded portion +which, fused with this latter, forms the articular surface for the +carpal bones. + +In the ox the forearm is short; in the sheep it is proportionally +longer. + +The bones of the carpus are six in number--four in the upper row, and +two in the lower; they form an irregular cuboid mass which contributes +to the formation of the region known as _the knee_ in ruminants, as in +the horse; we have already remarked that the name 'wrist' would be more +accurate. The anterior surface in its foremost part is vertical, and is +slightly convex from side to side. At its posterior and external part +the pisiform bone forms a prominence. + +The metacarpus consists of two bones only--one, well developed, which is +known as the principal metacarpal, or the _canon_ bone (this is the name +given to the region in the hoofed animals); and a rudimentary one, which +is situated at the superior and external aspect of the preceding +metacarpal. Sometimes there is found a third metacarpal at the internal +aspect; but, when present, it is but very slightly developed. + +The principal metacarpal consists of two metacarpals fused together; on +this account the bone is longitudinally marked in the median line by a +slight depression which marks the junction of the two bones of which it +is formed. In some ruminants (certain species of chevrotains) the +coalescence does not take place, and the two metacarpals remain +separate. + +The anterior surface of the principal metacarpal is convex transversely; +its posterior surface is flattened. The superior extremity of this bone +articulates by two facets with the two bones of the inferior row of the +carpus; on the internal part of the anterior surface of this extremity +is found a tubercle. The inferior extremity is divided into two parts by +a fissure or notch; each part is articular, and consists of two separate +condyles, which are separated from each other by an antero-posterior +crest; on each side of this crest, and behind, are found two sesamoid +bones. As for the external rudimentary metacarpal bone, it is nothing +more than a small, short tongue of bone; which, in goats and sheep, is +often absent. + +The division of the inferior extremity of the principal metacarpal into +two parts is correlated with the two perfect digits which give the foot +of the ruminant its forked appearance. Each digit consists of three +phalanges, which are directed obliquely downwards and forwards; further, +these phalanges are inclined a little outwards from the axis of the +limb, so that the two digits diverge from each other as they descend. + +The first phalanx, which is the longest, articulates superiorly with the +principal metacarpal; its inferior extremity terminates in a trochlea, +and the lip of this, which is situated towards the axis of the limb, +descends lower than that of the opposite side; this arrangement is +correlated with the divergent direction of the digits. The second +phalanx has its superior extremity moulded on the trochlea which +terminates the extremity of the first; its inferior extremity is +articular, and elongated from before backwards. On the posterior +surface of this extremity is found a sesamoid bone. + +With regard to the third phalanx, it presents the form of a triangular +pyramid, and displays a postero-superior concave surface with which the +second phalanx articulates; an anterior, convex surface, which +terminates in a point on its anterior part; and an internal surface, +which is flattened. The third phalanx of each digit is contained in a +hoof (_onglon_). + +There is also found in ruminants two imperfect rudimentary digits, which +are represented by two small bones situated behind the articulation of +the metacarpal and the digits which we have just been studying. These +rudimentary digits are each enveloped in a layer of horn; they +constitute the _spurs_. The two digits of the ruminants represent the +third and fourth fingers of the human hand; the two lateral digits, +greatly atrophied, are the homologues of the second and fifth fingers; +the thumb is not present. + +It is the same as regards the metacarpal bones, which form, by their +union, the principal metacarpal; the external represents the fourth +metacarpal, and the internal the third. It is to the latter that the +tubercle, of which we have already made mention, belongs; and with the +signification of which, because it gives attachment to a muscle, we +shall concern ourselves in the section on myology (see Radial Muscles). + +=Unguligrades=: =Horse= (Fig. 40).--The scapula is narrow, compared with +that of the animals we have just been considering. The anterior border +is convex in its superior portion, and concave in its inferior; the +posterior border is slightly hollowed out. The supraspinous fossa is +less in extent than the infraspinous; but the difference is less +than that between the same fossae in the ox and the sheep; in the +ox, as we have already indicated, the proportion is one-third; in +the horse, one-half. The spine, which disappears at the extremities, +is rough and thick in its middle third, there forming a kind of +tuberosity--_tuberosity of the spine_. Above and in front of the glenoid +cavity is found a strong process consisting of a rugous base, and a +summit which is directed inwards. This forms a kind of hook curved +towards the inside; it represents the coracoid process. The scapula is +surmounted by the cartilage of prolongation, of which the superior +border, which is thin and curved, is parallel to the superior border of +the prominence of the withers; the cartilage forms, consequently, the +lateral surface of this region. The cartilage of prolongation undergoes +ossification in old horses. The humerus is short; the bicipital groove, +situated on the anterior surface of the superior extremity, separates +the greater tuberosity from the lesser, and is divided into two parts by +a median ridge; it is this portion of the humerus which forms the +prominence known as the _point of the shoulder_, or _point of the arm_. +The deltoid impression well deserves the name of tuberosity which has +been given to it, for it is very prominent; the musculo-spiral groove is +very deep. + +[Illustration: FIG. 40.--SKELETON OF THE HORSE: LEFT LATERAL SURFACE. + +1, Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical vertebra; 6, +first dorsal vertebra; 7, eighteenth and last dorsal vertebra; 8, lumbar +vertebrae; 9, sacrum; 10, coccygeal vertebrae; 11, sternum; 12, xiphoid +appendix; 13, eighteenth and last sternal rib; 14, costal cartilage; 15, +scapula; 16, cartilage of extension; 17, great tuberosity of the +humerus; 18, deltoid crest; 19, olecranon process; 20, radius; 21, +carpus; 22, pisiform; 23, principal metacarpal; 24, metacarpal, +external rudimentary; 25, large sesamoids; 26, first phalanx; 27, +second phalanx; 28, third phalanx; 29, ilium, showing external iliac +fossa; 30, pubis; 31, tuberosity of the ischium; 32, great trochanter; +33, infratrochanteric crest, or third trochanter; 34, supracondyloid +fossa of the femur; 35, knee-cap; 36, anterior tuberosity of the tibia; +37, the fibula; 38, tarsus astragalus; 39, calcaneum; 40, principal +metatarsal; 41, rudimentary external metatarsal; 42, large sesamoids; +43, first phalanx; 44, second phalanx; 45, third phalanx. + +_To face p. 64._] + +At the inferior extremity, the trochlea is large; the portion +corresponding to the condyle of the humerus in man is, in proportion to +the latter, of small extent. The olecranon fossa is deep. The epicondyle +and the epitrochlea are somewhat different from those of the human bone. +In the latter, the epitrochlea is salient towards the inner side, +causing an increased transverse diameter of the inferior extremity of +the humerus. In the horse--it is the same in ruminants--this tuberosity +projects backwards, folds on itself in forming the internal boundary of +the olecranon cavity, and exceeds in diameter, in the antero-posterior +direction, the prominence of the epicondyle, which presents a nearly +similar arrangement. This latter has, however, a part which, projecting +externally, is situated at the inferior part of a crest, that forms the +posterior boundary of the musculo-spiral groove. The result is that, +contrary to the condition found in the human being, the epicondyle is +more prominent transversely than the epitrochlea, but this latter is +more salient on the posterior aspect. The epitrochlea and the epicondyle +offer a larger surface for the origin of muscles of the forearm than the +same prominences in the human bone do for the analogous muscles of the +same region. + +Some veterinary anatomists have given to the inferior and external +articular surface of the humerus the name of trochlea; and to the +internal one, that of condyle. On this account they designate the +external prominence as the epitrochlea, and the internal one as the +epicondyle. In addition to the fact that this point of view is not +legitimate, it produces inevitable confusion when comparing the parts +with those of the human humerus, and this confusion exists, not alone in +describing the bone, but also in the description of the muscular +attachments, and in the comparison of the muscles of the forearm of +quadrupeds with the corresponding muscles in the human species. + +The radius is placed in front of the ulna; its body, slightly convex +forwards, has the anterior surface convex transversely, and the +posterior surface plane in the same direction. It is to the external +part of this latter that the ulna is applied, which is completely fused +with the radius. + +The superior extremity of the radius is a little larger than the +inferior. Its superior aspect, concavo-convex, moulded on the inferior +articular surface of the humerus, presents internally two cavities, +which receive the lips of the trochlea, and, externally, another, +smaller, cavity, which receives the condyle. The radius articulates with +the trochlea and the condyle, having appropriated a portion of the ulna, +as is proved by the presence of the coronoid process, which belongs to +the former. This superior extremity presents, internally, a tuberosity +into which the biceps is inserted; this is the bicipital tuberosity; and +on the other side is another tuberosity, which is a little more +prominent than the preceding. + +The inferior extremity, which is flattened from before backwards, is +furrowed on its anterior surface by grooves for the passage of muscles +(the names of the muscles whose tendons pass in these grooves have +already been given on p. 43). It articulates at the lower end with the +superior row of the carpus, and it terminates laterally in tuberosities: +one, external, on which is found a groove for the tendon of the lateral +extensor of the phalanges, the homologue of the special extensor of the +little finger; the other, internal, is a little more prominent than the +one we have just described. These tuberosities are visible under the +skin which covers the superior and lateral parts of the region known as +the _knee_; but which, we again repeat, is no other than the wrist. + +The ulna has a triangular shaft, situated at the posterior surface of +the radius, with which it is fused. It disappears completely at the +level of the inferior third of the forearm. Occasionally, in some +horses, the ulna is abnormally long, in the form of a slender tongue of +bone; and extends to the neighbourhood of the external tuberosity of the +inferior extremity of the radius (see Fig. 79, p. 196). Its superior +extremity is chiefly represented by the olecranon process, which is +voluminous in bulk, and forms the projection known as the point of the +elbow. This process is flattened laterally; its internal surface is +excavated; the anterior surface, which is concave, forms a part of the +great sigmoid cavity; the remainder of the cavity is formed by the +radius. + +In the ass, the ulna is a little longer than in the horse--that is to +say, it descends lower; and the radius is a little more convex +anteriorly. + +The carpal bones are seven in number--four in the superior row, and +three in the inferior. The trapezium is wanting in the latter. +Sometimes, however, in certain varieties of horses the trapezium is +developed, but then it is no more than a very small osseous nodule. The +pisiform bone, situated at the external part of the first row of bone, +is prominent posteriorly. It is of rounder form and flattened from +without inwards. It articulates with the trapezium and the radius. It +presents, on its external surface, a groove for the passage of the +tendon of the posterior ulnar muscle, which is named by veterinary +anatomists the _external flexor of the metacarpus_. + +The carpus, as a whole, is of an irregularly cuboid shape; its anterior +surface, slightly convex from side to side, forms the skeleton of the +region of the _knee_ (wrist). The metacarpus is formed of three bones: +the principal metacarpal and the two rudimentary ones. + +The principal metacarpal, which forms the region of the _canon_, is +directed vertically; its anterior surface is slightly convex +transversely. This surface is covered by a number of tendons, which +slightly alter its appearance; so that it is the principal base of this +part of the fore-limb. Its posterior surface is flattened. The superior +extremity of this metacarpal presents plane surfaces, variously +inclined, with which the bones of the inferior row of the carpus +articulate. On the anterior surface, and a little to the inner side, is +found a tuberosity, which is destined for the insertion of _the anterior +extensor of the metacarpus_, the homologue of the radial muscles. The +inferior extremity is formed by two condyles, an internal and an +external; between which is found a median crest. + +This extremity, the superior extremity of the first phalanx, which +articulates with it, together with two sesamoid bones--the great +sesamoids--which are situated on its posterior surface, collectively +form the region which from its rounded outlines is called the _ball_. + +With regard to the rudimentary metacarpals, external and internal, to +which some authors give the name of _fibulae_, they are applied to the +sides of the posterior surface of the principal metacarpal. They are +elongated bones, of which the superior extremity, which is a little +thickened, is called the _head_; the lateral bones of the second row of +the carpus partly rest on the heads of these. They become more slender +as they descend, and terminate opposite the inferior fourth of the +principal metacarpal. Each ends in a slight swelling, to which the name +_button_ has been given. The internal one is the better developed. + +The rudimentary metacarpals are vestiges of atrophied digits, as will be +explained further on. + +The single finger of the horse consists of three phalanges. The first +phalanx, which is directed obliquely downwards and forwards, corresponds +to the constricted region situated below the 'ball,' and known as the +_pastern_. It is flattened from before backwards; its anterior surface +is convex transversely, while the posterior surface is plane. Its +superior extremity is moulded on the inferior extremity of the principal +metacarpal, and its inferior extremity, which is smaller, presents a +trochlea with which the second phalanx articulates. This is also +directed downwards and forwards, and is shorter. It corresponds to the +region which, situated between the pastern and the hoof, is known as the +_cornet_. + +The third phalanx, situated entirely within the hoof, has the same +direction as the first and second. It is large and broad, and presents +three surfaces separated by well-marked angular borders (see Fig. 96). +The anterior surface is oblique downwards and forwards; it is convex +transversely. The inferior surface is slightly hollowed, and is in +relation with the sole, or plantar surface of the hoof. + +The superior surface, which is articular, is divided by a median ridge +into two lateral cavities, which correspond to the trochlea on the +inferior surface of the lower extremity of the second phalanx. The +inferior border corresponds in shape with the hoof. The superior border +presents in its median part a projection, _the pyramidal eminence_, +which prolongs at this level the anterior surface of the bone. Finally, +the posterior border, which is concave, is in contact with a sesamoid +bone, _the lesser sesamoid_, which increases the superior articular +surface behind, and is also in contact with the second phalanx. + +As we have just seen, the horse possesses but one digit. In the +ancestors of the animal--that is, in the prehistoric species which +are now extinct (_orohippus_, _miohippus_, _protohippus_, or +_hipparion_)--the number of digits was larger; this fact conclusively +proves that the rudimentary metacarpals of the existing horse are +vestiges of digits which have disappeared through want of use. In the +first of those ancestors--orohippus--there were four digits; all save +the first, the thumb, being then developed. In the others of the series +there existed but three digits. It must, however, be noted that in those +animals it is always the digit which corresponds to the middle finger of +the pentedactyl hand that is longest. In other less ancient species the +lateral fingers are reduced to the condition of mere splints of bone. It +follows from what has been said that the digit which persists in the +equine species should be considered as the third finger, and that the +rudimentary metacarpals represent lateral digits considerably +atrophied. + +This disappearance of the lateral digits cannot excite surprise when we +consider the functions of the organs. Becoming useless, they must +undergo gradual atrophy from want of use. + +There undoubtedly is, in this former existence of supplementary digits +in the horse, something analogous to what we still find in the pig; +where the two principal digits are accompanied by two shorter ones, +which very probably, from their infrequent use, are destined to +disappear in a more or less distant future. + + +Proportions of the Arm, the Forearm, and the Metacarpus + +As a supplement to the study of the anterior limbs which we have just +finished, it appears necessary to give some indications of the relative +proportions of certain of the segments which form these limbs in the +plantigrades, the digitigrades, and the ungulates. + +First, we would remark that, in following this order of classification, +the scapula becomes less and less narrow, and assumes a form more and +more elongated. In order to convince ourselves of this, it will be +sufficient to study the bone first in man, then in the bear, the cat, +dog, ox, and finally in the horse. + +As to the proportions of length, which are those we should chiefly +study, we shall commence with the comparison of the forearm and +arm--that is to say, the radius and the humerus. The radius is found to +be longer in proportion to the humerus, as the number of digits is +smaller, and the hand loses more and more the functions of an organ of +prehension. In man, the radius is shorter than the humerus; in the +horse, on the contrary, it is longer. + +To give an idea of this proportion, we shall employ what is known as the +antibrachial index. This index gives the relation which exists between +the length of the forearm and that of the humerus; the length of this +latter, whatever may be the actual measurement, is represented by a +fixed figure, the number 100. A very simple arithmetical operation +gives the proportion-- + + forearm x 100 + -------------, the quotient obtained furnishes the index. + humerus + +The index is less than 100 if the forearm is shorter than the bone of +the arm. The index is more than 100 if, on the contrary, the forearm is +longer. + +In man, the radius is shorter than the humerus; indeed, in adult +individuals of the white race the average index is 74. + +In the bear, the length of the radius approaches closely to that of the +humerus; the index is about 90. In the skeleton of a bear in the +anatomical museum of the Ecole des Beaux-Arts, the humerus is 33 +centimetres in length, and the radius 30 centimetres. + +In the cat, the radius is very little shorter than the humerus. In the +dog they are equal. The antibrachial index of the latter is, +accordingly, 100. + +In the horse, the radius is longer than the humerus; the index is +therefore above 100. Thus, in the skeleton of the horse which we have in +the museum of the Ecole des Beaux-Arts, the index is 113--length of +humerus, 29 centimetres; length of radius, 33 centimetres. In other +skeletons which we have measured we found: in one, 108--humerus, 34 +centimetres; radius, 37 centimetres; in another, 116--humerus, 25 +centimetres; radius, 29 centimetres. + +The metacarpal bone undergoes, relatively to the humerus, a proportional +elongation, analogous to that of the forearm. + +In man, the length of the metacarpus is contained about 5-1/2 times in +that of the humerus; in the bear, it is contained 4 times; in the dog, +2-1/2 times; in the horse, 1-1/3 times only. + +It is well known that the proportions vary according to race, and that +what we have here given are but the general indications. + + +The Articulations of the Anterior Limbs + +The knowledge of human arthrology which we presume the reader to have +previously acquired makes it unnecessary for us to enter into numerous +details regarding the configuration of the articular osseous surfaces +and the disposition of the fibrous bands that retain them in position. +Accordingly, in the description which follows, and also in that of the +articulations of the posterior limbs, we shall occupy ourselves but very +briefly with the details above referred to, so as to devote ourselves +especially to the indication of the movements--that is to say, of that +which, while easily comprehended on recollection of former studies, +presents the greatest interest from the artistic standpoint in these +studies in comparative anatomy. + +=The Scapulo-Humeral Articulation.=--The head of the humerus and the +glenoid cavity of the scapula being in contact, the two bones are bound +together by a rather loose articular capsule, which is strengthened by +the muscles of this region which fulfil the function of active +ligaments. + +This articulation, so movable in every direction in the human species, +is not so much so in quadrupeds; the arm in the latter, as also the +shoulder, being kept in contact with the lateral region of the thorax by +the numerous muscles which surround it. + +Of the movements performed by the humerus, flexion and extension are the +most extensive; those of abduction and adduction are much less so. + +It is necessary, before proceeding further, to determine what the two +principal movements which we have just mentioned really are, viz., +flexion and extension. + +We know that in man the displacements of the humerus which take place in +the antero-posterior direction are known as movement or projection +forwards, and movement or projection backwards, respectively. We do not +say that the humerus is flexed or extended, because, in reality, on +account of the position which the skeleton of the shoulder occupies, it +is not able to flex or place itself on the line of prolongation of the +scapula with which it articulates. + +In quadrupeds it is not so. The humerus and the scapula are contained in +almost the same vertical plane; and the bone of the arm can take, in +relation to the latter, the positions characteristic of flexion and +extension--that is, of approach to the scapula and removal from it. + +What makes the meanings of these terms a little confusing is that, in +human anatomy, some authors consider the backward movement of the +humerus as extension, and the forward movement as flexion; in order to +be able to compare these movements to those that the femur executes in +relation to the pelvis. + +Now, in our opinion, the indication of this correspondence is not +absolutely necessary; since it ceases to be exact if we wished, from the +point of view of the direction given to other segments of the skeleton, +to establish the same relation between the elbow and the articulation of +the knee. + +It is therefore indispensable, when discussing quadrupeds, to +discontinue these terms, in order the more readily to recognise that: in +flexion the inferior extremity of the humerus is directed backwards; in +extension, on the contrary, it is directed forwards. In the first case +the humerus approaches the scapula; in the second, on the contrary, it +moves away from it. + +These movements, which take place during walking, are executed in the +following manner: When one of the anterior limbs is at the end of that +stage of progression which is called support (see p. 289, Displacements +of the Limbs)--that is to say, during the time that the foot remains in +contact with the ground, whilst the trunk is moving forward--the +direction of this limb becomes more and more oblique downwards and +backwards. At a certain moment the limb is raised from the ground, to be +carried forwards, in order to be again pressed on the ground, and +recommence a new resting stage. In these different phases the humerus is +flexed. But at the moment that the limb, when carried forwards, is about +to resume its contact with the ground it becomes directed obliquely +downwards and forwards; then the humerus is in the position of +extension. + +During these movements of the humerus, there exists an essential +factor--that is, the scapular balance. (It is the same as what occurs in +man when he balances his arm in the antero-posterior plane.) When the +humerus is flexed, the scapula moves in such a way that the superior +portion projects forwards; when it is extended, the scapula, on the +other hand, is inclined more backwards. But it is necessary to add that, +during these displacements, the scapulo-humeral angle varies; it tends +to close during the flexion of the humerus, and becomes more open during +extension. + +The movements and the relations of the humerus and the scapula are +clearly represented in Figs. 41 and 42, reproduced from the +chromophotographic studies of Professor Marey--studies relative to the +analyses of the movements of the horse.[13] They show clearly the +movements of flexion and extension of the humerus, also the balancing of +the scapula which accompanies the movements. + + [13] E. J. Marey, 'Analyses of the Movements of the Horse by the + Chromophotograph' (_La Nature_, June 11, 1898). + +[Illustration: FIG. 41.--FLEXION OF THE HUMERUS: RIGHT ANTERIOR LIMB OF +THE HORSE, EXTERNAL SURFACE (AFTER A CHROMOPHOTOGRAPHIC STUDY BY +PROFESSOR MAREY).] + +[Illustration: FIG. 42.--EXTENSION OF THE HUMERUS: RIGHT ANTERIOR LIMB +OF THE HORSE, EXTERNAL SURFACE (AFTER A CHROMOPHOTOGRAPHIC STUDY BY +PROFESSOR MAREY).] + +=The Articulation of the Elbow, or the Humero-ulnar Articulation.=--In +this articulation, which is constructed in the form of a true hinge, the +movements of flexion and extension alone are possible. In flexion, the +forearm, directed forwards, is folded on the arm, with which, in certain +circumstances, it comes in contact. For example, in a horse of mettle +which leaps over an elevated obstacle, the animal forcibly raises his +fore-limbs by flexing them. Flexion is produced to the same extent, and +even more so, and for a longer period, in felides which crouch. + +In extension, on the contrary, the forearm is carried backward. This +movement being limited only by the contact of the tip of the olecranon +with the bottom of the olecranon fossa of the humerus, the forearm is +enabled, in this case, to move until it is in line with the arm. For +example, during walking, when one of the anterior limbs, having reached +the end of its resting stage, is considerably inclined downwards and +backwards. + +The apex of the olecranon process--that is to say, the point of the +elbow--forms a marked prominence, more salient in flexion than in +extension, as in the corresponding region of the human elbow. + +=The Radio-ulnar Articulation.=--It is in the dog and the cat, in which +the two bones of the forearm articulate by their extremities only, and +remain separate in the rest of their extent, that the articulations call +for special notice. + +In the upper part, the radius rotates on itself; while below, it rotates +around the ulna. It follows that the forearm, which in all quadrupeds is +in a state of permanent pronation, can, in carnivora, take the position +of supination, or rather, of demi-supination. In fact, whatever be the +mobility of the two bones of the forearm, the movement is not able to +bring the palmar surface to the front, but only to direct it towards the +median line. + +=The Articulation of the Wrist.=--Here are found, as in man, three +superimposed articulations: the radio-carpal, intercarpal, and +carpo-metacarpal. + +If we remember the movements which take place at the plane of these +articulations in man, and take account of the fact that the mobility of +the limbs is reduced just in proportion as they are simplified in +structure so as to become organs of support only, we can easily +comprehend that, in the horse and the ox, and, in a word, animals that +have a canon bone, the movements of the wrist are little varied in +character, while in carnivorae, on the other hand, they are relatively +more so. + +We will remember that in the ox and the horse the region of the wrist is +called the _knee_. + +In flexion, the hand is bent backwards; in extension it is carried +forwards. These two movements take place especially in the radiocarpal +and intercarpal articulations. In the first of these articulations, it +is the superior row of the carpus which glides backwards and forwards on +the corresponding articular surface of the forearm. In the second +articulation, it is the second row which moves; gliding on the inferior +articular surfaces of the row above it. This inferior row carries the +metacarpus with it; for the carpo-metacarpal articulation is much less +mobile than either of the other two. + +In flexion, the articular surfaces are separated from one another in +front; and the changes of form which result from this are noticeable on +the anterior surface of the 'knee.' Moreover, at that moment this region +contrasts markedly in its outlines with the parts above it and below +it--that is to say, with the corresponding surfaces of the forearm and +of the canon bone. + +As for the lateral movements, by which the hand is inclined outwards and +inwards in its movements at the wrist, they exist to an appreciable +extent in the cat and the dog only; in order to understand this, it is +enough to compare the shape of the articular surfaces of this region in +carnivora and the horse, for example. In the latter, those surfaces are +almost plane; in the cat, on the contrary, they are curved (inferior +surface of the forearm, concave; superior border of the carpus, convex). +These latter, then, are, in form, similar to those which exist at the +same level in the human being; this explains the possibility of +analogous movements of the whole hand--that is to say, of the movements +of abduction and adduction. + +=The Metacarpo-phalangeal Articulations.=--With regard to the mobility, +it is in these articulations, as in those of the wrist--that is to say, +although in all quadrupeds the first phalanges can be flexed and +extended on the metacarpus, it is only in the cat and dog that lateral +movement is possible. Indeed, in the horse, in which the principal +metacarpal terminates inferiorly in two convex surfaces, which are +separated by a crest; and where the whole articulates with a cavity on +the superior extremity of the first phalanx; because of the hinging of +these surfaces, there can only be movements of opening and closing of +this articulation. The first phalanx is directed backwards during +flexion and forwards during extension. In the dog and the cat the digits +can be separated from each other, and also drawn together--that is to +say, abducted and adducted; but, as in man, these movements can be made +only when the first phalanges are in the state of extension. During +flexion they are impossible, because of the tension of the lateral +ligaments, which increases as the flexion is more pronounced. This can +be demonstrated, for example, in the cat, which, in order to separate +the digits, opens the hand widely--that is to say, forcibly raises the +first phalanges. + +=The Interphalangeal Articulations.=--The phalanges are in contact with +one another by surfaces, which, on one side, are of trochlear form, and, +on the other, are moulded on these trochleae; accordingly, at the level +of these articulations, the movements of flexion and extension only can +take place. + +In the felidae, the claws which the third phalanges bear cannot be +utilized when the latter are in a state of extension, at which time, +being forcibly raised, they are, in fact, placed on the outer sides of +the phalanges, which are grooved to receive them. But when the animal +wishes to use them, it flexes those third phalanges, of which the +terminal extremity is then projected forward, and the claws are ready to +fulfil their function. But at the same time it extends the first +phalanges, to produce a certain tension of the flexors of the digits, +and thus enable the latter to act with greater efficacy, with a minimum +of contraction. We can demonstrate this action experimentally on +ourselves. It is enough to carry the first phalanges forcibly into a +state of extension; the third phalanges then become flexed, quite +spontaneously, by the tension of the tendons of the flexors which are +inserted into them. + +At the same time, if we examine the felidae which we have taken as +examples, when the first phalanges are in the state of extension, the +digits will be found to be separable, as we have already indicated in +connection with the metacarpo-phalangeal articulations, with the result +that the claws are then able to lacerate a wider surface. + +The extension of the ungual phalanx, which determines the retraction of +the claw and stops its action, is the mechanical result of an elastic, +fibrous apparatus which is attached to each of the third phalanges, and +has its origin of the second. + + +THE POSTERIOR LIMBS[14] + + [14] Examine Figs. 21, 33, 34, 38, 39, 49. + +The posterior limbs are divided, as are the inferior limbs of the human +being, of which they are the homologues, into four parts: pelvis, thigh, +leg, and foot. + + +The Pelvis + +The pelvis, which incompletely limits the abdominal cavity, inferiorly +in the vertical position of the body and posteriorly in the normal +attitude of quadrupeds, is formed by the iliac bones and sacrum--the +coccyx forming a prolongation of the latter. We have already described +the two latter (pp. 10 and 11) in connection with the vertebral column, +of which they form the inferior or posterior portion or segment, +according to the attitude of the individual. + +=The Iliac Bone.=--The iliac or coxal bone, is a paired or +non-symmetrical bone, united below to its fellow of the opposite side, +while it is separated from it above by the sacrum. + +In all animals, as well as in man, the iliac bone, at the beginning of +life, consists of three parts, which afterwards unite and fuse together +and join at the middle of the bottom of a deep cavity which is situated +on the outer aspect of the bone--the cotyloid cavity. + +Of those three portions when examined in the human iliac bone, that +above the cavity is the ilium; that on the inside is the pubis; and the +last, the lower one, is the ischium. In quadrupeds, the iliac bone +being, in its entirety, directed much more obliquely downwards and +backwards, the relative position of these constituent parts is a little +modified: the ilium is in front, the pubis is still internal, but in a +more inferior position, and the ischium is behind the cotyloid cavity. +We notice this peculiarity of the development of the iliac bone because +it is customary to continue to apply to the osseous regions which +correspond to these parts the names by which they were known when +independent bones. + +[Illustration: FIG. 43.--THE LEFT ILIAC BONE OF THE HUMAN BEING: +EXTERNAL SURFACE, PLACED IN THE POSITION WHICH IT WOULD OCCUPY IN THE +SKELETON OF A QUADRUPED. + +1, Cotyloid cavity; 2, ilium; 3, iliac crest; 4, anterior iliac crest; +5, posterior iliac spine; 6, pubis; 7, tuberosity of the ischium; 8, +obturator foramen; 9, ischiadic spine.] + +[Illustration: FIG. 44.--LEFT ILIAC BONE OF A QUADRUPED (HORSE): +EXTERNAL SURFACE. + +1, Cotyloid cavity; 2, ilium, external iliac fossa (directed upward in +the horse); 3, iliac crest; 4, anterior iliac spine (directed inwards in +the horse, it is the angle of the haunch); 5, posterior iliac spine +(directed inwards in the horse; it is the angle of the haunch); 6, +pubis; 7, tuberosity of the ischium; 8, obturator foramen; 9, ischiadic +spine, or subcotyloid foramen.] + +The bones which form the skeleton of the pelvis of quadrupeds are +proportionally more elongated and less massive than those of the human +pelvis (Figs. 43 and 44). + +We find, on the external surface of the iliac bone, the cotyloid cavity, +whose border is interrupted by the cotyloid notch; a deep notch which +looks downwards. + +In front of this cavity is the ilium. This portion, narrow in the part +which is next the cavity, is directed forwards and upwards, expanding +more and more as it passes upwards. It presents an external or superior +surface (external in some animals, superior in others), which recalls +the external iliac fossa; and an internal or inferior surface, at the +superior part of which is found the auricular surface for articulation +with the sacrum. + +The anterior border of the ilium is rough; this is the iliac crest, at +the extremities of which we find, below or outside, a prominence which +corresponds to the anterior superior iliac spine of man; and internally +another projection which corresponds to the posterior iliac spine. + +Immediately above the cotyloid cavity is a rough crest, which is known +as the _supracotyloid crest_, which is, however, no other than the +homologue of the sciatic spine. In front of this prominence, the border +of the ilium, which is notched, forms the great sciatic notch. + +If, still taking the cotyloid cavity as the point of departure, we +proceed inwards--that is, towards the median line of the body--we find +the pubis; if in a posterior direction, the ischium. These two portions, +pubis and ischium, limit an oval orifice, the subpubic foramen. + +In the human skeleton, the pubis of one side is united to that of the +opposite side, to form the pubic symphysis. In the animals which we are +now studying a portion of the ischium enters into the formation of the +symphysis; in other words, it is formed, not only by the body of the +pubis, but also by the descending branch or ramus of the pubis and a +portion of the ascending branch or ramus of the ischium, which are fused +with those of the opposite side. It results that, though in the human +being the symphysis is short and the ischio-pubic arch large, in +quadrupeds it is the opposite. In them the arch is a mere slot, and +being formed by the ischium alone, merits the name of the ischial arch. +The ischio-pubic symphysis is very large, and forms a horizontal surface +relatively extensive, a sort of floor, on which rest certain organs +which occupy the cavity of the pelvis. + +The posterior and external angle of the ischium is rough and prominent; +it is the tuberosity of the ischium. This forms a projection under the +skin; it also does in man when the trunk is strongly inclined forwards, +while the thighs are maintained in the vertical position. In +marsupials--opossum, kangaroo, and phalanger--the pelvis at its pubic +region is surmounted by two bones, situated one on each side of the +median line, and arranged in the form of a fork of two prongs (Fig. 45). +These, which are called _marsupial bones_, support the pouch which, in +animals of this genus, lodges their young, which, at the time of birth, +are incapable of supporting a separate existence, their development +being absolutely incomplete. + +[Illustration: FIG. 45.--PUBIC REGION OF THE PELVIS OF A MARSUPIAL +(PHALANGER, FOX). + +1, Symphysis pubis; 2, obturator foramen; 3, marsupial bones.] + +In the cetaceans--for example, the dolphin--because of the absence of +posterior limbs, the pelvis is represented by two separate bones only, +which have no connection with the vertebral column. In birds, the pelvis +is remarkable for its elongated form (see for its form Fig. 21, and for +details Fig. 46). The cotyloid cavity is pierced by an opening, and +presents on its posterior border, which is here a little prominent, a +surface with which the great trochanter is in contact. + +The ilium is very highly developed, and is fused in the median line with +the ilium of the opposite side, the last dorsal vertebrae, the lumbar +vertebrae, and the sacrum. Because of these relations with the dorsal +vertebrae, it is in contact anteriorly with the last ribs, which +consequently emerge from each side of the iliac region of the pelvis. + +The ischium forms a plate of bone which, in part, closes the external +portion of the cavity of the pelvis. Its superior border is separate for +a certain distance from the external border of the ilium; there is thus +left an opening of more or less considerable size, which represents or +takes the place of the great sciatic notch. + +[Illustration: FIG. 46.--PELVIS OF A BIRD (THE COCK): EXTERNAL SURFACE, +LEFT SIDE. + +1, Ilium; 2, ischium; 3, pubis; 4, inferior extremity of the pubis; 5, +sciatic foramen; 6, oval foramen, homologous to the obturator; 7, +coccygeal vertebrae.] + +The pubis, long and slender, is in connection with the inferior border +of the ischium, of which it follows the general direction; and +circumscribes with this latter, below the cotyloid cavity, an oval +orifice, which is the homologue of the obturator foramen. Its inferior +extremity reaches beyond the corresponding part of the ischium, bending +towards the middle line, but without joining the pubis of the opposite +side. On this account there is no symphysis pubis in birds. +Nevertheless, an exception must be noted in the case of the ostrich, the +pubic bones of which meet in the middle line, and are articulated in +form of a symphysis. + + +The Thigh + +A single bone, the femur, forms the skeleton of this portion of the +lower limb. + +=The Femur.=--The bone of the thigh is, in man, directed downwards and +inwards; this obliquity, we may remind the reader, is due to the +difference in length of the two condyles which form its inferior +extremity; the internal is the more prominent, the result of which is +that when the femur is held vertically, the internal condyle descends +lower than the external. Now, as those two articular expansions rest on +the horizontal plane formed by the upper extremity of the tibia, it +follows that the superior part of the femur inclines towards the side of +the shorter condyle--that is to say, outwards--and that, the leg being +vertical, it and the bone of the thigh unite in forming an angle, of +which the apex is directed towards the inner side of the knee. + +In many mammals the two condyles are equally prominent, the result of +which is that the femur inclines neither inwards nor outwards, but is +contained in a plane parallel to the axis of the trunk; while the leg is +included in the same plane. Nevertheless, although contained in the +plane which we have just indicated, the femur is obliquely placed, and +directed downwards and forwards; it accordingly forms, with the pelvis, +an angle, of which the opening is directed to the anterior aspect of the +body. + +In reptiles and in birds the femur and leg are both placed in the same +plane, but this plane is not parallel to the axis of the trunk. This is +the result, on the one hand, of the thorax being wide, and, on the other +hand, of the femur, which is directed forwards, being in contact by its +anterior extremity with the lateral aspect of the costal region, it is +thus necessarily placed in a direction forwards and outwards, and the +knee is further removed from the axis of the trunk than is the +articulation which unites the thigh with the pelvis. + +The femur, like the humerus, is almost completely enveloped by muscular +masses, which bind it to the lateral walls of the abdomen. Its inferior +extremity alone is free, and is always the more so in proportion to its +elongation--that is to say, as it belongs to an animal whose foot is +more divided. The femur in this respect conforms to the law which we +have indicated in connection with the bone of the arm, in which the +development, as to length, is in proportion to the division of the hand. + +If we compare the femur of certain animals with that of man, we see that +the corresponding details of form are readily recognisable, but they are +slightly modified. Thus, on examining the superior extremity, we find +there a head, a neck, a great trochanter, and a lesser; but the neck is +usually short and thick, and the great trochanter does not occupy the +same level with regard to the articular head of the bone. In man, the +great trochanter does not rise to the level of the head of the femur; in +the dog and the cat it approaches that level; in the horse and in +ruminants it rises above it. + +With regard to the inferior extremity, its surfaces undergo +modifications which are further accentuated as we pass from the +digitigrades to the ungulates, or unguligrades. We know that in man the +femoral trochlea is continuous behind, without interruption, with the +condyles--that is to say, that each of the condyles is the continuation +of one of the lips of the trochlea. We have just said that the trochlea +is continuous without interruption with the condyles; this is accurate. +Nevertheless, we must remark that, at the level of the junction of these +surfaces, the bone presents a slight constriction, which is more marked +on the external than on the internal aspect. This constriction, which is +but slightly marked in man, is accentuated in the dog and the cat; in +the ruminants and the solipeds it is still more pronounced so that we +may say that in these latter the trochlea and the condyles are almost +completely separated. + +There is another modification in regard to the prominence and extent of +the two lips of the trochlea. In man, the external lip of the trochlea +reaches higher than the internal, and it is more prominent in front. In +the dog, these lips are equal with regard to thickness, but the external +still reaches higher than the internal; in the cat, they are equal in +every respect; in ruminants and solipeds the internal lip is wider, +thicker, and rises higher than the external. + +In animals the trochlea is, as a general rule, narrower than in man, and +the condyles are more prominent posteriorly; so that, when viewed from +one of the lateral aspects, the inferior extremity of the femur is, in +them, better developed in the antero-posterior direction. + +In birds, the femur is shorter than the bones of the leg; its great +trochanter is in contact with a prominence which occupies the posterior +part of the border of the cotyloid cavity. Instead of articulating at +the level of the knee, with the knee-cap and tibia only, as in man, it +articulates, in addition, with the superior extremity of the fibula. A +similar arrangement is found in marsupials and reptiles. + +=The Knee-cap.=--This bone, developed in the thickness of the tendon of +the triceps muscle of the thigh, is in contact, by its posterior +surface, with the femoral trochlea. The two articular surfaces which are +applied to the lips of the trochlea present, with regard to their +extent, an inequality which is in proportion to the arrangement which we +have above indicated--that is, while in man it is the external surface +which is the larger, in the horse it is the internal. We shall see what +the general form of the knee-cap is when we come, later on, to study +more particularly the posterior limbs of some animals. + + +The Leg + +The skeleton of the leg consists of two bones: the tibia and the fibula. +The tibia is the more internal and the larger of the two; the fibula is +slender, and situated on the outer side, and a little posterior to, the +preceding. The fibula is more or less developed according to the +species; in some it is complete, in others it is very much atrophied. + +This peculiarity may be compared with that which we have drawn attention +to regarding the development of the ulna; but here the seriation is less +distinct. Not only in the different species, but even in the individuals +of the same species, the development of the fibula presents little +regularity. In quadrupeds, the bones of the leg are directed obliquely +downwards and backwards, so that they form, with the femur, which is +directed obliquely downwards and forwards, an angle, the apex of which +is placed at the anterior surface of the knee. + +=Tibia.=--The tibia of quadrupeds is readily comparable with that of +man; as in the case of the latter, its shaft has three surfaces--an +external, which is hollowed out in its upper portion, and becomes +anterior below; an internal, slightly convex and subcutaneous; the +posterior, which presents, in its superior part, a crest, the oblique +line of the tibia, and some rugosities. The borders separate the +surfaces. The anterior border, or crest of the tibia, is prominent in +its superior part; below it gradually disappears in passing towards the +internal aspect of the inferior extremity. The external and internal +borders separate the corresponding surfaces from the posterior one. + +The superior extremity is thick, and expands in forming three +tuberosities: two lateral and an anterior. The anterior tuberosity, +situated at the superior part of the crest of the tibia, is very +prominent; for this reason the superior extremity is very much expanded +in the antero-posterior direction--hence it results that this diameter +is equal to the transverse, and sometimes even greater. In man, it is +the latter which is the larger. The anterior tuberosity is visible under +the skin. + +The inferior extremity, less thick, is prolonged internally by a +prominence which corresponds to the internal malleolus of man. In +animals whose fibula is but slightly developed the tibia presents, on +the external part of its inferior extremity, a small prominence, which +replaces the fibular malleolus. The ruminants must, however, be +excepted, in which we find in this region a special bone, which certain +authors look on as the inferior part of the fibula (see p. 97). The +inferior surface of this extremity of the tibia is articular; and is in +contact with one of the tarsal bones, the astragalus. Because the +superior surface of this latter has the form of a pulley, a pulley much +more marked than that on the human astragalus, the corresponding surface +of the tibia, which has the opposite form, presents two lateral +cavities, separated by a median ridge, which is directed forwards and +slightly outwards; this ridge projects into the groove of the pulley. + +=The Fibula.=--This bone, situated at the back of the external +surface of the tibia, is, as we have said, more or less developed. Its +superior extremity, or head, articulates with the external tuberosity +of the tibia. Its inferior extremity, when it exists--it is this +which disappears in animals which have the fibula incompletely +developed--forms a prominence which, placed on the external surface of +the inferior extremity of the tibia, articulates with the astragalus, +and recalls the external malleolus of man. + +We have stated above that it is the inferior extremity of the fibula +which disappears when the bone is incompletely developed; it is +necessary to except the bat, in which the fibula, fairly well developed +at its inferior extremity, by which it articulates with the tibia, thins +off in its superior portion, and does not reach the corresponding +extremity of the latter. Further, as in this animal the surface of the +knee, which corresponds to the anterior surface of the same region in +other animals, is turned backwards, the result is that the fibula is +situated on the inner side of the tibia, instead of being placed on the +outer. + + +The Foot + +The foot, in animals, as well as in man, is formed of three portions, +which, as we pass from the part which articulates with the leg towards +the terminal extremity, are: the tarsus, the metatarsus, and the toes. +These three portions are the homologues of the carpus, the metacarpus, +and the fingers, which, as we have already seen in the case of the hand, +are the osseous groups which form its skeleton. The tarsus is formed of +short bones, as the carpus is; these are, in man, seven in number. The +bones are arranged in two rows: one, the posterior, formed of two bones +superimposed--the astragalus, by which the tarsus articulates with the +leg, and the calcaneum, which forms the prominence of the heel; and an +anterior row formed of five juxtaposed ones--the cuboid, situated +externally, and the scaphoid internally, in front of which are found the +three cuneiforms. To the tarsus succeeds the metatarsus, whose form +reminds us very much of that of the metacarpals. + +With regard to the toes, which we enumerate in proceeding from the most +internal to the most external, they are formed of phalanges, which are +three in number for the four outer toes; but the number is reduced to +two in the case of the first--that is, the so-called great-toe. + +The bones of the tarsus are not seven in all animals; they are fewer in +ruminants and solipeds. We already know that, in the latter, the +metacarpals and the digits are equally reduced in number; the same is +the case for the metatarsals and the toes. We will analyze these +differences when dealing with the species individually. + +When we studied the anterior limbs, we saw in passing from the +plantigrades to the digitigrades, and finally the ungulates, or +unguligrades, as the hand became hyperextended, the carpus was raised +and more and more removed from the ground. We shall establish the +existence of the same condition in the posterior limbs; in the +plantigrades the tarsus rests on the ground; in the digitigrades it is +removed from it; while in the unguligrades the distance which separates +it from the point of support is still more considerable; and it is, +indeed, necessary to imagine that if these latter were plantigrades, +would occupy the position on the ground which is indicated by Fig. 47. + +In veterinary anatomy the tarsus is called the _ham_; a name we adopt +in conformity with usage, but which we cannot but regret, as in human +anatomy the ham is the region of the posterior surface of the knee. + +The general arrangement of the region of the digits of the posterior +limbs in birds, presents some points of interest. + +We shall merely say with regard to the metatarsus, that it is formed by +a single bone, which in the cock is furnished towards its inferior third +with a pointed process, the _spur_. At the inferior part, there is, +however, found another, which is but very slightly developed, and with +which the first phalanx of the innermost toe articulates. + +The toes are, in the majority of species, four in number:[15] an +internal, which is directed backwards, and corresponds to the great-toe; +the others are directed forwards. This arrangement is constant in +grallatores (wading birds), gallinaceae[16] (domestic fowls), and +raptores (birds of prey). + + [15] In spite of the fact that the custom is to designate the terminal + portions of the foot of birds by the name of digits, we prefer to + employ here the terms _foot_ and _toes_. In adopting this + decision we believe we are acting according to a more didactic + method. Homology of names should, in our opinion, always + accompany homology of regions. + + [16] With regard to the gallinaceae, we must add that in certain + varieties the number of toes is five; those which are directed + forwards are three in number; the internal one which passes + backward, is double. The two toes which are the subject of this + special arrangement are placed very close together, and are + nearly always superimposed. This condition is found in the Houdan + and Dorking breeds. + +[Illustration: FIG. 47.