.-bridge 
 !.j iological Serie 
 
 THE VERTEBRATE SKELETON 
 
MEDICAL SCHOOL 
 
 .Ibort .'7abian Uelin 
 .orial 
 
 WS*L 
 

 M 4 
 
CAMBRIDGE BIOLOGICAL SERIES. 
 
 GENERAL EDITOR : ARTHUR E. SHIPLEY, M.A. 
 
 FELLOW AND TUTOR OF CHRIST'S COLLEGE, CAMBRIDGE. 
 
 THE 
 
 VERTEBRATE SKELETON. 
 
EonUon: C. J. CLAY AXD SONS, 
 
 CAMBRIDGE UNIVERSITY PRESS WAREHOUSE, 
 
 AVE MARIA LANE, 
 
 AND 
 
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 136, GOWER STREET, W.C. 
 
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 [All Rights reserved.] 
 
THE 
 
 VERTEBRATE SKELETON 
 
 BY 
 
 SIDNEY H. REYNOLDS, M.A., 
 
 TRINITY COLLEGE, CAMBRIDGE J 
 
 LECTURER AND DEMONSTRATOR IN GEOLOGY AND ZOOLOGY AT UNIVERSITY 
 COLLEGE, BRISTOL. 
 
 (Eambtfoge : 
 
 AT THE UNIVERSITY PRESS. 
 
 1807 
 J> 
 
 [All Rights reserved.] ' 
 
Cambridge : 
 
 PRINTED BY J. & C. F. CLAY, 
 AT THE UNIVERSITY PRESS. 
 
QLS21 
 
 -R46 
 
 1397 
 
 PEBFACE. 
 
 IN the following pages the term skeleton is used in its 
 widest sense, so as to include exoskeletal or tegumentary 
 structures, as well as endoskeletal structures. It was thought 
 advisable to include some account of the skeleton of the 
 lowest Chordata animals which are not strictly vertebrates, 
 but it seemed undesirable to alter the title of the book in 
 consequence. 
 
 The plan adopted in the treatment of each group has 
 been to give first an account of the general skeletal characters 
 of the group in question and of its several subdivisions ; 
 secondly to describe in detail the skeleton of one or more 
 selected types ; and thirdly to treat the skeleton as developed 
 in the group organ by organ. 
 
 A beginner is advised to commence, not with the intro- 
 ductory chapter, but with the skeleton of the Dogfish, then 
 to pass to the skeletons of the Newt and Frog, and then 
 to that of the Dog. After that he might pass to the intro- 
 ductory chapter and work straight through the book. I have 
 endeavoured to make the account of each type skeleton 
 complete in itself; this has necessitated a certain amount of 
 
 6111 
 
VI PREFACE. 
 
 repetition, a fault that I have found it equally difficult to 
 avoid in other parts of the book. 
 
 Throughout the book generic names are printed in italics ; 
 and italics are used in the accounts of the type skeletons for 
 the names of membrane bones. Clarendon type is used to 
 emphasise certain words. In the classificatory table the 
 names of extinct genera only, are printed in italics. 
 
 In a book in which an attempt is made to cover to some 
 extent such a vast field, it would be vain to hope to have 
 avoided many errors both of omission and commission, and 
 I owe it to the kindness of several friends that the errors are 
 not much more numerous. I cannot however too emphatically 
 say that for those which remain I alone am responsible. 
 Messrs C. W. Andrews, E. Fawcett, S. F. Harmer, J. Graham 
 Kerr, and B. Rogers have all been kind enough to help me 
 by reading proofs or manuscript, while the assistance that I 
 have received from Dr Gadow during the earlier stages and 
 from Prof. Lloyd Morgan and Mr Shipley throughout the 
 whole progress of the work has been very great. To all these 
 gentlemen my best thanks are tendered. 
 
 All the figures except 1, 35, 55, and 84 were drawn by 
 Mr Edwin Wilson, to whose care and skill I am much in- 
 debted. The majority are from photographs taken by my 
 sister Miss K. M. Reynolds or by myself in the British 
 Museum and in the Cambridge University Museum of 
 Zoology, and I take this opportunity of thanking Sir W. H. 
 Flower and Mr S. F. Harmer for the facilities they have 
 afforded and for permission to figure many objects in the 
 museums respectively under their charge. I have also to 
 thank (1) Prof, von Zittel for permission to reproduce figs. 27, 
 41, 52, 69, 70, 80, 106 A, and 107 c; (2) Sir W. H. Flower 
 and Messrs A. and C. Black for figs. 1 and 84; (3) Prof. O. C. 
 
PREFACE. vn 
 
 Marsh and Dr H. Woodward for fig. 35 ; (4) Dr C. H. Hurst 
 and Messrs Smith, Elder, and Co. for fig. 55. 
 
 A few references are given, but no attempt has been made 
 to give anything like a complete list. The abbreviations 
 of the titles of periodicals are those used in the Zoological 
 Record. 
 
 I have always referred freely to the textbooks treating of 
 the subjects dealt with, and in particular I should like to 
 mention that the section devoted to the skeleton of mammals 
 is, as it could hardly fail to be, to a considerable extent based 
 on Sir W. H. Flower's Osteology of the Mammalia. 
 
 SIDNEY H. REYNOLDS. 
 
 March 10, 1897. 
 
CONTENTS. 
 
 CHAPTER I. 
 
 PAGK 
 
 Introductory account of the skeleton in general .... 1 
 
 CHAPTER II. 
 
 Classification 30 
 
 CHAPTER III. 
 
 Skeleton of Hemichordata, Urochordata and Cephalochordata . 50 
 
 CHAPTER IV. 
 
 Skeletal characters of the Vertebrata. The skeleton in the Cyclo- 
 
 stomata 53 
 
 CHAPTER V. 
 
 Skeletal characters of the Ichthyopsida. Characters of the several 
 
 groups of Pisces 59 
 
 CHAPTER VI. 
 
 The skeleton of the Dogfish (Scyllium canicula) .... 71 
 
X CONTENTS. 
 
 CHAPTER VII. 
 
 PAGE 
 
 The skeleton of the Codfish (Gadus morrhua) and the skull of 
 
 the Salmon (Salmo salar] . 83 
 
 CHAPTER VIII. 
 
 General account of the skeleton in Fishes 104 
 
 CHAPTER IX. 
 
 Characters of the several groups of Amphibia .... 183 
 
 CHAPTER X. 
 
 The skeleton of the Newt (Molge cristata) 138 
 
 CHAPTER XI. 
 
 The skeleton of the Frog (Eana temporaria) .... 151 
 
 CHAPTER XII. 
 
 General account of the skeleton in Amphibia . . . .168 
 
 CHAPTER XIII. 
 
 Skeletal characters of the Sauropsida. Characters of the several 
 
 groups of Keptiles 189 
 
 CHAPTER XIV. 
 
 The skeleton of the Green Turtle (Chelone midas) . . . 214 
 
 CHAPTER XV. 
 
 The skeleton of the Crocodile (Crocodilus palustris) . . . 237 
 
 CHAPTER XVI. 
 
 General account of the skeleton in Keptiles 270 
 
CONTENTS. XI 
 
 CHAPTER XVII. 
 
 PAGE 
 
 Characters of the several groups of Birds ..... 295 
 
 CHAPTER XVIII. 
 
 The skeleton of the Wild Duck (Anas boschas) .... 302 
 
 CHAPTER XIX. 
 
 General account of the skeleton in Birds 328 
 
 CHAPTER XX. 
 
 Characters of the several groups of Mammalia .... 343 
 
 CHAPTER XXI. 
 
 The skeleton of the Dog (Canis familiaris) 374 
 
 CHAPTER XXII. 
 
 General account of the skeleton in Mammalia. The exoskeleton 
 
 and vertebral column . .416 
 
 CHAPTER XXIII. 
 
 General account of the skeleton in Mammalia (continued}. The 
 
 skull and appendicular skeleton 455 
 
LIST OF ILLUSTRATIONS. 
 
 FIG. PAGE 
 
 1 Diagrammatic sections of various forms of teeth ... 6 
 
 2 Cervical vertebrae of an Ox (Bos taurus) .... 15 
 
 3 Diagram of the skeleton of Amphioxus lanceolatus . . 51 
 
 4 Dorsal, lateral, and ventral views of the skull of Petro- 
 
 myzon marinus 56 
 
 5 Skull of a male Chimaera monstrosa 65 
 
 6 Lateral view of the skull of a Dogfish (Scyllium canicula) . 75 
 
 7 Semidorsal view of the pectoral girdle and fins of a Dogfish 
 
 (Scyllium canicula) . 80 
 
 8 Dorsal view of the pelvic girdle and fins of a male Dogfish 
 
 (Scyllium canicula) 81 
 
 9 Dorsal and ventral views of the cranium of a Salmon (Salmo 
 
 salar) from which most of the membrane bones have been 
 
 removed 88 
 
 10 Lateral view of the chondrocranium of a Salmon (Salvio 
 
 salar) 90 
 
 11 Lateral view of the skull of a Salmon (Salmo salar) . . 92 
 
 12 Mandibular and hyoid arches of a Cod (Gadus morrhua) . 99 
 
 13 Eight half of the pectoral girdle and right pectoral fin of a Cod 
 
 (Gadus morrhua) 102 
 
 14 Diagram of a section through the jaw of a Shark (Odontaspis 
 
 americanus) showing the succession of teeth . . . 107 
 
 15 Part of the lower jaw of a Shark (Galeus) .... 108 
 
 16 Skulls of Notidanus and Cestracion ..... 118 
 
 17 Dorsal view of the branchial arches of Heptanchus . . 120 
 
 18 Lateral view of the skull of a Sturgeon (Acipenser sturio) . 122 
 
 19 Dorsal and ventral views of the cranium of Ceratodus miolepis 125 
 
 20 Lateral view of the skeleton of Ceratodus miolepis . . 128 
 
 21 Dorsal, ventral and lateral views of the skull of a Newt (Molge 
 
 cristata) 142 
 
 22 Ventral and lateral views of the shoulder-girdle and sternum 
 
 of an old male Crested Newt (Molge cristata) . . . 146 
 
LIST OF ILLUSTRATIONS. Xlll 
 
 FIG. PAOK 
 
 23 Eight posterior and anterior limbs of a Newt (Molge 
 
 cristata) 148 
 
 24 Dorsal and ventral views of the cranium of a Common Frog 
 
 (Rana temporaria) 155 
 
 25 Dorsal and ventral views of the cranium of a Common Frog 
 
 (Rana temporaria) from which the membrane bones have 
 mostly been removed . . . 157 
 
 26 Lateral view of the skull and posterior view of the cranium of 
 
 a Common Frog (Rana temporaria) 159 
 
 27 Dorsal view of the skull of a Labyrinthodont (Capitosaurus 
 
 nasutus) 176 
 
 28 Ventral view of the cranium, and lateral view of the cranium 
 
 and mandible of Siphonops annulatus .... 178 
 
 29 Visceral arches of Amphibia : A, Molge cristata ; B, Rana 
 
 temporaria, adult; C, Tadpole of Rana; D, Siredon pisci- 
 formis 181 
 
 30 Shoulder-girdle and sternum of an adult male Common Frog 
 
 (Rana temporaria), and of an adult female Docidophryne 
 gigantea 183 
 
 31 A, Eight antibrachium and manus of a larval Salamander 
 
 (Salamandra maculosa); B, Eight tarsus and adjoining 
 bones of Molge sp 186 
 
 32 Lateral and dorsal views of the skull of an Ichthyosaurus . 196 
 
 33 Lateral view and longitudinal section of the skull of a Lizard 
 
 (Varanus varius) ......... 201 
 
 34 Lateral view of the shoulder-girdle of a Lizard (Varanus) . 202 
 
 35 Eestored skeleton of Ceratosaurus nasicornis . . . 206 
 
 36 Dorsal and ventral views of the carapace of a Loggerhead 
 
 Turtle (Thalassochelys caretta) 216 
 
 37 Plastron of a Green Turtle (Ghelone midas) .... 218 
 
 38 The skull of a Green Turtle (Ghelone midas) . . .223 
 
 39 Longitudinal vertical section through the cranium of a Green 
 
 Turtle (Chelone midas) 226 
 
 40 Anterior limb of a young Hawksbill Turtle (Chelone imbri- 
 
 cata), and posterior limb of a large Green Turtle (Chelone 
 midas) 234 
 
 41 The first four cervical vertebrae of a Crocodile (Crocodilus 
 
 vulgaris) 239 
 
 42 Anterior view of a late thoracic and the first sacral vertebrae 
 
 of a Crocodile (Crocodilus palustris) 242 
 
XIV LIST OF ILLUSTRATIONS. 
 
 43 Palatal aspect of the cranium and mandible of an Alligator 
 
 (Caiman Jatirostris) 245 
 
 44 Lateral view of the skull of an Alligator (Caiman latirostris) . 248 
 
 45 Longitudinal section through the skull of an Alligator (Caiman 
 
 latirostris) 253 
 
 46 Sternum and associated membrane bones of a Crocodile 
 
 (Crocodilus palustris) 261 
 
 47 Left half of the pectoral girdle of an Alligator (Caiman 
 
 latirostris) 262 
 
 48 Right anterior and posterior limbs of an Alligator (Caiman 
 
 latirostris) 264 
 
 49 Pelvis and sacrum of an Alligator (Caiman latirostris) . 267 
 
 50 Preparation of part of the right mandibular ramus of Croco- 
 
 dilus palustris 274 
 
 51 Dorsal and ventral views of the skull of a Common Snake 
 
 (Tropidonotus natrix) 279 
 
 52 Skull of Hatteria (Sphenodon punctatus) .... 282 
 
 53 Hyoids of an Alligator (Caiman latirostris), and of a Green 
 
 Turtle (Chelone midas) 285 
 
 54 Ventral view of the shoulder-girdle and sternum of Loemanctus 
 
 longipes 287 
 
 55 Left half of the skeleton of a Common Fowl (Gallus bankiva) 301 
 
 56 The wing of a Wild Duck (Anas boschas) .... 304 
 
 57 Wings of a Wild Duck with the coverts removed (Anas 
 
 bosc.has) . 305 
 
 58 Dorsal and ventral views of the pelvis and sacrum of a Duck 
 
 (Anas boschas) 311 
 
 59 Skull of a Duck (Anas boschas) 312 
 
 60 A, Ventral view of the cranium of a Duck (Anas boschas) ; B, 
 
 Cranium and mandible seen from the left side , . 313 
 
 61 Lateral view of the pelvis and sacrum of a Duck (Anas boschas) 325 
 
 62 Third cervical vertebra of an Ostrich (Struthio camelus) . 331 
 
 63 Shoulder-girdle and sternum of A, Black Vulture (Vultur 
 
 cinereus) ; B, Peacock (Pavo cristatus) ; C, Pelican (Pelica- 
 
 nus conspicillatus) 337 
 
 64 Bones of the right wing of A, a Penguin; B, an Ostrich 
 
 (Struthio camelus) and C, a Gannet (Sula alba) . . . 339 
 
 65 Pelvic girdle and sacrum of A, Cassowary (Casuarius galeatus); 
 
 B, Owen's Apteryx (A. oweni)-, C, Broad-billed Rhea (R. 
 macrorhyncha) ; D, Ostrich (Struthio camelus) . . . 340 
 
LIST OF ILLUSTRATIONS. XV 
 
 no. PAGE 
 
 66 Ventral view of the shoulder-girdle and sternum of a Duckbill 
 
 (Ornithorhynchus paradoxus) 347 
 
 67 Cervical vertebrae of a Ca'ing Whale (Globicephalus mclas) . 354 
 
 68 Dentition of a Dog (Canis familiar is) 375 
 
 69 Atlas and axis vertebrae of a Dog (Canis familiaris) . . 379 
 
 70 Second thoracic and second lumbar vertebrae of a Dog (Canis 
 
 familiaris) 382 
 
 71 Diagram of the relations of the principal bones in the Mamma- 
 
 lian skull 385 
 
 72 Vertical longitudinal section through skull of a Dog (Canis 
 
 familiaris) 387 
 
 73 Dorsal view of the cranium of a Dog (Canis familiaris) . . 389 
 
 74 Diagram of the mammalian tympanic cavity and associated 
 
 bones 391 
 
 75 Ventral view of the cranium of a Dog (Canis familiaris) . . 396 
 
 76 Sternum and sternal ribs of a Dog (Canis familiaris) . . 403 
 
 77 Bones of the left upper arm and fore-arm of a Dog (Canis 
 
 familiaris) 407 
 
 78 Bight innominate bone, A, of a full-grown Terrier ; B, of a 
 
 Collie Puppy 410 
 
 79 Left leg bones of a Dog (Canis familiaris) . . . .411 
 
 80 A, Eight manus; B, Eight pes of a Dog (Cam's famili- 
 
 aris) 413 
 
 81 Skull of a young Indian Ehinoceros (R. unicornis) showing the 
 
 change of the dentition 421 
 
 82 Palatal aspect of the cranium and mandible of a Donkey (Equus 
 
 asinus) 431 
 
 83 Skull of Procavia (Dendrohyrax) dorsalis .... 433 
 
 84 Carnassial or sectorial teeth of Carnivora . . . . 436 
 
 85 Mandible of Isabelline Bear (Ursus isabellinus) . . . 438 
 
 86 Left mandibular ramus of the Sea Leopard (Ogmorhinus 
 
 leptonyx) 439 
 
 87 Cervical vertebrae of a young Fin Whale (Balaenoptera 
 
 musculus) 444 
 
 88 Atlas and axis vertebrae of an Ox (Bos taurm) . . . 445 
 
 89 First and second thoracic vertebrae of an Ox (Bos taunts) . 449 
 
 90 Skulls of Tasmanian Wolf (Thylacinus cynocephalus) and 
 
 Hairy-nosed Wombat (Phascolomys latifrons) . . . 456 
 
 91 Skull of Two-fingered Sloth (Choloepus didactylus) . . 458 
 
 92 Skull of Rhytina stelleri 460 
 
XVI LIST OF ILLUSTRATIONS. 
 
 FIG. PAGE 
 
 93 Lateral view and longitudinal section of the skull of a young 
 
 Ca'ing Whale (Globicephahis melas) 463 
 
 94 Cranium and mandible of a Pig (Sus scrofa) . . . 466 
 
 95 Mandible of a Hippopotamus (Hippopotamus amphibius) . 467 
 
 96 Skull of a young Indian Elephant (Elephas indicus) . . 474 
 
 97 Longitudinal section of the skull of a young Indian Elephant 
 
 (Elephas indicus) 475 
 
 98 Half-front view of the skull of a Porcupine (Hystrix cristata) . 477 
 
 99 Skulls of an old and of a young Gorilla (Gorilla savagei) . 483 
 
 100 Malleus, stapes, and incus of Man, Dog, and Eabbit . . 485 
 
 101 Skeleton of a Cape Buffalo (Bubalus coffer) . . . .492 
 
 102 Lateral and dorsal views of the shoulder-girdle and part of 
 
 the sternum of the Spiny Anteater (Echidna aculeata) . 494 
 
 103 Skeleton of a Llama (Auchenia glama) .... 496 
 
 104 Dorsal view of the sternum and right half of the shoulder- 
 
 girdle of Mus sylvaticus 498 
 
 105 Anterior surface of the right humerus of a Wombat (Phasco- 
 
 lomys latifrons) 500 
 
 106 Manus of Perissodactyles : A, Left manus of Tapirus ; B, 
 
 Right manus of Titanotherium ; C, Left manus of Chalico- 
 therium giganteum 508 
 
 107 Left manus of A, Coryphodon hamatus; B, Phenacodus pri- 
 
 maevus ; C, Procavia (Dendrohyrax) arboreus . . . 510 
 
 108 Left anterior and posterior limbs and limb girdles of Uinta- 
 
 therium mirabile . . 516 
 
 109 Left femur of an Ox (Bos taurus) and of a Sumatraii Rhinoceros 
 
 (Rhinoceros sumatrensis) . . . . . . .518 
 
 110 Pes of A, a Tapir (Tapirus americanus) ; B, a Rhinoceros 
 
 (Rhinoceros sumatrensis) ; C, Hipparion gracile ; D, a Horse 
 (Equus caballus) 524 
 
 ERRATA. 
 
 p. 172, note, for 14 read 15. 
 
 p. 279, description of figure, for Tropidinotus read Tropidonotus. 
 p. 287, description of figure, for shoulder-girdle of sternum read 
 
 shoulder-girdle and sternum, 
 p. 393, middle of page, for VIII read VII. 
 p. 427, line 2, for Grampus read Killer. 
 
CHAPTER I. 
 
 INTRODUCTORY ACCOUNT OF THE SKELETON IN 
 GENERAL. 
 
 BY the term skeleton is meant the hard structures whose 
 function is to support or to protect the softer tissues of the 
 animal body. 
 
 The skeleton is divisible into 
 
 A. The EXOSKELETON, which is external ; 
 
 B. The ENDOSKELETON, which is as a rule internal ; 
 though in some cases, e.g. the antlers of deer, endoskeletal 
 structures become, as development proceeds, external. 
 
 In Invertebrates the hard, supporting structures of the 
 body are mainly exoskeletal, in Vertebrates they are mainly 
 endoskeletal ; but the endoskeleton includes, especially in 
 the skull, a number of elements, the dermal or membrane 
 bones, which are shown by development to have been originally 
 of external origin. These membrane bones are so intimately 
 related to the true endoskeleton that they will be described 
 with it. The simplest and lowest types of both vertebrate 
 and invertebrate animals have unsegmented skeletons ; with 
 the need for flexibility however segmentation arose both in 
 the case of the invertebrate exoskeleton and the vertebrate 
 endoskeleton. The exoskeleton in vertebrates is phylogeneti- 
 cally older than the endoskeleton, as is indicated by both 
 R. 1 
 
2 THE VERTEBRATE SKELETON. 
 
 palaeontology and embryology. Palaeontological evidence is 
 afforded by the fact that all the lower groups of vertebrates 
 Fish, Amphibia, and Reptiles had in former geological periods 
 a greater proportion of species protected by well-developed 
 dermal armour than is the case at present. Embryological 
 evidence tends the same way, inasmuch as dermal ossifications 
 appear much earlier in the developing animal than do the 
 ossifications in the endoskeleton. 
 
 Skeletal structures may be derived from each of the three 
 germinal layers. Thus hairs and feathers are epiblastic in 
 origin, bones are mesoblastic, and the notochord is hypo- 
 blastic. 
 
 The different types of skeletal structures may now be con- 
 sidered and classified more fully. 
 
 A. EXOSKELETAL STRUCTURES. 
 
 I. EPIBLASTIC (epidermal). 
 
 Exoskeletal structures of epiblastic origin may be developed 
 on both the inner and outer surfaces of the Malpighian layer of 
 the epidermis 1 . Those developed on the outer surface include 
 hairs, feathers, scales, nails, beaks and tortoiseshell; and 
 are specially found in vertebrates higher than fishes. Those 
 developed on the inner surface of the Malpighian layer include 
 only the enamel of teeth and some kinds of scales. With 
 the exception of feathers, which are partly formed from the 
 horny layer, all these parts are mainly derived from the Mal- 
 pighian layer of the epidermis. 
 
 1 The skin consists of an outer layer of epiblastic origin, the 
 epidermis, and an inner layer of mesoblastic origin, the dermis. The 
 epidermis is divided into two principal layers, an outer one, the horny 
 layer or stratum corneum, and an inner one, the stratum Malpighii. The 
 innermost part of the stratum corneum is distinguished as the stratum 
 lucidum, and the outermost part of the stratum Malpighii as the stratum 
 granulosum. 
 
INTRODUCTORY. EPIBLASTIC STRUCTURES. 3 
 
 Hairs are slender, elongated structures which arise by 
 the proliferation of cells from the Malpighian layer of the 
 epidermis. These cells in the case of each hair form a short 
 papilla, which sinks inwards and becomes imbedded at the 
 bottom of a follicle in the dermis. Each hair is normally 
 composed of an inner cellular pithy portion containing much 
 air, and an outer denser cortical portion of a horny nature. 
 Sometimes, as in Deer, the hair is mainly formed of the pithy 
 portion, and is then easily broken. Sometimes the horny part 
 predominates, as in the bristles of Pigs. A highly vascular 
 dermal papilla projects into the base of the hair. 
 
 Feathers, like hairs, arise from epidermal papillae which 
 become imbedded in pits in the dermis. But the feather germ 
 differs from the hair germ, in the fact that it first grows 
 out like a cone on the surface of the epidermis, and that 
 the horny as well as the Malpighian layer takes part in its 
 formation. 
 
 Nails, claws, hoofs, and the horns of Oxen are also 
 epidermal, as are such structures as the scales of reptiles, of 
 birds' feet, and of Manis among mammals, the rattle of the 
 rattlesnake, the nasal horns of Rhinoceros, and the baleen 
 of whales. All these structures will be described later. 
 
 Nails arise in the interior of the epidermis by the thicken- 
 ing and cornification of the stratum lucidum. The outer 
 border of the nail soon becomes free, and growth takes place 
 by additions to the inner surface and attached end. 
 
 When a nail tapers to a sharp point it is called a claw. 
 In many cases the nails more or less surround the ends of 
 the digits by which they are borne. 
 
 Horny beaks of epidermal origin occur casing the jaw- 
 bones in several widely distinct groups of animals. Thus 
 among reptiles they are found in Chelonia (tortoises and 
 turtles) as well as in some extinct forms ; they occur in all 
 living birds, in Ornithorhynchus among mammals, and in the 
 larvae of many Amphibia. 
 
 12 
 
4 THE VERTEBRATE SKELETON. 
 
 In a few animals, such as Lampreys and Ornithorhynchus, 
 the jaws bear horny tooth-like structures of epidermal origin. 
 
 The enamel of teeth and of placoid scales is also epi- 
 blastic in origin 1 , and it may be well at this point to give 
 some account of the structure of teeth, though they are 
 partly mesoblastic in origin. The simplest teeth are those 
 met with in sharks and dogfish, where they are merely the 
 slightly modified scales developed in the integument of the 
 mouth. They pass by quite insensible gradations into normal 
 placoid scales, such as cover the general surface of the body. 
 A placoid scale 2 is developed on a papilla of the dermis 
 which projects outwards and backwards, and is covered by the 
 columnar Malpighian layer of the epidermis. The outer layer 
 of the dermal papilla then gradually becomes converted into 
 dentine and bone, while enamel is developed on the inner side 
 of the Malpighian layer, forming a cap to the scale. The 
 Malpighian and horny layers of the epidermis get rubbed off 
 the enamel cap, so that it comes to project freely on the sur- 
 face of the body. 
 
 As regards their attachment teeth may be (1) attached 
 to the fibrous integument of the mouth, or (2) fixed to the 
 jaws or other bones of the mouth, or (3) planted in grooves, 
 or (4) in definite sockets in the jaw-bones (see p. 107). 
 
 Teeth in general consist of three tissues, enamel, dentine 
 and cement, enclosing a central pulp-cavity containing blood- 
 vessels and nerves. Enamel is, however, often absent, as in all 
 living Edentates. 
 
 Enamel generally forms the outermost layer of the crown 
 or visible part of the tooth ; it is the hardest tissue occurring 
 in the animal body and consists of prismatic fibres arranged at 
 right angles to the surface of the tooth. It is characterised by 
 its bluish- white translucent appearance. 
 
 1 The enamel of the pharyngeal teeth of some Teleosteans is hypo- 
 blastic in origin. 
 
 2 See also p. 71. 
 
INTRODUCTORY. TEETH. 5 
 
 II. MESOBLASTIC (mesodermal). 
 
 Dentine or ivory generally forms the main mass of a 
 tooth. It is a hard, white substance allied to bone. When 
 examined microscopically dentine is seen to be traversed by 
 great numbers of nearly parallel branching tubules which 
 radiate outwards from the pulp-cavity. In fishes as a rule, 
 and sometimes in other animals, a variety of dentine con- 
 taining blood-vessels occurs, this is called vasodentine. 
 
 Cement or crusta petrosa forms the outermost layer of 
 the root of the tooth. In composition and structure it is 
 practically identical with bone. In the more complicated 
 mammalian teeth, besides enveloping the root, it fills up the 
 spaces between the folds of the enamel. 
 
 The hard parts of a tooth commonly enclose a central pulp- 
 cavity into which projects the pulp, a papilla of the dermis 
 including blood-vessels and nerves. As long as growth con- 
 tinues the outer layers of this pulp become successively calcified 
 and added to the substance of the dentine. In young growing 
 teeth the pulp-cavity remains widely open, but in mammals 
 the general rule is that as a tooth gets older and the crown 
 becomes fully formed, the remainder of the pulp becomes 
 converted into one or more tapering roots which are im- 
 bedded in the alveolar cavities of the jaws. The opening of 
 the pulp-cavity is then reduced to a minute perforation at the 
 base of each root. A tooth of this kind is called a rooted 
 tooth. 
 
 But it is not only in young teeth that the pulp-cavity 
 sometimes remains widely open; for some teeth, such as the 
 tusks of Elephants and the incisor teeth of Rodents, form 
 no roots and continue to grow throughout the animal's 
 life. Such teeth are said to be rootless or to have persistent 
 pulps. 
 
 An intermediate condition is seen in some teeth, such as 
 the grinding teeth of Horses These teeth grow for a very 
 long time, their crowns wearing away as fast as their bases 
 
THE VERTEBRATE SKELETON. 
 
 FIG. 1. DIAGRAMMATIC SECTIONS OF VARIOUS FORMS OF TEETH 
 (from FLOWER). 
 
 I. Incisor or tusk of elephant, with pulp-cavity persistently open at 
 base. II. Human incisor during development with root imperfectly 
 formed, and pulp-cavity widely open at base. III. Completely formed 
 human incisor, with pulp-cavity contracted to a small aperture at the 
 end of the root. IV. Human molar with broad crown and two roots. 
 V. Molar of Ox, with the enamel covering the crown, deeply folded and 
 the depressions filled with cement. The surface is worn by use, other- 
 wise the enamel coating would be continuous at the top of the ridges. 
 In all the figures the enamel is black, the pulp white, the dentine 
 represented by horizontal lines, and the cement by dots. 
 
INTRODUCTORY. TEETH. 7 
 
 are produced; finally however definite roots are formed and 
 growth ceases. 
 
 The teeth of any animal may be homodont, that is, all 
 having the same general character, or heterodont, that is, 
 having different forms adapted to different functions. The 
 dentition is heterodont in a few reptiles and the majority of 
 mammals. 
 
 SUCCESSION OF TEETH. In most fishes, and many amphibians 
 and reptiles the teeth can be renewed indefinitely. In sharks, 
 for example, numerous rows of reserve teeth are to be seen 
 folded back behind those in use (see fig. 15). The majority of 
 mammals have only two sets of teeth, and are said to be diphy- 
 odont ; some have only a single series (monophyodont). 
 
 DEVELOPMENT OF TEETH. A brief sketch of the method in 
 which development of teeth takes place in the higher verte- 
 brates may here be given. Along the surface of the jaws a 
 thickening of the epiblastic epithelium takes place, giving rise 
 to a ridge, which sinks inwards into the tissue of the jaw, 
 and it is known as the primary enamel organ. At the points 
 where teeth are to be developed special ingrowths of this 
 primary enamel organ take place, and into each there projects 
 a vascular dental papilla from the surrounding mesoblast of 
 the jaw. Each ingrowth of the enamel organ forms an 
 enamel cap, which gradually embraces the dental papilla, 
 and at the same time appears to be pushed on one side, owing 
 to the growth not being uniform. The external layer of 
 the dental papilla is composed of long nucleated cells, the 
 odontoblasts, and it is by these that the dentine is formed. 
 Similarly the internal layer of the enamel organ is formed of 
 columnar enamel cells, which give rise to the enamel. The 
 mesoblastic cells surrounding the base of the tooth give rise 
 to the cement. 
 
 Bone is in many cases exoskeletal, but it will be most 
 conveniently described with the endoskeleton. 
 
8 THE VERTEBRATE SKELETON. 
 
 The scales of fish are wholly or in part mesoblastic 
 in origin, being totally different from those of reptiles. The 
 cycloid and ctenoid scales of Teleosteans (see p. 105) are thin 
 plates coated with epidermis. They are sometimes bony, but 
 as a rule are simply calcified. Ganoid scales are flat plates 
 of bone coated with an enamel-like substance, and articulating 
 together with a peg and socket arrangement; they are pro- 
 bably identical with enlarged and flattened placoid scales. 
 
 The armour plates of fossil Ganoids, Labyrinthodonts, 
 and Dinosaurs, and of living Crocodiles, some Lizards and 
 Armadillos, are composed of bone. They are always covered 
 by a layer of epidermis. 
 
 The antlers of deer are also composed of bone ; they 
 will be more fully described in the chapter on mammals. 
 It may perhaps be well to mention them here, though they 
 really belong to the endoskeleton, being outgrowths from the 
 frontal bones. 
 
 B. ENDOSKELETAL STRUCTURES. 
 I. HYPOBLASTIC. 
 
 (a) The notochord is an elastic rod formed of large 
 vacuolated cells, and is surrounded by a membranous sheath 
 of mesoblastic origin. It is the primitive endoskeleton in 
 the Chordata, all of which possess it at some period of their 
 existence; while in many of the lower forms it persists through- 
 out life. Even in the highest Chordata it is the sole repre- 
 sentative of the axial skeleton for a considerable part of the 
 early embryonic life. A simple unsegmented notochord 
 persists throughout life in the Cephalochordata, Cyclostomata, 
 and some Pisces, such as Sturgeons and Chimaeroids. 
 
 (b) The enamel of the pharyngeal teeth of the Salmon 
 and many other Teleosteans is hypoblastic in origin. The 
 epiblast of the stomodaeum, in which the other teeth are 
 developed, passes into the hypoblast of the mesenteron in 
 which these pharyngeal teeth are formed. 
 
INTRODUCTORY. BONE. 9 
 
 II. MESOBLASTIC. 
 
 The most primitive type of a mesoblastic endoskeleton 
 consists of a membranous sheath surrounding the notochord, 
 as in Myxine and its allies. The first stage of complication 
 is by the development of cartilage in the notochordal sheath, 
 as in Petromyzon. Often the cartilage becomes calcified in 
 places, as in the vertebral centra of Scyllium and other Elas- 
 mobranchs. Lastly, the formation of bone takes place ; it 
 generally constitutes the most important of the endoskeletal 
 structures. 
 
 Bone may be formed in two ways : 
 
 (1) by the direct ossification of pre-existing cartilage, 
 when it is known as cartilage bone or endochondral bone ; 
 
 (2) by independent ossification in connective tissue ; it is 
 then known as membrane or dermal or periosteal bone. 
 
 With the exception of the clavicle 1 all the bones of the trunk 
 and limbs, together with a large proportion of those of the 
 skull, are preformed in the embryo in cartilage, and are grouped 
 as cartilage bones : while the clavicle and most of the roofing 
 and jaw-bones of the skull are not preformed in cartilage, being 
 developed simply in connection with a membrane. Hence it 
 is customary to draw a very strong line of distinction between 
 these two kinds of bone; in reality however this distinction 
 is often exaggerated, and the two kinds pass into one another, 
 and as will be shown immediately, the permanent osseous 
 tissue of many of those which are generally regarded as 
 typical cartilage bones, is really to a great extent of periosteal 
 origin. The palatine bone, for instance, of the higher verte- 
 brates in general is preceded by a cartilaginous bar, but is 
 itself almost entirely a membrane bone. 
 
 Before describing the development of bone it will be well 
 to briefly describe the structure of adult bone and cartilage. 
 
 1 It is usual to regard the clavicle as a membrane bone, but Kolliker 
 has shown that in rabbit embryos of about the 17th day it is cartilaginous. 
 
10 THE VERTEBRATE SKELETON. 
 
 The commonest kind of cartilage, and that which pre- 
 forms so many of the bones of the embryo, is hyaline cartilage. 
 It consists of oval nucleated cells occupying cavities (lacunae) 
 in a clear intercellular semitransparent matrix, which is pro- 
 bably secreted by the cells. Sometimes one cell is seen in each 
 lacuna, sometimes shortly after cell-division a lacuna may con- 
 tain two or more cells. The free surface of the cartilage 
 is invested by a fibrous membrane, the perichondrium. 
 
 Bone consists of a series of lamellae of ossified substance 
 between which are oval spaces, the lacunae, giving rise to 
 numerous fine channels, the canaliculi, which radiate off in 
 all directions. The lacunae are occupied by the bone cells 
 which correspond to cartilage cells, from which if the bone is 
 young, processes pass off into the canaliculi. It is obvious 
 that the ossified substance of bone is intercellular in character, 
 and corresponds to the matrix of cartilage. 
 
 Bone may be compact, or loose and spongy in character, 
 when it is known as cancellous bone. In compact bone 
 many of the lamellae are arranged concentrically round 
 cavities, the Haversian canals, which in life are occupied by 
 blood-vessels. Each Haversian canal with its lamellae forms 
 a Haversian system. In spongy bone instead of Haversian 
 canals there occur large irregular spaces filled with marrow, 
 which consists chiefly of blood-vessels and fatty tissue. The 
 centre of a long bone is generally occupied by one large con- 
 tinuous marrow cavity. The whole bone is surrounded by 
 a fibrous connective tissue membrane, the periosteum. 
 
 THE DEVELOPMENT OF BONE. 
 
 Periosteal ossification. An example of a bone en- 
 tirely formed in this way is afforded by the parietal. The 
 first trace of ossification is shown by the appearance, below 
 the membrane which occupies the place of the bone in the 
 early embryo, of calcareous spicules of bony matter, which 
 are laid down round themselves by certain large cells, the 
 
INTRODUCTORY. DEVELOPMENT OF BONE. 11 
 
 osteoblasts. These osteoblasts gradually get surrounded by 
 the matter which they secrete and become converted into bone 
 cells, arid in this way a mass of spongy bone is gradually pro- 
 duced. Meanwhile a definite periosteum has been formed round 
 the developing bone, and on its inner side fresh osteoblasts 
 are produced, and these with the others gradually render the 
 bone larger and more and more compact. Finally, the middle 
 layer of the bone becomes again hollowed out and rendered 
 spongy by the absorption of part of the bony matter. 
 
 Endochondral ossification 1 . This is best studied in the 
 case of a long bone like the femur or humerus. Such a long 
 bone consists of a shaft, which forms the main part, and two 
 terminal portions, which form the epiphyses, or portions 
 ossifying from centres distinct from that forming the shaft or 
 main part of the bone. 
 
 In the earliest stage the future bone consists of hyaline 
 cartilage surrounded by a vascular sheath, the perichondrium. 
 
 Then, starting from the centre, the cartilage becomes per- 
 meated by a number of channels into which pass vessels from 
 the perichondrium and osteoblasts. In this way the centre 
 of the developing shaft becomes converted into a mass of 
 cavities separated by bands or trabeculae of cartilage. This 
 cartilage next becomes calcified, but as yet is not converted 
 into true bone. The osteoblasts in connection with the 
 cavities now begin to deposit true endochondral spongy bone, 
 and then after a time this becomes absorbed by certain 
 large cells, the osteoclasts, and resolved into marrow or vas- 
 cular tissue loaded with fat. So that the centre of the shaft 
 passes from the condition of hyaline cartilage to that of 
 calcined cartilage, thence to the condition of spongy bone, and 
 finally to that of marrow. At the same time beneath the 
 
 1 In compiling these paragraphs on Histology, free use has been 
 made of Klein and Noble Smith's Atlas of Histology, the small Histo- 
 logies of Klein and Schafer, Huxley's Elementary Physiology, and Lloyd 
 Morgan's Animal Biology. 
 
12 THE VERTEBRATE SKELETON. 
 
 perichondrium osteoblasts are developed which also begin to 
 give rise to spongy bone. The perichondrium thus becomes 
 the periosteum, and the bone produced by it, is periosteal or 
 membrane bone. So that while a continuous marrow cavity is 
 gradually being formed in the centre of the shaft, the layer of 
 periosteal bone round the margin is gradually thickening, and 
 becoming more and more compact by the narrowing down of its 
 cavities to the size of Haversian canals. The absorption of 
 endochondral and formation of periosteal bone goes on, till 
 in time it comes about that the whole of the shaft, except 
 its terminations, is of periosteal origin. At the extremities 
 of the shaft, however, and at the epiphyses, each of which 
 is for a long time separated from the shaft by a pad of 
 cartilage, the ossification is mainly endochondral, the peri- 
 osteal bone being represented only by a thin layer. 
 
 Until the adult condition is reached and growth ceases, the 
 pad of cartilage between the epiphysis and the shaft continues 
 to grow, its outer (epiphysial) half growing by the formation of 
 fresh cartilage as fast as its inner half is encroached on by the 
 growth of bone from the shaft. The terminal or articular 
 surfaces of the bone remain throughout life covered by layers 
 of articular cartilage. 
 
 Even after the adult condition is reached the bone is 
 subject to continual change, processes of absorption and fresh 
 formation going on for a time and tending to render the bone 
 more compact. 
 
 METHODS IN WHICH BONES ARE UNITED TO ONE ANOTHER. 
 
 The various bones composing the endoskeleton are united 
 to one another either by sutures or by movable joints. 
 
 When two bones are suturally united, their edges fit 
 closely together and often interlock, being also bound together 
 by the periosteum. 
 
 In many cases this sutural union passes into fusion or 
 ankylosis, ossification extending completely from one bone to 
 
INTRODUCTORY. JOINTS. 13 
 
 the other with the obliteration of the intervening suture. This 
 feature is especially well marked in the cranium of most birds. 
 
 The various kinds of joints or articulations 1 may be sub- 
 divided into imperfect joints and perfect joints. 
 
 In imperfect joints, such as the in tervertebral joints of 
 mammals, the two contiguous surfaces are united by a mass 
 of fibrous tissue which allows only a limited amount of motion. 
 
 In perfect joints the contiguous articular surfaces are 
 covered with cartilage, and between them lies a synovial 
 membrane which secretes a viscid lubricating fluid. 
 
 The amount of motion possible varies according to the 
 nature of the articular surfaces ; these include 
 
 a. ball and socket joints, like the hip and shoulder, in 
 which the end of one bone works in a cup provided by an- 
 other, and movements can take place in a variety of planes. 
 
 b. hinge joints, like the elbow and knee, in which as 
 in ball-and-socket joints one bone works in a cup provided 
 by another, but movements can take place in one plane only. 
 
 THE ENDOSKELETON. 
 
 The endoskeleton is divisible into axial and appendi- 
 cular parts ; and the axial skeleton into 
 
 1. the spinal column, 
 
 (a. the cranium, 
 
 2. the skull {...,,. . 111 + 
 
 [o. the jaws and visceral skeleton, 
 
 3. the ribs and sternum 2 . 
 
 I. THE AXIAL SKELETON. 
 
 1. THE SPINAL COLUMN. 
 
 The spinal column in the simplest cases consists of an 
 
 1 See Huxley's Elementary Physiology, Revised edition, London, 1886, 
 p. 180. 
 
 2 Strictly speaking the jaws, visceral skeleton, ribs and sternum do 
 not form part of the axis, but it is convenient to group them as parts of 
 the axial skeleton. 
 
14 THE VERTEBRATE SKELETON. 
 
 unsegmented rod, the notochord, surrounded by the skeleto- 
 genous layer, a sheath of mesoblastic origin, which also 
 envelops the nerve cord. Several intermediate stages connect 
 this simple spinal column with the vertebral column charac- 
 teristic of higher vertebrates. A typical vertebral column 
 may be said to consist of (1) a series of cartilaginous or bony 
 blocks, the vertebral centra, which arise in the sheath 
 surrounding the notochord. They cause the notochord to 
 become constricted and to atrophy to a varying extent, though 
 a remnant of it persists, either permanently or for a long 
 period, within each centrum or between successive centra. 
 (2) From the dorsal surface of each centrum arise a pair of 
 processes which grow round the spinal cord and unite above 
 it, forming a dorsal or neural arch. (3) A similar pair 
 of processes arising from the ventral surface of the centrum 
 form the ventral or haemal arch. To the ventral arch 
 the ribs strictly belong, and it tends to surround the ventral 
 blood-vessels and the body cavity with the alimentary canal 
 and other viscera. 
 
 A neural spine or spinous process commonly projects 
 upwards from the dorsal surface of the neural arch, and a pair 
 of transverse processes project outwards from its sides. 
 When, as is commonly the case, the two halves of the haemal 
 arch do not meet, the ventral surface of the centrum often 
 bears a downwardly-projecting hypapophysis. 
 
 The character of the surfaces by which vertebral centra 
 articulate with one another varies much. Sometimes both 
 surfaces are concave, and the vertebra is then said to be 
 amphicoelous ; sometimes a centrum is convex in front and 
 concave behind, the vertebra is then opisthocoelous, some- 
 times concave in front and convex behind, when the vertebra 
 is procoelous. Again, in many vertebrae both faces of the 
 centra are Hat, while in others they are saddle- shaped, as in the 
 neck vertebrae of living birds, or biconvex, as in the case of 
 the first caudal vertebra of crocodiles. 
 
INTRODUCTORY. VERTEBRAE. 
 
 15 
 
 In the higher vertebrates pads of fibro-cartilage the 
 intervertebral discs are commonly interposed between 
 
 2-- 
 
 10 
 
 FIG. 2. CERVICAL VERTEBRAE OF AN Ox (Bos taunts). 
 
 A, is the fifth; B, the fourth 
 
 1. neural spine. 
 
 2. transverse process. 
 
 3. hypapophysis. 
 
 4. convex anterior face of the 
 
 centrum. 
 
 5. concave posterior face of the 
 
 centrum. 
 
 C, the third. x (Camb. Mus.) 
 
 6. prezygapophysis. 
 
 7. postzygapophysis. 
 
 8. vertebrarterial canal. 
 
 9. neural canal. 
 
 10. inferior lamella of transverse 
 process. 
 
 successive centra, these or parts of them often ossify, especially 
 in the trunk and tail, and are then known as intercentra. 
 
 The vertebrae of the higher forms can generally be arranged 
 in the following five groups, each marked by certain special 
 characteristics : 
 
 1. The cervical or neck vertebrae. These connect 
 the skull with the thorax, and are characterised by relatively 
 great freedom of movement. They often bear small ribs, but 
 are distinguished from the succeeding thoracic vertebrae by 
 the fact that their ribs do not reach the sternum. The first 
 cervical vertebra which articulates with the skull is called 
 the atlas, but a study of the nerve exits shows that the first 
 
16 THE VERTEBRATE SKELETON. 
 
 vertebra is not serially homologous throughout the Ichthy- 
 opsida, so that it is best to reserve the term atlas for the first 
 vertebra in Sauropsida and Mammalia. 
 
 2. The thoracic vertebrae (often called dorsal) bear 
 movably articulated ribs which unite ventrally with the 
 sternum. 
 
 3. The lumbar vertebrae are generally large, and are 
 often more movable on one another than are the thoracic 
 vertebrae. They bear no ribs. 
 
 4. The sacral vertebrae are characterised by the fact 
 that they are firmly fused together, and are united with the 
 pelvic girdle by means of their transverse processes and rudi- 
 mentary ribs. 
 
 5. The caudal or tail vertebrae succeed the sacral. 
 The anterior ones are often fused with one another and with 
 the sacrals, but they differ from true sacral vertebrae in that 
 there are no rudimentary ribs between their transverse pro- 
 cesses and the pelvic girdle. They often bear V-shaped 
 .chevron bones. 
 
 In fish and snakes the vertebral column is divisible into 
 only two regions, an anterior trunk region, whose vertebrae bear 
 ribs, and a posterior tail region, whose vertebrae are ribless. 
 
 2. THE SKULL. 
 
 Before giving a general account of the adult skull it will 
 be well to briefly describe its development. 
 
 GENERAL DEVELOPMENT OF THE CRANIUM*. 
 
 Shortly after its appearance, the central nervous system 
 becomes surrounded by a membranous mesodermal investment 
 which in the region of the spinal cord is called the skeleto- 
 genous layer or perichordal sheath, while in the region 
 
 1 F. M. Balfour, Comparative Embryology, vol. n., London, 1881, 
 p. 465. W. K. Parker and G. T. Bettany, The Morphology of the Skull, 
 London, 1877. 
 
INTRODUCTORY. DEVELOPMENT OF THE CRANIUM. 17 
 
 of the brain it is called the membranous cranium. Ventral 
 to the central nervous system is the notochord, which extends 
 far into the region of the future cranium, and like the 
 nervous system, is enclosed by the skeletogenous layer. The 
 primitive cartilaginous cranium is formed by histological 
 differentiation within the substance of the membranous 
 cranium and always consists of the following parts : 
 
 (a) the parachordals. These are a pair of flat curved 
 plates of cartilage, each of which has its inner edge grooved 
 where it comes in contact with the notochord. The para- 
 chordals, together with the notochord, form a continuous 
 plate, which is known as the basilar plate. The basilar 
 plate is the primitive floor below the hind- and mid-brain. 
 In front the parachordals abut upon another pair of carti- 
 laginous bars, the trabeculae, the two pairs of structures being 
 sometimes continuous with one another from the first ; 
 
 (6) the trabeculae which meet behind and embrace the 
 front end of the notochord. Further forwards they at first 
 diverge from one another, and then converge again, enclosing 
 a space, the pituitary space. After a time they generally 
 fuse with one another in the middle line, and, with the para- 
 chordals behind, form an almost continuous basal plate. The 
 trabeculae generally appear before the parachordals. They 
 form the primitive floor below the fore-brain ; 
 
 (c) the cartilaginous capsules of the three pairs of sense 
 organs. At a very early stage of development involutions 
 of the surface epiblast give rise to the three pairs of special 
 sense organs the olfactory or nasal organs in front, the optic 
 in the middle, and the auditory behind. The olfactory and 
 auditory organs always become enclosed in definite cartilagi- 
 nous capsules, the eyes often as in the Salmon, become 
 enclosed in cartilaginous sclerotic capsules, while sometimes, 
 as in mammals, their protecting capsules are fibrous. 
 
 Each pair of sense capsules comes into relation with part 
 R. 2 
 
18 THE VERTEBRATE SKELETON. 
 
 of the primitive cranium, and greatly modifies it. Thus the 
 auditory or periotic capsules press on the parachordals till 
 they come to be more or less imbedded in them. Perhaps 
 owing to the pressure of the nasal capsules the trabeculae 
 fuse in front, and then grow out into an anterior pair of 
 processes, the cornua trabeculae, and a posterior pair, the 
 antorbital processes, which together almost completely sur- 
 round the nasal capsules. The sclerotic capsules of the eyes 
 greatly modify the cranium, although they never become 
 completely united with it. 
 
 The cartilaginous cranium formed of the basal plate, to- 
 gether with the sense capsules, does not long remain merely 
 as a floor. Its sides grow vertically upwards, forming the 
 exoccipital region of the cranium behind, and the ali- 
 sphenoidal and orbitosphenoidal regions further forwards. 
 In many forms, such as Elasmobranchs, all these upgrowths 
 meet round the brain, roofing it in and forming an almost 
 complete cartilaginous cranium. But in most vertebrata, 
 while in the occipital region, the cartilaginous cranium is 
 completed dorsally, in the alisphenoidal and orbitosphenoidal 
 regions the cartilage merely forms the lateral walls of the 
 cranium, the greater part of the brain having dorsal to it a 
 wide space, closed by merely membranous tissue in connection 
 with which the large frontal and parietal bones are subse- 
 quently formed. 
 
 The SKULL includes 
 
 a. the cranium, 
 
 b. the jaws and visceral skeleton. 
 
 The cranium can be further subdivided into 
 
 (1) an axial portion, the cranium proper or brain 
 case; 
 
 (2) the sense capsules. The capsules of the auditory 
 and olfactory sense organs are always present, and as has been 
 
INTRODUCTORY. THE CRANIUM. 19 
 
 already mentioned, in many animals the eye likewise is 
 included in a cartilaginous capsule. 
 
 (1) THE CRANIUM PROPER Or BRAIN CASE. 
 
 The cranium varies much in form and structure. In lower 
 vertebrates, such as Sharks and Lampreys, it remains entirely 
 cartilaginous and membranous, retaining throughout life much 
 of the character of the embryonic rudiment of the cranium of 
 higher forms. The dogfish's cranium, described on pp. 73 to 
 76, is a good instance of a cranium of this type. But in the 
 majority of vertebrates the cartilage becomes more or less 
 replaced by cartilage bone, while membrane bones are also 
 largely developed and supplant the cartilage. 
 
 The cranium of most vertebrates includes a very large 
 number of bones whose arrangement varies much, but one 
 can distinguish a definite basicranial axis formed of the 
 basi-occipital, basisphenoid, and presphenoid bones, which is 
 a continuation forwards of the axis of the vertebral column. 
 From the basicranial axis a wide arch arises, composed of a 
 number of bones, which form the sides and roof of the brain- 
 case. These bones are arranged in such a manner that if both 
 cartilage and membrane bones are included they can be divided 
 into three rings or segments. The hinder one of these seg- 
 ments is the occipital, the middle the parietal, and the anterior 
 one the frontal. 
 
 The occipital segment is formed of four cartilage, bones, the 
 basi-occipital below, two exoccipitals at the sides, and the 
 supra-occipital above. The parietal segment is formed of 
 the basisphenoid below, two alisphenoids at the sides and 
 two membrane bones, the parietals above, and the frontal 
 segment in like manner consists of the presphenoid below, 
 the two orbitosphenoids at the sides, and two membrane 
 bones, the frontals, above. The parietals and frontals, being 
 membrane bones, are not comparable to the supra-occipital, 
 in the way that the presphenoid and basisphenoid are to the 
 basi-occipital. 
 
 22 
 
20 THE VERTEBRATE SKELETON. 
 
 The cartilage bones of the occipital segments are derived 
 from the parachordals of the embryonic skull, those of the 
 parietal and frontal segments from the trabeculae. 
 
 In front of the presphenoid the basicranial axis is con- 
 tinued by the mesethmoid. 
 
 (2) THE SENSE CAPSULES. 
 
 These enclose and protect the special sense organs. 
 
 (a) Auditory capsule. 
 
 The basisphenoid is always continuous with the basi- 
 occipital, but the alisphenoid is not continuous with the ex- 
 occipital as the periotic or auditory capsule is interposed 
 between them. Each periotic capsule has three principal 
 ossifications ; an anterior bone, the pro-otic, a posterior bone r 
 the opisthotic, and a superior bone, the epi-otic. 
 
 These bones may severally unite, or instead of uniting 
 with one another they may unite with the neighbouring bones. 
 Thus the epi-otic often unites with the supra-occipital, and the 
 opisthotic with the exoccipital. 
 