--POSTERIOR LIMB OF THE HORSE PLACED IN THE +POSITION WHICH IT SHOULD OCCUPY IF THE ANIMAL WERE A PLANTIGRADE: LEFT +LIMB, EXTERNAL SURFACE. + +1, Tibia; 2, astragalus; 3, calcaneum; 4, metatarsus; 5, first phalanx; +6, second phalanx; 7, third phalanx.] + +In climbing birds (parrots, woodpeckers, and toucans), the innermost +toe is not only directed backward, but the external toe accompanies it +in that direction; consequently, there are two posterior and two +anterior toes. Sometimes they are all directed forwards; this +disposition is found in the martins. In some birds, the number of toes +is reduced to three: the cassowary shows this reduction; in others, the +number is still further diminished--the ostrich, for example, has but +two. + +[Illustration: FIG. 48.--SKELETON OF THE FOOT OF A BIRD (THE COCK): LEFT +SIDE, EXTERNAL SURFACE. + +1, Metatarsus; 2, spur; 3, rudimentary metatarsal; 4, first toe; 5, +second toe; 6, third toe; 7, fourth toe.] + +Further, we find that, in general, the number of the phalanges +increases, when we examine the toes in commencing with the most internal +(Fig. 48): this has two; then the following one three; that which comes +next in order has four; and the most external toe has five. The +phalanges of this last are short; so that, although it is formed by a +larger number of bones, it is not the longest of the toes. + + +THE POSTERIOR LIMBS IN SOME ANIMALS. + +=Plantigrades=: =Bear= (Fig. 33, p. 50).--The external iliac fossa is +very deep. The femur is longer than the bones of the leg; the great +trochanter does not reach the level of the head of the femur. The +fibula is well developed; it is united to the tibia at its superior and +inferior extremities only. + +The foot, which, as in the case of the hand, rests on the ground by the +whole extent of its plantar surface, presents five toes; the shortest of +these is the internal--that is, the toe which corresponds to the +great-toe in man; the third and fourth are the longest, and they are +almost equal; there is a very slight difference in favour of the fourth, +which is slightly superior in dimensions to the third. + +=Digitigrades=: =Cat=, =Dog= (Fig. 34, p. 52).--The external iliac +fossa, which looks outwards, is deep; the iliac crest is convex +anteriorly, the convexity is continued from one iliac spine to the +other. + +[Illustration: FIG. 49.--PELVIS OF THE DOG, SEEN FROM ABOVE. + +1, Iliac crest; 2, external iliac fossa; 3, sacrum; AA', bi-iliac +diameter; BB', bi-ischial diameter.] + +In the dog, the distance which separates the anterior iliac spines is +less than that which separates the ischia (Fig. 49). On a skeleton which +we measured, the transverse diameter, the distance from the anterior +iliac spine of one side to that of the opposite side, was 8 centimetres, +whilst the distance which separated the ischia was 105 millimetres; on +another skeleton, the first measurement was 127 metres, and the second +was 146 millimetres. It seems to us unnecessary to multiply examples. + +In the cat, the iliac spines are but slightly marked; the result is +that the iliac crest is almost confounded with the inferior and superior +borders of the ilium. The two diameters referred to above are almost +equal (Fig. 50). + +We draw particular attention to what we have just noted in regard to the +transverse proportions of the iliac and ischiatic regions of the dog and +the cat. These relations are evidently of importance with regard to +shape, since the iliac crests and the ischia are noticeable beneath the +skin. + +[Illustration: FIG. 50.--PELVIS OF A FELIDE (LION), VIEWED FROM ABOVE. + +1, Iliac crest; 2, external iliac fossa; 3, sacrum; AA', bi-iliac +diameter; BB', bi-ischial diameter.] + +In the dog, the shaft of the femur is slightly convex in front; but in +the cat it is straight. The borders of the shaft are slightly marked, so +that it is almost cylindrical. The _linea aspera_, less prominent than +in man, gains in width what it loses in elevation; it constitutes what +may almost be called a rough _surface_. This surface is narrower in its +middle portion than at its extremities, where it bifurcates to go +upwards to the two trochanters, and downwards to the two condyles. At +the superior extremity, the neck is short, the great trochanter reaching +almost to the level of the head of the femur; the digital _cavity_, +which is situated on the internal surface of the great trochanter, is +very deep. At its inferior extremity it projects strongly backward. The +trochlea is narrow; in the cat its two lips are equally prominent, while +in the dog the external is a little more elevated than the internal, +which on its part is a little thicker. The trochlea is still more +independent of the condyles than in the human femur; it is separated +from these latter by a slight constriction. + +The knee-cap is long and narrow. + +The tibia of the dog is slightly curved from before backward: it has the +form of an elongated S; this conformation is in great part due to the +very marked projection of the anterior tuberosity and of the superior +portion of the crest, which, a little below that tuberosity, turns +abruptly backwards, and thus describes a curve the concavity of which is +directed forward. The superior part of the external surface is very much +hollowed out. + +The superior extremity is much thicker than the inferior one. It is not +only wide in the transverse direction, but is more especially extended +from before backwards; the prominence of the anterior tuberosity is the +cause of the elongation of this antero-posterior diameter. On the +posterior part of the external tuberosity is found a surface to which +the superior extremity of the fibula is applied. + +The inferior extremity presents an articular surface, which is formed of +two lateral cavities, separated by a crest, which is directed obliquely +forwards and outwards. The internal part is prominent, and forms the +internal malleolus. + +With regard to the fibula, it is united to the tibia by its extremities +and by the inferior half of its shaft. This latter is more expanded +below than in its upper part. The superior extremity is flattened from +without inwards. The inferior extremity projects beyond the articular +surface of the tibia, and forms the external malleolus, which, instead +of, as in man, descending further than the tibial malleolus, stops at +the same level, and even descends a little less than does the latter. + +In the cat, the curve of the tibia is less pronounced; this is due to +the fact that the crest, instead of being concave in its middle portion, +is slightly convex anteriorly. The fibula, less flattened than that of +the dog, is united to the tibia by its extremities only, and is separate +in the rest of its extent. + +The bones of the tarsus are seven in number, and arranged as in man, +with this difference (which is easily comprehended), that their general +relations are changed on account of the vertical direction of the +tarsus. For example, the astragalus, instead of being above the +calcaneum, is situated in front of it; the cuneiform bones, instead of +being situated in front of the scaphoid, are found below it, etc. + +These animals have but four well-developed metatarsals; that which +corresponds to the great-toe is represented merely by a small +style-shaped bone, situate at the internal part of the region. + +Nevertheless, we find this toe fully developed in some dogs. +Notwithstanding this, the bones which form it are, however, but +rudimentary, and much smaller than those of the innermost digit of the +fore-limb. + +Sometimes it is double; this condition is demonstrable in individuals +belonging to breeds of large size. The median metatarsals are more fully +developed than the other bones of the same region which are next them. +Viewed as a whole, the metatarsal bones are a little longer than the +metacarpals; the result is that the distance which separates the tarsus +from the ground is a little greater than that which separates the carpus +from the plane on which the anterior limbs rest. The length of the +calcaneum still further exaggerates this difference, and, as in the +animals with which we shall occupy ourselves later on, the projection +which this bone forms is distinctly higher than that which is produced +by the pisiform. + +The metatarsus, as a whole, is a little narrower than the metacarpus; +not only on account of the presence of a thumb in the anterior limb, +but, further, because the bones of this latter region are wider than +those of the corresponding part of the posterior limb. + +The phalanges closely resemble those of the anterior limbs. + +=Unguligrades=: =Pig= (Fig. 38, p. 58).--The pelvis in this animal +presents a few of the characters which we shall again meet with in the +ruminants and the solipeds; however, the posterior (or internal) iliac +spines are relatively more widely separated from one another than in the +latter. This arrangement reminds us of that found in the carnivora. + +The femur presents nothing very special. The knee-cap is thick, and +ovoid in outline. + +The fibula is completely developed, as in the carnivora; and is +connected with the tibia at both its extremities. + +The tarsus consists of seven bones. The astragalus and the calcaneum +differ slightly from those of ruminants. + +The foot, like the hand, has two median digits which rest on the ground +by their third phalanges; and an internal and an external digit, which +are removed from it. The metatarsals are a little longer than the +metacarpals. + +[Illustration: FIG. 51.--PELVIS OF THE OX: SUPERIOR SURFACE. + +1, Iliac crest; 2, external iliac fossa; 3, sacrum; AA', bi-iliac +diameter; BB', bi-ischiadic diameter.] + +=Unguligrades=: =Sheep=, =Ox= (Fig. 39, p. 61).--The pelvis of ruminants +of this group closely resembles that of the horse, which we will study +later on (see p. 99). That which we must at once point out is that, with +regard to the ratio formed by a comparison of the bi-iliac and +bi-ischiatic diameters, it may be placed between the ratio obtained in +comparing those diameters in the pelvis of the carnivora and that of the +solipeds. Indeed, in the ruminants, the distance which separates the +ischia exceeds the width of one iliac only, and does not equal, as in +the felide, the total width of the anterior part of the pelvis (Fig. +51). In the skeleton of the ox, which forms part of the anatomical +museum of the Ecole des Beaux-Arts, the bi-ischiadic diameter is 39 +centimetres, whilst the width of one iliac crest is 29 centimetres, so +that, in contrast to that which we find in the dog, the width of the +ischiadic region is less than that formed in front by the addition of +the iliac crests. + +The great trochanter is large, and extends beyond the level of the plane +in which the head of the femur is found. + +In the ox, the linea aspera, instead of being a narrow crest, is spread +out, and forms in reality a surface; the posterior surface of the femur. +At the inferior and external part of this surface is situated a cavity +which surmounts the corresponding condyle, and is known as the +_supracondyloid fossa_. On the internal part of the same region there +are a series of tubercles, which, because of their position in relation +to the corresponding condyle, constitute the _supracondyloid crest_. + +The internal lip of the trochlea is much thicker and much more prominent +than the external. + +The details which we have just now examined in connection with the ox +are less marked in the sheep. + +The trochlea, narrow as a whole, is clearly separate from the condyles +by a very marked constriction. + +The patella, which is thickened in the antero-posterior direction, has +the shape of a triangular pyramid with the base upwards. Its posterior +surface, which articulates with the trochlea, presents an arrangement +which is adapted to the disposition of this latter--that is to say, the +surface which is in contact with the internal lip is larger than that +which articulates with the lip of the opposite side. + +The tibia of the ox is proportionately shorter than that of the sheep. +The shaft of this bone is flattened from before backwards, in its +inferior half. The median crest of the articular surface of the inferior +extremity is the most prominent part of that region. + +[Illustration: FIG. 52.--TARSUS OF THE OX: POSTERIOR LEFT LIMB, +ANTERO-EXTERNAL SURFACE. + +1, Tibia; 2, coronoid bone of the tarsus; 3, superior articular surface +of the astragalus; 4, inferior articular surface of the astragalus; 5, +calcaneum; 6, cuboido-scaphoid bone; 7, great cuneiform bone--the small +cuneiform bone is situated at the back of the latter; 8, principal +metatarsal--the small, or rudimentary, metatarsal bone is very small; it +is situated at the back of the preceding, and is not to be seen in the +sketch. It would be visible if the view were directly lateral, but then +the superior and inferior articular surfaces of the astragalus would be +less apparent.] + +The fibula is extremely atrophied. The shaft and superior extremity of +this bone are represented merely by a simple ligamentous cord, which is +sometimes ossified. There remains of the fibula, as a portion well and +distinctly developed, the inferior extremity only. This presents itself +under the form of a small bone situated in the region ordinarily +occupied by the inferior extremity of the outer bone of the leg--that is +to say, the external part of the inferior extremity of the tibia; this +little bone articulates with the astragalus and the calcaneum. Some +authors consider it to be a tarsal bone, and describe it under the name +of the coronoid bone of the tarsus (Fig. 52, 2). It is not, perhaps, +quite legitimate to describe it as a bone of this region, for it has +not a homologue in the tarsus of other animals. Its external surface is +rough; its superior border is furnished with a small pointed process +occupying a depression which is provided for it by the tibia. It reaches +lower down than the latter, and forms in this way a sort of external +malleolus, which frames, on the outer aspect, the mortise in which the +astragalus is maintained. + +The tarsus, as a whole, has an elongated form; it is formed of five +bones: the astragalus, calcaneum, cuboid and scaphoid, which coalesce, +to form a single bone, and two cuneiform bones, which correspond to the +second and third cuneiform bones of the human foot. These cuneiforms are +called, from their size, commencing internally, by the names small and +great cuneiform. + +The calcaneum is long and narrow; it is longer than that of the horse; +it is on the anterior and external part that the bone (coronoid tarsal +bone) which represents the inferior extremity of the fibula is situated. +It forms the prominence known as _the point of the ham_, a prominence +which is no other than the heel, which, in the unguligrades, is, as we +have already said, very far removed from the ground. + +The astragalus, which is elongated in the vertical direction, has three +articular surfaces disposed in the form of trochleae: a superior +trochlea, which is in contact with the skeleton of the leg, and which is +present in all animals; an inferior, which replaces the articular head +found on the anterior aspect of the astragalus in man; this articulates +with the portion of the scaphoido-cuboid that corresponds to the +scaphoid; and, lastly, a posterior trochlea with which the calcaneum +articulates. Of these three trochleae, the superior is the most strongly +marked. Between this latter and the inferior is found, on the anterior +surface of the astragalus, a deep depression, which, during flexion of +the foot on the leg, receives a prominence which the inferior extremity +of the tibia presents in its median portion. + +We can easily recognise the trochleae which we have been discussing, in +the little bones which children use 'to play at bones'; these bones are +no other than the astragali of sheep. + +We have already mentioned that the scaphoid and the cuboid are +ankylosed; they form by their union an irregular bone, on which the +astragalus and calcaneum are supported. + +The cuneiforms articulate with the internal half of the superior +extremity of the principal metatarsal; the external half of this +metatarsal articulates with the portion of bone which represents the +cuboid. + +The metatarsus is represented by a principal metatarsal, formed by the +coalescence of two metatarsals; we also find in this region a very small +rudimentary metatarsal. + +The metatarsus is a little longer than the metacarpus; its transverse +measurement is a little less; on the other hand, it is a little thicker +in antero-posterior direction; from these two differences it results +that the body of the metatarsus is quadrilateral, whereas the metacarpus +presents only an anterior and a posterior surface. + +The rudimentary metatarsal is a very small roundish bone, situated at +the back of the superior extremity of the principal metatarsal. + +The phalanges closely resemble those of the anterior limbs; +nevertheless, the first and second phalanges differ from the latter in +the fact that they are a little longer and narrower. + +At the back of the metatarso-phalangeal articulations, as in the +corresponding region of the anterior limbs, are found the sesamoid +bones. Such also exist at the articulations of the second and third +phalanges. + +=Unguligrades=: =Horse= (Fig. 40, p. 64).--The pelvis of the horse +presents a general form which sharply differentiates it from that of the +carnivora; in fact, the ilium is twisted in such a way that the external +iliac fossa does not look outwards, but upwards. It results from this +twist that the anterior iliac spine, which we have seen to be directed +downwards in the carnivora, has become external; and this prominence is +much farther removed from the vertebral column than in the dog or cat. +On the other hand, the posterior iliac spine, which is directed upwards +in the carnivora, has become internal; it is also placed nearer to the +vertebral column, with the result that the distance which separates this +spine from that of the bone of the opposite side is proportionately +less. + +The internal iliac spine, which is conical in shape, and curved upwards, +forms a prominence known as _the angle of the crupper_; the external +iliac spine, thick and provided with tuberosities, forms a +clearly-defined prominence; this is the angle of the _haunch_. + +The iliac crest, extending directly from one spine to the other, is +curved, its concavity being turned upwards. The external iliac fossa, +which looks upward, is limited anteriorly by this crest, and is, like +the latter, slightly hollowed. The portion of the bone which connects +the ilium to the region occupied by the cotyloid cavity is extremely +narrow; posteriorly, the bone enlarges again to form the ischial and +pubic portions. + +The tuberosity of the ischium, thick and curved upwards, but less so +than in the ox, forms the most prominent part of the posterior border of +the region of the thigh; this projecting portion, so sharply defined in +spare subjects, is known as the _point_ or _angle of the buttock_. +Contrary to what we have indicated in the case of the dog, the distance +which separates the ischiatic tuberosities is inconsiderable in +proportion to that which we find between the external iliac spine of one +side and that of the opposite. The bi-ischiatic diameter does not even +equal the width of one iliac bone measured at the level of its crest +(Fig. 53). On the skeleton of the horse in the Ecole des Beaux-Arts, the +distance which separates the tuberosities of the ischia is 225 +millimetres; that between the two spines of each iliac bone is 25 +centimetres. + +The anterior region of the crupper is thus much broader than that +occupied by the ischia. + +The femur is relatively short. Its shaft is rectilinear, and does not +present the anterior convexity which is found on the human femur, and +which we indicated when discussing that of the dog. The shaft of the +bone, instead of being prismatic and triangular, presents four surfaces; +the anterior, internal, and external, almost pass into each other, being +separated one from the other merely by rounded and slightly marked +borders; the posterior surface, which is plane, replaces the linea +aspera, which in the horse, instead of presenting the appearance of a +crest, is considerably widened. The numerous irregularities which this +surface presents give insertion to the muscles which correspond to those +attached to the linea aspera. + +Between this posterior surface and the external is found a rough +prominence which curves forward; this was designated by Cuvier the +_third trochanter_; it replaces the external branch of the superior line +of bifurcation of the linea aspera; other authors call it the +_infratrochanteric crest_, because it is situated below the great +trochanter. At the inferior part of the same region is found a deep +fossa, the borders of which are rough; this is the _supracondyloid +fossa_. + +[Illustration: FIG 53.--PELVIS OF THE HORSE: SUPERIOR SURFACE. + +1, Iliac crest; 2, external iliac fossa; 3, sacrum; AA', bi-iliac +diameter; BB', bi-ischiatic diameter.] + +Between the posterior surface and the internal are found: above, the +lesser trochanter, which is long and rough; below, at the level of the +supracondyloid fossa, an equally rough surface known by the name of the +_supracondyloid crest_. + +The superior extremity is flattened from before backwards. The neck is +not well marked. The great trochanter is very prominent, and projects +beyond the level of the head of the femur. We divide the great +trochanter into three parts: the summit, which is the most elevated +portion; the convexity, which is situated in front; and the crest, +formed by muscular impressions, situated outside and below the +convexity. The digital fossa is situated behind and below the summit of +the great trochanter. With regard to the lesser trochanter, it is placed +so far down that it really forms part of the shaft of the bone, with +which, besides, we have described it. + +On the inferior extremity of the femur are two condyles and a trochlea; +the condyles are clearly separated from this latter by a marked +constriction. + +The trochlea is directed with a slight obliquity downwards and inwards; +its internal lip is much thicker and more prominent than the external; +this is, accordingly, a condition exactly the opposite of that which +characterizes the corresponding region of the human femur. + +The knee-cap is lozenge-shaped; its superior angle projects upward, and +produces a prominence at the part which corresponds to the base of the +human patella, the part which is here the thickest portion of the bone. +Its anterior surface is convex and rough. Its posterior surface presents +two lateral articular facets, separated by a crest; this surface is in +contact with the trochlea of the femur, and, as it is the internal lip +of the latter which is the more developed, it results therefrom that the +internal articular surface of the knee-cap is larger than the external. + +The knee-cap contributes to the formation of the region of the posterior +limb which is called the _stifle_. + +The tibia is large in its upper portion; in its inferior part it is +flattened from before backwards. The posterior surface of the shaft +presents an oblique line, below which are found vertical rough lines for +the insertion of muscles. The external surface is hollowed out in its +upper part. The anterior tuberosity of the tibia rises just to the level +of the flat articular surface; it is hollowed in its median portion by a +vertical groove of elongated form, which receives the ligament that +binds the knee-cap to the tibia. The external tuberosity is more +prominent than the internal; in it is found a groove for the passage of +the anterior tibial muscle. + +The inferior extremity, flattened from before backwards, presents a +surface which is moulded on the trochlea of the astragalus; the median +crest of this surface is thick, and descends lower posteriorly than the +tuberosities which are situated on the external and internal aspects of +this extremity. + +Of the two tuberosities, that which is internal is comparable to the +internal malleolus of man, the one on the outer side forms a sort of +external malleolus; but this latter here belongs to the tibia, and not +to the fibula. + +The fibula, in fact, does not reach the inferior extremity of the tibia; +it is a poorly developed bone, elongated and terminating inferiorly in a +point, at the middle of the shaft of the tibia or at its lower third. +Its superior extremity, which is slightly expanded, articulates with the +tuberosity which occupies the outer aspect of the corresponding +extremity of the tibia. + +The bones of the tarsus are six in number: the calcaneum and astragalus +form the upper row; the cuboid, scaphoid, and two cuneiforms form the +lower (Fig. 54). + +The astragalus has not, as in ruminants, an inferior trochlea for +articulation with the scaphoid; this portion of the bone presents a +surface which is slightly convex. It articulates with the tibia by a +trochlea that occupies not only the superior surface, but also the +anterior. This trochlea, which is directed slightly obliquely downwards +and outwards, has a very pronounced form; its lips, which are extremely +prominent, determine by their anterior part one of the features which we +recognise on the anterior aspect of the _ham_--a feature which is still +more accentuated when the metatarsus (_canon_) is extended on the leg. +On the internal surface of the astragalus is found a tubercle, which +forms a projection in the corresponding region of the ham. + +The calcaneum, which is not quite so long as that of the ox, forms by +its summit a prominence which is called _the point of the ham_. + +The cuboid is small; the scaphoid is large, and flattened from above +downwards. Of the two cuneiforms, the more external is the larger; it +closely resembles the scaphoid; it is flattened from above downwards as +is the latter; but it is a little smaller in size. The small cuneiform, +which occupies the inner side of the tarsus, is the smallest bone in +this region; it is sometimes divided into two parts; this raises the +number of the cuneiforms to three, and that of the bones of the tarsus +to seven. + +[Illustration: FIG. 54.--TARSUS OF THE HORSE: LEFT POSTERIOR LIMB, +ANTERIOR SURFACE. + +1, Tibia; 2, internal tuberosity of the inferior extremity of the tibia +(homologue of the internal malleolus of man); 3, external tuberosity of +the inferior extremity of the tibia (homologue of the external +malleolus); 4, median crest lodged in the groove of the pulley of the +astragalus; 5, pulley of the astragalus; 6, internal tuberosity of the +astragalus; 7, calcaneum; 8, cuboid; 9, scaphoid; 10, great cuneiform, +the small cuneiform is placed behind this latter; 11, principal +metatarsal; 12, external rudimentary metatarsal. The internal +rudimentary metatarsal, being more slender than the external, does not +appear in the figure.] + +The bones of the metatarsus and the phalanges are equal in number to the +corresponding bones in the anterior limbs; they are formed on a type +analogous to that of these latter. Accordingly, we shall merely indicate +the differences which characterize them. + +The principal metatarsal is longer than the metacarpal of the same +class; its shaft is more cylindrical; its inferior extremity is somewhat +thicker. The external rudimentary metatarsal is better developed than +the internal; in the metacarpus the reverse is the case. + +The phalanges so far resemble those of the anterior limb that, as +differential characters, we need point out only the following: the first +phalanx of the hind-foot is a little shorter than that of the fore-foot; +its inferior extremity is a little narrower, and its superior extremity +a little thicker. The second phalanx is a little less expanded +laterally. + +The difference in appearance which the three phalanges, anterior and +posterior, respectively present are to be borne in mind; for they are +correlated to the general form of the fore and hind feet. We will +establish this point when we come to study the hoof (see Figs. 101 and +102, p. 257). In the fore-foot the ungual phalanx has its inferior +surface limited externally by a circular border, while the same bone of +the hind-foot has this surface a little narrower, more concave, and +limited by two curved borders which unite anteriorly to form an +angle--an arrangement which gives to the general outline of this region +the form of the letter V. + + +Articulations of the Posterior Limbs + +=The Coxo-femoral Articulation.=--The head of the femur is received in +the cotyloid cavity; these are the osseous surfaces in contact in this +articulation. They are maintained in position by a fibrous capsule and a +round ligament. To this latter is found attached, in the horse, a +fasciculus which, commencing, as does the round ligament, at the +depression on the head of the femur, emerges from the cotyloid cavity by +the notch which is present in its circumference, and is attached to the +anterior border of the pubes, to blend with the tendon of the rectus +muscle of the abdomen. This is the pubio-femoral ligament. + +The movements which this joint permits are the same in the quadrupeds as +in man, but less extensive. They are: flexion and extension, abduction +and adduction, the two latter being much more limited than the former. +There is also rotation. + +By flexion, the inferior extremity of the femur is directed forwards; +the bone of the thigh then takes a more oblique direction than the +normal. This movement takes place, for example, when the animal carries +forward one of its hinder limbs. Extension, which takes place in an +inverse sense, is produced when the foot is fixed on the ground, while +the body is projected forward. It is also produced in the action of +kicking. + +As for the lateral movements--viz., abduction and adduction--they are +less extensive than the preceding movements. The absence of the +pubio-femoral ligament in other quadrupeds than the horse explains why +in them abduction is less limited than in the latter. Indeed, it is the +tension of this ligament, occasioned by the abduction of the thighs, +which arrests more quickly the movement in question. + +=Articulation of the Knee.=--This articulation, as in man, is formed by +the femur, the patella, and the tibia. + +In the horse the ligament of the patella is not single, but consists of +three parts, designated, on account of their position, by the respective +names of external, internal, and median patellar ligaments. The two +former come from the angles on the corresponding borders of the +knee-cap; the median springs from the anterior surface and inferior +angle of the same bone. They all three pass to their termination on the +anterior tubercle of the tibia. The external ligament is the strongest, +and the internal ligament the least developed. + +In the dog, the cat, the pig, and the sheep, the patellar ligament +consists of a single band. The articulation is further strengthened on +the sides by lateral ligaments--an internal and an external. + +With regard to the principal movements, these are flexion and extension, +to which may be added movements of rotation of limited extent. In +flexion, the leg bends on the thigh; its inferior extremity is directed +upwards and backwards; the angle which the tibia naturally forms with +the femur becomes less obtuse. + +But it should be understood that one part of this description--that +which has relation to the leg--holds good only when the femur is in its +normal condition, or in flexion. Indeed, at the close of the movement in +which, during a step, the foot is in contact with the ground--that is, +at the termination of the resting stage--the inferior extremity of the +tibia is directed backwards. But the femur is then in a state of +extension, and in regard to this latter the attitude of the leg is +unchanged. + +[Illustration: FIG. 55.--EXTENSION OF THE LEG: RIGHT POSTERIOR LIMB OF +THE HORSE, EXTERNAL SURFACE. (AFTER A CHRONOGRAPHIC STUDY BY PROFESSOR +MAREY.)] + +At this moment, notwithstanding the direction, which recalls that which +it has at the time of flexion, the leg is not bent on the thigh; on the +contrary, it is almost in the line of its continuation (Fig. 55). As we +have done in connection with the articulations of the anterior limbs, we +borrow this figure from the interesting chronophotographic studies of +Professor Marey.[17] + + [17] E. J. Marey, 'Analysis of the Movements of the Horse by the + Chronophotograph' (_La Nature_, June 11, 1898). + +=The Tibio-tarsal Articulation and of the Bones of the Tarsus.=--In the +region which veterinary anatomists call the ham, the articulations of +the leg and foot alone call for special study in the case of the horse. +The articulations of the bones of the tarsus, and of these with the +metatarsus, do not offer any interest with regard to mobility, this +being almost wholly absent at that level. + +The leg and the astragalus, in a general way, are placed in contact by +such articular surfaces that the resulting joint, which is a true hinge, +permits movements of flexion and extension only. Indeed, as we have +indicated above, the tibia is furnished, on the inferior surface, with a +crest that fits into the deep groove which is situated on the +corresponding surface of the astragalus. + +During flexion, the anterior surface of the foot tends to approach the +anterior surface of the leg, the angle formed by these two segments +becoming more and more narrowed. The displacement in the opposite +direction characterizes extension. + +In other quadrupeds, the articulations which bind together the bones of +the tarsus possess a little more freedom of movement. The shape of these +bones, and particularly the shape of the surfaces of the astragalus, +which are in contact with them, allow movements in this region, in the +case of the dog and cat, which, without being so extensive as those of +the human foot, in the subastragaloid articulation, nevertheless, recall +the mobility which we find in the human species at this level--that is +to say, rotation, abduction, and adduction of the foot. + +As for the articulations of the metatarsus with the phalanges, and of +the phalanges with one another, they resemble those of the anterior limb +too closely that it should be necessary to study them here. Such a study +would be, in this case, but a repetition (see p. 76, a description of +the articulations in question). + + +THE HEAD IN GENERAL, AND IN SOME ANIMALS IN PARTICULAR + +When we compare, by the examination of one of their lateral aspects, the +skull of man and the same region in other mammals, it is easy to observe +that the relative development of the cranium and face is entirely +different. In the case of man the cranium is large, and the face +relatively small; in animals the face is proportionally much more highly +developed. The measure of the facial angle permits us to note these +differences, and the figures relative to the value of this angle are +sufficiently demonstrative to induce us to indicate those which are, in +a general way, connected with some of the forms in individuals which +here occupy our attention. In the first place, we must remember that the +angle in question is more acute, as the cranium is less developed in +proportion to the facial region (Figs. 56 and 57). It is especially to +this character that we wish to draw attention. + + Man 70 deg.-80 deg. + Cat 41 deg. + Dog 28 deg.-41 deg. + Sheep 20 deg.-25 deg. + Ox 18 deg.-20 deg. + Ass 12 deg.-16 deg. + Horse 11 deg.-13 deg. + +Besides, in animals the cranium is very prominent superiorly, and the +face, more or less elongated, is sharply projected downwards and +forwards; in man the cranial region occupies not only the superior, but +also the posterior part; the face is short and of a compact form. The +human head, in its general aspect, may be compared to a sphere, while +the skull of the quadrupeds presents the aspect of a quadrangular +pyramid, with the base turned upwards and the summit at the incisor +teeth. + +=Direction of the Head.=--Before entering on the study of the bones of +the head, it is necessary, in our opinion, to agree as to the position +in which we shall suppose it to be placed. + +The question may seem to be one of little importance; nevertheless, it +cannot be regarded as indifferent, since authors are not all agreed on +this subject. + +Some suppose it to be placed vertically--that is, with the incisor teeth +turned directly downwards. Others, on the contrary, suppose it to be +placed horizontally, resting on the whole length of the lower jaw, the +face being then turned upwards. These two extreme methods of arrangement +appear to us to possess inconveniences--at least, for comparison with +the human head. + +[Illustration: FIG. 56.--HUMAN SKULL: MEASURE OF THE FACIAL ANGLE BY THE +METHOD OF CAMPER. ANGLE BAC = 80 deg. + +The internal wall of the cranial cavity is marked by the dotted line.] + +[Illustration: FIG. 57.--SKULL OF THE HORSE: MEASURE OF THE FACIAL ANGLE +BY THE METHOD OF CAMPER.[18] ANGLE BAC = 13 deg. + +The internal wall of the cranial cavity is shown by the dotted line.] + + [18] We have indicated on this sketch of the skull of the horse the + facial angle measured by the method of Camper, in order that the + correspondence with Fig. 56 may be more complete. But it is + certain that the procedure here employed is in practice not + satisfactory, since the apex of the angle, as we can demonstrate, + is found to be situated within the contour of the head, and that, + consequently, it is rather difficult to localize it precisely in + the case of a given skeleton. Further, because of the absence of + the base of the nose in the complete skull, the auriculo-nasal + line cannot be accurately fixed. It would be the same for most + other animals. This is why the method employed for these latter + is preferably that of Cuvier, or, again, that of Cloquet. In the + former, the apex of the angle of Camper is transferred to the + free border of the upper incisors, but these teeth may be absent, + and, on the other hand, ruminants are destitute of them. In the + second, the same apex is placed at the alveolar border, and the + angle then becomes fairly easy to appreciate. + +Indeed, if, when the head is vertical, the same regions of the face +(forehead, nose) are, in the case of animals as well as man, turned +forward, the lower jaw ceases to merit its appellation, as it is then +situated, not below, but behind the upper. Furthermore, if this +position is chosen, for example, for modelling or drawing, it cannot be +obtained without difficulty when we have to deal with an isolated piece +of the skeleton, on account of the absence of equilibrium, which it is +necessary to obviate. It is true that the question of convenience should +not take precedence of all others, and it suffices for us in this +connection to recall, in regard to the human pelvis, that, although the +older anatomists used to represent it as resting commodiously on the +three angles which terminate it at its lower part (ischial tuberosities +and coccyx), this attitude being false, it is customary now to incline +the superior aspect forwards, inasmuch as this arrangement more nearly +conforms to reality, in spite of the fact that it is a little more +difficult so to dispose an isolated pelvis. Further, to return to the +head; if its vertical direction can be demonstrated, for example, in +many horses, it is not sufficiently general to be adopted as the classic +position. + +In regard to the facility of placing in position, the horizontal +direction is certainly to be preferred; but this is also far removed +from the natural position in the animal while in the state of repose. On +the other hand, the mind is not satisfied with the idea that certain +regions of the face, such as the nose and the forehead, are then +directed upwards. And yet it is necessary to come to a decision, seeing +that what we are now investigating applies also to the position to which +it is necessary to give the preference in placing the skeleton of the +head when we wish to draw it in profile. That which we adopt is a +compromise, but to us it seems more rational. + +The position of the head of the horse, to be normal, should be such as +to give it an inclination of 45 deg. In this case the lower jaw is still +posterior; and, for this reason, we see in adopting this position some +inconveniences from a didactic point of view. Accordingly, we will +suppose the head brought a little nearer to the horizontal, and this, +from the imaginative point of view, has certainly an advantage which we +cannot afford to neglect when addressing artists. + +Indeed, let us suppose that to a clay model of a human head we wish to +give the aspect of the head of a quadruped. We should elevate the +occiput; and then, taking hold of the lower part of the face, we should +lengthen it, not in a direction precisely antero-posterior, but +downwards and forwards. It is obviously this latter procedure which, on +the other hand, is carried out when a person wishes to give to his own +face some resemblance to the muzzle of a quadruped. + +It is true that, in the position we have adopted, the face is directed +obliquely downwards and forwards, and that there may result a certain +confusion in describing the position of its different parts. On +this account, with the object of not making complications, we +purpose, for the present, to substitute, for example, for the term +'antero-superior'--which when speaking of the position of the forehead +and nose would be more exact--the term 'anterior,' which is sufficiently +comprehensible. The mouth will be, for the same reason, referred to as +being situated at the inferior part of the face, and not the +antero-inferior. + +=The Skull.=--The elevation of the cranial region becomes especially +appreciable when we examine the occipital bone. Before verifying this +fact, it is not superfluous to recall the general arrangement which this +bone presents in the human skull. A portion of the occipital bone +occupies the base of the skull; but this base in man is horizontal; to +this region succeeds the shell-shaped portion of the occipital bone, +which, passing vertically upwards, forms with the preceding portion an +angle situated at the level of the external occipital protuberance, and +of the curved line which starts from it on each side. In animals a +portion of the occipital bone is horizontal, it is true; but this bone +being sharply bent at the level of the occipital foramen and condyles, +the result is that the portion which surmounts these latter looks +backwards, and is limited above by the external occipital protuberance, +which forms the culminating point of the skull; this point is situated +between the ears. + +[Illustration: FIG. 58.--SKULL OF ONE OF THE FELIDAE (JAGUAR): LEFT +LATERAL ASPECT. + +1, Posterior surface of the occipital bone; 2, external occipital +protuberance; 3, condyle of the occipital bone; 4, jugular process; 5, +parietal bone; 6, frontal bone; 7, orbital process; 8, orbital cavity; +9, squamous portion of the temporal bone; 10, external auditory canal, +in front of which is situated the zygomatic process; 11, tympanic bulla; +12, superior maxillary bone; 13, intermaxillary or incisor bone; 14, +nasal bone; 15, anterior orifice of the nasal cavity; 16, malar bone; +17, ungual or lachrymal bone; 18, inferior maxillary bone; 19, condyle +of the inferior maxillary bone; 20, coronoid process; 21, incisor teeth; +22, canine teeth; 23, molar teeth.] + +[Illustration: FIG. 59.--SKULL OF THE LION: LEFT LATERAL ASPECT. + +This figure is intended to show that in the lion the contour of the face +between the nasal bones and the cranial region is more flattened than in +other felidae, such as the tiger, jaguar, panther, and domestic cat. This +difference is shown by comparison of this figure with the preceding one +(Fig. 58). We are indebted to M. Tramond, the well-known naturalist, for +the indication of this differential character which, from the artistic +plastic point of view, is one of real interest.] + +This protuberance, prolonged on each side by the superior curved line of +the occipital bone, is so much the more prominent as this bone bends +sharply a second time, so as to form a third portion, which, looking +forwards, forms part of the anterior aspect of the skull, and proceeds +to articulate with the parietals. On this third portion is found a crest +which, proceeding from the occipital protuberance, is continuous in +front with the parietal crests, to which we will again refer in speaking +of the parietal bones. + +On the inferior surface of the human occipital bone are found, at the +level of, and external to, the condyles two bony elevations which bear +the name of _jugular eminences_. They are long in quadrupeds, and +constitute what are designated by some authors the _styloid processes_, +but they must not be confounded with the processes of the same name +which in the case of man form part of the temporal bone. These processes +are very highly developed in the pig, horse, ox, and sheep. + +In the ox, the occipital bone is deprived of the protuberance, and is +not bent on itself in the anterior portion, neither does it form the +most salient part of the skull; this latter, which is situated at the +level of the horns, belongs to the frontal bone. In the pig, also, the +occipital bone is not bent upon itself in its anterior portion, but +forms the summit of the head. The occipital protuberance, hollowed on +its posterior surface, rises vertically, and rests upon the parietal +bone, with which it forms an acute angle. + +The parietals, two separate bones in the dog and the cat, but fused in +the median line in the ox, sheep, and horse, are of special interest in +regard to the two crests which, in the carnivora, and also in the pig +and the horse, occupy their external surface, and, after diverging from +one another, are continued by a crest which crosses the frontal bone +and ends at the external orbital process of the latter bone. + +These crests, known as the _parietal_ or _temporal crests_, recall both +in position and relations the temporal curved line of the parietal bone +of man. They contribute, as in the case of the latter, to the formation +of the boundaries of the temporal fossa. + +[Illustration: FIG. 60.--SKULL OF THE DOG: LEFT LATERAL ASPECT. + +1, Posterior surface of the occipital bone; 2, external occipital +protuberance; 3, occipital condyle; 4, jugular process; 5, parietal +bone; 6, frontal bone; 7, orbital process; 8, orbital cavity; 9, +external auditory canal, in front of which is found the zygomatic +process; 10, tympanic bulla; 11, superior maxillary bone; 12, +intermaxillary or incisor bone; 13, nasal bone; 14, anterior opening of +the cavity of the nasal fossae; 15, malar bone; 16, lachrymal bone; 17, +inferior maxillary bone; 18, condyle of the inferior maxillary bone; 19, +coronoid process; 20, incisor teeth; 21, canine teeth; 22, molar teeth.] + +In the carnivora, these crests are situated, throughout their whole +length, in the median line, the temporal fossae being, accordingly, as +extended as they possibly can be. In certain species, the development of +these crests is such that they form by their union a vertical plate, +which, in separating the two temporal fossae, gives them a greater depth. +In the pig, the parietal crests, analogous in this respect to the +temporal curved lines of the parietal bones of man, are separated by an +interval, proportionately less extended, however, than that of the human +skull. The parietal bone in the ox and the sheep does not enter into the +formation of the anterior surface of the skull; it is formed by an +osseous plate, narrow and elongated transversely, which, with the +occipital bone, constitutes the base of the region of _the nape of the +neck_. It is bent upon itself at the level of its lateral portions so as +to occupy the temporal fossa. + +The anterior surface of the frontal bone, which is depressed in the +median line in the dog, but plane in the horse, is limited by two +crests, which, situated on the prolongation of the parietal crests, +diverge more and more from one another in proportion as they occupy a +lower position. This surface terminates externally in two processes, +which are the homologues of the external orbital processes of the human +frontal bone. + +The superior border of these orbital processes, situated on the +prolongation of the corresponding parietal crests, contributes to limit +the temporal fossa. Each of these orbital processes terminates in the +following manner: In the bear, dog, cat, and pig, in which the orbital +cavities are incompletely bounded by bone, this process, slightly +developed, is not in connection, by its inferior extremity, with any +other part of the skeleton of the region. In the ox and the sheep, it +articulates with a process of the malar bone. In the horse, it +articulates with the zygomatic process of the temporal bone. The +inferior margin of this process forms a part of the boundary of the +anterior opening of the orbital cavity. + +The supra-orbital foramen, which does not exist in carnivora, occupies +in the horse the base of the orbital process. In the ox, it is situated +a little nearer the middle line; and its anterior orifice opens into an +osseous gutter which is directed upwards towards the base of the horn, +while inferiorly it meets the inferior border of the frontal bone; in +the sheep this groove is but slightly developed. In this latter, as in +the ox, it is the frontal bone which forms the most elevated portion of +the skull. In fact, being bent upon itself at a certain level, its +external surface is formed of two planes: one, posterior, which is +inclined downwards and directed backwards; the other, anterior, is also +inclined downwards, but with a forward obliquity. At the union of these +planes the bone forms an elbow, on either side of which are found the +osseous processes on which the horns are mounted. + +[Illustration: FIG. 61.--SKULL OF THE PIG: LEFT LATERAL ASPECT. + +1, Occipital bone; 2, condyle of the occipital; 3, jugular process; 4, +parietal bone; 5, parietal crests; 6, frontal bone; 7, orbital process; +8, orbital cavity; 9, external auditory canal; 10, zygomatic process; +11, superior maxillary bone; 12, intermaxillary or incisor bone; 13, +nasal bone; 14, anterior orifice of the cavity of the nasal fossae; 15, +malar bone; 16, lachrymal bone; 17, inferior maxillary bone; 18, condyle +of the inferior maxillary bone; 19, incisor teeth; 20, canine teeth; 21, +molar teeth.] + +In the bear, the anterior margin of the frontal bone is prolonged by two +small tongues of bone, which, descending on the lateral borders of the +nasal bones, articulate with the superior half of the latter. + +The temporal bone is, as in man, furnished with a squamous portion, +from which springs the zygomatic process, which is directed towards the +face, to terminate in the following manner: in the carnivora, the pig, +and ruminants, it articulates with the malar bone by its inferior +border; in the horse, it insinuates itself as a sort of wedge between +the malar bone and the orbital process of the frontal bone, with which +it articulates, as we have already pointed out, and contributes, by a +portion situated in front of this articulation, to form the boundary of +the anterior opening of the corresponding orbital cavity. As in man, the +zygomatic process arises by two roots: one, transverse, behind which is +situated the glenoid cavity of the temporal bone; the other, +antero-posterior, which proceeds to join above with the superior curved +line of the occipital bone. + +Behind the glenoid cavity is found the external auditory canal, and, +further back still, the mastoid process. This latter, but slightly +developed in the carnivora, a little more so in the ruminants, and still +more in the horse, has its external surface traversed by a crest, _the +mastoid crest_, which, after becoming blended with the antero-posterior +root of the zygomatic process, proceeds with this latter to join the +superior occipital curved line. + +Below the auditory canal is situated a round prominence, highly +developed in carnivora; this is _the tympanic bulla_, also called _the +mastoid protuberance_; it is an appendage of the tympanum. + + +The Face + +The bone of this region, around which all the others come to be grouped, +is, as in man, the superior maxillary. The relations of this maxillary +with the neighbouring bones is not exactly the same in all animals; for +example, in the ox, sheep, and horse, in which the bones of the nose are +wide in their upper part, and in which the lachrymal bone, which is very +highly developed, encroaches on the face, the superior maxillary does +not meet the frontal bone; it is separated from it by the above-named +bones. It unites with it, on the other hand, in the dog and the cat. In +the bear, it is separated from the bones of the nose by a small tongue +of bone which springs from the anterior border of the frontal--a +process which we have noticed in connection with this latter. + +[Illustration: FIG. 62.--THE SKULL OF THE OX: LEFT LATERAL ASPECT. + +1, Occipital condyle; 2, jugular process; 3, parietal bone; 4, frontal +bone; 5, osseous process, which serves to support the horn (horn-core); +6, orbital cavity; 7, external auditory canal, in front of which is +found the zygomatic process; 8, temporal fossa; 9, superior maxillary +bone; 10, intermaxillary or incisor bone; 11, nasal bone; 12, anterior +orifice of the cavity of the nasal fossae; 13, malar bone; 14, lachrymal +bone; 15, inferior maxillary bone; 16, condyle of the inferior maxillary +bone; 17, incisor teeth; 18, molar teeth.] + +In the pig, ox, sheep, and horse, the external surface is traversed, to +a greater or less extent, by a crest which is situated on the +prolongation of the inferior border of the malar bone. This crest, which +is straight in the horse, but curved with its convexity upwards in the +ox and the sheep, is known as _the maxillary spine_ or _the malar +tuberosity_: it gives attachment to the masseter muscle, and, in the +horse, is distinctly visible under the skin. It does not exist in the +carnivora. On the same surface is situated the sub-orbital foramen. + +The inferior border is hollowed out into alveoli, in which are implanted +the superior molar and canine teeth. This border is prolonged forwards +from the alveolus, which corresponds to the first molar tooth, to +terminate, after a course more or less prolonged, at the alveolus of the +canine. This space, more or less considerably expanded, which thus +separates these teeth is called the _interdental space_; but this +denomination is not applicable to ruminants, because these latter +possess neither canine nor incisor teeth in the upper jaw (see p. 125, +dentition of the ox and sheep). The superior maxillary bone of one side +and that of the opposite side do not meet in the median line in the +region which corresponds to the incisor teeth; they are separated by a +bone which, in the human species, is present only at the commencement of +life, and afterwards coalesces with the maxilla; this is the +intermaxillary or incisor bone. This bone, which is paired, is formed of +a central part, which bears the superior incisor teeth; it is prolonged +upwards and backwards by two processes: one, external, which insinuates +itself between the superior maxillary and the nasal bone, except in the +sheep, in which it remains widely separated from the latter; the other, +internal, which is united to that which belongs to the bone of the +opposite side to form part of the floor of the cavity of the nasal +fossae; the external border of this process, which is separated from the +body of the bone by a notch, forms the internal boundary of the +corresponding _incisor opening_ or the _incisor slit_. Owing to the +absence of superior incisors in ruminants, the intermaxillary bone +presents no alveoli. + +The malar bone, and the os unguis or lachrymal, are more or less +developed according to the species considered. With regard to the malar +bone, it is most important to notice the part which it takes in the +formation of the zygomatic arch, and that its inferior border +contributes to form the crest to which is attached the masseter muscle. + +As for the nasal bones, they present differential characters which, as +they affect the form of the region which they occupy, are worthy of +notice. + +[Illustration: FIG. 63.--SKULL OF THE HORSE: LEFT LATERAL ASPECT. + +1, Posterior surface of the occipital bone; 2, external occipital +protuberance; 3, occipital condyle; 4, jugular process; 5, parietal +bone; 6, frontal bone; 7, orbital cavity; 8, zygomatic process of the +temporal bone; 9, external auditory canal; 10, mastoid process; 11, +superior maxillary bone or _maxilla_; 12, intermaxillary or incisor +bone; 13, nasal bone; 14, anterior orifice of the cavity of the nasal +fossae; 14', malar bone; 15, lachrymal bone; 16, inferior maxillary bone +or _mandible_; 17, inferior maxillary fissure; 18, condyle of the +inferior maxillary bone; 19, coronoid process of the inferior maxillary +bone; 20, incisor teeth; 21, canine teeth; 22, molar teeth.] + +Their dimensions in length are proportional to those of the face. Very +small in man, they are more developed in carnivora. We recognise in the +latter the two curves which characterize them in the human species, and +which we clearly notice when we view them on one of their lateral +aspects: a concavity above, and a convexity below. These curves are more +or less accentuated--very strongly marked in the bulldog, and scarcely +at all in the greyhound. Moreover, in the carnivora also the nasal bones +are wider below than above, and form, by their junction, a semicircular +notch which limits, in its superior portion, the anterior opening of the +cavity of the nasal fossae. In the horse they present an opposite +arrangement with regard to their dimensions in width; broad above, each +terminates below by forming a pointed process which, separated from the +intermaxillary bones, is prolonged in front of the nasal orifice. + +The inferior maxillary bone is, as in man, formed of a body and two +branches. But among the many special characteristics of form and size +which sharply differentiate it from the human bone, one detail must be +indicated; this is the absence of a mental prominence. Hence it results +that the anterior border of the body of the lower jaw, instead of being +directed obliquely downwards and forwards, is, on the contrary, oblique +downwards and backwards, and that in certain animals this border is +actually found almost exactly on the prolongation of the inferior border +of the body of the bone. + +On the external surface of the body are found the three mental foramina. +The superior border is hollowed out by alveoli. + +With regard to the branches (_rami_), they terminate in two processes: +one, the posterior, is the condyle; the other, situated more forwards, +is the coronoid process, which gives insertion to the temporal muscle. +These two processes are separated by the sigmoid notch. + +For reasons which we will explain further on (see p. 127, movements of +the lower jaw), the condyle presents differences of form. In the +carnivora, it is strongly convex from before backwards, expanded +transversely, and firmly mortised in the glenoid cavity of the temporal +bone; in the ruminants, it is less convex from before backwards, it is +more slightly concave in the transverse direction; in the rodents--we +give as an example the hare (Fig. 64)--the condyle is still convex from +before backwards, but it is flattened from without inwards. + +In the animals in which the muscles of mastication are very highly +developed, and especially in the carnivora, the osseous regions occupied +by these muscles are more extensive and more deep than in the human +species. The length of the coronoid process, the depth of the temporal +fossa, the extent of the zygomatic arch, the appearance of the external +surface of each of the rami of the lower jaw, deeply hollowed out for +accommodation of the masseter, and to provide extensive surfaces of +insertion for this muscle, are sure proofs furnished by the skeleton of +the occasionally enormous development of the muscles of mastication. + +In the carnivora, a rather strong process, which is directed backwards, +occupies the angle of the inferior maxilla; it is, accordingly, situated +below the region of the condyle. + +[Illustration: FIG. 64.--SKULL OF THE HARE: LEFT LATERAL ASPECT. + +1, External occipital protuberance; 2, occipital condyle; 3, parietal +bone; 4, frontal bone; 5, orbital process; 6, orbital cavity; 7, +zygomatic process; 8, external auditory canal; 9, superior maxillary +bone; 10, intermaxillary or incisor bone; 11, nasal bone; 12, anterior +opening of the nasal fossa; 13, malar bone; 14, inferior maxillary bone; +15, condyle of the inferior maxillary bone; 16, incisor teeth; 17, molar +teeth.] + +The teeth which the jaws carry vary in number, and even in appearance, +according to species; it is useful to note their differences. In order +to establish the nature of these latter more effectively, we will first +recall the fact that in man the teeth, thirty-two in number, are equally +distributed between the jaws, and are divided into incisors, canines, +and molars, of which the arrangement is thus formulated: + + 5_m._ 1_c._ 2_i._ | 2_i._ 1_c._ 5_m._ + --------------------+-------------------- = 32.[19] + 5_m._ 1_c._ 2_i._ | 2_i._ 1_c._ 5_m._ + + [19] _I.e._, _i_, incisors; _c_, canines; _m_, molars. + +We also note that the incisors are edged, the canines are pointed, and +that the molars, cubical in shape, have their surface of contact +provided with tubercles. + +The teeth of the cat are thirty in number; they are thus arranged: + + 4_m._ 1_c._ 3_i._ | 3_i._ 1_c._ 4_m._ + --------------------+-------------------- = 30. + 3_m._ 1_c._ 3_i._ | 3_i._ 1_c._ 3_m._ + +Those of the dog number forty-two: + + 6_m._ 1_c._ 3_i._ | 3_i._ 1_c._ 6_m._ + --------------------+-------------------- = 42. + 7_m._ 1_c._ 3_i._ | 3_i._ 1_c._ 7_m._ + +In these animals, the incisors, such as are not damaged by use, are +furnished, on the free border of their crown, with three tubercles, of +which one, the median, is more developed than those which are situated +laterally. We denote these teeth, commencing with those nearest the +median line, by the names _central incisors_ or _nippers_, +_intermediate_ and _corner incisors_. The canines, or _fangs_, are long +and conical; they are curved backwards and outwards. The upper canines, +which are larger than those of the lower jaw, are separated from the +most external of the incisors (_corner_) by an interval in which the +canines of the lower jaw are received. The lower canines, on the other +hand, are in contact with the neighbouring incisors, and are each +separated from the first molar which succeeds them by a wider interval +than that which is situated between the corresponding teeth in the upper +jaw. + +The molars differ essentially from the teeth of the same class in the +human species. Their crown terminates in a cutting border bristling with +sharp-pointed projections; this formation indicates that these teeth are +principally designed for tearing. During the movement of raising the +lower jaw, which is so energetic in the carnivora, they act, indeed, in +the same manner as the two blades of a pair of scissors. The largest +molars are: in the dog, the fourth of the upper jaw, and the fifth in +the opposite one; in the cat, the third both above and below. + +The pig has forty-four teeth disposed in the following manner: + + 7_m._ 1_c._ 3_i._ | 3_i._ 1_c._ 7_m._ + --------------------+-------------------- = 44. + 7_m._ 1_c._ 3_i._ | 3_i._ 1_c._ 7_m._ + +Of the incisors, the nippers and the intermediate ones of the upper jaw +have their analogues in those of the horse; in the lower jaw, the +corresponding teeth, straight, and directed forward, rather resemble the +same incisors in rodents. The corner incisor teeth are much smaller, and +are separated from the neighbouring teeth. The canine teeth, also called +_tusks_ or _tushes_, are greatly developed, especially in the male. The +molars increase in size from the first to the last; they are not +cutting, as in the carnivora, but they are not flattened and provided +with tubercles on their surfaces of contact as in the herbivora. + +In the ox and the sheep the teeth are thirty-two in number: + + 6_m._ 0_c._ 0_i._ | 0_i._ 0_c._ 6_m._ + --------------------+-------------------- = 32. + 6_m._ 0_c._ 4_i._ | 4_i._ 0_c._ 6_m._ + +As we see from this dental formula, the incisors are found only in the +lower jaw; they are replaced in the upper jaw by a thick cartilaginous +pad on which the inferior incisors find a surface of resistance. + +These have their crowns flattened from above downwards, and gradually +become thinner from the root to the anterior border, which is edged and +slightly convex. These teeth gradually wear away. In proportion to the +progress of this wear, on account of the fact that it involves the +anterior borders and upper surfaces of the incisor teeth, and that these +teeth are narrower towards the root than at the opposite extremity, the +intervals which separate them tend to become wider and wider; and when +the roots become exposed by the retraction of the gums, they are then +separated from one another by a considerable interval. The molars have +their grinding surface comparable to that of the horse; they increase in +size from the first to the sixth. + +The teeth of the horse are forty in number; they are thus distributed: + + 6_m._ 1_c._ 3_i._ | 3_i._ 1_c._ 6_m._ + --------------------+-------------------- = 40. + 6_m._ 1_c._ 3_i._ | 3_i._ 1_c._ 6_m._ + +As they become worn, these teeth continue to grow, and as, on the one +hand, this phenomenon takes place throughout the whole life of the +animal, and, on the other hand, the process of wear brings out and makes +visible at the surface of friction parts formerly deeper and deeper, and +of which the configuration varies at different levels, there result +special features which permit the determination of the age of the animal +by an examination of its jaws. The incisors are called, commencing with +those situated nearest the middle line, _central incisors_ or _nippers_, +_intermediate_ and _corner incisors_. The canines, also designated as +the _fangs_, exist only in the male. It is exceptional to find them in +the mare, and when they exist in this latter they are less developed +than those of the horse. The molars have cuboid crowns; the surface of +friction is almost square in the case of the upper molars, and is +inclined so as to look inwards; in the case of the inferior ones, it is +a little narrowed, and is inclined so as to look outwards. In the upper +jaw the external surface of the crown is hollowed by two longitudinal +furrows; in the lower jaw the same surface has only one furrow, which at +times is but slightly marked. + +In the hare the teeth are twenty-eight in number: + + 6_m._ 0_c._ 2_i._ | 2_i._ 0_c._ 6_m._ + --------------------+-------------------- = 28. + 5_m._ 0_c._ 1_i._ | 1_i._ 0_c._ 5_m._ + +The four incisors of the upper jaw are divided into two groups; one of +these is formed by the two principal teeth, the other by two very small +incisors which are placed behind the preceding. + +Having studied the jaws and examined the arrangement of the teeth, we +should say a few words on the movements which the lower jaw is able to +execute. In man, these movements are varied in character: the jaw is +lowered and raised; it can also be projected forwards and drawn +backwards, or carried to the right or left side by lateral movements. +Owing to the different modes of nutrition of animals, with which the +shape of the teeth is clearly correlated, being more specialized than in +the human species, the lower jaw is moved in a fashion less varied and +in the direction most suitable for the mastication of the foods which +form the aliment of the species considered. Moreover, this is plainly +shown in the skeleton by the shape of the condyle of the lower jaw (see +p. 122, different forms of this condyle). In the carnivora, whose teeth, +as we have seen, are all cutting ones, the jaw rises and falls; the food +then is, if we consider the two jaws, cut as by the blades of a pair of +scissors. In the ruminants, the incisors exist only in the lower jaw, +but the molars are thick and well developed; the food is ground by these +latter as by millstones, and the movements which favour this action are, +above all, the lateral. As for the rodents, in which the incisors are +formed for filing down and cutting through hard resisting bodies, their +lower jaw moves in the antero-posterior direction, in such a way that +the inferior incisors alternately advance and recede beneath those of +the upper jaw. The free cutting border of these teeth effectively +fulfils the function to which they are destined; their constant wear +preserves and revivifies the chisel edge which characterizes them, +without leading to their destruction, for the incisors in rodents are of +continuous growth. + + +THE SKULL OF BIRDS + +=The Skull of Birds= (Fig. 65).--If, because it is less important from +the artistic point of view, we do not consider it necessary to describe +in detail the skull of birds, we yet think it useful to indicate, in +their general lines, the peculiarities it presents. + +In this group the skull is generally pear-shaped; to the cranium, of +which the bones are arranged in such a way as to give it a form more or +less spherical, succeeds a face more or less elongated, according as the +bill is more or less developed. + +In general, the bones of the skull coalesce very early, with the result +that it is only in very young individuals that we can determine their +presence. + +We find the skull to consist of an occipital bone, two parietals, a +frontal, etc.; we will indicate but one detail in connection with these +bones: it is the presence of a single condyle for the articulation of +the occipital bone with the atlas. We also note the quadrate bone, which +is situated on the lateral part of the cranium, is movable on this +latter, and acts as an intermediary between it, the bones of the face, +and the lower jaw. The quadrate bone is regarded as a detached portion +of the temporal; on the signification of this we do not now propose to +dwell. + +[Illustration: FIG. 65.--SKULL OF THE COCK: LEFT LATERAL SURFACE. + +1, Occipital bone; 2, parietal bone; 3, frontal bone; 4, ethmoid bone; +5, cavity of the tympanum; 6, quadrate bone; 7, superior maxillary bone; +8, malar bone; 9, nasal bone; 10, 10, intermaxillary bone; 11, nasal +orifice; 12, os unguis or lachrymal bone; 13, inferior maxillary bone.] + +On the anterior portion of the face we find the nasal bones, which, +articulating with the frontal on one side, circumscribe, on the other, +the posterior border of the nares. The nasal bone of the one side is +separated from that of the opposite by the intermaxillary or +premaxillary bone, which forms the skeleton of the superior mandible. + +The superior maxillaries, which are rudimentary, are situated on the +lateral parts, and prolonged backward by an osseous style which +articulates with the quadrate bone; this styloid bone, the homologue of +the malar, is designated by certain authors as the _jugal_ or +_quadrato-jugal_ bone. + +It is with the quadrate bone also that the inferior maxillary +articulates. + + + + +CHAPTER II + +MYOLOGY + + +The first point to decide in commencing this study is the order in which +we shall consider the different muscles which we have to examine. It +must not be forgotten that in the present work we compare the +organization of animals with that of man, which we already know, and +that it is on the construction of this latter that, in these studies, +the thought must at each instant be carried back in order to establish +this comparison. Now, the general tendency which we notice in our +teaching of anatomy, when one regards the region of the trunk in the +human figure (a living model or a figure in the round), is first to +consider the anterior aspect. It is the latter that, for this reason, we +study at the very beginning; we next deal with the posterior surface of +the trunk, because it is opposite; lastly, the lateral surfaces, because +they unite with the preceding surfaces, the one to the other. + +In studying an animal, it is usually by one of its lateral aspects that +one first observes it; it is, in fact, by these aspects that it presents +its greatest dimensions, and that the morphological characters as a +whole can be more readily appreciated. Hence, possibly, the order of +description adopted in most texts, or in the figures which accompany +them. The first representation of the human figure as a whole, in a +treatise on anatomy, represents the anterior aspect; the first view of +the horse as a whole, in a treatise on veterinary anatomy, for example, +is, on the other hand, a lateral view. + +We break with this latter custom, and, without taking into account the +tendency above indicated, we will commence our analysis with the study +of the aspect of the trunk, which corresponds to the anterior aspect of +the same region in man. + +The first muscles usually presented for study to artists being the +pectorals, it is their homologues that we will first describe here. We +will afterwards describe the abdominal region, then the muscles which +occupy the dorsal aspect of the trunk. With regard to the lateral +surfaces, they will be found, by this fact alone, almost completely +studied, since the muscles of the two preceding (back and abdomen), +spreading out, so to speak, over them, contribute to their formation. +Nothing further will remain but to incorporate with them the muscles of +the shoulder; but these will be studied in connection with the anterior +limbs, from which they cannot be separated. + +The neck, in man, may be considered in an isolated fashion, because, on +account of its narrowness in proportion to the width of the shoulders, +it is clearly differentiated from the trunk; for this reason we combine +the study of it with that of the head. In animals, because of the +absence or slight development of the clavicles, the neck is generally +too much confounded with the region of the shoulders to make it +legitimate to separate it from that region in too marked a fashion. It +will, accordingly, be considered next. + +We will then undertake the study of the muscles of the limbs, and end +with the myology of the head. + + +THE MUSCLES OF THE TRUNK + +We shall divide them into muscles of the thorax, of the abdomen, and of +the back. + + +Muscles of the Thorax + +=The Pectoralis Major= (Fig. 66, 1, 2; Fig. 67, 3, 4; Fig. 68, 7; Fig. +69, 10; Fig. 70, 11).--Further designated by the name of _superficial +pectoral_, this muscle is described in treatises on veterinary anatomy +as formed of two portions: an anterior one, called the _sterno-humeral_ +muscle; the other, situated below and behind the preceding, bearing the +name of _sterno-aponeurotic_. + +It occupies the region of the breast, and, as a whole, it takes origin +from the median portion of the sternum, from which it is directed +towards the arm and forearm. + +The anterior portion (sterno-humeral muscle)--thick, forming an +elevation under the skin, and really constituting the pectoral +region--is directed downwards and outwards to be inserted into the +anterior margin of the humerus--that is to say, to the ridge which +limits in front the spiral groove of this bone. + +The other part (sterno-aponeurotic muscle) is situated more posteriorly, +and corresponds to the region known in veterinary anatomy as the +_inter-fore-limb space_, which is limited laterally on each side by the +superior portion of the forearm, of which the point of junction with the +trunk bears the name _ars_. Arising from the sternum, as we have above +indicated, this portion is directed outwards, to be joined with the +terminal aponeurosis of the sterno-humeral, and with that which covers +the internal surface of the forearm. + +All things considered, the sterno-humeral muscle may be regarded as the +representative of the upper fibres of the great pectoral of man, of +which the attachments, owing to the more or less complete absence of the +clavicle in the domestic mammals, the fibres must be concentrated on +the sternum; the sterno-aponeurotic portion then representing the +inferior fasciculae of the same muscle. + +[Illustration: FIG. 66.--MYOLOGY OF THE HORSE: ANTERIOR ASPECT OF THE +TRUNK. + +1, Pectoralis major (sterno-humeral); 2, pectoralis major +(sterno-aponeurotic); 3, mastoido-humeralis; 4, point of the shoulder; +5, sterno-mastoid or sterno-maxillary: 6, inferior portion of the +platysma myoides of the neck, divided; 7, triceps cubiti; 8, brachialis +anticus; 9, radialis (anterior extensor of the metacarpus); 10, scapular +region.] + +The great pectoral muscle of one side is separated from that of the +opposite side along the median line, and especially above and in front, +by a groove which is more or less deep, according as the muscles are +more or less developed. At the bottom of this groove, suggestive of that +which exists in the corresponding region in man, is found, as in this +latter, the median portion of the sternum. + +The preceding description particularly applies to the arrangement which +the great pectoral presents in the horse; in other animals it is marked +by some distinctive characters. In the pig, it is inserted into the +sternum as far only as the level of the third costal cartilage; in the +ox and sheep, it extends as far as the sixth; in the dog, it is +attached to the two first sternal pieces only--that is to say, as far as +the third costal cartilage. Moreover, in the latter, as in the cat, the +two portions which we have indicated are less readily distinguished. + +The great pectoral, by its contraction, draws the fore-limb towards the +middle line--that is to say, adducts it. + +=The Pectoralis Minor= (Fig. 67, 6; Fig. 68, 8; Fig. 69, 11; Fig. 70, +12, 26).--This muscle, also called the _deep pectoral_, is, in animals, +larger than the superficial pectoral, therefore certain authors prefer +to give to this muscle and the preceding one the names of deep and +superficial pectoral respectively. This nomenclature is evidently +legitimate, and conforms more to reality, since it does not bring in the +notion of dimensions which here is found in contradiction to +nomenclature; but, in order to establish more clearly the parallelism +with the corresponding muscles in man, we think it better, nevertheless, +to give them the names by which it has been customary to designate them +in connection with the latter. + +We will recall at the outset that the lesser pectoral muscle in man is +completely covered by the great. In animals this is not the case; the +lesser pectoral being very highly developed, projects beyond the great +pectoral posteriorly, and occupies to a greater or less extent the +inferior surface of the abdomen. + +It also consists of two parts: one anterior, which we designate by the +name of _sterno-prescapular_; the other, posterior, bearing that of +_sterno-humeral_.[20] + + [20] This division of the pectorals certainly complicates the + nomenclature of these muscles; nevertheless, it introduces no + insuperable difficulty from the mnemonic point of view. But where + the study becomes less profitable, and comparison with the + corresponding muscles in man more complicated, is in adopting the + nomenclature of Bourgelat. Indeed, the great pectoral is + designated by this author the 'common muscle of the arm and + forearm,' while the lesser pectoral (or deep pectoral) is called + the 'great pectoral' in its sterno-trochinian and 'lesser + pectoral' in its sterno-prescapular portion. We do not consider + it necessary to give the other theories relative to the + homologies of these, notwithstanding the very real interest which + they present from the purely anatomical point of view, as they + have but few applications in the study of forms. + +The sterno-prescapular muscle, being covered by the sterno-humeral, has +little interest for us. It arises from the sternum, and is directed +towards the angle formed by the junction of the scapula and humerus; +then it is reflected upwards and backwards, to terminate on the anterior +margin of the shoulder by insertion into the aponeurosis, which covers +the supraspinatus muscle. + +We can, especially in the horse after removal of the skin, recognise it, +at the level of this region, in the interspace limited by the +superficial muscles (Fig. 70, 26). + +In the dog and cat this portion of the muscle does not exist. The other +division of the muscle, the sterno-trochinian, is more interesting. It +arises from the abdominal aponeurosis and the posterior part of the +sternum; hence it passes forward, turns under the superficial pectoral, +and is inserted into the lesser tuberosity (trochin) of the humerus. + +In the pig, dog, and cat, it is inserted into the greater tuberosity +(trochiter) of the bone of the arm. + +The superior border of this muscle is in relation with a superficial +vein, which is distinctly visible in the horse--the subcutaneous +thoracic vein, which in this animal is called the vein of the spur. + +The sterno-humeral muscle, in contracting, draws the shoulder and the +whole anterior limb backwards. + +=Serratus Magnus= (Fig. 67, 2; Fig. 69, 8; Fig. 70, 9).--This muscle, +which is situated on the lateral aspect of the thorax, is covered to a +considerable extent by the shoulder, the posterior muscular mass of the +arm, and by the great dorsal muscle. + +It arises by digitations from the external surface of the dorsal +vertebrae; from the first eight in the horse, ox, and dog. + +[Illustration: FIG. 67.--MYOLOGY OF THE HORSE: INFERIOR ASPECT OF THE +TRUNK. + +1, Anterior extremity of the sternum; 2, point of the shoulder and +inferior portion of the mastoido-humeral muscle; 3, pectoralis major +(sterno-humeral); 4, pectoralis major (sterno-aponeurotic); 5, point of +the elbow; 6, pectoralis minor (sterno-trochinian); 7, serratus magnus; +8, external oblique; 9, sheath of the rectus abdominis; 10, linea alba; +11, the umbilicus; 12, external oblique divided in order to expose the +rectus abdominis; 13, rectus abdominis.] + +The muscular bundles, converging as they proceed, towards the scapula, +pass under this bone, to be inserted into the superior portion of the +subscapular fossa, near the spinal border. The inferior portion of its +posterior digitations is visible in the ox and in the horse; these +digitations are less visible in the pig. They are not seen at all in the +dog (Fig. 68) or cat, for in these animals the great dorsal muscle +covers them completely. + +The great serratus muscle, by the position which it occupies and the +arrangement that it presents, forms with the corresponding muscle of the +opposite side a sort of girth, which supports the thorax, and at the +same time helps to fix the scapula against the latter. + +When it contracts, in taking its fixed point at the ribs, it draws the +superior portion of the scapula downwards and backwards in such a way +that this bone has its inferior angle directed forwards and upwards. If +it takes its fixed point at the shoulder, it then acts on the ribs, +raises them, and so becomes a muscle of inspiration. + +Because of the connections of the serratus magnus with the levator +anguli scapulae, some authors consider it as united with the latter. But +as the latter muscle is visible only in the region of the neck (see p. +157), and as it is separately described in man, we prefer to distinguish +them from one another. We shall recall the connections to which we have +just made allusion when describing the cervical region. + + +Muscles of the Abdomen + +The abdominal wall is, as in man, formed by four large muscles: the +external oblique, the internal oblique, and the transversalis, which +form the lateral walls, and the rectus abdominis, situated on each side +of the middle line of the abdomen. This latter, because of the general +direction of the trunk in quadrupeds, has its superficial surface +directed downwards. + +The arrangement of these muscles closely corresponds to that which we +find in the human species. + +=The External Oblique Muscle= (Fig. 67, 8, 12; Fig. 68, 5; Fig. 69, 9; +Fig. 70, 10).--This muscle arises, by digitations, from a number of +ribs, which varies according to the species, the number of the ribs +being itself variable for each of them, as we pointed out in connection +with the osteology of the thorax. Indeed, the great oblique arises from +the eight or nine posterior ribs in the dog and the ox, and from the +thirteen or fourteen posterior in the horse. It is attached, besides, to +the dorso-lumbar aponeurosis. + +These attachments are arranged in a line directed obliquely upwards and +backwards, and the first digitations--that is to say, the most anterior +ones--dovetail with the posterior digitations of origin of the great +serratus muscle. + +The fleshy fibres are directed downwards and backwards, and terminate in +an aponeurosis which covers the inferior aspect of the abdomen, and +proceeds to form the linea alba by joining with that of the muscle of +the opposite side, and also to be inserted into the crural arch. + +This aponeurosis of the external oblique is covered by an expansion of +elastic fibrous tissue, which doubles it externally, and which is known +as the _abdominal tunic_. This latter is further developed as the organs +of the digestive apparatus are more voluminous, and their weight, +consequently, more considerable. For this reason, in the large +herbivora, as the ox and the horse, this tunic is extremely thick, +whereas in the pig, cat, and dog it is, on the contrary, reduced to a +simple membrane. Indeed, in these latter, the abdominal viscera being +less developed, the inferior wall of the abdomen does not require so +strong a fibrous apparatus for supporting them. The great oblique, when +it contracts, compresses the abdominal viscera in all circumstances +under which this compression is necessary; it also acts as a flexor of +the vertebral column. + +=The Internal Oblique Muscle.=--This muscle, which is covered by the +preceding, arises from the anterior superior iliac spine (external angle +in ruminants and solipeds) and the neighbouring parts. From this origin +its muscular fibres, the general direction of which is opposite to that +of the fibres of the external oblique, diverging, proceed to terminate +in an aponeurosis, which contributes to the formation of the _linea +alba_, and to be attached superiorly to the internal surface of the last +costal cartilages. It has the same action as the great oblique. What it +presents of special interest is the detail of form which it determines +in the region of the flank; this detail is _the cord of the flank_. It +is characterized by an elongated prominence which, starting from the +iliac spine, is directed obliquely downwards and forwards, to terminate +near the cartilaginous border of the false ribs. + +Often very apparent in the ox, and still more so in the cow, the cord in +question contrasts with the depression which surmounts it; this +depression is situated below the costiform processes of the lumbar +vertebrae, and is called the _hollow of the flank_. It is so much the +more marked as the mass of the intestinal viscera is of greater weight. + +We sometimes meet with a case of the presence of this hollow in the +horse. But when in the latter, the flank is well formed, the hollow is +scarcely visible, and the cord but slightly prominent. It is only in +emaciated subjects that these details are found clearly marked. + +=Transversalis Abdominis.=--This muscle being deeply situated does not +present any interest for us. We will, however, point out, in order to +complete the series of muscles which form the abdominal wall, that the +direction of its fibres is transverse, and that they extend from the +internal surface of the cartilages of the false ribs, and the costiform +processes of the lumbar vertebrae to the _linea alba_. + +=The Rectus Abdominis= (Fig. 67, 13; Fig. 68, 6).--This muscle, +enclosed, as it is in man, in a fibrous sheath (Fig. 67, 9) formed by +the aponeuroses of the lateral muscles of the abdomen, is a long and +wide fleshy band, which, as in the human species, reaches from the +thorax to the pubis. + +What distinguishes it in quadrupeds is that there are costal attachments +which extend further on the sternal surface of the thorax, and the +number of its aponeurotic insertions, which, in general, is more +considerable. These are, indeed, six or seven in number in the pig and +in ruminants, and about ten in the horse. + +It is true that we may find but three in the cat and dog; still, we +often find as many as six. These intersections are not marked on their +exterior by transverse grooves, such as we find in the human species in +individuals with delicate skin and whose adipose tissue is not very much +developed. + +The rectus abdominis is covered, in its anterior portion, by the +sterno-trochinian muscle (posterior segment of the small pectoral). In +contracting, this muscle brings the chest nearer the pelvis, and as a +result flexes the vertebral column. It also contributes to the +compression of the abdominal viscera. + +=Pyramidalis Abdominis.=--This unimportant little muscle, which in man +is situated at the lower part of the abdomen, extends from the pubis to +the _linea alba_. It is not present in the domestic animals. + +We consider it interesting, however, to point out, although the fact is +not a very useful one as regards external form, that this muscle is +distinctly developed in marsupials. + +We know that in the opossum, the kangaroo, and the phalanger fox, the +young are brought forth in an entirely incomplete state of development, +and that, during a certain period, they are obliged to lodge in a pouch +which is placed at the lower part of the abdomen of the mother. Now, +this pouch contains the mammary glands; but the young, being too feeble +to exercise the requisite suction, the pyramidal muscles come to their +assistance. These muscles, in contracting, approximate to one another +two bones which are placed above the pubis, the (so-called) marsupial +bones (see Fig. 80); by their approximation the bones in question, which +are placed behind and on the outer side of the mammary glands, compress +the latter, and thus is brought about the result which the little ones, +on account of their feebleness, would, without that intervention, be +incapable of obtaining for themselves. + + +Muscles of the Back + +=Trapezius= (Fig. 68, 1, 2; Fig. 69, 1, 2; Fig. 70, 1, 2).--This muscle, +more or less well developed, according to the species, is divided into +two portions, of which the names indicate the respective situations--a +cervical and a dorsal. + +These two parts, considered in the order in which we find them, take +their origin from the superior cervical ligament and from the spinous +processes of the first dorsal vertebrae. From these different points the +fibres are directed towards the shoulder; the anterior are, +consequently, oblique downwards and backwards, and the posterior are +directed downwards and forwards. They are inserted into the scapula in +the following manner: the fibres of the dorsal portion are attached to +the tuberosity of the spine; those of the cervical region are also fixed +into the same spine, but into a considerably larger surface. + +The cervical portion occupies, in the region of the neck, an area +relatively smaller than the corresponding portion of the trapezius in +man. This diminished degree of development results from the absence, +complete, or nearly so, of the clavicle in the animals which we are now +considering. We remember, that the trapezius of man is partly inserted +into the clavicle, and the disappearance of this latter cannot fail to +bring modifications in the general disposition of the corresponding +portion of the muscle. There results a disconnection of this latter, and +it becomes united to other muscular fibres to form a muscle with which +we shall soon have to deal--the mastoido-humeral (see p. 150). + +As specific differences we should add that the trapezius occupies a more +or less extensive portion of the median and superior regions of the +neck; terminating at a considerable distance from the head in the dog +and horse, it, on the contrary, approaches it in the pig and in +ruminants. The cervical portion, when it contracts, draws the scapula +upwards and forwards, the dorsal portion draws it upwards and backwards. +When the trapezius acts as a whole the scapula is raised. + +[Illustration: FIG. 68.--MYOLOGY OF THE DOG: SUPERFICIAL LAYER OF +MUSCLES. + +1, Trapezius, cervical portion; 2, trapezius, dorsal portion; 3, +superior outline of the scapula; 4, latissimus dorsi; 5, external +oblique muscle; 6, rectus abdominis; 7, pectoralis major of the right +side; 8, pectoralis minor (sterno-trochinian); 9, 9, mastoido humeral +muscle; 10, tendinous intersection, at the level of which is found a +rudimentary clavicle; 11, sterno-mastoid muscle; 12, infrahyoid muscles; +13, omo-tracheal or acromio-tracheal muscle; 14, splenius; 15, levator +anguli scapulae; 16, deltoid muscle, spinal portion; 17, deltoid, +acromial portion; 18, superior extremity of the humerus; 19, +supraspinatus; 20, infraspinatus; 21, biceps cubiti; 22, brachialis +anticus; 23, triceps cubiti, long head; 24, triceps cubiti, external +head; 25, olecranon process; 26, radialis (anterior extensor of the +metacarpus); 27, iliac crest; 28, gluteus maximus; 29, gluteus medius; +30, biceps cruris; 31, semitendinosus; 32, semi-membranosus; 33, +gastrocnemius; 34, tensor of the fascia lata; 35, sartorius; 36, fascia +lata drawn up by the triceps; 37, the patella or knee-cap; 38, +ischio-coccygeal muscle; 39, superior sacro-coccygeal; 40, lateral +sacro-coccygeal; 41, inferior sacro-coccygeal.] + +=The Latissimus Dorsi= (Fig. 68, 4; Fig. 69, 5; Fig. 70, 5).--This +muscle arises by an aponeurosis, the so-called dorso-lumbar aponeurosis, +from the spinous processes of the last dorsal vertebrae (the seven last +in the dog, fourteen or fifteen last in the horse), from the spinous +processes of the lumbar vertebrae, and from the last ribs. Its fleshy +fibres are directed downwards and forwards, being more oblique in +direction posteriorly, and pass on the inner side of the posterior +muscular mass of the arm, to be inserted into the internal lip of the +bicipital groove of the humerus, or, a little lower down, on the median +portion of the internal surface of the same bone. This latter mode of +insertion is met with in the horse and the ox. + +The anterior fibres cover the posterior angle of the scapula (as in man, +where the corresponding angle, but in this case inferior, is covered by +the same muscle), and, a little higher up, are in their turn concealed +by a portion of the dorsal fibres of the trapezius. It covers, to a +greater or less extent, the great serratus muscle. These relations are +similar to those found in the human species. + +We find that the fleshy fibres of the great dorsal are prolonged more or +less backwards if we examine this muscle in the dog, the ox, the pig, +and the horse. Indeed, the fibres reach to the thirteenth rib in the dog +and the cat (that is to say, the last rib), the eleventh in the ox, +tenth in the pig, and twelfth only in the horse. We say 'only' in +connection with this last because it is necessary to remember that the +ribs are eighteen in number on each side of the thorax of this animal, +and that, accordingly, the fleshy fibres of the great dorsal muscle are, +relatively, of small extent. + +When this muscle contracts it flexes the humerus upon the scapula, and +helps to draw the whole of the anterior limb backwards and upwards. + +There is a muscular fasciculus which, because of its relations with the +muscle we have just been studying, is known as the _supplementary muscle +of the latissimus dorsi_. But as, on the other hand, this fasciculus is +in relation with the triceps, we shall in preference consider it in +relation with this latter (see p. 173). + +[Illustration: FIG. 69.--MYOLOGY OF THE OX: SUPERFICIAL LAYER OF +MUSCLES. + +1, Trapezius, cervical portion; 2, trapezius, dorsal portion; 3, outline +of the scapula; 4, spine of the scapula; 5, latissimus dorsi; 6, small +posterior serratus; 7, prominence caused by the costiform processes of +the lumbar vertebrae; 8, serratus magnus; 9, external oblique; 10, +pectoralis major (sterno-humeral); 11, mastoido-humeralis; 12, atlas; +13, atlas; 14, parotid gland; 15, sterno-mastoid muscle; 16, infrahyoid +muscles; 17, omo-trachelian or acromio-trachelian muscle; 18, deltoid; +19, brachialis anticus; 20, triceps, long head; 21, triceps, external +head; 22, olecranon; 23, radialis (anterior extensor of the metacarpus); +24, anterior iliac spine; 25, gluteus maximus; 26, gluteus medius; 27, +biceps cruris; 28, semitendinosus; 29, gastrocnemius; 30, tensor of the +fascia lata; 31, fascia lata covering the triceps of the thigh; 32, +patella; 33, ischio-coccygeal muscle; 34, superior ischio-coccygeal; 35, +lateral ischio-coccygeal; 36, inferior ischio-coccygeal.] + +The aponeurosis by which the great dorsal arises from the vertebral +column covers, as in man, the muscles which occupy the grooves situated +on each side of the spinous processes--the spinal muscles or common +muscular mass, if we regard them as a whole (Fig. 70, 7); the +sacro-lumbar and the long dorsal muscles covering the transverse spinal, +if we consider them as distinct. + +It would be superfluous to enter here into a detailed examination of +these muscles. + +If they are but little developed the spinous processes become prominent +under the skin; if they are more so they may by their thickness project +beyond the level of these processes, and these latter thus come to lie +in a groove more or less marked, which, on account of the division which +is determined by its presence, has caused the regions which it occupies +to be designated by the names _double back_ and _double loins_. + +The muscles are extensors of the vertebral column. + +Under the aponeurosis of the great dorsal muscle there is found in man +another muscle, the serratus posticus inferior, which, on account of +being deeply placed and its slight thickness, offers nothing of interest +in connection with the study of external form. It arises from the +spinous processes of the three last dorsal vertebrae and those of the +three first lumbar; it then passes upwards and outwards, and divides +into four digitations, to be inserted into the inferior borders of the +four last ribs. We repeat that it is covered by the great dorsal muscle. + +In the pig, ox, and horse, which have this latter muscle less developed +in its posterior portion, the same small serratus muscle, known as the +_posterior serratus_, is visible in the superficial layer of muscles +(Fig. 69, 6; Fig. 70, 6). The number of its digitations is more or less +considerable according to the species examined. + +=The Rhomboid Muscle= (Fig. 70, 21).--In order to make intelligible the +position of the rhomboid in the superficial layer in quadrupeds, it +appears to us necessary to recall the anatomical characters of the +muscle as found in man. The rhomboid arises from the inferior portion of +the posterior cervical ligament, from the spinous process of the seventh +cervical vertebrae and the four or five upper dorsal; thence passing +obliquely downwards and outwards, it is inserted into the spinal border +of the scapula, into the portion of this border which is situated below +the spine; it sometimes extends to the middle of the interval which +separates this latter from the superior internal angle of the same bone. + +The portion of the muscle which arises from the cervical ligament and +the seventh cervical vertebra is often separated from the lower portion +by a cellular interspace. For this cause some anatomists have described +the rhomboid as consisting of two parts--the superior or small rhomboid +and the inferior or large rhomboid, on account of the position occupied +by each, and of their difference in volume. + +This muscle can only be seen in the region of the back, in the space +limited externally by the spinal border of the scapula, below by the +latissimus dorsi, and internally by the trapezius, which covers it in +the rest of its extent. It is not in this space that it is seen in +certain quadrupeds. As we pointed out in the section on osteology, the +spinal border of the scapula is short, and it seems to be due to this +limitation in length that the trapezius and the latissimus dorsi muscle +are, at this level, in contact the one with the other in such a way that +they fill up the interval in which the rhomboid is seen in man. + +In the horse we can partly see it in the superficial muscular layer, but +in the region of the neck only, at the superior border of the shoulder. +Indeed, as we have already pointed out, the trapezius does not reach the +occipital protuberance; for this reason a part of the anterior portion +of the rhomboid may be seen--that is, the portion which corresponds to +the superior part of the human muscle. + +But whether it be covered by the trapezius, or, as we find in the cat +and dog, by the _mastoido-humeral muscle_ (see p. 150), which is very +broad in this region, we do not the less recognise its presence; and in +the horse and ox, in particular, it forms an elongated prominence +beginning at the level of the scapula, and tapering as it ascends, +towards the posterior part of the head. + +[Illustration: FIG. 70.--MYOLOGY OF THE HORSE: SUPERFICIAL LAYER OF +MUSCLES. + +1, Trapezius, cervical portion; 2, trapezius, dorsal portion; 3, +superior outline of the scapula; 4, spine of the scapula; 5, +latissimus dorsi muscle; 6, small posterior serratus; 7, spinal muscles, +or common muscular mass; 8, ribs; 9, serratus magnus; 10, external +oblique; 11, pectoralis major (sterno-humeral); 12, pectoralis +minor (sterno-trochinian); 13, atlas; 14, parotid gland; 15, +mastoido-humeralis; 16, point of the arm; 17, sterno-mastoid, or +sterno-maxillary; 18, jugular groove; 19, infrahyoid muscles; 20, +omo-trachelian muscle; 21, rhomboid; 22, splenius; 23, levator anguli +scapulae; 24, deltoid; 25, supraspinatus; 26, terminal part of the +sterno-prescapular, a portion of the small pectoral muscle; 27, +brachialis anticus; 28, triceps cubiti, middle or long head; 29, triceps +cubiti, external head; 30, olecranon; 31, radial extensor (anterior +extensor of the metacarpus); 32, anterior iliac spine; 33, anterior +portion of the gluteus maximus--the aponeurosis of the muscle has been +divided in order to expose the gluteus medius; 34, posterior portion of +the gluteus maximus; 35, gluteus medius; 36, biceps cruris; 37, +semitendinosus; 38, point of the buttock; 39, gastrocnemius; 40, tensor +of the fascia lata; 41, triceps cruris; 42, ischio-coccygeal muscle; 43, +superior sacro-coccygeal; 44, lateral sacro-coccygeal; 45, inferior +sacro-coccygeal.] + +Its origins are similar to those which we have already described in the +human rhomboid. It arises from the cervical ligament and the spinous +processes of the foremost dorsal vertebrae; its fibres converge and pass +to the scapula, to be inserted into its superior or spinal border, or +into the internal surface of the cartilage of prolongation. + +It assists in keeping the scapula applied to the thoracic cage, and when +it contracts, draws the scapula upwards and forwards. + +Taking its fixed point at the scapula, it acts on the neck by its +anterior fibres, and extends it. + +We shall soon have occasion to mention this muscle again, in connection +with the study of the muscles of the neck. + +=The Cutaneous Muscle of the Trunk= (Fig. 71).--Immediately beneath the +skin which covers the neck, shoulders, and trunk is found a vast +cutaneous muscle, analogous to that which, in the human species, exists +only in the cervical region. + +This thin muscle, whose function is to move the skin which strongly +adheres to it, and in this way to remove from it material causes of +irritation (insects, for example), is of considerable thickness in the +region of the trunk; where it constitutes what certain authors have +designated by the name of _panniculus carnosus_. In this region it +extends from the posterior border of the shoulder to the thigh, and, in +the vertical direction, from the apices of the spinous process of the +dorso-lumbar vertebrae to the median line of the abdomen. + +Arising above from the supraspinous ligament of the dorso-lumbar and +sacral regions (except in the carnivora; see below) by an aponeurosis +which, posteriorly, covers the muscles of the hind-limbs, its fibres are +directed to the elbow, on which they are arranged in two layers: a +superficial, which becomes continuous with the panniculus muscle of the +shoulder; and a deep, which passes on the inner side of the shoulder to +be inserted into the internal surface of the humerus; this latter exists +only in the dog and cat. + +The most inferior fibres, behind, at the level of the knee-cap form a +triangular process which in the horse receives the name of the _stifle +fold_, from the name veterinarians give to the region of the +articulation of the knee. This fold of skin, which commences on the +antero-internal surface of this region, is directed upwards, and then +forwards, to end by gradually disappearing over the corresponding part +of the abdomen. + +[Illustration: FIG. 71.--MYOLOGY OF THE HORSE: PANNICULUS MUSCLE OF THE +TRUNK.] + +In the same animal the muscular fibres of the panniculus of the trunk +arise along a line which connects the stifle-joint to the withers, a +line which is, consequently, oblique upwards and forwards. Now, as the +fleshy layer is thicker than the aponeurosis, the result is that the +mode of constitution of this muscle can be recognised under the skin. +Indeed, we can see in some animals, occasionally very distinctly, a +slight elevation starting from the region of the abdomen in the +neighbourhood of the knee, and thence directed obliquely upwards and +forwards. This elevation is produced by the fleshy portion of the +panniculus. + +In the carnivora, the panniculus of the trunk is not attached to the +supraspinous ligament; it is blended with the same muscle of the +opposite side, passing over the spinous region of the vertebral column. + +From this arrangement results a great mobility of the skin which covers +the back. Further, it explains why it is possible to lift up this skin +along with the panniculus which it covers, and to which it adheres, +throughout the whole extent of the dorso-lumbar column. As we pointed +out above, there is also a panniculus muscle of the shoulder and one of +the neck. We will deal with them when treating of the regions to which +those muscles belong. + + +The Coccygeal Region + +As a sequel to the study of the muscles of the region of the trunk very +naturally comes the description of those which, belonging to the region +of the coccyx, are destined for the movements of the caudal appendix, of +which this latter constitutes the skeleton. The muscles may not seem to +be of much importance with regard to external form, but, as they form +part of the superficial muscular layer, and as the mass of each is +seen in the form of the tail in some animals (the lion, for example), +they merit our attention for a moment. A few lines will suffice to +give an idea of them. They are: the _ischio-coccygeal_, _superior +sacro-coccygeal_, _lateral sacro-coccygeal_, and _inferior +sacro-coccygeal_. + +=The Ischio-coccygeal= (Fig. 18, 38; Fig. 69, 33; Fig. 70, 42).--This +muscle, triangular in shape, better developed in the carnivora than in +the horse, arises from the spine of the ischium, or from the +supracotyloid crest, which replaces this latter in the solipeds and the +ruminants. Thence its fleshy mass is directed upwards, expanding as it +proceeds to be inserted into the transverse processes of the first two +coccygeal vertebrae after insinuating itself between two of the following +muscles, the lateral and inferior sacro-coccygeal. + +In the dog and cat, the muscle is in great part covered by the great +gluteal. In the ox, by a peculiar arrangement of the corresponding +region of the muscles of the thigh--an arrangement which we will examine +in connection with the study of the latter--it is more exposed than in +the horse, and gives origin to an outline which corresponds to its +general form in the region situated immediately below the root of the +tail. + +It is a depressor of the whole caudal appendix. + +=The Superior Sacro-coccygeal= (Fig. 68, 39; Fig. 69, 34; Fig. 70, +43).--The fasciculi which form this muscle arise from the crest of the +sacrum, and proceed thence to end successively on the coccygeal +vertebrae. It is in contact in the middle line with the corresponding +muscle of the opposite side. + +It raises the tail and inclines it laterally; if the muscle of one side +contracts at the same time as that of the other the tail is elevated +directly. + +=The Lateral Sacro-coccygeal= (Fig. 68, 40; Fig. 69, 35; Fig. 70, +44).