 Two other bones developed in the walls of the auditory 
 capsule are sometimes added, as in Teleosteans ; these are the 
 pterotic and sphenotic. 
 
 (b) Optic capsule. 
 
 The eye is frequently enclosed in a cartilaginous sclerotic 
 capsule, and in this a number of scale-like bones are often 
 developed. 
 
 Several membrane bones are commonly formed around the 
 orbit or cavity for the eye. The most constant of these is 
 the lachrymal which lies in the anterior corner; frequently too, 
 as in Teleosteans, there is a supra-orbital lying in the upper 
 part of the orbit, or as in many Reptiles, a postorbital lying in 
 the posterior part of the orbit. 
 
 (c) Nasal capsule. 
 
 In relation to the nasal capsules various bones occur. 
 
INTRODUCTORY. JAWS AND VISCERAL SKELETON. 21 
 
 The basicranial axis in front of the presphenoid is ossified,, 
 as the mesethmoid, dorsal to which there sometimes, as in 
 Teleosteans, occur a median ethmoid and a pair of lateral 
 ethmoids 1 . Two pairs of membrane bones very commonly 
 occur in this region, viz. the nasals which lie dorsal to the 
 mesethmoid, and the vomers (sometimes there is only one) which 
 lie ventral to it. 
 
 The part of the skull lying immediately in front of the 
 cranial cavity and in relation to the nasal capsules constitutes 
 the ethmoidal region. 
 
 There remain certain other membrane bones which are 
 often found connected with the cranium. Of these, one of 
 the largest is the parasphenoid which, in Ichthyopsids, is 
 found underlying the basicranial axis. Prefrontals often, as 
 in most reptiles, occur lying partly at the sides and partly in 
 front of the frontal, and postfrontala similarly occur behind the 
 orbit lying partly behind the f rentals and partly at their sides. 
 Lastly a squamosal bone is, as in Mammals, very commonly 
 developed, and lies external and partly dorsal to the auditory 
 capsules. 
 
 THE JAWS AND VISCERAL SKELETON. 
 
 In the most primitive fish these consist of a series of 
 cartilaginous rings or arches placed one behind another and 
 encircling the anterior end of the alimentary canal. Originally 
 they are mainly concerned with branchial respiration. 
 
 The first or maxillo-mandibular arch forms the upper 
 jaw and the lower jaw or mandible. 
 
 The second or hyoid arch bears gills and often assists 
 in attaching the jaws to the cranium. The remaining arches 
 may bear gills, though the last is commonly without them. 
 
 The above condition is only found in fishes, in higher 
 animals the visceral skeleton is greatly reduced and modified. 
 
 The first or maxillo-mandibular arch is divisible into a 
 
 1 Sometimes also called ectethmoids or parethmoids. 
 
22 THE VERTEBRATE SKELETON. 
 
 dorsal portion, the palato-pterygo-quadrate bar, which 
 forms the primitive upper jaw and enters into very close 
 relations with the cranium, and a ventral portion, Meckel's 
 cartilage, which forms the primitive lower jaw. The carti- 
 laginous rudiments of both these portions disappear to a 
 greater or less extent and become partly ossified, partly re- 
 placed by or enveloped in membrane bone. 
 
 The posterior part of the palato-pterygo-quadrate bar be- 
 comes ossified to form the quadrate, the anterior part to form 
 the palatine and pterygoid, or the two latter may be formed 
 partially or entirely of periosteal bone, developed round the 
 cartilaginous bar. Two pairs of important membrane bones, 
 the premaxillae and maxillae form the anterior part of the 
 upper jaw, and behind the maxilla lies another membrane 
 bone, the jugal or malar, which is connected with the quadrate 
 by a quadratojugal. The premaxillae have a large share in 
 bounding the external nasal openings or anterior nares. 
 
 In lower vertebrates the nasal passage leads directly into 
 the front part of the mouth cavity and opens by the posterior 
 nares. In some higher vertebrates, such as mammals and 
 crocodiles, processes arise from the premaxillae and palatines, 
 and sometimes from the pterygoids, which meet their fellows 
 in the middle line and form the palate, shutting off the nasal 
 passage from the mouth cavity and causing the posterior nares 
 to open far back. 
 
 The cartilage of the lower jaw is in all animals with 
 ossified skeletons, except the Mammalia, partly replaced by 
 cartilage bone forming the articular, partly overlain by a 
 series of membrane bones the dentary, splenial, angular, 
 supra-angular and coronoid. In many sharks large paired 
 accessory cartilages occur at the sides of the jaws ; and in a 
 few reptiles and some Amphibia, such as the Frog, the ossified 
 representative of the anterior of these structures occurs 
 forming the mento-meckelian bone. In mammals the lower 
 jaw includes but a single bone. 
 
INTRODUCTORY. RIBS AND STERNUM. 23 
 
 The quadrate in all animals with ossified skeletons, except 
 the Mammalia, forms the suspensorium of the mandible or the 
 skeletal link between the jaw and the cranium ; in the Mam- 
 malia, however, the mandible articulates with the squamosal, 
 while the quadrate is greatly reduced, and is now generally 
 considered to be represented by the tympanic ring of the ear. 
 
 The second visceral or hyoid arch in fishes consists of two 
 pieces of cartilage, a proximal 1 piece the hyomandibular, 
 and a distal 1 piece the cerato-hyal. The cerato-hyals of the 
 two sides are commonly united by a median ventral plate, the 
 basi-hyal. The hyoid arch bears gills on its posterior border, 
 but its most important function in most fishes is to act as the 
 suspensorium. In higher vertebrates the representative of 
 the hyomandibular is much reduced in size, and comes into 
 relation with the ear forming the auditory ossicles; the 
 cerato-hyal looses its attachment to the hyomandibular and 
 becomes directly attached to the cranium, forming a large part 
 of the hyoid apparatus of most higher vertebrates. 
 
 Behind the hyoid arch come the branchial arches. They 
 are best developed in fishes, in which they are commonly five 
 in number and bear gills. Their ventral ends are united in 
 pairs by median pieces, the copulae. 
 
 In higher vertebrates they become greatly reduced, and 
 all except the first and second completely disappear. In the 
 highest vertebrates, the mammals, the second has disappeared, 
 but in birds and many reptiles it is comparatively well 
 developed. 
 
 3. THE RIBS AND STERNUM. 
 
 The ribs are a series of segmentally arranged cartilagi- 
 nous or bony rods, attached to the vertebrae; they tend 
 to surround the body cavity, and to protect the organs 
 contained within it. Ribs are very frequently found 
 
 1 The proximal end of anything is the one nearest the point of origin 
 or attachment, the distal end is the one furthest from the point of origin 
 or attachment. 
 
24 THE VERTEBRATE SKELETON. 
 
 attached to the transverse processes of the vertebrae, but a 
 study of their origin in fish shows that they are really the 
 cut off terminations of the ventral arch, not of the transverse 
 processes which are outgrowths from the dorsal arch. In the 
 tail their function is to surround and protect structures like 
 the ventral blood-vessels which do not vary much in size, 
 consequently they meet one another, and form a series of 
 complete ventral or haemal arches. But the trunk contains 
 organs like the lungs and stomach which are liable to vary 
 much in size at different times, consequently the halves of the 
 haemal arch do not meet ventrally, and then the ribs become 
 detached from the rest of the haemal arch. Having once 
 become detached, they are able to shift about and unite them- 
 selves to various points of the vertebra. They frequently, as 
 has been already mentioned, become entirely attached to the 
 transverse process, or they may be attached to the transverse 
 process by a dorsal or tubercular portion and to the centrum 
 or to the ventral arch by a ventral or capitular portion. 
 
 In all animals above fishes the distal ends of the thoracic 
 ribs unite with a median breast bone or sternum which 
 generally has the form of a segmented rod. The sternum is 
 really formed by the fusion of the distal ends of a series of 
 ribs. In many animals elements of the shoulder girdle enter 
 into close relation with the rib elements of the sternum. 
 
 II. THE APPENDICULAK SKELETON. 
 
 This consists of the skeleton of the anterior or pectoral, 
 and the posterior or pelvic limbs, and their girdles. In every 
 case (except in Chelonia) the parts of the appendicular skele- 
 ton lie external to the ribs. 
 
 1. THE LIMB GIRDLES. 
 
 The Pectoral girdle 1 . In the simplest case the pectoral 
 or shoulder girdle consists of a hoop of cartilage incomplete 
 
 1 W. K. Parker, A Monograph of the Shoulder Girdle and Sternum, 
 Ray Soc. London, 1868. 
 
INTRODUCTORY. LIMB GIRDLES. 25 
 
 dorsally. It is attached by muscle to the vertebral column, 
 and is divided on either side into dorsal and ventral portions 
 by a cavity, the glenoid cavity, at the point where the 
 anterior limb articulates. In higher fishes this hoop is dis- 
 tinctly divided into right and left halves ; it becomes more or 
 less ossified, and a pair of important bones, the clavicles, are 
 developed in connection with its ventral portion. 
 
 In higher vertebrates ossification sets up in the cartilage 
 and gives rise on each side to a dorsal bone, the scapula, 
 and frequently to an anterior ventral bone, the precoracoid, 
 and a posterior ventral bone, the coracoid. The precoracoid 
 is often not ossified, and upon it is developed the clavicle 
 which more or less replaces it. In some forms a T shaped 
 interclavicle occurs, in others epicoracoids are found in front 
 of the coracoids. In all vertebrata above fish, except the great 
 majority of mammals, the coracoids are large and articulate 
 with the sternum. But in mammals the coracoids are nearly 
 always quite vestigial, and the pectoral girdle is attached to 
 the axial skeleton by the clavicle or sometimes by muscles and 
 ligaments only. 
 
 The Pelvic girdle 1 like the pectoral consists primitively 
 of a simple rod or hoop of cartilage, which in vertebrata above 
 fishes is divided into dorsal and ventral portions, by a cavity, 
 the acetabulum, with which the posterior limb articulates. 
 In the pelvic girdle as in the pectoral one dorsal, and (com- 
 monly) two ventral ossifications take place. The dorsal bone 
 is the ilium and corresponds to the scapula. The posterior 
 ventral bone is the ischium corresponding to the coracoid. 
 The anterior ventral bone is the pubis and is generally com- 
 pared to the precoracoid, but in some cases a fourth pelvic 
 element, the acetabular or cotyloid bone is found, and this 
 may correspond to the precoracoid. 
 
 The pelvic girdle differs from the pectoral in the fact that 
 the dorsal bones the ilia are nearly always firmly united to 
 1 See E. Wiedersheim, Zeitschr. wiss. Zool. vol. LIII. suppl. p. 43, 1892. 
 
26 THE VERTEBRATE SKELETON. 
 
 transverse processes of the sacral vertebrae, by means of 
 rudimentary ribs. The pubes and ischia generally meet in 
 ventral symphyses. 
 
 2. THE LIMBS. 
 
 It will be most convenient to defer a discussion of the 
 limbs of fishes to chap. vm. 
 
 All vertebrates above fishes have the limbs divisible into 
 three main segments : 
 
 Anterior or Fore limb. Posterior or Hind limb. 
 Proximal segment. upper arm or brachium. thigh. 
 
 Middle segment. fore-arm or antibrachium. shin or cms. 
 
 Distal segment. manus. pes. 
 
 The proximal segments each contain one bone, the hume- 
 rus in the case of the upper arm, and the femur in the case 
 of the thigh. The middle segments each contain two bones, 
 the radius and ulna in the case of the fore-arm, and the tibia 
 and fibula in the case of the shin. 
 
 The manus and pes are further subdivided into 
 
 (a) two or three proximal rows of bones forming the 
 wrist or carpus in the case of the manus, and the ankle or 
 tarsus in the case of the pes. 
 
 (b) a middle row called respectively the metacarpus 
 and metatarsus. 
 
 (c) a number of distal bones called the phalanges 
 which form the skeleton of the fingers and toes, or digits. 
 
 Typically the manus and pes both have five digits (pente- 
 dactylate). The first digit of the manus is commonly called 
 the pollex, and the first digit of the pes the hallux. 
 
 In a very simple carpus such as that of Chelydra, there 
 are nine bones. They are arranged in a proximal row of 
 
INTRODUCTORY. THE LIMBS. 27 
 
 three, the radiale, intermedium, and ulnare, the first being 
 on the radial side of the limb, and a distal row of five called 
 respectively carpale 1, 2, 3, 4, 5, beginning on the radial side. 
 Between these two rows is a single bone the centrale, or there 
 may be two. 
 
 Similarly there are nine bones in a simple tarsus such as 
 that of Salamandra. They form a proximal row of three, the 
 tibiale, intermedium and fibulare, and a distal row of five, 
 called respectively tarsale 1, 2, 3, 4, 5, beginning on the tibial 
 side. Between the two rows there is a centrale as in the 
 carpus, or there may be two. 
 
 The following names derived from human anatomy are 
 commonly applied to the various carpal and tarsal bones : 
 
 Carpus. Tarsus. 
 
 radiale = scaphoid tibiale ) 
 
 ,. ,. V astragalus 
 
 intermedium = lunar intermedium] 
 
 ulnare = cuneiform fibulare = calcaneum 
 
 centrale = central centrale = navicular 
 
 carpale 1 = trapezium tarsale 1 = internal cuneiform 
 ,, 2 = trapezoid ,, 2 = middle ,, 
 
 ,, 3 = magnum ,, 3 = external ,, 
 
 " I Cuneiform " r l = 
 
 5j ,, 5J 
 
 cuboid 
 
 NOTE. The above is the view commonly accepted concerning the 
 homology of the carpal and tarsal bones. But with regard to the 
 proximal row of tarsal bones there is difference of opinion. All anato- 
 mists are agreed that the calcaneum is the fibulare and that the inter- 
 medium is contained in the astragalus, but while the majority regard 
 the astragalus as the fused tibiale and intermedium, Baur considers 
 that a small bone found on the tibial side of the tarsus in Procavia, 
 many Eodents, Insectivores, and the male Ornithorhynchus, is the vesti- 
 gial tibiale, and regards the astragalus as the intermedium alone 1 . He 
 also considers that the mammalian scaphoid represents a centrale. 
 
 1 G. Baur, Beitrdge zur Morphogenie des Carpus und Tarsus der 
 Vertebraten, Theil 1. Batrachia. Jena, 1888, and Amer. Natural., vol. xix. 
 1885 (several papers). 
 
28 THE VERTEBRATE SKELETON. 
 
 MODIFICATIONS IN THE POSITIONS OF THE LIMBS'. 
 
 In their primitive position the limbs are straight and are 
 extended parallel to one another at right angles to the axis of 
 the trunk. Each limb then has a dorsal surface, a ventral 
 surface, an anterior or pre- axial edge, and a posterior or 
 postaxial edge. 
 
 In the anterior limb the radius and the pollex are pre- 
 axial, the ulna and the fifth finger are postaxial. In the 
 posterior limb the tibia and the hallux are pre-axial, the fibula 
 and the fifth toe are postaxial. The Cetacea and various extinct 
 reptiles, such as Ichthyosaurus and Plesiosaurus, have their 
 limbs in practically this primitive position. 
 
 The first modification from it is produced by the bending 
 ventrally of the middle segments of both limbs upon the 
 proximal segments, while the distal segment is bent in the 
 opposite direction on the middle segment. Then the ventral 
 surfaces of the antibrachium and crus come to look inwards, 
 and their dorsal surfaces to look outwards. The brachium 
 and manus, thigh and pes still have their dorsal surfaces 
 facing upwards and their ventral surfaces facing downwards 
 as before, and the relations of their pre- and postaxial borders 
 remain as they were. Many Amphibians and Reptiles, such 
 as tortoises, carry their limbs in this position. 
 
 In all higher vertebrates, however, a further change takes 
 place, each limb is rotated as a whole from its proximal end, 
 the rotation taking place in opposite directions in the fore and 
 hind limbs respectively. The anterior limb is rotated back- 
 wards from the shoulder, so that the brachium lies nearly parallel 
 to the body, and the elbow points backwards, the antibrachium 
 downwards, and the manus backwards ; the pre-axial surface of 
 the whole limb with the radius and pollex now faces outwards, 
 and the postaxial surface with the ulna and fifth finger now faces 
 
 1 This account is based on Chapter XX. of Flower's Osteology of the 
 Mammalia. London 1876. 
 
INTRODUCTORY. POSITIONS OF THE LIMBS. 29 
 
 inwards. In the Walrus and, to a certain extent, in the Sea- 
 lions the anterior limb remains throughout life in this position. 
 The posterior limb is also rotated, but the rotation in this 
 case takes place forwards, so that the thigh lies nearly parallel 
 to the body, the knee-joint pointing forwards ; the crus down- 
 wards and the pes forwards. The pre-axial surface of the 
 whole limb with the tibia and hallux looks towards the middle 
 of the body, the postaxial surface with the fibula and fifth toe 
 looks outwards. This is the position in which the hind limb 
 is carried in nearly all mammals. 
 
 In nearly all mammals a further change takes place in the 
 position of the anterior limb. The radius and ulna have 
 hitherto been parallel to one another, but now the lower end 
 of the radius, carrying with it the manus, comes to be rotated 
 forwards round the ulna, so that the manus, as well as the 
 pes, comes to be forwardly-directed, and its pre-axial surface 
 faces inwards. 
 
 In the majority of mammals the radius and ulna are per- 
 manently fixed in this, which is known as the prone position, 
 but in man and some other mammals the manus can be 
 pronated or turned into this position at will. When the 
 radius and ulna are parallel throughout their whole length 
 the manus is said to be in the supine position. 
 
 The extensor side of a limb is that to which the muscles 
 which straighten it are attached, the flexor side is that to 
 which the muscles which bend it are attached. 
 
CHAPTER II. 
 CLASSIFICATION. 
 
 THE following classification includes only the forms 
 mentioned in the succeeding pages. The relative value of 
 some of the terms employed in classification is not identical 
 throughout the book. This remark applies specially to the 
 term group, which is a convenient one, owing to its not having 
 such a hard and fast zoological meaning as has the term family, 
 for instance. The term group is applied in this book to 
 divisions of the animal kingdom of very different classificatory 
 importance. 
 
 PHYLUM CHORDATA. 
 
 SUBPHYLUM A. HEMICHORDATA. 
 
 Balanoglossus. 
 Cephalodiscus. 
 Rhabdopleura. 
 1 Phoronis. 
 
 (? Actinotrocha larval Phoronis). 
 
 % 
 
 SUBPHYLUM B. UROCHORDATA (TUNICATA). 
 Group LARVACEA and others. 
 
 SUBPHYLUM C. CEPHALOCHORDATA. 
 
 Amphioxus laricelet. 
 
 NOTE. In this chapter all the generic names printed in italics are 
 those of extinct animals. 
 
CLASSIFICATION. 31 
 
 SUBPHYLUM D. VERTEBRATA. 
 DIVISION (I). CYCLOSTOMATA. 
 
 Order 1. MARSIPOBRANCHII. 
 Family Myxinoidei. Myxine hag-fish. 
 
 Bdellostoma. 
 Family Petromyzontidae. Petromyzon lamprey. 
 
 (Ammocoetes larval lamprey.) 
 Family Palaeospondylidae. Palaeospondylus. 
 
 Order 2. OSTRACODERMI. 
 Suborder 1. HETEROSTRACI. 
 Family Pteraspidae. Pteraspis. 
 
 Suborder 2. OSTEOSTRACI. 
 Family Cephalaspidae. Cephalaspis. 
 
 Suborder 3. ANTIARCHA. 
 Family Asterolepidae. Pterichttiys. 
 Asterolepis. 
 
 DIVISION (II). GNATHOSTOMATA. 
 A. ICHTHYOPSIDA. 
 
 CLASS I. PISCES. 
 Order 1. ELASMOBRANCHII. 
 Suborder (1). ICHTHYOTOMI. 
 Family Pleuracanthidae. Xenacanthus. 
 Suborder (2). PLEUROPTERYGII. 
 
 Cladoselache. 
 Suborder (3). SELACHII. 
 
 Group SQUALIDAE. 
 
 Family Notidanidae. Heptanchus. 
 Hexanchus. 
 
 Chlamydoselache frill-gilled shark. 
 Family Cochliodontidae. Cochliodus. 
 
32 THE VERTEBRATE SKELETON. 
 
 Family Cestraciontidae. Cestracion Port Jackson 
 
 shark. 
 Acrodus, 
 
 Family Scylliidae. Scyllium spotted dog-fish. 
 Family Lamnidae. Odontaspis. 
 Family Carcharidae. Galeus tope. 
 Family Spinacidae. Acanthias spiny dog-fish. 
 
 Scymnus. 
 Family Squatinidae. Squatina (Rhina) angel fish. 
 
 Group BATOIDEI. 
 
 Family Pristidae. Pristis saw-fish. 
 Family Raiidae. Raia skate. 
 Family Myliobatidae. Myliobatis eagle ray. 
 Family Trygonidae. Trygon sting ray. 
 Family Torpedinidae. Torpedo electric ray. 
 
 Suborder (4). ACANTHODII. 
 Family Acanthodidae. Acanthodes. 
 Family Diplacanthidae. Diplacanthus. 
 
 Order 2. HOLOCEPHALI. 
 
 Family Chimaeridae. Chimaera rabbit fish. 
 Harriotta. 
 Callorhynchus. 
 Ischyodus. 
 
 Order 3. GANOIDEI. 
 Suborder (1). CHONDROSTEI. 
 Family Palaeoniscidae. Palaeoniscus, 
 
 Trissolepis. 
 Family Acipenseridae. Acipenser sturgeon. 
 
 Scaphirhynchus. 
 
 Family Polyodontidae. Polyodon (Spatularia) spoon- 
 beaked sturgeon. 
 Psephurus slender-beaked sturgeon. 
 
CLASSIFICATION. 33 
 
 Suborder (2). CROSSOPTERYGII. 
 Family Holoptychiidae. Holoptychius. 
 Family Rhizodontidae. Rhizodus. 
 Family Osteolepidae. Osteolepis. 
 Family Polypteridae. Polypterus bichir. 
 
 Calamoichthy s reed-fish . 
 
 Suborder (3). HOLOSTEI. 
 
 Family Lepidosteidae. Lepidosteus gar pike. 
 Family Semionotidae. Lepidotus. 
 Family Amiidae. Amia bow-fin. 
 
 Order 4. TELEOSTEI. 
 
 Suborder (1). PLECTOGNATHI. 
 Family Balistidae. Balistes file-fish. 
 Family Gymnodontidae. Diodon globe-fish. 
 Family Ostracionidae. Ostracion coffer-fish. 
 
 Suborder (2). PHYSOSTOMI. 
 Family Siluridae cat-fishes. 
 Family Cyprinidae. Cyprinus carp. 
 Family Esocidae. Esox pike. 
 Family Salmonidae. Salmo salmon. 
 Family Clupeidae. Clupeus herring. 
 
 Exocaetus 'flying fish'. 
 Family Muraenidae. Anguilla eel. 
 
 Suborder (3). ANACANTHINI. 
 
 Family Gadidae. Gadus cod, haddock, whiting. 
 Family Pleuronectidae. Solea sole. 
 
 Suborder (4). PHARYNGOGNATHI. 
 Family Labridae. Labrus wrasse. 
 
 Scarus parrot fish. 
 R. 3 
 
34 THE VERTEBRATE SKELETON. 
 
 Subordei (5). ACANTHOPTERYGII. 
 
 Family Cataphracti. Dactylopterus flying gurnard. 
 Family Percidae. Perca perch. 
 
 Order 5. DIPNOI. 
 Suborder (1). SIRENOIDEI. 
 Family Dipteridae. .Dipterus. 
 
 Family Monopneumona. Ceratodus barramunda. 
 Family Dipneumona. Protopterus African mud-fish. 
 
 Lepidosiren. 
 
 Suborder (2). ARTHRODIRA. 
 Family Coccosteidae. Coccosteus. 
 Dinichthys. 
 
 NOTE. Palaeontological research has disclosed the existence of a great 
 number of forms which seem to connect with one another almost all the 
 orders of fishes as usually recognised. Forms connecting the living 
 Ganoids with the Teleosteans have been especially numerous, so that 
 these terms Ganoid and Teleostean can hardly be any longer used in a 
 precise and scientific sense. This has rendered the subject of the classifi- 
 cation of fishes a very difficult one. Though unsuitable for adoption in 
 a work like the present, by far the most natural classification hitherto 
 proposed seems to be that of Smith Woodward 1 . He considers that the 
 course of development of fishes has followed two distinct lines, the auto- 
 stylic and hyostylic (see p. 119), and groups the various forms as follows: 
 
 HYOSTYLIC. AUTOSTYLIC. 
 
 Subclass 1. ELASMOBKANCHII. Subclass 3. HOLOCEPHALI. 
 
 1. Ichthyotomi. 1. (unknown). 
 
 2. Selachii. 2. Chimaeroidei. 
 
 3. Acanthodii. 3. (unknown). 
 Subclass 2. TELEOSTOMI. Subclass 4. DIPNOI. 
 
 1. Crossopterygii (Palaeozoic 1. Sirenoidei. 
 
 and Mesozoic). 
 
 2. Crossopterygii (Cainozoic). 2. (unknown). 
 
 3. Actinopterygii. 3. Arthrodira. 
 
 The primitive forms in each of these four subclasses have the fins 
 archipterygia (see p. 127). 
 
 1 A. Smith Woodward, Catalogue of Fossil Fishes in the British 
 Museum, Part II., Introduction, p. xii. 
 
CLASSIFICATION. 35 
 
 CLASS II. AMPHIBIA. 
 
 Order 1. URODELA. 
 Suborder (1). ICHTHYOIDEA. 
 Group A, PERENNIBRANCHIATA. 
 Family Menobranchidae. Menobranchus. 
 Family Proteidae. Proteus olm. 
 Family Sirenidae. Siren. 
 
 Group B. DEROTREMATA. 
 Family Amphiumidae. Megalobatrachus. 
 
 Cryptobranchus (Menopoma). 
 Amphiuma. 
 
 Suborder (2). SALAMANDRINA. 
 
 Family Salamandridae. Salamandra- salamander. 
 
 Molge newt. 
 Onychodactylus. 
 Amblystoma. 
 
 (Siredon axolotl, larval Am- 
 blystoma). 
 Batrachoseps. 
 Spelerpes (Gyrinophilus). 
 
 Order 2. LABYRINTHODONTIA. 
 Group Lepospondyli. Branchiosauru*. 
 Group Temnospondyli. Archegosaurus. 
 
 Nyrania. 
 Euchirosaurus. 
 Group Stereospondyli. Capitosaurus. 
 
 Mastodonsaurus. 
 Order 3. GYMNOPHIONA. 
 Family Caeciliidae. Siphonops. 
 Epicrium. 
 
 32 
 
36 THE VERTEBRATE SKELETON. 
 
 Order 4. ANURA. 
 Suborder (1). AGLOSSA. 
 Family Xenopidae. Xenopus. 
 Family Pipidae. Pipa Surinam toad. 
 
 Suborder (2). PHANEROGLOSSA. 
 
 Group ARCIFERA. 
 Family Discoglossidae. Discoglossus painted frog. 
 
 Bombinator fire-bellied frog. 
 Alytes midwife frog. 
 
 Family Pelobatidae. Pelobates toad frog. 
 Family Hylidae. Hyla green tree-frog. 
 Family Bufonidae. Bufo toad. 
 
 Docidophryne. 
 Family Cystignathidae. Ceratophrys horned frog. 
 
 Group FlRMISTERNIA. 
 
 Family Ranidae. Rana common and edible frogs. 
 Family Engystomatidae. Brachycephalus. 
 
 B. SAUROPSIDA. 
 
 CLASS I. REPTILIA 1 . 
 
 Order 1. THEROMORPHA. 
 
 Group Anomodontia. Dicynodon. 
 
 Udenodon. 
 
 Group Placodontia. Placodus. 
 Group Pariasamia. Pariasaurus. 
 
 Elginia. 
 
 Group Theriodontia. Dimetrodon. 
 Galesaurus. 
 Cynognathus. 
 
 1 This classification of reptiles is mainly based on that of Lydekker 
 (Catalogue of Fossil Reptiles in the British Museum) but in some respects 
 that of von Zittel has been followed. 
 
CLASSIFICATION. 37 
 
 Order 2. SAUROPTERYGIA. 
 Family Mesosauridae. Mesosaurus. 
 Family Nothosauridae. Nothosaurus. 
 Family Plesiosauridae. Plesiosaurus. 
 
 Pliosaurus. 
 
 Order 3. CHELONIA. 
 Suborder (1). TRIONYCHIA. 
 Family Trionychidae. Trionyx snapping turtle. 
 
 Suborder (2). CRYPTODIRA. 
 Family Dermochelydidae. Dermochelys (Sphargis) 
 
 leathery turtle. 
 
 Family Chelonidae. Ohelone green turtle. 
 Family Chelydridae. Chelydra terrapin. 
 Family Chersidae. Testudo tortoise. 
 Suborder (3). PLEURODIRA. 
 Family Chelydae. Chelys. 
 
 Order 4. ICHTHYOSAURIA. 
 Family Ichthyosauridae. Ichthyosauriis. 
 
 Order 5. RHYNCHOCEPHALIA. 
 Suborder (1). RHYNCHOCEPHALIA VERA. 
 Family Sphenodontidae. Sphenodon (Hatteria). 
 Family Rhynchosauridae. Hyperodapedon. 
 
 Suborder (2). PROGANOSAURIA. 
 Family Proterosauridae. Proterosaurus. 
 
 Order 6. SQUAMATA. 
 
 Suborder (1). LACERTILIA. 
 
 Group Lacertilia vera. 
 Family Geckonidae. Gecko. 
 Family Pygopodidae. Lialis scale-foot. 
 
38 THE VERTEBRATE SKELETON. 
 
 Family Agamidae. Draco flying lizard. 
 
 Agama. 
 
 Family Iguanidae. Iguana. 
 Family Anguidae. Ophisaurus (Bipes, Pseudopus). 
 
 Anguis blindworm. 
 
 Family Varanidae. Yaranus monitor. 
 Family Amphisbaenidae. Chirotes. 
 
 Amphisbaena. 
 
 Family Scincidae. Tiliqua (Cyclodus). 
 Scincus skink. 
 Chalcides (Seps). 
 
 Group Rhiptoglossa. 
 Family Chamaeleonidae. Chamaeleon. 
 
 Suborder (2). OPHIDIA. 
 
 Family Typhlopidae. Typhlops blind snake. 
 Family Boidae. Python. 
 
 Family Colubridae. Tropidonotus ringed snake. 
 Family Hydrophidae sea snakes. 
 Family Crotalidae. Crotalus rattlesnake. 
 
 Suborder (3). PYTHONOMORPHA. 
 Family Mosasauridae. Mosasaurus. 
 
 Order 7. DINOSAURIA. 
 Suborder (1). SAUROPODA. 
 Family Atlantosauridae. Brontosaurus. 
 Family Cetiosauridae. Morosaurus. 
 
 Suborder (2). THEROPODA. 
 
 Family Megalosauridae. Megalosaurus (Ceratosaurus). 
 Family Compsognathidae. Compsognathus. 
 
CLASSIFICATION. 39 
 
 Suborder (3). ORTHOPODA. 
 
 Section (a). STEGOSAURIA. 
 Family Scelidosauridae. Polacanthus. 
 Family Stegosauridae. Stegosaurus. 
 
 Section (b). CERATOPSIA. 
 Family Ceratopsidae. Polyonax (Ceratops). 
 
 Section (c). ORNITHOPODA. 
 Family Camptosauridae. Hypsilophodon. 
 Family Iguanodontidae. Iguanodon. 
 Family Hadrosauridae. Hadrosaurus. 
 
 Order 8. CROCODILIA. 
 Suborder (1). PARASUCHIA. 
 Family Phytosauridae. Phytosaurus (Belodon). 
 
 Suborder (2). EUSUCHIA. 
 
 Family Teleosauridae. Teleosaurus. 
 
 Metriorhynchus. 
 
 Family Goniopholidae. Goniopholis. 
 Family Alligatoridae. Alligator. 
 
 Caiman. 
 
 Jacare. 
 
 Family Crocodilidae. Crocodilus. 
 Family Garialidae. Garialis (Gavialis). 
 
 Order 9. PTEROSAURIA. 
 
 Family Pterodactylidae. Pterodactylus. 
 
 Family Rhamphorhynchidae. Rhamphorhynchus. 
 
 Family Pteranodontidae. Pteranodon. 
 
40 THE VERTEBRATE SKELETON. 
 
 CLASS II. AYES 1 . 
 
 Subclass (I). ARCHAEORNITHES. 
 Archaeopteryx. 
 
 Subclass (II). NEORNTTHES. 
 
 Order 1. RATITAE. 
 Group .flSpyornithes. 
 
 Group Apteryges. Apteryx kiwi. 
 
 Group Dinornithes. Moas. 
 
 Group Megistanes. Casuarius cassowary. 
 
 Dromaeus emeu. 
 
 Group Rheornithes. Rhea American ostrich, 
 Group Struthiornithes. Struthio ostrich. 
 
 Order 2. ODONTOLCAE. 
 wrornis. 
 
 Order 3. CARINATAE. 
 
 Group Iehthyomithiforrn.es. 
 
 I chiliy or nis. 
 
 Apatornis. 
 
 Odontopteryx. 
 
 Group Colymbiformes. 
 Subgroup Colymbi divers. 
 
 Group Sphenisciform.es. 
 
 Subgroup Sphenisci penguins. 
 
 1 This classification of birds is essentially that of Gadow and Selenka 
 in Bronn's Classen und Ordnungen des Thier-reichs, Band vi., Abth. iv., 
 Vogel. Leipzig, 1891. 
 
CLASSIFICATION. 41 
 
 Group Ciconiiformes. 
 
 Subgroup Steganopodes. Sula gannet. 
 
 Pelicanus pelican. 
 Phaethon frigate bird. 
 Phalacrocorax cormorant. 
 Subgroup Ardeae. Ardea heron 
 Subgroup Ciconiae. Leptoptilus adjutant. 
 Ciconia white stork. 
 
 Group Anseriformes. 
 
 Subgroup Palamedeae. Palamedea) 
 
 f screamers. 
 Chauna J 
 
 Subgroup Anseres. Anas wild duck. 
 Anser goose. 
 
 Plectropterus spur-winged goose. 
 Cygnus swan. 
 Mergus merganser. 
 
 Group Falconiformes. 
 
 Subgroup Cathartae. Cathartes American vulture. 
 Subgroup Accipitres. Falco falcon. 
 
 Vultur vulture. 
 
 Harpagus. 
 
 Gypogeranus secretary bird. 
 
 Group Tinamiform.es. 
 
 Subgroup Tinami. Tinamus. 
 
 Group Galliform.es. 
 
 Subgroup Galli. Gallus fowl. 
 
 Pavo peacock. 
 Subgroup Opisthocomi. Opisthocomus hoatzin. 
 
 Group Gruiformes. 
 
 Gruidae cranes. 
 
 Group Stereornithes. Phororhacos. 
 
42 THE VERTEBRATE SKELETON. 
 
 Group Charadriiformes. 
 
 Subgroup Limicolae. Charadriidae plovers. 
 
 Parra jacana. 
 
 Subgroup Lari. Laridae gulls. 
 Alcidae auks. 
 
 Subgroup Pteroclidae. Pterocles sandgrouse. 
 Subgroup Columbidae. Columbae pigeons. 
 Didus dodo. 
 Pezophaps solitaire. 
 Group Cueuliformes. 
 
 Subgroup Cuculi. Scythrops. 
 
 Subgroup Psittaci. Stringops owl-parrot. 
 
 Group Coraeiiformes. 
 
 Subgroup Coraciae. Coracias roller. 
 
 Buceros hornbill. 
 Upupa hoopoe. 
 Subgroup Striges. Owls. 
 Subgroup Cypseli. Cypselidae swifts. 
 
 Trochilidae humming-birds. 
 Subgroup Trogonidae. Trogons. 
 Subgroup Pici. Rhamphastos toucan. 
 Picus woodpecker. 
 
 Group Passeriformes. Crows, finches, larks, warblers, 
 
 and many others. 
 
 C. MAMMALIA 1 . 
 Class MAMMALIA. 
 
 Subclass (I). ORNITHODELPHIA or PROTOTHERIA. 
 Order. MOJJOTREMATA. 
 
 1 The classification adopted is almost entirely that given in Flower 
 and Lydekker's Mammals Living and Extinct. London, 1891. 
 
CLASSIFICATION. 43 
 
 Family Ornithorhynchidae. Ornithorhynchus duck- 
 bill. 
 
 Family Echidnidae. Echidna spiny anteater. 
 Group Multituberculata. Tritylodon. 
 
 Subclass (II). DIDELPHIA or METATHERIA. 
 
 Order. MARSUPIALIA. 
 Suborder (1). POLYPROTODONTIA. 
 Family Amphitheriidae. Phascolotherium. 
 
 Family Didelphyidae. Didelphys opossum. 
 
 Family Dasyuridae. Thylacinus Tasmanian wolf. 
 Sarcophilus Tasmanian devil. 
 Dasyurus. 
 Family Peramelidae. Perameles bandicoot. 
 
 Choeropus. 
 Family Notoryctidae. Notoryctes marsupial mole. 
 
 Suborder (2). DIPROTODONTIA. 
 
 Family Phascolomyidae. Phascolomys wombat. 
 Family Phalangeridae. Tarsipes. 
 
 Phalanger cuscus. 
 Phascolarctus koala. 
 Tkylacoleo. 
 
 Family Diprotodontidae, Diprotodon. 
 Family Nototheriidae. Nototherium. 
 Family Macropodidae. Macropus kangaroo. 
 Family Epanorthidae. Coenolestes. 
 
 Subclass (III). MONODELPHIA or EUTHERIA. 
 Order 1. EDENTATA. 
 
 Family Bradypodidae. Bradypus ) 
 
 nu 1 r sloths. 
 
 CholoepusJ 
 
44 THE VERTEBRATE SKELETON. 
 
 Family Megatheriidae. Megatherium ground sloth. 
 Family Myrmecophagidae. Myrmecophaga great ant- 
 eater. 
 
 Cycloturus two-toed ant- 
 eater. 
 
 Family Dasypodidae. ChlamydophorusA 
 Dasypus 
 Priodon -armadillos. 
 
 Tatusia 
 
 Family Glyptodontidae. Glyptodon. 
 Family Manidae. Manis pangolin. 
 Family Orycteropodidae. Orycteropus aard vark. 
 
 Order 2. SIREXIA. 
 
 Family Manatidae. Manatus manatee. 
 Family Rhytinidae. Rhytina S teller's sea-cow. 
 Family Halicoridae. Halicore dugong. 
 Family Halitheriidae. Halitherium. 
 
 Order 3. CETACEA. 
 Suborder (1). ARCHAEOCETI. 
 Family Zeuglodontidae. Zeuglodon. 
 
 Suborder (2). MYSTACOCETI or BALAENOIDEA. 
 Family Balaenidae. Balaena right whale. 
 
 Megaptera humpbacked whale. 
 Balaenoptera rorqual. 
 
 Suborder (3). ODONTOCETI. 
 Family Physeteridae. Physeter sperm whale. 
 
 Hyperoodon bottlenose. 
 
 Ziphius. 
 
 Mesoplodon. 
 Family Physodontidae. Physodon. 
 
CLASSIFICATION. 45 
 
 Family Squalodontidae. Squalodon. 
 Family Platanistidae. Platanista Gangetic dolphin. 
 Inia. 
 
 Pontoporia. 
 Family Delphinidae. Monodon narwhal. 
 
 Phocaena porpoise. 
 
 Orca killer. 
 
 Globicephalus Ca'ing whale. 
 
 Grampus. 
 
 Lagenorhynchus. 
 
 Delphinus dolphin. 
 
 Tursiops. 
 
 Prodelphinus. 
 
 Order 4. UNGULATA. 
 Division A. UNGULATA VERA. 
 Suborder (1). ARTIODACTYLA. 
 
 Section (a). SUINA. 
 
 Family Hippopotamidae. Hippopotamus. 
 Family Suidae. Sus pig. 
 Babirussa. 
 
 Phacochaerus wart hog. 
 Hyotherium. 
 Family Cotylopidae. Cotylops (Oreodon). 
 
 Cyclopidius. 
 
 Family Agriochoeridae. Agriochoerus. 
 Family Anoplotheriidae. Anoplotherium. 
 
 Section (b). TFLOPODA. 
 Family Camelidae. Camelus camel. 
 
 A uchenia llama. 
 Section (c). TRAGULINA. 
 
 Family Tragulidae. Dorcatherium (Hyomoschus) 
 chevrotain. 
 
46 THE VERTEBRATE SKELETON. 
 
 Section (d). RUMINANTIA or PECORA. 
 
 Family Cervidae. Moschus musk deer. 
 Cervus deer. 
 Cervulus muntjac. 
 Hydropotes Chinese water deer. 
 Family Giraffidae. Giraffa giraffe. 
 
 iSivatherium. 
 
 Family Antilocapridae. Antilocapra prongbuck. 
 Family Bovidae. Tetraceros four-horned antelope. 
 Gazella gazelle. 
 Bos ox. 
 Bison. 
 Bubalus buffalo. 
 
 Suborder (2). PERISSODACTYLA. 
 Family Tapiridae. Tapirus tapir. 
 Family Lophiodontidae. Lophiodon. 
 
 Hyracotherium. 
 
 Family Palaeotheriidae. Palaeotherium. 
 Family Equidae. Hipparion. 
 
 Equus horse. 
 Family Rhinoeerotidae. Rhinoceros. 
 
 Elasmotherium. 
 Family Titanotheriidae. Titanotherium (Brontops). 
 
 Palaeosyops. 
 
 Family Chalicotheriidae. Chalicotherium. 
 Family Macraucheniidae. Macrauchenia. 
 
 Division B. SUBUNGULATA. 
 
 Suborder (1). TOXODONTIA. 
 Family Astrapotheriidae. Astrapotherium. 
 Family Nesodontidae. Nesodon. 
 Family Toxodontidae. Toxodon. 
 Family Typotheriidae. Typotkerium. 
 
CLASSIFICATION. 47 
 
 Suborder (2). CONDYLARTHRA. 
 Family Phenacodontidae. Phenacodus. 
 
 Suborder (3). HYRACOIDEA. 
 Family Hyracidae. Procavia (Hyrax). 
 
 Suborder (4). AMBLYPODA. 
 Family Coryphodontidae. Coryphodon. 
 Family Uintatheriidae. Uintatherium (Dinoceras). 
 
 Suborder (5). PROBOSCIDEA. 
 Family Dinotheriidae. Dinotlierium. 
 Family Elephantidae. Mastodon. 
 
 Elephas elephant. 
 
 Group TlLLODONTIA. 
 
 Order 5. RODENTIA. 
 Suborder (1). SIMPLICIDENTATA. 
 
 Section SCIUROMORPHA. 
 Family Castoridae. Castor beaver. 
 
 Section MYOMORPHA. 
 Family Lophiomyidae. Lophiomys. 
 Family Muridae. Hydromys. 
 
 Acanthomys spiny mouse. 
 Mus mouse. 
 
 Family Spalacidae. Bathyergus. 
 Family Dipodidae. Dipus jerboa. 
 
 Pedetes Cape jumping-hare. 
 
 Section HYSTRTCOMORPHA. 
 Family Hystricidae. Hystrix porcupine. 
 Family Chinchillidae. Chinchilla. 
 
 Lagostomus viscacha. 
 
48 THE VERTEBRATE SKELETON. 
 
 Family Dasyproctidae. Coelogenys paca. 
 
 Dasyprocta agouti. 
 
 Family Caviidae. Cavia guinea-pig. 
 
 Hydrochaer us capybara . 
 
 Suborder (2). DUPLICIDENTATA. 
 Family Leporidae. Lepus hare and rabbit. 
 
 Order 6. CARNIVORA. 
 Suborder (1). CREODONTA. 
 Family Hyaenodontidae. Hyaenodon. 
 
 Suborder (2). CARNIVORA VERA or FISSIPEDIA. 
 Section ^LUROIDEA. 
 
 Family Felidae. Felis cat, lion, tiger. 
 
 Machaerodus sabre-toothed lion. 
 
 Family Viverridae. Viverra civet. 
 
 Paradoxurus palm civet. 
 
 Family Protelidae. Pro teles aard wolf. 
 Family Hyaenidae. Hyaena. 
 
 Section. CYNOIDEA. 
 Family Canidae. Canis dog, wolf, fox. 
 
 Section ARCTOIDEA. 
 Family Ursidae. Ursus bear. 
 Family Mustelidae. Latax sea otter. 
 
 Suborder (3). PINNIPEDIA. 
 Family Otariidae. Otaria sea lion. 
 Family Trichechidae. Trichechus walrus. 
 Family Phocidae. Ogmorhinus sea leopard. 
 
 Order 7. INSECTIVORA. 
 Suborder (1). DERMOPTERA. 
 Family Galeopithecidae. Galeopithecus 'flying lemur'. 
 
CLASSIFICATION. 49 
 
 Suborder (2). INSECTIVORA VERA. 
 
 Family Macroscelidae. Macroscelides jumping shrew. 
 Family Erinaceidae. Erinaceus hedgehog. 
 
 Gymnura. 
 
 Family Soricidae. Sorex shrew. 
 Family Talpidae. Talpa mole. 
 Family Potamogalidae. Potamogale. 
 Family Solenodontidae. Solenodon. 
 Family Centetidae. Microgale. 
 
 Centetes tenrec. 
 Family Chrysochloridae. Chrysochloris golden mole. 
 
 Order 8. CHIROPTERA. 
 
 Suborder (1). MEGACHIROPTERA. 
 Family Pteropidae. Pteropus flying fox. 
 
 Suborder (2). MICROCHIROPTERA. 
 Family Rhinolophidae. Horse-shoe bats. 
 Family Phyllostomatidae. Desmodus vampire. 
 
 Order 9. PRIMATES. 
 Suborder (1). LEMUROIDEA. 
 Family Tarsiidae. Tarsius tarsier. 
 Family Chiromyidae. Chiromys aye aye. 
 
 Suborder (2). ANTHROPOIDEA. 
 Family Hapalidae. Hapale marmoset. 
 Family Cebidae. Mycetes howling monkey. 
 
 Ateles spider monkey. 
 
 Family Cercopithecidae. Cynocephalus baboon. 
 
 Macacus. 
 Colobus. 
 
 Family Simiidae. Hylobates gibbon. 
 Simia orang. 
 Gorilla. 
 
 Anth ropopithecus chimpanzee. 
 Family Hominidae. Homo man. 
 R. 4 
 
CHAPTER III. 
 
 SKELETON OF HEMICHORDATA, UROCHORDATA, 
 AND CEPHALOCHORDATA. 
 
 SXJBPHYLUM A. HEMICHORDATA. 
 
 THE subphylum includes three genera, Balanoglossus 1 , Ce- 
 phalodiscus and Rhabdopleura ; and perhaps a fourth, Phoronis. 
 
 The skeletal structures found in Balanoglossus 2 are all 
 endoskeletal. They include 
 
 (1) The notochord. This arises as a diverticuluni from 
 the alimentary canal which grows forwards into the proboscis 
 and extends beyond the front end of the central nervous 
 system. It is hypoblastic in origin and arises in the same way 
 as does the notochord of Ampkioxus. Its cells become highly 
 vacuolated and take on the typical notochordal structure 3 . The 
 cavity of the primitive diverticulum becomes obliterated in front, 
 but behind it opens throughout life into the alimentary canal. 
 
 (2) The axial skeletal rods. These are a pair of chi- 
 tinous rods which lie ventral to the notochord and in the collar 
 region unite to form a single mass. 
 
 (3) The branchial skeleton. The gill bars separating 
 the gill slits from one another are strengthened by chitinous 
 rods in a way closely similar to that in Ampliioxus, But 
 between one primary forked rod and the next there are two 
 secondary unforked rods not one, as in Amphioxus. 
 
 (4) The chondroid tissue. This is of mesoblastic origin 
 and may be regarded as an imperfect sheath for the notochord. 
 
 In Cephalodiscus and Rhabdopleura as in Balanoglossus 
 
 1 The name Balanoglossus is used here in its widest sense to include 
 all the Enteropneusta. 
 
 2 See W. Bateson, Quart. J. Micr. Sci. n. s. vol. xxiv. 1884, p. 208 and 
 later; also E. W. Macbride, Ibid. vol. xxxvi. 1894, p. 385. 
 
 3 See p. 52. 
 
SKELETON OF UROCHORDATA AND CEPHALOCHORDATA. 51 ' 
 
 the notochord forms a small diverticulum growing forwards 
 from the alimentary canal into the proboscis stalk. 
 
 Recent researches on Phoronis 1 show the existence in the 
 collar region of the larva (ActinotrocJia) of a paired organ, 
 which is regarded by its discoverer as representing a double 
 notochord. 
 
 SUBPHYLUM B. UROCHORDATA (TUNICATA). 
 
 Skeletal structures of epiblastic and hypoblastic origin 
 occur in the Urochordata. Most Tunicates are invested by 
 a thick gelatinous test which often contains calcareous spicules, 
 and serves as a supporting organ for the soft body. The cells 
 of this test are mesodermal in origin. 
 
 In larval Tunicata and in adults of the group Larvacea 
 the tail is supported by a typical notochord, which is confined 
 to the tail. In all Tunicata except Larvacea all trace of 
 the notochord is lost in the adult. 
 
 SUBPHYLUM C. CEPHALOCHORDATA. 
 
 This subphylum includes the well-known genus Amphioxus 2 . 
 
 i 
 
 5 8 
 
 FIG. 3. DIAGRAM OF THE SKELETON OF Amphioxus lanceolatus x 3 
 (after a drawing in the Index collection at the Brit. Mus.). 
 
 1. skeleton of dorsal fin. 5. branchial skeleton. 
 
 2. notochord. 6. septa separating the myo 
 
 3. neural tube. tomes. 
 
 4. buccal skeleton. 7. skeleton of ventral fin. 
 
 In Amphioxus the skeleton is very simple. It contains no 
 trace of cartilage or bone and remains throughout life in a 
 
 1 A. T. Masterman, P. R. Soc. Edinb. 189596, p. 59 ; and Anat. Anz. 
 1896, p. 266. 
 
 2 See E. Ray Lankester, Quart. J. Micr. Sci. vol. xxix. n. s. 1889, p. 365. 
 W. B. Benham, Ibid. vol. xxxv. n. s. 1893, p. 97. J. W. Kirkaldy, Ibid, 
 vol. xxxvn. n. s. 1895, p. 303. The last-named writer divides the genus 
 into three subgenera. 
 
 42 
 
52 THE VERTEBKATE SKELETON. 
 
 condition corresponding to a very early stage in Vertebrata. 
 The skeleton of Amphioxus is partly hypoblastic, partly meso- 
 blastic in origin. 
 
 (a) Hypoblastic skeleton. 
 
 The notochord (fig. 3, 2) is an elastic rod extending along 
 the whole length of the body past the anterior end of the 
 nerve cord. It lies ventral to the nerve cord, and shows no 
 trace of segmentation. It is chiefly made up of greatly vacuo- 
 lated cells containing lymph, but near the dorsal and ventral 
 surfaces the cells are less vacuolated. The notochord is im- 
 mediately surrounded by a structureless cuticular layer, the 
 chordal sheath, and outside this comes the mesoblastic skeleto- 
 genous layer, which also surrounds the nerve cord. 
 
 The branchial skeleton. This consists of a series of 
 chitinous elastic rods which strengthen the gill bars and are 
 alternately forked and unforked ventrally. The forked rods 
 are primary, and are U-shaped in section, the unforked rods 
 are secondary, and are circular in section. All these rods are 
 united at intervals by transverse rods. 
 
 (b) Mesoblastic skeleton. 
 
 The buccal skeleton. On each side of the mouth there 
 is a curved bar resembling the notochord in structure. The 
 bars are segmented, and each segment bears a smaller rod 
 which supports a tentacle, the whole forming the buccal 
 skeleton (fig. 3, 4). 
 
 The notochord is enclosed in a thick sheath of connective 
 tissue continuous with a thinner sheath round the nerve cord. 
 The sheaths of the notochord and nerve cord together form the 
 skeletogenous layer, and prolongations of it form the myomeres 
 or septa between the myotomes or segments of the great lateral 
 muscles of the body. 
 
 The skeleton of each median fin consists of small 
 cubical masses of a gelatinous substance arranged in rows 
 (fig. 3, 1 and 7), and serving to strengthen the fins. 
 
CHAPTER IV. 
 
 SUBPHYLUM D. VERTEBRATA. 
 
 THE animals included in this great group all possess an 
 internal axial skeleton forming the vertebral column or back- 
 bone ; and a dorsal spinal cord. The vertebral column is 
 developed from the skeletogenous layer, which surrounds the 
 spinal cord together with the notochord and its sheath ; and 
 in the great majority of cases the notochord becomes more or 
 less modified and reduced in the adult. In some cases the 
 notochord remains unmodified and the skeletogenous layer 
 surrounding it is not segmented to form vertebrae, but in 
 every case the neural arches which protect the spinal cord 
 are segmented. The notochord never extends further forwards 
 than the mid-brain. 
 
 All true vertebrates possess a cranium or skeletal box 
 enclosing the brain. 
 
 (I.) CYCLOSTOMATA. 
 
 The mouth in living forms is suctorial and is not supported 
 by jaws. In some fossil forms the character of the mouth is 
 unknown. 
 
 Order I. MARSiPOBRANCHii 1 . 
 
 In these animals limbs and limb girdles are always com- 
 pletely absent. They have no exoskeleton except horny teeth. 
 
 The endoskeleton, excluding the notochord, is entirely 
 cartilaginous or membranous. The axial skeleton consists of 
 a cartilaginous cranium without jaws, succeeded by a thick 
 
 1 See W. K. Parker On the skeleton of the Marsipobranch fishes, 
 Phil. Trans. 1883, London. 
 
54 THE VERTEBRATE SKELETON. 
 
 persistent notochord enveloped in a sheath. The notochord 
 in living forms is unsegmented, but segmented cartilaginous 
 neural arches are present in some cases. A complicated series 
 of cartilaginous elements occurs in relation to the mouth, gills, 
 and sense organs. The median fins are supported by carti- 
 laginous pieces, the radialia. The order includes the Lampreys 
 and Hags. 
 
 Order II. OsTRACODERMi 1 . 
 