--Situated on the lateral part of the caudal region, this muscle +arises, in the dog, from the internal border of the iliac bone and the +external border of the sacrum; in the horse, it arises from the crest of +the sacrum. It is inserted into the coccygeal vertebrae. + +It produces lateral movement of the tail. + +=The Inferior Sacro-coccygeal= (Fig. 68, 41; Fig. 69, 36; Fig. 70, +43).--This muscle, which is fairly thick, arises from the inferior +surface of the sacrum and the corresponding surface of the sacro-sciatic +ligament; it is inserted into the coccygeal vertebrae. + +It depresses the caudal appendix. + + +Muscles of the Neck + +=Mastoido-humeralis= (Fig. 66, 3; Fig. 68, 9, 9, 10; Fig. 69, 12; Fig. +70, 15).--One of the most important muscles of the region of the neck in +man is the sterno-cleido mastoid. We recollect that, in its inferior +part, it is divided into two bundles, one of which arises from the +manubrium of the sternum, and the other from the inner third of the +clavicle, whence the denominations of the _sternal_ portion and +_clavicular_ portion. The muscle formed by the union of these two +portions is then directed obliquely outwards, backwards, and upwards, to +be inserted into the mastoid process of the temporal bone and the two +external thirds of the superior curved line of the occipital bone. + +Now, the animals which we are here considering have but a rudimentary +clavicle or are entirely without it. From the absence of this item of +the skeleton there necessarily result modifications in the arrangement +of the muscles of this region, which we must at the very outset explain, +before undertaking the special study of the muscle which is the subject +of the present paragraph. + +Let us suppose, for the more definite arrangement of our ideas, that the +clavicle is altogether absent, although we do find it in a rudimentary +state in some animals and completely developed in others (marmot, bat), +and we will proceed to indicate what this absence determines. + +The great pectoral muscle in man arises in part from the clavicle; this +origin not being possible in animals which have no clavicle, its +attachments, as we have already seen, are concentrated on the sternum. +The trapezius in man similarly arises in part from the clavicle; for the +reasons above indicated its clavicular fasciculi cannot exist in +distinct form in the animals which have no clavicle. + +The sterno-cleido mastoid, whose inferior attachments we mentioned +above, cannot have a clavicular portion. + +It is the same in the case of the deltoid, which, we know, arises in +part from the anterior bone of the shoulder. + +Of the four muscles which have partial clavicular origins in man, two +are known to us in connection with animals--the great pectoral and the +trapezius. What has become of the other two, the sterno-cleido mastoid +and the deltoid? + +It is this which we now proceed to investigate. After a fashion +simple enough, but which it is necessary to describe, the clavicular +fasciculi of the trapezius and the corresponding fasciculi of the +sterno-cleido mastoid are united the one to the other; the portion +of the deltoid which in man arises from the clavicle, by reason of the +absence of this latter, is also combined with the fleshy mass formed by +the preceding muscles. From this fusion results the muscle known as the +mastoido-humeral. This muscle, which consists of a long fleshy band +situated on the lateral aspect of the neck, takes its origin, as a +general rule, from the posterior surface of the skull and the upper part +of the neck, from which it passes obliquely downwards and backwards, +covering the scapulo-humeral angle--that is, the region known as the +point of the shoulder or arm--and is inserted into the anterior border +of the humerus, the border which, limiting anteriorly the musculo-spiral +groove, forms a continuation of the deltoid impression. On account of +the regions with which it is related, Bourgelat named this muscle _the +muscle common to the head, neck, and arm_. + +It is at the level of the scapulo-humeral angle that the vestiges of the +clavicle are found. + +This bone is represented in some animals--the pig, ox, and horse--by a +single tendinous intersection, more or less apparent, which extends +transversely from the scapula to the anterior extremity of the sternum. +In the dog and the cat, we find, besides, on the deep surface of the +muscle and at the level of this tendinous intersection, the rudiment of +the clavicle of which we made mention in the section on Osteology (see +p. 25). + +It is beneath the intersection, the existence of which we have just +pointed out, that is found that portion of the mastoido-humeral muscle +which corresponds to the clavicular fasciculi of the deltoid; that +portion which is situated above the intersection corresponds to the +clavicular fibres of the sterno-cleido-mastoid and of the trapezius. + +The mastoido-humeral presents certain varieties in different animals. + +In the dog and the cat, this muscle, which is blended above with the +sterno-mastoid (see p. 153), to be inserted with it into the mastoid +process and the mastoid crest, covers the neck for a considerable extent +from the superior curved line of the occipital bone to which it is +attached, to the trapezius with which it unites posteriorly, but from +which it separates below. Between these two extreme points of its +superior portion it is attached to the cervical ligament. + +In the pig and in ruminants, in which the trapezius approaches more +closely to the head, the mastoido-humeral occupies, in consequence, a +less extent of the cervical region. + +In the horse, the mastoido-humeral neither covers the neck nor joins the +trapezius; indeed, we have already shown that it is separated by a +considerable distance from the head. In the limited interval between +these two muscles a part of the rhomboid and parts of other muscles are +seen with which we shall soon be occupied. + +This muscle, as regards the horse, is described by some anatomists as +consisting of two parts: one anterior, or superficial; the other +posterior, or deep. In reality, the first only corresponds to the +mastoido-humeral, which we are considering; the posterior may be more +exactly regarded as representing a special muscle of quadrupeds, but +which is here a little deformed, the _omo-trachelian_ (see p. 155). + +When the mastoido-humeral contracts, taking its fixed point above, it +acts as an extensor of the humerus, and carries the entire fore-limb +forwards. If it takes its fixed point below--that is to say, at the +humerus--it inclines the head and neck to its own side. If it contracts +at the same time as the mastoido-humeral of the opposite side, then the +head and the neck are carried into the position of extension. + +=The Sterno-mastoid= (Fig. 66, 5; Fig. 68, 11; Fig. 69, 15; +Fig. 70, 17).--Having described the clavicular portion of the +sterno-cleido-mastoid in connection with the mastoido-humeral, because +it forms a part of the latter, we have, in order to complete the +homologies of this muscle, to study now that which corresponds to its +sternal portion. This is the _sterno-mastoid_ muscle. In all the +quadrupeds with which we are here concerned this muscle arises from the +anterior extremity of the sternum; narrow and elongated in form, it +passes towards the head in a direction parallel to the anterior border +of the mastoido-humeral, from which it is separated by an interspace +which, along its whole length, lodges superficially the jugular vein; +hence the name of _jugular groove_, which is given to this part of the +neck (Fig. 10, 18). + +It is inserted, in the case of the dog and cat, into the mastoid +process, where it is united with the mastoido-humeral; in the ox it is +divided into two portions--one which goes to the base of the occipital +bone, the other passing in front of the masseter is by the medium of +the aponeurosis of this latter attached to the zygomatic crest. This +latter part is considered by some writers as forming a portion of the +panniculus muscle of the neck. + +In the horse it is attached to the angle of the lower jaw by a tendon, +which an aponeurosis that passes under the parotid gland binds to the +mastoido-humeral muscle and the mastoid process. + +By reason of this insertion into the jaw, in the case of the solipeds, +this muscle is further named the _sterno-maxillary_. + +When it contracts, it flexes the head, and inclines it laterally. This +movement is changed to direct flexion when the two sterno-mastoid +muscles contract simultaneously. + +In man, the sterno-cleido-mastoid and the trapezius leave a triangular +space between them, which, being limited inferiorly by the middle third +of the clavicle, is known as the supraclavicular region; this region, +being depressed, especially in its inferior part, has also been given +the name of supraclavicular fossa--popularly called the '_salt-cellar_.' + +The muscles which form the floor of this region, passing from above +downwards, are: a very small portion of the complexus, splenius, levator +anguli scapulae, posterior scalenus, and anterior scalenus; then, +crossing these latter, and most superficial, is the omo-hyoid muscle. + +An analogous region, but of only slight depth, exists in quadrupeds; its +borders are formed by the mastoido-humeral and trapezius muscles. + +It is not limited below by the clavicle--we know, indeed, that this, or +the intersection which represents it, belongs to the mastoido-humeral +muscle--but by the inferior portion of the spine of the scapula. + +It is of greater or less extent according to the species considered. + +In the dog, cat, pig, and ox, it is narrow, for the muscles which bound +it approach one another pretty closely. It has, as in man, the form of a +triangle, with the apex above. In the horse it is much broader, and, +contrary to the arrangement which it presents in the human species, the +widest part is directed upwards. + +The muscles which we find there are, consequently, more or less +numerous. In the dog and cat they are: a portion of a muscle which we do +not normally meet with in man--the _omo-trachelian_--then in a +decreasing extent: supraspinatus, levator anguli scapulae and splenius. + +In the pig: the omo-trachelian, supraspinatus, and the terminal portion +of the sterno-prescapular--the anterior part of the lesser or deep +pectoral muscle. + +In the ox: the omo-trachelian only. + +But in the horse we find the omo-trachelian, the supraspinatus, and the +terminal extremity of the sterno-prescapular; then in a larger extent of +area the levator anguli scapulae and the splenius; and, finally, the +anterior portion of the rhomboid. + +Among the muscles which we have just enumerated are some that we have +already studied; these are the sterno-prescapular and the rhomboid. We +will examine the supraspinatus muscle in connection with the region of +the shoulder. + +As to the scaleni muscles and the complexus, they are deeply situated, +whereas the omo-hyoid is visible in the anterior region of the neck +only. + +There remain for us, accordingly, to examine, at the present juncture, +but the omo-trachelian, levator anguli scapulae, and splenius muscles. + +=The Omo-trachelian Muscle= (Fig. 68, 13; Fig. 69, 17; Fig. 70, +20).--Also called the _acromio-trachelian_, _levator ventri +scapulae_,[21] the _angulo-ventral muscle_, and the +_transverso-scapular_,[22] etc., this muscle is described by some +hippotomists as belonging to the mastoido-humeral, of which it then +forms its posterior or deep portion (see p. 153). + + [21] Ventri, because inserted into the inferior part of the spine of + the scapula, towards the acromion--that is, on the ventral + side--by contrast with the trapezius, which is attached higher up + (dorsal side) on the same process. + + [22] Among the many names given to this muscle, Arloing and Lesbre + recommend the adoption of the name 'transverse scapular' given by + Straus-Durckheim, or 'transverse of the shoulder' (Arloing and + Lesbre, 'Suggestions for the Reform of Veterinarian Muscular + Nomenclature,' Lyons, 1898). + +The omo-trachelian muscle is found in all mammalia, man alone excepted. +It is, however, sometimes found in the human being; but it then +constitutes an anomaly. + +In the dog, pig, and ox, it arises from the inferior part of the spine +of the scapula, in the region of the acromion, and terminates on the +lateral portion of the atlas. + +In the cat it is attached besides to the base of the occipital bone. It +is visible in the space limited by the trapezius and the +mastoido-humeral, the direction of which it crosses obliquely. + +In the horse it appears to be blended in clearly defined fashion with +the mastoido-humeral. Attached below, like this latter, to the anterior +border of the humerus, it covers the scapulo-humeral angle; and is +attached by its upper portion to the transverse processes of the first +four cervical vertebrae. + +We remember that the transverse processes are often, from their relation +with the trachea, known as the tracheal processes. Hence the word +'trachelian,' which forms part of the name of the muscle with which we +are now dealing. + +By its contraction it helps to draw the anterior limb forwards. + +When this muscle, as an abnormality, exists in man, it arises from +the clavicle or the acromion process, traverses the supraclavicular +fossa, and is inserted into the transverse processes of the atlas or +axis, or of both these vertebrae, or of the cervical vertebrae below +these latter. It is then known by the names of the _elevator of the +clavicle_ or _elevator of the scapula_, and, finally, as the +_cleido-omo-transversalis_ (Testut).[23] + + [23] L. Testut, 'Les anomalies musculaires chez l'homme expliquees par + l'anatomie comparee,' Paris, 1884, p. 97. A. F. Le Double, + 'Traite des variations du systeme musculaire de l'homme et de + leur signification au point de vue de l'anthropologie + zoologique,' Paris, 1897, t. i., p. 235. + +=The Levator Anguli Scapulae= (Fig. 68, 15; Fig. 70, 23).--As we have +pointed out (p. 136), the levator anguli scapulae, because of its +connections with the great serratus, is sometimes described with it. But +inasmuch as in human anatomy these two muscles are considered +separately, and that, in the superficial layer of muscles, they are seen +in different regions--the great serratus in the thoracic, and the +levator anguli scapulae in the cervical--we prefer to study them +separately. + +We remember that in man this muscle arises from the transverse processes +of the upper cervical vertebrae and is inserted into the superior portion +of the spinal border of the scapula, into the portion of this border +which is situated above the spine; it also contributes to the formation +of the floor of the supraclavicular region. + +When it contracts, it draws the superior portion of the scapula forwards +and upwards, and causes a see-saw movement, for at the same time the +inferior angle of the scapula is directed backwards. Taking its fixed +point at the shoulder, it directly extends the neck if the muscle of one +side acts at the same time as that of the opposite; but if only one +muscle contracts it inclines the neck to the corresponding side. + +It is to be noticed that during movements a little more active than the +ordinary the levator anguli scapulae, as moreover the other muscles of +the neck do, becomes very distinct. We have, indeed, often remarked +that, apart from these movements, each time the support of one of the +fore-limbs is brought into requisition a brusque contraction of the +muscles of this region accompanies it. + +This contraction gives the impression that, as on the one hand, each +support determines a momentary arrest of progression, a jolt, and on the +other hand, the head continues to be projected in the forward direction, +the latter should be retained. But it cannot be so except by an effort +in the opposite direction--that is to say, by the brusque contraction +which we have just pointed out. + +Analogous contractions also take place in a man while running at the +beginning of each contact of the lower limbs with the ground. + +We may add, apropos of this latter, that displacements of the head, +sometimes in very pronounced fashion, take place during simple walking, +and that every time one of the lower limbs is carried forwards the head +is projected in the same direction. These displacements, which we also +find take place in the horse in pacing, especially in the region of the +neck and head, seem then to have the effect of aiding the progression of +the body forwards. + +They occur especially in animals when drawing a heavy load, and in +individuals whose walking movements are executed with difficulty. + +It is necessary to repeat that, in these cases, the individual appears +to assist the movement of his body by the impetus which the projection +of his head forward determines, in order to add--and it is for this that +we have referred to the subject--that during the intervals between each +projection the head is carried backwards by a muscular contraction +similar to that above discussed. + +=The Splenius= (Fig. 68, 14; Fig. 70, 22).--In man, this muscle is +attached in the median line to the inferior half or two-thirds of the +posterior cervical ligament, to the spinous processes of the seventh +cervical, and four or five upper dorsal vertebrae; it passes obliquely +upwards and outwards, becomes visible in the supraclavicular region, +passes under the sterno-cleido-mastoid, and proceeds to duplicate the +cranial insertions of this latter; and, further, the most external +fasciculi of this muscle are inserted into the transverse processes of +the atlas and the axis. + +These separate superior attachments, and the division of the muscle +which results, have caused the splenius to be regarded as formed of two +portions: splenius of the head, and splenius of the neck. + +In the horse, this muscle, which is of voluminous dimensions, arises +from the superior cervical ligament, and the spinous processes of the +first four or five dorsal vertebrae; thence it proceeds to be inserted +into the mastoid crest, and the transverse processes of the atlas and +three or four vertebrae following. + +The region occupied superficially by the splenius is remarkable for the +prominence which this muscle, with the deeply-seated complexus, which is +equally bulky, determines at this level; it is situated above that +region of the neck, in which are seen in part the fasciculi of the +levator anguli scapulae. It terminates above and in front in the ridge, +which is sometimes very pronounced, which the transverse processes of +the atlas make on each side of this part of the neck. + +In the dog and the cat, the superior and anterior region of the neck is +thick and of rounded form, on account of the development which the +splenius presents in those animals; but it is covered by the +mastoido-humeral. + +This latter relation is also found in the ox, but the splenius in this +case is but slightly developed. + +When the splenius contracts it extends the head and neck, while +inclining them to its own side. + +If the splenius of one side contracts at the same time as that of the +opposite, the extension takes place in a direct manner--that is to say, +without any modifying lateral movement. + + +Infrahyoid Muscles + +Having studied the lateral surfaces of the neck, we must now examine the +anterior part of this region. Here, between the two sterno-mastoid +muscles, we find a space broader above than below, in which are situated +the larynx and the trachea, to the general arrangement of which is due +the cylindrical form which this region presents. This space corresponds +to that which in the neck of man is limited laterally by the +sterno-cleido-mastoid muscles, below by the fourchette of the sternum, +and above by the hyoid bone. In animals, as in man, it is called the +infrahyoid region. + +The hyoid bone in quadrupeds is situated between the two rami or +branches of the lower jaw. Owing to this disposition, the region above +this bone, instead of having its surface projecting a little beyond the +inferior border of the maxillary bone, is depressed. This is especially +so in the horse. It is there that we find in this animal the region +known as the _trough_ (_auge_); the larynx corresponds to that part +known as the _gullet_. + +The muscles which occupy the infrahyoid region are: the sterno-thyroid, +the sterno-hyoid, and the omo-hyoid. There is also a thyro-hyoid, but +because of its deep situation and its slight importance it offers no +interest from our point of view. + +=Sterno-thyroid and the Sterno-hyoid Muscles.=--These two muscles, long, +narrow, and flat, arise from the anterior extremity of the sternum; +then, covering the anterior surface of the trachea, they proceed to +terminate, the one on the thyroid cartilage, and the other on the hyoid +bone. The sterno-hyoid is superficial; it covers the sterno-thyroid, +which, however, projects a little on its outer side. + +=Omo-hyoid.=--This muscle does not exist in the dog or cat. It arises, +in the horse, from the cervical border of the scapula, where it blends +with the aponeurosis that envelops the subscapularis muscle, but in the +pig and the ox it arises from the deep surface of the mastoido-humeral +muscle. It is directed obliquely upwards and inwards, becoming +superficial at the internal border of the sterno-mastoid, and is +inserted into the hyoid bone. + +The region in which are united the portion of the neck which we have +just studied and the neighbouring part of the thorax--that is, the +breast--has certainly, in our opinion, a form less expressive than the +corresponding region in man. + +In the latter, indeed, the fourchette of the sternum, with the +hollow which it determines, the heads of the clavicles, and the +sterno-cleido-mastoid muscles, by the elevations which they produce, and +the trachea, by the situation which it occupies in the inferior part, +constitute a whole in which are admirably indicated, not only the forms +of the organs which constitute this region, but also the relations which +these organs have one with another; and, to a certain extent, their +respective functions. + +In making an exception in the case of the ox, in which a fold of skin, +the _dewlap_, which passes from the neck to the breast, constitutes an +element of form which possesses some expressive value; in the horse and +in the dog, which possess no sternal fourchette and no heads of +clavicles, the bones and the muscles are found nearly on the same plane. +This produces a uniformity which is evidently inferior, from an +aesthetic point of view, to the modelling of the corresponding region of +the human body. Such, at least, is our impression. + + +Suprahyoid Muscles + +As their name indicates, these muscles are found above the hyoid bone; +amongst those which should arrest our attention for a moment are the +mylo-hyoid and the digastric. + +=Mylo-hyoid.=--This muscle, forming a sort of fleshy sling which +contributes in great measure to form the floor of the mouth, is situated +between the lateral halves of the inferior maxillary bone. Arising on +each side from the internal oblique line of the mandible, its fibres are +directed towards the median line, to be inserted posteriorly into the +hyoid bone, and, between this bone and the anterior part of the +mandible, into a median raphe which unites these latter. + +=Digastric.=--This muscle arises from the styloid process of the +occipital bone and from the jugular process; it thence passes downwards +and forwards, and terminates variously, in different species. In the ox +and the horse it terminates in its anterior portion on the internal +surface of the inferior maxillary bone, close to the chin. But in the +horse a bundle of fibres is detached from the upper portion of the +muscle, to be inserted into the recurved portion of the jaw. It is to +this fasciculus that Bourgelat has given the name of '_stylo-maxillary +muscle_.' + +In the pig, dog, and cat, the digastric differs more from the +corresponding muscle in man; it is not, as in the latter, formed of two +parts. The anterior portion only exists. This consists of a thick +muscular mass, which is inserted into the middle of the internal surface +of the lower jaw. + +In the dog and cat it is clearly recognisable in the superficial layer +of muscles by the long and thick prominence which it produces below the +masseter, against the inferior border of the mandible (see pp. 235 and +237, the two figures showing the myology of the head of the dog). + +By its contraction, it draws the lower jaw downwards and backwards. + +=Panniculus of the Neck.=--This very thin muscle, which cannot be +recognised on the exterior, calls for little notice. + +We shall merely point out that it duplicates the skin of the cervical +region; but as the latter is only slightly adherent to it, the +panniculus of this region seems rather destined to maintain in position +the muscles which it covers than to displace the cutaneous covering. + +We recall the fact that in man, on the contrary, the muscle is very +evident at the instant of its contraction, and, for this reason, it +presents a very great interest with regard to external modelling, and it +plays an important part in the expression of the physiognomy. + + +MUSCLES OF THE ANTERIOR LIMBS + + +Muscles of the Shoulder + +=Deltoid= (Fig. 68, 16, 17; Fig. 69, 18; Fig. 70, 24).--This is the +first muscle we study in connection with the shoulder in human anatomy. +Indeed, its wholly superficial position, and especially the manner in +which it is separated from the surrounding muscles, its volume, and its +characteristic modelling, give it such an importance that, from the +didactic point of view, there is every indication for commencing with +this muscle in studying the region to which it belongs. If, in regard to +quadrupeds, we also commence with it, it is merely in deference to the +spirit of method, and for the sake of symmetry; for it is far from +presenting, in the latter, characters so distinctive and so clearly +defined. + +It is necessary to remark, at the outset, that in quadrupeds, on account +of the absence or slight development of the clavicle, the clavicular +portion of this muscle is, as we have shown, united to bundles of the +same kind belonging to the sterno-cleido-mastoid and trapezius to form +the mastoido-humeral (see p. 151). There exists, therefore, in an +independent form, the scapular portion only. + +It is this latter which, by itself alone, forms the deltoid of +quadrupeds, a muscle known, in veterinary anatomy, as _the long abductor +of the arm_. + +In the dog and the cat it consists of two parts, one of which arises +from the spine of the scapula; the other from the acromion process. +Thence it passes to the crest of the humerus, which limits the +musculo-spiral groove anteriorly, to be attached at a point which is +found, as in other quadrupeds, to be the homologue of the human deltoid +impression, or deltoid [V], of the human humerus. + +In the ox, in which the acromion process, which is very rudimentary, +does not attain the level of the glenoid cavity, the acromion portion is +but slightly marked off from that which takes its origin from the spine +of the scapula. + +Still, in the horse, which is completely deprived of an acromion +process, the deltoid muscle is correspondingly divided into two parts, +separated from one another by superficial interstices, but of which the +arrangement differs from that of the portions above indicated; one part, +the posterior, arises above from the superior part of the posterior +border, and the postero-superior angle of the scapula (exactly as if, in +man, certain fasciculi of the deltoid took their origin from the +axillary border and inferior angle of the scapula); the other, anterior, +arises from the tuberosity of the spine of the same bone. The two parts, +united inferiorly, proceed to be inserted into the deltoid impression or +infratrochiterian crest of the humerus. + +It is necessary to add that the deltoid is inserted into the humerus, +above the insertion of the mastoido-humeral. + +This muscle flexes and abducts the humerus, and also rotates it +outwards. + +With regard to the other muscles of the human shoulder, subscapularis, +supraspinatus, infraspinatus, teres minor and teres major, they are also +present in quadrupeds, but in a form more elongated, as the scapula has +its dimensions more extended from below upwards--that is, from the +glenoid cavity towards the superior or spinal border. + +=Subscapularis.=--This muscle occupies the subscapular fossa, from which +it takes its origin, leaving free the superior part where the surface is +found, to which are attached the serratus magnus and the levator anguli +scapulae. It passes towards the arm, to be inserted into the small +tuberosity of the humerus. It is an adductor of the arm. + +The subscapularis does not offer any interest from the point of view of +external form, for it is completely covered by the scapula. + +We speak of it, however, because we mention it in human anatomy, and +that it affords us here a new opportunity of bringing into prominence +the differences which exist in connection with the mobility of the +shoulder. + +We remember that in man, when the arm is abducted, and then raised a +little above the horizontal, the scapula see-saws, is separated, to a +certain extent, from the thoracic cage inferiorly and externally, and +that, on the superficial layer of muscles, we are then able to see in +the bottom of the armpit, at the level of the deep portion of the +posterior wall of the latter, a small part of the subscapularis muscle. + +In the animals with which we are here occupied it is not the same; for +they are incapable of performing with their fore-limbs a movement +analogous to that to which we have just referred, the humerus in their +case being retained in contact with the trunk by the muscular masses +which surround it. + +=Supraspinatus= (Fig. 68, 19; Fig. 70, 25; Fig. 72, 7).--This muscle, as +its name indicates, occupies the supraspinous fossa--that is to say, +that which, by reason of the direction of the scapula in quadrupeds, is +situated in front of rather than above the spine. It arises from this +fossa; and, further, from the external surface of the cartilage which +prolongs the scapula upwards in solipeds and ruminants. It projects more +or less beyond the supraspinous fossa in front. + +After passing downwards towards the humerus, it is inserted into the +summit of the great tuberosity or trochiter--that is to say, to a part +of this osseous prominence which represents the anterior facet of the +great tuberosity of the human humerus, into which, as we know, the +corresponding muscle is inserted. + +In solipeds and ruminants it is inserted, by a second fasciculus, into +the small tuberosity. + +In the pig and the horse its anterior border is in relation with the +terminal portion of the sterno-prescapular anterior portion of the small +or deep pectoral. + +The supraspinatus, which in man is completely covered by the trapezius, +is partly visible in the superficial layer of the cat, dog, pig, and +horse, in the lower part of the space limited by the mastoido-humeral +and the trapezius. It is crossed by the scapulo-trachelian. + +It is, in the ox, completely covered by these muscles, but its form, +notwithstanding this, is easily discerned by the prominence which it +produces. When it contracts, the supraspinatus muscle carries the +humerus into the position of extension. + +=Infraspinatus= (Fig. 68, 20; Fig. 72, 8).--This muscle, which occupies +the infraspinous fossa, which, in quadrupeds, is situated behind the +spine of the scapula, arises from the whole extent of this fossa, and in +solipeds and ruminants encroaches on the cartilage of prolongation. Its +fibres are directed downwards and forwards, to be inserted into the +great tuberosity of the humerus--the trochiter--below the insertion of +the supraspinatus. + +It is completely covered (ox and horse), or in part only (cat and dog), +by the portion of the deltoid which arises from the spine of the +scapula; nevertheless, its presence is revealed by the prominence which +it produces. + +It is an abductor and external rotator of the humerus. + +In connection with this muscle, which, as we have just pointed out, is +less seen in the superficial muscular layer than the supraspinatus, we +will draw attention to the fact that this arrangement is exactly the +reverse of that which is found in the human shoulder. In this latter it +is the supraspinatus which is not visible; while, on the contrary, the +infraspinatus is uncovered in a considerable part of its extent. We +further notice that it is accompanied by the teres minor, and that the +teres major, situated inferiorly, forms with these two muscles a fleshy +mass which, below, ends on the superior border of the great dorsal +muscle. + +In quadrupeds, in which the infraspinatus is so slightly visible, the +teres major and minor are not found at all in the superficial muscular +layer. + +Accordingly, we will say but few words about them. + +[Illustration: FIG. 72.--MYOLOGY OF THE HORSE--SHOULDER AND ARM: LEFT +SIDE, EXTERNAL SURFACE. + +1, Cartilage of prolongation of the scapula; 2, tuberosity of the spine +of the scapula; 3, superior extremity of the humerus; 4, inferior +extremity of the humerus; 5, radius; 6, ulna; 7, supraspinatus muscle; +8, infraspinatus; 9, teres minor; 10, biceps; 11, tendon of the biceps +passing over the anterior surface of the superior extremity of the +humerus; 12, brachialis anticus; 13, triceps, long head; 14, external +head of the triceps divided; 15, external head of the triceps reflected, +in order to expose the anconeus; 16, region normally occupied by the +external head of the triceps; 17, anconeus.] + +=Teres Minor= (Fig. 72, 9).--This muscle, also called in veterinary +anatomy _the short abductor of the arm_, arises from the posterior +border of the scapula (the external border in man), and is inserted +below the great tuberosity of the humerus, between the attachments of +the infraspinatus and deltoid. + +It is covered by the deltoid and the infraspinatus. + +=Teres Major.=--This muscle is known to veterinarians as _the abductor +of the arm_; it arises from the postero-superior angle of the scapula +(the inferior angle of the human scapula), from which it passes to be +inserted into the internal surface of the humerus. + +It is covered by the latissimus dorsi and the posterior muscular mass of +the arm. + +In brief, for the better understanding of the relations of the teres +major and minor muscles in quadrupeds, we may fancy the corresponding +muscles in man modified in the following manner: The infraspinatus, +thicker, covering the teres minor; latissimus dorsi, more extended in +its superior part, covering a large proportion of the teres major. As to +the relations of the teres minor with the deltoid, they exist in man, +seeing, in this case, the same muscle is, in its external portion, +covered by this latter. With regard to the relations of the teres major +with the posterior muscular mass of the arm, they also exist in man, +since the external surface of this muscle is covered by the triceps. + +These modifications are sufficient to render the small and large teres +muscles completely invisible in the superficial layer. + +The muscles of the shoulder which we have just been studying fulfil, +with regard to the articulation which they surround, the function of +active ligaments. This role is made necessary by the laxity of the +scapulo-humeral capsule--a laxity which renders it incapable by itself +of maintaining the bones in contact at this joint. + +The same condition exists in man. + +=Panniculus Muscle of the Shoulder.=--This thin muscle covers, as its +name implies, the region of the shoulder, and is the continuation +forward of the panniculus muscle of the trunk. + +It arises, by its superior part, from the region of the withers and from +the superior cervical ligament; thence its fibres descend directly +towards the elbow, to terminate at the level of the region of the +forearm. + +The muscle is not found in the pig or in the carnivora. + + +Muscles of the Arm + +We should remember, at the outset, that in man the muscles of the arm +are divided into two groups: one anterior, which contains the biceps, +brachialis anticus, and the coraco-brachialis; the other, posterior, +which is constituted by a single muscle, the triceps. + +In animals, we find them in the same number and arranged in analogous +fashion--that is to say, in two groups--with respect to the bone of the +arm. But then we find that they have undergone a transformation with +regard to their length, and it is the change of general aspect which +results from this modification that we proceed to examine. + +We know that in quadrupeds, and especially in the domestic animals, the +humerus is relatively short in proportion to the forearm. We have +already seen, in dealing with the bones, that whilst in the human +species the humerus is longer than the forearm, in the dog and cat these +two segments of the fore-limb are of equal length, and that the humerus +of the horse is, on the contrary, much shorter. Now, let us suppose the +human humerus to be shorter than it is in reality; the anterior muscles +undergoing, very naturally, the same reduction, will be uncovered only +slightly by those above--the deltoid and the great pectoral--or will +remain completely hidden by them. Thus would be found realized the +disposition which we meet with in quadrupeds of the muscles of this +region. + +With regard to the posterior muscular mass of the arm, it does not +undergo the same change. The muscle which constitutes it--the triceps +cubiti--occupies, on the contrary, a greater area. Let us suppose, +further--for it is the best method of comprehending the homologies which +now occupy our attention--the humerus of man to be shortened as before, +and directed downwards and backwards (as in quadrupeds), this bone would +form an acute angle with the axillary border of the scapula. Let us +suppose also that the long portion of the triceps, instead of arising +solely from the superior part of this axillary border, is attached to +the whole length of the latter, and that the triceps fills the whole +interior of the angle formed by the arm and the shoulder. We then shall +have an idea of what the triceps is in quadrupeds. It is necessary to +add that the general resemblance would be still more complete if the arm +were firmly supported by the side of the thorax, because in quadrupeds +it occupies an analogous position, determined by the arrangement of the +muscles which, proceeding from the trunk and neck, are attached to it. + + +Anterior Region + +=Biceps Cubiti= (Fig. 68, 21; Fig. 72, 10, 11).--This muscle, also +called _the long flexor of the forearm_, does not merit the name except +by its analogy with the corresponding muscle in man. Indeed, in the +domestic animals it is not divided into two parts; it is represented by +a single fasciculus, long and fusiform, situated on the front of the +humerus, and directed obliquely downwards and backwards, as the latter, +on its part, is also inclined. + +It arises above from a tubercle at the base of the coracoid process, +which surmounts the glenoid cavity of the scapula. Its tendon, which is +highly developed in the solipeds, occupies the bicipital groove. We +remember that in these latter the groove in question is divided into two +channels by a median prominence. + +The tendon in which the muscle ends is inserted into a tuberosity, +situated on the internal surface of the superior extremity of the +radius--the bicipital tuberosity. In the pig, the cat, and the dog, +there is detached from the tendon to which we have just referred a +fasciculus of the same nature, which, after having wound round the +radius, is inserted into the internal surface of the ulna, towards the +base of the olecranon process. From the inferior part of the muscle +arises a fibrous band, comparable to the aponeurotic expansion of the +human biceps; but, instead of passing downwards and inwards, as does the +latter, it terminates on the muscular mass which constitutes the +antero-external part of the forearm. + +The biceps is not seen in the superficial layer, except in the dog and +cat (in which the humerus is, in fact, proportionately long); and even +in them only to the slightest extent. It is covered partly in these +latter, and completely in other animals, by the great pectoral and the +inferior portion of the mastoido-humeral--that is to say, that part of +the latter which represents the whole of the clavicular fibres of the +human deltoid. + +The biceps is a flexor of the forearm on the arm. It also contributes to +the movement of extension of the humerus. + +=Brachialis Anticus= (Fig. 68, 22; Fig. 69, 19; Fig. 70, 27; Fig. 72, +12).--In veterinary anatomy further designated as _the short flexor of +the forearm_, this muscle, which is thick, occupies the musculo-spiral +groove, and arises from it, reaching upwards to just below the head of +the humerus. But it does not, as in man, extend to the internal surface +of the bone. + +Situated on the outside of the biceps, it is directed towards the +forearm, and terminates by a flattened tendon, which, dividing into two +slips, passes below the bicipital tuberosity, on the internal surface of +the radius, into which one of these slips is inserted, while the other +proceeds to terminate on the ulna. + +The inferior half of this muscle is visible on the superficial layer, in +the space limited posteriorly by the triceps brachialis, and below by +the muscles of the forearm, which correspond to the external muscles of +the human forearm, and in front by the great pectoral and the +mastoido-humeral. It is in the upper part of the interspace which +separates these latter from the brachialis anticus that the deltoid +insinuates itself to proceed to its insertion into the humerus. + +These relations precisely recall those which we meet with when we +examine the external surface of the human arm, with this difference, +however--that in the latter the anterior brachialis anticus is +extensively related, in front, to the biceps. However, in animals it is +not absolutely the same, since, as we have shown above, the biceps is +covered, more or less completely, by the mastoido-humeral and the great +pectoral. + +The brachialis anticus flexes the forearm on the arm. + +=Coraco-brachialis.=--In man this muscle, which occupies the superior +half, or third, of the internal surface of the humerus, is visible only +when the arm is abducted, and then especially when it approaches the +vertical position; indeed, it is only in this attitude that the region +which it occupies is accessible to view. + +But an analogous attitude not being possible in domestic animals, in +which the arm is fixed along the corresponding parts of the trunk, the +result is that the coraco-brachialis is always covered, and that, +consequently, it presents nothing of interest from our point of view. We +speak of it, then, merely in order to complete the series of the muscles +of the anterior surface of the arm, among which we rank it, in spite of +the fact that in veterinary anatomy it is described as a muscle of the +shoulder. + +It arises above from the coracoid process, and thence passes downwards +towards the internal surface of the humerus into which it is inserted, +more or less high up, according to the species. The coraco-brachialis is +an adductor of the arm. + + +Posterior Region + +=Triceps Cubiti= (Fig. 68, 23, 24; Fig. 69, 20, 21; Fig. 70, 28, 29; +Fig. 72, 13, 14, 15, 16).--This muscle, which is voluminous in the +quadrupeds with which we are here concerned, fits more or less +completely the angular space between the scapula and the humerus. Its +bulk forms a thick prominence, which surmounts the elbow and the +forearm. + +We should say, with regard to this mass, that if the deltoid does not +constitute in quadrupeds a prominence sufficient to remind one of that +which this muscle produces in man, the triceps, in producing an +analogous elevation, seems to replace in the general form of the body +the relief which the deltoid is incapable of producing. + +The triceps is divided into three portions, which, as in man, have the +names middle, or long head; external and internal heads. But that which +renders the nomenclature a little complicated is that veterinary +anatomists have given other names to these three parts: that of _great +extensor of the forearm_ (caput magnum) to the long head; _the short +extensor of the forearm_ (caput parvum) to the external head; and of +_medium extensor of the forearm_ (caput medium) to the internal.[24] + + [24] Other names given by certain authors to the parts of this muscle + which we have just enumerated still further complicate this + nomenclature. + +The long head is further designated by them under the names of the +_long_ or _great anconeus_; the _external head_ under those of _external +anconeus_, or _lateral_ or _short anconeus_; whilst the internal head +becomes the _internal anconeus_, or _median_. + +It is more especially the long portion and the external head which, +being visible on the external surface of the arm, contribute to the +external form. + +The long portion, which is triangular in shape and of considerable +development, arises in the cat and the dog from the inferior half or +two-thirds of the posterior border of the scapula (axillary border); +from the whole extent of that border as far as the superior posterior +angle in the pig, the ox, and the horse; it then passes downwards +towards the articulation of the elbow, to terminate in a tendon which is +inserted into the olecranon process. The portion of this muscle which is +next the scapula is covered by the deltoid. + +The external head, situated below the long portion, is directed +obliquely downwards and backwards. It arises from the curved crest +which, from the deltoid impression of the humerus, is directed upward to +meet the articular head of the same bone. This crest limiting the +musculo-spiral groove superiorly, and the brachialis anticus arising +from the whole extent of this groove, the result is that at this level +the external head is in relation with the brachialis anticus. From this +origin it is directed towards the elbow, to be inserted into the +olecranon, either directly or by the medium of the tendon of the long +portion. The part of this muscle which arises from the humerus is +covered by the deltoid. + +As for the internal head (Fig. 76, 4), which, in the superficial layer, +is only visible in its inferior part, on the internal aspect of the arm +in those animals in which the elbow is free of the lateral wall of the +thorax (the dog and the cat, for example), it arises from the internal +surface of the humerus, and thence proceeds to be inserted into the +olecranon. + +The triceps extends the forearm on the arm. + +A fourth muscle exists, which veterinary anatomists include in the study +of the three portions of the triceps which we have just been discussing, +in giving it the name of _small extensor of the forearm_. But, as this +muscle is no other than the anconeus, and as, in human anatomy, we +describe the latter, according to custom, in connection with the +forearm, it is when on the subject of the latter that we will concern +ourselves with it. This grouping of muscles cannot fail to give greater +clearness to the description of the muscles of these regions. + +=The Supplemental or Accessory Muscle of the Latissimus Dorsi= (Fig. 76, +2; Fig. 77, 1).--Because of the relations, to which we have already +referred (see p. 142), of this muscle with the triceps cubiti, its +description very naturally follows that of the latter. + +Indeed, this supplementary muscle of the great dorsal is further +designated in zoological anatomy under the name of _long extensor of the +forearm_; and this name indicates that its study may be united to that +of the triceps. + +Situated on the internal surface of the arm, it arises from the external +aspect of the tendon of the latissimus dorsi; it is very highly +developed in the horse, in which it also arises from the posterior +border (axillary) of the scapula; then, covering in part the internal +head of the triceps and also the long portion, on the superior border of +which it is folded, it proceeds to be inserted into the olecranon +process and the anti-brachial aponeurosis. + +It extends the forearm on the arm. Further, it makes tense the +aponeurosis into which it is inserted; this explains the name of _tensor +of the fascia of the forearm_, which is sometimes given to it. + +It seems to us interesting to add that, abnormally, we sometimes find in +man an analogue of this muscle. It is given off from the latissimus +dorsi, near the insertion of the latter into the humerus; it accompanies +the long head of the triceps and becomes fused with it. Sometimes it is +inserted into the olecranon process, at other times into the +antibrachial aponeurosis or the epitrochlea. It is on account of its +insertion into the last-mentioned, in some cases, that it is also +designated by the name of _dorso-epitrochlear_ muscle.[25] + + [25] L. Testut, 'Anomalies musculaires chez l'homme expliquees par + l'anatomie comparee,' Paris, 1884, p. 118. A. F. Le Double, + 'Traite des variations du systeme musculaire de l'homme et de + leur signification au point de vue de l'anthropologie + zoologique,' Paris, 1897, t. i., p. 203. Edouard Cuyer, + 'Anomalies musculaires' (_Bulletins de la Societe + Anthropologique_, Paris, 1893). + + +Muscles of the Forearm + +Before commencing the special examination of each of the muscles of this +region, it is absolutely indispensable to consider their general +arrangement, and to determine very clearly how we should study them. We +are too well convinced of the importance of this preliminary examination +to dismiss it without entering rather fully into it. Indeed, the region +on the myological study of which we are now entering is, unquestionably, +one of the most complicated with which we have to deal. We know besides, +in regard to the study of the forearm in man, how much a definite method +is necessary in order that the arrangement of the muscles of this region +be fixed in the memory, and that we are unable to obtain this result +otherwise than by grouping the twenty muscles which constitute it in +clearly defined regions. + +We also know that these muscles are first studied with the forearm in +the position of supination, and that it is only when they are well known +after having considered them in this position that we are able to +analyze and comprehend their forms when it is in pronation. + +Now, as we have pointed out in the section on osteology (see p. 34), the +forearm in quadrupeds is always in the position of pronation. Should we, +then, in order to maintain the symmetry with human anatomy, first study +the forearm in the position of supination? Evidently not. Besides the +fact that this would in some cases be impossible since--as in the horse, +for example--the radius and ulna are fused together, we should not gain +any advantage; this position being never completely realizable even in +those quadrupeds which have the radius relatively movable--as, for +example, in the cat. + +Accordingly, it is pronation which here, in connection with animals, +becomes the standard attitude from the point of view of description. +This is why, supposing that the reader knows well the muscles of the +human forearm in the position of supination, we should recall what is +the general arrangement occupied by these muscles when it is in +pronation. + +The fore-limb, being viewed on its anterior surface, presents above the +anterior aspect of the region of the elbow; but below, it is the +posterior surface of the wrist which is seen. Consequently, in the +superior part, we see the external and anterior muscles limiting the +hollow in front of the elbow; interiorly are found the posterior +muscles. + +The long supinator, passing obliquely downwards and inwards, divides, in +fact, the forearm into two parts: one supero-internal, the other +infero-external. In the first we see, but to an extent less and less +considerable, the pronator teres, the flexor carpi radialis, the +palmaris longus, and the flexor ulnaris; as to the flexors of the +digits, on account of the rotation of the radius, they are only visible +on the opposite surface--that is to say, on the surface of the wrist, +which is now posterior. In the second part we see the two radial +extensors, the common extensor of the fingers, the proper extensor of +the little finger, and the ulnar extensor which, inferiorly, remains +behind, by reason of the position of the ulna being unchanged, whilst +the anconeus is wholly posterior, since the direction of the elbow is +not modified. We also find, in this region, the long abductor of the +thumb, the short extensor of the thumb, the long extensor of the thumb, +and the special extensor of the index-finger, in the region where these +deep muscles become superficial. + +So that, to summarize, the external and posterior muscles occupy the +anterior and external regions of the forearm, whilst the anterior +muscles occupy rather the internal and posterior. It is in regarding +them after this manner--that is to say, arranged in these two +regions--that we proceed to study these muscles in quadrupeds. + + +Anterior and External Region + +=Supinator Longus.=--We know that this muscle, which is especially a +flexor of the forearm on the arm, plays, notwithstanding the name which +has been given it, a part of but little importance in the movement of +supination. + +It acts slightly, however, as a supinator, for, being very oblique +downwards and inwards at the time of pronation, it is able, while +tending to resume its vertical direction, to carry the radius outwards; +it places, in fact, the forearm in a position midway between pronation +and supination. + +We have just recalled these details, in order that it may be more easy +to understand why it does not exist in animals in which the radius and +ulna are fused together (horse, ox); and why, on the other hand, we find +traces of it in the cat and the dog, in which the radius--to a slight +extent, it is true--is able to rotate on the ulna. This displacement +being a little more considerable in the felide, the long supinator is a +little further developed than it is in the canine species; but, +notwithstanding, it is only rudimentary. + +The long supinator arises, above, from the external border of the +humerus; thence, in the form of a very narrow fleshy band, it passes +obliquely downwards and inwards, to be inserted into the inferior part +of the internal surface of the radius. + +It assists in turning the radius outwards and placing it in front of the +ulna, the movement of supination being capable of being but little +further extended. + +=First and Second External Radial Muscles=: _Extensor carpi radialis +longior and brevior_ (Fig. 73, 8; Fig. 74, 8, 9; Fig. 75, 8, 9).