 The forms included in this group have long been extinct, 
 being known only from beds of Upper Silurian and Lower 
 Devonian age. They differ much from all other known animals. 
 The exoskeleton is always greatly developed and includes 
 (1) large bony plates covering the anterior region; (2) scales 
 covering the posterior region. The plates are deeply marked 
 by canals belonging to dermal sense organs. Jaws are un- 
 known, and arches for the support of the appendicular skeleton 
 are rudimentary or absent. The tail is heterocercal (see p. 60). 
 
 Suborder (I). HETEROSTRACI. 
 
 The exoskeleton consists principally of calcifications form- 
 ing dorsal and ventral shields which cover the head and ab- 
 dominal region; the dorsal shield is formed of a few plates 
 firmly united, the ventral shield of a single plate. The shields 
 are composed of three layers, the middle layer being traversed 
 by canals belonging to the dermal sense organs which open to 
 the exterior by a series of pores. The tail is sometimes covered 
 by scales. The orbits are widely separated and laterally 
 placed. Paired appendages are absent. These curious forms 
 are found in beds of Upper Silurian and Lower Devonian age. 
 One of the best known genera is Pteraspis. 
 
 Suborder (2). OSTEOSTRACI. 
 
 The exoskeleton as in the Heterostraci consists of shields 
 and scales, the shields being divisible into three layers. The 
 
 1 See A. Smith Woodward, Catalogue of Fossil Fish' in the British 
 Museum, Part n. f 1891. A. Smith Woodward, Nat. Sci. vol. i. 1892, 
 p. 596. 
 
CYCLOSTOMATA. 55 
 
 anterior part of the body is covered dorsally by a single large 
 shield which differs from those of the Heterostraci in having 
 the inner layer ossified. The middle layer contains canals for 
 the passage of blood vessels, but the exoskeleton shows no 
 impressions of dermal sense organs. The posterior part of the 
 body is covered by large quadrangular scales. Paired append- 
 ages are absent, but median dorsal and caudal fins occur 
 supported by scales, not fin-rays. Cephalaspis, the best known 
 of these animals, occurs in beds of Lower Devonian age. 
 
 Suborder (3). ANTIARCHA. 
 
 The exoskeleton is formed of bony plates, the dorsal and 
 ventral shields each consisting of several symmetrically arranged 
 pieces. The tail may be covered with small scales or may be 
 naked. The head is articulated with the trunk, and its angles 
 are drawn out into a pair of segmented paddle-like append- 
 ages, covered with dermal plates. The orbits are close together. 
 A dorsal fin and traces of mouth parts occur in Pterichthys, 
 but the endoskeleton is unknown. The best known forms 
 Pterichthys 1 and Aster olepis occur in beds of Lower Devonian 
 age. 
 
 GENERAL ACCOUNT OF THE SKELETON OF 
 
 MARSIPOBRANCHII. 
 
 The Marsipobranchii are worm-like animals. The living 
 forms include two families, the Myxinoidei (Hags) genera 
 Myxine and Bdellostoma and thePetromyzontidae (Lampreys). 
 Three species of Petromyzon are known, P. fluviatilis, P. 
 marinus and P. planeri. The larval forms were for a long 
 time thought to belong to a separate genus and were called 
 Ammocoetes. 
 
 The Myxinoids, although very highly specialised in their 
 own way, are at distinctly a lower stage of development than 
 the adult Lamprey, and come nearer to the larval Lamprey or 
 Ammocoete. 
 
 1 See B. H. Traquair, Ann. Nat. Hist., ser. 6, vol. n. 1888, p. 485. 
 
56 
 
 THE VERTEBRATE SKELETON. 
 
 SPINAL COLUMN. 
 
 In Myxinoids and larval lampreys, the notochord is en- 
 closed in a thick chordal sheath, in connection with which in 
 the tail region there occur cartilaginous pieces forming neural 
 arch elements. In the trunk region, however, no cartilage 
 occurs in connection with the spinal column, the only cartilage 
 present being that forming the radialia of the dorsal fin. On 
 the other hand in most species of lamprey (Petromyzon) 
 cartilaginous pieces forming imperfect neural arches (fig. 4, 
 B, 13) are found lying in the tough skeletogenous layer dorsal 
 
 FIG. 4. A, DORSAL ; B, LATERAL AND C, VENTRAL VIEW OF THE 
 SKULL or Petromyzon marinus x 1 (after PARKER). 
 
 1. horny teeth. 8. 
 
 2. labial cartilage. 9. 
 
 3. anterior dorsal cartilage. 10. 
 
 4. posterior dorsal cartilage. 11. 
 
 5. nasal capsule. 
 
 6. auditory capsule. 12. 
 
 7. dorsal portion of trabeculae. 13. 
 
 lateral distal mandibular. 
 lingual cartilage, 
 branchial basket, 
 cartilaginous cup supporting 
 
 pericardium, 
 sheath of notochord. 
 neural plate. 
 
 to the notochord, and extending throughout the whole length 
 of the trunk and tail. Two of these pieces, which are probably 
 homologous with the neural plates (see p. 72) of Elasmobranchs, 
 occur to each neuromere, or segment as determined by the 
 
CYCLOSTOMATA. 57 
 
 spinal nerves. The dorsal and caudal fins are supported by 
 paired cartilaginous radialia which are connected proximally 
 with the skeletogenous layer. 
 
 THE SKULL. 
 
 In Myxinoids the cranium is a mere cartilaginous floor 
 without side walls or roof, and the trabeculae 1 end without 
 growing forwards into cornua. In Lampreys the trabeculae 
 grow forwards and send up plates of cartilage which meet 
 above (fig. 4, 7) and form side walls and a roof for part of the 
 brain case. In Lampreys a labial suctorial apparatus is well 
 developed, including a large ring-like piece of cartilage (fig. 4, 2) 
 which supports the oral funnel and bears a large armament of 
 horny teeth. In Myxinoids on the other hand the labial 
 skeleton is small and consists merely of barbels round the 
 mouth. 
 
 The olfactory organ of Myxinoids has a very curious 
 skeleton. It is covered with a kind of grating of cartilage 
 which is prolonged in front into a tube composed of a series of 
 imperfect cartilaginous rings. In Lampreys the olfactory 
 organ opens merely by a short membranous passage. In 
 correlation with the small development of the labial suctorial 
 apparatus in Myxinoids the lingual apparatus is very greatly 
 developed. The tongue in Myxine has been said to 'dominate 
 the whole body' (Parker). It is supported by a great median 
 cartilaginous bar which when followed forwards first becomes 
 bifid and still further forwards becomes four-cleft. 
 
 The horny teeth in Myxinoids are chiefly borne on the 
 very large supralingual apparatus. They form a double series 
 arranged in the form of an arch. In Myxine there are seven 
 large teeth and nine small ones on each side. In Bdellostoma 
 the teeth of the two rows are more equal in size. In Bdello- 
 stoma and Myxine it has been shown that imperfect calcified 
 teeth occur below the horny teeth. 
 
 1 See p. 17. 
 
58 THE VERTEBRATE SKELETON. 
 
 In Lampreys the lingual apparatus (fig. 4, C, 9) is well de- 
 veloped, but not excessively so. It consists of a long median 
 cartilaginous bar which ends in front with a semicircular piece 
 of cartilage supporting the median part of the tongue. 
 
 In both Myxinoids and Lampreys there is a complicated 
 branchial basket apparatus, but while in Myxinoids the basket 
 apparatus is interbranchial, formed deep within the head 
 near the hypoblastic lining of the throat, in Lampreys it is 
 extra -branchial and formed outside the head cavities (fig. 
 4, 10). The two sides of the basket apparatus in Myxine are 
 not symmetrical. In the interbranchial basket apparatus of 
 Myxinoids the hyoid and first and second branchial arches 
 can be recognised. Traces of the interbranchial skeleton of 
 Myxinoids can be detected in Lampreys, and similarly in 
 Myxinoids, there are indications of the extrabranchial skeleton 
 of Petromyzon. The branchial basket in Lampreys forms at 
 its posterior end a kind of cup which supports the pericardium 
 (fig. 4, 11). 
 
 A remarkable Cyclostome named Palaeosj)ondylus l has re- 
 cently been described from the Scottish Old Red Sandstone. 
 It differs however from all living Cyclostomes, in having a 
 spinal column formed of distinct vertebrae with well-developed 
 neural arches. The caudal fin is well developed and the dorsal 
 radialia are forked as in lampreys. The skull is well calcified 
 and the auditory capsules are specially large. The mouth is 
 very similar to that of lampreys, being circular and without 
 jaws ; it is provided with barbels or cirri. There is no trace 
 of limbs and the average length is only about 1 1J inches. 
 
 1 R. H. Traquair, Ann. Nat. Hist. vol. vi. 1890, p. 485 ; P. Phys. Soc. 
 Edinb. vol. xn. 189293, pp. 8794, and 312320. A. Smith Woodward, 
 Nat. Sci. vol. in. p. 128, 1893. 
 
CHAPTER V. 
 (II. ) GN ATHOSTOM AT A. 
 
 THE mouth is supported by definite jaws. 
 
 ICHTHYOPSIDA. 
 
 The epiblastic exoskeleton is generally unimportant, the 
 mesoblastic exoskeleton is usually well developed. 
 
 The notochord with its membranous sheath (1) may remain 
 unmodified, or (2) may be replaced by bone or cartilage derived 
 from the skeletogenous layer, or (3) may be calcified to a 
 varying extent. 
 
 The first vertebra is not homologous throughout the whole 
 series and so is not strictly comparable to the atlas of Saur- 
 opsids and Mammals. 
 
 The centra of the vertebrae have no epiphyses. The 
 skull may be (a) incomplete and membranous, or (6) more or 
 less cartilaginous, or (c) bony. Membrane bones are not 
 included in the cranial walls, and there are large unossified 
 tracts in the skull. When membrane bones are developed in 
 connection with the skull, a large parasphenoid occurs. The 
 basisphenoid is always small or absent. The skull may be 
 immovably fixed to the vertebral column, or may articulate 
 with it by a single or double occipital condyle. When the 
 occipital condyle is double, it is formed by the exoccipitals, 
 and the basi- occipital is small or unossified. The mandible 
 may be (a) cartilaginous, (b) partially ossified, or (c) membrane 
 bones may be developed in connection with it, if so, there is 
 
60 THE VERTEBRATE SKELETON. 
 
 usually more than one membrane bone developed in connection 
 with each half. 
 
 There are at least four pairs of branchial arches present 
 during development. The sternum, if present, is not costal 
 in origin. 
 
 CLASS I. PISCES. 
 
 The exoskeleton is in the form of scales, which may be 
 entirely mesoblastic or dermal in origin (e.g. cycloid and 
 ctenoid scales), or may be formed of both mesoblast and epi- 
 blast (e.g. placoid and ganoid scales). Large bony plates may 
 be derived from both these types of scale. In general fish 
 with a greatly developed dermal armour have the endoskeleton 
 poorly developed; and the converse also holds good. 
 
 The integument of the dorsal and ventral surfaces is 
 commonly prolonged into longitudinal unpaired fins, sup- 
 ported by an internal skeleton. These fins are distinguished 
 according to their position as dorsal, caudal and anal fins. 
 The dorsal and anal fins are used chiefly as directing organs, 
 the caudal fin is however a most important organ of pro- 
 pulsion. 
 
 Three types of tail are found in fishes, viz. : 
 
 1. The diphycercal, in which the axis is straight and 
 the tail is one-bladed and symmetrical, an equal proportion of 
 radialia 1 being attached to the upper and lower surfaces of the 
 axis. 
 
 2. The heterocercal, in which the tail is asymmetrical 
 and the axis is bent upwards, the proportion of radialia or of 
 fin-rays attached to its upper surface being much smaller than 
 that attached to its lower surface. 
 
 3. The home-cereal, in which the tail though ex- 
 ternally symmetrical, so far resembling the diphycercal type, is 
 internally really heterocercal, the great majority of the radialia 
 or of the fin-rays being attached to the lower surface of the axis. 
 
 1 See p. 79. 
 
PISCES. 61 
 
 The cranium in the simplest cases (e.g. Selachii) forms a 
 cartilaginous box enclosing the brain and sense organs ; in 
 bony fishes it is greatly complicated. When palatine or 
 pterygoid bones are present they are formed by the ossifi- 
 cation of cartilage ; in Sauropsida and Mammalia they are 
 laid down as membrane bones. There is no tympanic cavity 
 or auditory ossicle in relation to the ear. 
 
 There are two principal types of suspensorium by means of 
 which the jaws are attached to the cranium : 
 
 (1) The Autostylic. This is the primitive condition 
 in which the mandibular arch articulates with the base of the 
 cranium in front of the hyoid and in a similar manner. 
 
 (2) The Hyostylic. In this case the mandibular arch 
 becomes connected with the hyomandibular and supported by 
 the hyoid arch. These terms are more fully discussed in 
 Chapter VIII. 
 
 There is always an internal framework supporting the 
 gills ; it usually consists of the hyoid arch and five, rarely 
 six or seven, pairs of branchial arches. The limbs are repre- 
 sented by two pairs of fins, the pectoral and the pelvic ; they 
 are not divided into proximal, middle and distal portions. The 
 ribs do not unite with a median ventral sternum, or meet in 
 the midventral line in any other way in the trunk region. 
 
 Order I. ELASMOBRANCHII. 
 
 The exoskeleton is in the form of placoid scales which are 
 sometimes so numerous as to give the whole skin a rough 
 surface forming shagreen. In some cases the placoid scales 
 are enlarged to form plates or spines capped or coated with 
 enamel. These spines may be imbedded in the flesh in front 
 of the paired or unpaired fins, or may be attached to the tail. 
 They are specially characteristic of the suborder Acanthodii. 
 The endoskeleton is cartilaginous and true bone is never 
 found. Much of the skeleton, especially of the vertebral 
 
62 THE VERTEBRATE SKELETON. 
 
 column, is however often calcined, this being especially well 
 seen in the anterior part of the vertebral column of Rays 
 (Raiidae). In living forms cartilaginous biconcave vertebrae 
 are always well developed, but in some extinct forms the 
 notochord persists unconstricted. Neural and haemal arches 
 are however always developed ; they sometimes remain 
 separate, sometimes fuse with the centra. Ribs are often 
 wanting and when present are often not separated off from the 
 vertebrae. The cranium is a simple cartilaginous box whose 
 most prominent parts are the capsules which enclose the 
 sense organs. The skull is sometimes immovably fixed to 
 the vertebral column, sometimes articulates with it by means 
 of two condyles. There is no operculum and no representative 
 of the maxilla or premaxilla. The teeth are very variable. 
 Large pectoral and pelvic fins always occur. 
 
 The Elasmobranchii may be divided into four suborders : 
 
 (1) Ichthyotomi. 
 
 (2) Pleuropterygii. 
 
 (3) Selachii. 
 
 (4) Acanthodii. 
 
 Suborder (1). ICHTHYOTOMI \ 
 
 The members of this suborder range from the Devonian to 
 the Permian and so have long been extinct. 
 
 The endoskeletal cartilage has granular calcifications evenly 
 distributed throughout it. The notochord is unconstricted, but 
 the neural and haemal arches are well-developed, and the 
 neural spines are long and slender. There is a continuous 
 dorsal fin with separate basalia and radialia. The tail is di- 
 phycercal, and the pectoral fins are typical archipterygia -. 
 The pelvic fins of the male are prolonged to form claspers. 
 
 1 For this arid other groups of extinct fish see A. Smith Woodward, 
 Catalogue of Fossil Fish in the British Museum, Parts i. in. London, 
 188995. 
 
 2 See p. 127. 
 
PISCES. ELASMOBRANCHII. 63 
 
 The best known of these primitive Elasmobranchs are the 
 Pleuracanthidae. 
 
 Suborder (2). PLEUROPTERYGII. 
 
 This suborder was formed for the reception of Cladoselache, 
 an Elasmobranch found in the Lower Carboniferous of Ohio 1 . 
 
 The exoskeleton is in the form of small, thickly-studded 
 dermal denticles. The vertebral centra are unossified, and 
 the tail is strongly heterocercal. There were certainly five, 
 perhaps seven gill slits, and the suspensorium is apparently 
 hyostylic. The paired fins are, according to the view which 
 derives them by concentration from continuous lateral folds, 
 the most primitive known (see p. 129) and claspers are 
 absent. 
 
 Suborder (3). SELACHII. 
 
 Cartilaginous or partially calcified biconcave vertebrae are 
 always well developed ; they constrict the notochord inter- 
 vertebrally. The neural and haemal arches and spines are 
 stout and intercalary cartilages (interdorsalia) are present. 
 The tail is heterocercal, but in some cases (Squatina) ap- 
 proaches the diphycercal condition. In most cases the suspen- 
 sorium is hyostylic, the jaws being attached to the cranium 
 by means of the hyomandibular, and the palato-pterygo- 
 quadrate bar not being fused to the cranium. There are 
 generally five pairs of branchial arches, and gill rays are 
 borne on the posterior surface of the hyoid arch, and on both 
 the anterior and posterior surfaces of the first four branchial 
 arches. The J^otidanidae differ from most Selachians in two 
 respects, first as regards the suspensorium, Meckel's cartilage 
 articulating directly with the palato-pterygo-quadrate bar, and 
 not being connected with the hyoid arch ; and secondly as 
 regards the number of branchial arches, six pairs occurring 
 in Hexanchus and seven in Heptanchus. 
 
 The pectoral fins are without the segmented axis of the 
 1 See B. Dean, J. MorphoL vol. ix. pp. 87114, 1894, and Nat. Sci. 
 voL vin. p. 245, 1896. 
 
64 THE VERTEBRATE SKELETON. 
 
 archipterygium. In most cases they are sharply marked off 
 from the body and lie almost at right angles to it ; but in the 
 Rays they have the form of lateral expansions in the same 
 plane as the body, from which they are not sharply marked 
 off. The pelvic fins in the male bear long grooved cartilaginous 
 rods which are accessory copulatory organs or claspers. 
 
 There are two principal groups of Selachii, the Squalidae 
 or Sharks aijd Dogfish, and the Batoidei or Skates and Rays. 
 The Squalidae have the shape of ordinary fish, the pectoral 
 fins are vertically placed and the body ends in a powerful 
 heterocercal tail. The Batoidei have flattened bodies owing 
 to the great size and horizontal position of the pectoral fins. 
 The tail is long and thin and is often armed with spines. 
 The teeth in Selachii differ much in character in the different 
 forms, and are always arranged in numerous rows. They are 
 generally pointed and triangular or conical in the Squalidae, 
 while in the Batoidei they are often broad and flattened. 
 
 Suborder (4). ACANTHODII. 
 
 The fishes included in this group are all extinct and 
 in some respects are intermediate between Elasmobranchii 
 and Gaiioidei. The body is elongated and closely covered 
 with small scales consisting of dentine enamelled at the sur- 
 face. The notochord is persistent and the calcification of the 
 endoskeletal cartilage is only superficial. The tail is hetero- 
 cercal. The jaws bear small conical teeth, or in some cases 
 are toothless. The skeleton of all the fins differs from that of 
 modern Elasmobranchs in having the cartilaginous radialia 
 much reduced, and the fins are nearly always each provided 
 with an anterior spine, which except in the case of the pec- 
 toral fins is merely inserted between the muscles. These spines 
 are really enormous dermal fin-rays ; the pectoral fin-spine is 
 articulated to the pectoral girdle. 
 
 The suborder includes many well-known extinct forms like 
 Acanthodes and Diplacanthus ; it ranges from the Devonian to 
 the Permian. 
 
PISCES. HOLOCEPHALI. 
 
 65 
 
 Order II. HOLOCEPHALI. 
 This order includes a single suborder only. 
 Suborder. CHIMAEROIDEI. 
 
 These singular fish have the skin smooth and in living 
 forms almost or quite scaleless. The palato-pterygo-quadrate 
 bar and hyomandibular are fused to the cranium, and Meckel's 
 cartilage articulates directly with the part corresponding to the 
 quadrate. The skull is distinctly articulated with the spinal 
 
 10, 
 
 FIG. 5. SKULL OF A MALE Chimaera monstrosa (after HUBBECHT). 
 
 1. nasal capsule. 
 
 2. cartilaginous appendage to 
 the fronto-nasal region. 
 
 3. erectile appendage. 
 
 4. foramen by which the oph- 
 thalmic nerves leave the orbit. 
 
 5. foramen by which the oph- 
 thalmic branch of the Vth nerve 
 enters the orbit. 
 
 6. auditory capsule. 
 
 7. interorbital septum. 
 
 8. mandible articulating with 
 an outgrowth from the posterior 
 part of the palato-pterygo-quadrate. 
 
 9. teeth. 
 
 10. labial cartilage. 
 II. III. V. VII. IX. X. foramina 
 for the passage of cranial nerves. 
 
 column, the notochord is persistent and unconstricted, and the 
 skeletogenous layer shows no trace of metameric segmentation, 
 
 K. 5 
 
66 THE VERTEBRATE SKELETON. 
 
 though in the neural arches this segmentation is readily trace- 
 able. The neural arches of the first few vertebrae are fused 
 together and completely surround the notochord, while they 
 do not in other parts of the body. The tail is diphy cereal. 
 Of the living genera, in Callorhynchus there is no trace of 
 calcification in the skeletogenous layer, while in Chimaera rings 
 of calcification are found, there being three to five for each 
 vertebra as indicated by the foramina for the exit of the spinal 
 nerves. The pelvic fins are produced into claspers. Besides 
 the living genera Chimaera, Harriotta and Callorhynchus a 
 fair number of fossil forms are known, e.g. Ischyodus. 
 
 Order 3. GANOIDEI. 
 
 The fishes included under the term Ganoidei form a very 
 heterogeneous group, some of which closely approach the Dipnoi, 
 others the Elasmobranchii, others the Teleostei. The great 
 majority of them are extinct, only eight living genera being 
 known; these are all inhabitants of the northern hemisphere, 
 and with the exception of Acipenser, which is both fluviatile 
 and marine, are entirely confined to fresh water. 
 
 The following is a list of the living genera of Ganoids with 
 their respective habitats : 
 
 Acipenser. Rivers and seas of the northern hemisphere. 
 
 Scaphirhynchus. Mississippi and rivers of Central Asia. 
 
 Polyodon (Spatularia). Mississippi. 
 
 Psepkurus. Yan-tse-kiang, and Hoangho. 
 
 Polypterus. Rivers of tropical Africa. 
 
 Calamoichthys. Some rivers of West Africa. 
 
 Lepidosteus. Freshwaters of Central and North America 
 and Cuba. 
 
 Amia. Rivers of Carolina. 
 
 The exoskeleton is very variable, thus the body may be : 
 
 (a) Naked or with minute stellate ossifications as in 
 
 the Polyodontidae. (b) Partially covered with large detached 
 
PISCES. GANOIDEI. 67 
 
 bony plates as in Scaphirhynchus and Acipenser. (c) Entirely 
 covered with rhomboidal ganoid scales as in Lepidosteus, 
 Polypterus, Palaeoniscus and many extinct forms, (d) Covered 
 with rounded scales shaped like the cycloid scales of Teleosteans 
 as in Amia. (e) Having the trunk and part of the tail covered 
 with rhomboidal scales, and the remainder of the tail with 
 rounded scales as in Trissolepis. 
 
 The teeth also are very variable. The endoskeleton shows 
 every stage of transition from an almost entirely cartilaginous 
 state as in Acipenser to a purely bony state as in Lepidosteus. 
 Sometimes, as in Acipenser, the notochord persists, and its 
 sheath is unsegmented ; sometimes, as in Lepidosteus, there 
 are fully formed vertebrae. The tail may be heterocercal, as 
 in Acipenser, or diphy cereal as in Polypterus. The cartila- 
 ginous cranium is always covered with external membrane 
 bone to a greater or less extent, and the suspensorium is 
 markedly hyostylic. The pectoral girdle is formed of two 
 parts, one endoskeletal and cartilaginous, corresponding with 
 the pectoral girdle of Elasmobranchs, and one exoskeletal 
 and formed of membrane bones, corresponding with the cla- 
 vicular bones of Teleosteans. The pelvic fins are always 
 abdominal. The fins often, as in Polypterus, have spines 
 (fulcra) attached to their anterior borders. 
 
 The order Ganoidei may be divided into three suborders : 
 
 (1) CHONDROSTEI. Living genera Acipenser, Scaphi- 
 rhynchus, Polyodon and Psephurus. 
 
 (2) CROSSOPTERYGII. Living genera Polypterus. and 
 Calamoichthys. 
 
 (3) HOLOSTEI. Living genera Lepidosteus and Amia. 
 
 Suborder (1). CHONDROSTEI. 
 
 The skull is immovably fixed to the vertebral column. 
 By far the greater part of the skeleton is cartilaginous. 
 The notochord is persistent and unconstricted, its sheath is 
 membranous, but cartilaginous neural and haemal arches are 
 
 52 
 
68 THE VERTEBRATE SKELETON. 
 
 developed. Intercalary pieces (interdorsalia) occur between 
 the neural arches, and similar pieces (interventralia) between 
 the haemal arches. The cranium is covered with membrane 
 bone, and teeth are but slightly developed. The tail is hetero- 
 cercal. Gill rays occur on the hyoid arch, and the gills are 
 protected by a bony operculum attached to the hyomandi- 
 bular. The skin (1) may be almost or quite naked, (2) may 
 carry bony plates arranged in rows, or may be covered (3) with 
 rhomboidal scales, or (4) partly with rhomboidal, partly with 
 cycloidal scales. 
 
 Suborder (2). CROSSOPTERYGII. 
 
 The exoskeleton has the form of cycloidal or rhomboidal 
 scales. The condition of the vertebral column differs in the 
 different genera. Sometimes, as in Polypterus, there are well- 
 developed ossified vertebrae; sometimes, as in many extinct 
 forms, the notochord persists and is unconstricted. The tail 
 may be diphycercal *or heterocercal. The pectoral and some- 
 times the pelvic fins consist of an endoskeletal axis bearing 
 a fringe of dermal rays. 
 
 Suborder (3). HOLOSTEI. 
 
 The exoskeleton has the form of cycloidal or rhomboidal 
 scales. The notochord is constricted and its sheath is seg- 
 mented and ossified, forming distinct vertebrae, which are 
 generally biconcave, sometimes opisthocoelous (Lepidosteus) . 
 The cartilaginous cranium is largely replaced by bone, and in 
 connection with it we find not only membrane bone, but 
 cartilage bone, as the basi-occipital, exoccipitals, and pro- otic 
 are ossified. The tail is heterocercal. The suspensorium 
 resembles that of Teleosteans, consisting of a proximal ossifi- 
 cation, the hyomandibular, which is movably articulated to 
 the skull and a distal ossification, the symplectic. The two 
 are separated by some unossified cartilage. The cartilaginous 
 upper and lower jaws are to a great extent surrounded and 
 replaced by a series of membrane bones. 
 
PISCES. TELEOSTEI. 69 
 
 Order 4. TELEOSTEI. 
 
 The exoskeleton is sometimes absent but generally consists 
 of overlapping cycloid or ctenoid scales. Bony plates are some- 
 times present, as in the Siluridae, or the body may be encased 
 in a complete armour of calcined plates, as in Ostracion. 
 Enamel is however never present, and the plates are entirely 
 mesodermal. The skeleton is bony, but in the skull much 
 cartilage generally remains. The vertebral centra are usually 
 deeply biconcave, and the tail is of the masked heterocercal 
 type distinguished as homocercal. In the skull the occipital 
 region is always completely ossified, while the sphenoidal 
 region is generally less ossified. The skull has usually 
 a very large number of membrane bones developed in connec- 
 tion with it. The teeth vary much in character in the different 
 members of the order, but are as a rule numerous and pointed, 
 and are ankylosed to the bone. The suspensorium is hyo- 
 stylic and the jaws have much the same arrangement as in 
 the Holostei. There are five pairs of branchial arches, of 
 which all except the last bear gill rays. A series of dermal 
 opercular bones is developed in connection with these arches. 
 The pectoral girdle consists almost entirely of dermal clavicular 
 bones. The pelvic girdle has disappeared, its place being taken 
 by the enlarged and ossified dermal fin-rays of the pelvic fins. 
 
 The group includes the vast majority of living fish (see 
 p. 33). 
 
 Order 5. DIPNOI. 
 
 The exoskeleton is of two types ; dermal bones are largely 
 developed in the head region, while the tail and posterior 
 part of the body may be naked or may be covered with over- 
 lapping scales. The cranium remains chiefly cartilaginous, 
 the palato-pterygo-quadrate bar is fused with the cranium, 
 and the suspensorium is autostylic. The gill clefts^ are feebly 
 developed and open into a cavity covered by an operculum. 
 The notochord is persistent and unconstricted, and the limbs 
 are archipterygia. The pelvic fins are without claspers. 
 
70 THE VERTEBRATE SKELETON. 
 
 Suborder (1). SiRENOiDEi 1 . 
 
 The head has well developed membrane bones. The trunk 
 is covered with overlapping scales and bears no bony plates. 
 Three pairs of teeth are present, two in the upper and one 
 in the lower jaw, the two principal pairs of teeth are borne on 
 the palato-pterygoids and splenials, while the third pair are 
 found in the vomerine region. The tail is diphycercal in 
 living forms. In the extinct Dipteridae it is heterocercal. 
 The pectoral girdle includes both membrane and cartilage 
 bones. The pelvic girdle consists of a single bilaterally 
 symmetrical piece of cartilage. 
 
 This suborder is represented by the living genera Ceratodus, 
 Protopterus and Lepidosiren, and among extinct forms by the 
 Dipteridae and others. 
 
 Suborder (2). ARTHRODIRA. 
 
 Bony plates are developed not only on the head but also 
 on the anterior part of the trunk, where they consist of a 
 dorsal, a ventral, and a pair of lateral plates which articulate 
 with the cranial shield. The posterior part of the trunk is 
 naked. The tail is diphycercal. The jaws are shear-like, and 
 their margins are usually provided with pointed teeth whose 
 bases fuse with the tissue of the jaw and constitute dental 
 plates. There seem to have been three pairs of these plates, 
 arranged as in the Sirenoidei, the principal ones in the upper 
 jaw being borne on the palato-pterygoids. Small pelvic fins 
 are present, but pectoral fins are unknown. 
 
 The Arthrodira occur chiefly in beds of Devonian and 
 Carboniferous age. Two of the best known genera are 
 Coccosteus from the European Devonian and Dinichthyx, a 
 large predatory form from the lower Carboniferous of Ohio. 
 
 1 A. Giinther, Phil. Trans, vol. 161, Part 11. 1871, p. 511. T. H. 
 Huxley, "On Ceratodus and the classification of fishes," P.Z.S. 1876, 
 p. 24. 
 
CHAPTER VI. 
 
 THE SKELETON OF THE DOGFISH 1 . 
 
 Scyllium canicula. 
 
 I. EXOSKELETON. 
 
 The exoskeleton of the dogfish is mainly composed of placoid 
 scales, each of which consists of a little bony base imbedded 
 in the skin, bearing a small backwardly-directed spine formed 
 of dentine capped with enamel. The scales are larger on 
 the dorsal than on the ventral surface, and on the jaws they 
 are specially large and regularly arranged in rows, there 
 forming the teeth. The margins of the jaws or lips are with- 
 out scales. 
 
 A second exoskeletal structure is found in the fins, all 
 of which, both paired and unpaired, have, in addition to their 
 cartilaginous endoskeleton, large numbers of long slender 
 horny fibres, the fin-rays, which are of exoskeletal origin. 
 
 II. ENDOSKELETON. 
 
 The endoskeleton of the dogfish consists almost entirely 
 of cartilage, which however may become calcified in places, 
 e.g. the centrum of each vertebra is lined by a layer of calcified 
 tissue. 
 
 The endoskeleton is divisible into an axial portion con- 
 sisting of the vertebral column, skull, and skeleton of the 
 median fins, and an appendicular portion consisting of the 
 skeleton of the paired fins and their girdles. 
 
 1 See Marshall and Hurst's Practical Zoology, 4th ed. London, 1895, 
 p. 214. 
 
72 THE VERTEBRATE SKELETON. 
 
 1. THE AXIAL SKELETON. 
 A. THE VERTEBRAL COLUMN AND RIBS. 
 
 The vertebral column consists of a series of some hundred 
 and thirty vertebrae, each of which is united with its pre- 
 decessor and successor in such a way as to allow a large 
 amount of flexibility. 
 
 These vertebrae are developed round an unsegmented 
 rod, the notochord, which forms the axial support of the 
 embryo. The notochord remains continuous throughout the 
 whole vertebral column, but is greatly constricted opposite the 
 middle of each vertebra, and thus rendered moniliform. The 
 vertebrae are divided into two groups, an anterior group of 
 trunk vertebrae, and a posterior group of caudal or tail 
 vertebrae. 
 
 A typical vertebra consists of a middle portion, the cen- 
 trum, a dorsal portion, the dorsal or neural arch, which 
 surrounds the spinal cord, and a ventral portion, the ventral 
 or haemal arch, which similarly encloses a space. 
 
 The tail vertebrae of the dogfish have this typical arrange- 
 ment, the trunk vertebrae have the haemal arches modified. 
 
 Each centrum is a short cylinder of cartilage surrounding 
 an hourglass-shaped cavity occupied by the notochord. The 
 neural arches are composed of three separate elements, the 
 vertebral neural plates (basidorsalia), intervertebral 
 neural plates (interdorsalia), and neural spines (supra- 
 dorsalia). 
 
 The vertebral neural plates are in the adult fused with 
 their respective centra, and are notched behind for the exit 
 of the ventral (motor) roots of the spinal nerves. The inter- 
 vertebral neural plates are polygonal pieces alternating 
 with the vertebral neural plates; they are notched behind, 
 but at a more dorsal level than are the vertebral neural plates, 
 
THE SKELETON OF THE DOGFISH. THE SKULL. 73 
 
 for the exit of the dorsal or sensory roots of the spinal 
 nerves. 
 
 The neural spines are small patches of cartilage filling 
 up the gaps between the dorsal ends of the neural plates. 
 
 The haemal arches (basiventralia) differ much in the 
 trunk and tail portions of the vertebral column. In the 
 trunk portion the centra are flattened below, and the two 
 halves of the haemal arch diverge from one another as blunt 
 ventri-lateral processes to which short cartilaginous rods, 
 the ribs, are attached. Further back at about vertebra 37, 
 the two halves of the haemal arch project downwards and 
 meet forming a complete arch. Further back still, towards 
 the hind end of the tail, the haemal arches bear median 
 haemal spines (ventrispinalia). 
 
 B. THE SKULL. 
 
 The skull of the dogfish remains cartilaginous throughout 
 the life of the animal, and has consequently a far more simple 
 structure than have the skulls of higher animals, in which 
 complication has been produced by the development of bone. 
 
 The skull consists of the following parts : 
 
 (1) a dorsal portion, the cranium, which lodges the brain, 
 and to the sides of which the capsules of the auditory and 
 olfactory sense organs are united. The cranium may be 
 compared to an unsegmented continuation of the vertebral 
 column ; 
 
 (2) a number of ventral structures, disconnected or only 
 loosely connected with the cranium. These together con- 
 stitute the visceral skeleton forming the jaw's and sup- 
 porting the gills. 
 
 (1) THE CRANIUM. 
 
 The Cranium is an oblong box, with a flattened floor and 
 a more irregular roof. Its sides are expanded in front owing 
 
74- . THE VERTEBRATE SKELETON. 
 
 to the olfactory capsules, and behind owing to the auditory 
 capsules, while in the middle they are deeply hollowed to form 
 the orbits. 
 
 (a) On the dorsal surface of the cranium the following 
 points should be noticed. First at the anterior end, the large 
 thin-walled nasal or olfactory capsules (fig. 6, 1), each of 
 which is drawn out into a narrow cartilaginous process. 
 
 The olfactory capsules have no ventral walls, and are 
 separated from one another by the internasal septum, which 
 is drawn out into a third slender process. These three pro- 
 cesses together constitute the rostrum (fig. 6, 2). 
 
 Behind the olfactory capsules comes a large, nearly circular, 
 hole, the anterior fontanelle, slightly behind which are the 
 two ophthalmic foramina. The dorsal and ventral bound- 
 aries of the orbits are respectively formed by the prominent 
 supra-orbital and sub-orbital ridges. Behind are the audi- 
 tory capsules (fig. 6, 8), each of which is marked by a pair 
 of prominent ridges, converging towards the middle line to a 
 pair of apertures. These apertures communicate with two 
 canals, the aqueductus vestibuli, which lead into the in- 
 ternal ear. The two ridges lodge respectively the anterior 
 and posterior vertical semicircular canals of the ear. 
 
 (6) The principal structures to be noted in a side view of 
 the cranium are contained in the orbit or eye-cavity. Near the 
 base of the orbit at its anterior end is seen the small orbito- 
 nasal foramen (fig. 6, 7), for the passage of blood-vessels, 
 not nerves. Above it is the large ophthalmic foramen 
 (fig. 6, 5) so prominent in a dorsal view of the skull ; through 
 it the ophthalmic branches of the fifth and seventh nerves 
 pass. Slightly further back near the ventral surface is 
 the large optic foramen (fig. 6, II.) for the passage of the 
 second nerve. Vertically above the optic foramen, near the 
 dorsal surface, is the very small foramen for the fourth 
 nerve (fig. 6, IV.). Behind and a little above the optic 
 
THE SKELETON OF THE DOGFISH. THE SKULL. 75 
 
 foramen is another small aperture, the foramen for the 
 third nerve. Behind and slightly below this is the large 
 foramen for the sixth and main branches of the fifth 
 and seventh nerves (fig. 6, V.). In front of and slightly 
 
 IX 
 
 FIG. 6. LATERAL VIEW OF THE SKULL OF A DOGFISH (Scyllium 
 canicula) x f . 
 
 1. nasal capsule. 
 
 2. rostrum. 
 
 3. interorbital canal. 
 
 4. foramen for hyoidean artery. 
 
 5. foramen for the exit of the 
 
 ophthalmic branches of 
 Vth and Vllth nerves. 
 
 6. foramen through which the 
 
 external carotid leaves the 
 orbit. 
 
 7. orbitonasal foramen. 
 
 8. auditory capsule. 
 
 9. foramen through which the 
 
 external carotid enters the 
 orbit. 
 
 10. ethmo -palatine ligament. 
 
 11. palato-pterygo-quadrate bar. 
 
 12. Meckel's cartilage. 
 
 13. hyomandibular. 
 
 14. cerato-hyal. 
 
 15. pharyngo-branchial. 
 
 16. epi-branchial. 
 
 17. cerato-branchial. 
 
 18. gill filaments, nearly all have 
 
 been cut off short for the 
 sake of clearness. 
 
 19. extra-branchial. 
 
 20. pre-spiracular ligament. 
 
 II. III. IV. V. Va. Vila, foramina 
 for passage of cranial nerves. 
 
 below this foramen are seen two other small apertures; the 
 more anterior and ventral of these (fig. 6, 4) is for the 
 passage of a vessel connecting the efferent artery of the hyoid 
 gill with the internal carotid artery inside the skull, the more 
 
76 THE VERTEBRATE SKELETON. 
 
 posterior and dorsal is for the interorbital canal (fig. 6, 3) 
 which unites the two orbital sinuses. Above and very slightly 
 in front of the large foramen for the sixth and main parts 
 of the fifth and seventh nerves, are two small foramina 
 (fig. 6, Va., and Vila.), through which the ophthalmic 
 branches of the fifth and seventh nerves enter the 
 orbit. Behind and slightly below the large foramen just 
 mentioned is a small hole through which the external carotid 
 enters the orbit (fig. 6, 9). 
 
 Behind the orbit is the auditory capsule. This is 
 marked below by a prominent surface for the articulation 
 of the hyomandibular, above which is the deep post- 
 orbital groove for the passage of a blood-vessel, connecting 
 the orbital and anterior cardinal sinuses. 
 
 (c) Passing to the posterior end of the cranium : in the 
 centre is seen the large foramen magnum through which 
 the brain and spinal cord communicate. The notochord 
 enters the skull just below this foramen, and on each side of 
 the notochord is a projection, the occipital condyle, by 
 which the first vertebra articulates with the skull. 
 
 External to the condyles are the prominent pneumo- 
 gastric foramina for the passage of the tenth nerves, and 
 further to the sides, just beyond the posterior vertical semi- 
 circular canals, are a pair of deep pits in which lie the 
 foramina for the ninth nerves (fig. 6, IX.). 
 
 (d) The broad and flat ventral surface of the cranium is 
 continued in front as the inter-nasal septum and terminated 
 laterally by the sub-orbital ridges. At a little behind the 
 middle it is traversed by two shallow grooves along which 
 the internal carotid arteries run. At the divergent ends of 
 these grooves are seen two small apertures through which the 
 external carotids enter the orbit (fig. 6, 9), and at the point 
 where they meet is a single small aperture through which the 
 internal carotid enters the cranium. 
 
THE SKELETON OF THE DOGFISH. VISCERAL SKELETON. 77 
 (2) THE VISCERAL SKELETON. 
 
 The Visceral skeleton forms a series of seven cartilagi- 
 nous arches or hoops, surrounding the anterior part of the 
 alimentary canal, and enclosing a wide but rather shallow 
 space. 
 
 (a) The first or mandibular arch is the largest of the 
 series, and forms the upper and lower jaws. Each half of the 
 upper jaw or palato-pterygo-quadrate bar is formed by a 
 thick cartilaginous rod which meets its fellow in the middle 
 line in front, the two being united by ligament. Each half is 
 connected to the cranium just in front of the orbit by the 
 ethnic-palatine ligament (fig. 6, 10), and at its hind end 
 articulates with one of the halves of the lower jaw. Each 
 half of the lower jaw or Meckel's cartilage (fig. 6, 12) is 
 a cartilaginous bar, wide behind but narrow in front, where 
 it is united to its fellow by a median ligament. Imbedded 
 in the tissue external to the upper jaw are a pair of 
 labial cartilages, and a similar but smaller pair are 
 imbedded in the tissue external to the lower jaw. 
 
 The jaws are developed from a structure whose dorsal and 
 ventral portions subsequently become of very different import- 
 ance. The ventral portion forms both upper and lower jaws, 
 the former being developed as an outgrowth from the latter. 
 The dorsal portion forms only the prespiracular ligament 
 (fig. 6, 20), a strong fibrous band containing a nodule of 
 cartilage, and running from the anterior part of the auditory 
 capsule to the point where the jaws are connected with the 
 hyomandibular. 
 
 (6) The hyoid arch consists of a pair of cartilaginous 
 rods which are attached at their dorsal ends to the cranium, 
 and are united ventrally by a broad median plate of cartilage, 
 the basi-hyal. Each rod is divided into a dorsal portion, 
 the hyomandibular and a ventral portion, the cerato-hyal. 
 
78 THE VERTEBRATE SKELETON. 
 
 The hyomandibular (fig. 6, 13) is a short stout rod of cartilage 
 projecting outwards, and somewhat backwards and downwards 
 from the cranium, with which it articulates behind the orbit 
 and below the postorbital groove. Its distal end articulates 
 with a rather long slender bar, the cerato-hyal (fig. 6, 14), 
 which is in its turn attached to the side of the basi-hyal. The 
 basi-hyal is a broad plate, rounded in front and drawn out 
 behind into two processes to which the two halves of the 
 first branchial arch are attached. The posterior surfaces of 
 both hyomandibular and cerato-hyal bear slender cartilaginous 
 processes, the gill rays. The hyoid arch forms the main 
 suspensorium or means by which the jaws are attached to 
 the cranium. This attachment is chiefly brought about by 
 a series of short ligaments which connect the posterior ends 
 of both upper and lower jaws with the hyomandibular, but 
 there is also a ligament connecting the lower jaw with the 
 cerato-hyal. The attachment of the jaws to the cranium is 
 also partially effected by the prespiracular and ethmo-palatine 
 ligaments. 
 
 (c) Each of the five branchial arches is a hoop, in- 
 complete above and formed of four or more pieces of cartilage. 
 The most dorsal elements, the pharyngo-branchials, are 
 flattened, pointed plates whose free inner ends run obliquely 
 backwards, and terminate below the vertebral column. They 
 are connected at their outer ends with the short broad epi- 
 branchials (tig. 6, 16) which lie at the sides of the pharynx. 
 From the epi-branchials arise the long cerato-branchials 
 (fig. 6, 17) which run forwards and inwards along the ventral 
 wall of the pharynx. The first four cerato-branchials are 
 connected with small rods, the hypo-branchials, which run 
 backwards to meet one another in the middle line. The last 
 two pairs of hypo-branchials and the fifth cerato-branchials 
 are connected with a broad median plate, the basi-branchial. 
 Along the outer sides of the second, third and fourth cerato- 
 
THE SKELETON OF THE DOGFISH. MEDIAN FINS. 79 
 
 branchials are found elongated curved rods, the extra- 
 branchials (fig. 6, 19). The epi- branchials and cerato- 
 branchials bear gill rays along their posterior borders. 
 
 C. THE SKELETON OF THE MEDIAN FINS. 
 
 The dorsal fins have a skeleton consisting of a series of 
 short cartilaginous rods, the basals or basalia, which slope 
 obliquely backwards. Their bases are imbedded in the 
 muscles of the back, while their free ends bear a number 
 of small polygonal cartilaginous plates, the radials or radialia. 
 Associated with this cartilaginous skeleton are a number of 
 long slender horny fibres, the fin-rays, which have been already 
 referred to in connection with the exoskeleton. The skeleton 
 of the other median fins mainly consists of these fibres, the 
 cartilaginous portion being reduced or absent. 
 
 2. THE APPENDICULAR SKELETON. 
 
 This includes the skeleton of the two pairs of limbs and of 
 their respective girdles. 
 
 THE PECTORAL GIRDLE forms a crescent-shaped hoop of 
 cartilage, incomplete above and lying just behind the visceral 
 skeleton. The midventral part of the hoop is the thinnest 
 portion, and is drawn out -in front into a short rounded process 
 which is cupped dorsally and supports part of the floor of the 
 pericardium (tig. 7, 1). On each side of this flattened mid- 
 ventral portion the arch becomes very thick and bears on its 
 outer border a surface with which the three basal cartilages 
 of the fin articulate. The dorsal ends or scapular portions 
 of the girdle form a pair of gradually tapering horns. 
 
 THE PECTORAL FIN articulates with the pectoral girdle by 
 means of three basalia or basal cartilages, the pro-pterygium, 
 meso-pterygium and meta-pterygium. The most anterior 
 and the smallest of these is the pro-pterygium (fig. 7, 5), 
 
80 
 
 THE VERTEBRATE SKELETON. 
 
 while the most posterior one, the meta-pterygium. (fig. 7, 3), 
 is much the largest. Along the outer borders of the three 
 
 FIG. 7. SEMIDORSAL VIEW OF THE PECTORAL, GIRDLE AND FINS 
 
 OF A DOGFISH (Scyllium canicula) x f . 
 The gaps between the radialia are blackened. 
 
 1. hollow in the midveiitral part 5. 
 
 of the pectoral girdle which 6. 
 
 supports the pericardium. 7. 
 
 2. dorsal (scapular portion) of 8. 
 
 pectoral girdle. 9. 
 
 3. meta-pterygiuin. 
 
 4. meso-pterygium. 
 
 pro-pterygium. 
 pro-pterygial radial, 
 meso-pterygial radial, 
 meta-pterygial radial, 
 outline of the distal part of 
 
 the fin which is supported 
 
 by horny fin-rays. 
 
 basalia are arranged a series of close set cartilaginous pieces, 
 the radialia. The pro-pterygium supports only a single radial, 
 which is however much larger than any of the others. The 
 meso-pterygium also supports only a single radial which divides 
 distally. 
 
THE SKELETON OF THE DOGFISH. PELVIC GIRDLE. 81 
 
 long narrow 
 
 The meta-pterygium bears about twelve 
 radials, the first nine of which are traversed by a transverse 
 joint at about two- thirds of the way from their origin. Suc- 
 ceeding the radials are a series of small polygonal pieces of 
 cartilage arranged in one or more rows and attached to the ends 
 of the radials, and finally the fin is completed by the dermal 
 fin-rays. 
 
 FIG. 8. DORSAL VIEW OF THE PELVIC GIEDLE AND FINS OF A 
 MALE DOGFISH (Scy Ilium canicula). 
 
 1. pelvic girdle. 
 
 2. basi-pterygium. 
 
 3. clasper. 
 
 4. radialia. 
 
 THE PELVIC GIRDLE is much smaller than the pectoral. 
 It is formed of a stout nearly straight bar of cartilage placed 
 transversely across the ventral region of the body. The bar 
 has no dorsal or lateral extensions, and is terminated by short 
 blunt processes. It bears on its posterior surface a pair of 
 facets with which the pelvic fins articulate. 
 
 THE PELVIC FIN is smaller and more simply constructed 
 than is the pectoral. It consists of a long, somewhat curved 
 R. 6 
 
82 THE VERTEBRATE SKELETON. 
 
 rod, the basi-pterygium (fig. 8, 2), running directly backwards 
 on the inner side of the fin, and articulating in front with the 
 pelvic girdle. From its outer side arise a series of about 
 fourteen parallel cartilaginous radials which bear smaller 
 polygonal pieces. The anterior one or two of these radials may 
 articulate independently with the pelvic girdle. In the adult 
 male dogfish the distal end of the basi-pterygium bears a stout 
 rod nearly as long as itself, and grooved on the dorsal surface. 
 This is the skeleton of the clasper (fig. 8, 3). 
 
CHAPTER VII. 
 THE SKELETON OF THE CODFISH 1 . (Gadus morrhua.) 
 
 I. EXOSKELETON. 
 
 The exoskeleton includes 
 
 (1) Scales. These are of the type known as cycloid 
 and consist of flat rounded plates composed of concentrically 
 arranged laminae of calcined matter, with the posterior margin 
 entire. The anterior end of each scale is imbedded in the skin 
 and is overlapped by the preceding scales. 
 
 (2) The teeth. These are small, pointed, calcified struc- 
 tures arranged in large groups on the premaxillae, mandible, 
 vomer, and superior and inferior pharyngeal bones. 
 
 (3) The fin-rays. These are delicate, nearly straight 
 bony rods which support the fins. 
 
 II. ENDOSKELETON. 
 
 The endoskeleton of the Codfish, though partially carti- 
 laginous, is mainly ossified. 
 
 It is divisible into an axial portion, including the skull, 
 vertebral column, ribs, and skeleton of the median fins, and 
 an appendicular portion, including the skeleton of the 
 paired fins and their girdles. 
 
 1. THE AXIAL SKELETON. 
 A. THE VERTEBRAL COLUMN. 
 
 This consists of a series of some fifty-two vertebrae, all com- 
 pletely ossified. 
 
 1 See T. J. Parker's Zootomy, London, 1884, p. 86. 
 
 02 
 
84 THE VERTEBRATE SKELETON. 
 
 It is divisible into two regions only, viz. the trunk region, 
 the vertebrae of which bear movable ribs, and the caudal or 
 tail region, the vertebrae of which do not bear movable ribs. 
 
 Trunk vertebrae. 
 
 These are seventeen in number; the ninth may be de- 
 scribed as typical of them all. It consists of a short deeply 
 biconcave centrum whose two cavities communicate by a 
 narrow central canal. From the dorsal surface of the anterior 
 half of the centrum arise two strong plates, the dorsal or 
 neural processes, which are directed obliquely backwards 
 and meet forming the dorsal or neural arch. This is pro- 
 duced into a long backwardly - directed dorsal or neural 
 spine. 
 
 From the lower part of the anterior edge of each neural 
 arch arise a pair of blunt triangular projections which over- 
 hang the posterior half of the preceding centrum, and bear a 
 pair of flattened surfaces which correspond to the anterior 
 or pre-zygapophyses of most vertebrae, they differ however 
 from ordinary pre-zygapophyses in the fact that they look 
 downwards and outwards. From the posterior end of the 
 centrum arise a pair of short blunt processes each of which 
 bears an upwardly- and inwardly-directed articulating surface 
 corresponding to a post-zygapophysis. 
 
 The two halves of the ventral arch form a pair of large 
 ventri-lateral processes which arise from the anterior half 
 of the centrum and pass outwards and slightly backwards and 
 downwards. 
 
 Behind these there arises on each vertebra a second out- 
 growth which is small and flattened, and like the ventri- 
 lateral process serves to protect the air-bladder. The surface 
 of the centrum is marked by more or less wedge-shaped de- 
 pressions, one in the mid-dorsal line, and two on the ventral 
 surface immediately mesiad to the bases of the ventri-lateral 
 process. There are also a number of smaller depressions. 
 
THE SKELETON OF THE CODFISH. VERTEBRAE. 85 
 
 The space between one centrum and the next is in the fresh 
 skeleton filled up by the gelatinous remains of the notochord. 
 
 The first few vertebrae differ from the others in having 
 very short centra and no ventri-lateral processes. 
 
 The first vertebra comes into very close relation to the 
 posterior part of the skull, articulating with the exoccipitals. 
 In the next few vertebrae the centra gradually lengthen, 
 and at the fourth or fifth vertebra the ventri-lateral pro- 
 cesses appear and gradually increase in size as followed back. 
 They likewise gradually come to arise at a lower level on the 
 centrum, and also become more and more downwardly directed, 
 till at the last trunk vertebra they nearly meet. 
 
 The neural spines of the anterior trunk vertebrae are 
 much longer than those of the posterior ones, that of the first 
 vertebra being the largest and longest of all, and articulating 
 with the skull. The spinal nerves pass out through wide 
 notches or spaces between the successive neural arches. 
 
 Caudal vertebrae. 
 
 The caudal vertebrae are about thirty -five in number, 
 each consists of a centrum with a slender backwardly-directed 
 dorsal or neural arch, similar to those of the posterior trunk 
 vertebrae. The two halves of the ventral or haemal arch 
 however do not form outwardly-directed ventri-lateral pro- 
 cesses, but arise on the ventral surface of the centrum, and 
 passing downwards meet and enclose a space; they thus 
 form a complete canal, and are prolonged into a backwardly- 
 directed ventral or haemal spine. The anterior haemal 
 arches are much larger than the corresponding neural arches, 
 but when followed back they gradually decrease in size, till at 
 about the twenty-fourth caudal vertebra they are nearly as 
 small as the neural arches. The last caudal vertebra is suc- 
 ceeded by a much flattened hypural bone or urostyle, which 
 together with the posterior neural and haemal spines supports 
 the tail-fin. 
 