--Fused +together, these muscles form by their union what veterinary anatomists +call _the anterior extensor of the metacarpus_. But we should add that +these two muscles are united so much the more intimately as we examine +them in passing successively from the cat to the dog, pig, ox, and +horse. Thus, in the cat they are often distinct; in the dog, they unite +only at the level of the middle third of the radius, and interiorly they +have two tendons; in the pig, the ox, and the horse they are completely +united, and there exists but a single tendon. + +The _anterior extensor of the metacarpus_, which is situated behind the +long supinator when the latter exists, occupies the external aspect of +the forearm; its well-defined form absolutely recalls the prominence on +the superior part of the external margin of the human forearm. + +It arises superiorly from the portion of the external border of the +humerus which is situated above the epicondyle and behind the +musculo-spiral groove. Its fleshy mass appears in the angular space +bounded by the brachialis anticus and the triceps. The superior portion +is covered by the external head of the triceps; yet, in the dog, the +superior portion of its humeral attachment is the only part so covered. +This muscle is directed forward and downwards; it is also inclined a +little inwards in such manner as to proceed to occupy the anterior +aspect of the forearm. + +Its fleshy belly is narrowed below, and, towards the inferior part of +the forearm, is continued by a tendinous portion which is situated on +the anterior surface of the carpus, after having traversed the median +groove of the inferior extremity of the radius. + +In the cat and the dog, in which the union of the two radial extensors +is incomplete, the two tendons are inserted into the front of the base +of the second and third metacarpal bones; consequently, as in man, into +the metacarpals of the index and middle fingers. + +In the ox, the tendon, which is single, is inserted into the internal +and anterior half of the superior extremity of the principal metacarpal. + +In the pig, this tendon is attached to the base of the large internal +metacarpal. + +In the horse, the corresponding tendon is attached to a tubercle which +is situated on the anterior surface of the base of the principal +metacarpal, a little internal to the median plane of the latter. + +[Illustration: FIG. 73.--MYOLOGY OF THE DOG: LEFT ANTERIOR LIMB, +EXTERNAL ASPECT. + +1, Mastoido-humeralis; 2, biceps; 3, brachialis anticus; 4, triceps, +long portion; 5, triceps, external head; 6, olecranon process; 7, +epicondyle; 8, radialis muscles (anterior extensor of the metacarpus); +9, extensor communis digitorum (anterior extensor of the phalanges); 10, +extensor minimi digiti (lateral extensor of the phalanges, or common +extensor of the three external digits); 11, posterior ulnar (external +flexor of the metacarpus); 12, pisiform bone; 13, anconeus; 14, extensor +ossis metacarpi pollicis and extensor primi internodii pollicis (oblique +extensor of the metacarpus); 15, radius; 16, anterior ulnar (oblique +flexor of the metacarpus); 17, external border of the hypothenar +eminence (abductor of the little finger).] + +In order to properly understand and remember the respective positions +occupied by these inferior insertions, it must be remembered that the +human forearm being in the position of pronation, the tendons of the +radials are attached to the bases of the metacarpals nearest to the +thumb--that is to say, those occupying an internal position as regards +the fourth and fifth metacarpals. + +As its name indicates, this muscle extends the metacarpus. Consequently +it is, in the horse, an extensor of the canon-bone. + +It is also an adductor of the hand in those animals (cat, dog) in which +the radio-carpal articulation, analogous in form to the corresponding +articulation in man, permits lateral movements of the hand on the +forearm. The union of the fleshy bodies of the two radials is sometimes +found in the human species. + +=Supinator Brevis.=--As in the case of the long supinator, the short +supinator is found only in animals in which the radius can be rotated to +a greater or less extent around the ulna; therefore this muscle is not +found in the pig, the ox, or the horse; but it forms part of the forearm +of the cat and the dog. + +Deeply situated at the region of the elbow, the short supinator has +little interest for us. All that we will say of it is that it goes from +the external part of the inferior extremity of the humerus to the +superior part of the radius; and that it is, in carnivora, the essential +agent in the production of the movement of supination. + +=Extensor Communis Digitorum= (Fig. 73, 9, 10, 11; Fig. 74, 10, 11, +12).--Also named in veterinary anatomy the _anterior extensor of the +phalanges_, this muscle is situated external to and behind the anterior +extensor of the metacarpus already described. + +In the human being, the common extensor of the fingers springs, in its +superior part, from the bottom of a depression, situated on the outer +side of and behind the elbow, and limited in front by the muscular +prominence which the long supinator and the first radial extensor form +at that level. At the bottom of this hollow or fossette is found the +epicondyle, which gives origin, amongst other muscles, to the common +extensor of the fingers. It is necessary to add that it is most +prominently visible during supination, and that it tends to be effaced +during pronation. + +[Illustration: FIG. 74.--MYOLOGY OF THE OX: LEFT ANTERIOR LIMB, EXTERNAL +ASPECT. + +1, Mastoido-humeralis; 2, pectoralis major; 3, deltoid; 4, brachialis +anticus; 5, triceps; 6, triceps, external head; 7, olecranon; 8, radial +extensors (anterior extensor of the metacarpus); 9, insertion of the +tendon of the anterior extensor of the metacarpus to the tubercle of the +superior extremity of the principal metacarpal; 10, 11, extensor +communis digitorum (10, proper extensor of the inner digits; 11, common +extensor of the two digits); 12, tendon of the common extensor of the +two digits; 13, band of reinforcement from the suspensory ligament of +the fetlock; 14, external tuberosity of the superior extremity of the +radius; 15, extensor minimi digiti (proper extensor of the external +digit); 16, tendon of the proper extensor of the external digit; 17, +posterior ulnar (external flexor of the metacarpus); 18, pisiform; 19, +extensor ossis metacarpi pollicis and extensor primi internodii pollicis +(oblique extensor of the metacarpus); 20, ulnar portion of the deep +flexor of the toes; 21, tendon of the superficial flexor of the toes +(superficial flexor of the phalanges); 22, tendon of the deep flexor of +the toes (deep flexor of the phalanges); 23, suspensory ligament of the +fetlock.] + +An analogous arrangement is met with in animals. But the muscular +prominence is formed by the united radial extensors, and the fossette, +because of the permanent pronation of the forearm, is scarcely +recognisable. Likewise, with regard to the dog, we may say that it does +not exist, on account of the prominence which the epicondyle forms in +that animal (Fig. 73, 7). + +In connection with this prominence of the epicondyle, it is interesting +to add that this detail recalls the relief which the same process +produces on the external aspect of the human elbow when the forearm is +flexed on the arm. We know that, in this case, the epicondyle is +exposed, because the muscles which mask it in supination (long supinator +and long radial extensor) are displaced and set it free during flexion. +But, in the dog, as in other quadrupeds besides, the forearm is, in the +normal state, flexed on the arm; the latter being oblique downwards and +backwards, and the former being vertical. Further, the epicondyle is +well developed. + +The muscle with which we are now occupied, long and vertical in +direction, arises from the inferior part of the external border of the +humerus (there it is covered by the anterior extensor of the metacarpus, +from which it is freed a little lower down) and from the external and +superior tuberosity of the radius. In the carnivora, it arises from the +epicondyle. Its fleshy body is fusiform in shape, becomes tendinous in +the lower half of the forearm, and then divides into a number of slips, +varying in number according to the species; this division is correlated +to that of the hand--that is to say, with the number of the digits. +Before reaching this latter, the common extensor of the digits passes +through the most external groove on the anterior surface of the inferior +extremity of the radius. + +[Illustration: FIG. 75.--MYOLOGY OF THE HORSE: LEFT ANTERIOR LIMB, +EXTERNAL ASPECT. + +1, Mastoido-humeral; 2, pectoralis major; 3, deltoid; 4, brachialis +anticus; 5, triceps, long head; 6, triceps, external head; 7, olecranon; +8, radial extensors (anterior extensor of the metacarpus); 9, insertion +of the tendon of the anterior extensor of the metacarpus into the +tubercle of the superior extremity of the principal metacarpal; 10, +extensor communis digitorum (anterior extensor of the phalanges); 11, +tendon of the anterior extensor of the phalanges; 12, reinforcing band +arising from the suspensory ligament of the fetlock; 13, external +tuberosity of the superior extremity of the radius; 14, extensor minimi +digiti (lateral extensor of the phalanges); 15, tendon of the lateral +extensor of the phalanges; 16, fibrous band which this latter receives +from the tendon of the anterior extensor of the phalanges; 17, fibrous +band which the same tendon receives from the carpal region; 18, +posterior ulnar (external flexor of the metacarpus); 19, pisiform; 20, +extensor ossis metacarpi pollicis and extensor primi internodii pollicis +(oblique flexor of the metacarpus); 21, ulnar portion of the deep flexor +of the digits; 22, flexor digitorum profundus; 23, 23, tendon of the +flexor digitorum sublimis (superficial flexor of the phalanges); 24, 24, +tendon of the flexor digitorum profundus (deep flexor of the phalanges); +25, sesamoid prominence; 26, suspensory ligament of the fetlock; 27, +external rudimentary metacarpal.] + +In the cat and the dog, the four tendons which result from the division +of the principal tendon go to the four last digits, and each of them is +inserted, as in the human species, to the second and third phalanges. + +In the pig, the anterior extensor of the phalanges is rather complicated +in its arrangement. Its fleshy body is divided into four bundles +terminated by tendons, which in turn divide and join certain digits; +whence the special names given to each of these fasciculi, commencing +with the most internal, of: _proper extensor of the great inner toe_; +_common extensor of the two inner toes_; _common extensor of the two +outer toes_; and _proper extensor of the great outer toe_. + +In the ox, the same muscle is divided into two bundles: the internal +proceeds to the internal toe, the external is common to the two toes. + +In the horse, the tendon of the anterior extensor of the phalanges is +divided into two parts of unequal bulk. The smaller of these tendinous +slips, which is the more external, unites at the level of the superior +part of the metacarpus with the tendon of the muscle which we are about +to study in the following paragraph (Fig. 75, 16). The larger, after +having reached the anterior surface of the digit, is attached to the +anterior aspect of the first and second phalanges, and then forms a +terminal expansion which is inserted into the pyramidal eminence of the +third. + +At the level of the first phalanx this tendon receives on each of its +lateral aspects a strengthening band, which proceeds from the terminal +extremity of _the suspensory ligament of the fetlock_,[26] and crosses +obliquely downwards and forwards over the surface of the first phalanx +to join the extensor tendon (Fig. 75, 12). + + [26] See p. 200 for a description of this ligament. + +A similar arrangement is found in the ox. + +This band is noticeable under the skin which covers the lateral aspects +of the ham. + +As the name indicates, this muscle extends the phalanges, one upon the +other. It also contributes to the extension of the hand, as a whole, on +the forearm. + +=Extensor Minimi Digiti= (Fig. 73, 10; Fig. 74, 15, 16; Fig. 75, 14, +15).--This muscle, _the lateral extensor of the phalanges_ of veterinary +anatomy, situated on the external surface of the forearm, behind the +common extensor of the digits, arises, as a rule, from the epicondyle +(dog, cat), or from the external surface of the superior extremity of +the radius (horse). The tendon succeeding to the fleshy body appears +towards the lower third of the forearm, and at the level of the wrist +lies in a groove analogous to that which in man is hollowed out for the +passage of the corresponding tendon at the level of the inferior +radio-ulnar articulation. This groove corresponds to the same +articulation in animals in which the ulna is well developed, such as the +dog and the cat; but it belongs to the radius when the inferior +extremity of the ulna does not exist--for example, in the horse. Indeed, +in this animal the groove in question is found on the external surface +of the carpal extremity of the radius. + +In the dog, the tendon is divided into three parts, which, crossing +obliquely the tendons of the common extensor of the digits, pass to the +three external digits, to be inserted by blending with the corresponding +tendons of the latter into the third phalanges of those digits. + +Thus is explained the name of _common extensor of the three external +digits_ which is sometimes given to this muscle. + +In the cat, there is a fourth tendon, which passes to the index-finger, +so that the name _common extensor of the four external digits_ is in +this case legitimate, and the lateral extensor of the phalanges is also +a common extensor, as is the anterior extensor of the phalanges, or +common extensor of the digits. + +In the pig, the tendon, which is single, is inserted into the external +digit, for which reason it has received the name of the _proper extensor +of the small external digit_. This muscle is, then, really the homologue +of that which exists in the human species. + +In the ox, it is called the _proper extensor of the external digit_; it +is as thick as the common extensor. + +Finally, in the horse, the muscle is little developed. Its fleshy body, +thin and flattened from before backwards, becomes distinctly visible +only below the middle of the forearm. Above, it is enclosed in a limited +space, bounded in front by the common extensor of the digits, and +behind by the posterior ulnar; there these two muscles approach each +other so closely that from the point of view of external form they seem +to be nearly in contact. + +The tendon, after receiving the small fasciculus from the common +extensor (Fig. 75, 16), as well as a fibrous band emanating from the +external surface of the carpus (Fig. 75, 17), is situated at the +external side of the tendon of the anterior extensor of the phalanges, +and is inserted into the anterior surface of the superior extremity of +the first phalanx. + +This muscle extends the digit or digits into which it is inserted. It +also assists in the movement of extension of the hand as a whole. + +=Posterior Ulnar= (_Extensor carpi ulnaris_) (Fig. 73, 11; Fig. 74, 17; +Fig. 75, 18).--Designated by veterinary anatomists as the _external +flexor of the metacarpus_,[27] or _external cubital_, this muscle is +situated in the posterior region of the external surface of the forearm, +behind the lateral extensor of the phalanges. + + [27] Certain authors give it the name of _ulnar extensor of the + wrist_. It is true that in the human being this is its action; + but in quadrupeds, owing to its insertion into the pisiform, it + draws the hand into the position of flexion. + +It arises from the epicondyle; its fleshy body, thick but flattened, is +directed vertically towards the carpus, and its tendon is inserted into +the external part of the superior extremity of the metacarpus, after +having given off a fibrous band, which takes its attachment on the +pisiform. + +It is inserted, in the cat and the dog, into the superior extremity of +the fifth metacarpal; in the pig to the external metacarpal; in the ox +to the external side of the canon-bone; in the horse to the superior +extremity of the external rudimentary metacarpal. + +This muscle flexes the hand on the forearm, and in animals in which the +radio-carpal articulation permits, by its formation, it inclines the +hand slightly outwards--that is, abducts it. + +=Anconeus= (Fig. 72, 17; Fig. 73, 13).--We have already stated (p. 174) +that the anconeus is included with the triceps brachialis in zoological +anatomy, and that veterinary anatomists give it the name of _small +extensor of the forearm_.[28] + + [28] It is also called by some authors, the _small anconeus_. + +In the dog it recalls, as to position, the human anconeus, but with this +difference--that, in the latter, the anconeus, triangular in outline, +has one of its angles turned outwards (the epicondyloid attachment) and +one of its sides turned towards the olecranon. Here it is entirely the +opposite. The anconeus, similarly triangular, is broader externally. At +this level it takes its origin from the external border of the humerus, +the epicondyle, and the external lateral ligament of the articulation of +the elbow; thence its fibres converge towards the external surface of +the olecranon, to be there inserted. + +It is in relation, anteriorly and inferiorly, with the posterior ulnar +muscle. It is covered superiorly by the external head of the triceps. In +the cat the disposition of the anconeus is analogous. But in the other +quadrupeds with which we are here concerned it is completely covered by +the external head of the triceps. It really participates in the +formation of the triceps; and seeing that it takes origin from the +posterior surface of the humerus at the margin of the olecranon fossa +(Fig. 72), and proceeds thence towards the olecranon to be inserted, we +can understand why veterinary anatomists have connected its study with +that of the posterior muscular mass of the arm. + +This muscle is an extensor of the forearm on the arm. + +We proceed now to inquire what the deep muscles of the posterior region +of the human forearm become in quadrupeds: the long abductor of the +thumb, the short extensor of the thumb, the long extensor of the thumb, +the proper extensor of the index. We know that in every instance these +muscles, which are deeply seated at their origin, become superficial +afterwards. + +In quadrupeds, on account of the position in which the forearm is +placed--viz., pronation--the corresponding muscles occupy the anterior +aspect of this region. + +=Long Abductor of the Thumb= (_Extensor ossis metacarpi pollicis_) =and +Short Extensor of the Thumb= (_Extensor primi internodii pollicis_) +(Fig. 73, 14; Fig. 74, 19; Fig. 75, 20).--United one to the other in +man, blended in quadrupeds, they form in the latter the muscles to which +veterinary anatomists give the name of _oblique extensor of the +metacarpus_. + +This muscle arises from the median portion of the skeleton of the +forearm. There it is covered by the common extensor of the digits and +that of the small digit (anterior extensor and lateral extensor of the +phalanges). Then, at the internal border of the first of these muscles, +it becomes superficial, passes downwards and inwards, crosses +superficially the anterior extensor of the metacarpus, reaches the +inferior extremity of the radius, and becomes lodged in the most +internal of the grooves situated on the anterior surface of this +extremity, passes on the internal side of the carpus, and is inserted +into the superior extremity of the most internal metacarpal--that is, to +the first metacarpal, or metacarpal of the thumb--in the dog and cat; to +the internal rudimentary metacarpal in the horse. + +It is an extensor of the metacarpal into which it is inserted; but as, +if we recall the extreme examples given above, in the dog the first +metacarpal is not very mobile, and in the horse the internal rudimentary +metacarpal is absolutely fixed to the bone which it accompanies, it is +more exact to add that this muscle is principally an extensor of the +metacarpus as a whole. + +And yet, in the cat and the dog, it is also able to adduct the first +metacarpal bone. It must be understood that this movement would be +abduction, if the hand could be placed in the position of complete +supination, as in the human species. + +=Long Extensor of the Thumb= (_Extensor secundi internodii pollicis_) +=and Proper Extensor of the Index= (_Extensor indicis_).--These two +muscles are blended together by their fleshy bodies, so that the single +name of _proper extensor of the thumb and index_ is preferable. This +muscle is but of slight importance from our point of view, for it is +extremely atrophied, and so much the more as the number of the digits is +lessened. + +It arises, as the preceding, from the skeleton of the forearm, and there +it is deeply placed. Below, towards the carpus, its tendinous part +becomes superficial, to end in the following manner: + +In the carnivora, the tendon divides into two very slender parts, which +are inserted into the thumb and the index. In the pig, the tendon is +blended with that of the common extensor of the internal digits. +Finally, in the ox and the horse, it is sometimes regarded as being +blended with the common or anterior extensor of the phalanges. But to us +it appears more rational to say that it does not exist, which, moreover, +is explained by the digital simplification of the hand. + + +Internal and Posterior Region + +=Pronator Teres= (Fig. 76, 8).--This muscle, as may easily be +understood, undergoes, as do the supinators, a degree of degeneration in +proportion to the loss of mobility of the radius on the ulna. In animals +in which the bones of the forearm are not fused it exists; in those, on +the other hand, in which this segment has become simply a supporting +column, it is not developed--at least, in a normal manner. + +It is, consequently, found best marked in the dog and the cat. + +Forming, as in man, the internal limit of the hollow of the elbow, the +pronator teres has a disposition analogous to that which characterizes +the corresponding muscle in the human species. It arises from the +epitrochlea (internal condyle), proceeds downwards and outwards, and is +inserted into the middle portion of the body of the radius. + +It is into the hollow in front of the elbow, which this muscle +contributes to limit, that the biceps and the brachialis anticus dip. + +In the pig and the ox it is atrophied. + +In the horse it does not exist. We may, however, sometimes find it, but +in an abnormal form. We were able to demonstrate its presence in the +form of a fleshy tongue situated on the internal side of the elbow +(Fig. 78) in a horse which we dissected many years ago in the laboratory +of the School of Fine Arts. Moreover--and the fact seemed to us an +interesting one--the forearm to which the muscle belonged had an ulna of +relatively considerable development (Figs. 79 and 80).[29] + + [29] Edouard Cuyer, 'Abnormal Length of the Ulna and Presence of a + Pronator Teres Muscle in a Horse' (_Bulletin de la Societe + d'Anthropologie_, Paris, 1887). + +This muscle is a pronator. + +=Flexor Carpi Radialis= (Fig. 76, 10; Fig. 77, 7).--Called by veterinary +anatomists _the internal flexor of the metacarpus_, this muscle, which +is found on the internal aspect of the forearm, is situated behind the +pronator teres when this muscle exists, whilst in the animals which are +deprived of the latter the flexor carpi radialis has in front of it the +internal border of the radius, which separates it from the anterior +extensor of the metacarpus. + +It is necessary to add that the flexor carpi radialis is similarly +separated from the anterior extensor of the metacarpus by the internal +border of the radius in animals in which the pronator teres exists, but +then only in that part of the forearm which is situated below this +latter. + +The flexor carpi radialis arises from the epitrochlea. Its fleshy body, +fusiform in shape, descends vertically, and terminates in a tendon on +the posterior surface of the bases of the second and third metacarpals +in the dog and the cat, on the metacarpal of the large internal digit in +the pig, on the internal side of the metacarpus in the ox, and on the +superior extremity of the internal rudimentary metacarpal in the horse. + +We see clearly, in this latter, a superficial vein which, in the shape +of a strong cord, passes along the anterior border of the flexor carpi +radialis; it is the subcutaneous median or internal vein, which, forming +the continuation of the internal metacarpal vein, joins the venous +system of the arm, after having crossed obliquely the corresponding part +of the radius. + +=Palmaris Longus.=--This muscle, which exists distinctly in some +animals, but whose absence is far from being rare in the human species, +is not developed as a distinct muscle in any of the domestic quadrupeds. + +[Illustration: FIG. 76.--MYOLOGY OF THE DOG: LEFT ANTERIOR LIMB, +INTERNAL ASPECT. + +1, Biceps; 2, long extensor of the forearm (supplementary or accessory +muscle of the great dorsal); 3, triceps, long head; 4, triceps, internal +head; 5, olecranon; 6, epitrochlea (internal condyle); 7, radial +extensors (anterior extensor of the metacarpus); 8, pronator teres; 9, +radius; 10, flexor carpi radialis (internal flexor of the metacarpus); +11, anterior ulnar (oblique flexor of the metacarpus); 12, superficial +flexor of the digits; 13, deep flexor of the digits; 14, flexor longus +pollicis (radial fasciculus of the deep flexor of the digits); 15, +pisiform bone.] + +And yet some authors announce its presence in the dog, and describe it +as becoming detached, in the form of a cylindrical bundle, from the +anterior surface of the fleshy mass of the deep flexor of the digits +(see p. 196) to proceed then by a tendon which divides into two parts, +to terminate in the palm of the hand, where it blends with the tendons +of the superficial flexor, which are destined for the third and fourth +digits. + +These authors give to this muscle the name of _palmaris longus_, and +attribute to it the action of flexing the hand. + +=Anterior Ulnar= (_Flexor carpi ulnaris_) (Fig. 73, 16; Fig. 76, 11; +Fig. 77, 8).--Called by veterinary anatomists the _oblique flexor of the +metacarpus_, or _internal ulnar_, this muscle occupies the internal part +of the posterior aspect of the forearm in the ox and the horse, while in +the dog it occupies rather the external part. + +This difference arises from the fact that in this latter, as in man, the +anterior ulnar is separated from the flexor carpi radialis by an +interval in which we see, on the internal aspect of the forearm, just at +the level of the elbow, the flexors of the digits. This interval is so +much the wider as there is no palmaris muscle to subdivide its extent +(Fig. 81). In the horse, the interval in question does not exist. In +this animal, indeed, the anterior ulnar is in contact with the radial +flexor, so that this muscle can occupy only a region belonging rather to +the internal surface of the forearm (Fig. 82). + +In the dog the anterior ulnar is in contact with the posterior ulnar. +This relation recalls that which is found in man, where the two muscles +are merely separated by the crest of the ulna (Fig. 81). But in the +horse, in which the anterior ulnar has, so to speak, slid towards the +internal aspect, this muscle is separated above from the posterior +ulnar, and it is in the interval separating these two muscles that we +are able to perceive, but this time at the back of the forearm, the +muscular mass of the flexors of the digits (Fig. 82). + +[Illustration: FIG. 77.--MYOLOGY OF THE HORSE: ANTERIOR LIMB, LEFT SIDE, +INTERNAL ASPECT. + +1, Long extensor of the forearm (supplementary or accessory muscle of +the latissimus dorsi); 2, radialis muscles (anterior extensor of the +metacarpus); 3, tendons of extensor ossis metacarpi pollicis extensor +primi internodii pollicis united (oblique extensor of the metacarpus); +4, tendon of extensor communis digitorum (anterior extensor of the +phalanges); 5, strengthening band from the suspensory ligament of the +fetlock; 6, internal surface of the radius; 7, flexor carpi radialis +(internal flexor of the metacarpus); 8, anterior ulnar (oblique flexor +of the metacarpus); 9, pisiform bone; 10, 10, tendon of the superficial +flexor of the digits (superficial flexor of the phalanges); 11, 11, +tendon of the deep flexor of the digits (deep flexor of the phalanges); +12, sesamoid prominence; 13, suspensory ligament of the fetlock; 14, +internal rudimentary metacarpal.] + +The anterior ulnar arises above from the epitrochlea and the olecranon; +thence it is directed towards the carpus, to be inserted into the +pisiform bone. It proceeds therefore from the inner side of the elbow to +the outer side of the upper part of the hand; it consequently crosses +the posterior surface of the forearm obliquely. This is why, as we have +pointed out above, it receives the name of the oblique flexor of the +metacarpus. + +It is not unprofitable to recall in this connection that there is an +internal flexor of the metacarpus, which is the flexor carpi radialis; +and an external flexor of the metacarpus, which is the posterior ulnar +(in human anatomy, extensor carpi ulnaris). It is between these two +muscles that we find the oblique flexor--the anterior ulnar which we +have just been studying. + +This muscle flexes the hand on the forearm. + +=Superficial Flexor of the Digits= (_Flexor digitorum sublimis_) (Fig. +76, 12; Fig. 77, 10, 10).--This muscle arises from the epitrochlea; +thence it passes towards the hand, becomes tendinous, passes in a groove +on the posterior aspect of the carpus, and terminates on the palmar +surface of the phalanges in furnishing a number of tendons proportioned +to the digital division of the hand. Whatever the number, to which we +will again refer, each tendon is attached to the second phalanx, after +bifurcating at the level of the first, so as to form a sort of ring, +destined to give passage to the corresponding tendon of the deep flexor. +This ring and this passage have gained for the muscle the name of +_perforated flexor_. + +In the dog and the cat the principal tendon is divided into four parts, +which go to the four last digits. + +In the ox it is divided into two parts only; as, moreover, in the pig, +whose superficial flexor is destined for the two large digits only, the +lateral digits receiving no part of it. + +Finally, in the horse the tendon is single. + +We have previously pointed out that in the carnivora this muscle is +visible on the internal and posterior aspects of the forearm, in the +interval which is limited in front by the flexor carpi radialis and +behind and outside by the anterior ulnar. + +Certain details are still to be added to the description of this +muscle. We will enter on an analysis of them after we have given some +indications relative to the following muscle: + +=Deep Flexor of the Digits= (_Flexor digitorum profundus_) (Fig. 75, 21, +22; Fig. 76, 12; Fig. 77, 11, 11).--This muscle is covered by the +superficial flexor. It arises from the epitrochlea, from the radius, and +from the ulna, either from the olecranon process--as in the ox, pig, and +horse--or from almost the whole extent of the shaft of the same bone, as +in the cat and dog. + +[Illustration: FIG. 78.--LEFT ANTERIOR LIMB OF THE HORSE: INTERNAL +ASPECT. + +1, Internal flexor of the metacarpus or great palmar; 2, inferior part +of the biceps; 3, inferior part of the brachialis anticus; 4, internal +lateral ligament of the elbow; 5, pronato teres muscle.] + +The radial fasciculus represents in the domestic quadrupeds the long +proper flexor muscle of the thumb in man. For this reason we shall +describe the muscle afresh in the following paragraph: + +The fleshy bundles of which we have just spoken terminate in a tendon +which afterwards divides into slips, the number of which is in +proportion to the digital division of the hand. These slips then pass +through the slit or _buttonhole_ in the tendon of the superficial +flexor, and proceed to terminate on the third phalanx; hence the name of +_perforating_, which is also given to the deep flexor of the digits. + +In the dog and the cat the tendon is divided into five portions, each of +which proceeds to one of the digits. The internal tendon, which is +destined for the thumb, terminates on the second phalanx of this digit. + +In the pig the tendon divides into four tendons destined for the four +digits. + +In the ox there are but two tendons. + +In the horse the tendon is single. + +As their names indicate, these muscles, both superficial and deep, flex +the digits. In addition to this, they flex the hand on the forearm. + +We mentioned above that certain details relative to the superficial +flexor must be analyzed in a special way. We now add that this should +also be done with regard to the deep flexor. The point in question is +the arrangement which the tendons of these muscles present at the level +of the palmar region of the hand. + +It is easy, in the case of the dog or the cat, to picture to one's self +this arrangement, especially if we recollect that which exists in the +human species. The tendons of the flexors are placed on a kind of +muscular bed formed by the union of the muscles of the region, but, +moreover, from the point of view of external form, these tendons are not +of very great importance. + +But in the ox and the horse it is quite otherwise. From the +simplification of the skeleton of the hand, and the reduction of the +number of movements which the bones that form it are able to execute, +there naturally results a diminution of its muscular apparatus. Apart +from the existence of muscular vestiges of but little importance, we can +say that, in reality, the hand does not possess any muscles. On its +palmar aspect are found only the tendons of the flexors of the digits, +and as these tendons are large, and the hand long, they give origin to +external forms which it is necessary to examine. + +[Illustration: FIG. 79.--LEFT ANTERIOR LIMB OF THE HORSE: EXTERNAL +ASPECT. + +1, Ulna of abnormal length.] + +[Illustration: FIG. 80.--LEFT ANTERIOR LIMB OF THE HORSE: EXTERNAL +ASPECT. + +1, Normal ulna.] + +In the horse, which we take as a type, the tendons of the flexors, after +being retained in position at the carpus by a fibrous band, the _carpal +sheath_, which recalls the anterior annular ligament of the human +carpus, and having passed this region, descend vertically, remaining +separated from the posterior surface of the metacarpus, so that the skin +sinks slightly on the lateral parts in front of the thick cord which +these tendons form. This cord is known by the name of _tendon_. + +The flexors then reach the fetlock, and occupy the groove formed by the +peculiar arrangement of the two large sesamoid bones. They are retained +in position at this level by a fibrous structure, which forms the +metacarpo-phalangeal sheath. They then reach the phalanges, being +directed obliquely downwards and forwards, as, moreover, the latter are +also inclined. Then the tendon of the superficial flexor divides into +two slips, which are inserted into the second phalanx, between which +slips passes the tendon of the deep flexor, which in its turn goes to be +inserted, in the form of an expansion, into the semilunar crest, by +which the inferior surface of the third phalanx is divided into two +parts.[30] + + [30] See, as regards this crest, in the paragraph relative to the hoof + of the solipeds, the figures which represent the third phalanx, + viewed on its inferior surface (Figs. 101 and 102, p. 258). + +The part which these tendons play is of great importance in the large +quadrupeds. + +These tendons, in fact, in addition to the action determined by the +contraction of the fleshy fibres to which they succeed, maintain the +angle formed by the canon-bone and the phalangeal portion of the hand, +and prevent its effacement under the weight of the body during the time +of standing. Their strong development, and the position they occupy, +make this understood, without it being necessary to insist on it +further. + +We mentioned above that the 'tendon' descends vertically from the carpus +towards the fetlocks. This is as it should be. But, in some horses, it +is oblique downwards and backwards, so that the canon, instead of being +of equal depth from before backwards in its whole length, is a little +narrower in its upper part. + +This results from the fact that the tendons of the flexors, too firmly +bound by the carpal sheath, gradually separate as they pass from the +metacarpus, going to join the fetlock; hence the obliquity pointed out +above. This abnormality producing a deleterious result, in the sense +that the tendinous apparatus acts with less strength as an organ of +support, it constitutes a defect of conformation which is expressed by +saying that the tendon has 'failed.' + +=Long Proper Flexor of the Thumb= (_Flexor longus pollicis_) (Fig. 76, +14).--As we have already pointed out, this muscle is represented in +quadrupeds by the radial bundle of the deep flexor of the digits, so +that the two muscles are in reality blended the one to the other. This +union is sometimes found, but only as an abnormality, in the human +species. We have met some examples of this in the course of our +dissections. + +=Pronator Quadratus.=--This muscle conforms to the general law which we +have already pointed out in connection with those which have for their +action the rotation of the radius around the ulna. We remember, indeed, +that when the bones of the forearm are fused with one another, the +muscles which are destined to produce a mobility which has then become +impossible disappear at the same blow. + +[Illustration: FIG. 81.--DIAGRAM OF THE POSTERIOR PART OF A TRANSVERSE +SECTION PASSING THROUGH THE MIDDLE OF THE LEFT FORE-LIMB OF THE DOG: +SURFACE OF THE INFERIOR SEGMENT OF THE SECTION. + +1, Radius; 2, ulna; 3, posterior ulnar; 4, anterior ulnar; 5, great +palmar (_flexor carpi radialis_); 6, flexors of the digits.] + +[Illustration: FIG. 82.--DIAGRAM OF A HORIZONTAL SECTION OF THE MIDDLE +OF THE FOREARM OF THE LEFT LEG OF THE HORSE: SURFACE OF THE INFERIOR +SEGMENT OF THE SECTION. + +1, Radius; 2, ulna; 3, posterior ulnar; 4, anterior ulnar; 5, great +palmar (_flexor carpi radialis_); 6, flexors of the digits.] + +For this cause we do not find the square pronator in either the ox or +the horse, but can demonstrate its presence in the dog and the cat. + +It is very deeply situated. This is why, and also on account of the plan +which we have traced for ourselves, we will simply say that it is +situated on the postero-internal aspect of the skeleton of the forearm, +and that it extends from the ulna to the radius. + +It seems to us, however, sufficiently interesting to add that, instead +of occupying, as in the human species, the inferior fourth of the two +bones, it extends, particularly in the dog, over their whole length, +with the exception of their superior and inferior extremities. + + +Muscles of the Hand + +We will first recall that, in man, the palm of the hand is divided into +three regions: a median palmar region, which is occupied by the tendons +of the flexors of the digits, the lumbricales, and, deeply, by the +interosseous muscles; an external region, or thenar eminence, formed by +the muscles destined for the movements of the thumb; an internal region, +or hypothenar eminence, which contains the muscles proper to the small +digit and the palmar cutaneous muscle. + +These muscles are found, more or less developed, in the dog and the cat. + +In the ox and the horse we meet with no vestige of the muscles of the +thenar or hypothenar eminences. Nevertheless, in these animals we find +the muscles which belong to the central region of the palm. We refer to +the lumbricales and the interosseous. + +Although this fact has no relation to the object of our study, it +appears to us interesting to announce that there are traces of the +lumbricales found in the solipeds. These muscles are represented by two +fleshy bundles, situated one on each side of the tendon of the deep +flexor, above the ring of the tendon of the superficial flexor. These +small muscles are continued as slender tendons, which become lost in the +fibrous tissue of the _spur_, which is the horny process situated at the +posterior part of the fetlock, and which is covered by the hairs, more +or less abundant, which constitute the _wisp_. + +As for the interosseous muscles, they are represented by the _suspensory +ligament of the fetlock_, and by two other small muscles, tendinous +throughout, which are situated between the principal metacarpal and the +rudimentary ones. + +The suspensory ligament of the fetlock is considered an interosseous +muscle, on account of the red fleshy striations which it contains, and +from certain relations which it forms with the tendon of the common +extensor of the digits or anterior extensor of the phalanges. This +ligament (Fig. 75, 26; Fig. 77, 13), which plays an important part in +the standing position as a support of the foot, is a fibrous band +situated between the tendons of the flexors of the digits and the +principal metacarpal. It arises above, from the second row of the +carpals, descends towards the fetlock, where it divides into two +branches, which are inserted into the large sesamoid bones. At the same +level, this ligament gives off two fibrous bands which, passing +downwards and forwards, join the tendon of the anterior extensor of the +phalanges, blending with it, after having each crossed one of the +lateral aspects of the pastern. We have already referred to these bands +(p. 183). + +It is with these latter that are blended the long and slender tendons +which form in a great measure the two other interosseous muscles +previously described. + +A ligament of the same kind is found in the ox (Fig. 74, 23). + + +MUSCLES OF THE POSTERIOR LIMBS + + +Muscles of the Pelvis + +The muscles which specially interest us in this region, because of their +superficial position, are the gluteus maximus and the gluteus medius. As +for the gluteus minimus, it is deeply situated, and more or less sharply +marked off from the second of the preceding muscles. + +Inasmuch as the gluteus medius is more simple in arrangement than the +maximus, and will aid us in arranging our ideas in connection with the +latter, it is with the study of it that we will commence. + +=Gluteus Medius= (Fig. 68, 29; Fig. 69, 26; Fig. 70, 35).--This muscle, +as in man, occupies the external iliac fossa. But this latter being +directed differently in the digitigrades and the ungulates, as we have +pointed out in the section on osteology (see pp. 91 and 99), the muscle +in question has consequently not the same direction in the two groups of +animals, being turned outwards in the first, and upwards in the second. + +It is the thickest of the glutei, and gives to the region which it +occupies a rounded form. + +From the iliac fossa from which it arises the fleshy fibres are directed +towards the femur, to be inserted into the great trochanter. It is +covered by an aponeurosis, and in part by the great gluteal. It +completely covers the small gluteal, which veterinary anatomists +designate by the name of the _deep gluteal_. + +In the carnivora it does not pass in front of the iliac crest, but, in +the ox, and more particularly in the horse, it is prolonged anteriorly, +and thus covers, to a certain extent, the muscles of the common mass. + +When it contracts, taking its fixed point at the pelvis, the gluteus +medius extends the thigh, which it is also able to abduct. If, on the +other hand, its fixed point is on the femur, it acts on the trunk, which +it raises, producing oscillating movements of the pelvis. It contributes +in this way to the action of rearing. We also see it distinctly appear +by the prominence which it produces in the dog, which, according to the +time-honoured phrase, _fait le beau_. + +=Gluteus Maximus= (Fig. 68, 28; Fig. 69, 25; Fig. 70, 33, 34).--The +great gluteal muscle, further designated in veterinary anatomy the +_superficial gluteal_, is proportionately less developed in quadrupeds +than in man. Indeed, in the latter, where it is of very great thickness, +its volume is due to the important function which it fulfils in +maintaining the biped attitude. + +In quadrupeds it contributes to form the superficial part of the crupper +and the external surface of the thigh. It is divided into two parts: one +anterior, the other posterior. + +With regard to this latter, it will be necessary to indicate how it has +been sometimes regarded, and to what portion of the muscular system in +man it corresponds. But we believe that it is better to see beforehand, +without any preconceived idea, how these two parts are arranged. + +In the dog, the anterior portion of the gluteus maximus arises from the +sacrum, while some fibres situated further forward arise from the +surface of the gluteus medius, near the iliac spine, and from the tensor +of the fascia lata with which these fibres are blended. The posterior +portion, united to the preceding--that is to say, to those of its fibres +which arise from the sacrum--takes its origin from the first coccygeal +vertebra. These two portions are directed towards the femur, to be +inserted into the great trochanter, and to the external branch of the +superior bifurcation of the linea aspera. + +In the cat, the posterior bundle is less definitely blended with the +anterior. By a long and slender tendon which, behind, turns around the +great trochanter, and passes along the surface of the fascia lata, it +proceeds to join the knee-cap. + +In the pig, the posterior portion is much more developed. + +In the horse, the anterior portion arises from the internal iliac spine +(posterior in man), from the external iliac spine (anterior in man), +and, between these two osseous points, from the aponeurosis, which +covers the gluteus medius. Between these two origins the muscle is +deeply grooved, so that the tendency is to divide into two portions, +each of which is directed towards one of the iliac angles. In this +groove the gluteus medius is to be seen. + +The fleshy bundles converge, and are directed towards the external +aspect of the femur, to be inserted into the osseous prominence known as +the third trochanter, after passing beneath the fleshy fibres of the +posterior portion. The latter, which is more considerable than the +preceding portion, arises above from the sacral crest, from the +aponeurosis which envelops the coccygeal muscles, from the sacro-sciatic +ligament, and from the tuberosity of the ischium. From this origin it +passes downwards, expands, then, describing a curve with the convexity +behind, it becomes narrowed, and proceeds to be inserted by a deep +fasciculus into the third trochanter, to the fascia lata, and, lastly, +to the knee-cap by the inferior part of its tendon. + +Above, its posterior border is covered by the semi-tendinosus; +interiorly, the same border is in relation with the biceps femoris. + +In the ox, the two parts of the great gluteal muscle are blended +together. + +The long and broad fleshy band which they form arises in a manner +corresponding to that which we have just indicated in connection with +the horse, except that it has no attachment to the femur. The fascia +lata adheres strongly to its anterior border for a considerable length. +The form of the superior border of the great gluteal muscle of this +animal differs from that of the analogous portion in the horse. This +difference results from the peculiar aspect which the corresponding +region of the pelvis presents, and from the fact that, in the ox, as the +semi-tendinosus does not cover the portion of the great gluteal which +arises from the tuberosity of the ischium, the attachments of this +muscle to the sacro-sciatic ligament are uncovered. + +Its descending portion, as a whole, has a rectilinear form, and does not +form a curve such as we indicated in the case of the horse. + +The anterior portion of the great gluteal flexes the thigh. As regards +the posterior portion, it extends the thigh, and abducts it. + +The action of this latter portion is particularly interesting as regards +the horse, because of the great development of the muscular mass which +this region presents in this animal. If the muscle takes its fixed point +above, it acts, in the extension of the thigh during walking, by +projecting the trunk forward during the whole time that the hind-limb to +which it belongs is in contact with the ground. If, on the contrary, it +takes its fixed point below, it makes the pelvis describe a see-saw +movement, upwards and backwards, on the coxo-femoral articulation, and +so contributes to the action of rearing. + +Now that we have a knowledge of the disposition of the great gluteal +muscle, the moment has come to inquire what is the signification of its +posterior portion. The action of the anterior part being clearly +comparable to the human great gluteal, there can be no doubt as regards +the homology of this portion, so we will not insist on it further. + +Of the posterior portion it is wholly different, for it is the homologue +of a fleshy bundle annexed to the great gluteal of man, but which is not +developed except as an abnormality. + +Indeed, we sometimes find, placed along the inferior border of the great +gluteal, a fleshy fasciculus, separated from this muscle by a slight +interspace. This fasciculus, long and narrow, takes origin from the +summit of the sacrum, or the coccyx, and goes to partake of the femoral +insertions of the muscle which it accompanies. We further note a muscle +of the same kind, and presenting the same aspect, which comes from the +tuberosity of the ischium. Notwithstanding the difference which exists, +it is this abnormal fasciculus of man which in the quadrupeds here +studied is considered as constituting the posterior portion of the great +gluteal. + +Bourgelat, considering this posterior portion as belonging to the biceps +cruris, to which, it is true, it adheres, forms of them a muscle which +he designates under the name of the _long vastus_. The anterior +fasciculus of this long vastus is none other than the posterior portion +of the great gluteal which we have just been studying. + + +Muscles of the Thigh + +These muscles are divided into three regions: posterior, anterior, and +internal. + +In a corresponding manner to that which we described in connection with +the arm, the thigh is applied to the side of the trunk, and is free, +more or less, only at the level of the inferior part. + +Further, by reason of this shortening of the femur, the great gluteal +muscle, which is elongated in the ox and the horse, for example, +occupies in part the region corresponding to that which in man is +occupied by the muscles of the thigh, which here are reduced in length. +In other words, they are not superposed, as in the human species, but +juxtaposed. This is what we will verify further on. + +The thigh, as a whole, is flattened from without inwards, its transverse +diameter being less in extent than its antero-posterior. Its external +surface is slightly rounded; that is, of course, in quadrupeds with +sufficiently well-developed muscles. Its internal surface is known as +the _flat of the thigh_. + + +Muscles of the Posterior Region + +It is not unprofitable to recall to mind what muscles form the +superficial layer of this region in the human being. They are the biceps +cruris, semi-tendinosus, and semi-membranosus. We now proceed to +discover their analogues in quadrupeds. + +=Biceps Cruris= (Fig. 68, 30; Fig. 69, 27; Fig. 70, 36).--It is this +which, according to Bourgelat, forms the central and posterior portions +of the long vastus muscle which we have mentioned above. + +We know that the biceps of man is so named from the two portions which +form its upper part. In domestic quadrupeds, and also in the majority of +the mammals, this muscle is reduced to a single portion, that which +comes from the pelvis. It is therefore the portion which arises from the +femur which does not exist. This condition is sometimes found as an +abnormality in the human species. + +The biceps arises from the tuberosity of the ischium; hence it is +directed, widening as it goes, towards the leg, where it terminates by +an aponeurosis which blends with the fascia lata and the aponeurosis of +the leg, and then proceeds to be attached to the anterior border or +crest of the tibia. By its inferior portion it limits externally the +posterior region of the knee--the popliteal space. + +A fibrous intersection traverses the biceps in its whole length, with +the result that the muscle looks as if formed of two portions, one of +which is situated in front of the other. + +In the dog and the cat it also arises from the sacro-sciatic ligament. +At this level its contour is distinguishable from that which corresponds +to the gluteal muscles, so that we there find two prominences one above +the other. The superior is formed by the gluteal muscles; the inferior +corresponds to the tuberosity of the ischium. The two prominences are +separated by a depression, from which the biceps emerges. We draw +attention to this form, the character of which is so expressive of +energy in the carnivora. + +In these animals the biceps is inserted, by its anterior fibres, into +the articulation of the knee, while in the rest of its extent it covers +in great measure by its aponeurosis the external aspect of the leg. + +In the pig, the biceps is but slightly marked off from the posterior +part of the great gluteal. In the ox, the division between these two +muscles is a little more distinct. + +In the horse, the sciatic origin of the biceps is covered by the +semi-tendinosus, so that it only becomes free lower down, to appear in +the space limited behind by the semi-tendinosus, and in front by the +posterior part of the gluteus maximus. + +When the biceps contracts, taking its fixed point from above, it flexes +the leg and helps to extend the thigh. If, on the other hand, it takes +its fixed point from below, it lowers the ischium, makes the pelvis +undergo a see-saw movement, and acts thus in the movement of rearing. It +is sometimes called, on account of one of its actions, and the position +which it occupies, the 'external flexor, or peroneal muscle of the leg.' + +=Semi-tendinosus= (Fig. 68, 31; Fig. 70, 37; Fig. 87, 1; Fig. 88, 1; +Fig. 89, 28).