86 THE VERTEBRATE SKELETON. 
 
 B. THE RIBS. 
 
 The ribs are slender, more or less cylindrical bones at- 
 tached to the postero-dorsal faces of the ventri-lateral pro- 
 cesses of all the trunk vertebrae except the first and second. 
 The earlier ones are thicker and more curved ; the later ones 
 thinner and more nearly straight. The ribs are homologous 
 with the distal parts of the haemal arches of the caudal 
 vertebrae. 
 
 Associated with the ribs are a second series of rib-like 
 bones, the intermuscular bones. These are slender, curved 
 bones which arise from the ribs or from the ventri-lateral 
 processes at a distance of about an inch from the centra, and 
 curve upwards, outwards and backwards. In the anterior 
 region where the ventri-lateral processes are short they arise 
 from the ribs, further back they arise from the ventri-lateral 
 processes. 
 
 C. THE UNPAIRED OR MEDIAN FINS. 
 
 These are six in number, three being dorsal, one caudal 
 and two anal. 
 
 The dorsal and anal fins each consist of two sets of 
 structures, the fin-rays and the interspinous bones. Each 
 fin-ray forms a delicate, nearly straight, bony rod which 
 becomes thickened and bifurcated at its proximal or vertebral 
 end, while distally it is transversely jointed and flexible, 
 frequently also becoming more or less flattened. 
 
 The first dorsal fin has thirteen rays, the second, sixteen to 
 nineteen, the third, seventeen to nineteen. The first anal fin 
 has about twenty-two, the second anal fourteen. In each 
 fin the posterior rays rapidly decrease in size when followed 
 back. 
 
 The interspinous bones of the dorsal and anal fins 
 alternate with the neural and haemal spines respectively, and 
 form short, forwarclly-projecting bones, each attached proxi- 
 mally to the base of the corresponding fin-ray. 
 
THE SKELETON OF THE CODFISH. CAUDAL FIN. 87 
 
 The caudal fin consists of a series of about forty-three 
 rays which radiate from the posterior end of the vertebral 
 column, being connected with the urostyle or hypural bone, 
 and with the posterior neural and haemal spines without the 
 intervention of interspinous bones. Like the other fin-rays 
 those forming the caudal fin are transversely jointed, and are 
 widened and frayed out distally. 
 
 The tail -fin in the Cod is homocercal, i.e. it appears 
 to be symmetrically developed round the posterior end of 
 the vertebral column, though in reality a much greater pro- 
 portion is attached below the end of the vertebral column than 
 above it. It is a masked heterocercal tail. 
 
 THE SKULL. 
 
 Owing to the fact that very little cartilage remains in 
 the skull of the adult Codfish, its relation to the completely 
 cartilaginous skull of the Dogfish is not easily seen. Before 
 describing it therefore, the skull of the Salmon will be de- 
 scribed, as it forms an intermediate type. 
 
 THE SKULL OF THE SALMON 1 . 
 
 The Salmon's skull consists of (1) the chondrocranium, 
 which remains partly cartilaginous and is partly converted 
 into cartilage bone, especially in the occipital region, (2) a 
 large series of plate-like membrane bones. 
 
 THE CHONDROCRANIUM. 
 
 This is an elongated structure, wide behind owing to the 
 fusion of the large auditory capsules with the cranium, and 
 elongated and tapering considerably in front ; in the middle 
 it is much contracted by the large orbital cavities. 
 
 DORSAL SURFACE OF THE CRANIUM. 
 
 In the centre of the posterior end of the dorsal surface 
 is the supra- occipital (fig. 9, A, 1) with a prominent posterior 
 
 1 See W. K. Parker and G. T. Bettany, The Morphology of the Skull, 
 London, 1877, chap. 3. 
 
88 
 
 THE VERTEBRATE SKELETON. 
 
 B 
 
 ,8 
 
 18 
 
 FlG. 9. A. DORSAL AND B. VENTRAL VIEW OF THE CRANIUM OF A SALMON 
 
 (Salmo solar) from which most of the membrane bones have been 
 removed (after PARKER). Cartilage is dotted. 
 
 1. supra-occipital. 
 
 2. epi-otic. 
 
 3. pterotic. 
 
 4. sphenotic. 
 
 5. frontal. 
 
 6. median ethmoid. 
 
 7. parietal. 
 
 8. lateral ethmoid. 
 
 9. para sphenoid. 
 
 10. vomer. 
 
 11. exoccipital. 
 
 12. opisthotic. 
 
 13. alisphenoid. 
 
 14. orbitosphenoid. 
 
 16. foramen for passage of an 
 
 artery. 
 
 17. pro-otic. 
 
 18. articular surface for hyo- 
 
 mandibular. 
 
 II. VII. IX. X. foramina for the 
 passage of cranial nerves. 
 
THE SKULL OF THE SALMON. 89 
 
 ridge. It is separated by two tracts of unossified cartilage 
 from the large series of bones connected with the auditory 
 organ. The first of these is the epi-otic (fig. 9, 2), which is 
 separated by only a narrow tract of cartilage from the supra- 
 occipital, and is continuous laterally with the large pterotic 
 (fig. 9, A, 3) which overlaps in front a smaller bone, the 
 sphenotic (fig. 9, 4). Both epi-otic and pterotic are drawn out 
 into rather prominent backwardly-projecting processes. 
 
 The greater part of the remainder of the dorsal surface 
 is formed of unossified cartilage which is pierced by three 
 large vacuities or fontanelles. The anterior fontanelle is 
 unpaired, and lies far forward near the anterior end of the 
 long cartilaginous snout, the two larger posterior ones lie 
 just in front of the supra-occipital and lead into the cranial 
 cavity. In front of the orbit the skull widens again, and 
 is marked by two considerable lateral ethmoid (fig. 9, 8) 
 ossifications. In front of these are a pair of deep pits, the 
 nasal fossae, at the base of which are a pair of foramina 
 through which the olfactory nerves pass out ; they communicate 
 with a space, the middle narial cavity, seen in a longitu- 
 dinal section of the skull. 
 
 The long cartilaginous snout is more or less bifid in front, 
 especially in the male (fig. 9). 
 
 POSTERIOR END OF THE CRANIUM. 
 
 The foramen magnum forms a large round hole leading 
 into the cranial cavity, and is bounded laterally by the two 
 exoccipitals and below by them, and to a very slight extent 
 by the basi-occipital, the three bones together forming a 
 concave occipital condyle by which the vertebral column 
 articulates with the skull. 
 
 The exoccipitals are connected laterally with a fourth 
 pair of auditory bones, the opisthotics, and just meet the 
 epi-otics dorsolaterally, while dorsally they are separated by a 
 wide tract of unossified cartilage from the supra-occipital. 
 
 The opisthotics are connected laterally with the pterotics. 
 
90 
 
 THE VERTEBRATE SKELETON. 
 
 SIDE OF THE CRANIUM. 
 
 At the posterior end is seen the basi-occipital in contact 
 above with the exoccipital, which is pierced by a prominent 
 
 1 
 
 10 
 
 17 
 
 FIG. 10. LATERAL VIEW OF 
 salar) (after PARKER). 
 Cartilage is dotted. 
 1. supra-occipital, 
 epi-otic. 
 pterotic. 
 opisthotic. 
 exoccipital. 
 basi-occipital. 
 parasphenoid. 
 sphenotic. 
 alisphenoid. 
 orbitosphenoid. 
 lateral- or ectethmoid. 
 
 9. 
 10. 
 11. 
 
 THE CHONDROCRANIUM OF A SALMON (SdlmO 
 
 A few membrane bones are also shown. 
 
 12. olfactory pit ; the vomerine 
 teeth are seen just below. 
 
 14. pro-otic. 
 
 15. basisphenoid. 
 
 16. foramen for the passage of 
 
 an artery. 
 
 17. anterior fontanelle. 
 
 18. posterior fontanelle. 
 
 I. II. V. VII. IX. X. foramina 
 for the passage of cranial nerves. 
 
 foramen for the exit of the tenth nerve. In front of this lies 
 a small foramen, sometimes double, for the ninth nerve. 
 
 In front of the exoccipital is the large pro-otic pierced 
 by two prominent foramina. Through the more dorsal of these 
 (fig. 10, VII.) the facial nerve passes out, while the more 
 ventral (fig. 10, 16) is for the passage of an artery. Dorsal to 
 the exoccipital are the opisthotic and pterotic, and dorsal to 
 
THE SKULL OF THE SALMON. 91 
 
 the pro-otic is the sphenotic. The pterotic is marked by a 
 prominent groove often lined by cartilage, which is continued 
 forwards along a tract of cartilage between the pro-otic and 
 sphenotic. With this groove the hyomandibular articulates. 
 
 There are considerable ossifications in the sphenoidal region 
 of the side of the cranium. The anterior boundary of the pos- 
 terior fontanelle is formed by the large alisphenoid, which 
 is continuous behind with the pro-otic and sphenotic, and 
 below with a slender basisphenoid. Both in front of and 
 behind the basisphenoid there are considerable vacuities in the 
 walls of the cranium ; through the posterior of these openings 
 (fig. 10, V.) the main part of the trigeminal nerve passes out, 
 and through the anterior one, the optic (fig. 10, II.). The 
 alisphenoid is continuous in front with the orbitosphenoid 
 (fig. 10, 10), which is pierced by the foramen for the exit of 
 the first nerve (fig. 10, I.), and in front of the orbitosphenoid 
 there is a large vacuity. The lateral ethmoid is seen in the 
 side view as well as in the dorsal view. Further forwards are 
 seen the olfactory pits, and the long cartilaginous snout. 
 
 A ventral view of the cartilaginous cranium shows much 
 the same points as the side view. The basisphenoid appears 
 on the surface immediately in front of the basi-occipital. 
 
 THE SKULL WITH MEMBRANE BONES. 
 
 The dorsal surface. The greater part of the dorsal 
 surface in front of the supra-occipital is overlaid by a pair 
 of large rough f rentals (figs. 9, A, 5, and 10, 5). They cover 
 the posterior fontanelles and stretch over from the sphenotic 
 to the lateral ethmoid, forming a roof for the orbit. They 
 meet in the middle line behind, but in front are separated 
 by a narrow tract of unossified cartilage, and are overlapped 
 by the median ethmoid (figs. 9, A> 6, and 11, 6). At the sides 
 of the supra occipital behind the f rentals are a pair of small 
 parietals (tigs. 9, A, 7, and 11, 7). 
 
 In a ventral view the cranium is seen to be chiefly 
 
92 
 
 THE VERTEBRATE SKELETON. 
 
 FIG. 11. LATERAL VIEW OF THE SKULL or A SALMON (Salmo solar) 
 (after PARKER). Cartilage is dotted. 
 
 1. supra-occipital. 
 
 2. epi-otic. 
 
 3. pterotic. 
 
 4. sphenotic. 
 
 5. frontal. 
 
 6. median ethmoid. 
 
 7. parietal. 
 
 8. nasal. 
 
 9. lachrymal. 
 
 10. sub-orbital. 
 
 11. supra-orbital. 
 
 12. cartilaginous sclerotic. 
 
 13. ossification in sclerotic. 
 
 14. meso-pterygoid. 
 
 15. meta-pterygoid. 
 
 16. palatine. 
 
 17. jugal. 
 
 18. quadrate. 
 
 19. maxilla. 
 
 20. premaxilla. 
 
 21. articular. 
 
 22. angular. 
 
 23. dentary. 
 
 24. hyomandibular. 
 
 25. symplectic. 
 
 26. epi-hyal. 
 
 27. cerato-hyal. 
 
 28. hypo-hyal. 
 
 29. glosso-hyal. 
 
 30. opercular. 
 
 31. sub-opercular. 
 
 32. infra- opercular. 
 
 33. pre-opercular. 
 
 34. supratemporal. 
 
 35. branchiostegal rays. 
 
 36. basi-branchiostegal. 
 
THE SKULL OF THE SALMON. 93 
 
 covered by two large membrane bones, the parasphenoid 
 (fig. 9, B, 9) behind, the vomer in front. A view of the 
 posterior end differs from that of the cartilaginous cranium 
 only in the fact that the end of the parasphenoid appears 
 lying ventral to the basi-occipital. 
 
 The lateral view differs very markedly from that of the 
 cartilaginous cranium, there being a great development of 
 membrane bone in connection with the jaws and branchial 
 apparatus. Lying dorsally are seen the median ethmoid, frontal, 
 parietal, and supra-occipital as before. Lying external to 
 the middle of the median ethmoid is seen the small nasal 
 (fig. 11, 8), and below the hinder part is the lachrymal The 
 lachrymal (fig. 11, 9) forms the first of a series of seven small 
 bones which surround the orbit forming the orbital ring. 
 Of these the one lying immediately in the mid ventral line of 
 the orbit is the sub-orbital, while the one lying in the mid- 
 dorsal line and attached to the frontal is the supra-orbital 
 (fig. 11, 11). The orbit has a cartilaginous sclerotic in which 
 are two small ossifications (fig. 11, 13) laterally placed. 
 
 BONES OF THE UPPER JAW. 
 
 The palato-pterygo-quadrate bar is in a very different 
 condition from that of the dogfish, it is partially cartilaginous, 
 partially converted into cartilage bone, partially overlapped by 
 membrane bone. It is narrow in front but becomes much 
 broader and deeper when followed back. Its anterior end forms 
 the palatine which bears teeth, and in front is completely 
 ossified, while behind the cartilage is only sheathed by bone. 
 
 Just behind the palatine the outer part of the cartilage is 
 ossified, forming two small bones, the pterygoid and meso- 
 pterygoid, while behind them is a larger, somewhat square 
 bone, the meta-pterygoid (fig. 11, 15). 
 
 Below the meta-pterygoid is a tract of unossified carti- 
 lage, and then comes the quadrate (fig. 11, 18). 
 
94 THE VERTEBRATE SKELETON. 
 
 The lower angle of the quadrate bears a cartilaginous con- 
 dyle with which the mandible articulates. In front of the 
 palatine the cartilaginous snout is overlapped by three mem- 
 brane bones, the jugal, maxilla and preinaxilla. 
 
 The premaxilla (fig. 11, 20), the largest of these, overlaps 
 the maxilla behind ; both bones bear teeth. The jugal (fig. 11, 
 17) lies above the maxilla and overlaps it in front. 
 
 THE LOWER JAW. 
 
 The lower jaw is a strong bar and is like the upper jaw, 
 partly cartilaginous, forming Meckel's cartilage, partly ossi- 
 fied, and sheathed to a considerable extent in membrane bone. 
 
 The outer side and posterior end is ossified, forming the 
 large articular (fig. 11, 21), but the condyle is cartilaginous 
 and the anterior part of the articular forms merely a splint on 
 the outer side of Meckel's cartilage, which extends beyond it 
 for a considerable distance. The angle of the jaw just below 
 the condyle is formed by a small angular (fig. 11, 22), and the 
 anterior two-thirds of the jaw is sheathed in the large tooth- 
 bearing dentary (fig. 11, 23). , 
 
 THE HYOID ARCH. 
 
 The hyoid arch has a number of ossifications in it and is 
 closely connected with the mandibular arch. 
 
 The hyomandibular (fig. 11, 24) is a large bone which 
 articulates with a shallow groove lined by cartilage and formed 
 partly in the pterotic, partly in front of it. The hyomandibular 
 is overlapped in front by the meta-pterygoid, while below it 
 tapers and is succeeded by a small area of unossified cartilage 
 followed by the forwardly-directed symplectic which fits 
 into a groove in the quadrate. 
 
 The unossified tract between the hyomandibular and sym- 
 plectic is continuous in front with a strong bar, which remains 
 partly cartilaginous and is partly converted into cartilage 
 bone. The proximal part is ossified, forming the epi-hyal, the 
 
THE SKULL OF THE SALMON. 
 
 middle part forms the cerato-hyal (fig. 11, 27), in front of 
 which is the small hypo-hyal. The hyoid arches of the two 
 sides are united by the large tooth-bearing glosso-hyal (fig. 11, 
 29). Attached to the lower surface of the hyoid arch are a series 
 of twelve flat branckiostegal rays (fig. 11, 35). Each overlaps 
 the one in front of it, the posterior one being the largest. The 
 branchiostegal rays of the two sides are united in front by an 
 unpaired membrane bone, the basi-branchiosteyal (fig. 11, 36). 
 
 Opercular bones. Behind the hyomandibular there is a 
 large bony plate, the operculum, formed of four large mem- 
 brane bones. The anterior of these, the pre-opercular (fig. 11, 
 33), is crescentic in shape, and with its upper end a small 
 supra-temporal (fig. 11, 34) is connected. 
 
 Behind the upper part of the pre-opercular is the largest of 
 the opercular bones, the opercular proper. Its lower edge 
 overlaps the sub-opercular, and both opercular and sub- 
 opercular are overlapped by the infra- opercular (fig. 11, 32) 
 in front. The infra -opercular is in its turn overlapped by 
 the pre-opercular. 
 
 BRANCHIAL ARCHES. 
 
 There are five branchial arches, the first four of which 
 bear gill rays. Each of the first three consists of a shorter 
 upper portion directed obliquely backwards and outwards, 
 and a longer lower portion forming a right angle with the 
 upper and directed obliquely forwards and inwards. The 
 greater part of each arch is ossified. 
 
 The upper part of either of the first two consists of a short 
 tapering pharyngo-branchial directed inwards, and of a 
 long epi-branchial tipped with cartilage at both ends. The 
 junction of the upper and lower parts is formed by a carti- 
 laginous hinge-joint between the epi-branchial and cerato- 
 branchial. The cerato-branchial is a long bony rod sepa- 
 rated by a short area of cartilage from the hypo -branchial, 
 which is succeeded by the basi-branchial meeting its fellow 
 
96 THE VEHTEBRATE SKELETON. 
 
 in the middle line. The fourth arch has a short epi-branchial 
 and no ossified pharyn go-branchial, while the fifth is reduced 
 to little more than the cerato-branchial, which bears a few 
 teeth on its inner edge. All the branchial arches have pro- 
 jecting from their surfaces a number of little processes which 
 act as strainers. The first and fourth arches have one series 
 of these, the second and third have two. 
 
 THE SKULL OF THE CODFISH 1 . 
 
 A full description having been already given of the Salmon's 
 skull, that of the Codfish will be described in a briefer manner. 
 The skull is very fully ossified, and the great number of plate- 
 like bones render it a very complicated structure. 
 
 THE CRANIUM. 
 
 At the posterior end of the dorsal surface is the large 
 supra-occipital, which is drawn out behind into the large 
 blade-like occipital spine. On each side of the supra-occi- 
 pital are the small irregular parietals, while in front of it the 
 roof of the skull is mainly formed by the very large unpaired 
 frontal. 
 
 A complicated series of bones are developed in connection 
 with the auditory capsule, which forms a large projecting 
 mass united with the side of the cranium and drawn out be- 
 hind into a pair of strong processes, the epi-otic and parotic 
 processes. Both these processes are connected behind with a 
 large Y-shaped bone, the post-temporal (fig. 13, 1), which will 
 be described when dealing with the pectoral girdle. The epi- 
 otic process is formed by the epi-otic, which is continuous in 
 front with the parietal. The parotic process is formed by 
 two larger bones, a more dorsal one, the pterotic, and a more 
 ventral and internal one, the opisthotic, which is continuous 
 in front with the large pro-otic. Intervening between the 
 
 1 T. J. Parker, Zootomy, London, 1884, p. 91. 
 
THE SKELETON OF THE CODFISH. THE SKULL. 97 
 
 pterotic and frontal is another rather large bone, the sphenotic, 
 this articulates below with the pro-otic. The pterotic and 
 sphenotic together give rise to a large concave surface by 
 which the hyomandibular articulates with the cranium. 
 Several of the cranial nerves pass out through the bones of 
 the auditory capsule. The ninth leaves by a foramen near 
 the posterior border of the opisthotic, the fifth and seventh by 
 a notch in the anterior border of the pro-otic. 
 
 A number of bones are likewise developed in connection 
 with the orbit forming the orbital ring. Of these the most 
 anterior, the lachrymal, is much the largest, the others are 
 five to seven in number, the most ventral being the suborbital. 
 The sclerotic coat of the eye is cartilaginous. 
 
 Two pairs of bones and one unpaired bone are developed in 
 connection with the olfactory capsules, of these, the nasals 
 are narrow bones lying next the lachrymals, but nearer the 
 middle line ; they overlap the second pair of bones, the ir- 
 regular lateral ethmoids. These meet one another in the 
 middle line, and are overlapped behind by the frontal. They 
 articulate laterally with the lachrymal and palatine, and ven- 
 trally with the parasphenoid. 
 
 In a posterior view the foramen magnum and the four 
 bones which surround it and together form the occipital seg- 
 ment are well seen. On the ventral side is the basi-occipital, 
 terminated posteriorly by a slightly concave surface which 
 articulates with the centrum of the first vertebra. The sides 
 of the foramen magnum are formed by the exoccipitals, a 
 pair of very irregular bones, pierced by a pair of prominent 
 foramina for the exit of the tenth nerves. The exoccipitals 
 also bear a pair of surfaces for articulation with corresponding 
 ones on the neural arch of the first vertebra. The most dorsal 
 of the four bones is the supra- occipital. 
 
 On the ventral surface of the cranium in front of the basi- 
 occipital is seen the parasphenoid, a very long narrow bone 
 which underlies the greater part of the cranium. Behind, it 
 R. 7 
 
98 THE VERTEBRATE SKELETON. 
 
 articulates dorsally with the basi-occipital and dorsolaterally 
 with the pro-otics and opisthotics, in front it articulates 
 dorsally with the lateral ethmoid and ventrally with the 
 vomer. At the sides of the parasphenoid are the small ali- 
 sphenoids articulating above with the postf rentals, in front 
 with the frontals, and behind with the pro-otics. 
 
 The vomer is an unpaired bone lying immediately in front 
 of the parasphenoid. In front it terminates with a thickened 
 curved margin bearing several rows of small teeth ; behind 
 it tapers out into a long process which underlies the anterior 
 part of the parasphenoid. Immediately dorsal to the vomer 
 is another median bone, the median ethmoid] this is truncated 
 in front and tapers out behind into a process which fits into a 
 groove on the ventral side of the frontal. 
 
 BONES IN CONNECTION WITH THE UPPER JAW. 
 
 These bear a close resemblance to those of the Salmon. 
 The most anterior bone is the premaxilla, a thick curved bone 
 meeting its fellow in the middle line. The point of junction 
 of the two is drawn out into a short process, and the oral 
 surface is thickly covered with small teeth. The dorsal ends 
 of the premaxillae are seen in the fresh skull to meet a large 
 patch of cartilage. Behind the premaxilla is the maxilla, a 
 long rod-like toothless bone, somewhat expanded at the upper 
 end where it articulates with the premaxilla and vomer. 
 
 Articulating in front with the anterior end of the maxilla 
 and with the lateral ethmoid is a very irregular bone, the 
 palatine (fig. 12, 1); it articulates behind with two flat 
 bones, the pterygoid and meso-pterygoid. The ptery- 
 goid is united behind with two more bones, the quadrate 
 (fig. 12, 4) and meta-pterygoid. The quadrate is a rather 
 stout irregular bone, bearing on its lower surface a promi- 
 nent saddle-shaped articulating surface for the mandible. 
 The palatine, pterygoid and quadrate bones are the ossified 
 
THE SKELETON OF THE CODFISH. UPPER JAW. 99 
 
 representatives of the palato-ptery go-quad rate bar of the 
 Dogfish. 
 
 FIG. 12. MANDIBULAR AND HYOID ARCHKS OF A COD (Gadus 
 
 morrhua) x (Brit. Mus.). 
 
 1. palatine. 
 
 2. meso-pterygoid. 
 
 3. pterygoid. 
 
 4. quadrate. 
 
 5. symplectic. 
 
 6. meta-pterygoid. 
 
 7. hyomandibular. 
 
 8. angular. 
 
 9. articular. 
 
 10. dentary. 
 
 11. inter- hyal. 
 
 12. epi-hyal. 
 
 13. cerato-hyal. 
 
 14. hypo-hyal. 
 
 15. uro-hyal. 
 
 16. branchiostegal rays. 
 
 The quadrate is united behind with the symplectic 
 (fig. 12, 5), and the meta-pterygoid with the symplectic and 
 hyomandibular, both of which bones will be described im- 
 mediately in connection with the hyoid arch. 
 
 72 
 
100 THE VERTEBRATE SKELETON. 
 
 THE LOWER JAW. 
 
 The lower jaw or mandible like that of the Salmon is 
 partly cartilaginous, forming Meckel's cartilage, partly 
 formed of cartilage bone, partly of membrane bone. Meckel's 
 cartilage is of course not seen in the dried skull. 
 
 The lower jaw includes one cartilage bone, the articular 
 (fig. 12, 9), this is a large bone connected by a saddle- 
 shaped surface with the quadrate. Meckel's cartilage lies in 
 a groove on its under surface, and projects beyond it in front. 
 The angular is a small thick bone united to the lower surface 
 of the articular at its posterior end. The dentary (fig. 12, 10) 
 is a large tooth-bearing bone meeting its fellow in the middle 
 line in front, while the articular fits into a deep notch at its 
 posterior end. 
 
 THE HYOID ARCH. 
 
 The hyomandibular (fig. 12, 7) is a large irregular bone, 
 articulating by a prominent rounded head with the spbenotic 
 and pterotic. It is united in front with the meta-pterygoid 
 and symplectic, and sends off behind a strong process which 
 articulates with the opercular. The symplectic is a long 
 somewhat triangular bone drawn out in front into a process 
 which fits into a groove on the inner surface of the quadrate. 
 The distal portion of the hyoid arch is strongly developed and 
 consists of first the inter-hyal (fig. 12, 11), a short bony rod, 
 which articulates dorsally with a patch of cartilage intervening 
 between the posterior part of the hyomandibular and the sym- 
 plectic. Below it is united with the apex of the triangular 
 epi-hyal, a bone suturally connected with the large cerato- 
 hyal (fig. 12, 13) which unites distally with two small hypo- 
 hyals. To the cerato-hyal are attached a series of seven 
 strong curved cylindrical rods, the branchiostegal rays. The 
 first of these is the smallest and they increase in size up to the 
 last. The four dorsal ones are attached to the outer surface 
 of the cerato-hyal, the three ventral ones to its inner surface. 
 
THE SKELETON OF CODFISH. BRANCHIAL ARCHES. 101 
 
 Interposed between the hypo-hyals of the two sides is an 
 unpaired somewhat triangular plate, the uro-hyal or basi- 
 branchiosteyal (fig. 12, 15). 
 
 THE BRANCHIAL ARCHES. 
 
 The branchial arches are five in number and consist of 
 the following parts on each side. The dorsal end is formed of 
 the supra-pharyngeal bone, a large irregular bone covered 
 ventrally with teeth of a fair size, and representing the fused 
 pharyngo-branchials of the four anterior arches. Its external 
 surface is continuous with four small epi-branchials which 
 pass horizontally backwards and outwards. Their distal ends 
 meet four long cerato-branchials which are directed for- 
 wards and inwards and form the principal part of the arches. 
 
 Each of the first three cerato-branchials articulates ven- 
 trally with a hypo-branchial, and the hypo-branchials of 
 the two sides are united in the middle line by an unpaired 
 basi-branchial. The third hypo-branchial is much flattened. 
 The fourth cerato-branchial is united by cartilage with the 
 posterior surface of the third hypo-branchial, which it meets 
 near the middle line. 
 
 The fifth arch consists only of the cerato-branchial, a wide 
 structure covered with teeth and generally called the inferior 
 pharyngeal bone. 
 
 The skeleton of the operculum consists of the same four 
 bones as in the Salmon, namely the opercular, the infra- 
 opercular, the pre-opercular and the sub-opercular. Of these 
 the anterior bone, the pre-opercular, is the largest, while the 
 infra-opercular is the smallest. The opercular has a facet for 
 articulation with the hyomandibular. 
 
 2. THE APPENDICULAR SKELETON. 
 
 THE PECTORAL GIRDLE. 
 
 This is of a highly specialised type. Membrane bones are 
 greatly developed, and the cartilage bones, the scapula and 
 coracoid, are much reduced in size and importance. 
 
102 
 
 THE VERTEBRATE SKELETON. 
 
 The largest bone in the shoulder girdle is the clavicle 
 (tig. 13, 3), which is irregularly crescent shaped, thick in front 
 
 FIG. 13. THE EIGHT HALF or THE PECTORAL GIRDLE AND RIGHT 
 PECTORAL FIN OF A COD (Gadus morrhua) x \ (Brit. Mus.). 
 
 post-temporal. 5. scapula, 
 
 supra-clavicle. 6. post-clavicle, 
 
 clavicle. 7. bracbial ossicles, 
 
 coracoid. 8. dermal fin-rays. 
 
 and tapering off behind. To the outer side of its upper part 
 is attached a thick cylindrical bone, the supra-clavicle, which 
 passes upwards and is connected with a strong V shaped 
 bone, the post-temporal. The apex of the V meets the supra- 
 clavicle, the inner limb articulates with the epi-otic process, 
 the outer with the parotic process. Projecting downwards from 
 the upper part of the clavicle is a long bony rod, flattened 
 
THE SKELETON OF THE CODB'ISH. THE FINS. 103 
 
 proximally and cylindrical and pointed distally, this is the 
 post-clavicle (fig. 13, 6). 
 
 The scapula (fig. 13, 5) is a small irregular plate of bone 
 attached to the inner side of the middle of the clavicle. The 
 coracoid 1 is a larger plate of similar character, irregularly 
 triangular in shape, attached to the inner side of the clavicle 
 immediately below the scapula. The scapula and coracoid 
 bear the pectoral fin. 
 
 THE PECTORAL FINS. 
 
 Each of these consists of four small irregular bones, the 
 brachial ossicles (fig. 13, 7), bearing a series of about nineteen 
 dermal Jin-rays. The brachial ossicles represent the reduced 
 and modified radialia and basalia of cartilaginous fish such as 
 the dogfish. The fin-rays (fig. 13, 8) which form the whole 
 external portion of the fin are long slender rods having 
 essentially the same character as those of the unpaired fins. 
 
 THE PELVIC GIRDLE. 
 
 The pelvic girdle in the Cod as in other Teleosteans is 
 entirely absent, its place being taken by the enlarged basi- 
 pterygia of the fins. 
 
 THE PELVIC FINS. 
 
 These have a very anomalous position in the Cod, being 
 attached to the throat in front of the pectoral girdle. Each 
 consists of a basal portion, the basi-pterygium, and of a 
 number of dermal rays. The basi-pterygium consists of an 
 expanded ventral portion which meets its fellow below in the 
 middle line, and to which the rays are attached, and of an in- 
 wardly-directed dorsal portion which also meets its fellow and 
 is imbedded in the flesh. The rays are six in number and 
 are long slender structures similar to those of the other fins. 
 
 1 According to G. Swirski, Sckultergurtel des Hechtes, Dorpat, 1880, 
 the true coracoid is aborted, and the so-called coracoid of Teleosteans is 
 really the precoracoid. 
 
CHAPTER VIII. 
 
 GENERAL ACCOUNT OF THE SKELETON IN 
 FISHES 1 . 
 
 EXOSKELETON. 
 
 The most primitive type of exoskeleton is that found in 
 Elasmobranchs and formed of placoid scales; these are tooth- 
 like structures consisting of dentine and bone capped with 
 enamel, and have been already described (p. 4). In most 
 Elasmobranchs they are small and their distribution is fairly 
 uniform, but in the Thornback skate, Raia clavata, they have 
 the form of larger, more scattered spines. In adult Holo- 
 cephali and in Polyodon and Torpedo there is no exoskeleton, 
 in young Holocephali, however, there are a few small dorsal 
 ossifications. 
 
 The plates or scales of many Ganoids may have been 
 formed by the gradual fusion of elements similar to these 
 placoid scales, and often bear a number of little tooth-like 
 processes. In Lepidosteus, Polypterus, and .many extinct 
 species, these ganoid scales, which are rhomboidal in form 
 and united to one another by a peg and socket articulation, 
 enclose the body in a complete armour. In Trissolepis part of 
 the tail is covered by rhomboidal scales, while rounded scales 
 cover the trunk and remainder of the tail. Acipenser and 
 Scaphirhynchus have large dermal bony plates which are not 
 rhomboidal in shape and do not cover the whole body. In 
 
 1 The following general works on fishes may be referred to : Bashford 
 Dean, Fishes, Living and Fossil, New York, 1895. A. Giinther, An 
 Introduction to the Study of Fishes, Edinburgh, 1880. A. A. W. Hubrecht 
 and M. Sagemehl, Fische in Bronn's Classen und Ordnungen des Thier- 
 reichs, Band vi. Leipzig, 1876. 
 
THE SKELETON IN FISHES. SCALES AND FIN-RAYS. 105 
 
 Acipenser a single row extends along the middle of the back 
 and two along each side. 
 
 The majority of Teleosteans have thin flattened scales 
 which differ from those of Ganoids in being entirely meso- 
 dermal in origin, containing no enamel. There are two prin- 
 cipal types of Teleostean scales, the cycloid and ctenoid. A 
 cycloid scale is a flat thin scale with concentric markings 
 and an entire posterior margin. A ctenoid scale differs in 
 having its posterior margin pectinate. The Dipnoi have over- 
 lapping cycloid scales. The rounded scales of Amia and of many 
 fossil ganoids such as Holoptychius are shaped like cycloid 
 scales, but differ from them in being more or less coated with 
 enamel. In Eels and some other Teleosteans the scales are 
 completely degenerate and have almost disappeared. Some 
 Teleosteans, like Diodon hystrix, have scales with triradiate 
 roots from which arise long sharp spines directed backwards. 
 These scales, which resemble teeth, contain no enamel ; they 
 become erect when the fish inflates its body into a globular 
 form. Many Siluroids have dermal armour in the form of 
 large bony plates which are confined to the anterior part 
 of the body. In Ostracion the whole body is covered by 
 hexagonal plates, closely united together. 
 
 The fin-rays are structures of dermal origin which entirely 
 or partially support the unpaired fins, and assist the bony 
 or cartilaginous endoskeleton in the support of the paired fins. 
 
 In Elasmobranchs, Dipnoi, and Chondrosteous ganoids the 
 skeletons of the fins are, as a rule, about half of exoskeletal, 
 half of endoskeletal origin, the proximal and inner portion 
 being cartilaginous and endoskeletal, the distal and outer portion 
 being exoskeletal, and consisting of horny or of more or less 
 calcified fin-rays. In bony Ganoids and Teleosteans the endo- 
 skeletal parts are greatly reduced and the fins come to consist 
 mainly of the fin-rays, which are ossified and frequently become 
 flattened at their distal ends. 
 
 The fin-rays of the ventral part of the caudal fin are carried 
 
106 THE VERTEBRATE SKELETON. 
 
 by the haemal arches ; those of the dorsal and anal fins and 
 of the dorsal part of the caudal fin generally by interspinous 
 bones, which in adult Teleosteaiis alternate with the neural 
 and haemal spines. In Dipnoi these interspinous bones arti- 
 culate with the neural and haemal spines. In many Siluroids 
 the anterior rays of the dorsal and pectoral fins are developed 
 into large spines which often articulate with the endoskeleton, or 
 are sometimes fused with the dermal armour plates. Similar 
 spines may occur in Ganoids in front of both the dorsal and 
 anal fins. Polypterus has a small spine or fulcrum in front of 
 each segment of the dorsal fin. Such spines are often found 
 fossilised, and are known as iclithyodorulites. 
 
 Similar spines are found in many Elasmobranchs, but they 
 are simply inserted in the fiesh, not articulated to the endo- 
 skeleton. They also differ from the spines of Teleosteans 
 and Ganoids in the fact that they are covered with enamel, 
 and often have their edges serrated like teeth. In the extinct 
 Acanthodii they generally occur in front of all the fins, paired 
 and unpaired. 
 
 In Trygon, the Sting-ray, the tail bears a serrated spine 
 which is used for purposes of offence and defence. Many 
 ichthyodorulites may have been spines of this nature fixed to 
 the tail, rather than spines situated in front of the fins. The 
 spines, which are always found in front of the dorsal fin in 
 Holocephali, agree with those of Elasmobranchs in containing 
 enamel, and with those of Teleosteans in being articulated to 
 the endoskeleton. 
 
 TEETH. 
 
 The teeth of fish 1 are subject to a very large amount of 
 variation, perhaps to more variation than are those of any 
 other class of animals. Sometimes, as in adult Sturgeons, 
 they are entirely absent, sometimes they are found on all the 
 
 i See W. G. Eidewood, Nat. Sci. vol. vin. 1896, p. 380. Full references 
 are there given to the literature of the subject. 
 
THE SKELETON IN FISHES. THE TEETH. 
 
 107 
 
 bones of the mouth, and also on the hyoid and branchial 
 arches. The teeth are all originally developed in the mucous 
 membrane of the mouth, but they afterwards generally become 
 
 5-' 
 
 FIG. 14. DIAGRAM OF A SECTION THROUGH THE JAW OF A SHARK (Odontaspis 
 
 americanus) showing the 
 specimen and diagram). 
 
 1. teeth in use. 
 
 2. teeth in reserve. 
 
 3. skin. 
 
 4. cartilage of the jaw. 
 
 5. encrusting calcification 
 
 succession of teeth (Brit. Mus. from 
 
 cartilage. 
 
 6. connective tissue. 
 
 7. mucous membrane of the 
 
 mouth, 
 of 
 
 attached to firmer structures, especially to the jaws. In 
 Elasmobranchs, however, they are generally simply imbedded 
 in the tough fibrous integument of the mouth. Their attach- 
 ment to the jaws may take place in three different ways. 
 
 (1) By an elastic hinge-joint, as in the Angler (Lophius), 
 and the Pike (Esox lucius). In the Angler the tooth is held 
 by a fibrous band attaching its posterior end to the subjacent 
 bone, in the Pike by uncalcified elastic rods in the pulp cavity. 
 
 (2) By ankylosis, i.e. by the complete union of the cal- 
 cined tooth substance with the subjacent bone. This is the 
 commonest method among fish. 
 
108 
 
 THE VERTEBRATE SKELETON. 
 
 (3) By implantation in sockets. This method is not very 
 common among fish. The teeth are sometimes, as in -Lepi- 
 dosteus, ankylosed to the base of the socket. In this genus 
 there is along each ramus of the mandible a median row of 
 large teeth placed in perfect sockets, and two irregular lateral 
 rows of small teeth ankylosed to the jaw. 
 
 Dentine, enamel and cement are all represented in the teeth 
 of fishes, but the enamel is generally very thin, and cement is 
 but rarely developed. Dentine forms the main bulk of the 
 teeth; it is sometimes of the normal type, but generally differs 
 from that in higher vertebrates in being vascular, and is 
 known as vasodentine. A third type occurs, known as osteo- 
 dentine ; it is traversed by canals occupied by marrow, and is 
 closely allied to bone. 
 
 FIG. 15. PAKT OF THE LOWEB JAW OF A SHABK (Galeus) 
 (from OWEN after ANDREA. 
 
 1. teeth in use. 
 
 2. reserve teeth folded back. 
 
 3. part of the caudal spine of 
 
 a Sting-ray (Trygon) which has 
 pierced the jaw and affected the 
 growth of the teeth. 
 
 The teeth are generally continually renewed throughout life, 
 but sometimes one set persists. 
 
 The teeth of Selachii are fundamentally identical with 
 
THE SKELETON IN FISHES. THE TEETH. 109 
 
 placoid scales. They are developed from a layer of dental germs 
 which occurs all over the surface of the skin, except in the 
 region of the lips. At this point the layer of tooth-producing 
 germs extends back into the mouth, being projected by a fold 
 of the mucous membrane (fig. 14, 7). Here new teeth are 
 successively formed, and as they grow each is gradually 
 brought into a position to take the place of its predecessor 
 by the shifting outwards of the gum over the jaw. Owing to 
 this arrangement sharks have practically an unlimited supply 
 of teeth (figs. 14 and 15). 
 
 Two principal types of teeth are found in ELASMOBRANCHS. 
 In Sharks and Dogfish, on the one hand, the teeth are very 
 numerous, simple, and sharp-pointed, and are with or without 
 serrations and lateral cusps. Many Rays and fossil Elasmo- 
 branchs, on the other hand, have broad flattened teeth adapted 
 for crushing shells. Intermediate conditions occur between 
 these two extremes. Thus in Cestracion and many extinct 
 sharks, such as Acrodus, while the median teeth are sharp, 
 the lateral teeth are more or less flattened and adapted for 
 crushing. In various species belonging to the genus Raia the 
 teeth of the male are sharp, while those of the female are blunt. 
 A very specialised dentition is met with in the Eagle-rays 
 (Myliobatidae), in which the jaws are armed with flattened 
 angular tooth-plates, arranged in seven rows, forming a com- 
 pact pavement ; the plates of the middle row are very wide 
 and rectangular, those of the other rows are much smaller and 
 hexagonal. Lastly, in Cochliodus the individual crushing 
 teeth are fused, forming two pairs of spirally-coiled dental 
 plates on each side of each jaw. Pristis, the Saw-fish, has a 
 long flat cartilaginous snout, bearing a double row of persist- 
 ently-growing teeth planted in sockets along its sides. Each 
 tooth consists of a number of parallel dentinal columns, united 
 at the base, but elsewhere distinct. 
 
 In the HOLOCEPHALI Ckimaera, Hariotta and Callorhyn- 
 c h us only three pairs of teeth or dental plates occur, two 
 
110 THE VERTEBRATE SKELETON. 
 
 pairs in the upper jaw, one in the lower. These structures 
 persist throughout life and grow continuously. The upper 
 tooth structures are attached respectively to the ethmoid or 
 vomerine region of the skull, and to the palato-pterygoids. The 
 vomerine teeth are small, while those attached to the mandible 
 and the palato-pterygoid region are large and bear several 
 roughened ridges adapted for grinding food. The teeth of 
 the two opposite sides of the jaw meet in a median symphysis. 
 The teeth of Chimaera are more adapted for cutting, those of 
 Callorhynchus for crushing. Many extinct forms are known, 
 some of whose teeth are intermediate in structure between 
 those of Chimaera and Callorhynchus. 
 
 The teeth of GANOIDS are also extremely variable. Among 
 living forms, the Holostei are more richly provided with teeth 
 than are any other fishes, as they may occur on the pre- 
 maxillae, maxillae, palatines, pterygoids, parasphenoid, voiners, 
 dentaries, and splenials. Among the Chondrostei, on the other 
 hand, the adult Acipenseridae are toothless ; small teeth how- 
 ever occur in the larval sturgeon, and in Polyodon many 
 small teeth are found attached merely to the mucous membrane 
 of the jaws. Many fossil Ganoids have numerous flattened or 
 knob-like teeth, borne on the maxillae, palatines, vomers and 
 dentaries. Others have a distinctly heterodont dentition. 
 Thus in Lepidotus the prernaxillae bear chisel-like teeth, while 
 knob-like teeth occur on the maxillae, palatines and vomers. 
 In Rhizodus all the teeth are pointed, but while the majority 
 are small a few very large ones are interspersed. 
 
 In TELEOSTEANS, too, the teeth are eminently variable both 
 in form and mode of arrangement. They may be simple and 
 isolated, or compound, and may be borne on almost any of the 
 bones bounding the mouth cavity, and also as in the Pike, on 
 the hyoid and branchial arches. The splenial however never 
 bears teeth and the pterygoid and parasphenoid only rarely, 
 thus differing from the arrangement in the Holostei. 
 
 The isolated teeth are generally conical in form and are 
 
THE SKELETON IN FISHES. THE TEETH. Ill 
 
 ankylosed to the bone that bears them. Such teeth are, 
 with a few exceptions such as Balistes, not imbedded in 
 sockets nor replaced vertically. 
 
 In some fish beak-like structures occur, formed partly of 
 teeth, partly of the underlying jaw bones. These beaks are of 
 two kinds : (1) In Scarus, the parrot fish, the premaxillae and 
 dentaries bear numerous small, separately developed teeth, 
 which are closely packed together and attached by their 
 proximal ends to the bone, while their distal ends form a 
 mosaic. Not only the teeth but the jaws which bear them 
 are gradually worn away at the margins, while both grow 
 continuously along their attached edge. (2) In Gymnodonts, 
 e.g. Diodon, the beaks are formed by the coalescence of broad 
 calcified horizontal plates, which when young are free and 
 separated from one another by a considerable interval. 
 
 In some Teleosteans the differentiation of the teeth into 
 biting teeth and crushing teeth is as complete as in Lepi- 
 dosteus. Thus in the Wrasse (Labrus), the jaws bear conical 
 slightly recurved teeth arranged in one or two rows, with some 
 of the anterior ones much larger than the rest. The bones of 
 the palate are toothless, while both upper and lower pharyngeal 
 bones are paved with knob-like crushing teeth ; such pharyn- 
 geal teeth occur also in the Carp but are attached only to the 
 lower pharyngeal bone, the jaw bones proper being toothless. 
 
 In DIPNOI the arrangement of the teeth is very similar to 
 that in Holocephali. The mandible bears a single pair of 
 grinding teeth attached to the splenials, and a corresponding 
 pair occur on the palato-pterygoids. In front of these there 
 are a pair of small conical vornerine teeth loosely attached to the 
 ethmoid cartilage. The palato-pterygoid teeth of Ceratodus 
 are roughly semicircular in shape with a smooth convex inner 
 border, and an outer border bearing a number of strongly 
 marked ridges. The teeth of the extinct Dipteridae resemble 
 those of Ceratodus but are more complicated. 
 
112 THE VERTEBRATE SKELETON. 
 
 ENDOSKELETON. 
 
 SPINAL COLUMN l . 
 
 The spinal column of fishes is divisible into only two 
 regions, a caudal region in which the haemal arches or ribs 
 meet one another ventrally, and a precaudal region in which 
 they do not meet. 
 
 The various modifications of the spinal column in fishes 
 an be best understood by comparing them with the arrange- 
 ment in the simplest type known, namely Amphioxus. In 
 Amphioxus the notochord is immediately surrounded by a 
 structureless cuticular layer, the chordal sheath. Outside this 
 is the skeletogenous layer, which in addition to surrounding 
 the notochord and chordal sheath embraces the nerve cord 
 dorsally, and laterally sends out septa forming the myomeres. 
 
 The CARTILAGINOUS GANOIDS 2 Acipenser, Polyodon and 
 Scaphirhynchus are the simplest fishes as regards their spinal 
 column. The notochord remains permanently unconstricted 
 and is enclosed in a chordal sheath, external to which is the 
 skeletogenous layer. In this layer the development of carti- 
 laginous elements has taken place. In connection with each 
 neuromere, or segment as determined by the points of exit of 
 the spinal nerves, there are developed two pairs of ventral 
 cartilages, the ventral arches (basiventralia) and intercalary 
 pieces (interventralia) ; and at least two pairs of dorsal pieces, 
 the neural arches (basidorsalia) and intercalary pieces (inter- 
 dorsalia). The lateral parts of the. skeletogenous layer do not 
 become converted into cartilage, so there are no traces of 
 vertebral centra. The ventral or haemal arches meet one 
 another ventrally and send out processes to protect the ven- 
 tral vessels. The neural arches do not meet, but are united 
 by a longitudinal elastic band. 
 
 In Cartilaginous ganoids the only indications of metameric 
 
 1 See H. Gadow and E. C. Abbott, Phil. Trans, vol. 186 (1895) B. 
 pp. 163221. 
 
 2 C. Hasse, Zeitschr. wiss. Zool. LVII. 1893, p. 76. 
 
THE SKELETON IN FISHES. VERTEBRAL COLUMN. 113 
 
 segmentation are found in the neural and haemal arches. The 
 case is somewhat similar with the Holocephali and Dipnoi. 
 
 In the HOLOCEPHALI the nqtochord grows persistently 
 throughout life, and is of uniform diameter throughout the 
 whole body except in the cervical region and in the gradually 
 tapering tail. The chordal sheath is very thick and includes a 
 well-marked zone of calcification which separates an outer zone of 
 hyaline cartilage from an inner zone. There are also a number 
 of cartilaginous pieces derived from the skeletogenous layer 
 which are arranged in two series, a dorsal series forming the 
 neural arches and a ventral series forming the haemal arches. 
 These do not, except in the cervical region, meet one another 
 laterally round the notochord and form centra. To each 
 neuromere there occur a pair of basidorsals, a pair of inter- 
 dorsals, and one or two supradorsals. In the tail the arrange- 
 ment is irregular. 
 
 In the DIPNOI as in the Holocephali the notochord grows 
 persistently and uniformly, and the chordal sheath is thick 
 and cartilaginous though there are no metamerically arranged 
 centra. The neural and haemal arches and spines are cartila- 
 ginous and interbasalia (intercalary pieces) are present. The 
 basidorsalia and basiventralia do not in Ceratodus meet 
 round' the notochord and enclose it except in the anterior part 
 of the cervical and posterior part of the caudal region. 
 
 In ELASMOBRANCHII the chordal sheath is weak and the 
 skeletogenous layer strong. Biconcave cartilaginous vertebrae 
 are developed, and as is the case in most fishes, constrict the 
 notochord vertebrally. 
 
 Two distinct types of vertebral column can be distinguished 
 in Elasmobranchs ! : 
 
 1. In many extinct forms and in the living Notidanidae, 
 
 1 C. Hasse, Das naturliche System der Elasmobranchier auf Grundlage 
 des Baues und der Entwickelung ihrer Wirbelsdule, Jena, 1879 and 1885, 
 and "Die fossilen Wirbel, Morph. Studieu i. iv.," Morphol. Jahrb. Bd. n. 
 in. and iv. 1876 78. 
 
 R. 8 
 
114 THE VERTEBRATE SKELETON. 
 
 Cestracion, and Squatina, the dorsal and ventral arches do not 
 meet one another laterally round the centrum, and conse- 
 quently readily come away from it. 
 
 2. In most living Elasmobranchs the arches meet laterally 
 round the centrum. 
 
 The vertebrae are never ossified but endochondral calcifica- 
 tion nearly always takes place, though it very rarely reaches 
 the outer surface of the vertebrae. Elasmobranchs are some- 
 times subdivided into three groups according to the method 
 in which this calcification takes place : 
 
 1. Cyclospondyli (Scymniis, Acanthias), in which the 
 calcified matter is deposited as one ring in each vertebra. 
 
 2. Tectospondyli (Squatina, Raia, Trygon), in which 
 there are several concentric rings of calcification. 
 
 3. Asterospondyli (Notidanidae, Scyllium, Cestracion), 
 in which the calcified material instead of forming one simple 
 ring, extends out in a more or less star-shaped manner. 
 
 In Heptanchus the length of the vertebral centra in the 
 middle of the trunk is double that in the anterior and posterior 
 portions, and as the length of the arches does not vary, the 
 long centra carry more of them than do the short centra. 
 
 In many Rays the skull articulates with the vertebral 
 column by distinct occipital condyles. 
 
 In BONY GANOIDS the skeletogenous layer becomes calcified 
 ectochondrally in such a way that the notochord is pinched in 
 at intervals, and distinct vertebrae are produced. Ossification 
 of the calcified cartilage rapidly follows. In Amia the verte- 
 brae are biconcave, in Lepidosteus they are opisthocoelous, cup 
 and ball joints being developed between the vertebrae in a 
 manner unique among fishes. The notochord entirely disap- 
 pears in the adult Lepidosteus, but at one stage in larval life 
 it is expanded vertebrally and constricted intervertebrally in 
 the manner usual in the higher vertebrata, but unknown 
 elsewhere among fishes. 
 
THE SKELETON IN FISHES. THE FINS. 115 
 
 The tail of Amia is remarkable from the fact that as a 
 rule to each neuromere, as determined by the exit of the 
 spinal nerves, there are two centra, a posterior one which 
 bears nothing, and an anterior one which bears the neural and 
 haemal arches, these being throughout the vertebral column 
 connected with the centra by cartilaginous discs. 
 
 In most TELEOSTEANS but not in the Plectognathi the neural 
 arches are continuous with the centra, which are nearly always 
 deeply biconcave. 
 
 In some cases many of the anterior vertebrae are anky- 
 losed together and to the skull. The vertebrae often articu- 
 late with one another by means of obliquely placed flattened 
 surfaces, the zygapophyses. The centrum in early stages of 
 development is partially cartilaginous, but the neural arches 
 and spines in the trunk at any rate, pass directly from the 
 membranous to the osseous condition. 
 
 FINS. 
 
 The most primitive fins are undoubtedly the unpaired ones, 
 which probably originally arose as ridges or folds of skin 
 along the mid-dorsal line of the body, and passed thence 
 round the posterior end on to the ventral surface, partially 
 corresponding in position and function to the keel of a ship. 
 
 In long 'fish' which pass through the water with an 
 undulating motion such simple continuous fins may be the 
 only ones found, as in Myxine. To support these median fins 
 skeletal structures came to be developed ; these show two 
 very distinct forms, viz. cartilaginous endoskeletal pieces, the 
 radialia, and horny exoskeletal fibres, the Jin-rays. Me- 
 chanical reasons caused the fin to become concentrated at 
 certain points and reduced at intervening regions. Thus a 
 terminal caudal fin arose and became the chief organ of 
 propulsion, and the dorsal and ventral fins became specialised 
 to act as balancing organs. 
 
 In some of the earlier Elasmobranchs, the Pleuracanthidae, 
 
 82 
 
116 THE VERTEBRATE SKELETON. 
 
 the endoskeletal cartilaginous radialia are directly con- 
 tinuous with outgrowths from the dorsal and ventral arches 
 of the vertebrae, and form the main part of the fin. In 
 later types of Elasmobranchs the horny exoskeletal fin-rays 
 have comparatively greater prominence. In bony fish, as has 
 been already stated, the horny fibres are replaced by bony 
 rays of dermal origin, and at the same time complete reduc- 
 tion and disappearance of the cartilaginous radialia takes 
 place. 
 
 THE CAUDAL FIN. 
 
 The caudal region of the spinal column in fishes is of 
 special importance. It is distinctly marked off from the rest 
 of the spinal column by the fact that the ventral or haemal 
 arches meet one another and are commonly prolonged into 
 spines, while in the trunk region they do not meet but com- 
 monly diverge from one another. 
 
 In some fish the terminal part of the caudal region of the 
 spinal column retains the same direction as the rest of the 
 spinal column. The blade of the caudal fin is then divided 
 into two nearly equal portions, and is said to be diphycercal. 
 This condition is generally regarded as the most primitive one ; 
 it occurs in the Ichthyotomi, Holocephali, all living Dipnoi, 
 Polypterus and some extinct Crossopterygii, and a few Selachii 
 and Teleostei. It occurs also in deep-sea fish belonging to 
 almost every group, and under these conditions obviously 
 cannot be regarded as primitive, but must be looked on as 
 a feature induced by the peculiar conditions of life. 
 