--This muscle forms the contour of the thigh posteriorly, +so that when the latter is viewed from the side, it is the +semi-tendinosus above all that forms the outline. But, as we shall soon +see, it is in this case more distinct above than below, because of the +deviation which it undergoes in order to occupy by its inferior part the +internal side of the leg. + +In the dog, the cat, and the ox, the semi-tendinosus arises from the +tuberosity of the ischium only, as in the human species. In the pig, it +also takes origin higher up from the sacro-sciatic ligament and the +coccygeal aponeurosis. In the horse, it extends still further, for it is +also attached to the crest of the sacrum. + +The indication of these origins is of importance from the point of view +of external form, and to convince ourselves of this it is sufficient to +compare, in the ox and the horse, the region of the pelvis situated +below the root of the tail. In the ox, whose semi-tendinosus arises from +the tuberosity of the ischium only, this region is depressed, and the +cavity which is formed at this level is limited behind by the +tuberosity, which we know is very thick and prominent above. This causes +the superior part of the crupper to be less oblique than in the horse. +This characteristic is more especially marked in the cow, the bull +having this region of a more rounded form. + +In the horse, on account of the semi-tendinosus ascending to the coccyx, +and even to the sacrum, the depression in question does not exist, and +the presence of the tuberosity of the ischium is only slightly revealed. + +Descending from the origin indicated above, and inclining more and more +inwards, the semi-tendinosus proceeds to blend with the aponeurosis of +the leg, to be inserted into the anterior border of the tibia, after +crossing over the internal surface of the latter. It forms the internal +boundary of the popliteal space. + +When this muscle contracts, taking its fixed point at the pelvis, it +flexes the leg. If, on the other hand, it takes its fixed point at the +tibia, it makes the pelvis describe a see-saw movement, and acts +accordingly in the movement of rearing. + +It is sometimes named the 'internal or tibial flexor of the leg,' in +opposition to the crural biceps, which, as stated above, is then the +external flexor of the same region. + +=Semi-membranosus= (Fig. 68, 32; Fig. 87, 2; Fig. 88, 2).--This muscle, +situated on the inner side of the semi-tendinosus, can be seen only when +the thigh is regarded on its posterior aspect. + +It is only by reason of the homology of situation with the corresponding +muscle in man that we give the name under which we are studying it; +indeed, its structure is different, for it does not present the long, +broad, aponeurotic tendon which, in its superior part, characterizes +this muscle in the human species. + +It arises above from the inferior surface of the ischium, and from the +tuberosity of the same bone. In the pig, and especially in the horse, it +passes further upwards, to arise from the aponeurosis of the coccygeal +muscles. So that if we compare it with that of the ox, which does not +extend beyond the ischium, we find that it is associated with the +semi-tendinosus in determining the difference of aspect to which we have +already called attention in connection with the region of the pelvis +situated below the root of the tail. + +The semi-membranosus is then directed downwards and forwards, to take +its place on the internal surface of the thigh, where it is partly +covered by the gracilis muscle. It is inserted in the following manner: + +In the dog and the cat it is divided into two parts, anterior and +posterior. The first, the more developed, is attached to the internal +surface of the inferior extremity of the femur; the second to the +internal tuberosity of the tibia. + +The same arrangement occurs in the ox. + +In the horse it is inserted into the internal surface of the internal +condyle of the femur. + +The semi-membranosus is an extensor of the thigh when it takes its fixed +point at the pelvis; it is also an adductor of the lower limb. If it +takes its fixed point below it assists in the action of rearing. + +It is now necessary for us, especially as regards the horse, to add some +indications relative to the exterior forms of the region constituted by +the semi-membranosus and semi-tendinosus. These two muscles form, by +their union, a surface contour, slightly projecting and of elongated +form, which occupies the posterior border of the thigh, the contour +corresponding to the region known as the _buttock_, in spite of the +fact that none of the gluteal muscles take any part in the structure of +this region. But the appearances, to a certain extent, justify the +preservation of this name. Indeed, because of the groove which separates +the gluteal region of one side from that of the opposite side, and from +the position of the anal orifice in the superior part of this groove, we +may admit the name which, in hippology, has been given to this part of +the thigh. + +In addition to the reasons just given, and which are justified +especially by the position occupied by the muscular mass formed by the +union of the two muscles, there is another which, this time, has a +relation to a certain detail of form. In the superior part of the +convexity, which the gluteal region describes in the greater part of its +extent, there is found a more salient point, greatly accentuated in lean +animals, due to the presence of the tuberosity of the ischium; it is the +_point_ or _angle of the buttock_. At this level, and near the median +line, the semi-membranosus, not aponeurotic, but fleshy, and even +thicker there than anywhere else, sometimes produces a sharply localized +prominence. And as this prominence is situated on the outer side of the +anal orifice, the resemblance to a small 'buttock' is still more marked. + +In lean horses a deep groove separates the mass formed by the +semi-membranosus and semi-tendinosus from that of the other muscles of +the thigh situated more in front; this groove is known by a name which +in this case is remarkably expressive--that of the 'line of poverty.' + +If we examine the gluteal region as a whole by looking at the thigh from +the side, we plainly see the graceful curve produced by the general +convexity above indicated. We return to this point, in order to add +that, in its lower part, this curve alters its character; that is to +say, it is replaced by a slight concavity. This, which is designated +under the name of _the fold of the buttock_, is situated close to the +level of articulation of the leg with the thigh-bone. + + +Muscles of the Anterior Region + +First we recall that in man the anterior muscles of the thigh are: the +triceps cruris, the tensor of the fascia lata, and the sartorius. + +=Triceps Cruris= (Fig. 8, 36; Fig. 69, 31; Fig. 70, 41; Fig. 84, 2; Fig. +87, 3; Fig. 88, 3).--This muscle, which occupies the greater part of the +space between the pelvis and the anterior aspect of the femur, consists +of three parts: an external, or vastus externus; an internal, or vastus +internus; and a median or long portion, or rectus femoris. This division +accordingly recalls that which characterizes the human triceps cruris. +Furthermore, as in the case of the latter, the vastus externus and the +vastus internus take their origin from the shaft of the femur, while the +long portion arises from the pelvis. The _vastus externus_ arises from +the external lip of the linea aspera of the femur (or from the external +border of the posterior surface of this bone in the ox and the horse, in +which the linea aspera, considerably widened, especially in the latter, +forms a surface), and from the external surface of the shaft of the +femur. From this origin its fibres pass downwards and forwards, to be +inserted into the tendon of the long portion of the muscle and into the +patella. + +In the dog and the cat the vastus externus is the most voluminous of the +three portions which constitute the triceps muscle. It is covered by the +fascia lata; but notwithstanding this, its presence is revealed by a +prominence which occupies the external surface of the thigh, and +surmounts, in the region of the knee, the more slightly developed one +which is produced by the knee-cap. + +The _vastus internus_, situated on the inner surface of the thigh, takes +its origin from the corresponding surface of the femur, and proceeds +towards the patella. + +The rectus femoris arises from the iliac bone, above the cotyloid +cavity; its fleshy body, which is fusiform, and situated in front of and +between the two vasti muscles, is directed towards the patella, into +which it is inserted by a tendon, which receives the other two +portions. + +It is covered in front by the tensor of the fascia lata, and contributes +with the vastus externus to form the upper prominence of the knee. + +The ligamentous fibres, which, as in man, unite the knee-cap to the +tibia, transmit to this latter the action determined by the contraction +of the triceps. This muscle is an extensor of the leg. Furthermore, the +rectus femoris, or long portion, acts as a flexor of the thigh. + +=Tensor Fascia Lata= (Fig. 68, 34, 36; Fig. 69, 30, 31; Fig. 70, +40).--This muscle, generally larger in quadrupeds than in man, is flat +and triangular, and occupies the superior and anterior part of the +thigh. + +It arises from the anterior iliac spine (inferior in carnivora, external +in the ox and the horse); it is prolonged downwards by an aponeurosis +(fascia lata) which occupies the external aspect of the thigh, proceeds +to be inserted into the patella and blend with the aponeurosis of the +biceps muscle. + +It covers the rectus and vastus externus portions of the triceps cruris; +it is also in relation with the gluteal muscles. + +The tensor of the fascia lata flexes the thigh, and serves to raise the +lower limb as a whole. + +=Sartorius= (Fig. 68, 35; Fig. 87, 4, 5; Fig. 88, 5).--This muscle, long +and flattened, is called by veterinarians _the long adductor of the +leg_. + +Before beginning the study of its position in quadrupeds, it is +necessary to remember that in man, where the thigh has a form almost +conical, the sartorius commences on the anterior face of this latter, +and is directed downwards and inwards to reach the internal surface of +the knee. + +But now let us suppose the thigh flattened from without inwards; there +will evidently result from this a change in situation with regard to the +muscle in question. In fact, when this supposition is admitted, it is +easy to imagine that in a great part of the extent in which the +sartorius is normally anterior it will become internal. This is why, +these conditions being realized in quadrupeds, we shall find that, in +some of them, the sartorius is situated on the aspect of the thigh which +is turned to the side of the trunk. + +In the dog and the cat it arises from the anterior iliac spine, and from +the half of the border of the bone situated immediately below it; but +the fibres from this second origin being hidden by the tensor of the +fascia lata, on the inner side of which they are situated, viewing the +external surface of the thigh, the muscle seems to arise from the iliac +spine only. + +The sartorius in these animals is divided into two parts, which, in +general, are placed in contact. One of these fasciculi is anterior; the +other is situated further back. The first is visible on the anterior +border of the thigh, in front of the tensor of the fascia lata, but +below it inclines inwards; in its superior part also, a small extent of +the internal surface is occupied by it. The second, which, as we have +said, is situated further back, belongs wholly to the inner surface of +the thigh; it is this portion which arises from the inferior border of +the ilium (this is the homologue of the anterior border of the human +iliac bone). + +The two fasciculi then pass towards the knee, being in relation with the +rectus and the vastus internus of the triceps. The anterior fasciculus +is inserted into the patella. The posterior unites with the tendons of +the gracilis (see below) and semi-tendinosus, and then proceeds to be +inserted into the superior part of the internal surface of the tibia. + +On account of their different insertions these two parts receive the +names of _the patellar sartorius_ and _tibial sartorius_ respectively. + +In the ox and the horse the sartorius is still more definitely situated +on the internal surface of the thigh. Consisting of a single fasciculus, +representing the tibial sartorius of the cat and the dog, it arises in +the abdominal cavity from the fascia covering the iliac muscle, then +passes under the crural arch, and terminates, by an aponeurosis which +blends with that of the gracilis, on the inner fibres of the patellar +ligament. In short, the sartorius is of interest to us in the carnivora +only, and especially on account of its anterior or patellar fasciculus. + +It is an adductor of the leg and a flexor of the thigh. + + +Muscles of the Internal Region + +The ilio-psoas pectineus and the adductors which we study in man, in +connection with the internal aspect of the thigh, offer little of +interest from the point of view of external form in quadrupeds; it is +for this reason that we will disregard them. + +The gracilis alone merits description. + +=Gracilis= (Fig. 87, 9; Fig. 88, 6).--Designated in veterinary anatomy +under the name of _the short adductor of the leg_, this muscle, expanded +in width, occupies the greater part of the internal surface of the +thigh, _or flat of the thigh_, as this region is also called. Let us +imagine, in man, the internal surface of the thigh broader, and the +internal rectus more expanded, and we shall have an idea of the same +muscle as it exists in quadrupeds. + +The gracilis arises from the ischio-pubic symphysis and from the +neighbouring regions; thence it is directed towards the leg to be +inserted into the superior part of the internal surface of the tibia, +after being united to the tendons of the sartorius and semi-tendinosus. +We find, accordingly, at this level, an arrangement which recalls the +general appearance of what in man receives the name of _the goose's +foot_ (_pes anserinus_). + +It is between this muscle and the sartorius, at the superior part of the +internal surface of the thigh, in the region which recalls the triangle +of Scarpa, that we are able, especially in the cat and the dog, to see +the adductor muscles of the thigh. We also partly see there, in these +animals, the vastus internus and the rectus of the triceps (see Fig. +87). The gracilis is an adductor of the thigh. + + +Muscles of the Leg + +We will divide the leg into three regions: anterior, external, and +posterior. With regard to the internal region, there are no muscles +which belong exclusively to it; for it is in great measure formed by the +internal surface of the tibia, which, as in man, is subcutaneous. + + +Muscles of the Anterior Region + +We first note that in the human species the tibialis anticus, extensor +proprius pollicis, extensor longus digitorum and the peroneous tertius +or anticus, form the subcutaneous layer of this region. We now proceed +to study these muscles in quadrupeds. + +[Illustration: FIG. 83.--MYOLOGY OF THE HORSE: THE ANTERIOR TIBIAL +MUSCLE (FLEXOR OF THE METATARSUS), LEFT LEG, ANTERIOR VIEW. + +1, Femoral trochlea; 2, tibia; 3, tendinous portion of the tibialis +anticus; 4, cuboid branch of same; 5, 5, its metatarsal branch; 6, +fleshy portion; 7, cuneiform branch of its tendon; 8, metatarsal branch +of the same tendon; 9, extensor longus digitorum (anterior extensor of +the phalanges turned outwards); 10, peroneus brevis (lateral extensor of +the phalanges).] + +=Tibialis Anticus= (Fig. 83; Fig. 84, 6; Fig. 85, 4; Fig. 87, 10; Fig. +88, 10, 11).--It is further named by veterinarians the _flexor of the +metatarsus_. + +In the dog and the cat this muscle, which is rather large, arises from +the external tuberosity of the tibia and from the crest of this bone. In +its superior part it is flat, but lower down it is thick and produces a +prominence in front of the tibia. Finally, it becomes tendinous, and +passes towards the tarsus; thence it is directed towards the inner side +of the metatarsus, and is inserted into the great-toe, this latter being +sometimes well developed, but also often merely represented by a small +bony nodule on which the muscle is then fixed. + +In the other animals with which we here occupy ourselves, the tibialis +anticus presents a complexity which would be incomprehensible unless +this muscle be first studied in the horse. + +In this latter the tibialis anticus consists of two distinct portions, +placed one in front of the other: a fleshy portion, and a tendinous +portion running parallel to it. + +The muscle is covered, except on its internal part and inferiorly, by a +muscle with which we will occupy ourselves later on--that is, the common +extensor of the toes. + +The tendinous portion of the tibialis anticus (Fig. 83), especially +covered by the extensor of the toes, arises from the inferior extremity +of the femur, from the fossa situated between the trochlea and the +external condyle; thence it descends towards a groove which is hollowed +out on the external tuberosity of the tibia, and is directed towards the +tarsus, where it divides into two branches, which are inserted into the +cuboid bone and the superior extremity of the principal metatarsal. +These two parts form a ring through which the terminal tendon of the +fleshy portion of the same muscle passes. + +This fleshy portion, situated behind the preceding, arises from the +superior extremity of the tibia, on the borders of the groove in which +the tendinous portion lies; thence it passes downwards for a short +distance on the inner side of the common extensor of the toes, which +covers it in the rest of its extent. It ends in a tendon which, after +passing through the tendinous ring above noticed, divides into two +branches. One of these branches is inserted into the anterior surface +of the superior extremity of the principal metatarsal, the other into +the second cuneiform bone. + +[Illustration: FIG. 84.--MYOLOGY OF THE DOG: LEFT HIND-LIMB, EXTERNAL +ASPECT. + +1, Biceps cruris and fascia lata, divided in order to expose the upper +part of the muscles of the leg; 2, inferior portion of the triceps +cruris; 3, patella; 4, semi-tendinosus; 5, inferior extremity of the +femur; 6, tibialis anticus (flexor of the metatarsus); 7, extensor +longus digitorum (anterior extensor of the phalanges); 8, tibia; 9, +peroneus longus; 10, peroneus brevis; 11, fifth metatarsal; 12, +fasciculus detached from the peroneus brevis and passing towards the +fifth toe; 13, external head of gastrocnemius; 14, tendo-Achillis; 15, +calcaneum; 16, flexor digitorum sublimis; 17, 17, tendon of the flexor +digitorum sublimis; 18, flexor longus pollicis (portion of the deep +flexor of the toes); 19, dorsal muscle of the foot (short extensor of +the toes).] + +In the ox the same two portions of the tibialis anticus exist, but with +this capital difference--that the anterior portion is fleshy, +superficial, and blended for a great part of its length with the common +extensor of the toes. + +The portion which corresponds to that which is fleshy in the horse +arises from the tibia; below, it ends on the inner surface of the +superior extremity of the metatarsus and the cuneiform bones. That which +represents the tendinous part, which is also fleshy, as we have just +pointed out, arises above with the common extensor of the toes, from the +femur, in the fossa situated between the trochlea and the external +condyle; whilst below, after having given passage to the tendon of the +preceding portion, as in the horse, it is inserted into the metatarsus +and the cuneiform bones. + +In the pig, the tibialis anticus presents an arrangement nearly similar +to that which we have just described. + +It seems to us of interest to add that it has been sought to ascertain +to what muscle of the human leg the tendinous part of the tibialis of +the horse corresponds--a part which has become fleshy in the pig and the +ox. + +According to some authors, it represents the peroneus tertius; but that +muscle is situated on the outer side of the common extensor of the toes; +and here the portion with which it has been compared is placed on the +inside. It has also been likened to a portion of the common extensor of +the toes, but it does not pass to the latter. Lastly, it has been +considered as being the homologue of the proper extensor of the +great-toe; but why, then, in the ox, which has no great-toe, is it so +highly developed? Nevertheless, its position and its relations +sufficiently warrant this method of comprehending it. The tibialis +anticus is a flexor of the foot. It is also able, in animals in which +the tarsal articulations allow of the movement, to rotate the foot +inwards. + +[Illustration: FIG. 85.--MYOLOGY OF THE OX: LEFT LEG, EXTERNAL ASPECT. + +1, Gluteus maximus and biceps cruris; 2, semi-tendinosus; 3, patella; 4, +tibialis anticus (flexor of the metatarsus); 5, extensor longus +digitorum (anterior extensor of the phalanges); 6, fasciculus of the +extensor longus digitorum, which is considered as the representative of +the tendinous portion of the tibialis anticus in the horse; 7, peroneus +longus; 8, peroneus brevis (proper extensor of the external toe); 9, +external head of gastrocnemius; 10, soleus; 11, tendo-Achillis; 12, +calcaneum; 13, tendon of the extensor longus digitorum (superficial +flexor of the phalanges); 14, flexor longus pollicis and tibialis +posticus (deep flexor of the phalanges); 15, tendon of the superficial +flexor of the toes; 16, tendon of the deep flexor of the toes; 17, +suspensory ligament of the fetlock.] + +With regard to the tendinous part, called by veterinarians the _cord of +the flexor of the metatarsus_, it serves, in the horse, to produce the +flexion of the metatarsus when the knee is already flexed; it thus acts +in a passive fashion, which is explained by its resistance and the +position which it occupies in relation to these two articulations. + +=Extensor Proprius Pollicis.=--This muscle exists only in the dog and +the cat, and there in a rudimentary condition. + +It is covered by the common extensor of the toes and the tibialis +anticus, and passes, accompanied by the tendon of this latter muscle, to +terminate on the second metatarsal, or the phalanx, which articulates +with it. When the first toe exists in the dog, it is inserted into this +by a very slender tendon. + +=Extensor Longus Digitorum= (Fig. 83, 9; Fig. 84, 7; Fig. 85, 5, 6; Fig. +86, 4; Fig. 87, 12; Fig. 88, 7).--It is also called by veterinarians +_the anterior extensor of the phalanges_. + +In the dog and the cat this muscle is to be seen in the space limited +behind by the peroneus longus and in front by the tibialis anticus. +Above it is covered by this latter. In the lower half of the leg, it is +also in relation, on the inner side, with the tibialis anticus; but +behind it is separated from the peroneus longus by the external surface +of the shaft and inferior extremity of the tibia. This arrangement, +besides, recalls that which is found in man, the peroneus longus of the +latter diverging in the same way, at this level, from the common +extensor, and leaving exposed the corresponding portion of the skeleton +of the leg. + +This muscle, fusiform in shape, arises at its upper part from the +external surface of the inferior extremity of the femur, then its tendon +passes into a groove hollowed on the external tuberosity of the tibia. +The fleshy body which succeeds is directed towards the tarsus, but +before reaching it is replaced by a tendon. This tendon, at the level of +the metatarsal bones, divides into four slips, which pass towards the +toes, and are inserted into the second and third phalanges of the +latter. + +In the horse it covers, to a great extent, the tibialis anticus, so that +it is the latter which forms the large fusiform prominence especially +noticeable in the middle region, to which the contour of the anterior +surface of the leg is due. + +[Illustration: FIG. 86.--MYOLOGY OF THE HORSE: LEFT HIND-LIMB, EXTERNAL +ASPECT. + +1, Semi-tendinosus; 2, biceps cruris; 3, patella; 4, extensor longus +digitorum (anterior extensor of the phalanges); 5, reinforcing band +arising from the ligament of the fetlock; 6, peroneus brevis (lateral +extensor of the phalanges); 7, external head of gastrocnemius; 8, +soleus; 9, tendo-Achillis; 10, calcaneum; 11, tendon of the superficial +flexor of the toes (superficial flexor of the phalanges); 12, flexor +longus pollicis and tibialis posticus (deep flexor of the phalanges); +13, 13, tendon of the superficial flexor of the phalanges; 14, 14, +tendon of the deep flexor of the phalanges; 15, suspensory ligament of +the fetlock; 16, principal metatarsal: 17, external rudimentary +metatarsal.] + +It arises above from the inferior extremity of the femur, from the fossa +situated between the trochlea and the external condyle; therefore, it +has a common origin with the tendinous portion of the tibialis anticus, +or flexor of the metatarsus. + +The tendon, which at the level of the inferior part of the leg succeeds +to the fleshy body, passes in front of the tarsus, the principal +metatarsal, and receives the tendon of the peroneus brevis which we will +describe later on. It then reaches the anterior surface of the fetlock. +There it presents an arrangement analogous to that which we have pointed +out in connection with the anterior extensor of the phalanges--a muscle +which, in the fore-limbs, corresponds to the common extensor of the +digits; that is to say, it is inserted, in form of an expansion, into +the pyramidal prominence of the third phalanx, after having formed +attachments to the first and second, and having received on each side a +strengthening band from the suspensory ligament of the fetlock. + +In the ox the long extensor of the toes is united above, and for a great +part of its length, with the portion of the tibialis anticus, which +represents, albeit in the fleshy state, the tendinous cord of the latter +in the horse. + +In common with this portion, it arises from the inferior extremity of +the femur. Thence it passes towards the tarsus and divides into two +fasciculi, internal and external, which are continued by tendons. These +pass towards the phalanges, and, in case of the common extensor of the +digits belonging to the fore-limbs, the internal is destined for the +internal toe, and the external is common to the two toes. + +[Illustration: FIG. 87.--MYOLOGY OF THE DOG: LEFT HIND-LIMB, INTERNAL +ASPECT. + +1, Semi-tendinosus; 2, semi-membranosus; 3, triceps cruris (vastus +internus); 4, sartorius (patellar); 5, sartorius (tibial); 6, patella; +7, first or middle adductor; 8, small and great adductor united; 9, +gracilis; 10, tibialis anticus (flexor of the metatarsus); 11, tibia; +12, tendon of extensor longus digitorum (anterior extensor of the +phalanges): 13, gastrocnemius, inner head; 14, tendo-Achillis; 15, +calcaneum; 16, popliteus; 17, superficial flexor of the toes; 18, flexor +longus pollicis (portion of the deep flexor of the toes); 19, flexor +longus digitorum (portion of the deep flexor of the toes); 20, tendon of +the tibialis posticus.] + +[Illustration: FIG. 88.--MYOLOGY OF THE HORSE: LEFT HIND-LEG, INTERNAL +ASPECT. + +1, Semi-tendinosus; 2, semi-membranosus; 3, triceps cruris (vastus +internus); 4, patella; 5, sartorius; 6, gracilis; 7, extensor longus +digitorum common extensor of the toes (anterior extensor of the +phalanges); 8, tendon of the preceding muscle; 9, reinforcing band given +off by the suspensory ligament of the fetlock; 10, tibialis anticus +(flexor of the metatarsus), its tendinous portion; 11, tibialis anticus +(flexor of the metatarsus), its fleshy portion; 12, cuneiform branch of +the tendon of this fleshy portion; 13, internal head of gastrocnemius; +14, popliteus; 15, tendon of the flexor brevis digitorum (superficial +flexor of the phalanges); 16, flexor longus pollicis and tibialis +posticus (deep flexor of the phalanges); 17, flexor longus digitorum +(oblique flexor of the phalanges); 18, 18, tendon of the superficial +flexor of the phalanges; 19, 19, tendon of the deep flexor of the +phalanges; 20, suspensory ligament of the fetlock; 21, principal +metatarsal; 22, internal rudimentary metatarsal.] + +In the pig the general arrangement of the muscle is similar, but the +tendons end in a manner which is a little more complicated. Apart from +the fasciculi which correspond to the tendinous portion of the tibialis +anticus (fleshy here, as in the ox), the long extensor of the toes at +the level of the tarsus divides into three tendons: the internal goes to +the great internal toe; the middle bifurcates in the upper part of the +digital portion of the foot, and each of its branches goes towards one +of the great-toes; the external divides to pass towards each of the two +small toes, and towards the great ones; but this latter disposition is +not constant. + +By its contraction the muscle which we have just studied extends the +phalanges and flexes the foot. + +=Peroneus Tertius.=--This muscle is not found in domestic quadrupeds. + +We should remember, nevertheless, that certain authors consider as +representing it the tendinous portion of the anterior tibial of the +horse, or the corresponding portion now fleshy, of the same muscle in +the pig and the ox. It is by reason of this fact that it is called the +third peroneal, notwithstanding that in the numerical order of the +peroneals it is rather the first. + +But that which still further complicates this question of nomenclature +is that some authors give this name of third to a peroneal which, in the +carnivora, is situated more definitely in the group of external muscles +(see below, =Short Lateral Peroneal=). + + +Muscles of the External Region + +In man, two muscles constitute this region; they are the peroneus longus +and peroneus brevis. + +=Peroneus Longus= (Fig. 84, 9; Fig. 85, 7).--This muscle does not exist +in the domestic animals; only in the flesh-eaters, the pig and the ox +excepted. + +It is in relation superiorly with the tibialis anticus, and inferiorly +with the common extensor of the toes; in the ox, it is in contact with +this latter muscle throughout its whole length. + +The peroneus longus arises from the external tuberosity of the tibia; +towards the middle of the leg it is replaced by a tendon. This proceeds +towards the tarsus, but previously it passes between the tibia and +fibula. In the ox it is situated in front of the coronoid tarsal bone; +we recollect that this bone is regarded as representing the inferior +extremity of the fibula (see p. 97). Then it passes into a groove +belonging to the cuboid bone or to the cuboido-scaphoid bone in the ox, +traverses obliquely the posterior aspect of the tarsus, and is inserted +into the rudimentary bone which represents the first toe; or, if this +does not exist, into the innermost of the metatarsal bones. + +This muscle is an extensor of the foot. It also rotates it outwards in +the animals in which the articulation permits this latter movement. + +=Peroneus Brevis= (Fig. 83, 8; Fig. 83, 10; Fig. 84, 10; Fig. 86, +6).--In the dog and the cat, this muscle is covered in part by the +peroneus longus, and arises from the inferior half of the tibia and the +fibula; at the level of the tarsus it becomes tendinous, passes into a +groove hollowed out on the external surface of the inferior extremity of +the fibula, and terminates on the external aspect of the superior +extremity of the fifth metatarsal. A little before this insertion it +crosses the tendon of the long peroneal in passing to the outer side of +the latter. + +To the short peroneal muscle is found annexed a very thin fasciculus +which lies upon it. This fasciculus arises from beneath the head of the +fibula, and is soon replaced by a thin tendon, which, accompanying that +of the short peroneal, proceeds towards the foot, after having traversed +the groove in the inferior extremity of the fibula; passes along by the +fifth metatarsal (Fig. 84, 12); blends at the level of the first phalanx +of the fifth toe with the corresponding tendon of the long extensor of +the toes, and partakes of the insertions of this tendon. + +This fasciculus is designated by some authors under the name of the +peroneal of the fifth toe, or the proper extensor of the same toe. But +what makes still further complications is that other authors regard it +as an anterior, or third, peroneal. Now, these names are those which +other anatomists have applied to the fasciculus of the anterior tibial, +which, in the pig and the ox, is fused in part with the long extensor of +the toes. Hence there results a confusion which is truly regrettable. + +In brief, we can, without inconvenience, consider it as a fasciculus of +the short peroneal muscle. + +We sometimes find in man, but abnormally, an arrangement which partly +recalls that which we have just indicated. It consists in a duplication +of the tendon of the short peroneal, one of the branches of which goes +to the fifth metatarsal, and the other to the fifth toe; it is sometimes +a single fasciculus which goes to the phalanges of this latter. We have +met with examples of these anomalies.[31] In the pig, the short peroneal +is situated on the same plane as the long. It consists of two clearly +distinct fasciculi, which arise from the fibula. The tendon of the +anterior fasciculus proceeds to the great external toe--that is to say, +the fourth, of which it is the proper extensor. The posterior fasciculus +terminates on the small external toe, the fifth, of which it is in like +manner the extensor. + + [31] Edouard Cuyer, 'Anomalies, Osseous and Muscular' (_Bulletins de + la Societe d'Anthropologie_, Paris, 1891). + +In the ox, the fleshy fibres of the short peroneal arise from a fibrous +band which replaces the fibula, and from the external tuberosity of the +tibia. Situated behind the long peroneal and on the same plane, it +terminates in a tendon which appears at the level of the inferior part +of the leg; it passes in front of the canon, and is inserted into the +external toe, of which it is the proper extensor. + +In the horse, it is the sole representative of the peroneal muscles, and +veterinary anatomists have given it the name of _the lateral extensor of +the phalanges_. + +Its fleshy body arises above from the external lateral ligament of the +knee-joint, and from the whole length of the fibula. In the middle third +of the leg it is narrowed; lower down it is replaced by a tendon. This +is lodged in a groove hollowed on the external surface of the inferior +extremity of the tibia; then after passing along the external surface of +the tarsus, it is directed forward, and proceeds to blend towards the +middle of the canon-bone with the tendon of the long extensor of the +toes, or anterior extensor of the phalanges, of which it shares the +insertions. It extends the phalanges into which it is inserted. It also +flexes the foot. + + +Muscles of the Posterior Region + +It will not be unprofitable to recall to mind that, in man, the muscles +of this region are arranged in two layers: a superficial layer +consisting of the gastrocnemius and soleus, to which is added a muscle +of little importance, the plantaris, and a deep layer formed by four +muscles--the popliteus, flexor longus digitorum, tibialis posticus, and +flexor longus pollicis. + +The gastrocnemius and soleus, independent in their upper portion, unite +below in a common tendon; they thus form also a triceps muscle, which we +designate under the name of the triceps of the leg, or triceps suralis, +because it forms the elevation of the calf of the leg (from _sura_, +calf). + +=Gastrocnemius= (Fig. 83, 9, 11; Fig. 84, 13, 14; Fig. 86, 7, 9; Fig. +88, 13).--The external and internal heads of the gastrocnemius, distinct +from one another only in their upper portion, arise from the shaft of +the femur, above the condyles, on the borders of the popliteal surface, +to a relatively considerable extent in the great quadrupeds. + +At this level they are situated in the popliteal region--that is to say, +in the space limited externally by the biceps, and internally by the +semi-tendinosus. But as they descend to a rather low level on the leg in +quadrupeds, and especially in carnivora, they do not, properly speaking, +determine a projection of the calf of the leg. However, they pass from +this region but to be soon continued by a tendon--the tendo-Achillis, +which is inserted into the calcaneum. + +Now, the region of the tarsus is called by veterinarians _the ham_, the +posterior surface of which is angular, because of the oblique direction +of the leg with regard to the vertical direction of the metatarsus and +the presence of the calcaneum; the prominence which this surface +presents has received the name of _the point of the ham_, and the tendon +which ends there that of _the cord of the ham_. + +But the tendo-Achillis does not alone form this cord. Indeed, as we will +soon see, the tendon of the superficial flexor of the toes takes part in +its formation. + +We may add, with regard to the tendo-Achillis, that it is more clearly +perceived as an external feature, because the skin sinks in front of it, +as it does in man, over the lateral parts of the region which it +occupies. + +The gastrocnemius, when it contracts, extends the foot on the leg. + +It serves to maintain the tibio-tarsal angle in the standing position, +and during walking, to determine the steadying of the hind-limbs, which +then, after the fashion of a spring, project the body forward. + +By an analogous movement they take part in the posterior projection of +the hind-limbs in the act of kicking; but they are not the only ones to +act in this case, the muscles of the buttock and thigh also being +brought into play. + +=Soleus= (Fig. 83, 10; Fig. 86, 8).--This muscle, much less developed in +quadrupeds than in man, does not exist in the dog. + +With regard to the soleus in the pig, Professor Lesbre says: 'Meckel +denied its existence; we, however, believe that it is united to the +external head of the gastrocnemius, its origin being transferred to the +femur.'[32] + + [32] F. X. Lesbre, 'Essai de Myologie comparee de l'homme et des + mammiferes domestiques en vue d'etablir une nomenclature unique + et rationelle,' Lyon, 1897, p. 169. + +But in animals in which it exists, this muscle, of but little +importance, occupies the outer side of the leg. It arises above from the +external tuberosity of the tibia, and terminates below in a tendon which +is united with that of the gastrocnemius. + +The soleus has the same action as these latter. + +=Plantaris.=--In quadrupeds this muscle is blended with the superficial +flexor of the toes, which we will study afterwards. + +=Popliteus= (Fig. 87, 16; Fig. 88, 14).--In man, this muscle, which +occupies the posterior surface of the tibia, above the oblique line, is +completely covered by the gastrocnemius. + +In quadrupeds, where it is more voluminous, it projects internally +beyond the gastrocnemius, so that it is seen in the internal and +superior part of the region of the superficial layer of muscles, +immediately behind the internal surface of the tibia, which, as we know, +is subcutaneous. + +The popliteus arises from the external surface of the external condyle +of the femur. Thence its fibres which diverge pass to be inserted into +the superior part of the posterior surface and of the internal border of +the tibia. It is in this latter region that it projects beyond the +gastrocnemius, but we may add that there it is more or less covered by +the semi-tendinosus. + +It flexes the leg, and rotates it forwards. + +=Superficial Flexor of the Toes= (Fig. 83, 13, 15; Fig. 84, 17; Fig. 86, +11, 13, 13; Fig. 87, 17; Fig. 88, 15, 18, 18).--In man, the homologue of +this muscle is found in the sole of the foot. It is called _the short +flexor of the toes_. It arises from the calcaneum, and passes to the +four outer toes. In quadrupeds, it rises as high as the back of the +knee, and is found blended with the plantaris. + +Further designated by the name of _the superficial flexor of the +phalanges_, covered in part by the gastrocnemius, with which it is in +relation for a great part of the course which it traverses, this muscle +arises from the posterior surface of the femur, on the external branch +of the inferior bifurcation of the linea aspera. In the horse, this +origin takes place in a depression situated above the external condyle, +in the supracondyloid fossa. Then it accompanies the gastrocnemius, and +becomes tendinous where the tendo-Achillis commences. It then winds +round the latter in placing itself on its inner side, then on its +posterior surface, and reaches the calcaneum. It accordingly +contributes, as we have already pointed out, to form the cord of the +ham. After having become expanded, and having covered as with a sort of +fibrous cap the bone of the heel, it descends behind the metatarsus, and +presents there an arrangement analogous to that which we pointed out in +connection with the superficial flexor of the digits--that is, it +contributes to form the _tendon_. This prominence, in the form of a +cord, we see behind the canon-bone in solipeds and ruminants. It +finally terminates in the same way as the muscle with which we have +compared it (see p. 197). + +In the horse, its fleshy body is but slightly developed, so that its +tendon alone is specially visible in the superficial muscular layer, but +in the dog and the cat it is large. Hence it results that its fleshy +body appears on each side of the inferior half of the gastrocnemius, and +produces an elevation which recalls that which the soleus produces on +each side of the same muscles in the human species. + +The muscles which follow form, with the popliteus, which we have already +studied, the deep layer of the posterior region of the leg. + +=Flexor Longus Digitorum= (Fig. 87, 19; Fig. 88, 17).--This muscle, in +man, is the only common flexor of the toes belonging to the muscles of +the leg. + +In comparison with the preceding muscle, it is a deep flexor. +Veterinarians have given it the name of _the oblique flexor of the +phalanges_. + +Visible on the internal aspect of the superficial layer of the muscles +of the leg, this muscle arises above from the posterior surface of the +external tuberosity of the tibia, becomes tendinous, passes towards the +metatarsus, and blends with the tendons of the posterior tibial and the +long proper flexor of the great-toe. In the dog and the cat it is +blended with this latter only. + +=Tibialis Posticus= (Fig. 85, 14; Fig. 86, 12; Fig. 87, 20; Fig. 88, +16).--This muscle arises from the external tuberosity of the tibia, and +from the head of the fibula. Thence it passes to the tarsus, and +terminates in different fashion in carnivora and other quadrupeds. + +In the dog and the cat, it is inserted into the ligamentous apparatus of +the tarsus, or into the base of the second metatarsal. + +In the other quadrupeds with which we are here occupied it is blended +with the long proper flexor of the great-toe. + +It is accordingly in the carnivora that the mode of termination of the +tibialis posticus most nearly resembles that of this same muscle in the +human species. From this independence there results a special action. + +It is an adductor and internal rotator of the foot. + +=Flexor Longus Pollicis= (Fig. 84, 18; Fig. 85, 14; Fig. 86, 12; Fig. +87, 18; Fig. 88, 16).--This muscle, as that in man, is the most external +of the deep layer of the leg. It is on the external aspect of the latter +we perceive it, between the peroneals and the gastrocnemius or +tendo-Achillis. + +It arises from the fibula and tibia, and is thence directed towards the +tarsus. It unites with the long common flexor of the toes to form with +it _the deep flexor of the phalanges_, of which it is the principal +fasciculus. We may add that in the dog and the cat the posterior tibial +remains independent of this latter, but that in the pig, ox, and horse +the posterior tibial is united to the preceding to form with them the +deep flexor muscle. + +Thus constituted, the deep flexor goes towards the phalanges, where it +terminates as the deep flexor of the digits of the fore-limbs (see p. +197). In animals possessed of a canon it contributes to form the +_tendon_ (Fig. 85, 16; Fig. 86, 14, 14; Fig. 88, 19, 19). + + +Muscles of the Foot + +We must remember that on the dorsal surface of the foot in man we find +but a single muscle--the dorsalis pedis. The remaining subcutaneous +structures of this region consist of the tendons of the anterior muscles +of the leg which occupy this dorsal aspect. + +=Dorsalis Pedis= (Fig. 84, 19).--Also called the extensor brevis +digitorum, the dorsalis pedis muscle is found in all domestic +quadrupeds; but its development is so much the less as the number of +digits is more reduced. + +In the dog and the cat it arises from the calcaneum, and is inserted +into the three internal toes (the first toe excepted) by uniting with +the corresponding tendons of the common extensor. + +In the pig its disposition is analogous. + +As for the dorsalis pedis of the ox and the horse, it is extremely +rudimentary, and occupies the superior part of the canon. It is a small, +fleshy body, situated on the anterior surface of the metatarsus, which +arises from the calcaneum, whence it passes to unite at its inferior +extremity with the tendon of the extensor of the phalanges. + +As regards the muscles of the sole of the foot, we think it unnecessary +to occupy ourselves at any length with them because of their slight +importance with regard to external form. + +We will only recall that in the median portion of this plantar surface +we find in man the short flexor of the toes, which in quadrupeds arises +higher up, from the posterior surface of the femur; that it belongs to +the muscles of the leg; and that it forms the superficial flexor of the +toes, which we have already studied. + +We may further add that the suspensory ligament of the fetlock in +ruminants and solipeds represents, as in the fore-limbs, the +interosseous muscles. + + +MUSCLES OF THE HEAD + +We will divide these muscles into two categories: masticatory and +cutaneous. + + +Masticatory Muscles + +The muscles of this group which specially interest us are the masseter +and the temporal. As regards the pterygoids, since they are situated +within the borders of the inferior maxillary bone, and consequently do +not reach the surface, we shall not require to occupy ourselves with +them here. + +=Masseter= (Fig. 89, 2; Fig. 90, 1; Figs. 91, 92).--For those who have +studied the masseter of man, it is not difficult to recognise that of +quadrupeds. Nevertheless, the particular aspect which it presents in +different species gives to its study a certain interest. + +Arising from the zygomatic arch, and passing downwards and backwards, it +is inserted into the external surface of the ramus of the mandible and +into its angle. + +Its posterior border is in relation with the parotid gland (Fig. 90, 14; +Figs. 91, 92), this gland being situated between the corresponding +border of the lower jaw bone and the transverse process of the atlas. +Such are the general characters; the following are the particular ones: + +In the carnivora it is thick and convex. In the horse it is flat, but +more expanded; it forms the _flat of the cheek_. In the ox it is flat, +as in the latter; but, while being less thick, it is more prolonged in +the vertical direction. + +The form of the osseous parts which give it origin is, besides, in +relation with these differences, and explains the peculiar characters +which the masseter presents. + +[Illustration: FIG. 89.--MYOLOGY OF THE DOG: MASTICATORY MUSCLES (A +DEEPER DISSECTION THAN THAT SHOWN IN FIG. 90). + +1, Zygomatic arch; 2, masseter; 3, temporal exposed by the suppression +of the auricular and occipital muscles and the pinna of the ear; 4, +auditory canal; 5, inferior maxillary bone; 6, digastric.] + +Indeed, in the dog and the cat the zygomatic arch, strongly convex, +springs up in a marked manner from the plane of the lateral aspects of +the skull. + +In the horse the same arch, less prominent externally, is prolonged by a +rectilinear crest on the superior maxillary bone, where it is continued +in forming the zygomatic or maxillary spine. + +In the ox the same crest ascends a good way towards the inferior margin +of the orbit in a curved direction with the concavity inferior, to +redescend afterwards on the external surface of the superior maxilla. + +The masseter is an elevator of the lower jaw. It acts, above all, as in +the human species, in the process of mastication. + +=Temporal Muscle= (Fig. 89, 3).--The development of the temporal is in +proportion to the energy of the movements of elevation which the lower +jaw has to execute. + +It arises from the temporal fossa, and is inserted into the coronoid +process of the inferior maxilla. + +Its development, enormous in the carnivora, is such that the muscle +projects beyond its fossa. It is less voluminous in the horse, and still +less so in the ox. In the latter, indeed, the temporal fossa, although +deep, is of small extent (see Fig. 62, p. 119); the frontal bone being +large, it is found to be thrown back on the lateral walls of the +cranium, below the osseous processes which support the horns and +overhang the fossa in question, as well as the muscle which it contains. + +It is covered by the auricular muscles, and by the base of the pinna of +the ear. + +Like the masseter, the temporal is an elevator of the lower jaw. + + +Cutaneous Muscles of the Head + +=Occipito-Frontalis.=--The epicranial aponeurosis is extremely thin. In +the dog the occipital muscle occupies the superior part of the head; it +overlies the temporal muscle. + +With regard to the frontal muscle, which is of great extent in the ox +(Fig. 91, F), it is represented in the horse and the carnivora by a +small fleshy fasciculus only, the _fronto-palpebral muscle_, similar to +the superciliary muscle. This, occupying the superior and internal part +of the border of the orbit, ends by blending its fibres with those of +the orbicular muscle of the eyelids at the region of the eyebrow. + +=Orbicularis Palpebrarum= (Fig. 90, 2; Figs. 91, 92).--This annular +muscle surrounds the palpebral orifice, and takes its origin on the +internal part of the orbital region. In the horse it arises, by a small +tendon, from a tubercle which occupies the external surface of the os +unguis, or lachrymal bone. + +This muscle determines the narrowing and closure of the palpebral +orifice. + +=Pyramidalis Nasi.=--The pyramidal muscle is not found in the domestic +animals. It appears to be blended with the internal elevator of the +upper lip and wing of the nose; this is easy of comprehension if we bear +in mind the relative position of these two muscles in the human species. + +[Illustration: FIG. 90.--MYOLOGY OF THE DOG: MUSCLES OF THE HEAD. + +1, Masseter; 2, orbicularis palpebrarum; 3, zygomaticus major; 4, +lachrymal (this muscle is sometimes described under the name of the +small zygomatic); 5, levator labii superioris proprius; 6, levator +labii superioris alaeque nasi; 7, caninus; 9, buccinator; 11, +zygomatico-auricularis; 12, external temporo-auricularis; 14, parotid +gland; 15, parotido-auricularis; 16, inferior maxillary bone; 17, +digastric.] + +=Corrugator Supercilii.=--This muscle is represented by the +fronto-palpebral muscle noticed above, which is by some regarded as a +vestige of the frontal. + +=Zygomaticus Major= (Fig. 90, 3; Figs. 91, 92).--This is the +_zygomatic-labial_ of veterinarians. This muscle is of an elongated +form, and has a ribbon-like aspect. + +In the dog and the cat it arises from the base of the pinna of +the ear, from the portion of this base which bears the name of +scutiform cartilage. (With regard to this cartilage, see p. 242, +=Zygomatico-auricularis=.) From this it is directed downwards and +forwards, to terminate, after having crossed the masseter, on the deep +surface of the skin of the corresponding labial commissure. + +This mode of termination is the same in the ox and the horse; but where +the muscle differs is at the level of its upper extremity. There it +ascends less than in the carnivora. In the ox it arises from the +zygomatic arch in the neighbourhood of the temporo-maxillary +articulation; in the pig and the horse its origin is still lower, on the +surface of the masseter, close to the maxillary spine. + +When it contracts, it draws upwards the labial commissure. + +Now, in man, we remember, it is the great zygomatic that, by an action +of the same kind, determines the essential characters of the expression +of laughing. + +There is, accordingly, a connection to be established between those +displacements which are similar and the analogy of facial expression +which necessarily results from them.[33] + + [33] Edouard Cuyer, 'The Mimic,' Paris, 1802. + +=Zygomaticus Minor= (Fig. 90, 4; Figs. 91, 92).--The existence of this +muscle has not been clearly demonstrated. Nevertheless, Straus-Durckheim +noted its presence in the horse, and described it as 'a muscle arising +by two heads, of which one, the superior, arises from the malar bone +below the orbit, and passes downwards and forwards over the +fibro-adipose layer which supports the moustache. The second, the +inferior, arises from the alveolar border in front of the second molar +tooth, and passes forward to be inserted into the same fibro-adipose +layer.'[34] + + [34] H. Straus-Durckheim, 'Anatomie descriptive et comparative du + chat,' Paris, 1845, t. ii., p. 210. + +In connection with other quadrupeds, it is described by certain authors +as a very thin muscle, arising below the cavity of the orbit, where it +is blended with the fibres of the internal elevator of the upper lip and +the ala of the nose; thence it proceeds to terminate below by uniting +with the subcutaneous muscle. But this muscle is regarded by other +authors as the lachrymal muscle, which does not exist in this state in +man, but of which the development is particularly remarkable, as to +extent, in the ox, in which it descends as far as the buccinator. + +According to other authors, some of the fibres of this muscle constitute +the small zygomatic. + +[Illustration: FIG. 91.--MYOLOGY OF THE OX: MUSCLES OF THE HEAD. + +1, Masseter; 2, orbicularis palpebrarum; F, frontalis; 3, zygomaticus +major; 4, lachrymal (this muscle is sometimes described under the +name of small zygomatic); 5, levator labii superioris proprius; 6, +levator labii superioris alaeque nasi; 7, levator anguli oris or +caninus; 8, orbicularis oris; 9, buccinator; 10, maxillo-labial; 11, +zygomatico-auricularis; 12, external temporo-auricularis; 14, parotid +gland; 15, parotido-auricularis; 16, inferior maxillary bone.] + +=Levator Labii Superioris Proprius= (Fig. 90, 5; Figs. 91, 92).--Also +named by veterinarians the _supramaxillo-labial_, or again, the _proper +elevator of the upper lip_, this muscle arises from the external surface +of the superior maxillary bone, passes under the superficial elevator, +which we shall study in the succeeding paragraph, and goes to be +inserted into the thickness of the lip, to which its name indicates that +it belongs. + +The peculiarities of this muscle in different animals are the following: + +In the dog and the cat it arises behind the infra-orbital foramen. + +In the pig it arises from a depression below the orbital cavity, and its +fleshy body is terminated in front by a strong tendon in the upper part +of the snout, in which it divides into fasciculi. + +In the ox it arises from the maxillary spine. + +In the horse it arises below the orbital cavity; then, after having +crossed the superficial elevator, it ends in a tendinous expansion, +situated in the median line between the nasal fossae. This expansion +divides into fasciculi, which end in the thickness of the upper lip. + +By the contraction of this muscle, the lip is raised, on one side only, +if a single muscle contracts, or in its whole extent, if the two muscles +act simultaneously. + +=Internal Elevator (or Superficial) of the Upper Lip and the Wing of the +Nose= (_levator labii superioris alaeque nasi_) (Fig. 90, 6; Figs. 91, +92).