 In the great majority of fish the terminal part of the 
 caudal region of the spinal column is bent dorsal wards, and 
 the part of the blade of the caudal fin which arises on the 
 dorsal surface is much smaller than is that arising on the 
 ventral surface. Such a fin is said to be heterocercal. 
 
 Strictly speaking all fish whose tails are not diphycercal 
 have heterocercal tails, but the term is commonly applied 
 
THE SKELETON IN FISHES. THE SKULL. 117 
 
 to two-bladed tails in which the spinal column forms a definite 
 axis running through the dorsal blade, while the ventral blade 
 is enlarged and generally forms the functional part of the 
 tail. Such heterocercal tails are found in nearly all Elasmo- 
 branchii, together with the living cartilaginous Ganoidei, 
 and many extinct forms belonging to the same order; Lepi- 
 dosteus, Amia, and the Dipteridae among Dipnoi, have tails 
 which, though obviously heterocercal, are not two-bladed. 
 
 The vast majority of the Teleostei and some extinct Ga- 
 noidei have heterocercal tails of the modified type to which 
 the term homocercal is applied. The hypural bones which 
 support the lower half of the tail fin become much enlarged, 
 and frequently unite to form a wedge-shaped bone which be- 
 comes ankylosed to the last ossified vertebral centrum. The 
 fin-rays then become arranged in such a way as to produce a 
 secondary appearance of symmetry. Some homocercal fish 
 such as the Perch have the end of the notochord protected 
 by a calcified or completely ossified sheath, the urostyle, to 
 which several neural and haemal arches may be attached, and 
 which becomes united with the centrum of the last vertebra ; 
 in others such as the Salmon the end of the notochord is pro- 
 tected only by laterally placed bony plates. 
 
 THE SKULL. 
 
 It is often impossible to draw a hard and fast line between 
 the cranium and the vertebral column. This is the case for 
 instance in Acipenser (fig. 18, 16) among Chondrostei, in Amia 
 among Holostei, and in Ceratodus and Protopterus among 
 Dipnoi. The occipital region of the skull in Amia is clearly 
 formed of three cervical vertebrae whose centra have become 
 absorbed into the cranium, while the neural arches and spines 
 are still distinguishable. 
 
 The simplest type of cranium is that found in ELASMO- 
 BRANCHS: it consists of a simple cartilaginous box, which is 
 generally immovably fixed to the vertebral column, though 
 
118 
 
 THE VERTEBRATE SKELETON. 
 
 in some forms, like Scymnus and Galeus, a joint is indicated, 
 and in others, such as the Rays, one is fairly well developed. 
 
 FIG. 16. A. SKULL OF Notidanus 
 
 (Brit. Mus.). B. SKULL OF 
 
 Cestracion x (after GEGENBAUB). In neither case are the branchial 
 arches shown. 
 
 6. Meckel's cartilage. 
 
 7. teeth. 
 
 1. rostrum. 
 
 2. olfactory capsule. 
 
 3. ethmo-palatine process. 
 
 4. palatine portion of palato- 
 
 pterygo-quadrate bar. 
 
 5. quadrate portion of bar. 
 
 8. labial cartilage. 
 
 9. hyomandibular. 
 10. postorbital process. 
 
 II. optic foramen. 
 
 The cranium in Elasmobranchs is never bony, though the 
 cartilage is sometimes calcined. It is drawn out laterally 
 into an antorbital process in front of the eye, and a post- 
 
THE SKELETON IN FISHES. THE SKULL. 119 
 
 orbital process behind it. The nasal capsules are always carti- 
 laginous, and the eye, as a general rule, has a cartilaginous 
 sclerotic investment. The cranium is often prolonged in 
 front into a rostrum which is enormously developed in Pristis 
 and some Rays. The cartilaginous roof of the cranium is 
 rendered incomplete by the presence of a large hole, the an- 
 terior fontanelle. 
 
 Two pairs of labial cartilages (fig. 16, B, 8) are often 
 present. They lie imbedded in the cheeks outside the anterior 
 region of the jaws, and are specially large in Squatina. 
 
 As regards the visceral arches 1 the simplest and most primi- 
 tive condition of the jaws is that of the Notidanidae, in which 
 the niandibular and hyoid arches are entirely separate. In 
 these primitive fishes the palato-pterygo-quadrate bar articu- 
 lates with the postorbital process (fig. 16, 10), while further 
 forwards it is united to the cranium by the ethmo-palatine 
 ligament. The hyoid arch is small and is broadly overlapped by 
 the niandibular arch. The term autostylic is used to describe 
 this condition of the suspensorium. From this condition we 
 pass in the one direction to that of Cestracion (fig. 16, B), in 
 which the whole of the palato-pterygo-quadrate bar has become 
 bound to the cranium, and in the other to that of Scyllium. 
 In Scyllium (fig. 6), while the ethmo-palatine ligament is 
 retained, the postorbital articulation of the palato-pterygo- 
 quadrate has been given up, so that the palato-pterygo-quadrate 
 comes to abut on the hyomandibular and is attached to it by 
 ligaments. The pre-spiracular ligament (fig. 16, 20) running 
 from the auditory capsule also assists in supporting the jaws. 
 
 Lastly we come to the purely hyostylic condition met 
 with in Rays, in which the niandibular arch is entirely sup- 
 ported by the hyomandibular. In some Rays the hyoid is 
 attached to the posterior face of the hyomandibular near its 
 proximal end, and may even come to articulate with the 
 cranium. 
 
 1 See H. B. Pollard, Anat. Am. x. 1894. 
 
120 THE VERTEBRATE SKELETON. 
 
 The visceral arches of Elasmobranchs may be summa- 
 rised as follows : 
 
 1. The mandibular arch, consisting of a much reduced 
 dorsal portion, the pre-spiracular ligament, and a greatly de- 
 veloped ventral portion from which both upper and lower 
 jaws are derived. The mandible (Meckel's cartilage) is the 
 original lower member of the mandibular arch, and from it 
 arises an outgrowth which forms the upper jaw or palato- 
 pterygo-quadrate bar. In Scymnus this bears a few branchio- 
 stegal rays. 
 
 2. The hyoid arch, which consists of the hyomandibular 
 and the hyoid, and bears branchiostegal rays on its posterior 
 face. 
 
 3. The branchial arches, generally five in number, all 
 of which except the last bear branchiostegal rays. In the 
 Notidanidae the Dumber of branchial arches is increased 
 
 FIG. 17. DORSAL VIEW OF THE BRANCHIAL ARCHES OF 
 
 Heptanchus. (From GEGENBAUR). 
 
 1. basi-hyal. 7. pharyiigo-branchial, common 
 
 2. cerato-hyal. to the sixth and seventh 
 
 3. second hypo -branchial. arches. 
 
 4. first cerato-branchial. 8. basi-branchial of second arch. 
 
 5. first epi-branchial. 9. basi-branchial, common to the 
 
 6. first pharyngo-branchial. sixth and seventh arches. 
 
THE SKELETON IX FISHES. THE SKULL. 121 
 
 beyond the normal series, thus in Hexanchus there are six, and 
 in Heptanchus seven. There are six also in Chlamydoselache 
 and Protopterus. 
 
 4. The so-called external branchial arches which are carti- 
 laginous rods attached to all the visceral arches. They are 
 especially large in Cestracion. 
 
 The skull in HOLOCEPHALI is entirely cartilaginous. The 
 palato-pterygo-quadrate bar is fixed to the cranium, and to 
 it the mandible articulates. There is a well-marked joint 
 between the skull and the spinal column. 
 
 In living Cartilaginous GANOIDS the primitive cartilaginous 
 cranium is very massive, and is greatly prolonged anteriorly, 
 while posteriorly it merges into the spinal column. Although it 
 is mainly cartilaginous a number of ossifications take place in 
 the skull, and membrane bones are now found definitely de- 
 veloped, especially in connection with the roof of the cranium. 
 In Acipenser (fig. 18) the ossifications in the cartilage include 
 the pro-otic, which is pierced by the foramen for the fifth nerve, 
 the alisphenoid, orbitosphenoid, ectethmoid, palatine, pterygoid, 
 meso-pterygoid, hyomandibular (fig. 18, 11), cerato-hyal, all the 
 cerato-branchials, and the first two epi-branchials. Most of 
 these structures are, however, partly cartilaginous, though 
 they include an ossified area. The membrane bones too of 
 Acipenser are very well developed, they include a bone occu- 
 pying the position of the supra-occipital, and form a complete 
 dorsal cephalic shield. Resting on the ventral surface are a 
 vomer and a very large parasphenoid (fig. 18, 3). There is a 
 bony operculum attached to the hyomandibular, and membrane 
 bones representing respectively the maxilla and dentary are 
 attached to the jaws. The suspensorium is most markedly 
 hyostylic. The palato-pterygo-quadrate bar has a very curious 
 shape and is quite separate from the cranium. It is connected 
 to the hyomandibular by a thick symplectic ligament con- 
 taining a small bone homologous with the symplectic of 
 Teleosteans. 
 
122 
 
 THE VERTEBRATE SKELETON. 
 
 Polyodon differs much from Acipenser, the membrane bones 
 not being so well developed though they cover the great carti- 
 laginous snout. 
 
 The skull in Polypterus (Crossopterygii) shows a great 
 advance towards the condition met with in Teleostei. The 
 cranium remains to a great extent unossified, and large dorsal 
 and ventral fontanelles pierce its walls. It is covered by a 
 
 FIG. 18. LATERAL VIEW OF THE SKULL OF A STURGEON (Acipenser 
 sturio). Nearly all the membrane bones have been removed (Brit. 
 Mus.). 
 
 palatine. 
 
 hyomandibular. 
 
 pharyngo-branchial. 
 
 epi-branchial. 
 
 cerato-branchial. 
 
 hypo-branchial. 
 
 nasal cavity. 
 
 orbit. 
 
 parasphenoid. 
 
 vomer. 
 
 pterygoid. 
 
 maxilla. (The dotted line 
 running from 6 passes 
 into the mouth cavity.) 
 
 dentary. 
 
 symplectic. 
 
 10. 
 11. 
 12. 
 13. 
 14. 
 15. 
 16. 
 17. 
 18. 
 19. 
 
 coalesced anterior vertebrae. 
 
 inter-hyal. 
 
 cerato-hyal. 
 
 rib. 
 
 great development of membrane bones, paired nasals, frontals, 
 parietals, supra- and post-temporals, and dermo-supra-occipitals 
 among others being present. The palato-ptery go- quadrate bar 
 is fused to the cranium, and in connection with it the following 
 paired membrane bones appear, palatine, ecto-, meso- and meta- 
 pterygoid, and further forwards jugal, vomer, maxilla and 
 premaxilla. The membrane bones developed in connection 
 
THE SKELETON IN FISHES. THE SKULL. 123 
 
 with each ramus of the mandible are the dentary, angular, 
 and splenial, in addition to the cartilage bone the articular. 
 Several large opercular bones occur. There are also a pair of 
 large jugular or gular plates, and several large opercular bones. 
 
 In Bony Ganoids both cartilage bone and membrane 
 bone is well developed. The pro-otics and exoccipitals are 
 well ossified, but the supra-occipital and pterotics are not. 
 Lateral ethmoids are developed, and there are ossifications in 
 the sphenoidal region which vary in different 'forms. The 
 place of the cartilaginous palato-pterygo-quadrate is taken by 
 a series of bones, the quadrate behind and the palatine, ecto-, 
 meso- and meta-pterygoids in front. In. Lepidosteus, however, 
 the palatine and pterygoid are membrane bones, as they are 
 in Polypterus and the Frog. Paired maxillae, premaxillae, 
 vomers and a parasphenoid occur forming the upper jaw and 
 roof of the mouth, and a series of membrane bones are found 
 investing the mandible and forming the operculum. 
 
 In Amia 1 membrane bones are as freely developed as they 
 are in Teleosteans ; they include on each side a squamosal, 
 four opercular bones, a lachrymal, a pre-orbital, one or two 
 suborbitals, two large postorbitals and a supratemporal ; while 
 investing the mandible, besides the dentary, splenial, angular, 
 and supra-angular, there is an unpaired jugular. The articular 
 too is double and a mento-meckelian occurs. In Amia teeth 
 are borne on the premaxillae, maxillae, vomers, palatines and 
 pterygoids. 
 
 Bony Ganoids are the lowest animals in which squamosal 
 bones are found, and they do not occur in Teleosteans. 
 
 The suspensoriuin in bony Ganoids, as in the Chondrostei, 
 is hyostylic, and there are two ossifications in the hyoman- 
 dibular cartilage, viz. the hyomandibular, and the symplectic. 
 
 1 T. W. Bridge, "The Cranial Osteology of Amia calva," J. Anat. 
 Physiol. norm. path. 1876, vol. xi. p. 605. K. Shufeldt, "The Osteology 
 of Amia calva," Ann. Rep. of the Commissioner for Fish and Fisheries, 
 Washington, 1885. 
 
124 THE VERTEBRATE SKELETON. 
 
 The skull of TELEOSTEI is very similar to those of Lepidosteus 
 and Amia. Although the bony skull is greatly developed and 
 very complicated, much of the original cartilaginous cranium 
 often persists. Membrane bones are specially developed on 
 the roof of the skull where they include the parietal, frontal, 
 and nasal bones. The same bones are developed in connection 
 with the upper jaw and roof of the mouth as in bony Ganoids, 
 but only two membrane bones occur in the lower jaw, viz. the 
 angular and' dentary. A number of large ossifications take 
 place in the cartilage of the auditory capsules. In some forms 
 parts of the last pair of branchial arches are broadened out 
 and form the pharyngeal bones which bear teeth. The oper- 
 cular bones and those of the upper and lower jaws are quite 
 comparable to those of bony Ganoids. 
 
 A full account of the Teleostean skull has been given in 
 the case of the Salmon (pp. 87 96) and the Cod (pp. 96 
 101). 
 
 In DIPNOI the skull is mainly cartilaginous, but both 
 cartilage- and membrane-bone occur also. Cartilage-bone is 
 found in the ossified exoccipitals, while of membrane-bones 
 Protopterus has among unpaired bones a fronto-parietal, a 
 median ethmoid, and a parasphenoid, and among paired bones 
 nasals and large supra-orbitals. The skull of Ceratodus (fig. 19) 
 has an almost complete roof of membrane bones, including some 
 whose homology is doubtful. The ethmo-vomerine region is 
 always cartilaginous, but bears small teeth. The palato- 
 pterygo-quadrate bar is ossified and firmly united to the 
 cranium, and the mandible articulates directly with it (auto- 
 stylic). Membrane bones are freely developed in connection 
 with the mandible, dentary, splenial, and angular bones being 
 all present. There are two opercular bones. 
 
 In the extinct Dipteridae the cranium is very completely 
 covered with plates of dermal bone, and the skeleton in 
 general is more ossified than is the case in recent Dipnoi. 
 
 Six pairs of branchial arches occur in Protopterus ; Cera- 
 
THE SKELETON IN FISHES. THE RIBS. 
 
 125 
 
 todus and Lepidosiren have five, like most other fish. The 
 branchial arches bear gill rakers. 
 
 ....10 
 
 .-11 
 
 FIG. 19. DORSAL (TO THE LEFT) AND VENTRAL (TO THE RIGHT) VIEWS 
 OP THE CRANIUM OF Ceratoclus iiiiolepis (after GUNTHER). 
 
 6. 
 
 cartilaginous part of the 7. 
 
 quadrate with which the 8. 
 
 mandible articulates. 9. 
 
 scleroparietal. 10. 
 
 frontal. 11. 
 
 ethmoid. 12. 
 
 nares. 13. 
 
 orbit. 14. 
 
 pre-opercular (squamosal). 
 second rib. 
 first rib. 
 vomerine tooth, 
 palato-pterygoid tooth, 
 palato-pterygoid. 
 parasphenoid. 
 interopercular. 
 
 RIBS. 
 
 As has been already mentioned (p. 24), although ribs 
 commonly appear to be the cut-off ends of the transverse pro- 
 cesses, they are really elements derived from the ventral or 
 haemal arch. 
 
 In Elasmobranchii and other cartilaginous fish they have 
 the form of small cartilaginous structures imperfectly separated 
 
126 THE VERTEBRATE SKELETON. 
 
 from the diverging halves of the ventral arch, and are often 
 absent. 
 
 In Teleostei and bony Ganoids they often have different at- 
 tachments in different parts of the body. In the tail region they 
 are not differentiated from the two halves of the ventral arch, 
 which meet in the middle line, and are prolonged into a 
 haemal spine. In the posterior trunk region they sometimes 
 form distinct processes diverging from the two halves of the 
 ventral arch ; while further forward they may shift their 
 attachment so as to arise from the dorsal side of the two 
 halves of the ventral arch and at some distance from their 
 ends, which now diverge as veritri- lateral processes. 
 
 APPENDICULAR SKELETON. 
 PECTORAL GIRDLE. 
 
 The simplest type of pectoral girdle is found in Elasmo- 
 branchs. It is entirely cartilaginous and consists of a curved 
 ventrally-placed rod, ending dorsally in two horn-like scapular 
 processes which are sometimes attached to the cranium or 
 vertebral column. In Rays the shoulder girdle is very large, 
 and has a distinct suprascapular portion forming a broad plate 
 attached to the neural spines of the vertebrae. There is often 
 a cup-like glenoid cavity for the articulation of the limb ; this 
 cavity is specially large in Rays and is much pierced by holes. 
 In Dipnoi the cartilaginous girdle still occurs, but on it there is 
 a deposit of membrane bone forming the clavicle, inf raclavicle, 
 and supraclavicle. These bones, which with the exception of 
 the clavicle, are unknown in higher vertebrates, are better 
 developed in Ganoids, and best of all in Teleosteans. They 
 are connected by the supra- temporal with the epi-otic and 
 opisthotic regions of the cranium. Owing to this development 
 of dermal bone, the original cartilaginous arch becomes much 
 reduced, but ossifications representing the scapula and cora- 
 coid occur in bony Ganoids and Teleosteans. 
 
THE SKELETON IN FISHES. PAIRED FINS. 127 
 
 PELVIC GIRDLE. 
 
 In Elasmobranchs the pelvic girdle consists of a short 
 ventral rod of cartilage representing the ischium and pubis, 
 which does not send up dorsal iliac processes. In Ohimaera 
 the pelvic girdle has a flattened pointed iliac portion, and 
 ventrally an unpaired movable cartilaginous plate which 
 bears hooks and is supposed to be copulatory in function. 
 Claspers of the usual type are present as well. The Dipnoi 
 have a primitive kind of pelvis in the form of a cartilaginous 
 plate lying in the mid ventral line and drawn out into three 
 horns anteriorly. In Ganoids the pelvis has almost entirely 
 disappeared, though small cartilaginous vestiges of it remain 
 in Polypterus. In Teleosteans even these vestiges are gone, 
 and in these fish and Ganoids the place of the pelvis is taken 
 by the enlarged basi-pterygia (meta-pterygia) of the fins. 
 
 PAIRED FINS 1 . 
 
 As regards the origin of the limbs or paired fins of fishes 
 there are two principal views. One view, that of Gegenbaur, 
 considers that limbs and their girdles are derived from visceral 
 arches which have migrated backwards. The other view, which 
 probably now has the greater number of supporters, considers 
 that the paired fins of fishes are of essentially the same nature 
 as the median fins. 
 
 According to Gegenbaur's view 2 the archipterygium of 
 Ceratodus (fig. 20) represents the lowest type of fin ; it con- 
 sists of a central cartilaginous axis bearing a large number of 
 radialia. The dorsal or pre- axial radialia are more numerous 
 than the ventral or postaxial, and at the margin of the fin 3 the 
 
 1 A. Smith Woodward, Nat. Sci. vol. 1. 1892, p. 28. Further references 
 are here given on the literature of the subject. 
 
 2 C. Gegenbaur, Ueber das Archipterygium, Jena Zeitschr. der Wirbel- 
 thiere, 2 e Heft, 1873, vol. 7, and MorphoL Jahrb. xxn. 1894, p. 119. 
 
 3 The fins of Ceratodus are very variable, no two being exactly alike. 
 Sometimes even the main axis bifurcates. See W. A. Haswell, Linn. 
 Soc. N. S. Wales, vol. vn. 1882. 
 
128 
 
 THE VERTEBRATE SKELETON. 
 
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THE SKELETON IN FISHES. PAIRED FINS. 129 
 
 cartilaginous endoskeletal radialia are replaced by horny exo- 
 skeletal fin-rays. 
 
 It is impossible here to give a full discussion of the rival 
 views, but some of the points which support Gegenbaur's view 
 may be mentioned. The fact that migration of visceral arches 
 has to be assumed is no difficulty, as it is obvious that 
 migration in the opposite direction has taken place in many 
 Teleosteans such as the Cod, whose pelvic fins are attached 
 to the throat in front of the pectorals. If migration did take 
 place, the pelvic fins being older than the pectoral should be 
 the more modified, and this is the case. Again, if the pectoral 
 girdle is a modified branchial arch, it must at some period 
 have carried a gill, and in Protopterus it does bear a vestigial 
 gill. 
 
 According to the view more prevalent at the present time, 
 the paired fins have been derived from two continuous folds 
 of skin and their skeletal supports running forward from the 
 anal region along the sides of the body, their character being 
 similar to the fold that gave rise to the median fins. In 
 support of this view it may be argued that the paired and 
 unpaired fins are often identical in structure, and that some 
 Elasmobranch embryos do show a ridge running between the 
 pectoral and pelvic fins. Then from this continuous fold two 
 pairs of smaller folds may have been specialised off, and in 
 each a number of cartilaginous radialia may have been de- 
 veloped. The fin of Cladoselache from the Carboniferous of 
 Ohio apparently illustrates this condition. It consists of 
 certain basal pieces which do not project beyond the body 
 wall and bear a number of unsegmented cartilaginous radialia, 
 which show crowding together and are sometimes bifurcated 
 distally ; they extend throughout the whole fin from the body 
 wall to the margin. From this fin the archipterygium might 
 be easily derived by the enlargement of one of the middle 
 radialia and the segmentation and partial fusion of them all. 
 Whether the archipterygium be a primitive or secondary 
 
 R. 9 
 
130 THE VERTEBRATE SKELETON. 
 
 type of fin, when it is once reached it is easy to derive all the 
 other types from it. The fins of the other living Dipnoi, 
 Protopterus and Lepidosiren are simply archipterygia from 
 which the radialia have almost or completely disappeared, 
 leaving only the segmented axes. Archipterygia too are found 
 in the pectoral fins of the Ichthyotomi, but the postaxial 
 radialia are much reduced. 
 
 The ichthyopterygium, or type of fin, characteristic of 
 many modern Elasmobranchs such as Scyllium, may have been 
 derived from the archipterygium by the gradual reduction of 
 the rays on the postaxial side of the axis and their condensation 
 on the pre-axial side. The Ichthyotomi such as Xenacanthus 
 show one stage in the reduction of the post-axial rays, and a 
 further stage is seen in the Notidanidae and some other sharks 
 like Scymnus and Acanthias, in which a few postaxial rays 
 still remain. The condensation of the pre-axial rays when 
 further continued leads to one of the rays getting an attach- 
 ment to the girdle. Thus the fin comes to articulate with the 
 girdle by two basalia or basal pieces ; a third attachment is 
 formed in the same way and the three basalia are called re- 
 spectively pro-, meso-, and meta-pterygia. By some authors the 
 meta-pterygium and by others the meso-pterygium is regarded 
 as homologous with the axis of the archipterygium. 
 
 The pectoral fins of Elasmobranchs vary very much in 
 their mode of attachment. In some of the sharks, including 
 the Notidanidae and Scy Ilium, all three basalia articulate with 
 the pectoral girdle, while in others such as Cestracion the 
 meta-pterygium is excluded. In Rays the pro-pterygium and 
 the meta-pterygium are long and narrow and diverge much 
 from one another; other basalia work their way in between 
 the meso-pterygium and meta-pterygium, and come to arti- 
 culate with the pectoral girdle. Sometimes they fuse and 
 form a second meso-pterygium. The radialia are greatly 
 elongated and are segmented. 
 
 In Chimaera all three basalia are present, but the meso- 
 
THE SKELETON IN FISHES. PAIRED FINS. 131 
 
 pterygium is shifted and does not articulate with the pectoral 
 girdle J . 
 
 In Acipenser and Polyodon the pectoral fin is built on the 
 same type as in Elasmobranchs, but becomes modified from the 
 fact that the pro-pterygium is replaced by dermal bone which 
 forms a large marginal ray. Extra meso-pterygia are formed 
 in the same way as in Rays. 
 
 In Polypterus the pro- and meta-pterygia have ossified 
 while the meso-pterygium remains chiefly cartilaginous; the 
 fin-rays are also chiefly ossified. 
 
 In Amia, Lepidosteus, and certain Teleosteans like Salmo, 
 not only the pro-pterygium but the meso-pterygium is almost 
 suppressed by the marginal ray. 
 
 In the great majority of Teleosteans a still further stage is 
 reached, the endoskeletal elements, the basalia and radialia 
 are almost entirely suppressed and the fin comes to consist 
 entirely of ossified fin-rays of dermal origin. 
 
 In some Teleosteans Exocaetus, a herring, and Dactylo- 
 pterus, a gurnard the pectoral fins are so enormously developed 
 that by means of them the fish is able to fly through the air 
 for considerable distances. The skeleton of these great fins is 
 almost entirely composed of dermal bone. 
 
 PELVIC FIN. 
 
 The pelvic fin is almost always further removed from the 
 archipterygial condition, and is in general more modified than is 
 the pectoral. Thus in the Ichthyotomi, while the pectoral fins 
 are archipterygia similar to those of Ceratodus, the pelvic fins 
 consist of an axis bearing rays on the postaxial side only, and 
 prolonged distally into a clasper. In Dipnoi however the 
 pelvic fins are very similar to the pectoral. In Elasmobranchs 
 the meso-pterygium is missing, the pro-pterygium is small or 
 absent, and the fin is mainly composed of the meta-pterygium 
 
 1 Some of these views with regard to the homologies of the parts of 
 the fins are not accepted by all anatomists. 
 
 92 
 
132 THE VERTEBRATE SKELETON. 
 
 (generally called basi-pterygium) and its radialia. The males 
 in Elasmobranchii and Holocephali have the distal end of the 
 metapterygium prolonged into a clasper. 
 
 In Ganoids and in Teleosteans the loss of the pelvic girdle 
 causes the pelvic fin to be still further removed from the 
 primitive state. There is always a large basi-pterygium which 
 lies imbedded in the muscles and meets its fellow at its proximal 
 end. In Cartilaginous Ganoids it has a secondary segmenta- 
 tion. Its relation to its fellow is subject to much variation 
 in Teleosteans, sometimes as in the Perch the two are in 
 contact throughout, sometimes as in the Salmon they meet 
 distally as well as proximally, but are elsewhere separated by 
 a space, sometimes as in the Pike and Bony Ganoids they 
 diverge widely. The radialia are articulated to the basi- 
 pterygium. In Cartilaginous Ganoids and Polypterus they 
 are well developed, in other Ganoids and in Teleosteans they 
 are in the main replaced by dermal fin-rays. 
 
 In some Teleosteans such as the Cod the pelvic fins have 
 migrated from their usual position and come to be attached 
 to the throat in front of the pectoral fins. Fish with this 
 arrangement are grouped together as jugulares. 
 
CHAPTER IX. 
 CLASS II. AMPHIBIA 1 . 
 
 AMPHIBIA differ markedly from Pisces in the fact that 
 in the more abundant and familiar forms the skin is naked, 
 and that when the integument is prolonged into median fins 
 they are devoid of fin-rays. The notochord may persist, but 
 bony vertebral centra are always developed. These are some- 
 times biconcave, sometimes procoelous, sometimes opistho- 
 coelous. There is only one sacral vertebra, except in rare 
 cases. The cartilaginous cranium persists to a considerable 
 extent but is more or less replaced by cartilage bone, and 
 overlain by membrane bone. The basi-occipital is not com- 
 pletely ossified, and the skull articulates with the vertebral 
 column by means of two occipital condyles formed by the 
 exoccipitals. 
 
 There is a large parasphenoid, but there are no ossifications 
 in the basisphenoidal, presphenoidal, and alisphenoidal re- 
 gions. In most cases the epi-otics and opisthotics are ossified 
 continuously with the exoccipitals. 
 
 The palato-pterygo-quadrate bar is firmly united to the 
 cranium, so the skull is autostylic. The palatines and 
 pterygoids are membrane bones. Teeth are nearly always 
 borne on the vomers and commonly on the maxillae and 
 
 1 T. H. Huxley, Amphibia (Encyclopedia Britannica). 
 
134 THE VERTEBRATE SKELETON. 
 
 premaxillae. There are no sternal ribs, and the sternum is 
 very intimately related to the pectoral girdle. There are no 
 obturator foramina. The limbs are as in the higher verte- 
 brata, divisible into upper arm, fore-arm, and manus (wrist 
 and hand), and into thigh, shin, and pes (ankle and foot) 
 respectively. The posterior limb is, as a rule, pentedactylate, 
 but in nearly every case the pollex is vestigial or absent. 
 
 Order 1. URODELA 1 . 
 
 The Urodela are elongated animals with a naked skin, a 
 persistent tail, and generally four short limbs. 
 
 The vertebral centra are opisthocoelous or biconcave, and 
 there are numerous precaudal vertebrae. Portions of the 
 notochord commonly persist in the intervertebral spaces. In 
 the skull there is no sphenethmoid forming a ring encircling 
 the anterior end of the brain, its place being in many cases 
 partly taken by a pair of orbitosphenoids. There is no 
 quadra tojugal, and the quadrate is more or less ossified. The 
 mandible has a distinct splenial, and the articular is ossified. 
 
 There is no definite tympanic cavity. The hyoid apparatus 
 is throughout life connected to the quadrate by ligament, and 
 a large basilingual plate does not occur. The ribs are short 
 structures with bifurcated proximal ends. In the pelvis the 
 pubis remains cartilaginous, and there is a bifid cartilaginous 
 epipubis. The bones of the fore-arm and shin remain distinct, 
 and the manus never has more than four digits. 
 
 Suborder (1). ICHTHYOIDEA. 
 
 The vertebrae are amphicoelous, but the notochord re- 
 mains but little constricted throughout the whole length of 
 the vertebral column. Three or four branchial arches nearly 
 always persist in the adult. The cartilages of the carpus 
 and tarsus remain unossified. 
 
 1 See E. Wiedersheim, Morpkol. Jahrb. Bd. in. 1877, p. 459. 
 
AMPHIBIA. URODELA. 135 
 
 The Ichthyoidea may be subdivided again into two 
 groups : 
 
 A. Perennibranchiata, whose chief distinguishing skeletal 
 characters are that the skull is elongated, the premaxillae are 
 not ankylosed, the maxillae are vestigial or absent ; there are 
 sometimes no nasals, and the palatines bear teeth ; 
 
 e.g. Siren, Proteus, Menobranchus. 
 
 B. Derotremata, whose chief distinguishing skeletal cha- 
 racters are that there are large maxillae and nasals \ teeth are 
 borne by both maxillae and premaxillae ; there are no pala- 
 tines ; and both pectoral and pelvic limbs are always present ; 
 
 e.g. Amphiuma, Megalobatrachus, Cryptobranclm-s. 
 
 Suborder (2). SALAMANDRINA. 
 
 The vertebrae are opisthocoelous. The skull is broad, and 
 teeth are borne by both premaxillae and dentaries. Nasal 
 bones are present. The remains of only two branchial arches 
 are found in the adult. The carpus and tarsus are more or 
 less ossified. 
 
 This suborder includes the Newts (Molge), Salamanders 
 (Salamandra), and Amblystoma. 
 
 Order 2. LABYRINTHODONTIA 1 . 
 
 These are extinct Amphibia with a greatly developed 
 dermal exoskeleton, which is generally limited to the ventral 
 surface. The body and tail are long and in some cases limbs 
 are absent. The teeth are pointed and often have the dentine 
 remarkably folded. The vertebrae are amphicoelous, and are 
 generally well ossified. The skull is very solid, and has a 
 greatly-developed secondary roof which hides the true cranium 
 
 1 See A. Fritsch, Fauna der Gaskohle, Prague, 1883-85-86, also writings 
 of Cope, Credner, Huxley, H. v. Meyer, Miall. 
 
136 THE VERTEBRATE SKELETON. 
 
 and is very little broken up by fossae. Paired dermal supra- 
 occipitals are found, and there is an interparietal foramen. 
 The epi-otics and opisthotics form a pair of bones distinct from 
 the exoccipitals. Four simple limbs of moderate length are 
 generally present, and in some cases all four limbs are pente- 
 dactylate. Among the better known genera of Labyrinthodonts 
 are Mastodonsaurus, Nyrania, and Archegosaurus. 
 
 Order 3. GYMNOPHIONA J . 
 
 These animals form a group of abnormal worm-like Am- 
 phibia having an exoskeleton in the form of subcutaneous 
 scales arranged in rings. The vertebrae are biconcave and are 
 very numerous; very few however belong to the tail. The 
 skull has a complete secondary bony roof, the mandible 
 bears teeth and has an enormous backward projection of the 
 angular. The hyoid arch has very slender cornua and no 
 distinct body, it is attached neither to the cranium nor to 
 the suspensorium. The ribs are very long and there are no 
 limbs or limb girdles, 
 
 Order 4. ANURA. 
 
 These are tailless Amphibia, which except in a few in- 
 stances, are devoid of an exoskeleton. The vertebrae are as 
 a rule procoelous, and are very few in number. The post- 
 sacral part of the spinal column ossifies continuously, forming 
 an unsegmented cylindrical rod, the urostyle. Remains of the 
 notochord persist, lying vertebrally, i.e. enclosed within the 
 centra of the several vertebrae, and not as in Urodela lying 
 between one vertebra and the next. The skull is very short 
 and wide. The mandible is almost always, if not invariably, 
 toothless. 
 
 The f rentals and parietals on each side are united so as to 
 form a pair of fronto-parietals, and a girdle-like sphenethmoid 
 is present. 
 
 1 See R. Wiedersheim, Anatomie der Gymnophionen, Jena, 1879. 
 
AMPHIBIA. ANURA. 137 
 
 The quadrate is not generally ossified. A pre-dentary or 
 mento-meckelian bone is commonly present in the mandible, 
 and a single bone represents the angular and splenial. The 
 branchial arches are much reduced in the adult, and the distal 
 ends of the cornua unite to form a flat basilingual plate of a 
 comparatively large size. 
 
 Ribs are very little developed. Clavicles are present. 
 The ilia are very greatly elongated. The anterior limb has 
 four well-developed digits and a vestigial pollex, and is of 
 moderate length ; the radius and ulna have fused. The 
 posterior limb is greatly elongated and is pentedactylate ; the 
 tibia and fibula are fused, while the calcaneura and astragalus 
 are greatly elongated, and it is largely owing to them that 
 the length of the limb is so great. The group includes the 
 Frogs and Toads, the predominant Amphibia of the present 
 time. 
 
CHAPTER X. 
 THE SKELETON OF THE NEWT (Molge cristata}. 
 
 I. EXOSKELETON. 
 
 The skin of the Newt is quite devoid of any exoskeletal 
 structures. The only exoskeletal structures that the animal 
 possesses are the teeth, and these are most conveniently de- 
 scribed with the endoskeleton. 
 
 II. ENDOSKELETON. 
 
 The endoskeleton of the Newt, though ossified to a con- 
 siderable extent, is more cartilaginous than is that of the frog. 
 It is divisible into an axial portion including the vertebral 
 column, skull, ribs, and sternum, and an appendicular por- 
 tion including the skeleton of the limbs and their girdles. 
 
 1. THE AXIAL SKELETON. 
 
 A. THE VERTEBRAL COLUMN. 
 
 This consists of about fifty vertebrae arranged in a regular 
 continuous series. The first vertebra differs a good deal from 
 any of the others ; the seventeenth or sacral vertebra and the 
 eighteenth or first caudal also present peculiarities of their 
 own. The remaining vertebrae are divided by the sacrum 
 into an anterior series of trunk vertebrae whicli bear fairly 
 
THE SKELETON OF THE NEWT. VERTEBRAE. 139 
 
 large ribs, and a posterior series of caudal vertebrae, all of 
 which except the first few are ribless. 
 
 THE TRUNK VERTEBRAE. 
 
 Any vertebra from the second to the sixteenth may be 
 taken as a type of the trunk vertebrae. 
 
 The general form is elongated and somewhat hour-glass 
 shaped, and the centra are convex in front and concave 
 behind ; an opisthocoelous condition such as this is quite ex- 
 ceptional in Anura. The note-chord may persist interverte- 
 brally 1 , but in the centre of each vertebra it becomes greatly 
 constricted or altogether obliterated, and replaced by marrow. 
 The superficial portion of the centrum is ossified, while the 
 articular surfaces are cartilaginous. The neural arches are 
 low and articulate together by means of zygapophyses borne 
 on short diverging processes. The anterior zygapophyses look 
 upwards, the posterior downwards. Each neural arch is drawn 
 out dorsally into a very slight cartilaginous neural spine. 
 
 On each centrum, at a little behind the middle line, there 
 arise a pair of short backwardly-directed transverse pro- 
 cesses; each of which becomes divided into two slightly 
 divergent portions, a dorsal portion which meets the tubercular 
 process of the rib and is derived from the neural arch, and a 
 ventral portion which meets the capitular process of the rib 
 and is derived from the ventral or haemal arch. The division 
 between these two parts of the transverse processes can be 
 traced back as far as the sacrum. 
 
 The first vertebra as already mentioned differs much 
 from all the others. It has no ribs, and presents anteriorly 
 two slightly divergent concave surfaces which articulate with 
 the occipital condyles of the skull. Between these surfaces 
 the dorsal portion of the anterior face of the centrum is 
 drawn out into a prominent odontoid process, the occur- 
 rence of which renders it probable that the first vertebra of 
 
 1 i.e. between one vertebra and the next. 
 
140 THE VERTEBRATE SKELETON. 
 
 the newt is really the axis, and that the atlas with the excep- 
 tion of the odontoid process has become fused with the skull. 
 The sacral vertebra or sacrum, differs from the vertebrae 
 immediately in front of it only in the fact that its transverse 
 processes are stouter and more obviously divided into dorsal 
 and ventral portions. 
 
 THE CAUDAL VERTEBRAE. 
 
 The caudal vertebrae are about twenty-four in number. 
 The anterior ones have hour-glass shaped centra, and short 
 backwardly-directed transverse processes. The middle and 
 posterior ones have rather shorter centra, and are without 
 transverse processes. The neural arches resemble those of the 
 trunk vertebrae, but each is drawn out into a rather high 
 cartilaginous neural spine abruptly truncated anteriorly. All 
 the caudal vertebrae except the first have also a haemal arch, 
 which is very similar to the neural arch, and is drawn out 
 into a haemal spine quite similar to the neural spine. Both 
 neural and haemal arches are ossified continuously with the 
 centra. 
 
 B. THE SKULL. 
 
 The skull of the newt is divisible into three principal 
 parts : 
 
 (1) an axial part, the cranium proper, which encloses 
 the brain and to which 
 
 (2) the capsules of the auditory and olfactory sense 
 organs are fused ; 
 
 (3) the skeleton of the jaws and hyoid apparatus. 
 The skull is much flattened and expanded, though not so much 
 as in the frog. 
 
 (1) THE CRANIUM PROPER. 
 
 The cranium proper or brain case is an unsegmented 
 tube which remains partly cartilaginous, and is partly con- 
 verted into cartilage bone, partly sheathed by membrane bone. 
 The roof and floor of the cartilaginous cranium are, as is 
 
THE SKELETON OF THE NEWT. THE CRANIUM. 141 
 
 the case also in the frog, pierced by holes or fontanelles, and 
 these are so large that the main part of the roof and floor 
 comes to be formed by membrane bone. 
 
 Two pairs of large ossifications take place in the cranial 
 walls. Of these the more posterior on each side represents 
 the exoccipital and all three periotic bones. It bears a 
 small convex patch of cartilage for articulation with the atlas, 
 and with its fellow forms the boundary of the foramen magnum. 
 
 Two foramina pierce the exoccipital just in front of the 
 occipital condyle and transmit respectively the glossopharyngeal 
 and pneumogastric (fig. 21, X) nerves. Lying laterally to 
 these nerve openings is seen a patch of cartilage, the stapes, 
 which is homologous with the stapes or proximal element of 
 the columellar chain in the frog. Further forward in front of 
 the stapes is the small opening for the exit of the facial nerve, 
 and seen in a lateral view close to the orbitosphenoid, that 
 for the trigeminal (fig. 21, C, 5). 
 
 In front of these large bones the lateral parts of the 
 cranial walls remain cartilaginous for a short distance, and 
 then there follow two elongated bones, the orbitosphenoids 
 (tig. 21, B and C, 11), pierced by the foramina for the exit 
 of the optic nerves. These bones partly correspond to the 
 sphenethmoid of the frog. 
 
 The membrane bones connected with the cranium are the 
 parietals, frontals and prefronto-lachrymals on the dorsal 
 surface, and the parasphenoid on the ventral surface. 
 
 The parietals (fig. 21, A and C, 6) roof over the posterior 
 part of the great dorsal fontanelle and overlap the exoccipito- 
 periotics. They meet one another along a sinuous suture in 
 the middle line, as do also the frontals which overlap them 
 in front. The frontals and parietals both extend for a short 
 distance down the sides of the cranium and meet the orbito- 
 sphenoids. The prefronto-lachrymals (fig. 21, A and C, 7) 
 connect the frontals with the maxillae. 
 
 On the ventral surface is the large parasphenoid (fig. 21, 
 
142 
 
 THE VERTEBRATE SKELETON. 
 
 22 
 
 FlG. 21. A DORSAL, B VENTRAL, AND C LATERAL VIEWS OF THE SKULL 
 
 OF A NEWT (Molge cristata) x 2^ (after PARKER). 
 
 The cartilage is dotted, the cartilage bones are marked with dots and 
 dashes, the membrane bones are left white. 
 
 1. premaxilla. 
 
 2. anterior nares. 
 
 3. posterior nares. 
 
 4. nasal. 
 
 5. frontal. 
 
 6. parietal. 
 
 7. prefronto-lachrymal. 
 
 8. maxilla. 
 
 9. vomero-palatine. 
 
 10. parasphenoid. 
 
 11. orbitosphenoid. 
 
 12. pterygoid. 
 
 13. squamosal. 
 
 14. pro-otic region of exoccipito- 
 
 periotic. 
 
 15. quadrate. 
 
 16. quadrate cartilage. 
 
 17. exoccipital region of exoc- 
 
 cipito-periotic. 
 
 18. articular. 
 
 19. articular cartilage. 
 
 20. dentary. 
 
 21. splenial. 
 
 22. middle narial passage. 
 
 II. V. VII. IX. X. foramina for 
 the exit of cranial nerves. 
 
THE SKELETON OF THE NEWT. SENSE CAPSULES. 143 
 
 B, 10), which is widest behind and overlapped anteriorly 
 by the vomero-palatines. 
 
 (2) THE SENSE CAPSULES. 
 
 The auditory capsules become almost completely ossified 
 continuously with the exoccipitals ; they have been already 
 described. 
 
 The nasal capsules are large and quite unossified though 
 they are overlain by membrane bone. They appear on the 
 dorsal surface between the anterior nares and the nasal process 
 of the premaxillae. They enclose the nasal organs, bound 
 the inner side of the anterior narial opening, and are con- 
 nected with one another posteriorly by a cartilaginous area. 
 
 Developed in connection with the nasal capsules are a pair 
 of rather large nasals (fig. 21, A and C, 4), which lie on the 
 dorsal surface immediately in front of the frontals. Each 
 forms part of the posterior boundary of one of the anterior 
 nares, and the two are separated from one another in 
 the middle line by the nasal process of the premaxillae 
 (fig. 21, A, 1), and the opening of the middle narial passage 
 (tig. 21, A and B, 22), which passes right through the skull. 
 
 On the ventral surface of the skull and forming the greater 
 part of the boundary of the posterior nares are two large 
 bones, the vomero-palatines (fig. 21, B and C, 9). Each consists 
 of a wide anterior portion, partly separated from its fellow in 
 the middle line by the ventral opening of the middle narial 
 passage, and of a long pointed posterior portion which is 
 separated from its fellow by the parasphenoid, and bears a row 
 of small pointed teeth formed of dentine capped with enamel. 
 
 (3) THE JAWS. 
 
 The upper jaw of the newt is a discontinuous structure 
 divided into two parts, an anterior part which consists of 
 membrane bones, the maxillae and premaxillae, and a posterior 
 part which remains mainly cartilaginous. 
 
 The premaxillae are united, forming a single bone, which in 
 
144 THE VERTEBRATE SKELETON. 
 
 a ventral view is seen to meet the maxillae and vomero- 
 palatines, and in a dorsal view to send back a nasal process 
 (fig. 21, A, 1) between the nasals. 
 
 The maxillae are large bones, each terminating in a point 
 posteriorly. A single row of teeth similar to those on the 
 vomero-palatines runs along the outer margin of the maxillae 
 and prem axillae. 
 
 The posterior part of the upper jaw forms a mass of 
 cartilage which extends forwards towards the maxilla as a 
 long pointed process whose ventral surface and sides are over- 
 lapped by a membrane bone, the pterygoid (fig. 21, 12). 
 
 The suspensorial bones include the quadrate and squa- 
 mosal. The quadrate (fig. 21, 15) which forms the true 
 suspensorium is directed forwards and outwards, and is 
 terminated by a patch of cartilage with which the mandible 
 articulates. 
 
 The lower jaw or mandible remains partly cartilaginous, 
 while its ossifications include two membrane bones and one 
 cartilage bone. The cartilage bone is the articular (fig. 21, C, 
 18), it forms the posterior part of the ramus, extends forwards 
 for some distance along its inner side, and is terminated 
 posteriorly by a patch of cartilage which articulates with the 
 quadrate. The dentary (fig. 21, C, 20) is a large bone which forms 
 the anterior part and nearly all the outer half of each ramus, 
 and bears teeth similar to those of the upper jaw. Attached 
 to its inner face is a long slender splenial (fig. 21, C, 21). 
 
 THE HYOID APPARATUS. 
 
 This consists of the hyoid arch and part of the first two 
 branchial arches. 
 
 The hyoid arch (fig. 21, A, 2) consists of a pair of cornua, 
 each of which is divided into two halves. The dorsal half 
 forming the cerato-hyal is mainly ossified though tipped with 
 cartilage, and is connected by ligament with the suspensorium. 
 The ventral half (hypo-hyal) is cartilaginous, and is connected 
 with the basi-branchial. 
 
THE SKELETON OF THE NEWT. RIBS AND STERNUM. 145 
 
 The branchial arches consist of a median piece, the 
 basi-branchial, which is ossified in the centre and cartila- 
 ginous at either end, and of two pairs of cerato-branchials 
 which are attached to the cartilaginous part (fig. 29, A, 8) 
 of the basi-branchial. The first cera to-branchial is chiefly 
 ossified, the second (fig. 29, A, 4) is a good deal smaller and 
 is cartilaginous. Both are united dorsally to a single epi- 
 branchial, which is terminated by a small cartilaginous area 
 at the free end but is elsewhere well ossified. 
 
 C. THE RIBS. 
 
 The ribs are short imperfectly ossified structures, bifid 
 at their proximal end where they articulate with the trans- 
 verse processes, and tipped both proximally and distally with 
 cartilage. The dorsal portion of the proximal end corresponds 
 to the tuberculum of the ribs of higher animals, and the 
 ventral portion to the capitiilum. Some of the anterior ribs 
 have a step-like notch on their dorsal surfaces. 
 
 The second to twelfth ribs are fairly equal in size, but 
 further back they decrease slightly. The ribs which connect 
 the sacral vertebrae with the ilia are however large. The short 
 ribs borne on the anterior caudal vertebrae are cartilaginous. 
 
 D. THE STERNUM. 
 
 The sternum (fig. 22, A, 6) is a rather broad plate of 
 cartilage, drawn out posteriorly into a median process marked 
 by a prominent ridge. On its antero-lateral margins it bears 
 surfaces for articulation with the pectoral girdle. 
 
 2. THE APPENDICULAR SKELETON. 
 
 A. THE PECTORAL GIRDLE. 
 
 This is of a very simple character, and remains throughout 
 life in an imperfectly ossified condition. It consists of a 
 dorsal scapular portion, and a ventral coracoid portion 
 partially divided into an anterior part, the precoracoid, and 
 a posterior part, the coracoid. 
 
 R. 10 
 
146 
 
 THE VERTEBRATE SKELETON. 
 
 The scapular portion is a slightly curved oblong plate; its 
 proximal third the scapula (fig. 22, 1) is ossified and bounds 
 part of the well-marked glenoid cavity (fig. 22, 4) ; its distal 
 portion forms a large oblong cartilaginous plate, the supra- 
 
 FlG. 22. A VENTKAL, AND B LATEKAL VIEW OF THE SHOULDER GIRDLE 
 AND STERNUM OF AN OLD MALE CRESTED NEWT (Mol(J6 CristCttd) X 3 
 
 (after PARKER). 
 
 1. scapula. 4. glenoid cavity. 
 
 2. suprascapula. 5. precoracoid. 
 
 3. coracoid. 6. sternum. 
 
THE SKELETON OF THE NEWT. ANTERIOR LIMB. 147 
 
 The precoracoid (fig. 22, 5) forms a small forwardly- 
 directed cartilaginous plate. The coracoid (fig. 22, 3) forms 
 a much larger plate, the greater part of which is unossified 
 and overlaps its fellow in the middle line, the two being over- 
 lapped by the sternum. Around the glenoid cavity is an area 
 which is mainly ossified and is continuous with the scapula. 
 
 B. THE ANTERIOR LIMB. 
 
 This is divisible into three parts, the upper arm or 
 brachium, the fore-arm or antibrachium, and the maims. 
 
 The upper arm includes a single bone, the humerus. 
 
 The humerus is a slender bone cylindrical in the middle 
 and expanded at either end, the proximal part forms a 
 rounded head which articulates with the glenoid cavity. 
 Along the proximal part of the anterior or pre-axial surface 
 runs a strong deltoid ridge. The proximal part of the post- 
 axial surface also bears a small outgrowth. 
 
 The fore-arm contains two bones, the radius and ulna, both 
 of which are small and imperfectly ossified at their terminations. 
 
 The radius (fig. 23, B, 11) or pre-axial bone is rather 
 the larger of the two, and is considerably expanded at its 
 proximal end. The ulna or post axial bone is somewhat 
 expanded distally, but is not drawn out proximally into an 
 olecranon process. 
 
 The manus consists of two parts, a group of small bones 
 forming the carpus or wrist, and the hand. 
 
 The carpus is in a very simple unmodified condition as 
 compared with that of the Frog. It consists of a proximal 
 row of two bones and a distal row of four, with one, the 
 centrale, interposed between. All these bones are small and 
 polygonal and are imbedded in a plate of cartilage. 
 
 The bones of the proximal row are a smaller pre-axial bone, 
 the radiale (fig. 23, B, 13), and a larger postaxial bone, which 
 represents the fused ulnare and intermedium of the very 
 simple carpus described on pp. 26 and 27. 
 
 102 
 
148 
 
 THE VERTEBRATE SKELETON. 
 
 The four bones of the distal row are respectively car- 
 palia 2, 3, 4 and 5. 
 
 The hand consists of four digits, that corresponding to 
 the thumb of the human hand, judging from the analogy of 
 the frog probably being the one that is absent. 
 
 Each digit consists of a somewhat elongated metacarpal 
 and of two or three phalanges. The metacarpals are contracted 
 in the middle and expanded at either end. They are connected 
 with the carpus by cartilage, and the articulations between the 
 several phalanges, and between the metacarpals and phalanges 
 are also cartilaginous. The second, third, and fifth digits 
 have two phalanges apiece, the fourth, which is the longest, 
 
 18- 
 
 m 
 
 FlG. 23. A RIGHT POSTERIOR, AND B RIGHT ANTERIOR LIMB OF A NEWT 
 
 x 1 (Molge cristata). 
 
 10. humerus. 
 
 11. radius. 
 
 12. ulna. 
 
 13. radiale. 
 
 14. intermedium and ulnare fused. 
 
 15. centrale of carpus, the pointing 
 
 femur. 
 
 tibia. 
 
 fibula. 
 
 tibiale. 
 
 intermedium. 
 
 fibulare. 
 
 centrale of tarsus. 
 
 tarsale 1. 
 
 tarsalia 4 and 5 fused. 
 
 I. II. III. IV. V. digits. 
 
 line passes across carpale 2. 
 
 16. carpale 3. 
 
 17. carpale 5. 
 
THE SKELETON OF THE NEWT. PELVIC GIRDLE. 149 
 
 has three. The second metacarpal in the specimen examined 
 and figured articulates partly with carpale 2, partly with 
 carpale 3. 
 
 C. THE PELVIC GIRDLE. 
 
 The pelvic girdle of the Newt is in a much less modified 
 condition than is that of the Frog (see p. 165). It consists 
 of a dorsal element, the ilium, a posterior ventral element, 
 the ischium, and an anterior ventral element, the pubis, to 
 which is attached an epipubis. 
 
 The ilium is a somewhat cylindrical bone which at its 
 ventral end meets the ischium, and forms part of the ace- 
 tabulum. It is then directed upwards and slightly back- 
 wards, and is attached to the ribs of the sacral vertebra. 
 
 The ischia are a pair of somewhat square bones which 
 meet one another in the middle line ; they form part of the 
 acetabulum, and are united to the ilia above. 
 
 In front of the ischia is a narrow cartilaginous area which 
 represents the pubes. Projecting forwards from it is a bifid 
 cartilaginous epipubis. 
 
 D. THE POSTERIOR LIMB. 
 
 This is divisible into a proximal portion, the thigh, a 
 middle portion, the crus or shin, and a distal portion, the 
 pes. 
 
 The thigh consists of a single bone, the femur (fig. 23, A,l), 
 which has a thin shaft and expanded ends. The anterior 
 part of the pre-axial border and posterior part of the postaxial 
 border bear slight outgrowths. 
 
 The'crus or shin includes two short bones, the tibia and 
 fibula, which are nearly equal in length. The pre-axial bone 
 or tibia is a straight bone thickest at its proximal end, the 
 postaxial bone or fibula (fig. 23, A, 3) is a rather stouter 
 curved bone of nearly equal diameter throughout. 
 
 The pes includes the tarsus or ankle, and the foot. 
 