--This is the muscle veterinarians designate _the supranaso-labial_. + +Arising from the frontal and nasal bones, it thence passes towards the +upper lip, where it is inserted as well as into the wing of the nose. + +In the ox it is united above with the frontal muscle, and below is +divided into two fasciculi, between which pass the elevator described +above and the canine muscle. + +In the horse it is also divided into two fasciculi; but the arrangement +is the opposite as regards, their relations with neighbouring muscles, +in this animal and in the preceding. + +In the ox the external fasciculus is covered by the external elevator +and the canine, which pass under the internal fasciculus; in the horse +the deep elevator passes under the two fasciculi, and the canine passes +under the external bundle, and afterwards covers the internal. + +In the pig, the internal elevator is wanting. + +As its name indicates, it raises the upper lip and the wing of the +nose. + +=Transversus Nasi.=--In the horse this muscle, which is very thin, is +situated on the dorsum of the nose, and proceeds to be inserted into the +cartilaginous skeleton of the nostrils. In the pig, it occupies an +analogous situation. It does not exist in the ox or in carnivora. The +transversus nasi is a dilator of the nostrils. + +[Illustration: FIG. 92.--MYOLOGY OF THE HORSE: MUSCLES OF THE HEAD. + +1, Masseter; 2, orbicularis palpebrarum; 3, zygomaticus major; 4, +lachrymal (this muscle is sometimes described under the name of the +small zygomatic); 5, external elevator (or deep) of the upper lip and +ala of the nose; 6, internal elevator (or superficial) of the upper lip +and of the ala of the nose; 7, levator anguli oris or caninus; 8, +orbicularis oris; 9, buccinator; 10, maxillo-labialis; 11, +zygomatico-auricularis; 12, temporo-auricularis externus; 13, +cervico-auricularis; 14, parotid gland; 15, parotido-auricularis; 16, +inferior maxillary bone.] + +=Caninus= (Fig. 90; Figs. 7, 91, 92).--This is the muscle called by +veterinarians _the great supramaxillo-nasal_. + +In the dog and the cat it is situated below the inferior border of the +external elevator of the upper lip, of which it follows the direction. +It arises, as does this latter, from the external surface of the +maxilla, and goes also to terminate in the upper lip by blending with +the internal elevator of this lip and of the alae of the nose. It raises +the upper lip. + +In the ox, it arises from the maxillary spine, and then divides into +three parts; the superior passes under the internal portion of the +internal elevator of the upper lip and the alae of the nose, and goes +into the nostril; whilst the two others, situated lower down, terminate +in the upper lip. + +In the pig, it is formed of two superimposed fasciculi, which arise from +the spine of the maxilla and the impressions in front of it. These two +fasciculi terminate in the snout, which they move laterally. + +In the horse, it is situated at a certain distance from the external +elevator; in the preceding animals it is in contact with the latter. +Arising behind from the external surface of the maxilla, in front of the +maxillary spine, it is directed towards the anterior part of the face, +passes under the external portion of the internal elevator (it is the +opposite of this in the ox), and proceeds, on expanding, to terminate in +the skin of the nostril. By its contraction it dilates the latter. + +=Orbicularis Oris= (Fig. 91, 8; Fig. 92).--This muscle, very fleshy in +the solipeds and the ruminants, is arranged as a ring round the buccal +orifice, in the thickness of the lips, where it is blended with the +other muscles of this region. + +Having for its function the narrowing of the orifice it surrounds, it +acts during suction and in the prehension of food. + +=Triangularis Oris.=--This muscle does not exist in domestic quadrupeds. + +=Quadratus Menti.=--In the pig and the carnivora, it arises from the +anterior part of the body of the inferior maxillary bone, and passes at +the other end to terminate in the corresponding portion of the lower +lip, which it depresses by its contraction. + +In the ox and the horse this muscle does not exist; it is replaced for +the depression of the lower lip, which it affects in other animals, by +supplemental fibres of the buccinator. + +=The Prominence of the Chin.=--Below the lower lip in the horse is +situated the so-called _prominence of the chin_, limited posteriorly by +the _beard_, a depressed region which gives point to the curb of the +bridle. + +The prominence, which also exists in the ox, is a fibro-muscular pad +which blends with the orbicular muscle of the lips, and receives on its +superior aspect the insertion of the two muscles (_levator menti_) by +which it is suspended. These arise, above, on each side of the symphysis +of the inferior maxillary bone. They raise the lower lip with force, and +they are the agents which, as we can sometimes observe in the horse, +make it click against the upper lip, suddenly projecting it upwards. +This action sometimes becomes a habit, and its continuance constitutes a +vice. + +A corresponding structure is found in the pig and in the carnivora, but +in them it does not produce an external prominence such as we have +described. + +=Buccinator= (Fig. 90, 9; Figs. 91, 92).--Further designated by the name +of _alveolo-labial_, this muscle is situated on the lateral portions of +the face, in the thickness of the cheeks. It consists of two layers, one +superficial and the other deep. + +The deep portion arises from the portion of the alveolar border of the +superior maxillary bone which corresponds to the molar teeth, and from +the anterior border of the ramus of the mandible. Thence it is directed +forwards, passes under the superficial layer, and blends with the fibres +of the orbicular muscle of the lips. To this part of the buccinator some +authors give the name of molar muscle. + +The superficial portion is formed by fibres which pass from the alveolar +border of the superior maxillary bone to the corresponding border of the +opposite bone. It is very highly developed in the herbivora. + +This muscle acts especially during mastication; it serves to press back +again under the molar teeth the portions of food which fall outside the +dental arch. + +In the pig, the ox, and the horse, a muscle which is considered as +supplemental to the buccinator is placed along the inferior border of +the latter. + +This muscle, which we describe separately under the names of +_maxillo-labialis_ (Fig. 91, 10; Fig. 92) and _depressor of the lower +lip_, is clearly distinct from the buccinator, especially in the horse. +It arises, behind, with the deep layer of the muscle to which it is +annexed, from the anterior border of the ramus of the lower jaw; in +front it terminates in the thickness of the lower lip. + +In the ox, it is more intimately united with the buccinator. + +It depresses the lip to which it is attached, and displaces it laterally +when it acts on one side only. + +In the human species, the pinna of the ear being generally immobile, the +muscles which belong to it are, very naturally, considerably atrophied. +Accordingly, the auricular muscles, anterior, superior, and posterior, +are reduced to pale and thin fleshy lamellae, whose action is revealed in +certain individuals, only in a way which may be said to be abnormal. + +It is not the same in quadrupeds. The pinna of the ear is extremely +mobile, and its displacements have a real value from the point of view +of physiognomical expression. It is therefore necessary to review the +muscles which move this pinna without giving them, at the same time, +more importance than they merit, since in themselves they do not +determine the formation of surface reliefs, which are sufficiently +apparent. + +Notwithstanding that for certain of these muscles it is possible to +trace their analogy with those of the auricular region of man, it is +very difficult, because of their complexity, to trace this analogy for +all. This is why we shall not be able here, as we have done for the +other muscles of the subcutaneous layer, to give at the head of each +paragraph the name of a human muscle, and then to group in the same +paragraph the muscles which correspond to it in different quadrupeds. +Therefore the nomenclature and the divisions adopted for these latter +must serve us as a base or starting-point. + +Because the pinna of the horse's ear is so very mobile, we will first +begin with a study of its auricular muscles. + +=Zygomatico-auricularis= (Fig. 92, 11).--This muscle, which is formed of +two small bands of fleshy fibres, arises from the zygomatic arch in +blending with the orbicular muscle of the eyelids; thence it is +directed towards the base of the pinna of the ear, and is inserted into +this base, and also into the cartilaginous plate situated in front of +and internal to this, and resting on the surface of the temporal muscle; +this is the scutiform cartilage. + +The zygomatico-auricularis, which we look on as the homologue of the +anterior auricular of man, draws the pinna of the ear forwards. + +=Temporo-auricularis Externus= (Fig. 92, 12).--This, which is thin and +very broad, covers the temporal muscle. + +It arises from the whole extent of the parietal crest, blending in this +plane, in its posterior half, with the muscle of the opposite side. +Thence it is directed outwards towards the pinna of the ear, and is +inserted into the internal border of the scutiform cartilage and on the +inner side of the concha--that is to say, of the conchinian +cartilage--which forms the principal part of the pinna. We are +supposing, in the description of the muscles which move it, that this +pinna has its opening directed outwards. + +The external temporo-auricular, which recalls, from its situation, the +superior auricular of man, is an adductor of the ear; besides, it causes +it to describe a movement of rotation from without inwards, so as to +direct its opening forwards. + +=Scuto-auricularis Externus.=--This muscle may be considered as +supplementary to the external temporo-auricular; the concha fasciculus +of this latter partly covers it. + +Extending from the scutiform cartilage to the inner side of the concha, +it contributes to the movement of rotation by which the opening of the +pinna of the ear is directed forwards. + +=Cervico-auricular Muscles= (Fig. 92, 13).--These muscles, three in +number, are situated behind the pinna of the ear; they are called, from +their mode of superposition, the superficial, middle, and deep. + +These arise, all three, from the superior cervical ligament, and pass +from there towards the cartilage of the concha. They recall, as regards +situation, the posterior auricular muscle of man. + +=Superficial Cervico-auricular= (_Cervico-auricularis +superioris_).--This muscle, inserted into the posterior surface of the +concha, draws this cartilage backwards and downwards. + +=Middle Cervico-auricular= (_Cervico-auricularis medius_).--Situated +between the two other muscles of the same group, it proceeds, after +having covered the superior extremity of the parotid gland, to be +inserted into the external part of the base of the concha. It determines +the rotation of this concha in such a way as to direct the opening of +the ear backwards. + +=Deep Cervico-auricular= (_Cervico-auricularis inferioris_).--Covered by +the preceding muscle and the superior portion of the parotid, it is +inserted into the base of the pinna of the ear, and has the same action +as the middle cervico-auricular. + +=Parotido-auricularis= (Fig. 92, 15).--This is a long and thin fleshy +band which arises from the external surface of the parotid gland, and +tapering as it passes upwards towards the pinna of the ear, is inserted +into the external surface of the base of the concha, below the inferior +part of the angle of reunion of the two borders which limit its opening. + +It inclines the pinna outwards; it is, accordingly, an abductor of the +pinna. + +=Temporo-auricularis Internus.=--This muscle is covered by the external +temporo-auricular and the superior cervico-auricular. It arises from the +parietal crest, and is inserted into the internal surface of the concha. +It is an adductor of the pinna of the ear. + +There are, finally, an internal scuto-auricular muscle and a +tympano-auricular; but they do not present any interest for us; we can +simply confine ourselves to making mention of them. + +In the ox, because of the situation of the temporal fossa and the fact +that the external temporo-auricular muscle is applied, as in the horse, +over the muscle which this fossa contains, this temporo-auricular muscle +does not reach the middle line (Fig. 91, 12). + +But in the cat and the dog this muscle covers all the upper part of the +head (Fig. 90, 12). It is divided into two parts: the interscutellar and +the fronto-scutellar. + +The interscutellar is a single muscle, thin and broad, covering the +temporal muscle and a portion of the occipital, extending from the +scutiform cartilage of the pinna of one side to the same cartilage of +the pinna belonging to the side opposite. It approximates the two pinnae +to one another by bringing them each into the position of adduction. + +The fronto-scutellar arises from the orbital process of the frontal +bone, and from the orbital ligament, which at this level completes the +interrupted osseous boundary of the orbital cavity. Thence it is +directed, widening as it proceeds, towards the scutiform cartilage, and +is there inserted by blending with the corresponding part of the great +zygomatic. Its action is analogous to that of the preceding muscle; but, +further, it directs the opening of the pinna forwards. + +These are the muscles which act, for example, when the dog, having his +attention strongly attracted by any cause, pricks up his ears and turns +the openings forward, in order the better to understand every sound +which proceeds, or may possibly proceed, from that which he observes. +From this, which may be extremely well seen in some individuals, results +the appearance of vertical wrinkles of the skin in the interval between +the pinnae of the ears, these being caused by the folding of the +integument, whilst the pinnae approach one another. These movements, with +which are associated fixation of look and a widening of the palpebral +fissure, produce a peculiarly expressive look; this is why they merit +our attention. + +=Zygomatico-auricularis= (Fig. 90, 11).--Arises from the internal +surface of the great zygomatic, passes towards the pinna of the ear, and +goes to be inserted into the external part of the base of the pinna, +below its opening, to a prominence which corresponds to the antitragus +of the human ear. It is to this antitragus, but proceeding from another +direction, that the parotido-auricular muscle is inserted (Fig. 90, 15). + +With regard to the cervico-auriculars, they are all three present. The +superior, or superficial, situated behind the interscutellar portion of +the external temporo-auricular, has its origin on the median line of the +neck; thence it passes towards the pinna of the ear, blending its fibres +with those of the interscutellar muscle, and is inserted into the +scutiform cartilage and the internal surface of the pinna. + +Such are the principal muscles of the ear in the carnivora; it would +seem to us superfluous to dwell on the others of this region, so that we +will here conclude the study of the muscles in general, and that of the +myology of the head in particular. + + + + +CHAPTER III + +EPIDERMIC PRODUCTS OF THE TERMINAL EXTREMITIES OF THE FORE AND HIND +LIMBS + + +We will first recall to mind that among the quadrupeds some are found of +which the fingers and toes have their third phalanges terminated by +claws--these are the unguiculates; and that in others the terminal +extremity of each limb is completely encased in a horny envelope, the +hoof--these are the ungulates. + +In the first group, the claws remind us to a certain extent of the +arrangement of the nails in man; the inferior aspect of the paws is +covered by an epidermic layer, thick and protective, which may be +likened to the skin, correspondingly thick, which covers in the greater +part of its extent the plantar surface of the foot in the human species. + +In the second group, the surface by which the third phalanx rests on the +ground is correspondingly protected, but this time by a layer of horn +which belongs to the hoof. + +After the preceding remarks, our study will be found to fall into a +natural division, and it is in the order which we have just followed for +the purpose of indicating its existence that we now proceed to study the +nature and form of the different elements which complete or protect the +digital extremities of the thoracic and abdominal limbs. + +=Claws.=--These horny coverings of the third phalanges, which we have to +consider only in the dog and cat, may be compared with the nails of man, +with which, however, they present, as is well understood, characteristic +differences. + +The claws are compressed laterally, curved on themselves, and are +terminated in front by a sharp point in the felide, but more blunted in +the dog. Their superior border is convex and thick. We may say, +therefore, that a claw is a sort of hollow tube, in the form of a cone +flattened in the transverse direction, in which the third phalanx is +set, and which is itself set in a groove formed by a kind of osseous +hood which occupies the base of this third phalanx (see Fig. 37, p. 57). + +This definition is exact, as regards the general appearance; but, when +more closely scrutinized, it is not sufficient. The tube in question is +not formed of a single piece; each of the claws is formed by a lamina +laterally folded, but of which the borders are not exactly joined +together inferiorly; they leave between them a small interval, and this +is filled by a layer of more friable horny substance, to which has been +given the name of plantar nail. This arrangement, which is clearly +defined in the dog (Fig. 93), is comparable to that which we shall +afterwards meet with in connection with the sole of the hoof of the +horse (see Fig. 100, p. 257). In the dog and the cat, the weight of the +limb resting on the inferior surface of the phalanges, it was necessary +that the region of the plantar surface of the foot corresponding to +these latter should be protected; this is the function of certain +fibro-adipose pads, which are situated there, and which are designated +by the name of _plantar tubercles_. + +=Plantar Tubercles= (Fig. 94).--These tubercles, or dermic cushions, are +divided, in each paw, into _tubercles of the digits_ (or of the toes), a +_plantar tubercle_, and, on the fore-limbs, a _tubercle of the carpus_. + +The tubercles of the fingers (or of the toes) are of the same number as +the latter. That which belongs to the thumb is but little developed, but +the others are more so. They are in relation with the plantar surfaces +of the second and third phalanges, so that when the paw is in contact +with the ground the articulation which, in each of the fingers or toes, +joins these phalanges, rests on the corresponding pad. + +The plantar tubercle is larger than the preceding. It is of a more or +less rounded form; sometimes it is triangular, and then comparable in +outline to the ace of hearts, the point of which is, in this case, +turned towards the claws; its margin being sometimes strongly indented, +it may also have a trilobate form. It is on it that rest the +metacarpo-phalangeal or metatarso-phalangeal articulations, according to +the limb studied. The tubercle of the carpus, situated at the level of +the posterior surface of this latter, is less important than the +preceding, the region which it occupies not reaching the ground during +walking. But it is not to be neglected from the point of view of +external form, because of the prominence which it produces. + +[Illustration: FIG. 93.--CLAW OF THE DOG: INFERIOR SURFACE. + +1, Horny lamina of the claw; 2, plantar nail; 3, tubercle of the +corresponding digit.] + +[Illustration: FIG. 94.--LEFT HAND OF THE DOG: INFERIOR SURFACE, PLANTAR +TUBERCLES. + +1, 1, 1, 1, 1, Tubercles of the fingers; 2, plantar tubercle; 3, +tubercle of the carpus.] + +In the ungulates the terminal extremity of the limb is, as we have above +pointed out, enclosed in a horny envelope which is no other than the +hoof. + +We will first study the hoof of the horse--a hoof which is single for +each of the limbs, inasmuch as in this animal each of these has but a +single digit. + +=Hoofs of the Solipeds.=--We will first study the hoof as regarded in a +general way--that is, without taking into account the limb to which it +belongs. We will afterwards point out the differences presented when the +hoofs of the fore and hind limbs are compared. + +In connection with the external forms of the horse, the study which we +are now commencing is of great importance. But, before entering upon it, +it appears to us necessary to rapidly examine what the hoof contains +(Fig. 95). + +[Illustration: FIG. 95.--VERTICAL ANTERO-POSTERIOR SECTION OF THE FOOT +OF A HORSE. + +1, Third phalanx; 2, fibro-cartilage; 3, podophyllous tissue; 4, +inferior part of the wall; 5, section of the wall of the hoof; 6, +cutigerous cavity; 7, tendon of the anterior extensor of the phalanges; +8, reinforcing band coming from the suspensory ligament of the fetlock; +9, tendon of the superficial flexor of the phalanges; 10, tendon of the +deep flexor of the phalanges.] + +In the interior of this horny box we find the third phalanx, a small +sesamoid bone placed opposite to the posterior border of the latter, a +portion of the inferior extremity of the second phalanx, and the +tendons, which terminate at this region. + +To the third phalanx are added two fibro-cartilaginous plates, flattened +laterally, which prolong backwards the bone to which they are annexed. +The inferior border of each of these fibro-cartilages is fixed by its +anterior part to two osseous prominences situated at each of the angles +which terminate the small phalanx behind; these prominences are: _the +basilar process_ and _the retrorsal process_ (Fig. 96); by its posterior +part, this border is continuous with a structure known as _the plantar +cushion_ (see further on). + +The posterior border is directed obliquely upwards and forwards. The +superior border, which is convex or rectilinear, is thin, and is +separated from the posterior border by an obtuse angle. Finally, the +anterior border, which is directed obliquely downwards and backwards, is +united to the ligamentous apparatus, which keeps the second and third +phalanges in contact. + +These fibro-cartilages, at their upper extremities, project beyond the +hoof, and therefore assist in the formation of the lateral regions of +the foot,[35] at the part which is called the _crown_. They project less +above the hoof in the posterior limbs. + + [35] Here, for the first time, apropos of the hoof, we use the word + 'foot.' As in osteology and in myology we have, for the sake of + clearness of comparison, designated under this name the region + limited above by the tarsus, it is necessary to point out here + that we employ the same word for a more restricted region. This + we did in conformity with the usage of veterinarians, who so + designate the region of the hoof. It is necessary to explain this + double employment of the word, and, further, to show the + particular meaning ascribed to it. + +[Illustration: FIG. 96.--THIRD PHALANX OF THE HORSE: LEFT ANTERIOR LIMB, +EXTERNAL SURFACE. + +1, Pyramidal eminence; 2, surface, for articulation with the inferior +extremity of the second phalanx; 3, basilar process; 4, retrorsal +process.] + +The posterior and inferior borders of these cartilages meet at an acute +angle. The angle so formed, or cartilaginous bulb, constitutes the base +of the region, which is commonly called the _heel_--a part of the foot +which, as its name implies, is situated posteriorly, but which we must +not confound, as we might be led to do, with the region occupied by the +calcaneum. We know from our previous studies of comparative osteology +that this latter is situated much higher up. + +The _plantar cushion_ is a sort of fibrous wedge which occupies the +interval bounded by the fibro-cartilaginous plates which we have just +been studying. Its inferior surface, the form of which we shall find to +be reproduced by a portion of the corresponding surface of the hoof, is +prolonged anteriorly into a point, while behind it is divided into two +branches, which, diverging from one another, join the posterior angles +of the fibro-cartilages. These two branches are separated by a median +excavation. + +The different constituent elements which we have just been discussing +give elasticity to the foot. + +To finish the examination of the parts contained in the hoof, we will +add that among them is also found what is called the fleshy _envelope_, +or _flesh_ of the foot. + +We divide the latter into three regions: the podophyllous tissue, +striated or laminated flesh which is spread out over the anterior +surface of the third phalanx; the pad, or the hardened skin which +corresponds to the upper border of the hoof, and forms a prominence +above the podophyllous tissue; and the villous flesh, or velvety tissue +which covers the plantar surface of the third phalanx and the plantar +cushion. These three tissues form as a whole the keratogenic +membrane--that is to say, that which produces horny tissue, and +consequently regenerates the hoof. + +It is this latter that we now proceed to study. + +When we examine its anterior surface or the opposite one, the hoof of +the horse has the shape of a truncated cone with the base below and the +summit cut off obliquely downwards and backwards (Fig. 97). + +Viewed on one of its lateral aspects, it may be compared to a truncated +cylinder placed on the surface of the section (Fig. 98). We particularly +call attention to this latter comparison, for it singularly aids us in +making a representation of the foot of the horse when viewed laterally. + +Notwithstanding that the hoof forms apparently a homogeneous whole, it +consists of three parts, which may be separated from one another by +maceration. The indication of such disunion, artificially produced, may +seem useless. It is not so, however, for this division of the hoof will +permit us to carry out the study of the latter in a clearer, and +consequently a more satisfactory, way. The three parts in question are +the _wall_, or _crust_, the _sole_, and the _frog_. + +The _wall_ is that portion of the hoof which we see when the foot rests +on the ground. It is a plate of horn which, applied to the anterior and +lateral surfaces of the foot, diminishes in height as it approaches the +posterior part of the region. Posteriorly and at each side the wall is +folded on itself, and is then directed forwards to terminate in a point, +after having enclosed the frog, which we will soon study. + +[Illustration: FIG. 97.--LEFT ANTERIOR FOOT OF THE HORSE: ANTERIOR +ASPECT. + +1, Outer side; 2, inner side.] + +Although the wall forms a continuous whole, it has been divided into +regions to which special names are given. The anterior part, from the +superior border to the inferior, is called the _pince_ or _toe_ for a +width of 4 to 5 centimetres. External to the toe, and on each side of +it, for a distance of 3 or 4 centimetres, is the _nipple_. Behind the +_nipples_ are the _quarters_. Still further back, where the wall folds +on itself, forming the _buttress_, is found the region of the _heels_. +Finally, the portions of the wall which form its continuation in passing +forward are called the _bars_.[36] These are only visible on the +inferior surface of the hoof (see Fig. 100). + + [36] It is to the angle of inflexion or heel that some authors give + the name of buttress; it is the bars which other authors + designate in this fashion. + +The wall, convex transversely, is, in its anterior part (viz., the +_toe_) inclined strongly downwards and forwards. This obliquity tends to +become gradually effaced on the lateral parts to such a degree that at +the quarters it becomes almost perpendicular to the surface of the +ground. + +The internal quarter is less rounded than the external; in addition to +this (Fig. 97), it approaches more nearly to the vertical direction. + +[Illustration: FIG. 98.--LEFT ANTERIOR FOOT OF THE HORSE: EXTERNAL +ASPECT. + +1, Fetlock; 2, spur or beard; 3, pastern; 4, outline determined by the +external fibro-cartilage; 5, acute angle; 6, nipple; 7, quarter; 8, +heel.] + +In our opinion, this latter difference clearly recalls certain +characters of the general form of the human foot. In fact, the latter +has its dorsal surface inclined downwards and outwards, whereas its +internal border may be said rather to be vertical. A transverse section +of the foot (Fig. 99) justifies this comparison, which to us appears +interesting, not only as regards the resemblance which exists between +these organs of support, but, further, because it constitutes a mnemonic +which enables us, on condition that we remember the form of the human +foot, to recall the above-described character of that of the horse. + +The greater convexity of the outer portion of the hoof is found equally +on the human foot; the external border of this foot is more convex than +the opposite one. + +The inferior border of the wall (Fig. 100) is, in the case of unshod +horses, always in wear when in contact with the ground. It is intimately +united to the circumference of the sole (see further on). + +[Illustration: FIG. 99.--VERTICAL AND TRANSVERSE SECTION OF A LEFT HUMAN +FOOT: OUTLINE OF THE DIVIDED SURFACE OF THE POSTERIOR SEGMENT OF THIS +SECTION (DIAGRAMMATIC FIGURE). + +AA', Vertical axis passing through the middle of the leg and the second +toe; 1, outer side; 2, inner side.] + +The superior border is hollowed on its internal surface by a groove, the +cutigerous cavity or basil, which lodges the cushion (see Fig. 95). We +have described this latter above, in connection with the flesh of the +foot. + +The substance of the wall presents a fibrous appearance which is pretty +strongly pronounced. The constituent fibres from which this appearance +results are directed from the superior border towards the inferior in +parallel and regular lines. + +The _sole_ is a horny plate which occupies the inferior surface of the +hoof (Fig. 100). It is situated between the inferior border of the wall +and the bars; and, on account of the oblique direction of these latter, +it presents a strongly-marked groove of a [V]-form, with the opening +directed backwards. In this depression is lodged the frog. + +The inferior surface is concave, and thus forms a sort of vault, more or +less deep, according to the individual. The sole has a scaly, laminated +aspect. + +We have seen (Fig. 93, and p. 249) that on the inferior surface of the +claws of carnivora is found a small interval which is filled by a plate +of a more friable horny substance, to which has been given the name of +the plantar nail. It seems to us that there is an interesting +relationship between the said plantar nail and the sole which we have +just been studying. + +[Illustration: FIG. 100.--INFERIOR SURFACE OF A FORE-HOOF OF THE HORSE: +LEFT SIDE. + +1, Internal border of the wall (toe); 2, wall; 3, quarter; 4, heel; 5, +bar; 6, sole; 7, frog; 8, median cavity; 9, prominence of the frog; 10, +lateral cavity.] + +Indeed, these two horny structures appear to be homologous. Is not the +lamina of the claw comparable to the wall of the hoof? And does not the +interval which occurs at the inferior part of this latter, and is filled +by the sole, recall that which, in extremely reduced form, is filled by +the plantar portion of the claws? + +The _frog_ (Fig. 100) is a mass of horn, in form of a wedge, with its +apex in front, which occupies the space limited laterally by the +recurved portions of the wall (the bars) and the posterior border of the +sole. + +It covers the plantar cushion previously described (p. 252) and +reproduces its form. + +Its inferior surface is hollowed out in the middle by an excavation, +which is known as the _median lacuna_. This cavity separates the +branches of the frog, which terminate posteriorly by two swellings which +are known as _the prominences of the frog_, forming two rounded +elevations situated above the claws. These same branches unite in front +of the median lacuna to form the body of the frog. This latter, in its +anterior part, gradually narrows, and terminates in a point which +occupies the bottom of the hollow limited laterally by the bars of the +wall and the posterior border of the sole. + +Between the lateral surfaces of the frog and the bars are found two +angular cavities--_the lateral lacunae_, or the _commissures of the +frog_. + +[Illustration: FIG. 101.--THIRD PHALANX OF THE HORSE: LEFT ANTERIOR +LIMB, INFERIOR VIEW. + +1, External border; 2, internal border; 3, semilunar crest; 4, 4, +re-entrant processes.] + +[Illustration: FIG. 102.--THIRD PHALANX OF THE HORSE: LEFT POSTERIOR +LIMB, INFERIOR VIEW. + +1, External border; 2, internal border; 3, semilunar crest; 4, 4, +re-entrant processes.] + +As an indispensable complement to the study which we have just +made, it is necessary to add that the hoofs of the fore-limbs and +those of the hind ones present differences of form which cannot be +ignored--differences which we are already able to conjecture by looking +at the respective third phalanges which terminate those limbs, and +especially at their inferior surfaces (Figs. 101, 102). + +The hoofs of the fore-limbs (see Fig. 100), viewed on their plantar +surface, are more rounded than those of the hind-limbs (Fig. 103)--so +that their external contour may be compared to a semicircle--whilst the +hind-hoofs, which are narrow and of more oval shape, rather recall by +their form the aspect of an ogive. + +This seems to result from the fact that the fore-limbs support the more +considerable part of the weight of the animal. The best proof which can +be given of this overweighting is the eagerness with which very often, +when a horse is stopped near the edge of a footpath, for example, he +places his fore-feet on the latter. In thus raising his fore-quarters, +he throws part of his weight backwards, and in this way relieves his +fore-limbs. + +[Illustration: FIG. 103.--INFERIOR SURFACE OF A HIND-HOOF OF A HORSE: +LEFT SIDE. + +1, External border; 2, internal border.] + +With regard to the difference of form which we have just pointed out, we +have sometimes heard the following comparison made: the contour of the +hoofs of the fore-limbs, viewed from below, recalls that of an apple; +that of the hoofs of the hind-limbs recalls the outline of a pear. + +As a mnemonic this comparison is insufficient, for nothing connects +either of the forms indicated with the region to which the hoofs belong. + +We much prefer one made for us this very year by one of the students of +our course at the School of Fine Arts, after the lecture in which we had +just pointed out the differences in question. Giving the idea of a +semicircle and an ogive, which we described above, he remarked to us +that the idea would perhaps be more easily fixed in the memory if we +associated with it the idea of the chronological order in which the +Roman and ogival art succeeded. Indeed, as the Roman art preceded the +ogival art, so the hoofs which have the semicircular form precede those +which have the form of an ogive. + +This interpretation appeared to us ingenious; this is why we wished to +give it here a place which seems to us to be merited. + +[Illustration: FIG. 104.--LEFT POSTERIOR FOOT OF A HORSE: EXTERNAL +ASPECT.] + +The wall of the hoof of a fore-limb, viewed on one of its lateral +surfaces (see Fig. 98), is more oblique than that of one of the +hind-hoofs looked at in the same way (Fig. 104). This difference, very +marked especially at the region of the toe, is correlated with that of +the direction of the pastern. In fact, in the anterior limbs this is a +little more oblique than in the opposite ones. + +We have still to describe, in connection with the horse, some epidermic +tissues, which are known as _chestnuts_. + +The chestnut is a small, horny plate which is found on the internal +surface of each of the limbs, at a level differing on the anterior from +that of the posterior ones. + +On the anterior limbs the chestnut is situated on the internal surface +of the forearm, towards the middle part, or the inferior third of this +region. On the posterior limbs it is developed on the back of the +superior extremity of the internal surface of the canon, towards the +inferior part of the ham--that is, the tarsus. + +[Illustration: FIG. 105.--FOOT OF THE OX: LEFT SIDE, ANTERO-EXTERNAL +VIEW. + +1, Internal hoof; 2, external hoof; 3, internal surface of this latter; +4, internal spur.] + +Inasmuch as some authors consider the chestnuts as being vestiges of the +thumb and the great-toe, we propose giving a mnemonic which will enable +us to remember their situation, or, rather, their difference of level. + +If we consider that the thumb, in the human species, is longer than the +first toe, we may easily remember that the chestnut is placed higher in +the anterior limbs than in the posterior ones. Indeed, if we suppose a +digit taking its origin at these points, it will be longer in front (the +thumb) than behind (the first toe). + +=Hoofs of the Ox and the Pig.=--The ox has four hoofs on each foot--two +which contain the third phalanges, and two others, rudimentary, situated +at the posterior aspect of the limb, at the level of the inferior part +of the canon; these latter bear the name of _spurs_. We will occupy +ourselves especially with the former (Fig. 105). + +Each of the hoofs presents three faces which, if we consider them in +relation to the median axis of the limb to which they belong, are: +external, internal, and inferior. The external surface resembles the +wall of the hoof of the horse. The internal surface is slightly concave +from before backwards, so that the external and internal hoofs of the +same foot are not in contact with each other, except by the extremities +of this surface, and that an interval separates them between these two +points. The inferior surface, slightly depressed, ends behind in a +swelling produced by the plantar cushion, which covers a thin lamina of +horn. + +At the anterior part of the hoof these three surfaces unite in forming a +well-marked angle which, on account of the concavity of the internal +surface, is slightly curved towards the axis of the foot. + +The pig has also four hoofs--two for the great digits and two for the +lateral digits. They recall those of the ox. + + + + +CHAPTER IV + +PROPORTIONS + + +Inasmuch as we have taken for granted, in connection with the present +volume, that before entering on the study of the anatomy of quadrupeds +the reader was prepared for it by a sufficient knowledge of human +anatomy, it is quite natural that we should extend the same supposition +to the study of proportions. + +For this reason, the definition of proportions, considered from a +general point of view, their signification, their function and their +utility, are questions which it would be superfluous to enter upon here. +We will content ourselves by calling to mind that the common measure +chosen by preference is the length of the head, and that, ordinarily, it +is with it that we compare the dimensions of other parts. + +Among the animals whose structure we have examined, there is one of +which the proportions deserve to be marked in preference to every other: +this is the horse. + +Wherefore this preference? In the first place, it is because of the +overwhelming position which this animal occupies in the artistic +representation of quadrupeds; that it is more frequently associated with +man; that, notwithstanding its division into different races, its +general proportions may be referred to a special type. + +It is also because the indications relative to these proportions will +suffice to show the way which the artist must follow in order to find +for himself, at the time when the necessity for it arises, the +proportions which characterize the other animals. + +Our intention is not, in connection with the subject which now occupies +us, to enter into a deep discussion on the various opinions which have +been set forth. We desire, above all, to give some indications which, +from the practical point of view, can be utilized in the representation +of the horse, and at the beginning to demonstrate the advantages of +these indications. Now, there is a fact which we have had occasion to +note; it is the following: almost invariably, when a person who is +little accustomed to represent the horse, or not previously informed of +certain proportions of lengths, begins to draw from nature, the error +generally committed is that of making the head too small and the body +too long. Is it a preconceived idea which is the cause that one regards +them in this manner? Perhaps. At all events, certain artists who have +made the representation of horses their special study have even had this +habit. It is therefore necessary to be informed of the proportions; this +is the object of the study which we are now undertaking. + +Bourgelat,[37] in the eighteenth century, fixed for the first time and +in complete fashion the proportions of the horse; it is he, +consequently, who created the aesthetics of the horse. It is but justice +to recall the fact. His system has a point of analogy with that which is +employed to determine the human proportions. Indeed, Bourgelat chose the +length of the head as a standard of measurement, and the subdivisions of +the head for measures of less extent. 'Since beauty,' said he,[38] +'resides in the congruity and proportion of the parts, it is absolutely +necessary to observe the dimensions, individual and relative, and in +order to acquire a knowledge of the proportions, to assume a kind of +measure which can be indiscriminately common for all horses. The part +which can serve as a standard of proportion for all the others is the +head. Take a measurement between two parallel lines--one tangent to the +nape of the neck or the summit of the forelock, the other tangent to +the extremity of the anterior lip--a line perpendicular to these two +tangents will give you its geometrical length. Divide this length into +three portions, and give to these three parts a special name, which may +be applied indefinitely to all heads--as, for example, that of _prime_. +Any head whatsoever will, accordingly, in its geometrical length, always +have three _primes_; but all the parts which you will have to consider, +whether in their length, in their height, or in their width, cannot +constantly have either one prime, or a prime and a half, or three +primes; subdivide, then, each _prime_ into three equal parts, which you +will name _seconds_, and as this subdivision will not suffice to give +you a just measure of all the parts, subdivide anew each _second_ into +twenty-four _points_, so that a head divided into three _primes_ will +have, by the second division, nine _seconds_, and two hundred and +sixteen _points_ by the last.' + + [37] Claude Bourgelat, founder of the veterinary schools in France. He + was born at Lyons in 1712, and died at Paris in 1779. + + [38] Bourgelat, 'Elements de l'art veterinaire. Traite de la + conformation exterieure du cheval,' Paris, edition of 1785, p. + 133. + +But where this system appears to us to have lost somewhat of its unity +is when the author transforms it, in pointing out the following mode of +procedure: 'But the head itself may err by default of proportion. This +part is not, indeed, considered as either too short or too long, too +thin or too thick, but by comparison with the body of the animal. Now, +the body, being required to have--whether in length, reckoning from the +point of the arm to the prominence of the buttock, or in height, +reckoning from the summit of the withers to the ground--two heads and a +half; whenever the head, by its geometrical length, shall give, in +length or in height, to the body measured more than two and a half times +its own length, it will be too short; and if it gives less, it will be +too long. + +'In the case in which one of these faults exists there would be no +further question of establishing by its geometrical length the +proportions of the other parts. Give up this common measure, and measure +the height or the length of the body; divide the length or the height +into five equal portions; take, then, two of these divisions, divide +them into _primes_, _seconds_, and _points_, corresponding to the +divisions and subdivisions which you would have made of the head, and +you will have a common measure, such as the head would have given you if +it had been proportionate.'[39] + + [39] Bourgelat, _loc. cit._, p. 135. + +[Illustration: FIG. 106.--THE PROPORTIONS OF THE HORSE (AFTER +BOURGELAT). + +_To face p. 265._] + +We understand, up to a certain point, that Bourgelat may have been able +to give this advice which, generally speaking, is sufficiently +practical, since, in certain cases, he was able to pronounce that such a +head was too small or too large. But it is always mischievous, with +regard to the effect produced on the reader, to propose to him, in the +application of a rule, to suppress the foundation on which this rule is +established. Besides, even if all the measurements compared with the +two-fifths of the length of the body are proportionate with regard to +one another, the animal, in spite of this, since the head must be taken +into consideration, will, in a strict sense, be none the less +disproportioned. + +The proportions given by Bourgelat are as follows[40] (Fig. 106): + + [40] _Ibid._, p. 136, and onward. + +1. =Three geometrical lengths of the head= give: + +_The full height_ of the horse, reckoned from the forelock to the ground +on which he rests, provided that the head be well placed.[41] + + [41] By 'the head being well placed,' Bourgelat means 'vertically + posed,' the outline of the forehead then coinciding with a + vertical line, which at the other end touches the anterior + portion of the nose. + +2. =Two heads and a half= (B)[42] equals: + + [42] The letters in parentheses relate to the corresponding measures + marked by the same letters on the third diagram of Fig. 106. + +_The height of the body_ from the summit of the withers to the ground. + +_The length of the same body_, those of the forehand and of the +hind-quarter taken as a whole from the point of the arm to the point of +the buttock inclusive. + +3. =An entire head= (A) gives: + +_The length of the forepart_ from the summit of the withers to the +termination of the neck. + +_The height of the shoulders_ from the summit of the elbow to the top of +the withers. + +_The thickness of the body_ from the middle of the belly to the middle +of the back. + +_The width_ from one side to the other. + +4. =A head measured from the top of the forelock to the commissure of +the lips= (C). This measurement slightly curtailed, unless the mouth is +very deeply cleft, equals: + +_The length of the crupper_, taken from the superior point of the +anterior angle of the ilium to the tuberosity of the ischium, forming +the point of the buttock. + +_The width of the crupper or of the haunches_, taken from the inferior +points of the angles of the ilia. + +_The height of the crupper_, viewed laterally, taken from the summit of +the posterior angles of the ilia to the point of the patella, the leg +being in a state of rest. + +_The lateral measure of the posterior limb_, from the point of the +patella, to the lateral and salient part of the ham, to the right of the +articulation of the tibia with the trochlea. + +_The perpendicular height of the articulation above named_ above the +ground. + +_The distance from the point of the arm_ to the angle formed by the +junction of the head and neck. + +_The distance from the summit of the withers_ to the junction of the +neck with the thorax. + +5. =Twice this last measure= (C)[43] gives almost: + + [43] The proportions given in the two paragraphs 6 and 7 are, under + another form, the same as those pointed out in paragraph 2, with + this difference, that in this latter they are more clearly + expressed. + +_The distance of the summit of the withers_ to the tip of the patella. + +_The distance of the point of the elbow_ to the summit of the crupper or +the posterior angles of the ilia. + +6. =Three times this measure, plus a half-width of the pastern, the +equivalent of two heads and a half=, will give: + +_The height of the body_, taken from the top of the withers to the +ground. + +_Its length_, taken from the point of the arm to the point of the +buttock inclusive. + +7. =This same measure, plus the entire width of the pastern=, gives: + +_The total length of the body_, taken accurately. + +8. =Two-thirds the length of the head= (D) will equal: + +_The width of the chest_, from the tip of one arm to that of the other, +from outside to outside. + +_The horizontal measurement of the crupper_ taken between two verticals, +of which one forms a tangent to the buttock, and the other passes +through the summit of the crupper and touches the tip of the patella. + +_The third of the length of the hind-quarter and of the body_ taken +together, as far as the vertical from the withers, touching the elbow. + +_The anterior length of the hind-limb_, taken from the tuberosity of the +tibia to the fold of the ham. + +9. =One-half of the length of the head= (E) is the same as: + +_The horizontal distance from the tip of the arm_ to the vertical line +from the summit of the withers and touching the elbow. + +_The width of the neck_, viewed laterally, taken from its insertion in +the trough of the jaw to the roots of the first hairs of the mane, on a +line which forms with the superior contour two equal angles. + +10. =One-third of the entire length of the head= (F) gives: + +_The height of its superior part_ from the summit of the forelock to a +line which passes through the most salient points of the orbits. + +_The width of the head_ below the lower eyelids. + +_The lateral width of the forearm_, taken from its anterior origin to +the point of the elbow. + +11. =Two-thirds of this length=[44] (G) gives: + + [44] That is to say, two-ninths of the whole length of the head. + +_The distance of the point of the elbow_ above the plane of the lower +surface of the sternum. + +_The depression of the back_ in relation to the summit of the withers. + +_The lateral width of the posterior limbs near the hams._ + +_The space or distance of the forearms from one ars_[45] to the +opposite. + + [45] We call the region where the superior and internal part of the + forearm is joined to the trunk the 'ars.' The space between the + ars of one side and the ars of the opposite side is called the + 'inter-ars.' + +12. =One-half of the third of the entire length of the head=[46] (H) +equals: + + [46] That is to say, one-sixth of the total length of the head. + +_The thickness of the forearm_, viewed from the front, and taken +horizontally from the ars to its external surface. + +_The width of the crown of the fore-feet_ whether from one side to the +other, or from before backwards. + +_The width of the crown of the hind-feet_, from one side to the other +only. + +_The width of the posterior fetlocks_, taken from the front to the +origin of the spur. + +_The width of the knee_ seen from the front. Note: this measure is a +little too large. + +_The thickness of the ham._ Note: this measure is a little under the +mark. + +13. =One-fourth of the third of the length of the head=[47] (I) gives: + + [47] That is, one-twelfth of the length of the head. + +_The thickness of the canon of the fore-limb_: that of the hind-quarter +is a little thicker. + +14. =One-third of this same measure=[48] (K) equals: + + [48] That is, a ninth of the length of the head. + +_The thickness of the fore-limb close to the knee_ in its narrowest +part. + +_The thickness of the posterior pasterns_, viewed laterally. + +15. =The height from the elbow to the fold of the knee= (L) is the same +as: + +_The height from this same fold to the earth._ + +_The height from the patella to the fold of the ham._ + +_The height from the fold of the ham to the crown._ + +16. =The sixth part of this measure= (M) gives: + +_The width of the canon of the fore-limb_, viewed laterally, in the +middle of its length. + +_The fetlock_, viewed from the front. + +17. =The third of this same measure= (N) is very nearly equal to: + +_The width of the ham_, from the fold to the point. + +18. =A fourth of this measure= (O) gives: + +_The width of the knee_, measured laterally. + +_The length of the knee._ + +19. =The interval between the eyes from one great angle to the other= +(P) equals: + +_The width of the hind-leg_, viewed laterally, from the cleft of the +buttocks to the inferior part of the tuberosity of the tibia. + +20. =One-half of this interval between the eyes= (1/2 P) gives: + +_The width of the posterior canon-bone_, viewed laterally. + +_The width of the fetlock of the fore-limb_, from its anterior summit to +the root of the spur. + +Finally, the difference of the height of the crupper with respect to the +summit of the withers. + +It is certain that the multiplicity of these proportions, and above all +the exaggeration of details into which Bourgelat fell in indicating +certain of the measures which constitute the bases of some of them, may +repel the reader. + +For this cause we desire to add to the preceding, and also because the +question which we are treating would be incomplete without it, the +results obtained and published by other more modern authors, and in +particular by Colonel Duhousset.[49] + + [49] E. Duhousset, 'Le Cheval,' Paris, 1881. + +This author, one of whose constant occupations is the measurement of the +different regions of the horse, has the incontestable merit of having +drawn attention to this question, and of having strained all his +energies in the propagation of the knowledge which until then was little +diffused. Among the proportions which he recommends, there are some +which are the result of his own observations; whilst others, which he +has verified and adopted, are the result of a judicious selection of +those given by Bourgelat, which we have just reproduced in the preceding +pages. + +We join thereto also certain indications furnished by MM. A. Goubeaux +and G. Barrier,[50] distinguishing these latter by the initials (G. and +B.) of their authors (Fig. 107). + + [50] Armand Goubeaux and Gustave Barrier, 'De l'exterieure du Cheval,' + Paris, 1882. + +=The length of the head almost exactly equals=: + +1. Depth from the back to the belly, N, O,[51] the thickness of the +body.[52] + + [51] Look for the points indicated by these letters on Fig. 107, which + is related to the proportions which are here discussed. + + [52] The proportion previously indicated by Bourgelat (see p. 265, + paragraph 3). + +2. From the summit of the withers to the point of the arm, H, E. + +3. From the superior fold of the stifle to the point of the ham, J', J. + +4. From the point of the ham to the ground, J, K. + +5. From the dorsal angle of the scapula to the point of the haunch, D, +D. + +[Illustration: FIG. 107.--PROPORTIONS OF THE HORSE (AFTER COLONEL +DUHOUSSET).] + +6. From the passage of the girth to the fetlock, M, I, or higher in +large horses and racers; to the middle of the fetlock or lower for small +ones and those of medium size. + +7. From the superior fold of the stifle to the summit of the crupper in +those specimens whose coxo-femoral angle is very open. This distance is +always much less in others (G. and B.).[53] + + [53] A proportion relative to the same region, and which at the outset + might appear similar, is pointed out by Bourgelat (see p. 266, + paragraph 4). But there exists a difference, for Bourgelat + compared the length of the head, measured from the forelock to + the commissure of the lips, and not that of the entire head, to + the distance which separates the summit of the rump and the tip + of the patella. + +=Two and a half times the length of the head= gives: + +1. The height of the withers, H, above the ground.[54] + + [54] This proportion is that given by Bourgelat (see p. 265, paragraph + 2). + +2. The height of the summit of the crupper above the ground.[55] + + [55] Consequently the withers and the crupper, being the same height, + are situated on the same horizontal plane. Bourgelat, on the + contrary, points out a difference of level in connection with + these regions. According to him the summit of the crupper is + situated below the horizontal plane passing the withers, and this + distance equals half of the space which separates the great angle + of one eye from that of the other (see p. 269, paragraph 20). + +3. Very often the length of the body, from the point of the arm to that +of the buttock, although for a long time the type of Bourgelat had been +set aside as a conventional model, short and massive.[56] + + [56] See p. 265, paragraph 2. + +And M. Duhousset adds to this: + +'The drawing that we offer, which has two heads and a half in height and +length, is that of a horse which we frequently meet with' (see Fig. 107; +see also p. 279, where we again consider this question of the length of +the body of the horse). + +'The crupper, from the point of the haunch to that of the buttock, D, F, +is always less than that of the head. This difference varies from 5 to +10 centimetres. The width of the crupper, from one haunch to the other, +often very slightly exceeds its length.' MM. Goubeaux and Barrier add +that frequently it equals it.[57] + + [57] If we refer to the proportions indicated by Bourgelat, we shall + find that the proportions relative to the crupper are also + indicated there (see p. 266, paragraph 4). + +'The crupper, such as we have just defined it, D, H, may also be found +to a fair degree of exactness, as regards length, four times on the same +horse.' + +1. From the point of the buttock to the inferior part of the stifle, F, +P. + +2. The width of the neck, a little in front of the withers to a little +above the point of the arm, S, X.[58] + + [58] MM. Goubeaux and Barrier replace this by the following: 'The + width of neck at its inferior attachment from its insertion into + the chest to the origin of the withers, S, X.' Bourgelat + discovered the same proportion (see p. 266, last line of + paragraph 4). + +3. From this latter point to below the lower jaw, X, Q, when the head is +naturally placed parallel to the shoulders, E, H.[59] + + [59] MM. Goubeaux and Barrier replace this by the following: 'From the + insertion of the neck into the chest to the lower border of the + lower jaw, X, Q, when the head is parallel to the shoulder.' + +4. From the nape to the nostrils, _n, n'_.[60] + + [60] MM. Goubeaux and Barrier add: 'Or to the commissure of the lips.' + It is thus, besides, that Bourgelat measured the head for + comparison with the crupper (see p. 266, paragraph 4). + +The measure of =half of the head= also acts as a good guide for the +construction of the horse, when we know that it frequently applies to +many of the parts--to wit: + +1. From the forehead above the eyes, perpendicular to the line which is +tangent to the lower jaw, P, Q. + +2. Outline of the neck at the level of the base of the head, Q, L.[61] + + [61] Proportion indicated by Bourgelat (see p. 267, paragraph 9). + +3. From the crown of the fore-foot to below the knee, T, T'. + +4. In the legs, from the base of the fetlock to that of the ham, U, V. + +5. Finally, it is nearly of the length of the humerus from the point E +to the radius.[62] + + [62] MM. Goubeaux and Barrier replace these by the following: + + 1. 'From the most prominent part of the lower jaw to the profile + of the forehead above the eye, P, Q (thickness of the head). + + 2. 'From the throat to the superior border of the neck behind the + nape, Q, L (attachment of the head). + + 3. 'From the inferior part of the knee to the crown, T, T'. + + 4. 'From the base of the ham to the fetlock, U, V. + + 5. 'Finally, from the point of the arm to the articulation of the + elbow (approximate length of the arm).' + + +PROPORTIONS OF THE HEAD OF THE HORSE[63] + + [63] Extract from the work of MM. Goubeaux and Barrier on the exterior + of the horse. As before, the initials G. and B. of these authors + are added. + +Although it is very difficult, says M. Duhousset, when we speak of +measurements taken on the living animal, to formulate other than +approximations, we believe we have determined with sufficient accuracy +the following results, which are the outcome of our numerous +observations. The head which we present is that of a horse which we have +frequently come across as a mean term between the highly bred and the +draught horse. Under this heading, it will not be devoid of interest to +accompany with dimensions the two drawings to which are consigned the +measurements in question. + +=Head viewed in Profile= (Fig. 108).--Length, A, B, from the nape to the +margin of the lips, 0.60 metre. + +Thickness, C, D, from the angle of the lower jaw to the anterior surface +(a half-head), 0.30 metre. This line passes through the middle of the +eye, taken perpendicularly, to the profile of the anterior surface. Many +common horses present it, especially the heavier draught horses; in +finely-bred subjects it is a little shorter (G. and B.). + +Depth, I, H, of the neck in its narrowest part (a half-head), 0.30 +metre. It is frequently greater; this is noticeable in all instances +where the superior parts of the neck are deficient in fineness. It is +this which we see in draught horses, and in those which become too +fleshy (G. and B.). + +Distance, O, R, of the internal commissure of the eye from the superior +border of the commissure of the nostril (G. and B.) (a half-head), 0.30 +metre. It is more considerable on the common head, and on that which is +too long. + +Distance, A, O, from the nape to the internal angle of the eye, 0.22 +metre. This distance is equivalent to the thickness of the head, P, Q, +taken perpendicularly from the profile of the anterior surface, and +passing at the level of the maxillary fissure and spine. + +It is, again, equal to Q, O, from the internal angle of the eye to the +maxillary fissure; and to P, G, from the middle of the face to the +commissure of the lips (G. and B.). + +The distance, P, E, from the middle of the face to the maxillary spine +is about the sixth of the total length of the head--0.10 metre. + +[Illustration: FIG. 108.--PROPORTIONS OF THE HEAD OF THE HORSE, VIEWED +IN PROFILE (AFTER COLONEL DUHOUSSET).] + +The line B, E, reckoned from the extremity of the lips to the maxillary +spine, is equal: + +To E, F, from the maxillary spine to the external auditory meatus, to be +seen only on the skull; + +To H, G, from the insertion of the neck in the trough to the commissure +of the lips (G. and B.); + +To Q, R, from the maxillary fissure to the superior commissure of the +nostril (G. and B.); + +To Q, B, from the fissure of the maxilla to the border of the lips (G. +and B.); + +To O, D, from the internal angle of the eye to the angle of the lower +jaw, provided that the line C, D be in proportion (G. and B.). + +[Illustration: FIG. 109.--THE SAME DESIGN AS THAT OF FIG. 108, ON WHICH +WE HAVE INDICATED, BY SIMILAR LINES, THE PRINCIPAL CORRESPONDING +MEASUREMENTS. + +Half the length of the head, and the dimensions which equal it; distance +which separate the nape from the internal angle of the eye, and the +dimensions which equal it; distance which separates the internal angle +of the eye from the border of the lips, and the dimensions which equal +it.[64]] + + [64] It is thus that in our teaching, but by means of lines of + different colours, we present the proportions reproduced in Fig. + 108. Experience has demonstrated to us that this replacement of + letters by conventional lines renders the proportions more easily + appreciable, and that these lines, striking the eye more + forcibly, then impress themselves better on the memory. Fig. 111 + bears the same relation to Fig. 110. + +Finally, very frequently to O, H, from the internal angle of the eye to +the insertion of the throat into the maxillary trough (G. and B.). + +An equality still more frequent is that which exists between the +distances: + +O, B, from the internal angle of the eye to the margin of the lips; + +A, H, from the nape to the insertion of the throat into the maxillary +trough; + +And H, B, from this latter point to the margins of the lips. + +[Illustration: FIG. 110.--PROPORTIONS OF THE HEAD OF THE HORSE, SEEN +FROM THE FRONT (AFTER COLONEL DUHOUSSET).] + +=The Head, Front View= (Fig. 110).--If, to continue our examination, +adds M. Duhousset, we regard the head from the front, we find its +greatest width at A, B, the extreme points of the orbital arches. + +This width is 22 centimetres. + +It is again equal to: + +A, C, from one arch to the nape; + +A, D, from one arch to the middle of the face. + +D, E, from the middle of the face to the margin of the lips. + +From the auditory canal, G, to the maxillary spine, F, is the same +distance as from this point to the margins of the lips, E, or, better, +to the end of the teeth. + +[Illustration: FIG. 111.--THE SAME FIGURE AS FIG. 110, ON WHICH WE HAVE +MARKED BY SIMILAR LINES THE PRINCIPAL MEASUREMENTS WHICH CORRESPOND +THERETO. + +Distance which separates one of the orbital arches from that of the +opposite side, and the dimensions which equal it; distance which +separates the auditory meatus from the maxillary spine, and the +dimensions which equal it; distance which separates one maxillary spine +from that of the opposite side, and the dimensions which equal it; +distance which separates the lip of one side from that of the opposite, +and the dimensions which equal it.[65]] + + [65] See the note relative to Fig. 109. + +The line G, C, from the auditory meatus to the nape, is equal to the +sixth of the head, 10 centimetres; the line A, G, from the orbital arch +to the auditory meatus, is a little longer, and measures 12 +centimetres. + +The distance F, I, comprised between the maxillary spines, is 18 +centimetres. + +It is equal to: + +O, O, the distance between the internal angles of the eyes (G. and B.); + +F, R, the distance from the maxillary spine to the superior commissure +of the corresponding nostril (G. and. B.); + +F, P, from the maxillary spine to the _salt-cellar_.[66] + + [66] We designate under the name _salt-cellar_ a depression situated + external to the frontal region and above the eye. + +From the nape to the internal angle of the eye, C, O, is the same +distance as from this latter point to the commissure of the lips, O, T; +and from the maxillary spine to the upper lip F, S (G. and B.). + +The distance apart, T, T, of the two commissures of the lips gives, very +nearly, the distance from the superior border of the orbital arch to the +base of the ear or the auditory meatus. In the state of rest, the outer +limit of the separation of the nostrils does not exceed the width of the +knee;[67] we frequently find the same distance intercepted above the +nape by the tranquil ears. In the figure (Fig. 110) we have +intentionally represented them directed in a different plane, in order +to show that when the pinna is turned backward, it none the less +preserves the contour of bracket form, more or less pronounced according +to the breeding of the subject, and characterizing in repose the +interior curves of the ear. + + [67] We remind our readers that the name 'knee' is given by + veterinarians to the region occupied by the carpus. + +The extreme limit of the lips, M, N, but very slightly exceeds that of +the nostrils; on many heads of harmonious proportions this distance is +found to be the half of A, B. + +In order not to interrupt the course of the preceding exposition, we +decided to withhold till afterwards some reflections which have been +suggested to us by certain of the proportions which are there indicated. +The proportions in question are important--we may even say that they are +fundamental, for they have for object the relation which exists between +the length of the head, the height of the body, and the length of the +latter. + +We have already seen that, according to Bourgelat, the length of the +head is contained two and a half times in the length of the body, from +the point of the arm to the point of the buttock; and, also, two and a +half times in the height measured from the apex of the withers to the +ground (see p. 265). We saw afterwards that M. Duhousset, having adopted +these proportions, pointed out, further, that the same dimension was +again found equally to exist from the summit of the crupper to the +ground--a height which Bourgelat considered as being of less extent. +There results, then, from the latter proportions, which we have just +recalled, this interesting fact: that they simplify very much, from the +point of view of design, the placing in position of the horse, on the +condition always that this latter be always viewed directly on one of +its lateral aspects. + +[Illustration: FIG. 112.--HORSE OF WHICH THE LENGTH CONTAINS MORE THAN +TWO AND A HALF TIMES THAT OF THE HEAD, AND OF WHICH THIS DIMENSION (A, +B) EXCEEDS THE HEIGHT.] + +Indeed, in this case, if we except the neck and the head, the body, +inasmuch as its height and its length are equal, may be inscribed in a +square, of which one of the sides corresponds to the withers and to the +summit of the crupper, two of the other sides to the point of the arm +and to that of the buttock the fourth being represented by the ground. +This is simple, but this simplicity even has its inconveniences. + +It follows that this proportion, thus expressed, seems to exclude from +every artistic representation certain categories of horses, which upon +the whole might be regarded as beautiful, and the existence of which in +any case it would be a pity not to indicate. + +[Illustration: FIG. 113.--HORSE OF WHICH THE LENGTH CONTAINS MORE THAN +TWO AND A HALF TIMES THAT OF THE HEAD, AND OF WHICH THIS DIMENSION (A, +B) EXCEEDS THE HEIGHT.] + +Let us examine at the outset that which is relative to the length of the +body, equal to two and a half times the length of the head. This +proportion is sometimes met with, and therefore may be considered exact; +but it is necessary to add that its existence is not discoverable in the +majority of cases. That for some authors it constitutes a perfect model +we will not gainsay, but it is our impression that, when it exists, the +head appears a little large, or, more exactly, the body a little short. + +Without attaining exactly to three times the length of the head, as some +authors (Saint-Bel, Vallon) have announced, the body of the horse, +nevertheless, measured as is stated above, frequently contains it more +than two and a half times. We give in support of this some outline +reproductions, executed after photographs (Figs. 112, 113, 114). + +There still remains the question regarding the equality of the height +and of the length of the body of the horse. + +This equality, after the proportions previously indicated, would seem +bound to appear in all the cases observed. Now, if we measure the +examples reproduced in Figs. 112, 113, and 114, we shall see that +sometimes the two dimensions are unequal, the height being greater than +the length, or inversely. + +[Illustration: FIG. 114.--HORSE OF WHICH THE LENGTH CONTAINS MORE THAN +TWO AND A HALF TIMES THAT OF THE HEAD, AND OF WHICH THIS DIMENSION (A, +B) IS INFERIOR TO THE HEIGHT.] + +It is the same, if we examine a certain number of specimens; we are able +to determine that the proportion chosen in preference by authors is not +exactly that which is oftenest met with. It will, very probably, be +objected that it is so for the most beautiful types, and that the +indifferent ones are generally the more numerous. The essential thing +would be to know, above all, if the type of two heads and a half of +length and of height is really the only beautiful one. However that may +be, of the fifty African horses measured by M. Duhousset, only fourteen +possessed the equality indicated; twenty-six were less long than high, +and ten more long than high.[68] + + [68] E. Duhousset, 'The Horse,' Paris, 1881. + + + + +CHAPTER V + +THE PACES OF THE HORSE + + +As a completion of the studies we have just been making, some notions +relative to the paces of the horse seem to us to be absolutely +indicated. + +Let it be permitted to us to remind the reader in this connection that +we have already been for twenty-one years occupied with this question, +and that by means of an articulated figure, a sort of movable mannikin, +we have endeavoured to demonstrate to artists the differences which +characterize the various paces of the horse.[69] The arrangement then +employed cannot, evidently, be used in the present volume, but we will +inspire ourselves, in the preparation of the present chapter, with the +elements of demonstration which we have employed, and which, in the +course of our teaching, we have had the satisfaction of seeing +favourably received. + + [69] Edouard Cuyer, 'Les Allures du Cheval,' demonstrated with the aid + of a coloured, separable, and articulated table, Paris, 1883. + + This table was the subject of a note communicated to the Academy + of Sciences by Professor Marey ('Comptes rendus de l'Academie de + Sciences') at the meeting of June 26, 1882. On the other hand, it + has been the subject of a presentation which we have had the + honour of being permitted to make to the Academy of Fine Arts at + the meeting of November 4, 1882. + + The fasciculus in question has been since united with a more + complete whole as regards the study of the horse. E. Cuyer and E. + Alex, 'Le Cheval: Exterieur, Structure et Fonctions, Races,' avec + 26 planches coloriees, decoupees et superposees, Paris, 1886. + +The progressive movements by which an individual transports himself +from one place to another do not operate according to a unique method +and with a constantly uniform velocity. These various modes of +progression are designated under the name of _paces_. + +It is extremely difficult to analyze, by simple observation, the +movements which characterize these gaits. Let us, for example, examine +the displacements made by the limbs of a horse during that of walking; +if we have no notion of these displacements, it will be, so to speak, +impossible to determine in what order they are executed. The sight of +the imprints left on the ground by the hoofs is not a sufficient means +of demonstration, especially for artists. The noise made by the blows of +these limbs, or by the little bells of different timbre suspended from +them, are absolutely in the same case. + +Processes enabling us to fix or to register the paces are in every way +preferable. Such really exist; they are: instantaneous photography and +those which constitute the graphic method of Professor Marey. The +results given by the photograph are certainly appreciable; but, from the +didactic point of view, we give the preference to the graphic method, +the general characters and the mode of application of which we now +proceed to analyze.[70] + + [70] We cannot too strongly recommend the reading of the excellent + works which Professor Marey has published, and which have for + their object the study of movements, as well as the exhibition of + the procedures which he has employed. E. J. Marey, 'La Machine + Animale,' Paris, 1873; 'La Methode graphique dans les Sciences + experimentales,' Paris, 1884; 'Le Vol des Oiseaux,' Paris, 1890; + 'Le Mouvement,' Paris, 1894. + +It is necessary to understand first of all, in this connection, that +which relates to a man's walking pace. + +The method of Professor Marey rests on the following principle: Suppose +two rubber globes connected with one another by a tube. If we compress +one of these globes, the air which it contains will be driven into the +other, and will afterwards return when the pressure has ceased. Nothing +more simple, evidently; but it is necessary to describe it in detail in +order the better to comprehend that which follows: The walker who is the +subject of experiment is furnished with special shoes (Fig. 115), having +thick indiarubber soles, hollowed in the interior, so that the whole +thus constituted forms a sort of hollow cushion which is compressed +under the influence of the pressure of the foot on the ground. A tube +which is attached to a registering apparatus, which the person who is +walking carries in his hand, communicates with this cavity (Fig. 116). +This apparatus is formed of a metal drum, which is closed at its upper +part by a flexible membrane. Each time that one of the man's feet +presses on the ground, the air contained in the cavity of the sole of +the shoe is driven into the drum, which we have just mentioned, and the +flexible membrane of this drum is elevated. To this membrane is attached +a vertical rod which supports a horizontal style. + +[Illustration: FIG. 115.--EXPERIMENTAL SHOES, INTENDED TO RECORD THE +PRESSURE OF THE FOOT ON THE GROUND.] + +When the membrane, as we have just seen, is elevated, the style is +lifted, and then descends when the pressure of the foot ceases. It +traces these displacements on a leaf of paper, the surface of which is +covered with a thin layer of lamp-black, which it removes by its +contact; different parts of this surface are successively presented to +it, the paper being rolled round a cylinder which is turned on its axis +by means of a clockwork movement. It is necessary to add that the +inscription is made, in the study of the walk of man, by means of two +styles, each corresponding to one of the feet. + +The tracings thus obtained, which are read from left to right, are +sufficiently simple; but to understand them properly, it is necessary to +remember that the style undergoes a movement of ascensional displacement +during each pressure of a foot, and that, on the other hand, it +descends when the latter is separated from the ground. We also see, on +the tracing which it leaves, a line which ascends and then descends; the +meaning of this is that first the foot presses on the ground, and is +afterwards raised from it. + +[Illustration: FIG. 116.--RUNNER FURNISHED WITH THE EXPLORATORY AND +REGISTERING APPARATUS OF THE VARIOUS PACES.] + +On the tracing (Fig. 117), the line D relates to the right foot; the +line G, which is dotted so that it may not be confused with the +preceding, corresponds to the left foot. The line G first ascends; the +meaning of which is that the left foot presses on the ground; afterwards +it descends: this indicates that the pressure of the foot has ceased. It +is the same for the right foot. As we see, the pressures succeed each +other; when the left foot touches the ground, the right is separated +from it; when the latter presses the ground, it is the left which no +longer rests there. + +The line O is related to the movements of the body, as indicated by the +oscillations of the head. We will neglect these. + +But this tracing, which serves us for an example, is not, it must indeed +be said, of very easy reading; it would be still less so if the paces of +a horse were registered, for there would then be four lines, the +entanglement of which would cause greater complication. + +These difficulties of reading need be no longer feared, if we transform +the tracing into a notation by means of the following diagram. + +There are drawn (Fig. 118) below the graphic tracing two horizontal +lines (1, 2). From the point where the line D rises (commencement of the +pressure of the right foot), and from the point where this same line +descends (end of the same pressure), we let fall two vertical lines +joining the two horizontal ones mentioned above. At this plane, and +between the two vertical lines, we mark a broad white one (_a, b_). This +expresses, by its length, the duration of the period of pressure of the +right foot. In doing the same for the line G, we obtain for the +indication of a pressure of the left foot an interval of the same kind, +in which are marked cross-lines, or which is tinted gray, in order to +avoid all confusion with the preceding tracing. + +[Illustration: FIG. 117.--TRACING OF THE RUNNING OF A MAN (AFTER +PROFESSOR MAREY.) + +D, Pressures and elevations of the right foot; G, pressures and +elevations of the left foot.] + +This notation can, with sufficient exactitude, be compared to that which +is employed in the musical scale. The horizontal lines 1 and 2 represent +the _compass_. We there also see _notes_; these are the bars indicating +the pressure, of which the value--that is to say, the duration--is +represented by the length of these bars. It is the same with regard to +the intervals of _silence_: these are expressed by the intervals which +separate the pressures, and correspond to the moments in which, during +certain paces, such as running, the body is raised from the ground. +Besides, we see intervals of this kind on the notation reproduced (Fig. +118) relative to the running of man. + +[Illustration: FIG. 118.] + +[Illustration: FIG. 119.] + +In order to make the signification of these tracings still better +understood, we reproduce four varieties of them (Fig. 119). + +The first notation is that of ordinary walking. The pressures succeed +each other regularly. + +The second shows what takes place during the ascent of a staircase. At a +certain moment, the weight of the body is upon both feet at the same +time, one of them not quitting the lower step, until the other is +already in contact with the step above. Accordingly, there is thus +produced an overriding of the pressures. + +The third is relative to running, and has already been represented in +Fig. 118. The pressures of the feet are separated by the times of +suspension. + +The fourth also represents running, but in this case more rapid and +characterized by the shorter pressures, the slightly longer periods of +suspension intervals, and the quicker succession of movements. + +Before putting aside the indications relating to the walking movements +of man--indications which it was necessary to give in order to render +intelligible those which are connected with the paces of the horse--we +have yet to fix the value of that which we call 'a step.' + +It is generally admitted that a step is constituted by the series of +movements which are produced between the corresponding phases of the +action of one foot and that of the other--for example, between the +moment at which the right foot commences its pressure on the ground and +that at which the left foot commences its own. It is necessary to adopt +here another method of looking at it, and to regard the preceding as +being but a _half-step_. The step should then be defined as being +constituted by the series of movements which are executed between two +similar positions of the same foot--as, for example, between the +commencement of a pressure of the right foot and the similar phase of +the following pressure of the same foot. We shall soon understand the +importance of this definition. + +Before entering on the details of the paces of the horse, it is +necessary to see how the limbs of the latter oscillate during the period +of a complete step; or, which is the same thing, to determine what the +displacements are which a limb executes between two similar positions of +its foot. + +If we examine one of the limbs during a forward movement of the animal, +we see that this limb passes through two principal phases: (1) It is +raised from the ground; (2) it resumes contact with the ground. Each of +these phases is divided into three periods of time, which we proceed to +analyze in connection with the anterior limb. + +[Illustration: FIG. 120.--SWING OF THE RAISED ANTERIOR LIMB (AFTER G. +COLIN).[71] + +C, Lifting; B, suspension; A, placing.] + + [71] G. Colin, 'Traite de Physiologie Comparee des Animaux,' third + edition, Paris, 1886. + +The foot quits the ground (Fig. 120, C); this may be called _lifting_; +the limb is oblique in direction downwards and backwards. This same limb +is flexed and carried forward (Fig. 120, B), and, as it is supported by +the action of its flexors, this is the period named _suspension_; the +hoof is vertical. Then the limb is carried still further forward, +becoming extended (Fig. 120, A); the heel is lowered, and the foot, +being oblique, is directed towards the ground; this is the _placing_. + +Then takes place pressure (Fig. 121). The foot has just been placed on +the ground; the limb is oblique in direction downwards and forwards; +this we call _commencement of the pressure_ (Fig. 121, A). Then the +body, being carried forward, whilst the hoof, D, is fixed on the ground, +the limb becomes vertical: this stage is _mid-pressure_ (Fig. 121, B). +Finally, the progression of the body continuing, the limb becomes +oblique downwards and backwards; it is now at the _termination of +pressure_ (Fig. 121, C), and proceeds to lift itself anew if another +step is to be made. + +In conclusion, the inferior extremity of the limb describes, from its +elevation to its being placed on the ground, an arc of a circle around +its superior extremity (Fig. 121, D); whilst, during the pressure, it is +its superior extremity which describes one around its inferior +extremity, then fixed on the ground (Fig. 121, D). + +[Illustration: FIG. 121.--SWING OF THE ANTERIOR LIMB ON THE POINT OF +PRESSURE (AFTER G. COLIN). + +A, Commencement of the pressure; B, centre of the pressure; C, +termination of the pressure.] + +If we simultaneously examine the two fore-limbs, we remark that when one +of them begins its pressure the other ends it, and _vice versa_. + +As to the hind-limbs, the oscillations are similar to those of the fore +ones. In the second half of the pressure--that is, when they are passing +from the vertical direction (Fig. 122, A) to extreme obliquity backwards +(Fig. 122, C)--the effect of their action is to give propulsion to the +body. + +The fore and hind limbs make the same number of steps, and the steps +have the same length. + +The limbs of any quadruped--but we make special allusion to those of +the horse--are divided into groups in the following manner: + +The anterior pair constitutes the _anterior biped_. The _posterior +biped_ is that formed by the posterior limbs. + +The name of _lateral biped_ serves to designate the whole formed by the +two limbs of the same side. The right fore-limb and the right hind-limb +form the _right lateral biped_. The two others form the _left lateral +biped_. + +[Illustration: FIG. 122.--POSTERIOR LIMB, GIVING THE IMPULSE (AFTER G. +COLIN). + +A, Commencement of pressure; B, centre of pressure; C, termination of +pressure.] + +A fore-limb and hind-limb belonging to the opposite side form a +_diagonal biped_, which also takes the name of the fore-limb which forms +a part of it. Thus, _the right diagonal biped_ is formed by the +association of the right fore-limb and the left hind one. The _left +diagonal biped_ is, consequently, the inverse. + +It is necessary to remember well these preliminary indications; it is +the only means of comprehending with facility that which is about to +follow. + +Let us first return to the grouping of the limbs. The denominations +_anterior_ and _posterior bipeds_ render clearly perceptible the +comparison which consists in regarding a horse when walking as capable +of being represented by two men marching one behind the other, and +making the same number of steps. According as they move the legs of the +same side at the same time in 'covering the step,' or march in +contretemps step, we find reproduced all the rhythms which characterize +the different paces of the horse. + +[Illustration: FIG. 123.--NOTATION OF THE AMBLING GAIT IN THE HORSE +(AFTER PROFESSOR MAREY).] + +Professor Marey has studied these paces by a similar method to that +which he adopted for the walking of man, and which we have already +described. He employed hollow balls fixed under the hoofs, and a +registering apparatus with four styles, each corresponding to one of the +limbs. The tracing obtained is rather complicated, since two sets of +lines are found marked. But a notation similar to that of which we have +spoken can be discovered, and its exact signification should now be +determined. For this purpose, we have selected the most simple (see Fig. +123). We there see, placed in two superimposed lines, the pressure +markings of the right feet (white bands), and of the left feet (gray +bands). On the upper line are found those related to the fore-legs; the +lower lines contain those associated with the hind-legs. It is, in +brief, the superposition of two notations of the human walking +movements. And seeing that, as we have previously pointed out, we may +make a comparison between a quadruped and two men placed one behind the +other, it is easy to understand the significance of the superimposed +notations, if we accustom ourselves to look on them as the notations of +two bipeds. + +To read these notations--that is, to learn to know what occurs at each +of the movements of the pace--it is necessary, indeed, to remember that +they should be examined in vertical sections; it is to each of these +sections--of these vertical divisions--that each of the movements which +we more particularly wish to analyze corresponds. + +We proceed to study first the pace of ambling, because it is the most +simple; we shall then consider the trot, and, finally, we shall examine +that which is the most complicated, viz., the step. + +[Illustration: FIG. 124.--THE AMBLE: RIGHT LATERAL PRESSURE.[72]] + + [72] The figures which, in the present study, reproduce the different + paces, have been made from our articulated horse (see the note on + p. 282). + +=The Amble.=--To give an exact idea of the general character of the +amble, let us fancy the two men whom we discussed above marching one +behind the other and walking in step--that is, moving the legs of the +same side simultaneously. They will thus represent the amble, which, +indeed, results from the alternate displacements of the lateral bipeds; +the limbs of the same side (right or left) execute the same movements in +the same time. + +This is what the notation indicates (Fig. 123). We there see that the +pressures of the right fore-foot, marked by the white bands in the upper +range, are exactly superposed on those of the right hind one, which are +marked by a similar band on the lower line; this means that the +pressures took place in the same time. We there see also a similar +arrangement of the gray bands, which has a similar significance for the +left fore and hind feet. + +And if we recollect the three phases of pressure (see p. 289, and Figs. +121, 122), we shall comprehend, in looking at the diagrams, that, at the +initial stage (A), the limbs are commencing their pressure, and are +oblique downwards and forwards; that afterwards (B) the two limbs are +vertical, since they are at the middle of the pressure stage; and that +finally (C) they are oblique downwards and backwards, for it is then the +termination of their pressure (Fig. 124). + +[Illustration: FIG. 125.--NOTATION OF THE GAIT OF THE TROT IN THE HORSE +(AFTER PROFESSOR MAREY).] + +During the time that the right limbs are pressing (notation, white +bands) the left limbs are raised; afterwards these latter take up the +pressure (gray bands), and then the right limbs are raised in their +turn. + +During the pace of ambling the weight of the body, which is wholly +sustained by the limbs of one side only, is not in equilibrium, so that +the limbs which are raised return by a brisk movement to the position of +support in order to re-establish it. + +=The Trot.=--We have just seen that, in order to represent the amble, +the two marchers moved their right limbs simultaneously, and then their +left ones. + +Let us suppose now that the hinder man anticipated by half a pace the +movement of the front one, then will be found realized the association +and the nature of the displacements of the limbs during the pace of the +trot. + +By this anticipation of a half-step (we have defined, p. 288, what is to +be understood by the word _step_), it follows that when the marcher who +is in front advances his right leg it is the left leg of the marcher who +follows him that is carried in the same direction. We should thus +conclude from this that the trot is characterized by a succession of +displacements of the diagonal bipeds. + +[Illustration: FIG. 126.--THE TROT; RIGHT DIAGONAL PRESSURE.] + +[Illustration: FIG. 127.--THE TROT; TIME OF SUSPENSION.] + +Indeed, if we examine the notation of this gait (Fig. 125), we see that +with the pressure of the right fore-foot is found associated the +pressure of the left hind-foot. It is, accordingly, a typical diagonal +biped (Fig. 126). + +[Illustration: FIG. 128.--NOTATION OF THE PACE OF STEPPING IN THE HORSE +(AFTER PROFESSOR MAREY). + +L, Right lateral pressure; D, right diagonal pressure; L', left lateral +pressure; D', left diagonal pressure.] + +But it is necessary to add that these groups of pressures do not succeed +one another without interruption, except in the slow trot. In the +ordinary trot, or in that in which the animal's strides are very long, +the body between each of the double pressures which we have just been +considering is projected forward with such force that it remains for an +instant separated from the ground. This is what we designate by the name +of _time of suspension_ (Fig. 127). The notation in this case would be +slightly different from that which we reproduce above, in this sense: +that between the diagonal pressures there then would be found an +interval, since during the time the body is suspended none of the feet +can produce a pressure-mark (see, with regard to these intervals, the +notations of the running of a man, Fig. 118, and Fig. 119, 3, 4). + +=The Walk.=--Although slow, a feature which would seem to make it +possible to permit its analysis in a horse when walking, this pace is +difficult to comprehend without sufficient preliminary study. + +[Illustration: FIG. 129.--THE STEP: RIGHT LATERAL PRESSURE.] + +[Illustration: FIG. 130.--THE STEP: RIGHT DIAGONAL PRESSURE.] + +We saw above that in order to represent the amble the marchers had to +move the legs of the same side simultaneously. We have also just seen +that in order to represent the trot the marcher at the back had to +anticipate by a half-step. Suppose, now, that this same marcher +anticipates the man in front by a quarter-step only, or by a +half-pressure period, and thus will be found realized the order of +succession of the limbs in the gait or pace called the _walk_. The feet +meet the ground one after the other, since they are each in advance by +half the duration of a pressure. The strokes are four in number during +the period of a step of this pace; in the amble and in the trot they do +not exceed two, for then the limbs strike the ground in lateral diagonal +pairs. + +[Illustration: FIG. 131.--THE GALLOP: FIRST PERIOD.] + +[Illustration: FIG. 132.--THE GALLOP: SECOND PERIOD.] + +[Illustration: FIG. 133.--THE GALLOP: THIRD PERIOD.] + +[Illustration: FIG. 134.--THE GALLOP: TIME OF SUSPENSION.] + +If we examine the notation of the pace of walking (Fig. 128), we see +that the right fore-foot commences its pressure when the right +hind-foot is in the middle of its own, and that the hinder left begins +in the middle of that of the right fore-foot, and that it is itself at +the midst of its pressure when the left fore-foot touches the ground, +etc. In a word, the foot-fallings occur in the following order and at +regular intervals--the fore right foot is here considered as acting +first: right fore, left hind, left fore, right hind, and so on in +succession. + +[Illustration: FIG. 135.--NOTATION OF THE GALLOP DIVIDED INTO THREE +PERIODS OF TIME (AFTER PROFESSOR MAREY). + +1, First period; 2, second period; 3, third period.] + +As to the nature of the bipeds which succeed one another, it is easy to +understand them by means of the notation. In reading this from left to +right, we see that the associations of pressure are first made by the +two right feet, then by a right foot and a left one, then by two left +feet, and, finally, by a left and right. It is, accordingly, a +succession this time of lateral and diagonal pressures. + +[Illustration: FIG. 136.--NOTATION OF THE GALLOP OF FOUR PERIODS IN THE +HORSE (AFTER PROFESSOR MAREY). + +1, First period; 2, second period; 3, third period; 4, fourth period.] + +Thus, we find at the start a right lateral pressure (Fig. 129), next a +right diagonal (Fig. 130), then a left lateral; finally, a left diagonal +pressure. It is thus that the initial letters L, D, L', D' further +indicate the notations represented in Fig. 128. + +=The Gallop.=--The ordinary gallop is a pace of three phases. The first +is characterized by the fact that one hind-limb alone rests on the +ground (Fig. 131); in the second the animal is on a diagonal support +(Fig. 132); in the third it comes down on a fore-limb (Fig. 133). The +body is then raised (Fig. 134), and to this period of suspension succeed +anew the three modes of pressure indicated above. + +The gallop is said to be from either right or left. In the gallop from +the right, the right fore-leg is the more frequently in advance of its +neighbour; it is the last to be placed on the ground. The left foot of +the posterior biped is the one which commences the action. + +An entirely opposite arrangement characterizes the gallop from the left. + +[Illustration: FIG. 137.--LEAP OF THE HARE (AFTER G. COLIN).] + +The notation reproduced in Fig. 135 corresponds to the gallop from the +right. It is there seen, as we pointed out above, that in the first +phase the exclusive support of the left hind-foot takes place (1); that +afterwards, in the second, commence simultaneously, the pressures of the +left fore and the right hind foot (2); this is the left diagonal +support; and that finally, in the third, the body comes down on a +fore-limb, which is then the right (3); and that for a moment it is on +this limb alone that the animal rests. + +To these three phases on the notation succeeds an interval; this is the +period of suspension. + +The gallop of four phases only differs from the preceding in that the +foot-fallings of each diagonal biped occur at slight intervals, and give +distinct sounds. The notation is reproduced in Fig. 136. + +[Illustration: FIG. 138.--THE LEAP.] + +[Illustration: FIG. 139.--THE LEAP.] + +[Illustration: FIG. 140.--THE LEAP.] + +[Illustration: FIG. 141.--THE LEAP.] + +=The Leap.=--The leap is an act by which the body is wholly raised from +the ground and projected upwards and forwards to a greater or less +distance. + +It is prepared for by the flexing of the hind-limbs, which, by being +suddenly extended, project the body, and thus enable it to pass over an +obstacle. + +This preparatory arrangement is very remarkable in the leap of the lion, +the cat, and the panther, which execute springs of great length; in the +horse, in which the leap is not an habitual mode of progression, this +flexion of the hinder limbs is less marked. With this animal the leap is +generally associated with the gallop; nevertheless, it is sometimes made +from a stationary position. In observing the hare or the rabbit, in +which the leap is habitual, we notice (Fig. 137) that the hind-limbs, +being extremely flexed, rest on the ground as far as the calcaneum, are +then straightened by the action of their extensors, become vertical and +then oblique backwards at the moment the body is thrown forward into +space by the sudden extension of these limbs. + +The action of the extensors is energetic and instantaneous, and their +energy is greater than in ordinary progression, for it is required to +lift the body and to project it forcibly a more or less considerable +distance. It is the extreme rapidity of this action which enables the +animal to clear an obstacle, for without this condition the body would +be raised, but not separated from the ground. + +First of all, in reaching the obstacle to be cleared, the horse prepares +to leap by taking the attitude of rearing; the hind-limbs are flexed and +carried under the body, the fore-quarters are raised, and the different +segments of the fore-limbs are flexed (Fig. 138). + +[Illustration: FIG. 142.--THE LEAP.] + +[Illustration: FIG. 143.--THE LEAP.] + +One sudden trigger action produced by the violent contraction of the +extensors of the hind-legs then takes place, and the animal is projected +forwards, while he flexes the fore-legs more and more (Fig. 139). He +has then risen above the obstacle (Fig. 140). Then while he makes the +downward and forward balancing movement, and points his fore-limbs in +the same direction, he flexes the hind ones (Fig. 141). Whilst the +latter are further flexed, in order to pass the obstacle in their turn, +the fore-limbs which are extended come into contact with the ground +(Fig. 142). Finally, in the last phase of the leap, the animal, raising +himself in front, after the impact of his hind-feet has taken place +(Fig. 143), prepares to continue the pace at which he progressed before +meeting the obstacle which he had to clear. + + +THE END + + +_London: Bailliere, Tindall and Cox, 8, Henrietta Street, Covent Garden, +W.C._ + + + + + THE + ARTISTIC ANATOMY OF ANIMALS + +[Illustration] + + + + +SECTIONAL INDEX + + + PAGE + + =Generalities of Comparative Anatomy= 1 + + + OSTEOLOGY AND ARTHROLOGY + + =The Trunk:= + _Vertebral Column_ 4 + Sacrum 10 + Coccygeal vertebrae 11 + Direction and form of the vertebral column 11 + _Thorax_ 12 + Sternum 14 + Ribs and costal cartilages 14 + + =The Anterior Limbs:= + _Shoulder_ 20 + Scapula 21 + Clavicle 25 + _Arm_ 28 + Humerus 28 + General view of the form of the forearm and hand 34 + Forearm 38 + Hand 44 + + =The Anterior Limbs in Certain Animals:= + _Plantigrades_: Bear 49 + _Digitigrades_: Cat, dog 51 + _Unguligrades_: Pig 57 + Sheep, Ox 60 + Horse 64 + Proportions of the arm, the forearm, and metacarpus 70 + Articulations of the anterior limbs 71 + Scapulo-humeral articulation 72 + Humero-ulnar articulation, or elbow 74 + Radio-ulnar articulation 75 + Articulation of the wrist 75 + Metacarpo-phalangeal articulations 76 + Interphalangeal articulations 77 + + =The Posterior Limbs:= + _Pelvis_ 78 + Iliac bone 78 + _The Thigh_ 83 + Femur 83 + Knee-cap 85 + _The Leg_ 85 + Tibia 86 + Fibula 87 + _The Foot_ 87 + + =The Posterior Limbs in Some Animals:= + _Plantigrades_: Bear 90 + _Digitigrades_: Cat, dog 91 + _Unguligrades_: Pig 94 + Sheep, ox 95 + Horse 99 + Articulations of the posterior limbs 105 + Coxo-femoral articulation 105 + Femoro-tibial articulation, or knee 106 + Tibio-tarsal articulation, and of the bones of the tarsus 107 + + =The Head in General, and in Some Animals in Particular:= + Direction of the head 109 + The skull 112 + The face 118 + The skull of birds 127 + + + MYOLOGY + + =Muscles of the Trunk:= + Pectoralis major 131 + Pectoralis minor 133 + Serratus magnus 134 + + =Muscles of the Abdomen:= + External oblique 136 + Internal oblique 137 + Transversalis abdominis 138 + Rectus abdominis 138 + Pyramidalis abdominis 139 + + =Muscles of the Back:= + Trapezius 140 + Latissimus dorsi 142 + Rhomboid 144 + + =The Cutaneous Muscle of the Trunk= 147 + + =The Coccygeal Region:= + Ischio-coccygeal muscle 149 + Superior sacro-coccygeal muscle 150 + Lateral sacro-coccygeal muscle 150 + Inferior sacro-coccygeal muscle 150 + + =Muscles of the Neck:= + Mastoido-humeralis 150 + Sterno-mastoid 153 + Omo-trachelian 155 + Levator anguli scapulae 156 + Splenius 158 + + =Infrahyoid Muscles:= + Sterno-thyroid and sterno-hyoid 160 + Omo-hyoid 160 + + =Suprahyoid Muscles:= + Mylo-hyoid 161 + Digastric 161 + + =Panniculus of the Neck= 162 + + =Muscles of the Anterior Limbs:= + _Muscles of the Shoulder_ 162 + Deltoid 162 + Subscapularis 163 + Supraspinatus 164 + Infraspinatus 165 + Teres minor 166 + Teres major 166 + Panniculus muscle of the shoulder 167 + _Muscles of the Arm_ 168 + Anterior region 169 + Biceps 169 + Brachialis anticus 170 + Coraco-brachialis 170 + Posterior region 171 + Triceps 171 + _Supplemental or Accessory Muscle of the Latissimus Dorsi_ 173 + _Muscles of the Forearm_ 174 + Anterior and external region 176 + Supinator longus 176 + First and second external radial 176 + Supinator brevis 179 + Extensor communis digitorum 179 + Extensor minimi digiti 183 + Posterior ulnar 185 + Anconeus 185 + Long abductor of the thumb 186 + Short extensor of the thumb 187 + Long extensor of the thumb 187 + Proper extensor of the index 187 + Internal and posterior region 188 + Pronator teres 188 + Flexor carpi radialis 189 + Palmaris longus 189 + Anterior ulnar 191 + Superficial flexor of the digits 193 + Long proper flexor of the thumb 197 + Pronator quadratus 198 + _Muscles of the Hand_ 199 + + =Muscles of the Posterior Limbs:= + _Muscles of the Pelvis_ 200 + Gluteus medius 200 + Gluteus maximus 201 + _Muscles of the Thigh_ 204 + Muscles of the posterior region 205 + Biceps 205 + Semi-tendinosus 206 + Semi-membranosus 207 + Muscles of the anterior region 210 + Triceps 210 + Tensor fascia lata 211 + Sartorius 211 + Muscles of the internal region 213 + Gracilis 213 + _Muscles of the Leg_ 213 + Muscles of the anterior region 214 + Tibialis anticus 214 + Extensor proprius pollicis 219 + Extensor longus digitorum 219 + Peroneus tertius 224 + Muscles of the external region 224 + Peroneus longus 224 + Peroneus brevis 225 + Muscles of the posterior region 227 + Gastrocnemius 227 + Soleus 228 + Plantaris 228 + Popliteus 228 + Superficial flexor of the toes 229 + Flexor longus digitorum 230 + Tibialis posticus 230 + Flexor longus pollicis 231 + _Muscles of the Foot_ 231 + Dorsalis pedis 231 + _Muscles of the Head_ 232 + Masticatory muscles 232 + Masseter 232 + Temporal muscle 234 + Cutaneous muscles of the head 234 + Occipito-frontalis 234 + Orbicularis palpebrarum 234 + Pyramidalis nasi 235 + Corrugator supercilii 235 + Zygomaticus major 235 + Zygomaticus minor 236 + Levator labii superioris proprius 237 + Levator labii superioris alaeque nasi 238 + Transversus nasi 239 + Caninus 239 + Orbicularis oris 240 + Triangularis oris 240 + Quadratus menti 240 + Prominence of the chin 240 + Buccinator 241 + Maxillo-labialis 242 + Zygomatico-auricularis 242 + Temporo-auricularis externus 243 + Scuto-auricularis externus 243 + Cervico-auricular muscles 243 + Cervico-auricularis superioris 244 + Cervico-auricularis medius 244 + Cervico-auricularis inferioris 244 + Parotido-auricularis 244 + Temporo-auricularis internus 244 + Zygomatico-auricularis 245 + + + EPIDERMIC PRODUCTS OF THE TERMINAL EXTREMITIES OF THE FORE AND + HIND LIMBS + + Claws 247 + Plantar tubercles 248 + Hoofs of the solipeds 250 + Hoofs of ox and pig 261 + + * * * * * + + Proportions 262 + Proportions of head of horse 273 + (front view) 276 + + Paces of the horse 282 + Amble 293 + Trot 294 + Walk 296 + Gallop 300 + Leap 364 + + + + +ERRATA + + +P. 105, _Articulations_ of the Posterior Limbs. + +P. 107, Tibio-tarsal _Articulation_. + + + + +THE END + + +_London: Bailliere, Tindall and Cox, 8, Henrietta Street, Covent Garden, +W.C._ + + + + + +--------------------------------------------------------------------+ + | TRANSCRIBER'S NOTES: | + | | + | Footnotes have been moved to underneath the paragraph, table or | + | illustration they refer to. | + | | + | Illustrations have been moved so as to not disrupt the flow of the | + | text. Page numbers in the List of Illustrations and in references | + | have not been changed, and are therefore not always correct. | + | | + | The Table of Contents and the Sectional Index are not complete and | + | contain slightly different wording than the names of sections in | + | the text. This has been left as in the original work. | + | | + | The Errata have already been changed in the text. | + | | + | The author uses the terms chromophotograph and chronophotograph | + | (and derivations of these words); these words have not been | + | changed. The correct term in these cases is chronophotograph. | + | | + | Page 143, Fig. 69: atlas is mentioned twice (nrs. 12 and 13); only | + | nr. 13 indicates the atlas. | + | | + | The text used is that of the original work, including | + | inconsistencies in spelling, hyphenation and lay-out, and | + | differences between main text, footnotes and captions, except when | + | mentioned below. | + | | + | Changes made to the text: | + | Some minor obvious typographical errors have been corrected | + | silently. | + | Periods have been removed from some section headings for | + | consistency. | + | Page 2, footnote [2]: Mathias-Duval changed to Mathias Duval | + | (full name: Mathias-Marie Duval). | + | Page 23: _see_ replaced with see for consistency. | + | Page 44 (footnote 12): Edward Cuyer changed to Edouard Cuyer as | + | elsewhere. | + | Page 53, captions (2x): AA^1 changed to AA' as in drawing and | + | text. | + | Page 120, Fig. 63, caption: 14', malar bone added, 14 changed to | + | anterior orifice of the cavity of the nasal fossae (as in previous| + | figures). | + | Page 216: tendo-Achilles changed to tendo-Achillis as elsewhere. | + | Page 234: Fig. 0, 92 changed to Fig. 90, 2. | + | Page 254, Fig. 98: epternal changed to external. | + | Page 269, last paragraph: one anchor to same footnote deleted. | + | Page 325: L, D, L', D' changed to L, D, L', D'. | + | Footnotes 13, 17: La Natura changed to La Nature. | + +--------------------------------------------------------------------+ + + + + + +End of Project Gutenberg's Artistic Anatomy of Animals, by Edouard Cuyer + +*** END OF THIS PROJECT GUTENBERG EBOOK ARTISTIC ANATOMY OF ANIMALS *** + +***** This file should be named 38315.txt or 38315.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/3/8/3/1/38315/ + +Produced by Chris Curnow, Harry Lame and the Online +Distributed Proofreading Team at https://www.pgdp.net (This +file was produced from images generously made available +by The Internet Archive) + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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