150 THE VERTEBRATE SKELETON. 
 
 The tarsus consists of eight small bones arranged in a 
 proximal row of three, the tibiale, intermedium and fibu- 
 lare, and a distal row of four tarsalia, with one bone, the 
 centrale (fig. 23, A, 7), interposed between the two rows. 
 In the specimen examined, the tibiale, is a small bone 
 articulating with the tibia, the intermedium (fig. 23, A, 5) 
 is larger and articulates with both tibia and fibula, the 
 fibulare is the largest of the three and articulates with the 
 fibula. 
 
 The bones of the distal row are tarsalia 1, 2, 3, and a 
 bone representing 4 and 5 fused. In the specimen examined 
 tarsale 1 is pushed away dorsal ly (fig. 23, A, 8), so as to lie 
 between the tibiale and tarsale 2. All the tarsal bones are 
 small and somewhat polygonal, and are connected with one 
 another, and with the tibia and fibula on the one hand, and 
 with the metatarsals on the other by a thin layer of cartilage. 
 
 The five digits of the foot each consist of a metatarsal 
 and of a certain number of phalanges. In the specimen 
 examined, owing to the shifting of tarsale 1, the first meta- 
 tarsal as well as the second articulates with tarsale 2, while 
 the fifth metatarsal articulates partially with the bone repre- 
 senting the fused tarsalia 4 and 5, partially with the fibulare. 
 All the bones of the digits except the distal phalanges are 
 terminated at each end by cartilaginous epiphyses, the distal 
 phalanx of each digit has a cartilaginous epiphysis only on its 
 proximal end. 
 
 The first, second, and fifth digits have two phalanges 
 apiece, the third and fourth have three. 
 
 Figure 31 B, showing a Newt's tarsus copied from Gegen- 
 baur, has precisely the arrangement generally regarded as 
 primitive for the higher vertebrates, except that tarsalia 4 
 and 5 are fused. 
 
CHAPTER XL 
 
 THE SKELETON OF THE FROG 1 (Sana temporaria). 
 
 I. EXOSKELETON. 
 
 The skin of the frog is smooth and quite devoid of scales 
 or other exoskeletal structures. The only exoskeletal struc- 
 tures met with in the frog are : 
 
 1. The teeth, which are most conveniently described with 
 the endoskeleton. 
 
 2. The horny covering of the calcar or prehallux (see 
 p. 167). 
 
 II. ENDOSKELETON. 
 
 The endoskeleton of the adult frog consists partly of 
 cartilage, partly of bone and each of these types of tissue 
 occurs in two forms. The cartilage may be hyaline, as in 
 the omosternum and xiphisternum, or may be more or less 
 calcined as in part of the suprascapula and the epiphyses 
 of the limb bones. The bone may be cartilage bone, or 
 membrane bone. 
 
 The skeleton is divisible into an axial portion consisting 
 of the skull, vertebral column, and sternum, and an appen- 
 
 1 See A. Ecker, Die anatomie des Frosches, Braunschweig 1864, 
 translated by G. Haslam, Oxford, 1889, also A. M. Marshall, The Frog, 
 5th edition, Manchester and London, 1894. 
 
152 THE VERTEBRATE SKELETON. 
 
 dicular portion consisting of the skeleton of the limbs and 
 their girdles. 
 
 1. THE AXIAL SKELETON. 
 
 A. THE VERTEBRAL COLUMN. 
 
 The vertebral column is a tube, formed of a series of ten 
 bones which surround and protect the spinal cord. Of these 
 ten bones nine are vertebrae, while the tenth is a straight rod, 
 the urostyle, and is almost as long as all the vertebrae put 
 together. The second to eighth vertebrae inclusive have a very 
 similar structure, but the first and ninth differ from the others. 
 
 Any one of the second to eighth vertebrae forms a bony 
 ring with a somewhat thickened floor, the centrum or body, 
 which articulates with the centra of the immediately preceding 
 and succeeding vertebrae. The articulating surfaces are 
 covered with cartilage and are procoelous, or convex in front 
 and concave behind. The eighth vertebra is however amphi- 
 coelous or biconcave. The centrum of each vertebra encloses 
 an isolated vestige of the notochord. The neural arch forms 
 the roof and sides of the neural canal, which is very spacious 
 in the anterior vertebrae, but becomes more depressed in the 
 posterior ones. The arch bears the neural spine, a low 
 median ridge of variable character, and is drawn out in 
 front and behind, forming the two pairs of articulating 
 surfaces or zygapophyses by means of which the vertebrae 
 are attached together. Of these the anterior articulating 
 surfaces or prezygapophyses look upwards and slightly 
 inwards, while the posterior articulating surfaces or post- 
 zygapophyses look downwards and slightly outwards. The 
 sides of the neural arches are drawn out into a pair of 
 prominent transverse processes. Those of the second 
 vertebra look somewhat forwards, those of the third look 
 directly outwards or somewhat forwards, while those of 
 the fourth, fifth, and sixth are directed slightly backwards, 
 and those of the seventh and eighth nearly straight outwards. 
 
THE SKELETON OF THE FROG. SPECIAL VERTEBRAE. 153 
 
 All the transverse processes are terminated by very small carti- 
 laginous ribs. 
 
 SPECIAL VERTEBRAE. 
 
 The first vertebra is a ring-like structure with a much 
 depressed centrum. It bears in front two oval concave sur- 
 faces for articulation with the condyles of the skull, while the 
 centrum is terminated behind by a prominent convex surface. 
 There are as a rule no transverse processes, and the post- 
 zygapophyses look downwards and outwards. Occasionally 
 however transverse processes do occur. Projecting forwards 
 from the centrum is a minute process better developed in the 
 Newt. This resembles an odontoid process, and it has hence 
 been supposed that the first vertebra is homologous with the 
 axis of mammalia, and that the atlas of the frog is fused with 
 the skull. 
 
 The ninth vertebra has very stout transverse processes 
 directed backwards and somewhat upwards. They articulate 
 with the pelvic girdle and hence this vertebra is regarded as 
 the sacrum. The neural arch is much depressed, the centrum 
 is convex in front and bears on its posterior surface two short 
 rounded processes for articulation with the urostyle. 
 
 The urostyle is a long rod-like bone forming the posterior 
 unsegmented continuation of the vertebral column. It is 
 probably equivalent to three vertebrae, the tenth, eleventh, 
 and twelfth fused together, and to an unsegmented rod of 
 cartilage which lies ventral to the notochord. The anterior end 
 is expanded and bears two concave articular surfaces by means 
 of which it articulates with the sacrum. A prominent ridge 
 runs along the dorsal surface, but gradually diminishes when 
 traced back. The anterior portion contains a canal which is 
 a continuation of the neural canal. At a point not far from 
 the anterior end, this canal communicates with the exterior 
 by a pair of minute holes which correspond with the iiiter- 
 vertebral foramina. 
 
154 THE VERTEBRATE SKELETON. 
 
 B. THE SKULL 1 . 
 
 The skull of the Frog consists of three principal parts : 
 
 (1) an axial part, the cranium, proper, which encloses 
 the brain. To it are firmly fused 
 
 (2) the capsules of the olfactory and auditory 
 sense organs, 
 
 (3) lastly there is the hyoid apparatus and the skele- 
 ton of the jaws. 
 
 The skull is by no means so completely ossified as is the 
 vertebral column, but in addition to the cartilage bone, there 
 is a great development of membrane bone in connection 
 with it. 
 
 The skull has a peculiarly flattened and expanded form 
 depending on the wide lateral separation of the jaws from the 
 cranium. 
 
 (1) THE CRANIUM PROPER or Brain case. 
 
 This is an unsegmented tube, which is widest behind. It 
 remains to a considerable extent cartilaginous, but is partly 
 converted into cartilage bone, partly sheathed in membrane 
 bone. Its roof is imperfect, being pierced by three holes 
 or fontanelles, one large anterior fontanelle (fig. 25, A, 9), 
 and two smaller posterior fontanelles (fig. 25, A, 10). 
 
 The cartilage bones of the cranium proper are the two 
 exoccipitals and the sphenethmoid. 
 
 The exoccipitals (figs. 24, 25, and 26, 6) are a pair of 
 irregular bones bounding the foramen magnum at the posterior 
 end of the skull. They almost completely surround the foramen 
 magnum, and bear a pair of oval convex surfaces, the occipital 
 condyles, with which the first vertebra articulates. The bones 
 generally called the exoccipitals of the frog include the epi-otic 
 
 1 W. K. Parker, Phil. Trans. 161, 1871, p. 137, and W. K. Parker and 
 G. T. Bettany, The Morphology of the Skull, London, 1877, p. 136. 
 
THE SKELETON OF THE FROG. THE SKULL. 155 
 
 and opisthotic elements of many skulls, in addition to the 
 exoccipitals. 
 
 The patch of unossified cartilage immediately external. to 
 the occipital condyle is pierced by two small foramina, through 
 which the ninth and tenth nerves leave the cranial cavity. 
 The ninth nerve passes through the more external of these 
 foramina, the tenth through the one nearer the condyle. 
 
 A B 
 
 20 
 
 FlG. 24. A DORSAL, AND B VENTRAL VIEWS OF THE CRANIUM OF A 
 
 COMMON FROG (Rana temporaria) x 2 (after PARKER). 
 
 In this and the next two figs, cartilage is dotted, cartilage bones are 
 marked with dots and dashes, membrane bones are left white. 
 
 1. sphenethmoid. 
 
 2. fronto-parietal. 
 
 3. pterygoid. 
 
 4. squamosal. 
 
 6. exoccipital. 
 
 7. parasphenoid. 
 
 8. pro-otic. 
 
 9. quadratojugal. 
 
 10. maxilla. 
 
 11. nasal. 
 
 12. premaxilla. 
 
 13. anterior nares. 
 
 14. vomer. 
 
 15. posterior nares. 
 
 16. palatine. 
 
 18. columella. 
 
 19. quadrate. 
 
 20. occipital condyle. 
 II. optic foramen. 
 
 V. VII. foramen for exit of 
 trigeminal and facial nerves. 
 
 IX. X. foramina for exit of glos- 
 sopharyngeal and pneumogastric 
 
156 THE VERTEBRATE SKELETON. 
 
 The foramina lie however very close together and are some- 
 times confluent. The cranial walls for a considerable distance 
 in front of the occipitals are unossified, but the anterior end 
 of the cranial cavity is encircled by another cartilage bone, the 
 sphenethmoid (figs. 24 and 25, 1) or girdle bone. This 
 partly corresponds to the orbitosphenoids of the Newt's skull. 
 Anteriorly it is pierced by a pair of small foramina through 
 which the ophthalmic branches of the trigeminal nerve pass out. 
 
 The anterior part of the cranial cavity is divided into two 
 halves by a vertical plate, the mesethmoid. Some little 
 distance behind the sphenethmoid the ventro-lateral walls of 
 the cartilaginous cranium are pierced by a pair of rather pro- 
 minent holes, the optic foramina (figs. 24 and 25, B, n), and 
 at a similar distance further back, occupying a kind of notch 
 in the pro-otic are the large trigeminal foramina, through 
 which the fifth and seventh nerves leave the cranium. Between 
 the trigeminal and optic foramina are the very small foramina 
 for the sixth nerves (fig. 25, B, vi). 
 
 The membrane bones of the cranium proper include the 
 fronto-parietals and the parasphenoid. 
 
 The fronto-parietals (figs. 24 and 26, A, 2) form a pair of 
 long flat bones closely applied to one another in the middle line, 
 the line of junction being the sagittal suture. They cover 
 over the fontanelles and overlap the sphenethmoid in front. 
 
 The parasphenoid (figs. 24 and 26, B, 7) is a bone shaped 
 like a dagger with a very short handle. It lies on the ventral 
 surface of the cranium, the blade being directed forwards and 
 underlying the sphenethmoid; its lateral processes underlie 
 the auditory capsules. i 
 
 (2) THE SENSE CAPSULES. 
 
 The sense capsules are cartilaginous or bony structures 
 which surround the olfactory and auditory organs and are 
 closely united to the cranium. 
 
 The auditory capsules are fused with the sides of the 
 
THE SKELETON OF THE FROG. THE SKULL. 157 
 
 posterior end of the cranium just in front of the exoccipitals. 
 They are largely cartilaginous, but include in their anterior 
 
 A B 
 
 FlG. 25. A DOKSAL AND B VENTRAL VIEW OF THE CRANIUM OF A COMMON 
 
 FROG (Eana temporaria) from which the membrane bones have 
 mostly been removed. x2 (after PARKER). 
 
 1. sphenethmoid. 
 
 2. palatine. 
 
 3. pterygoid. 
 
 4. quadrate. 
 
 5. columella. 
 6 exoccipital. 
 
 7. ventral cartilaginous wall of 
 cranium. 
 
 8. 
 
 pro-otic. 
 9. anterior fontanelle. 
 
 10. right posterior fontanelle. 
 
 11. quadratojugal. 
 
 12. nasal capsule. 
 
 II. V. VI. IX. X. foramina for 
 exit of cranial nerves. 
 
 walls a pair of irregular cartilage bones, the pro-otics (figs. 
 24 and 25, 8). The cartilaginous area lying ventral to the 
 pro-otic and external to the exoccipital is pierced by a rather 
 prominent hole, the fenestra ovalis, which forms a com- 
 munication between the internal ear cavity, and a space the 
 tympanic cavity, which lies at the side of the head, and is 
 bounded externally by the tympanic membrane. The fenestra 
 ovalis is occupied by a minute cartilaginous structure, the 
 stapes, and articulated partly to this and partly to a slight 
 recess in the pro-otic is the columella (fig. 25, B, 5), a rod in 
 part bony and in part cartilaginous, whose outer end is 
 
158 THE VERTEBRATE SKELETON. 
 
 attached to the tympanic membrane. The columella and 
 stapes are together homologous with the mammalian auditory 
 ossicles and with the hyomandibular of Elasmobranchs. Some- 
 times the term columella is used to include the whole ossicular 
 chain, the columella together with the stapes. 
 
 The olfactory or nasal capsules (fig. 25, B, 12) are fused 
 with the anterior end of the cranium and differ from the 
 auditory capsules in being to a great extent unossified. There 
 are however two pairs of membrane bones developed in con- 
 nection with them, the vomers and the nasals. They are drawn 
 out into three pairs of cartilaginous processes, on the dorsal 
 surface into the prenasal and alinasal processes which bound 
 the external nares, and on the ventral surface towards the 
 middle line into the forwardly-projecting rhinal processes. 
 
 The nasals (figs. 24 and 26, 11) form a pair of triangular 
 bones lying dorso-laterally in front of the fronto-parietals. 
 Their bases are turned towards one another and their apices 
 are directed outwards and backwards. They correspond in 
 position with the prefrontals of the reptilian skull as well as 
 with the nasals. 
 
 The vomers are a pair of irregular bones lying on the 
 ventral surface of the olfactory capsules. Each bears on 
 its inner and posterior angle a group of minute pointed teeth, 
 while its outer border is drawn out into three or four small 
 slightly diverging processes, the two posterior of which form 
 the inner boundary of the posterior nares (fig. 24, B, 15). 
 
 (3) THE JAWS. 
 
 The upper jaw consists of a rod of cartilage connected 
 with the cranium near its two ends, but widely separated from 
 it in the middle. It is almost completely overlain by membrane 
 bone. With its posterior end the lower jaw articulates. 
 
 The membrane bones of the upper jaw include first the 
 premaxilla, a small bone meeting its fellow in the middle 
 line, and forming the extreme anterior end of the upper jaw. 
 It gives off on its dorsal surface a backwardly-projecting 
 
THE SKELETON OF THE FROG. THE SKULL. 159 
 
 process. It is connected behind with the maxilla (figs. 24 and 
 26, 10), a long flattened bone which forms the greater part of 
 
 FIG. 26. A, LATERAL VIEW OF 
 
 CRANIUM OF A COMMON FROG 
 
 1. sphenethmoid. 
 
 2. fronto-parietal. 
 
 3. pterygoid. 
 
 4. squamosal. 
 
 5. tympanic membrane. 
 
 6. exoccipital. 
 
 7. parasphenoid. 
 
 8. pro-otic. 
 
 9. quadratojugal, 
 
 10. maxilla. 
 
 11. nasal. 
 
 12. premaxilla. 
 
 13. anterior nares. 
 
 B 
 
 THE SKULL, B, POSTERIOR VIEW OF THE 
 
 (Rana temporaria) x 2 (after PARKER). 
 
 14. mento-meckelian. 
 
 15. dentary. 
 
 16. angulo-splenial. 
 
 17. basilingual plate. 
 
 19. quadrate. 
 
 20. columella. 
 
 21. occipital condyle. 
 
 22. anterior cornu of the hyoid 
 
 (cerato-hyal). 
 
 23. foramen magnum. 
 
 II. IX. X. foramina for the exit 
 of cranial nerves. 
 
 the margin of the upper jaw, and gives off near its anterior end 
 a short process which projects upwards and meets the nasal. 
 
 Both maxilla and premaxilla are grooved ventrally, and 
 bear, attached to the outer more* prominent margin of the groove, 
 a row of minute conical teeth. These teeth are pleurodont, 
 that is, are ankylosed by their bases and outer sides to the 
 margin of the jaw. Each tooth is a hollow cone, the basal 
 
160 THE VERTEBRATE SKELETON. 
 
 part of which is formed of bone, the apical part of dentine, 
 capped by a very weak development of enamel. 
 
 The posterior end of the maxilla is overlapped by a small 
 bone, the quadratojugal (figs. 24 and 26, 9), whose posterior 
 end forms part of the articular surface for the lower jaw. 
 Just behind the quadratojugal there is a small unossified area 
 which lies at the angle of the mouth, and is connected by a 
 narrow bar of cartilage with the cranium ; this forms the 
 quadrate (figs. 24 and 26, 19). A backwardly-directed out- 
 growth from the cartilaginous bar more or less completely 
 surrounds the tympanic membrane, forming the tympanic 
 ring. When followed back the maxilla and quadratojugal 
 diverge further and further from the cranium, till the angle 
 of the mouth comes to be separated from the foramen magnum 
 by a space nearly double the width of the cranium. This space 
 is bridged over to a considerable extent by two triradiate bones, 
 the pterygoid and squamosal. 
 
 The pterygoid (figs. 24 and 26, 3) is a large bone, whose 
 anterior limb runs forwards meeting the maxilla and palatine; 
 while its inner limb meets the auditory capsule and para- 
 sphenoid, and its outer limb runs backwards and outwards 
 to the angle of the mouth. The palatine is a small transversely- 
 placed bone, which connects the pterygoid with the anterior 
 part of the sphenethmoid. The squamosal (figs. 24 and 26, 4) 
 is a T-shaped bone whose anterior arm is pointed and passes 
 forwards to meet the pterygoid. The posterior upper arm is 
 closely applied to the pro-otic, while the posterior lower arm 
 meets the pterygoid and quadratojugal at the angle of the jaw, 
 and surrounds the narrow cartilaginous bar of the quadrate 
 which goes to join the cranium. The squamosal is probably 
 homologous with the squamosal together with the pre-opercular 
 of Bony Ganoids. 
 
 The quadrate and squamosal form the suspensorium. by 
 which the lower jaw is connected with the cranium. 
 
 The lower jaw or mandible consists of a pair of carti- 
 laginous rods (Meckel's cartilages) in connection with each 
 
THE SKELETON OF THE FROG. THE HYOID. 161 
 
 of which there are developed two membrane bones and one 
 cartilage, bone. The cartilage bone is the mento-meckelian 
 (fig. 26, A, 14), a very small ossification at the extreme anterior 
 end. The membrane bones are the angulo-splenial and the 
 dentary. The angulo-splenial is a strong flat bone which forms 
 the inner and lower part of the mandible for the greater 
 part of its length. Its dorsal surface is produced into a slight 
 coronoid process. The dentary (fig. 26, A, 15) is a flat 
 plate which covers the outer surface of the anterior half of the 
 mandible, as far forwards as the mento-meckelian. The lower 
 jaw is devoid of teeth. The part of Meckel's cartilage which 
 in most vertebrates ossifies, forming the articular bone, remains 
 unossified in the Frog. 
 
 THE HYOID APPARATUS. 
 
 The hyoid of the adult Frog is formed of the modified 
 hyoid and branchial arches of the tadpole. It consists of a 
 broad thin plate of cartilage, the basilingual plate (fig. 29, 
 B, 1), drawn out into two pairs of long processes, the comua. 
 The basilingual plate is broader in front than behind, and is 
 formed from the fused ventral ends of the hyoid and branchial 
 arches of the tadpole. 
 
 The anterior cornua (fig. 29, B, 2) form a pair of long 
 slender cartilaginous rods which project from the body of the 
 hyoid at first forwards, then backwards, and finally upwards 
 and somewhat forwards again, to be united to the auditory 
 capsules just below the fenestrae ovales. They are formed 
 from the dorsal portion of the hyoid arch of the tadpole and 
 are homologous with the cerato-hyals of the Dogfish. 
 
 The posterior cornua form a pair of straight bony rods 
 diverging outwards from the posterior end of the basilingual 
 plate. They are formed from the fourth branchial arches of 
 the tadpole, and differ from the rest of the hyoid apparatus 
 in being well ossified. 
 
 R. 11 
 
162 THE VERTEBRATE SKELETON. 
 
 The columellar chain, which has been already described 
 (p. 157), should be mentioned with the hyoid as it. is homo- 
 logous to the hyomandibular of fishes. 
 
 The sternum, of the Frog, though regarded as part of the 
 axial skeleton, is so intimately connected with the pectoral 
 girdle, that it will be described with the appendicular 
 skeleton. 
 
 2. THE APPENDICULAR SKELETON. 
 
 This consists of the skeleton of the two pairs of limbs and 
 their respective girdles. It is at first entirely cartilaginous 
 but the cartilage becomes later on mainly replaced by bone. 
 The only bone developed in connection with the appendi- 
 cular skeleton, which has no cartilaginous predecessor, is the 
 clavicle. 
 
 A. THE PECTORAL GIRDLE. 
 
 This consists originally of two half rings of cartilage en- 
 circling the sides of the body a short way behind the head. 
 These two halves meet one another in the ventral middle line, 
 and separate the anterior elements of the sternum from the 
 posterior ones. 
 
 Each half -ring bears on the middle of its outer and pos- 
 terior surface a prominent cup, the glenoid cavity, with 
 which the proximal arm-bone articulates. This cup divides 
 the half-arch into a dorsal scapular and a ventral coracoid 
 portion. 
 
 The scapular portion consists of two parts, the supra- 
 scapula and the scapula. 
 
 The suprascapula (fig. 30, A, 2) is a wide, thin plate 
 attached by its ventral and narrowest border to the scapula. 
 Its proximal and anterior half is imperfectly ossified, its whole 
 border or sometimes only its dorsal and posterior borders consist 
 of unaltered hyaline cartilage, while the rest of it is composed 
 of calcified cartilage. The scapula (fig. 30, A, 3) is a fairly 
 
THE SKELETON OF THE FROG. THE STERNUM. 163 
 
 stout rod of bone constricted in the middle, and forming the 
 dorsal half of the glenoid cavity. 
 
 The coracoid portion consists of three parts, the cora- 
 coid, precoracoid and clavicle. 
 
 The largest and most posterior of these is the coracoid 
 (fig. 30, A, 4) which like the scapula, is contracted in the 
 middle and expanded at the ends, especially at the ventral 
 end. It forms a large part of the glenoid cavity. The 
 ventral ends of the coracoids which meet one another in the 
 middle line are unossified, and form narrow strips of calcified 
 cartilage, the epicoracoids (fig. 30, A, 5) ; these are often 
 regarded as sternal elements. 
 
 The precoracoid forms a narrow strip of cartilage lying 
 in front of the coracoid, from which it is separated by the 
 wide coracoid foramen (fig. 30, A, 9). The dorsal end is 
 continuous with an area of unossified cartilage which separates 
 the coracoid and scapula and forms part of the glenoid cavity. 
 
 The clavicle is a narrow membrane bone closely attached 
 to the anterior surface of the precoracoid, its dorsal end is ex- 
 panded. 
 
 THE STERNUM. 
 
 The sternum consists of four parts arranged in two groups ; 
 two parts to each group. The anterior members are the epi- 
 sternum and omosternum. 
 
 The episternum (fig. 30, A, 10) is a thin almost circular 
 plate of cartilage much of which remains hyaline. 
 
 The omosternum (fig. 30, A, 11) is a slender bony rod 
 widest at its posterior end : it connects the episternum with 
 the ventral ends of the precoracoids. 
 
 The sternum proper is a short rod of cartilage sheathed 
 in bone ; it is contracted in the middle and expanded at each 
 end. It bears attached to its posterior end a broad some- 
 what bilobed plate of partially calcified cartilage, the xiphi- 
 sternum (fig. 30, A, 13). 
 
 112 
 
164 THE VERTEBRATE SKELETON. 
 
 B. THE ANTERIOR LIMB. 
 
 This is divisible into three parts, the upper arm or 
 brachium, the fore-arm or antibrachium, and the maims. 
 
 All the larger bones have their ends formed by prominent 
 epiphyses which do not unite with the shaft till late in life. 
 Their articulating surfaces are covered by hyaline cartilage. 
 
 In the upper arm there is a single bone, the humerus. 
 
 This has a more or less cylindrical shaft and articulates by 
 a prominent rounded head with the glenoid cavity. The 
 distal end shows a large rounded swelling on either side of 
 which is a condylar ridge, the inner or postaxial one being 
 the larger. A prominent deltoid ridge runs along the 
 proximal half of the anterior surface, and in the male frog a 
 second equally prominent ridge runs along the distal half of 
 the posterior surface. 
 
 The fore-arm consists of two bones, the radius and ulna, 
 united together and forming the radio-ulna. The two bones 
 are quite fused at their proximal ends where they form a 
 deep cup which articulates with the distal end of the humerus, 
 and is drawn out into a rather prominent backwardly-pro- 
 jecting olecranon process, which ossifies from a centre 
 distinct from that of the shaft. The distal end is distinctly 
 divided by a groove into an anterior radial and a posterior 
 ulnar portion. 
 
 The manus consists of two parts, the wrist or carpus 
 and the hand. 
 
 The carpus 1 consists of six small bones arranged in two 
 rows. The three bones of the proximal row are the ulnare, 
 radiale and centrale. The ulnare and radiale are about 
 equal in size and articulate regularly with the radio-ulna. The 
 centrale is pushed out of its normal position and lies partly on 
 the pre-axial side, partly in front of the radiale. Of the three 
 bones of the distal row the two pre-axial ones, carpalia 1 and 
 2, are small; carpale 2 articulates with the second metacarpal, 
 1 See G. B. Howes and W. Ridewood, P. Z. S., 1888, p. 141. * 
 
THE SKELETON OF THE FROG. PELVIC GIRDLE. 165 
 
 carpale 1 with both the first and second. The third bone is 
 large and articulates with the third, fourth and fifth meta- 
 carpals, it represents carpalia 3 5, with probably in addition 
 the representative of a second centrale. 
 
 The hand consists of four complete digits, and a vestigial 
 pollex reduced to a short metacarpal. 
 
 Each of the four complete digits consists of a metacarpal 
 and a variable number of phalanges. The first digit, as just 
 mentioned, has no phalanges, the second and third have two, 
 and the fourth and fifth have three. 
 
 C. THE PELVIC GIRDLE. 
 
 The pelvic girdle of the Frog is much modified from the 
 simple or general type found in the Newt (p. 149). 
 
 It is a V-shaped structure consisting of two halves which 
 are fused together in the middle line posteriorly, while in 
 front they are attached to the ends of the transverse pro- 
 cesses of the sacral vertebra. Each half bears at its posterior 
 end a deep cup, the acetabulum, with which the head of the 
 femur articulates. 
 
 Each half of the pelvis ossifies from two centres. The 
 anterior and upper half of the acetabulum, and the long 
 laterally compressed bar extending forwards to meet the sacral 
 vertebra ossify from a single centre and are generally called 
 the ilium ; it is probable however that they represent both 
 the ilium and pubis of mammals 1 . The posterior part of 
 this bone meets its fellow in a median symphysis. 
 
 The posterior third of the acetabulum is formed by a small 
 bone, the ischium, which likewise meets its fellow in a 
 median symphysis. 
 
 The ventral portion of the pelvic girdle never ossifies, even 
 in old animals being formed only of calcified cartilage. This 
 is generally regarded as the pubis, but it perhaps corresponds 
 to the acetabular bone of mammals. 
 
 1 See bottom of p. 187. 
 
166 THE VERTEBRATE SKELETON. 
 
 D. THE POSTERIOR LIMB. 
 
 This corresponds closely to the anterior limb and, like it, 
 is divisible into three parts, the thigh, the shin or cms and 
 the pes. 
 
 As was the case with the anterior limb, all the long bones 
 have their ends formed by prominent epiphyses which do not 
 unite with the shaft till late in life. 
 
 In the thigh there is only a single bone, the femur. 
 
 The femur is a moderately long, slender bone with a well- 
 ossified hollow shaft slightly curved in a sigmoid manner. 
 Both ends are expanded, the proximal end is hemispherical 
 and articulates with the acetabulum, the distal end is larger 
 and more laterally expanded. 
 
 The shin likewise includes a single bone, the tibio-fibula, 
 but this, as can be readily seen by the grooves at the proximal 
 and distal ends of the shaft, is formed by the fusion of two 
 distinct bones, the tibia and fibula. The tibio-fibula is longer 
 and straighter than the femur. 
 
 The pes consists of two parts, the ankle or tarsus and the 
 foot. 
 
 The tarsus consists of two rows of structures, very dif- 
 ferent in size. The proximal row consists of two long bones, 
 the tibiale and fibulare, which are united by common epi- 
 physes at the two ends, while in the middle they are widely 
 separated. The tibiale lies on the tibial or pre-axial side, 
 and the fibulare which is the larger of the two bones on 
 the fibular or postaxial side. The distal row of tarsals 
 consists of three very small pieces of calcified cartilage. The 
 postaxial of these is the largest, it articulates with the second 
 and third metatarsals and is probably homologous with tarsalia 
 2 and 3 fused. The middle one is very small, it articulates 
 with the first nietatarsal and is probably tarsale 1. The pre- 
 axial one articulates with the nietatarsal of the calcar, a 
 structure to be described immediately, and has been regarded 
 as a centrale. 
 
THE SKELETON OF THE FKOG. THE FOOT. 167 
 
 The foot includes five complete digits and a supplemental 
 toe as well. Each of the five digits consists of a long meta- 
 tarsal with epiphyses at both ends, and of a variable number 
 of phalanges. The first digit or hallux and the second have 
 two phalanges, the third three, the fourth, which is the largest, 
 four, and the fifth, three. The distal phalanges have epi- 
 physes only at their proximal ends, the others at both ends. 
 
 On the pre-axial side of the hallux is the supplemental 
 digit, the prehallux or calcar. It consists of a short meta- 
 tarsal and one or two phalanges, and is terminated distally by 
 a horny covering of epidermal origin. 
 
CHAPTER XII. 
 
 GENERAL ACCOUNT OF THE SKELETON IN 
 AMPHIBIA. 
 
 EXOSKELETON. 
 
 The exoskeleton, at any rate in most living forms, is very 
 slightly developed in Amphibia. The only representatives 
 of the epidermal exoskeleton are (1) the minute horny beaks 
 found coating the premaxillae and dentaries in Siren and the 
 tadpoles of most Anura, (2) the nails borne by the first three 
 digits of the pes in Xenopus and by the Japanese Salamander 
 Onychodactylus, (3) the horny covering of the calcar or pre- 
 hallux of frogs. The Urodela and nearly all the Anura, which 
 form the vast majority of living Amphibia, have naked skins. 
 A few Anura belonging to the genera Ceratophrys and Brachy- 
 cephalus have bony dermal plates developed in the skin of the 
 back, and these plates become united with some of the under- 
 lying vertebrae. 
 
 In the Gymnophiona the integument bears small cycloid 
 scales arranged in rings which are equal in number to the 
 vertebrae. These scales contain calcareous concretions. Scales 
 also occur between the successive rings. 
 
 In the Labyrinthodontia the dermal exoskeleton is in 
 many genera greatly developed. It is generally limited to the 
 ventral surface and consists principally of a buckler formed 
 of three bony plates, one median and two lateral. These 
 
THE SKELETON IN AMPHIBIA. THE TEETH. 169 
 
 plates protect the anterior part of the thorax, and are closely 
 connected with the adjacent endoskeleton. They probably 
 represent the interclavicle and clavicles. Behind this buckler 
 numerous scutes are generally developed, which often cover 
 the whole ventral surface, and may cover the whole body. 
 
 TEETH 1 . 
 
 In Amphibia teeth are generally present on the maxillae, 
 premaxillae and vomers, and except in Anura on the dentaries ; 
 sometimes they occur on the palatines as in many Urodela, most 
 Labyrinthodontia, and the Gymnophiona; less commonly on the 
 pterygoids as in Menobranchus, Siredon, some Labyrinthodontia, 
 and Pelobates cultripes*, or on the splenials as in Siren and Meno- 
 branchus, or parasphenoid as in Pelobates cultripes, Spelerpes 
 belli and Batrachoseps. In some Anura such as Bufo and Pipa 
 the jaws are toothless. 
 
 In Gymnophiona, Menobranchus, and Siredon, the teeth 
 are arranged in two concentric curved rows. The teeth of the 
 outer row are borne on the premaxillae and maxillae if present, 
 (the maxillae are absent in Menobranchus), the teeth of the 
 second row on the vomers and pterygoids in Menobranchus 
 and Siredon, and on the vomers and palatines in Gymnophiona. 
 In some Gymnophiona there is a double row of mandibular 
 teeth. The vomerine, palatine and parasphenoid teeth of all 
 forms are numerous and are not arranged in rows. 
 
 The teeth of all living Amphibia are simple conical struc- 
 tures ankylosed to the bone, and consisting of dentine, coated 
 or capped with a thin layer of enamel. In the Labyrinthodontia 
 teeth of more than one size are sometimes present. The dentine 
 of the basal part of the larger teeth is in some genera very 
 greatly folded, causing the structure to be highly complicated. 
 These folds, the intervals between which are filled with cement, 
 
 1 0. Hertwig. Ueber das Zahnsystem der Amphibien. Arch. mikr. 
 Anat. supplem. Bd. xi. 1875. 
 
 - G. A. Boulenger, P. Z. S. 1890, p. 664. 
 
170 THE VERTEBRATE SKELETON. 
 
 radiate inwards from the exterior and outwards from the large 
 pulp cavity. The basal part of the teeth of Ceratophrys 
 (Anura) has a similar structure. 
 
 ENDOSKELETON. 
 VERTEBRAL COLUMN. 
 
 Four regions of the vertebral column can generally be 
 recognised in Amphibia, viz. the cervical, the trunk or thoraco- 
 lumbar, the sacral and the caudal regions. In the limbless 
 Gymnophiona, however, only three regions, the cervical, tho- 
 racic, and post-thoracic can be made out. The cervical region 
 is limited to a single vertebra which generally differs from the 
 others in having no transverse processes or indication of ribs. 
 It is generally called the atlas, but it commonly bears a small 
 process arising from the anterior face of the centrum which 
 resembles the odontoid process of higher animals, and renders 
 it probable that the first vertebra of Amphibia corresponds 
 to the axis, not to the atlas. Amphibia generally have a 
 single sacral vertebra. 
 
 Three elements go to make up the vertebral column in 
 Amphibia, viz. 
 
 1. . the notochord, 
 
 2. the long vertebral centra, 
 
 3. inter vertebral cartilage which forms the joints between 
 successive centra. 
 
 The relations which these three elements bear to one 
 another are subject to much variation. The successive stages 
 can be well traced in the Urodela. 
 
 1. The first stage is found in larval Urodeles in general 
 and in adult Ichthyoidea, and some Salamandrina. In these 
 forms the notochord persists and retains approximately the 
 same diameter throughout the whole length of the vertebral 
 column. Bony biconcave centra are present and constrict it 
 
THE SKELETON IN AMPHIBIA. VERTEBRAL COLUMN. 171 
 
 to a certain extent vertebrally, while intervertebrally there is 
 a development of cartilage. The connection between the bony 
 vertebrae is effected mainly by the expanded notochord. 
 
 2. In the next stage, as seen in Gyrinophilus porphyriti- 
 cus, the growth of intervertebral cartilage has caused the 
 almost complete obliteration of the notochord intervertebrally, 
 and its entire disappearance vertebrally, i.e. in the centre of 
 each vertebra. The intervertebral cartilage now forms the main 
 connection between successive vertebrae, and sometimes cases 
 are found whose condition approaches that of definite articula- 
 tions. Readily recognisable remains of the notochord are still 
 found at each end of the intervertebral constriction. 
 
 3. In the third stage differentiation and absorption of the 
 intervertebral cartilage has given rise to definitely articulating 
 opisthocoelous vertebrae. These are found in most adult 
 Salamandrina. 
 
 The transverse processes of the earlier trunk vertebrae 
 are divided into two parts, a dorsal part which meets the 
 tubercular process of the rib and is derived from the neural 
 arch, and a ventral part which meets the capitular process of 
 the rib, and is derived from the ventral or haemal arch. In 
 the caudal vertebrae and often also in the posterior trunk 
 vertebrae the two processes are fused. 
 
 Siren and Proteus, although they possess minute posterior 
 limbs, have no sacral vertebrae, while Cryptobranchus lateralis 
 has two. The caudal vertebrae, except the first, have haemal 
 arches very similar to the neural arches. 
 
 In Labyrinthodontia the centra of the vertebrae are gene- 
 rally well ossified biconcave discs. In some forms however, like 
 Euchirosaurus, the centra are imperfectly ossified, and consist 
 of bony rings traversed by a wide notochord al canal. Each 
 ring is formed of four pieces, a large well-ossified neural arch, 
 a basal piece, and a pair of lateral pieces. Vertebrae of this 
 type are called rachitomous. 
 
172 THE VERTEBRATE SKELETON. 
 
 In the tail region of other forms each vertebra consists 
 of an anterior centrum bearing the neural arch, and a pos- 
 terior intercentrum 1 bearing chevron bones. Vertebrae of this 
 type are called embolomerous. Haemal arches similar to the 
 neural arches are often found as in Urodela. The transverse 
 processes are sometimes well developed and are divided into 
 tubercular and capitular portions. 
 
 In Gymnophiona the vertebrae are biconcave and are very 
 numerous, they sometimes number about two hundred and 
 thirty. Only quite the last few are ribless and so can be 
 regarded as post-thoracic vertebrae. The first vertebra has 
 nothing of the nature of an odontoid process. 
 
 In Anura the number of vertebrae is very greatly reduced, 
 only nine and the urostyle being present. Of these, eight are 
 presacral and one sacral. The urostyle is postsacral and 
 corresponds to three or more modified vertebrae. The first 
 vertebra is without transverse processes, the remaining pre- 
 sacral vertebrae have the transverse processes fairly large, 
 while the sacral vertebra has them very large, forming in 
 some genera widely expanded plates. The urostyle is a long 
 cylindrical rod which articulates with the sacrum generally by 
 two facets. Ankylosed to its anterior end are the remains 
 of two neural arches. 
 
 In Anura remains of the notochord are found in the centre 
 of each vertebra, i.e. vertebrally, while in the Urodela they 
 only occur intervertebrally. 
 
 The vertebrae in Anura are, as a rule, procoelous. The 
 eighth vertebra is however generally amphicoelous, while 
 the ninth commonly has one convexity in front, and two 
 behind. 
 
 In some forms such as Bombinator, Pipa, Liscoglossus and 
 Alytes they are opisthocoelous ; in others like Pelobates they 
 are variable. 
 
 1 See p. 14. 
 
THE SKELETON IN AMPHIBIA. THE SKULL. 173 
 
 THE SKULL'. 
 
 CRANIUM AND MANDIBLE. 
 
 In the Amphibian skull there are as a rule far fewer bones 
 than in the skull of bony fish. The primordial cartilaginous 
 cranium often persists to a great extent. Only quite a few 
 ossifications take place in it ; namely in the occipital region 
 the exoccipitals, further forwards the pro-otics, and at the 
 boundary of the orbital and ethmoidal regions the sphen- 
 ethmoid. The basi-occipital and basisphenoid are never 
 ossified. As in Mammalia there are two occipital condyles 
 formed by the exoccipitals. 
 
 Large vacuities commonly occur in the cartilage of both 
 floor and roof of the primordial cranium. These are roofed 
 over to a greater or less extent by the development of mem- 
 brane bone. Thus on the roof of the cranium there are paired 
 parietals, frontals, and nasals, and on its floor are paired 
 vomers, and a median unpaired parasphenoid. 
 
 In all living forms the parietals meet and there is no 
 interparietal foramen, though this exists in Labyrintho- 
 donts. 
 
 The palato-pterygo-quadrate bar is united at each end with 
 the cranium, but elsewhere in most cases forms a wide arch 
 standing away from it. The suspensorium is, as in Dipnoi 
 and Holocephali, autostylic. The palato-pterygo-quadrate bar 
 sometimes remains entirely cartilaginous, sometimes its pos- 
 terior half is ossified forming the quadrate. In connection 
 with it a number of membrane bones are generally developed, 
 viz. the maxillae, premaxillae, palatines, pterygoids, quadrato- 
 jugals, and squamosals. The pterygoids are, however, some- 
 times partially formed by the ossification of cartilage. The 
 
 1 See many papers by W. K. Parker published in the Phil. Trans, of 
 the Koyal Soc. 
 
174 THE VERTEBRATE SKELETON. 
 
 cartilage of the lower jaw and its investing membrane bones 
 generally have much the same relations as in bony fishes. 
 
 URODELA. The skulls of the various Urodeles show an 
 interesting series of modifications and differ much from one 
 another, but all agree in the absence of the quadratojugals, 
 in the fact that the palatines lie parallel to the axis of the 
 cranium, and in the large size of the parasphenoid. 
 
 The lower types Menobranchus, Siren, Proteus, and Am- 
 phiuma have longer and narrower skulls than do the higher 
 types. 
 
 Menobranchus has a very low type of skull which remains 
 throughout life in much the same condition as that of a young 
 tadpole or larval salamander. The roof and floor of the 
 cranium internal to the membrane bones are formed of fibrous 
 tissue, not of well-developed cartilage. The epi-otic regions of 
 the skull are ossified, forming a pair of large bones which lie 
 external to, and distinct from, the exoccipitals. Proteus and 
 the Labyrinthodonts are the only other Amphibia which have 
 these elements separately ossified. The parietals send a pair 
 of long processes forwards along the sides of the frontals. 
 Nasals and maxillae are absent, as is likewise the case in 
 Proteus. Teeth are borne on the vomers, premaxillae, ptery- 
 goids, dentaries and angulo-splenials. The suspensorium is 
 forwardly directed. 
 
 The skull of Siren resembles that of Menobranchus in 
 several respects, as in the forward direction of the suspen- 
 sorium and in the absence of maxillae, but differs in the 
 possession of nasals, in the toothless condition of the pre- 
 maxillae and dentaries, and in the fusion and dentigerous con- 
 dition of the vomers arid palatines. 
 
 Amphiuma has a skull which, though narrow and elongated, 
 differs from those of Menobranchus, Proteus, and Siren, and 
 resembles those of higher types in the following respects : 
 
 (1) the suspensorium projects nearly at right angles to 
 
THE SKELETON IN AMPHIBIA. THE SKULL. 175 
 
 the cranium instead of being directed forwards, (2) the 
 maxillae are well developed, and the premaxillae are com- 
 pletely ankylosed together, (3) there are no palatines. 
 
 The skulls of Megalobatrachiis, Cryptobranchus and Siredon 
 resemble those of the highest Urodeles the Salamanders in their 
 wide form, in having the pro-otics distinct from the exoccipitals 
 which are ossified continuously with the epi-otics and opisth- 
 otics, and in having no palatines, but differ in having the two 
 premaxillae separate, and in the arrangement of the vomerine 
 teeth which in Megalobatrachus and Cryptobranchus are placed 
 along the anterior boundaries of the bones, these meeting in 
 the middle line. In Siredon the vomers are separated by the 
 very large parasphenoid. 
 
 The suspensorium in Megalobatrachus and Cryptobranchus 
 projects at right angles to the cranium ; in Siredon it projects 
 somewhat downwards and forwards as in the Salamandrina. 
 
 Modifications of the vomers, pterygoids and palatines ac- 
 company the changes of the larval ichthyoid Siredon into the 
 adult salamandroid Amblystoma, the vomers especially come 
 to resemble to a much greater extent those of the Sala- 
 mandrina. 
 
 The ossification of the skull in the Salamandrina is carried 
 further than in the Ichthyoidea, 4 though the supra-occipital and 
 basi-occipital are not ossified. The skull differs from that in 
 the Ichthyoidea in the size of the part of the vomero-palatines 
 which lies in front of the teeth, in the frequent union of the 
 two premaxillae and in the ossification of all the periotic bones 
 continuously with the exoccipital. 
 
 The skull differs from that of Anura in the following 
 respects : 
 
 (1) the bones of the upper jaw do not form a complete 
 arch standing away from the cranium, and the maxillae are 
 not united to the quadrates by quadratojugals, (2) the long 
 axis of the suspensorium passes obliquely downwards and 
 forwards instead of downwards and backwards, (3) there is no 
 
176 
 
 THE VERTEBRATE SKELETON. 
 
 sphenethmoid encircling the anterior end of the brain, its place 
 being partly taken by a pair of orbitosphenoids, (4) there is no 
 definite tympanic cavity. 
 
 20' 
 
 21 
 
 FIG. 27. 
 
 10. 
 11. 
 
 DOKSAL VIEW OF THE SKULL OF A LiABYBINTHODONT (CupitO- 
 
 saurus nasutus)x% (from VON ZITTEL). 
 
 premaxilla. 12. postorbital. 
 
 nasal. 13. 
 
 maxilla. 14. 
 
 anterior nares. 15. 
 
 frontal. 16. 
 
 prefrontal. 17. 
 
 lachrymal. 18. 
 
 jugal. 19. 
 
 orbit. . 20. 
 
 parietal. 21. 
 postfrontal. 
 
 interparietal foramen. 
 
 squamosal. 
 
 supratemporal. 
 
 quadrato jugal. 
 
 quadrate. 
 
 epi-otic. 
 
 dermo-supra-occipital. 
 
 exoccipital. 
 
 foramen magnum. 
 
 LABYRINTHODONTIA. The skull in Labyrinthodontia is re- 
 markable for its extreme solidity, the large number of bones 
 which are present, and the extent to which the roofing over of 
 
THE SKELETON IN AMPHIBIA. THE SKULL. 177 
 
 the temporal and other fossae has taken place. In many 
 forms the surface of the bones is as in Crocodiles, strongly 
 sculptured (fig. 27, right half) with ridges and grooves which 
 probably lodged sensory organs. The bones forming the 
 roof of the skull are generally very uniform in size, perhaps 
 the most noticeable of them being the paired dermo-supra- 
 occipitals (fig. 27, 19). Paired dermo-supra-occipitals occur 
 also in certain Ganoids. The Labyrinthodont skull also 
 bears resemblance to that of many fish in the development 
 of a pair of long pointed epi-otics (fig. 27, 18), which remain 
 permanently distinct from the surrounding bones. The pa- 
 rietals are small and enclose between them the interparietal 
 foramen (fig. 27, 13). In some forms in which the head is 
 protected with an armour of scutes, these do not roof over 
 the interparietal foramen, and from this fact it has been 
 inferred that the Labyrinthodonts had a functional pineal 
 eye. Both supra- and infra-temporal fossae are partially or 
 completely roofed over by the postorbitals and large supra- 
 temporals (fig. 27, 15). 
 
 There is generally a ring of bones in the sclerotic coat 
 of the eye. The pterygoids do not meet in the middle line, 
 being separated by the parasphenoid. The palatines bear 
 teeth, and in some genera (Arckegosaurus) form long splints 
 lying along the inner side of the maxillae and more or less 
 surrounding the posterior nares. In others (Nyrania) they 
 lie in the normal position near the middle line, one on 
 each side of the parasphenoid. The vomers bear teeth and 
 sometimes meet in the middle line ; they are sometimes 
 confluent with the parasphenoid. On the ventral surface 
 of the cranium there are generally large palatal vacui- 
 ties. 
 
 In the mandible there is often a well-marked postglenoid 
 process, and the articular is generally completely ossified. 
 
 GrYMNOPHioNA. The skull bears a considerable resemblance 
 to that of Labyrinthodonts, especially in the arrangement of 
 R. 12 
 
178 
 
 THE VERTEBRATE SKELETON. 
 
 -10 
 
 12 
 
 FlG. 28. A, VENTRAL VIEW OF THE CRANIUM J B, LATERAL VIEW OF THE 
 
 CRANIUM AND MANDIBLE OF Siphonops aimulatus (after WIEDERSHEIM). 
 
 1. anterior nares. 
 
 2. naso-premaxilla. 
 
 3. frontal. 
 
 4. parietal. 
 
 5. maxilla. 
 
 6. vomer. 
 
 7. orbit. 
 
 8. quadrate united with 
 
 pterygoid in front. 
 
 9. squamosal. 
 
 10. exoccipital. 
 
 11. dentary. 
 
 12. angular. 
 
 13. basi-occipital and basisphe- 
 
 noid fused. 
 
 14. posterior narial opening sur- 
 the rounded by the palatine. 
 
 X. pneumogastric foramen. 
 
THE SKELETON IN AMPHIBIA. THE SKULL. 179 
 
 the bones which bound the mouth cavity. The cranium is 
 very hard, and is covered by a complete bony roof formed 
 mainly of the exoccipitals, parietals, frontals, prefrontals, 
 nasals and premaxillae. The nasals and premaxillae are 
 sometimes ossified continuously. There is a median unpaired 
 ethmoid whose dorsal end appears at the surface wedged in 
 between the frontals and parietals. The bone generally 
 regarded as the squamosal 1 is very large, and it and the 
 maxilla generally together surround the orbit, which, in 
 .Epicrium, has in it a ring of bones. The palatines form long 
 tooth-bearing bones fused with the inner sides of the maxillae; 
 they nearly surround the posterior nares. 
 
 The quadrate bears the knob, and the angular the cup 
 for the articulation of the mandible, a very primitive feature. 
 The mandible is also noticeable for the enormous backward 
 projection of the angular. 
 
 ANURA. In Anura the skull is very short and wide 
 owing to the transverse position of the suspensorium. There 
 is often a small ossification representing the quadrate. Some- 
 times as in Hyla and Alytes there is a fron to-parietal 
 fontanelle. 
 
 As compared with the skull in Urodela the chief charac- 
 teristics of the skull of Anura are : 
 
 1. the presence of a sphenethmoid, 
 
 2. the union of the frontals and parietals on each side, 
 
 3. the occasional occurrence of small supra- and basi- 
 occipitals, 
 
 4. the backward growth of the maxilla and its connection 
 with the suspensorium by means of the quadratojugal, 
 
 5. the dagger-like shape of the parasphenoid, 
 
 6. the occurrence of a definite tympanic cavity, 
 
 1 Perhaps this bone includes supra-orbital and postorbital elements. 
 
 122 
 
180 THE VERTEBRATE SKELETON. 
 
 7. the frequent occurrence of a pre-dentary or mento- 
 meckelian ossification in the mandible. 
 
 The skull of Pipa is abnormal, being greatly flattened and 
 containing little cartilage. The fronto-parietals are fused, and 
 there is no sphenethmoid. The quadrates are well developed 
 and the squamosals and parasphenoid differ much from those 
 of other Anura. 
 
 HYOID AND BRANCHIAL ARCHES. 
 
 In larval Amphibia the hyoid and four branchial arches 
 are generally present, and in adult Ichthyoidea they are 
 frequently almost as well represented as in the larva, and 
 are of use in strengthening the swallowing apparatus. They 
 are very well seen in Siredon, and consist of a hyoid attached 
 by ligaments to the suspensorium, followed by four branchial 
 arches of which the first and second are united by a copula 
 (fig. 29, D, 8), while the third and fourth are not. The hyoid 
 is not always the largest and best preserved of the arches, 
 for sometimes as in Spelerpes one of the branchials is far 
 larger than the hyoid. Four branchial arches occur in Siren 
 as in Siredon, but in Proteus there are only three. 
 
 In some larval Labyrinthodontia (Branckiosaurus) four 
 branchial arches are known to occur, and their arrangement 
 is almost precisely similar to that in Siredon. 
 
 In Gymnophiona the remains of only three branchial 
 arches occur in addition to the hyoid. The four arches are 
 all very similar to one another, each consists of a curved rod 
 of uniform diameter throughout. The hyoid is united with 
 the first branchial arch, but has no attachment to the 
 cranium. 
 
 In larval Anura (fig. 29, C) the arrangement of the 
 hyoid and branchial arches is much as in Urodela. In the 
 adult, however, the ventral parts of all the arches unite, form- 
 ing a compact structure, the basilingual plate (fig. 29, B, 1). 
 
THE SKELETON IN AMPHIBIA. THE HYOID. 
 
 181 
 
 The dorsal parts of the first three branchial arches disappear, 
 but those of the fourth become ossified and form the short, 
 stout thyrohyals or posterior cornua. The dorsal parts of the 
 hyoid arch in the adult form a pair of long bars, the anterior 
 
 FIG. 29. VISCERAL ARCHES OF AMPHIBIA. 
 
 A. Molge cristata (after PARKER). 
 
 B. Rana temporaria adult (after PARKER). 
 
 C. Tadpole of Rana (after MARTIN ST ANGE). 
 
 D. Siredon pisciformis (after CREDNER). 
 
 In each case the ossified portions are slightly shaded, while the carti- 
 laginous portions are left white. 
 
 1. basilingual plate. 
 
 2. hyoid arch. 
 
 3. first branchial arch. 
 
 4. second do. 
 
 5. third branchial arch. 
 
 6. fourth do. 
 
 7. tbyrohyal. 
 
 8. copula. 
 
18*2 THE VERTEBRATE SKELETON. 
 
 cornua, which are united to the periotic region of the skull iii 
 front of the fenestra ovalis either by short ligaments or by 
 fusion as in Bufo. In Pipa and Xenopus the first and 
 second branchial arches persist as well as the fourth (thyro- 
 hyal), but in Pipa the hyoid is wanting. 
 
 KIBS. 
 
 Ribs are generally very poorly developed in Amphibia. 
 In Anura they are in most cases absent; when present they 
 generally form minute unossified appendages attached to the 
 transverse processes, but in Discoglossus and Xenopus the 
 anterior vertebrae are provided with distinct ribs. In 
 Urodela and Labyrinthodontia they are generally short 
 structures, each as a rule attached to the vertebra by a 
 bifurcated proximal end. The number of rib-bearing vertebrae 
 varies, but the first and the posterior caudal vertebrae are 
 always ribless. The anterior caudal vertebrae too are gene- 
 rally ribless, but sometimes a few of them bear small ribs. 
 In Spelerpes the last two trunk vertebrae are ribless, and 
 hence may be regarded as lumbar vertebrae. 
 
 In Gymnophiona ribs are better developed than in any 
 other Amphibia; they occur on all the vertebrae except the 
 first and last few, and are attached to the transverse processes, 
 sometimes by single, sometimes by double heads. 
 
 Sternal ribs are almost unknown in Amphibia, but traces 
 of them occur in Menobranclius. 
 
 STERNUM. 
 
 In Amphibia the sternum is not very well developed; 
 sometimes as in Gymnophiona and Proteus no traces of it 
 occur, and in the Urodela it is never ossified. It is always 
 very intimately related to the pectoral girdle. In the Sala- 
 mandrina it has the form of a broad thin plate of cartilage, 
 grooved and overlapped by the coracoid. 
 
 In most Anura the sternum consists of a number of parts 
 
THE SKELETON IN AMPHIBIA. THE STERNUM. 183 
 
 A 
 
 FIG. 30. SHOULDER-GIRDLE AND STERNUM OF 
 
 A. An old male common Frog (Eana temporaria). 
 
 B. An adult female Docidophryne gigantea (after PARKER). 
 
 In both A and B the left suprascapula is removed. The parts left 
 unshaded are ossified ; those marked with small dots consist of hyaline 
 cartilage, those marked with large dots of calcified cartilage. 
 
 1. calcified cartilage of supra- 7. clavicle. 
 
 scapula. 8. glenoid cavity. 
 
 2. ossified portion of supra- 9. coracoid foramen. 
 
 scapula. 10. episternum. 
 
 3. scapula. 11. omosternum. 
 
 4. coracoid. 12. sternum. 
 
 5. epicoracoid. 13. xiphisternum. 
 
 6. precoracoid. 
 
184 THE VERTEBRATE SKELETON. 
 
 arranged in series. At the anterior end is a flat cartilaginous 
 plate with a bony basal stalk. This plate is called the epi- 
 stermim, and its stalk the omosternum. The continuity of 
 the sternum is now interrupted by a pair of cartilaginous 
 structures, the epicoracoids, which are shoulder-girdle elements, 
 and represent the unossified ventral ends of the coracoids. In 
 some cases cartilaginous epiprecoracoids can also be distin- 
 guished. Further back is the long sternum proper, while last 
 comes the xiphisternum, a broad expanded plate of cartilage. 
 
 In some Anura such as Pipa and Hyla the number of 
 sternal elements is considerably reduced. 
 
 APPENDICULAR SKELETON. 
 PECTORAL GIRDLE. 
 
 The most primitive Amphibian shoulder-girdle is found in 
 the Urodela. It consists of a dorsal element, the scapula, 
 a posterior ventral element, the coracoid, and an anterior 
 ventral element, the precoracoid. The clavicle is not de- 
 veloped, and the two coracoids overlap in the middle line. 
 The shoulder-girdle remains largely cartilaginous but the 
 proximal end of the scapula is ossified, and the ossification 
 may extend through part of the coracoid and precoracoid. 
 
 In Labyrinthodontia there is an exoskeletal ventral buckler 
 formed of three plates, a median one, which probably repre- 
 sents an interclavicle, and two lateral ones, which are probably 
 clavicles. Traces of endoskeletal structures, probably corre- 
 sponding to the precoracoid and scapula, are also known in 
 some cases. The Gymnophiona and some of the Labyrintho- 
 dontia have lost the pectoral girdle and limbs. 
 
 The ossification of the shoulder-girdle has gone on much 
 further in Anura than it has in Urodela. Clavicles are present 
 and the scapula and coracoid of each side are ossified from 
 separate centres. The distal part of the scapula forms a large 
 imperfectly ossified plate, the suprascapula. 
 
THE SKELETON IN AMPHIBIA. ANTERIOR LIMB. 185 
 
 The shoulder-girdle of Anura is however subject to con- 
 siderable variations. In the Toads (Bufonidae) the epicora- 
 coids or unossified ventral ends of the coracoids and pre- 
 coracoids overlap in the middle line (fig. 30, B, 5). This 
 arrangement is called Arciferous. In the Frogs, Ranidae, 
 and other forms belonging to the group Firmisternia, the 
 epicoracoids do not overlap but form a narrow cartilaginous 
 bar separating the ventral ends of the coracoids (fig. 30, A, 5). 
 
 ANTERIOR LIMB. 
 
 In many Amphibia and especially in the Urodela the 
 anterior limb has a very simple unmodified arrangement. 
 The humerus is straight and of moderate length, its ends are 
 rounded for articulation on the one hand with the shoulder- 
 girdle, and on the other hand with the radius and ulna. In 
 the Urodela the radius and ulna are distinct. In the Anura 
 they have fused, though the line of junction of the two 
 is not obliterated. Their proximal ends are hollowed for 
 articulation with the convex end of the humerus. 
 
 The manus in all recent Amphibia agrees in never having 
 more than four complete digits, but is subject to considerable 
 variation, this statement applying especially to the carpus. 
 
 In the larva of Salamandra (fig. 31, A), except that the 
 pollex is absent 1 , the inanus retains completely the condition 
 which is generally regarded as primitive for the higher 
 Vertebrata. It consists of an anterior row of three elements, 
 the ulnare, intermedium, and radiale, and a posterior row 
 of four, the carpalia 2, 3, 4, and 5. Interposed between the 
 two rows is a centrale. Menobranclius has a similar very 
 simple carpus. In most other Amphibia this simplicity is 
 lost. This loss may be due to : 
 
 (a) fusion of certain structures, e.g. in the adult Sala- 
 mandra the intermedium and ulnare have fused, 
 
 1 The first digit present is sometimes regarded as the pollex, but from 
 analogy with Anura it is probable that tbe pollex is the missing digit. 
 
186 
 
 THE VERTEBRATE SKELETON. 
 
 (b) displacement of structures, e.g. in Bufo viridis, the 
 centrale has been pushed up till it comes to articulate with 
 the radius, 
 
 (c) the development of supernumerary elements, especially 
 of extra centralia. In Megalobatrachus two or even three 
 centralia sometimes occur. 
 
 FIG. 31. A, EIGHT ANTIBRACHIUM AND MANUS OF A LARVAL SALAMAN- 
 DER (Salamandra maculosa) (after GEGENBAUR). 
 B, EIGHT TARSUS AND ADJOINING BONES OF Molge sp. (after 
 GEGENBAUR). 
 
 1. radius. 11. tibia. 
 
 2. ulna. 12. fibula. 
 
 3. radiale. 13. tibiale. 
 
 4. intermedium. 
 
 5. ulnare. 
 
 6. centrale. 
 
 7. carpale 2. 
 
 8. 3. 
 
 14. intermedium. 
 
 15. fibulare. 
 
 16. centrale. 
 
 17. tarsale 1. 
 
 18. tarsalia 4 and 5 fused. 
 
 9. 
 10. 
 
 I. II. III. IV. V. digits. 
 
 In the great majority of Amphibia while one digit, 
 probably the first, is absent, the other four digits are well 
 developed. In the forms however with degenerate limbs like 
 Amphiuma, Siren and Proteus the number of digits is still 
 
THE SKELETON IN AMPHIBIA. PELVIC GIRDLE. 187 
 
 further reduced. In Siren there are three or four, in Proteus 
 three, and in Amphiuma two or three digits in the manus. 
 
 In Anura the pollex is represented only by a short 
 metacarpal. There are sometimes traces of a pre-pollex. 
 The carpus often has two centralia and the intermedium 
 is absent. 
 
 In Labyrinthodontia the limbs are generally very simple 
 and resemble those of Urodela. In some forms, however, the 
 manus differs from that of all living Amphibia in possessing 
 five well-developed digits. 
 
 PELVIC GIRDLE. 
 
 The simplest Amphibian pelvis is that of some of the 
 Labyrinthodontia; thus in Mastodonsaurus it consists dorsally 
 of a short broad ilium placed vertically and attached to the 
 sacrum, and ventrally of a small pubis and of a large 
 ischium meeting its fellow in the middle line. In some 
 Labyrinthodonts the pubes as well as the ischia meet in 
 a ventral symphysis, and in many there are no obturator 
 foramina. In Siren, Gymnophiona and some Labyrinthodontia 
 the pelvic girdle and limbs are absent. 
 
 In Urodela the ventral element of the pelvis on each side 
 forms a flat plate which meets its fellow of the opposite side. 
 The anterior part of the plate, representing the pubis, gene- 
 rally remains cartilaginous throughout life ; the posterior 
 part representing the ischium is in almost every case well 
 ossified. Attached to the anterior end of the pubes there is 
 an unpaired bifid cartilaginous structure, the epipubis. The 
 ilia are vertically placed. 
 
 In most Anura the pelvis is peculiarly modified in corre- 
 lation with the habits of jumping. The long bone generally 
 called the ilium is placed horizontally and is attached at its 
 extreme anterior end to the sacrum. The ischium is ossified 
 and distinct. Ventrally in front of the ischium there is a 
 tract of unossified cartilage which is often regarded as the 
 
188 THE VERTEBRATE SKELETON. 
 
 pubis. In Xenopus, however, the bone corresponding to the 
 ilium of the Frog is seen to ossify from two centres, one 
 forming the ilium, the other, which lies at the symphysis, 
 being apparently the pubis. This makes it probable that the 
 so-called ilium of the Frog is really to be regarded as an ilio- 
 pubis, and renders the homology of the cartilaginous part 
 uncertain, but it probably corresponds to the acetabular bone 
 of mammals. In Xenopus also there is a minute epipubis 
 similar to that of Urodeles. 
 
 POSTERIOR LIMB. 
 
 In Urodela the posterior limb (fig. 31, B) closely resembles 
 the anterior limb, but is even less removed from the primitive 
 condition of the higher vertebrates in the fact that all five digits 
 are commonly present. The tibia and fibula are short bones 
 approximately equal in size. In some cases the number of 
 digits is reduced. Thus in Menobranchus the pes has four 
 digits, in Proteus it has two, and in Amphiuma two or three, 
 while in Siren the posterior limbs have atrophied. 
 
 In correlation with their habits of jumping, the posterior 
 limbs in Anura are much lengthened and considerably modified. 
 The tibia and fibula are completely fused. The intermedium 
 is absent, while the tibiale and fibulare are greatly elongated. 
 Tarsalia 4 and 5 are absent. Five digits are always present, 
 and there is a pre-hallux formed of two or more segments. 
 
 In general the posterior limbs in Labyrinthodontia bear the 
 closest resemblance to the anterior limbs ; in some cases three 
 centralia are found. 
 
 In Ichthyoidea, and in most Labyrinthodontia, the carti- 
 lages of the carpus and tarsus remain unossified; in Salaman- 
 drina and in Anura they are generally ossified. 
 
CHAPTER XIII. 
 SAUROPSIDA. 
 
 THIS great group includes the Reptiles and Birds and 
 forms the second of the three into which the Gnathostomata 
 may be divided. There is nearly always a strongly -developed 
 epiblastic exoskeleton which has the form of scales or feathers, 
 and in some cases a dermal exoskeleton is also well developed. 
 In living forms the notochord never persists, being replaced 
 by vertebrae, but in some extinct forms the centra are 
 notochordal. The vertebral centra are ossified, and only in 
 exceptionally rare cases have terminal epiphyses. The skull 
 is well ossified and has membrane bones incorporated in its 
 walls. 
 
 The occipital segment is completely ossified, and an inter- 
 orbital septum or bony partition separating the two orbits 
 is usually developed to a greater or less extent. The skull 
 generally articulates with the vertebral column by a single 
 occipital condyle into the composition of which the ex- 
 occipitals and basi-occipital enter in varying proportions. 
 The pro-otic ossifies, and either remains distinct from the 
 epi-otic 1 and opisthotic throughout life, or unites with them 
 only after they have fused with the adjacent bones. The 
 hyoid and branchial arches are much reduced ; and the 
 representative of the hyomandibular is connected with the 
 
 1 According to Baur a distinct epi-otic is not recognisable in the 
 reptilian skull. 
 
190 THE VERTEBRATE SKELETON. 
 
 auditory apparatus, forming the auditory ossicles 1 . Each 
 ramus of the mandible always consists of a cartilage bone, 
 the articular, and several membrane bones. The mandible 
 articulates with the cranium by means of a quadrate. The 
 ribs in Birds and some Reptiles bear uncinate processes, i.e. 
 small, flat, bony or cartilaginous plates projecting backwards 
 from their posterior borders. The sternum is not transversely 
 segmented as in mammals, and there are commonly distinct 
 cervical ribs. The ankle joint is intertarsal, or situated 
 between the proximal and distal row of tarsal bones, not 
 crurotarsal as in Mammalia. 
 
 CLASS I. 
 
 The axial skeleton is generally long, and that of the limbs 
 frequently comparatively short, or sometimes absent. 
 
 The exoskeleton generally has the form of epidermal 
 scales, which are often combined with underlying bony dermal 
 plates or scutes and may sometimes form a continuous armour. 
 Neither feathers nor true hairs are ever present. The verte- 
 bral column is generally divisible into the five usual regions. 
 The centra of the vertebrae vary enormously, and may be 
 amphicoelous, procoelous, opisthocoelous or flat, but they never 
 have saddle-shaped articulating surfaces. The quadrate is 
 always large, and is sometimes fixed, sometimes movable. 
 A transpalatine bone uniting the pterygoid and maxilla is 
 generally present. 
 
 Free ribs are often borne along almost the whole length 
 of the trunk and tail, and often occur attached to the cervical 
 vertebrae. The sacrum is generally composed of two vertebrae 
 which are united with the ilia by means of expanded ribs. 
 The sternum is rhomboidal, and may either be cartilaginous 
 
 1 H. Gadow, Phil. Trans., vol. 179, 1888. 
 
 2 See G. Baur, J. Morph., vol. i., 1887. K. Lydekker, Catalogue of 
 the Fossil Reptilia and Amphibia in the British Museum, Parts i. & u. 
 C. K. Hoffmann, Reptilien, in Bronn's Classen und Ordnungen des Thier- 
 reichs, Bd. vi., 3 abth. 187990. 
 
REPTILIA. THEROMORPHA. 191 
 
 or formed of cartilage bone, but never of membrane bone ; 
 it differs from that of birds also in the fact that it does not 
 ossify from two or more centres. An interclavicle is generally 
 present. There are always more than three digits in the 
 manus, and never less than three in the pes. In all living 
 reptiles the ilia are prolonged further behind the acetabula 
 than in front of them, and the bones of the pelvis remain as 
 a rule, distinct from one another throughout life. 
 
 The pubes (pre-pubes) and ischia both commonly meet in 
 ventral symphysis, and the acetabula are wholly or almost 
 wholly ossified. The metatarsals are not ankylosed together. 
 
 Order 1. THEROMORPHA '. 
 
 This order includes a number of mainly terrestrial, extinct 
 reptiles, which differ much from one another, and show remark- 
 able points of affinit} r on the one hand with the Labyrintho- 
 dont Amphibia, and on the other with the Mammalia. The 
 vertebrae are nearly always amphicoelous and sometimes have 
 notochordal centra. The skull is short and has the quadrate 
 immovably fixed. There is an interparietal foramen, and gene- 
 rally large supratemporal fossae bounded by supratemporal 2 
 arcades, but with no infratemporal 2 arcades; Elginia however 
 has the whole of the temporal region completely roofed over. 
 
 The teeth are placed in distinct sockets and are very 
 variable in form, the dentition sometimes resembling the 
 heterodont dentition of mammals. The humerus has distinct 
 condyles and an ent-epicondylar foramen 3 as in many mammals. 
 
 The pubis is fused with the ischium, and both pectoral and 
 pelvic girdles are remarkably solid. The obturator foramen 
 
 1 T. H. Huxley, Quart. J. Geol Soc., vol. xv. p. 649, 1859. R. Owen, 
 Catalogue of Fossil Reptiles of S. Africa in the British Museum, London, 
 1876. H. G. Seeley, various papers published in the P. R. Soc. London, 
 and Phil. Trans. 
 
 2 See pp. 281283. 
 
 3 An ent-epicondylar foramen is one piercing the humerus on its 
 inner side just above the condyle. 
 
192 THE VERTEBRATE SKELETON. 
 
 is remarkably small or even absent. The anterior ribs have 
 two articulating surfaces, and each articulates by its tuber- 
 culum with the transverse process, and by its capitulum with 
 the centrum as in mammals. 
 
 These reptiles occur chiefly in deposits of Triassic and 
 Permian age. Some of the best known genera are Dicynodon, 
 Udenodon, Placodus, Pariasaurus and Galesaurus. They will 
 be noticed in the general account of the skeleton in reptiles. 
 
 Order 2. SAUROPTERYGIA. 
 
 This order includes a number of extinct marine reptiles, 
 devoid of an exoskeleton. The tail is short, the trunk long, 
 and the neck in the most typical forms extremely long. The 
 vertebrae have slightly biconcave, or nearly flat centra. The 
 skull is relatively small and has large supratemporal fossae. 
 The teeth are placed in distinct sockets, and are generally 
 confined to the margins of the jaws ; they are sharp and 
 curved and are coated with grooved enamel. The premaxillae 
 are large, and there is an interparietal foramen. The quadrate 
 is firmly united to the cranium. The anterior nares are 
 separate and are placed somewhat close to the orbits. There 
 is no ossified sclerotic ring. The palatines and pterygoids 
 meet the vomers, and more or less completely close the palate, 
 and in some forms, e.g. Plesiosaurus, there is a distinct para- 
 sphenoid. Thoracic ribs are strongly developed and each 
 articulates with its vertebra by a single head. The cervical 
 vertebrae have well-marked ribs, which articulate only with 
 the centra, in this respect differing from those of Crocodiles. 
 The caudal vertebrae bear both ribs and chevron bones, and 
 abdominal splint-ribs are largely developed. 
 
 In the shoulder-girdle the coracoids are large and meet in a 
 ventral symphysis ; precoracoids and a sternum are apparently 
 absent, but parts generally regarded 1 as the clavicles and 
 
 1 According to Hulke they should be regarded as the omosternum, 
 the clavicles and interclavicle being wanting. 
 
REPTILIA. CHELONIA. 193 
 
 interclavicle are well developed. In the pelvis, the pubes and 
 ischia meet in a long symphysis. The limbs are pentedactylate, 
 and in the best known forms, the Plesiosauridae, form swim- 
 ming paddles. 
 
 The Sauropterygia occur in beds of Secondary age, and 
 some of the best known genera are Plesiosaurus, Pliosaurus 
 and Nothosaurus. 
 
 Order 3. CHELOXIA. 
 
 In the Tortoises and Turtles the body is enclosed in a bony 
 box, formed of the dorsal carapace, and a flat ventral buckler, 
 the plastron. Except in Dermochelys the carapace is partly 
 formed from the vertebral column and ribs, partly from dermal 
 bones. Both carapace and plastron are, except in Dermo- 
 chelys, Trionyx and their allies, covered with an epidermal 
 exoskeleton of horny plates, which are regularly arranged, 
 though their outlines do not coincide with those of the under- 
 lying bones. The thoracic vertebrae have no transverse pro- 
 cesses, and are quite immovably fixed, but the cervical and 
 caudal vertebrae are very freely movable. There are no lumbar 
 vertebrae. The skull is extremely solid, and frequently has a 
 very complete false roof. Teeth have been detected in embryos 
 of Trionyx but with this exception the jaws are toothless, 
 and are encased in horny beaks. The quadrate is firmly 
 fixed. The facial part of the skull is very short, and the 
 alisphenoidal and orbitosphenoidal regions are unossified. In 
 living forms there are no separate nasal bones, while large 
 pref rentals and postfrontals are developed. There is a com- 
 paratively complete bony palate chiefly formed of the palatines 
 and pterygoids. The anterior nares are united and placed at 
 the anterior end of the skull, and the premaxillae are very 
 small. There is no transpalatine bone and the vomer is 
 unpaired. The dentaries are generally fused together. 
 
 There are ten pairs of ribs, and each rib has only a single 
 R. 13 
 
194 THE VERTEBRATE SKELETON. 
 
 head and is partially attached to two vertebrae ; there are no 
 cervical or sternal ribs. There is no true sternum. 
 
 The three anterior elements of the plastron are respectively 
 homologous with the interclavicle and two clavicles of other 
 reptiles, while the remaining elements of the plastron are pro- 
 bably homologous with the abdominal ribs of Crocodiles. The 
 pectoral girdle lies within the ribs, and the precoracoids and 
 coracoids do not meet in ventral symphyses. The scapula and 
 precoracoid are ossified continuously. The pubis probably 
 corresponds with the prepubis of Dinosaurs. There are four 
 limbs each with five digits. 
 
 The order includes three suborders : 
 
 Suborder (1). TRIONYCHIA. 
 
 The carapace and plastron have a rough granular surface 
 covered with skin and without any horny shields. 
 
 The plastron is imperfectly ossified, and marginal bones 
 may be absent, or if present are confined to the posterior 
 portion of the carapace. The pelvis is not united to the 
 plastron. The cranium has not a complete false roof and the 
 head can be drawn back under the carapace. 
 
 The first three digits of both manus and pes bear claws, 
 and the fourth digit in each case has more than three pha- 
 langes. The most important genus is Tribnyx. 
 
 Suborder (2). CRYPTODIRA. 
 
 The carapace and plastron vary in the extent to which they 
 are ossified, and except in Dermochelys 1 and its allies are 
 covered by horny plates. Marginal bones are always present. 
 The head can generally be drawn back under the carapace. 
 The pelvis is not firmly united to the plastron. The cranium 
 often has a complete false roof, and in the mandibular articu- 
 lation the cup is borne by the cranium, and the knob by the 
 mandible. Among the more important genera are Dermo- 
 chelys, Ckelone, and Testudo. 
 
 1 See p. 272. 
 
REPTILIA. ICHTHYOSAURIA. 195 
 
 Suborder (3). PLEURODIRA. 
 
 The carapace and plastron are strongly ossified, and firmly 
 united to the pelvis. The head and neck can be folded late- 
 rally under the carapace, but cannot be drawn back under it. 
 The cranium has a more or less complete false roof, and in the 
 mandibular articulation the knob is borne by the cranium, and 
 the cup by the mandible. Chelys is a well-known genus. 
 
 Order 4. ICHTHYOSAURIA 1 . 
 
 The order includes a number of large extinct marine 
 reptiles whose general shape is similar to that of the Cetacea. 
 The skull is enormously large, and the neck short. The tail 
 is very long, and is terminated by a large vertically-placed 
 bilobed fin, the vertebral column running along the lower 
 lobe. The very numerous vertebrae are short and deeply bi- 
 concave. The vertebral column can be divided into caudal 
 and precaudal regions only, as the ribs which begin at the 
 anterior part of the neck are continued to the posterior end 
 of the trunk without being connected with any. sternum or 
 sacrum. The precaudal vertebrae bear two surfaces for the 
 articulation of the ribs, while in the caudal vertebrae the 
 two surfaces have coalesced. The caudal region is also 
 distinguished by its chevron bones. The vertebrae have 
 no transverse processes, and the neural arches are not 
 firmly united to the centra, and have only traces of zyga- 
 pophyses. The atlas and axis are similar to the other 
 vertebrae, but there is a wedge-shaped intercentrum be- 
 tween the atlas and the skull, and another between the 
 atlas and the axis. The skull is greatly elongated (fig. 32) 
 and pointed, mainly owing to the length of the premaxillae. 
 The orbits are enormous, and there is a ring of bones in the 
 sclerotic (fig. 32, 15). The anterior nares are very small ; and 
 
 1 R. Lydekker, Nat. Sci. vol. i. p. 514, 1892. Further references are 
 there given. 
 
 132 
 
196 
 
 THE VERTEBRATE SKELETON. 
 
 are placed far back just in front of the orbits. There is an 
 interparietal foramen, and the supratemporal fossae (fig. 32, 9) 
 
 FIG. 32. LATERAL (BELOW) AND DORSAL (ABOVE) VIEWS or THE SKULL OF 
 AN Ichthyosaurus. (Modified from Deslongchamps.) 
 
 1. pr em axilla. 
 
 2. maxilla. 
 
 3. nasal. 
 
 4. prefrontal 1 , 
 
 5. frontal. 
 
 6. postfrontal 1 . 
 
 7. anterior nares. 
 
 8. orbit. 
 
 9. supratemporal fossa. 
 
 10. interparietal foramen. 
 
 11. parietal. 
 
 12. squamosal. 
 
 13. supratemporal. 
 
 14. quadrate jugal. 
 
 15. sclerotic ring. 
 
 16. postorbital. 
 
 17. jugal. 
 
 18. lachrymal. 
 
 19. dentary. 
 
 20. articular. 
 
 21. angular. 
 
 are very large, while there are no infratemporal fossae. An 
 epipterygoid occurs. The quadrate is firmly fixed to the 
 cranium, and there is a large parasphenoid. There are large 
 prefrontals, but the frontals are very small. The very numer- 
 ous teeth are large and conical, and are placed in continuous 
 
 1 The exact position of the suture between the prefrontal and post- 
 frontal is not known. 
 
REPTILIA. ICHTHYOSAURIA. 197 
 
 grooves without being ankylosed to the bone. They are 
 confined to the jaw-bones. 
 
 The ribs are long, and the anterior ones have capitula and 
 tubercula. There is no sternum, but the ventral body wall 
 is strengthened by a complex system of abdominal splint ribs. 
 
 The pectoral girdle is strongly developed, the scapulae are 
 narrow, the coracoids broad, and meet ventrally without over- 
 lapping. There are probably no precoracoids, but clavicles 
 and a T-shaped interclavicle are well developed. 
 
 The limbs are very short, and completely modified into 
 swimming paddles. The humerus and femur are both short, 
 while the radius and ulna, tibia and fibula are generally still 
 further reduced to the form of short polygonal bones. 
 
 The digits are formed of longitudinal series of very numer- 
 ous small bones. The number of digits is five, but there 
 sometimes appear to be more owing to the bifurcation of 
 certain of them, or to the addition of marginal bones, either 
 to the radial or ulnar side of the limb. The humerus has no 
 foramen, and both humerus and femur are unique in that 
 they are distally terminated by concave surfaces instead of 
 by convex condyles. The pelvic limb is much smaller than 
 the pectoral. The pelvis has no bony connection with the 
 vertebral column, and all the component bones are small and 
 rod-like. 
 
 The Ichthyosau.ria are confined to beds of Secondary age 
 and by far the best known genus is Ichthyosaurus. 
 
 Order 5. RHYNCHOCEPHALIA. 
 
 This order includes the living Sphenodon (Hatteria) and 
 various extinct forms. The general shape of these animals is 
 lizard-like and the tail is long. 
 
 The vertebrae are amphicoelous or sometimes nearly flat, 
 and the notochord sometimes persists to some extent. Protero- 
 saurus differs from the other members of the order in having 
 opisthocoelous cervical vertebrae. 
 
198 THE VERTEBRATE SKELETON. 
 
 The sacrum is composed of two vertebrae. Ossified inter- 
 centra (interdorsalia) generally occur in the cervical and 
 caudal regions, and sometimes throughout the whole vertebral 
 column. In the skull the quadrate is immovably fixed and 
 united to the pterygoid. The palate is well ossified, while 
 the premaxillae which are often beak-like are never ankylosed 
 together. The jaws may be toothless or may be provided 
 with teeth which are usually acrodont (see p. 199). The 
 palatines frequently bear teeth, and in Proterosaurus teeth 
 occur also on the pterygoids and vomers. The rami of the 
 mandible are united by ligament at the symphysis except in 
 the Rhynchosauridae, in which the union is bony. Superior 
 and inferior temporal arcades occur. 
 
 The ribs have capitula and tubercula, and often uncinate 
 processes (see p. 190) as in birds. A pectoral girdle and 
 sternum, with clavicles and a T-shaped interclavicle are de- 
 veloped, and abdominal ribs are always found. The precoracoid 
 is however absent. The limbs are pentedactylate. 
 
 Sphenodon 1 (Hatteria) now living in some of the islands 
 of the New Zealand group, is certainly the most generalised 
 of all living reptiles. Though lizard-like in form it differs 
 from all living lizards in the possession of two temporal 
 arcades, abdominal ribs and a fixed quadrate ; and is often 
 considered to be nearly allied in many respects to the type 
 of reptile from which all the others took their origin. 
 
 Among the better known extinct forms are Proterosaurus 
 of Permian and Hyperodapedon of Triassic age. 
 
 Order 6. SQUAMATA. 
 
 This order includes the extinct Mosasaurians, and the 
 lizards and snakes which form the vast majority of living 
 reptiles. The trunk may be moderately elongated and provided 
 
 1 A. Giinther, On the Anatomy of Hatteria, Phil. Trans, vol. 157, 1867, 
 p. 595. 
 
REPTILIA. SQUAMATA. 199 
 
 with four short limbs as in lizards, or it may be limb- 
 less, extremely elongated, and passing imperceptibly into 
 the tail. The surface is generally completely covered with 
 overlapping horny epidermal scales, below which bony dermal 
 scutes may be developed. 
 
 The vertebrae are procoelous, rarely amphicoelous. There 
 are no intercentra, and the neural arches are firmly united to 
 the centra. Additional articulating surfaces, the zygosphenes 
 and zygantra, are often developed 1 . The sacrum is formed 
 of two or rarely three vertebrae, or may be wanting as in 
 Ophidia. In the skull an infratemporal arcade forming the 
 lower boundary of the infratemporal fossa is absent, and the 
 quadrate, except in the Chamaeleons, is movably articulated 
 to the squamosal. The palatal vacuities are large and the 
 nares are separate. There is often a distinct parasphenoid. 
 The teeth are either acrodont (i.e. ankylosed to the summit 
 of the jaw), or pleurodont, i.e. ankylosed to the inner side 
 of the jaw. The thoracic ribs each have a single head 
 which articulates with the centrum of the vertebra; while 
 uncinate processes and abdominal ribs never occur. 
 
 A pectoral girdle and sternum may be present, or may be 
 completely absent as in snakes. Except in snakes there are 
 generally four pentedactylate limbs which may either form 
 paddles or be adapted for walking. 
 
 Suborder (1). LACERTiLiA 2 . 
 
 The body is elongated, and as a rule four short pentedacty- 
 late limbs are present, but sometimes limbs are vestigial or 
 
 1 Zygosphenes are extra articulating surfaces borne upon the anterior 
 face of the neural arch ; they fit into corresponding structures, the 
 zygantra, which are borne on the posterior surface of the neural arch 
 of the preceding vertebra. Ordinary zygapophyses always accompany 
 them. 
 
 2 See E. D. Cope, P. Amer. Phil. Soc. vol. xxx. p. 185. 
 
200 THE VERTEBRATE SKELETON. 
 
 absent. The exoskeleton generally has the form of horny 
 plates, spines, or scales ; while sometimes as in the Chamae- 
 leons and Amphisbaenians it is absent. In other forms such 
 as Tiliqua and Scincus, the body has a complete armour of 
 bony scutes, whose shape corresponds with that of the over- 
 lying horny scales. 
 
 The vertebrae are precocious, rarely as in the Geckos 
 amphicoelous ; they are usually without zygosphenes and 
 zygantra, but these structures occur in the Iguanidae. The 
 sacral vertebrae of living forms are not ankylosed together, 
 and the caudal vertebrae usually have well-developed chevron 
 bones. 
 
 In the skull 1 the orbits are separated from one another, 
 only by an imperfectly developed interorbital septum, the 
 cranial cavity not extending forwards between them, while 
 the alisphenoidal region is unossified. The premaxillae may 
 be paired or united (Amphisbaenidae), and there is usually 
 an interparietal foramen. There may be a complete supra- 
 temporal 2 arcade bounding the lower margin of the supra- 
 temporal fossa, or the supratemporal fossa may be open below. 
 The quadratojugal is not ossified, and the quadrate articulates 
 with the exoccipital. There is no infratemporal arcade. There 
 is commonly a rod-like epipterygoid 3 (fig. 33, 14) connecting 
 the pterygoid and parietal. 
 
 Teeth are always present, and may be confined to the 
 jaws or may be developed also on the pterygoids and rarely 
 on the palatines ; they are either acrodont or pleurodont. 
 The rami of the mandible are suturally united. 
 
 A pectoral girdle is always present, and generally also a 
 sternum. Clavicles and a T-shaped interclavicle are commonly 
 present, but are absent in the Chamaeleons. 
 
 1 See W. K. Parker, Phil. Trans, vol. 170, 1879, p. 595. 
 
 2 See p. 281. 
 
 :{ Often called the columella cranii. 
 
REFflLIA. LACERTILIA. 
 
 19 20 
 
 L.J* 
 
 201 
 
 -S3 
 
 FIG. 33. A, LATERAL VIEW, AND 
 OF A LIZARD ( Varanus 
 
 1. premaxilla. 
 
 2. maxilla. 
 
 3. nasal. 
 
 4. lateral ethmoid. 
 
 5. supra-orbital. 
 
 6. lachrymal. 
 
 7. frontal. 
 
 8. postfrontal. 
 
 9. prefrontal. 
 
 10. basisphenoid. 
 
 11. pro-otic. 
 
 12. epi-otic. 
 
 13. pterygoid. 
 
 14. epipterygoid (columella 
 
 cranii). 
 
 15. jugal. 
 
 B, LONGITUDINAL SECTION OF THE SKULL 
 
 varius). x-f-. (Brit. Mus.) 
 
 16. transpalatine. 
 
 17. parasphenoid. 
 
 18. quadrate. 
 
 19. parietal. 
 
 20. squamosal. 
 
 21. supratemporal. 
 
 22. exoccipital. 
 
 23. dentary. 
 
 24. splenial. 
 
 25. supra-angular. 
 
 26. angular. 
 
 27. coronoid. 
 
 28. articular. 
 
 29. vomer. 
 
 30. basi-occipital. 
 
 31. orbitosphenoid. 
 
202 THE VERTEBRATE SKELETON. 
 
 There is no separate precoracoid but a precoracoidal pro- 
 cess (fig. 34, 7) of the coracoid is generally prominent. 
 
 FIG. 34. LATERAL VIEW or THE SHOULDER-GIRDLE OF Varanus. x f . 
 (Brit. Mus.). 
 
 1. suprascapula. 5. clavicle. 
 
 2. scapula. 6. interclavicle. 
 
 3. glenoid cavity. 7. precoracoidal process. 
 
 4. coracoid. 
 
 Sternal ribs are present in chamaeleons and scinks. The 
 limbs are in the great majority of cases pentedactylate and 
 the digits are clawed. The phalanges articulate by means 
 of condyles. Sometimes one or both pairs of limbs are 
 absent. When the posterior limbs are absent the pelvis is 
 also wanting, though the loss of the anterior limbs does not 
 lead to a corresponding loss of the pectoral girdle. 
 
 The pubis corresponds to the prepubis of Dinosaurs, and 
 both pubes and ischia meet in ventral symphyses. 
 
 The suborder includes the Lizards, Chamaeleons and Arn- 
 phisbaenians. 
 
 Suborder (2). OPHIDIA 1 . 
 The Ophidia or snakes are characterised by their greatly 
 
 1 See C. K. Hoffmann, in Bronn's Klassen und Ordnungen des Thier- 
 reichs, Bd. vi., 3 abth. 188590. 
 
REPTILIA. OPH1DIA. 203 
 
 elongated body and want of limbs. The body is covered with 
 overlapping horny scales and bony dermal scutes are never 
 present. The vertebrae are precocious, and are distinguishable 
 into two groups only, precaudal or rib-bearing, and caudal or 
 ribless. The atlas vertebra is also ribless. The neural arches 
 are always provided with zygospheiies and zygantra. Many 
 of the vertebrae have strong hypapophyses, and the caudal 
 vertebrae are without chevron bones. 
 
 In the skull the cranial cavity extends forwards between 
 the orbits, and is closed in front by downgrowths from the 
 f rontals and parietals which meet the well-ossified alisphenoids 
 and orbitosphenoids 1 . The cranium is strongly ossified, and 
 there are no parotic processes or interparietal foramen. There 
 are no temporal arcades and no epipterygoid. The premaxillae 
 if present are very small (fig. 51, 1) and usually toothless. 
 The quadrates articulate with the squamosals, and do not as 
 in Lacertilia meet the exoccipitals. The palatines do not 
 unite directly with the vomers or with the base of the cranium, 
 and the whole pala to-maxillary apparatus is more loosely con- 
 nected with the cranium than it is in Lacertilia. The ptery- 
 goids, and in most cases also the palatines, bear teeth. The 
 dentition is acrodont, and the rami of the mandible are united 
 only by an elastic ligament an important point serving to 
 distinguish the Ophidia from the Lacertilia. There is an 
 imperfectly developed interorbital septum, the ventral part 
 of which is formed by the paraspherioid. The postfrontal is 
 generally well developed, while the jugals and quadratojugals 
 are absent. There are never any traces of the anterior limbs 
 or pectoral girdle, but occasionally there are vestiges of a 
 pelvis and posterior limbs. 
 
 1 Some anatomists consider that the closing in of the brain case in 
 front is entirely due to the frontals and parietals. 
 
204 THE VERTEBRATE SKELETON. 
 
 Suborder (3). PYTHONOMORPHA'. 
 
 This suborder includes Mosasaurus and its allies, a group 
 of enormous extinct marine reptiles found in beds of Cre- 
 taceous age. 
 
 The skin is in most forms at any rate unprovided with 
 dermal scutes. The vertebrae may be with or without zygo- 
 sphenes and zygantra. The skull resembles that of lizards, 
 having an interparietal foramen, and a cranial cavity open 
 in front. The squamosal takes part in the formation of the 
 cranial wall, and the quadrate articulates with the squamosal, 
 not as in Lacertilia with the exoccipital. There are large 
 supratemporal fossae, bounded below by supratemporal arcades. 
 The teeth are large and acrodont, and occur on the pterygoids 
 as well as on the jaws. The two rami of the mandible are 
 united by ligament only. Pectoral and pelvic girdles are 
 present, but clavicles are wanting, and the pelvis is not as a 
 rule united to any sacrum. 
 
 The limbs are pentedactylate, and are adapted for swim- 
 ming, while all the limb bones except the phalanges are rela- 
 tively very short. The number of phalanges is riot increased 
 beyond the normal, and they articulate with one another by 
 flat surfaces. The terminal phalanges are without claws. 
 
 Order 7. DiNOSAURiA 2 . 
 
 The extinct reptiles comprising this order were all terres- 
 trial, and include the largest terrestrial animals known. They 
 
 1 E. D. Cope, Eep. U. 8. Geol. Surv., 1875, vol. n., The vertebrata 
 of the Cretaceous formations of the west. E. D. Cope, P. Boston Soc. 
 1862, xii. p. 250. 0. C. Marsh, Amer. J. Sci. 1872, vol. 3. B. Owen, 
 Quart. J. Geol. Soc. 1877, and 1878. 
 
 2 J. W. Hulke, Presidential address to the Geol. Soc. of London, 
 1883 and 1884. 0. C. Marsh, many papers in the Amer. J. Sci. from 
 1878 onwards, also in the Geol. Mag. E. Owen, History of British 
 fossil reptiles : Dinosauria (Palaeont. Soc.). 
 
REPTILIA. DINOSAURIA. 205 
 
 vary greatly in size and in the structure of the limbs, some 
 approach close to the type of structure met with in birds, 
 others are allied to crocodiles, 
 
 Passing to the more detailed characters : there is some- 
 times a well-developed exoskeleton having the form of bony 
 plates or spines. The vertebrae may be solid or their centra 
 may be hollowed internally ; their surfaces may be flat, bi- 
 concave or opisthocoelous. The sacrum is composed of from 
 two to six vertebrae. 
 
 As regards the skull, the quadrate is large and fixed, and 
 supratemporal and infratemporal fossae bounded by bone occur. 
 The teeth are more or less laterally compressed, and often 
 have serrated edges ; they may be placed in distinct sockets 
 or in a continuous groove. The ribs have capitula and tuber- 
 cula, and sternal ribs often occur. The scapula is very large, 
 the coracoid small, and there is no precoracoid, or T-shaped 
 interclavicle. Clavicles are only known in a few cases. In 
 the pelvis the ilium is elongated both in front of, and behind, 
 the acetabulum, sometimes the pre-pubis, sometimes the post- 
 pubis is the better developed. The anterior limbs are shorter 
 than the posterior, and the long bones are sometimes solid, 
 sometimes hollow. 
 
 There are three well-marked suborders of the Dinosauria. 
 
 Suborder (1). SAUROPODA 1 . 
 
 The reptiles belonging to this group were probably quadru- 
 pedal and herbivorous. 
 
 They have the cervical and anterior trunk vertebrae 
 opisthocoelous, while the posterior vertebrae are biconcave; 
 all the presacral, and sometimes the sacral vertebrae are 
 hollowed internally. The teeth are spatulate and without 
 serrated edges, they are always planted in distinct sockets, 
 and some of them are borne by the premaxillae. 
 
 1 The diagnostic characters of the different groups of Dinosaurs are 
 in the main those given by von Zittel. 
 
206 
 
 THE VERTEBRATE SKELETON. 
 

 REPTILIA. DINOSAURIA. 207 
 
 1. anterior nares. 5. scapula. 
 
 2. prominence on the nasal 6. coracoid. 
 
 bones which probably 7. ilium. 
 
 carried a horn. 8. pubis (pre-pubis). 
 
 3. pre-orbital vacuity. 9. ischium. 
 
 4. orbit. 
 
 The nares have the form of long slits and there are large 
 pre-orbital vacuities. 
 
 The limb bones are solid, and the anterior limbs are not 
 much shorter than the posterior ones. All the limbs are 
 plantigrade and pentedactylate, and the digits of the pes are 
 clawed. There is a large pre-pubis directed downwards and 
 forwards, meeting its fellow in a ventral symphysis, but there 
 is no post-pubis. 
 
 The Sauropoda are found in the secondary rocks of Europe 
 and N. America and include the largest land animals that are 
 known to have existed. Many of the best known forms such 
 as Brontosaurus and Morosaurus are North American. 
 
 Suborder (2). THEROPODA. 
 
 The members of this suborder were all carnivorous, and 
 from the small comparative size of the anterior limbs many of 
 them were probably bipedal. 
 
 The vertebrae are opisthocoelous or amphicoelous, their 
 neural arches are provided with zygosphenes and zygantra, 
 and their centra are frequently hollowed internally ; the limb 
 bones are also hollow, and in fact the whole skeleton is ex- 
 tremely light. The tail is of great length. The teeth are 
 pointed and recurved, and have one or both borders serrated ; 
 they are always planted in distinct sockets, and some of them 
 are borne by the premaxillae. There are large pre-orbital 
 vacuities. The digits of both manus and pes are terminated 
 by pointed ungual phalanges which must have borne claws. 
 In the pelvis the pre-pubes and ischia are slender bones, the 
 
208 THE VERTEBRATE SKELETON. 
 
 former meeting in a ventral symphysis. The ilia are very 
 deep vertically and there are no post-pubes. The astragalus 
 is closely applied to the tibia, in front of which it sends an 
 ascending process, sometimes the two bones appear to have 
 been ankylosed together, as in birds. The metatarsals are 
 elongated and the feet digitigrade. 
 
 The Theropoda vary greatly in size, one of the best known 
 genera Compsognathus was about as large as a cat, another, 
 Megalosaurus, perhaps as large as an elephant. Ceratosaurus 
 is the name of a well-known North American form regarded 
 by many authorities as identical with Megalosaurus. 
 
 Suborder (3). ORTHOPODA. 
 
 This suborder includes the most specialised of the Dino- 
 saurs, certain of which resemble the Theropoda in being 
 bipedal. In some of them such as Stegosaurus the exoskeleton 
 is strongly developed, in others such as Iguanodon it is 
 absent. 
 
 The vertebrae are solid and may be opisthocoelous, bi- 
 concave, or flat. The teeth are compressed and serrated, 
 often irregularly, and are frequently not set in distinct sockets. 
 The anterior part of the premaxillae is without teeth, and a 
 toothless pre-dentary or mento-meckelian bone is present. 
 The pre-orbital vacuities are small or absent, and the nares 
 are large and placed far forwards. 
 
 The most characteristic features of the group are found 
 in the pelvis which, except in the Ceratopsia, bears a striking 
 resemblance to that of birds. The ischium and post-pubis 
 are long slender bones directed backwards parallel to one 
 another, and the pre-pubis is also well developed. The ischium 
 has an obturator process. The limb bones are sometimes 
 hollow, sometimes solid. The anterior limbs are much shorter 
 than the posterior, pointing to a bipedal method of progression. 
 The pes is digitigrade or plantigrade, and has three, rarely four, 
 digits. 
 
REPTILIA. DINOSAURIA. 209 
 
 The suborder Orthopoda may be further subdivided into 
 three sections : 
 
 A. STEGOSAURIA. 
 
 A dermal exoskeleton is strongly developed. The verte- 
 bral centra are flat or biconcave, and neither they nor the 
 limb bones are hollowed out by internal cavities. The limbs 
 are plantigrade, the anterior ones short, the posterior ones 
 very large and strong. The post-pubis is well developed ; 
 
 e.g. Stegosaurus from the Upper Jurassic of Colorado. 
 
 B. CERATOPSIA. 
 
 There is sometimes a well-developed dermal exoskeleton 
 formed of small granules and plates of bone. The bones are 
 solid, and the vertebral centra flat. The cranium bears a 
 pair of enormous pointed frontal horns, and the parietal is 
 greatly expanded and elevated behind, forming with the 
 squamosals a shield which overhangs the anterior cervical 
 vertebrae. The premaxillae are united, and in front of them 
 is a pointed' beak-like bone which bites upon a toothless 
 predentary ossification of the mandible. The teeth have two 
 roots. The anterior limbs are but little shorter than the 
 posterior ones. There is no post-pubis ; 
 
 e.g. Polyonax from the uppermost Cretaceous of Montana. 
 
 C. ORNITHOPODA 1 . 
 
 There is no dermal exoskeleton. The cervical vertebrae 
 are opisthocoelous, and so are sometimes the thoracic. The 
 limb bones are hollow and the anterior limbs are much shorter 
 than the posterior ones. The feet are digitigrade and pro- 
 vided with long pointed claws. The post-pubis is long and 
 slender and directed back parallel to the ischium ; 
 
 e.g. Iguanodon from the European Cretaceous. 
 
 1 See 0. C. Marsh, Amer. J. Set. (3), vol. 48, 1894, p. 85. 
 R. 14 
 
210 THE VERTEBRATE SKELETON. 
 
 Order 8. CnocoDiLiA 1 . 
 
 This order includes the Crocodiles, Alligators and Garials 
 and various extinct forms, some of which are closely allied to 
 the early Dinosaurs. 
 
 There is always a more or less complete exoskeleton formed 
 of bony scutes overlain by epidermal scales ; these bony scutes 
 are specially well developed on the dorsal surface but may 
 occur also on the ventral. The vertebral column is divisible 
 into the five regions commonly distinguishable. In all living 
 forms the vertebrae, with the exception of the atlas and axis, 
 the two sacrals, and first caudal, are procoelous, but in many 
 extinct forms they are amphicoelous. The atlas (fig. 71) is 
 remarkable, consisting of four pieces, and the first caudal is 
 biconvex. 
 
 The teeth are, in the adult, planted in separate deep 
 sockets. The skull is very dense and solid, and all the 
 component bones including the quadrate are firmly united. 
 The dorsal surface of the skull is generally characteristically 
 sculptured. There is an interorbital septum, and the orbito- 
 sphenoidal and presphenoidal regions are imperfectly ossified. 
 Supratemporal, infratemporal, and post-temporal fossae occur, 
 but no interparietal foramen. In living genera there is a long 
 secondary palate formed by the meeting in the middle line of 
 the palatines, pterygoids and maxillae (fig. 43, A). 
 
 Cervical ribs (fig. 41, 8 and 9) are well developed, and arti- 
 culate with rather prominent surfaces borne on the neural 
 arches and centra respectively. The thoracic ribs articulate 
 with the long transverse processes, and sternal ribs and 
 
 1 See C. B. Briihl, Das skelet der Krokodiliden, Wien, 1862. C. K. 
 Hoffmann in Bronn's Klassen und Ordnungen des Thier-reichs, Bd. vi. 
 Abth. in. 188185. T. H. Huxley, Proc. Linn. Soc. (Zoology) 1860 
 vol. iv. p. 1. E. Owen, History of British fossil Reptiles. Crocodilia 
 (Palaeont. Soc.). A. Smith Woodward, Geol. Mag. 1885, 3rd dec. H. p. 
 496. A. Smith Woodward, Proc. of Geologists' Assoc. vol. ix. p. 288, 1886. 
 
REPTILIA. CROCODILIA. 211 
 
 abdominal splint ribs (fig. 46, 4) occur. The sternum is carti- 
 laginous, and both it and the shoulder-girdle are very simple. 
 The precoracoid is represented by merely a small process on 
 the coracoid, while the clavicles are absent, except in the 
 Parasuchia. In the pelvis (fig. 49) there is a large ilium, and 
 an ischium meeting its fellow in a ventral symphysis ; these 
 two bones form almost the whole of the acetabulum. In 
 front of the acetabulum, in the Eusuchia, projects a bone 
 which is generally called the pubis, but is in reality rather 
 an epipubis (fig. 49, 4), the true pubis being probably repre- 
 sented by a fourth element which remains cartilaginous for 
 some time, and later on ossifies and attaches itself to the 
 ischium. The limbs are small in proportion to the size of the 
 body, and are adapted for swimming or for shuffling along the 
 ground ; they are plantigrade and the bones are all solid. 
 In living forms the anterior limbs have five digits and the 
 posterior four, the fifth being represented only by a short 
 metatarsal. The first three digits in each case are clawed. 
 The calcaneum has a large back ward ly-projecting process. 
 
 The order Crocodilia may be subdivided into two sub- 
 orders. 
 
 Suborder (1). PARASUCHIA. 
 
 The vertebral centra are flat or biconcave. The pre- 
 maxillae are very large, and the nares are separated, and 
 placed far back. The posterior narial openings lie compara- 
 tively far forward between the anterior extremities of the 
 palatines. 
 
 The palatines and pterygoids do not form a secondary 
 palate. The supratemporal fossae are small, and open poste- 
 riorly, the lateral temporal fossae are very large. The parietals 
 and frontals are paired. Clavicles are present. The best 
 known and most important genus of these extinct crocodiles 
 is Belodon. 
 
 142 
 
212 THE VERTEBRATE SKELETON. 
 
 Suborder (2). EUSUCHIA. 
 
 The vertebrae are either biconcave or procoelous. The pre- 
 maxillae are small, and the anterior nares are united and 
 placed far forwards. The posterior nares lie far back, the 
 palatines and in living genera the pterygoids, meeting in the 
 middle line, and giving rise to a closed palate. The supra- 
 temporal fossae are surrounded by bone on all sides, and the 
 parietals, and often also the frontals are united. There are 
 no clavicles. The suborder includes the genera Crocodilus, 
 Alligator, Garialis and others living and extinct. 
 
 Order 9. PTEROSAURIA 1 . 
 
 These animals, called also the pterodactyles or Ornitho- 
 sauria, are a group of extinct reptiles, whose structure has 
 been greatly modified from the ordinary reptilian type for the 
 purpose of flight. 
 
 The skin was naked and they vary greatly in size and in 
 the length of the tail. The vertebrae and limb bones are 
 pneumatic just as in birds. The presacral vertebrae are pro- 
 coelous and have their neural arches firmly united to the 
 centra. The neck is long, the caudal vertebrae are amphi- 
 coelous, and from three to five vertebrae are fused together 
 in the sacral region. The skull is large and somewhat bird- 
 like, the facial portion being much drawn out anteriorly, and 
 the sutures being obliterated. It resembles that of other 
 reptiles in having large supratemporal fossae ; large pre-orbital 
 vacuities also occur. The jaws may be toothed or toothless, 
 and the teeth, when present, are imbedded in separate sockets. 
 The premaxillae are large, and the quadrate is firmly attached 
 to the skull. The rami of the mandible are united at the 
 
 1 See H. G. Seeley On the Organisation of the Ornithosauria, Journ. 
 Linn. Soc. (Zoology) vol. xin. p. 84. K. A. Zittel, Ueber Flugsaurier aus 
 dem lithographischen schiefer, Palaeontograph. xxix. p. 49. 
 
REPTILTA. PTEROSAURIA. 213 
 
 symphysis, and there is an ossified ring in the sclerotic. The 
 occurrence of a postfrontal and its union with the jugal 
 behind the orbit, are characteristic reptilian features. 
 
 The ribs have capitula and tubercula, and sternal and 
 abdominal ribs occur. The sternum has a well-developed keel, 
 and the scapula and coracoid are large and bird-like. There 
 are no clavicles or interclavicle. 
 
 The anterior limbs are modified to form wings by the great 
 elongation of the fifth digit, to which a membrane was at- 
 tached. The second, third and fourth digits are clawed and 
 are not elongated in the way that they are in bats. The 
 pollex, if present at all, is quite vestigial. 
 
 The pelvis is weak and small, and though the ilia are pro- 
 duced both in front of and behind the acetabula, in other 
 features the pelvis is not bird-like. The ischia are short and 
 wide, and the pubes are represented only by the pre-pubes. 
 The posterior limbs are small and the fibula is much reduced. 
 The pes is quite reptilian in type, and has five separate slender 
 metatarsals. The two best known genera are Pterodactylus, in 
 which the tail is short, and Rhamphorhynchus, in which it is 
 long. The Pterosauria are found throughout the Jurassic and 
 Cretaceous formations in both Europe and North America. 
 
CHAPTER XIV. 
 
 THE SKELETON OF THE GREEN TURTLE. 
 
 (Chelone midas.) 
 
 THE most striking feature as regards the skeleton of the 
 Turtle is that the trunk is enveloped in a bony box, the dorsal 
 portion of which is called the carapace, while the ventral 
 portion is the plastron. 
 
 I. EXOSKELETON. 
 
 a. The epidermal exoskeleton in the Green Turtle as 
 in all other Chelonia except Dermochelys, Trionyx and their 
 allies is strongly developed, its most important part consisting 
 of a series of horny shields which cover over the bony plates 
 of the carapace and plastron but do not at all correspond to 
 them in size and arrangement. 
 
 The shields covering over the carapace consist of three 
 rows of larger central shields, five (vertebral) shields being 
 included in the middle row and four (costal) in each lateral 
 row, and of a number of smaller marginal shields. 
 
 Of the marginal shields, that lying immediately in front of 
 the first vertebral is termed the nuchal, while the two suc- 
 ceeding the last vertebral are called sometimes pygal, some- 
 times supracaudal ; the remainder are the marginal shields 
 proper. 
 
 The epidermal covering of the plastron consists princi- 
 pally of six pairs of symmetrically arranged shields, called 
 
THE SKELETON OB 1 THE TURTLE. THE CARAPACE. 215 
 
 respectively the gular, humeral, pectoral, abdominal, 
 femoral, and anal, the gular being the most anterior. In 
 front of the gular shields is an unpaired intergular, and 
 the shields of the plastron are connected laterally with those 
 of the carapace, by five or six pairs of rather irregular infra- 
 marginal shields. Smaller horny plates occur on other parts 
 of the body, especially on the limbs and head. 
 
 Two other sets of structures belong also to the epidermal 
 exoskeleton, viz. (a) horny beaks with denticulated edges 
 which ensheath both upper and lower jaws, (b) claws, which 
 as a rule are borne only by the first digit of each limb. 
 Sometimes in young individuals the second digit is also clawed. 
 
 6. The dermal exoskeleton is strongly developed, and 
 is combined with endoskeletal structures derived from the ribs 
 and vertebrae to form the carapace. 
 
 The Carapace (fig. 36) consists of a number of plates 
 firmly united to one another by sutures. They have a very 
 definite arrangement and include : 
 
 (a) the nuchal plate (fig. 36, 1), a wide plate forming 
 the whole of the anterior margin of the carapace. It is 
 succeeded by three series of plates, eight in each series, which 
 together make up the main part of the carapace. Of these 
 the small 
 
 (b) neural plates 1 (fig. 36, A, 2) form the middle series. 
 They are closely united with the neural arches of the under- 
 lying vertebrae ; 
 
 (c) the costal plates 1 (fig. 36, A, 3) are broad arched 
 plates united to one another by long straight sutures. They 
 are united at their inner extremities with the neural plates, 
 but the boundaries of the two sets of plates do not regularly 
 correspond Each is united ventrally with a rib which pro- 
 jects beyond it laterally for some distance ; 
 
 1 Another view commonly held is that the neural and costal plates are 
 respectively formed by the expanded neural arches and ribs. 
 
216 
 
 THE VERTEBRATE SKELETON. 
 
 the marginal plates (fig. 36, 4) are twenty-three in 
 
 FlG. 36. A, DORSAL AND B, VENTRAL VIEW OF THE CARAPACE OF A 
 
 LOGGERHEAD TURTLE (Thalassochelys caretta), (after OWEN). 
 
 1. nuchal plate. 6. rib. 
 
 2. first neural plate. 7. 
 
 3. second costal plate. 8. 
 
 4. marginal plate. 9. 
 
 5. pygal plate. 
 
 thoracic vertebra. 
 first vertebral shield. 
 costal shield. 
 
THE SKELETON OF THE TURTLE. THE PLASTRON. 217 
 
 number, eleven lying on each side, while an unpaired one lies 
 in the middle line posteriorly. Many of them are marked by 
 slight depressions into which the ends of the ribs fit ; 
 
 (e) the pygal plates (fig. 36, 5) are two unpaired plates 
 lying immediately posterior to the last neural. 
 
 The sculpturing due to the epidermal shields is very 
 obvious on the carapace. 
 
 The plastron (fig. 37) consists of one unpaired ossification, 
 the entoplastron, and four pairs of ossifications called re- 
 spectively the epiplastra, hyoplastra, hypoplastra, and 
 xiphiplastra. 
 
 The epiplastra (fig. 37, 1) are the most anterior, they are 
 expanded and united to one another in the middle line in 
 front, while behind each tapers to a point which lies external 
 to a process projecting forwards from the hyoplastron. They 
 are homologous with the clavicles of other vertebrates. 
 
 The entoplastron or episternum (fig. 37, 2) which is 
 homologous with the interclavicle of other reptiles, is ex- 
 panded at its anterior end and attached to the symphysis 
 of the epiplastra, while behind it tapers to a point and ends 
 freely. 
 
 The hyoplastra are large irregular bones each closely 
 united posteriorly with the corresponding hypoplastron, and 
 drawn out anteriorly into a process which lies internal to that 
 projecting backwards from the epiplastron. Each gives off on 
 its inner surface a slender process which nearly meets its fellow, 
 while the anterior half of the outer surface is drawn out into 
 several diverging processes. 
 
 The hypoplastra (fig. 37, 4) are flattened bones re- 
 sembling the hyoplastra, with which they are united by long 
 sutures ; the posterior half of both outer and inner surfaces 
 is drawn out into a number of pointed processes. 
 
 The xiphiplastra are small flattened elongated bones 
 meeting one another in the middle line posteriorly. In front 
 they are notched and each interlocks with a process from the 
 
218 THE VERTEBRATE SKELETON. 
 
 hypoplastron of its side. The hyoplastra, hypoplastra and 
 
 FIG. 37. THE PLASTRON OF A GREEN TURTLE (Chelone midas). 
 xf. (Camb. Mus.) 
 
 1. epiplastron (clavicle). 4. hypoplastron. 
 
 2. entoplastron (interclavicle). 5. xiphiplastron. 
 
 3. hyoplastron. 
 
 xiphiplastra are homologous with the abdominal ribs of 
 Crocodiles. 
 
 II. ENDOSKELETOK 
 1. THE AXIAL SKELETON. 
 
 The axial skeleton includes the vertebral column, the ribs, 
 and the skull. 
 
THE SKELETON OF THE TURTLE. THE VERTEBRAE. 219 
 
 A. THE VERTEBRAL COLUMN AND RIBS. 
 
 The number of vertebrae in the Green Turtle is thirty- 
 eight, not a great number as compared with that in many 
 reptiles, and of these eighteen are caudal. 
 
 The vertebral column is divisible into four regions only 
 cervical, thoracic, sacral, and caudal. 
 
 THE CERVICAL VERTEBRAE. 
 
 These are eight in number, and are chiefly remarkable for 
 the great variety of articulating surfaces which their centra 
 present, and for their mobility upon one another. 
 
 The first or atlas vertebra differs much from all the others 
 and consists of the following parts : 
 
 a. the neural arch, formed of two separate ossifications 
 united in the mid-dorsal line ; 
 
 b. the inferior arch ; 
 
 c. the centrum, which is detached from the rest and 
 forms the odontoid process of the second vertebra. 
 
 Each half of the neural arch consists of a ventral portion, 
 the pedicel, which lies more or less vertically and is united 
 ventrally to the inferior arch, and of a dorsal portion, the 
 lamina, which lies more or less horizontally and meets its 
 fellow in the middle line in front, partially roofing over the 
 neural canal. Each pedicel bears a facet on its anterior 
 surface, which, with a corresponding one on the inferior arch, 
 articulates with the occipital condyle of the skull. Three 
 similar facets occur also on the posterior surface of the 
 pedicel and inferior arch, and articulate with the odontoid 
 process. The laminae meet one another in front, but do not 
 fuse, while behind they are separated by a wide triangular 
 space. They bear a pair of small downwardly-directed facets, 
 the postzygapophyses, for articulation with the prezyga- 
 pophyses of the second vertebra. 
 
220 THE VERTEBRATE SKELETON. 
 
 The inferior arch is a short irregular bone bearing two 
 converging facets for articulation with the occipital condyle 
 and odontoid process respectively. 
 
 The centrum or odontoid process has a convex anterior 
 surface for articulation with the neural and inferior arches, 
 and a concave posterior surface by which it is united with 
 the centrum of the second or axis vertebra. It bears pos- 
 teriorly a small epiphysis which is really a detached portion of 
 the inferior arch. 
 
 The second or axis and following five cervical vertebrae, 
 though showing distinct differences, resemble one another con- 
 siderably, each having a fairly elongated centrum with a keel- 
 like hypapophysis, each having also a neural arch with 
 prominent articulating surfaces, the anterior of which, or 
 prezygapophyses, look upwards and inwards, while the 
 posterior ones, the postzygapophyses, look downwards and 
 outwards. They however, as was previously mentioned, differ 
 very remarkably in the character of the articulating surfaces 
 of the centra. Thus the second and third vertebrae are 
 convex in front and concave behind, the fourth is biconvex, 
 the fifth is concave in front and convex behind. The sixth 
 is concave in front and attached to the seventh by a flat 
 surface behind, the seventh has a flat anterior face and two 
 slightly convex facets behind. The vertebrae all have short 
 blunt transverse processes and the second has a prominent 
 neural spine. 
 
 The eighth cervical vertebra is curiously modified, the 
 centrum is very short, has a rather prominent hypapophysis, 
 and is convex behind, while in front it articulates with the 
 preceding centrum by two concave surfaces. The neural arch 
 is deeply notched in front and bears two upwardly-directed 
 prezygapophyses, while behind it is very massive and is drawn 
 out far beyond the centrum, bearing a pair of flat postzyga- 
 pophyses. The top of the neural arch almost or quite meets 
 a blunt outgrowth from the nuchal plate. 
 
THE SKELETON OF THE TURTLE. THE VERTEBRAE. 221 
 
 THE THORACIC VERTEBRAE. 
 
 These are ten in number and are all firmly united with 
 the ribs and elements forming the carapace. 
 
 The first thoracic vertebra differs from the others, the 
 centrum is short and has a concave anterior surface articu- 
 lating with the centrum of the last cervical vertebra, and a 
 pair of prezygapophyses borne on long outgrowths. The 
 neural spine arises only from the anterior half of the centrum, 
 and is not fused to the carapace. Arising laterally from the 
 anterior part of the centrum are a small pair of ribs each of 
 which is connected with a process arising from the rib of the 
 succeeding vertebra. 
 
 The next seven thoracic vertebrae are all very similar, 
 each has a long cylindrical centrum, expanded at the ends, 
 and firmly united to the preceding and succeeding vertebrae. 
 The neural arches are flattened and expanded dorsally, and 
 are united to one another and to the overlying neural 
 plates ; each arises only from the anterior half of its respective 
 centrum, and overlaps the centrum of the vertebra in front of 
 it. Between the base of the neural arch and its successor is a 
 small foramen for the exit of the spinal nerve. There are no 
 transverse processes or zygapophyses. 
 
 To each thoracic vertebra from the second to ninth in- 
 clusive, there corresponds a pair of ribs (fig. 36, 6) of a rather 
 special character. Each is suturally united with the anterior 
 half of the edge of its own vertebra, and overlaps on to the 
 posterior half of the edge of the next preceding vertebra. 
 The ribs are much flattened, and each is fused with the cor- 
 responding costal plate, beyond which it projects to fit into 
 a pit in one of the marginal plates. 
 
 The tenth thoracic vertebra is smaller than the others, and 
 its neural arch does not overlap the preceding vertebra, it 
 bears a pair of small ribs which are without costal plates, but 
 meet those of the ninth vertebra. 
 
 There are no lumbar vertebrae. 
 
222 THE VERTEBRATE SKELETON. 
 
 THE SACRAL VERTEBRAE. 
 
 The sacral vertebrae are two in number, they are short 
 and wide, their centra are ankylosed together, and their neural 
 arches are not united to the carapace. 
 
 The first has the anterior face of the centrum concave and 
 the posterior flat, while both faces of the second are flat. 
 Each bears a pair of short ribs which meet the ilia, but are 
 not completely ankylosed either with them or the centra. 
 
 THE CAUDAL VERTEBRAE. 
 
 The caudal vertebrae are eighteen in number. The 
 centrum of the first is flat in front and is ankylosed to 
 the second sacral; behind it is convex. The others are all 
 very similar to one another, and decrease gradually in size 
 when followed back. Each has a moderately long centrum, 
 concave in front and convex behind, both terminations being 
 formed by epiphyses. The neural arch arises only from the 
 anterior half of the vertebra ; it bears a blunt truncated 
 neural spine and prominent pre- and post-zygapophyses. The 
 first seven caudal vertebrae bear short ribs attached to their 
 lateral margins, the similar outgrowths on the succeeding ver- 
 tebrae do not ossify from distinct centres, and are transverse 
 processes rather than ribs. 
 
 B. THE SKULL. 
 
 The skull of the Turtle is divisible into the following three 
 parts : 
 
 (1) the cranium ; 
 
 (2) the lower jaw or mandible ; 
 
 (3) the hyoid. 
 
 (1) THE CRANIUM. 
 
 The cranium is a very compact bony box, containing a 
 cavity in which the brain lies, and which is a direct continua- 
 tion of the neural canal of the vertebrae. 
 
THE SKELETON OF THE TURTLE. THE SKULL. 223 
 
 .1 
 
 17 
 
 FIG. 38. THE SKULL OF THE GREEN TURTLE (Chelone midas). x . 
 
 A, POSTERIOR HALF, B, ANTERIOR HALF. (Brit. MuS.) 
 
 1. parietal. 13. angular. 
 
 2. squamosal. 14. supra-angular. 
 
 3. quadrate. 15. premaxilla. 
 
 4. basisphenoid. 16. maxilla. 
 
 5. basi-occipital. 17. jugal. 
 
 6. quadratojugal. 18. postfrontal. 
 
 7. opisthotic. 19. vomer. 
 
 8. exoccipital. 20. prefrontal. 
 
 9. foramen magnum. 21. frontal. 
 
 10. splenial. 22. external auditory meatus 
 
 11. articular. leading into tympanic 
 
 12. dentary. cavity. 
 
224 THE VERTEBRATE SKELETON. 
 
 Like those of the skull as a whole its component bones may 
 be subdivided into three sets : 
 
 1 . those forming the brain-case or cranium proper ; 
 
 2. those developed in connection with the special sense 
 organs ; 
 
 3. those forming the upper jaw and suspensorial appa- 
 ratus. 
 
 Both cartilage and membrane bones take part in the forma- 
 tion of the skull, and a considerable amount of cartilage 
 remains unossified, especially in the ethmoidal and sphenoidal 
 regions. 
 
 1. The CRANIUM PROPER OR BRAIN-CASE. 
 
 The cartilage and membrane bones of the brain-case when 
 taken together can be seen to be more or less arranged in 
 three rings or segments, called respectively the occipital, 
 parietal, and frontal segments. 
 
 The occipital segment is the most posterior of these, and 
 consists of four cartilage bones, the basi-occipital, the two 
 exoccipitals and the supra-occipital; these bound the 
 foramen magnum. 
 
 The basi-occipital (figs. 38 and 39, 5) lies ventral to the 
 foramen magnum and only bounds a very small part of it ; it 
 forms one-third of the occipital condyle by which the skull 
 articulates with the atlas vertebra. It unites dorsally with 
 the exoccipitals and anteriorly with the basisphenoid. 
 
 The exoccipitals are rather small bones, which form the 
 sides and the greater part of the floor of the foramen magnum, 
 and two : thirds of the occipital condyle. Laterally each is 
 united with the pterygoid and opisthotic of its side. At the 
 sides of the occipital condyle each exoccipital is pierced by 
 a pair of foramina, the more dorsal and posterior of which 
 transmits the hypoglossal nerve. 
 
 The supra-occipital (fig. 39, 14) is a larger bone than the 
 others of the occipital segment. It forms the upper border 
 
THE SKELETON OF THE TURTLE. THE CRANIUM. 225 
 
 of the foramen magnum and is drawn out dorsally into a large 
 crest which extends back far beyond the occipital condyle. 
 In the adult the supra-occipital is completely ankylosed with 
 the epi-otics. 
 
 The Parietal segment. 
 
 The ventral portion of the parietal segment is formed by 
 the basisphenoid (figs. 38 and 39, 4) which lies immediately 
 in front of the basi-occipital. A triangular portion of it is 
 seen in a ventral view of the skull, but it is quickly over- 
 lapped by the pterygoids. It gives off dorsally a pair of 
 short processes which meet the pro-otics. 
 
 The alisphenoidal region is unossified and the only other 
 constituents of the parietal segment are the parietals (fig. 39, 1). 
 These are large bones which, after roofing over the cranial 
 cavity, extend upwards and become expanded into a pair of 
 broad plates which unite with the squamosal and bones of the 
 frontal segment to form a wide, solid, false roof to the skull. 
 Each also sends ventralwards a plate which meets an up- 
 growth from the pterygoid and acts as an alisphenoid. 
 
 The Frontal segment. 
 
 Of the frontal segment the basal or presphenoidal and 
 lateral or orbitosphenoidal portions do not become ossified, 
 the dorsal portion however includes three pairs of membrane 
 bones, the frontals, prefrontals and post/rentals. 
 
 Thefrontals are a pair of small bones lying immediately in 
 front of the parietals, and in front of them are the prefrontals 
 (tigs. 38 and 39, 20), a pair of similar but still smaller bones, 
 which are produced ventrally to meet the vomer and palatines. 
 They form also the dorsal boundary of the anterior nares. 
 The post/rentals (figs. 38 and 39, 18) are larger bones, united 
 dorsally to the frontals and parietals, posteriorly to the squa- 
 mosals, and ventrally to the jugals and quadra tojugals. All 
 three pairs of frontal bones, especially the postfrontals, take 
 part in the bounding of the orbits. 
 
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 THE VERTEBKATE SKELETON. 
 
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THE SKELETON OF THE TURTLE. SENSE CAPSULES. 227 
 
 2. THE SENSE CAPSULES. 
 
 Skeletal structures occur in connection with each of the 
 three special sense organs of hearing, sight, and smell. 
 
 The Auditory capsules. 
 
 The auditory or periotic capsule of the turtle is rather 
 large and its walls are well ossified, epi-otic, pro-otic and 
 opisthotic bones being present. 
 
 The epi-otic (fig. 39, 13) is the more dorsal of the three 
 bones, and in the adult is completely ankylosed with the supra- 
 occipital. 
 
 The opisthotic (fig. 39, 8) is the ventral posterior element. 
 On its inner side it is united to the supra-occipital above, 
 and to the exoccipital below ; it sometimes becomes com- 
 pletely fused with the exoccipital. In front it meets the 
 pro-otic, and on its outer side the squamosal and quadrate. 
 Its anterior portion is hollowed out by the cavity in which 
 the auditory organ lies, it gives off also a process which is 
 separated from the exoccipital by an oval foramen through 
 which the glossopharyngeal, pneumogastric, and spinal acces- 
 sory nerves leave the cranial cavity. 
 
 The pro-otic is the anterior element; it meets the supra- 
 occipital and opisthotic posteriorly, while anteriorly it is 
 separated from the alisphenoidal plate of the parietal and 
 pterygoid by a large oval foramen through which the maxillary 
 and mandibular branches of the trigeminal nerve pass out 
 (fig. 39, V 1 & 2). It is hollowed out posteriorly by the cavity 
 which the auditory organ lies, and its inner wall as seen in 
 longitudinal section is pierced by a foramen through which the 
 external carotid artery and facial nerve leave the cranial cavity, 
 the nerve finally leaving the skull through a small oval 
 foramen on the anterior face of the pro-otic near its junction 
 with the quadrate. 
 
 Between the pro-otic and opisthotic as seen in a longi- 
 tudinal section of the skull is a large opening constricted in the 
 
 152 
 
228 THE VERTEBRATE SKELETON. 
 
 middle. This is the internal auditory meatus (fig. 39, VIII.). 
 Through it the auditory nerve leaves the cranial cavity and 
 enters the ear. The ramus vestibularis leaves through the dorsal 
 part of the hole, the ramus cochlearis through the ventral. 
 
 The cavity of the auditory or periotic capsule communi- 
 cates with the exterior by a fairly large hole, the fenestra 
 ovalis, which lies between the opisthotic and pro-otic, and 
 opens into a deep depression, the tympanic cavity, which 
 is seen in a posterior view of the skull lying just external to 
 the exoccipital. The cavity communicates with the exterior by 
 a large opening, the external auditory meatus (fig. 38, 22). 
 
 Several other openings are seen in the tympanic cavity; 
 through one at the extreme posterior end the pneumogastric 
 and spinal accessory nerves leave the skull, and through 
 another, a little further forwards, the glossopharyngeal. 
 
 The auditory ossicles consist of a long bony columella, 
 whose inner end fits into the fenestra ovalis, while the outer 
 end is attached to a small cartilaginous plate, the extra- 
 eolumella, which is united to the tympanum. 
 
 The Optic capsules. 
 
 The skeletal structures developed in connection with the 
 optic capsule do not become united to the skull. They con- 
 sist of : 
 
 (a) the sclerotic, a cartilaginous sheath investing the eye 
 and bearing 
 
 (6) a ring of ten small bony scales. 
 
 There is no lachrymal bone. 
 
 The Olfactory or Nasal capsules. 
 
 The basicranial axis in front of the basisphenoid remains 
 cartilaginous, neither presphenoid nor mesethmoid bones are 
 developed, and the orbits in a dry skull communicate by a 
 wide space through which the second, third, fourth, and sixth 
 cranial nerves pass out. Separate nasal bones also do not 
 occur, the large prefrontals extending over the area usually 
 occupied by both nasals and lachrymals. 
 
THE SKELETON OF THE TURTLE. THE UPPER JAW. 229 
 
 The only bone developed in connection with the nasal 
 capsules is the vomer (fig. 39, 19), an unpaired bone lying 
 ventral to the mesethmoid cartilage, and in contact laterally 
 with the maxillae, premaxillae and palatines. 
 
 3. THE UPPER JAW AND SUSPENSORIAL APPARATUS. 
 
 A number of pairs of bones are developed in connection 
 with the upper jaw and suspensorial apparatus, one pair, the 
 quadrates, being cartilage bones, while the rest are all mem- 
 brane bones. 
 
 The squamosals (fig. 38, 2) are large bones which, lying 
 external to the auditory bones, extend dorsal wards to meet 
 the parietals and postfrontals, and form a large part of the 
 false roof of the skull. They are united ventrally with the 
 quadrates and quadratojugals. 
 
 Each quadrate (fig. 38, 3) forms the outer boundary of 
 the tympanic cavity, and is firmly united on its inner side with 
 the opisthotic, exoccipital, and pterygoid. Dorsally it is fixed 
 to the squamosal and anteriorly to the quadratojugal. Its 
 outer surface is marked by a deep recess, and it ends below 
 in a strong condyle with which the mandible articulates. In 
 front of the quadrates are a pair of thin plate-like bones, the 
 quadratojugals which are united in front to the jugals or malars. 
 
 The jugals (tig. 38, 17) are also thin plate-like bones, and 
 form part of the posterior boundary of the orbit. They are 
 attached dorsally to the postfrontals, and anteriorly to the 
 maxillae, while each also sends inwards a horizontal process 
 which meets the pterygoid and palatine. 
 
 The maxillae (figs. 38 and 39, 16) are a pair of large ver- 
 tically-placed bones, each drawn out ventrally into a straight, 
 sharp, cutting edge. They form the lateral boundaries of the 
 anterior nares, and each sends dorsalwards a process which 
 meets the post-frontal. Each also sends inwards a horizontal 
 palatine process, which meets the palatine and vomer, and 
 also forms much of the floor of the narial passage. 
 
230 THE VERTEBRATE SKELETON. 
 
 The premaxillae (figs. 38 and 39, 15) are a pair of very 
 small bones forming the floor of the anterior narial opening, 
 they are wedged in between the two maxillae, and send back 
 processes which meet the vomer and palatines. 
 
 The palatines (fig. 39, 10) are a pair of small bones firmly 
 united with the pterygoids behind, with the maxillae and jugals 
 externally, and with the vomer in the middle line. Each also 
 gives off a palatine plate which unites with the expanded lower 
 edge of the vomer, and forms the ventral boundary of the pos- 
 terior nares. Anteriorly the palatines form the posterior bound- 
 ary of a large foramen through which the ophthalmic branches 
 of the fifth and seventh nerves pass to the olfactory organs. 
 
 The pterygoids (fig. 39, 9) are a pair of large bones which 
 unite with one another by a long median suture. They are 
 united also with the palatines in front, and with the quadrate, 
 basisphenoid, basi-occipital, and exoccipitals behind. Each 
 also sends dorsal wards a short alisphenoid plate which 
 meets that from the parietal. 
 
 Piercing the posterior end of the pterygoid is the prominent 
 opening of the carotid canal; a bristle passed into this hole 
 emerges through a foramen lying between the pro-otic and the 
 alisphenoid process of the pterygoid. 
 
 (2) THE LOWER JAW OR MANDIBLE. 
 
 The mandible consists of one unpaired bone, formed by 
 the fusion of the two dentaries, and five pairs of bones, called 
 respectively the articular, angular, supra-angular, splenial 
 and coronoid. 
 
 The fused dentaries (fig. 38, 12) form by far the largest of 
 the bones ; they constitute the flattened anterior part of the 
 mandible, and extend back below the other bones almost to 
 the end of the jaw. 
 
 The coronoid is the most anterior of the paired bones, it 
 forms a prominent process to which the muscles for closing 
 the jaw are attached. 
 
THE SKELETON OF THE TURTLE. THE HYOID. 231 
 
 The articular (fig. 38, 1 1) is expanded, and with the supra- 
 angular forms the concave articulating surface for the quadrate. 
 
 The splenial (fig. 38, 10) is a thin plate applied to the inner 
 surface of the posterior part of the mandible. 
 
 The angular (fig. 38, 13) is a slender plate of bone lying 
 below the supra-angular and splenial. 
 
 (3) THE HYOID. 
 
 The hyoid apparatus is well developed, parts of the first two 
 branchial arches being found, as well as of the hyoid proper. 
 It consists of a more or less oblong flattened basilingual 
 plate or body of the hyoid which represents the fused 
 ventral ends of the hyoid and branchial arches of the embryo, 
 and is drawn out into a point anteriorly. The greater part is 
 formed of unossified cartilage, but at the posterior end it is 
 bilobed, and a pair of ossified tracts occur. To its sides are 
 attached three pairs of structures, which are portions of the 
 hyoid and first and second branchial arches respectively. 
 
 The free part of the hyoid consists of a small piece of 
 cartilage attached to the anterior part of the basilingual plate 
 at its widest portion (fig. 53, 2). 
 
 The anterior cornu or free part of the first branchial 
 arch is much the largest of the three structures. Its proximal 
 portion adjoining the basilingual plate is cartilaginous, as is 
 its distal end ; the main part is however ossified. 
 
 The posterior cornu or free part of the second branchial 
 arch (fig. 53, 4) consists of a short flattened cartilaginous bar 
 arising from the bilobed posterior end of the basilingual plate. 
 
 The hyoid apparatus has no skeletal connection with the 
 rest of the skull. 
 
 2. THE APPENDICULAR SKELETON. 
 
 This includes the skeleton of the two pairs of limbs and 
 their girdles. 
 
 THE PECTORAL GIRDLE. 
 
 The pectoral girdle has an anomalous position, being 
 
232 THE VERTEBRATE SKELETON. 
 
 situated internal or ventral to the ribs. It consists of three 
 bones, a dorsal bone, the scapula, an anterior ventral bone, 
 the precoracoid, and a posterior ventral bone, the coracoid. 
 
 The scapula is a small somewhat rod-shaped bone form- 
 ing about two-thirds of the glenoid cavity. At its proximal 
 end it is closely united with the precoracoid, the two bones 
 ossifying continuously. It tapers away distally, and is directed 
 dorsalwards towards the carapace. 
 
 The precoracoid forms an angle of about 130 with the 
 scapula, with which it is completely fused at its proximal end. 
 Its distal end is somewhat expanded and flattened, and is 
 terminated by a fibrocartilaginous epiprecoracoid which 
 meets its fellow. It takes no part in the formation of the 
 glenoid cavity. 
 
 The coracoid is a large flattened blade-shaped bone form- 
 ing about one-third of the glenoid cavity. It does not meet 
 its fellow in a ventral symphysis, and is terminated by a carti- 
 laginous epicoracoid. The glenoid articulating surfaces of 
 both scapula and coracoid are lined by a thick pad of car- 
 tilage. 
 
 THE ANTERIOR LIMB. 
 
 This is divisible into three portions, the upper arm, fore- 
 arm and manus. 
 
 The upper arm contains a single bone, the humerus. 
 
 The humerus (fig. 40, A, 1) is a stout, nearly straight, some- 
 what flattened bone widely expanded at both ends. At the 
 proximal end is the large hemispherical head, which articulates 
 with the glenoid cavity. Behind the head the bone is drawn 
 out into another large rounded process. Below the head the 
 shaft bears a small outgrowth which is continuous with a 
 larger one on the flexor surface (see p. 29). The bone is 
 terminated distally by the trochlea, consisting of three 
 partially distinct convex surfaces which articulate with the 
 bones of the fore-arm. 
 
THE SKELETON OF THE TURTLE. ANTERIOR LIMB. 233 
 
 The fore- arm includes two bones, the radius and ulna; 
 both these are small bones, and are immovably fixed to one 
 another proximally and distally. 
 
 The radius or pre-axial bone is the larger of the two, and 
 is a rod-like bone terminated at either end by an epiphysis. 
 It articulates at its proximal end with the humerus, and at 
 its distal end with the radiale or scaphoid bone of the carpus. 
 
 The ulna (fig. 40, A, 3) or post-axial bone is shorter than 
 the radius, and more expanded at its proximal end, where it 
 articulates with the humerus. It articulates distally with the 
 intermedium (lunar) and the ulnare (cuneiform) bones of the 
 carpus. All three bones of the arm have their terminations 
 formed by epiphyses which ossify from centres distinct from 
 those forming the shafts. 
 
 The Manus consists of the carpus or wrist and the hand 
 which includes the metacarpals and phalanges. 
 
 The carpus consists of a series of ten small bones, one of 
 which, the pisiform (fig. 40, A, 10), differs from the others in 
 being merely an ossification in the tendon of a muscle. The 
 remaining nine bones are arranged in a proximal row of three, 
 the ulnare (fig. 40, A, 6), intermedium, and radiale, and a 
 distal row of five (carpalia 1 5), each of which supports one 
 of the metacarpals. A ninth bone, the centrale (fig. 40, A, 7), 
 is wedged in between the two rows. The ulnare, intermedium 
 and pisiform are comparatively large flattened bones, the others 
 are small and cubical. 
 
 The hand. This is composed of five digits, each of which 
 consists of a metacarpal and of a varying number of phalanges. 
 
 The metacarpals. The first metacarpal (fig. 40, A, 11) 
 is a short flattened bone, the others are all elongated and 
 cylindrical, and are terminated proximally by slightly concave 
 surfaces, and distally by slightly convex ones. 
 
 The phalanges. The first and fifth digits both have two 
 phalanges, the second, third, and fourth have each three. The 
 distal phalanx of the first digit is stout and curved, and bears 
 
234 
 
 THE VERTEBRATE SKELETON. 
 
 -12 
 
 FIG. 40. A. ANTERIOR LIMB 
 imbricata) x (Brit. Mus.) 
 TURTLE (Chelone midas) x \ 
 
 1. humerus. 
 
 2. radius (almost hidden by 
 
 ulna). 
 
 3. ulna. 
 
 4. radiale. 
 
 5. intermedium. 
 
 6. ulnare. 
 
 7. centrale. 
 
 8. carpale I. 
 
 9. carpale IV. 
 
 10. pisiform. 
 
 11. first metacarpal. 
 
 OF A YOUNG HAWKSBILL TURTLE (Chelone 
 . B. POSTERIOR LIMB OF A LARGE GREEN 
 j- (Camb. Mus.). 
 
 12. femur, 
 the 13. tibia. 
 
 14. fibula. 
 
 15. tibiale intermedium and cen- 
 
 trale fused. 
 
 16. fibulare. 
 
 17. tarsale 1. 
 
 18. tarsale 2. 
 
 19. tarsalia 4 and 5 fused. 
 
 20. first metatarsal 
 
 21. fifth metatarsal. 
 
 i, ii, in, iv, v, digits. 
 
THE SKELETON OF THE TURTLE. PELVIC GIRDLE. 235 
 
 a horny claw ; those of the other digits are flattened and more 
 or less pointed. 
 
 THE PELVIC GIRDLE. 
 
 The pelvic girdle consists of three bones ; a dorsal bone, 
 the ilium, an anterior ventral bone, the pubis, and a pos- 
 terior ventral bone, the ischium. All three bones contribute 
 largely to the formation of the acetabulum, with which the 
 head of the femur articulates. 
 
 The ilium is a small slightly curved bone, which unites 
 ventrally with the pubis and ischium, and extends dorsal wards 
 and J^ack wards to meet the distal ends of the sacral ribs. 
 
 The pubis is the largest bone of the three ; its distal 
 end forms a wide bilobed plate, the inner lobe meeting its 
 fellow in a median symphysis, while the other lobe or lateral 
 process extends outwards. Attached to the symphysis in front 
 is a cartilaginous epipubis, while behind, the two pubes are 
 terminated by a wide rounded cartilaginous area. 
 
 The ischium, the smallest bone of the three, is flattened 
 and like the pubis meets its fellow in a median symphysis. 
 A narrow band of cartilage connects the symphysis pubis with 
 the symphysis ischii, and separates the two obturator fora- 
 mina from one another. 
 
 THE POSTERIOR LIMB. 
 
 This is divisible into three portions, the thigh, the crus or 
 shin, and the pes. 
 
 The thigh includes a single bone, the femur. 
 
 The femur (fig. 40, B, 12) is a short thick bone, with a 
 prominent rounded head articulating with the acetabulum. 
 Behind this head is a deep pit, beyond which is a roughened 
 area corresponding with the great trochanter of mammals. 
 The distal end is expanded and somewhat convex. 
 
 The bones of the crus or shin are the tibia and 
 fibula. These are both straight rod -like bones with expanded 
 
236 THE VERTEBRATE SKELETON. 
 
 terminations which closely approach one another, while else- 
 where the bones diverge considerably. 
 
 The terminations of all three of the leg bones are formed 
 by epiphyses. 
 
 The Pes consists of the tarsus or ankle, and the foot, 
 which is made up of five digits. 
 
 The tarsus. The tarsal bones of the Turtle do not retain 
 their primitive arrangement to such an extent as do the 
 carpals. They are arranged in a proximal row of two and a 
 distal row of four. Of the bones in the proximal row the 
 postaxial one is much the smaller and is the fibulare ; the 
 larger pre-axial one (fig. 40, B, 15) represents the tibiale, 
 intermedium, and centrale fused, and articulates with both 
 tibia and fibula. The first three distal tarsalia are all small 
 bones and are very similar in size, and each articulates regu- 
 larly with the corresponding metatarsal. The fourth bone 
 (fig. 40, B, 19) is much larger, and represents tarsalia 4 and 5 
 fused. The first two distal tarsalia articulate with the pre- 
 axial tarsal of the proximal row, the third only with its neigh- 
 bours the second, and the fused fourth and fifth. The latter 
 articulates with both bones of the proximal row. 
 
 Each digit consists of a metatarsal and of a varying num- 
 ber of phalanges. 
 
 The metatarsals. The first metatarsal (fig. 40, B, 20) 
 is broad and flattened, the second, third and fourth, are all 
 elongated bones with nearly flat terminations formed by small 
 epiphyses/ The fifth is large and flattened, and the articular 
 surface for the phalanx is situated somewhat laterally. 
 
 The phalanges. The first digit has two phalanges and is 
 the stoutest of them all ; its distal phalanx is sheathed in a 
 large horny claw. The other digits, of which the third is the 
 longest, have each three phalanges. The distal phalanges of 
 the second and third digits are flattened and pointed and bear 
 small horny claws. 
 
CHAPTER XV. 
 THE SKELETON OF THE CROCODILE. 
 
 THE species chosen for description is C. palustris, a form 
 occurring throughout the Oriental region, but the description 
 would apply almost equally well to any of the other species of 
 the genus Crocodilus, and with comparatively unimportant 
 modifications to any of the living Crocodilia. 
 
 I. EXOSKELETON. 
 
 The exoskeleton of the Crocodile is strongly developed and 
 includes elements of both epidermal and dermal origin. 
 
 a. The epidermal exoskeleton is formed of a number 
 of horny scales or plates of variable size covering the whole 
 surface of the body. Those covering the dorsal and ventral 
 surfaces are oblong in shape, and are arranged in regular rows 
 running transversely across the body. The scales covering 
 the limbs and head are mostly smaller and less regularly 
 arranged, and are frequently raised into a more or less obvious 
 keel. Those covering the dorsal surface of the tail are very 
 prominently keeled. 
 
 The epidermal exoskeleton also includes the horny claws 
 borne by the first three digits of both manus and pes. 
 
 b. The dermal exoskeleton. This has the form of 
 bony scutes which underlie the epidermal scales along the 
 dorsal surface of the trunk and anterior part of the tail. 
 
238 THE VERTEBRATE SKELETON. 
 
 Except in very young individuals the epidermal scales are 
 rubbed off from these scutes, which consequently come to pro- 
 ject freely on the surface of the body. Each scute is a nearly 
 square bony plate, deeply pitted or sculptured, and marked by 
 a strong ridge on its dorsal surface, while its ventral surface 
 is smooth. Contiguous scutes are united to one another by 
 interlocking sutures. 
 
 The scutes are arranged in two distinct areas, viz. (1) a 
 small anterior nuchal shield which lies just behind the head 
 and is formed of six large scutes more or less firmly united 
 together, and (2) a larger posterior dorsal shield covering the 
 whole of the back and anterior part of the tail, and formed 
 of smaller scutes, which are arranged in regular transverse 
 rows, and progressively diminish in size when followed back. 
 
 The teeth are exoskeletal structures, partly of dermal, 
 partly of epidermal origin. They lie along the margins of 
 the jaws and are confined to the premaxillae, maxillae and 
 dentaries. They are simple conical structures, without roots 
 each is in the adult placed in a separate socket, and is replaced 
 by another which as it grows comes to occupy the pulp cavity 
 of its predecessor. In the young animal the teeth are not 
 placed in separate sockets but in a continuous groove. This 
 feature is met with also in the Ichthyosauria. The groove 
 gradually becomes converted into a series of sockets by the 
 ingrowth of transverse bars of bone. The anterior teeth are 
 sharply pointed and slightly recurved, the posterior ones are 
 more blunt. 
 
 The upper jaw bears about nineteen pairs of teeth, the 
 lower jaw about fifteen pairs. The largest tooth in the upper 
 jaw is the tenth, and in the lower jaw the fourth. 
 
 The three living families of Crocodilia, the Crocodiles, 
 Alligators and Garials, can be readily distinguished by the 
 characters of the first and fourth lower teeth. In Alligators 
 both first and fourth lower teeth bite into pits in the upper 
 jaw ; in Garials they both bite into notches or grooves in 
 
SKELETON OF THE CROCODILE. VERTEBRAL COLUMN. 239 
 
 the upper jaw. In Crocodiles the first tooth bites into a pit, 
 the fourth into a notch in the upper jaw. 
 
 II. ENDOSKELETOK 
 1. THE AXIAL SKELETON. 
 
 This includes the vertebral column, the skull, and the ribs 
 and sternum. 
 
 A. THE VERTEBRAL COLUMN. 
 
 The vertebral column is very long, consisting of some sixty 
 vertebrae. It can be divided into the usual five regions, the 
 cervical, thoracic, lumbar, sacral, and caudal regions. 
 
 10 
 
 FIG. 41. 
 
 FlKST FOUR CEKVICAL VERTEBKAE OF A CROCODILE (C '. 
 
 (Partly after VON ZITTEL.) 
 
 pro-atlas. 7. tubercular portion of fourth 
 
 lateral portion of atlas, 
 odontoid process. 8. 
 
 ventral portion of atlas. 9. 
 
 neural spine of axis. 10. 
 
 postzygapophysis of fourth 
 vertebra. 
 
 cervical rib. 
 first cervical rib. 
 second cervical rib. 
 convex posterior surface of 
 
 centrum of fourth vertebra. 
 
 THE CERVICAL VERTEBRAE. 
 
 Counting as cervical all those vertebrae which are anterior 
 to the first one whose ribs meet the sternum, there are nine 
 cervical vertebrae, all of which bear ribs. 
 
 As a type of the cervical vertebrae the fifth may be taken. 
 
240 THE VERTEBRATE SKELETON. 
 
 It has a short cylindrical centrum deeply concave in front 
 and convex behind. From the anterior part of the ventral 
 surface of the centrum arises a short hypapophysis, and 
 on each side is a facet with which the lower limb (capi- 
 tulum) of the cervical rib articulates. The neural arch is 
 strongly developed and drawn out dorsally into a long neural 
 spine, in front of which are a pair of upstanding processes 
 bearing the prominent upwardly and inwardly directed pre- 
 zygapophyses. At the sides and slightly behind the neural 
 spine are a corresponding pair of processes bearing the post- 
 zygapophyses, which look downwards and outwards. At 
 the point where it joins the centrum the neural arch is drawn 
 out into a short blunt transverse process with which the 
 upper limb (tuberculum) of the cervical rib articulates. The 
 sides of the neural arch are slightly notched behind for the exit 
 of the spinal nerves. 
 
 The first or atlas vertebra differs much from any of the 
 others, and consists of four quite detached portions, a ventral 
 arch, with two lateral portions and one dorsal. The ventral 
 arch (fig. 41, 4) is flat below and slightly concave in front, 
 forming together with two flattened surfaces on the lateral 
 portions a large articulating surface for the occipital condyle 
 of the skull. Its posterior face is bevelled off and forms with 
 a second pair of facets on the lateral portions a surface with 
 which the odontoid process of the second vertebra articulates. 
 The postero-lateral surfaces of the ventral arch also bear a pair of 
 little facets with which the cervical ribs articulate. The lateral 
 portions are somewhat flattened and expanded, and bear in ad- 
 dition to those previously mentioned a pair of small downwardly 
 directed facets, the postzygapophyses, which articulate with the 
 prezygapophyses of the second vertebra. The dorsal portion 
 (fig. 41, 1) is somewhat triangular in shape, and overhangs the 
 occipital condyle. It is often regarded as the neural arch of a 
 vertebra in front of the atlas and is called the pro-atlas ; but 
 as it is a membrane bone it is not properly a vertebral element. 
 
SKELETON OF THE CROCODILE. VERTEBRAL COLUMN. 241 
 
 The second or axis vertebra also differs a good deal from 
 the other cervicals. The centrum is massive, and is terminated 
 in front by a very large slightly concave articulating surface 
 formed by the odontoid process (fig. 41, 3) which is united 
 with the centrum by suture only, and is really the detached 
 centrum of the first vertebra. The cervical rib (fig. 41, 9) 
 articulates with two little irregularities on the odontoid pro- 
 cess. The posterior surface of the centrum is convex. The 
 neural arch is strongly developed and terminated dorsally 
 by a long neural spine (fig. 41, 5), its sides are notched, 
 slightly in front and more prominently behind for the exit ofr 
 the spinal nerves. It is drawn out in front into two little 
 processes bearing a pair of upwardly and outwardly directed 
 prezygapophyses, while the postzygapophyses are similar to 
 those of the other cervical vertebrae. 
 
 The last two cervical vertebrae resemble the succeeding 
 thoracic vertebrae, in the increased length of the transverse 
 processes, and the shifting dorsalwards of the facet with which 
 the capitulum of the rib articulates. 
 
 THE THORACIC VERTEBRAE. 
 
 The thoracic vertebrae commence with the first of those 
 that bears ribs reaching the sternum. They are ten in 
 number, and the first eight are directly connected with the 
 sternum by ribs. 
 
 The third of them may be taken as a type. It has a 
 thick cylindrical centrum, concave in front and convex behind, 
 there is a slight hypapophysis, and the centrum is suturally 
 united with a strong neural arch enclosing a narrow neural 
 canal. The neural arch is drawn out dorsally into a wide 
 truncated neural spine, and laterally into two prominent 
 transverse processes, with the ends of which the tubercula of 
 the ribs articulate, while the capitulum articulates in each case 
 with a step-like facet (fig. 42, A, 3) on the anterior face of the 
 transverse process. The prezygapophyses (fig. 42, A, 2) are 
 R. 16 
 
242 
 
 THE VERTEBRATE SKELETON. 
 
 borne on outgrowths from the bases of the transverse pro- 
 cesses, and the postzygapophyses on outgrowths at the base of 
 the neural spine. 
 
 The thoracic vertebrae behind the third have no hypa- 
 pophyses, and the capitular facets gradually come to be placed 
 nearer and nearer the ends of the transverse processes, at the 
 same time becoming less prominent ; otherwise these vertebrae 
 are just like the third. 
 
 A B 
 
 FIG. 42. ANTERIOR VIEW OF A, A LATE THOBACIC AND B, THE FIKST SACRAL 
 
 VERTEBRA OF A YOUNG CROCODILE (C. palustris). X ^. 
 
 1. neural spine. 4. sacral rib. 
 
 5. surface which is united with 
 the ilium. 
 
 neural spine. 
 
 process bearing prezygapo- 
 
 physis. 
 facet for articulation with the 
 
 capitulum of the rib. 
 
 6. 
 
 concave anterior face of cen- 
 trum. 
 
 In the first and second thoracic vertebrae the capitulum of 
 the rib articulates, not with a facet on the transverse process, 
 but with a little elevation borne at the line of junction of the 
 centrum and neural arch. 
 
 THE LUMBAR VERTEBRAE. 
 
 These are five in number, and are precisely like the 
 posterior thoracic vertebrae, except in the fact that the 
 transverse processes have no facets for the articulation of ribs. 
 
SKELETON OF THE CROCODILE. VERTEBRAL COLUMN. 243 
 
 THE SACRAL VERTEBRAE. 
 
 These are two in number, and while the centrum of the 
 first is concave in front (fig. 42, B, 6) and nearly flat behind, 
 that of the second is flat in front and concave behind. Each 
 has a pair of strong ribs (fig. 42, B, 4) firmly ankylosed in the 
 adult with a wide surface furnished partly by the centrum, 
 partly by the neural arch. The distal ends of these ribs are 
 united with the ilia. The character of the neural spines and 
 zygapophyses is the same as in the thoracic vertebrae. 
 
 THE CAUDAL VERTEBRAE. 
 
 These are very numerous, about thirty-four in number. 
 The first differs from all the other vertebrae of the body in 
 having a biconvex centrum. The succeeding ones are procoe- 
 lous and are very much like the posterior thoracic and lumbar 
 vertebrae, having high neural spines and prominent straight 
 transverse processes. They differ however in having the 
 neural spines less strongly truncated above, and the transverse 
 processes arise from the centra and not from the neural 
 arches. When followed further back the centra arid neural 
 spines gradually lengthen while the transverse processes be- 
 come reduced, and after the twelfth vertebra disappear. 
 Further back still the neural spines and zygapophyses 
 gradually become reduced and disappear, as finally the neural 
 arch does also, so that the last few vertebrae consist simply of 
 cylindrical centra. 
 
 Each caudal vertebra, except the first and the last eleven 
 or so, has a V-shaped chevron bone attached to the postero- 
 ventral edge of its centrum. The anterior ones are the largest 
 and they gradually decrease in size till they disappear. 
 
 B. THE SKULL 1 . 
 
 The skull of the Crocodile is a massive depressed structure 
 
 1 Free use has been made of L. C. MialPs Studies in Comparative 
 Anatomy, i., The Skull in Crocodilia, London, 1878. See also W. K. 
 Parker, Tr. Z. S. t vol. xi. 1885, p. 263. 
 
 162 
 
244 THE VERTEBRATE SKELETON. 
 
 presenting a number of striking characteristics, some of the 
 more important of which are : 
 
 1. All the bones except the mandible, hyoid, and columella 
 are fir inly united by interlocking sutures. In spite of this, 
 however, growth of the whole skull and of the component 
 bones goes on continuously throughout life, this growth being 
 especially marked in the case of the facial as opposed to the 
 cranial part of the skull. 
 
 2. All the bones appearing on the dorsal surface are 
 remarkable for their curious roughened and pitted character ; 
 this feature is prominent also in. many Labyrinthodonts. 
 
 3. The size of the jaws and teeth is very great. 
 
 4. The mandibular condyle is carried back to some dis- 
 tance behind the occipital condyle. 
 
 5. The occipital plane (see p. 386) of the skull is vertical. 
 
 6. The length of the secondary palate is remarkably great, 
 and the vomer takes no part in its formation. 
 
 7. The posterior nares are placed very far back, the nasal 
 passages being as in mammals separated from the mouth by 
 the long secondary palate. 
 
 8. There is a complicated system of Eustachian passages 
 communicating at one end with the tympanic cavity and at 
 the other end with the mouth cavity. 
 
 9. The interorbital septum is mainly cartilaginous, the 
 presphenoidal and orbitosphenoidal regions remaining un- 
 ossified. 
 
 The skull is divisible into three parts : 
 
 (1) the cranium, (2) the lower jaw, (3) the hyoid. 
 
 The cranium may again for purposes of description be 
 divided into :-<- 
 
 1. the cranium proper or brain case ; 
 
 2. the bones connected with the several special sense 
 organs ; 
 
 3. the bones of the upper jaw, and suspensorial apparatus. 
 
SKELETON OF THE CROCODILE. THE SKULL. 245 
 
 1. THE CRANIUM PROPER OR BRAIN CASE. 
 
 The cartilage and membrane bones of the cranium proper 
 
 A B 
 
 FIG. 
 
 1. 
 2. 
 
 3. 
 4. 
 5. 
 
 6. 
 7. 
 8. 
 9. 
 10. 
 
 11. 
 
 43. PALATAL ASPECT A, OF THE CRANIUM, B, or THE MANDIBLE OF 
 AN ALLIGATOR (Caiman latirostris). x -|. (Brit. Mus.) 
 
 premaxilla. 12. 
 
 maxilla. 13. 
 
 palatine. 14. 
 
 pterygoid. 15. 
 
 posterior nares. 16. 
 
 transpalatine. 17. 
 
 posterior palatine vacuity. 18. 
 
 anterior palatine vacuity. 19. 
 
 basi-occipital. 20. 
 opening of median Eusta- 21. 
 
 chian canal, 
 jugal. 
 
 quadratojugal. 
 quadrate, 
 dentary. 
 splenial. 
 coronoid. 
 supra-angular, 
 angular, 
 articular. 
 
 lateral temporal fossa. 
 openings of vascular canals 
 leading into alveolar sinus. 
 
246 THE VERTEBRATE SKELETON. 
 
 when taken together can in most vertebrates be seen to be 
 more or less arranged in three rings or segments called respec- 
 tively the occipital, parietal and frontal segments ; in the 
 Crocodile however only the occipital and parietal segments 
 are clearly seen. 
 
 The occipital segment consists of four cartilage bones, 
 three of which together surround the foramen magnum. 
 
 The most ventral of these, the basi-occipital (figs. 43 
 and 45, 9), forms the single convex occipital condyle for 
 articulation with the atlas, bounds the base of the foramen 
 magnum, and is continuous laterally with two larger bones, 
 the exoccipitals (fig. 45, 24), which meet one another dor- 
 sally and form the remainder of the boundary of the foramen 
 magnum. Each is drawn out externally into a strong process, 
 which is united below with the quadrate, and above with the 
 squamosal by a surface seen in a disarticulated skull to be 
 very rough and splintered. In a longitudinal section the 
 anterior face of the exoccipital is seen to be closely united 
 with the opisthotic. 
 
 The exoccipital is pierced by a number of foramina, four 
 lying on the posterior surface. Just external to the foramen 
 magnum is a small foramen for the exit of the hypoglossal 
 nerve (figs. 44 and 45, XII). External to this is the foramen 
 for the pneumogastric (fig. 44, X), while more ventrally still 
 is the foramen (fig. 44, 15) through which the internal carotid 
 artery enters the skull. Some distance further to the side, 
 and more dorsally, is a larger foramen which gives passage 
 to the facial nerve and certain blood-vessels. 
 
 In a median longitudinal section of the skull the hypo- 
 glossal foramen is seen, and just in front of it a small foramen 
 for a vein. Further forwards the long slit-like opening 
 between the exoccipital and opisthotic is the internal audi- 
 tory meatus (fig. 45, VIII) through which the auditory 
 nerve leaves the cranial cavity and enters the internal 
 ear. 
 
SKELETON OF THE CKOCODILE. THE CRANIUM. 247 
 
 The supra-occipital (fig. 45, 5) is a small bone which 
 takes no part in the formation of the foramen magnum, and is 
 closely united in front with the epi-otic. It is characteristic of 
 Crocodiles that all the bones of the occipital segment have 
 their longer axes placed vertically, and that they scarcely if at 
 all appear on the dorsal surface. 
 
 In front of the occipital segment is the parietal segment. 
 The dorsal and ventral portions of the two segments are in 
 contact with one another, but the lateral portions are widely 
 separated by the interposition of the auditory and suspen- 
 sorial bones. 
 
 The basisphenoid (fig. 45, 12) is an unpaired wedge- 
 shaped bone, united along a deep vertical suture with the basi- 
 occipital. The two bones are, however, partially separated in 
 the mid-ventral line by a foramen, the opening of the median 
 Eustachian canal, which leads into a complicated system of 
 Eustachian passages ultimately communicating with the tym- 
 panic cavity. 
 
 The dorsal surface of the basisphenoid is well seen in a 
 section of the skull, but owing to the way it tapers ventrally, 
 it appears on the ventral surface only as a very narrow strip 
 of bone wedged in between the basi-occipital and pterygoids. 
 In a lateral view it is seen to be drawn out in front into an 
 abruptly truncated process, the rostrum, which forms part of 
 the interorbital septum. On the anterior part of the dorsal 
 surface is a deep pit, the pituitary fossa or sella turcica, 
 at the base of which are a pair of foramina, through which 
 the carotid arteries pass. Dorso-laterally the basisphenoid 
 articulates with the alisphenoids. 
 
 The alisphenoids (fig. 45, 13) are a pair of irregular bones 
 which arise from the basisphenoid antero-laterally, and are 
 united dorsally with the parietal, frontal, and postfrontals. 
 They bound most of the anterior part of the brain case, 
 and each presents on its inner face a deep concavity which 
 lodges the cerebral hemisphere of its side. Viewed from 
 
248 
 
 THE VERTEBRATE SKELETON. 
 
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SKELETON OF THE CROCODILE. THE CRANIUM. 249 
 
 the ventral side the two alisphenoids are seen to almost 
 or quite meet one another immediately below the frontal, 
 and then to diverge, forming an irregular opening partially 
 closed by cartilage in the fresh specimen, through which 
 the optic nerves leave the cranial cavity. Further back the 
 alisphenoids meet one another for a narrow area, and then 
 diverge again, so that between each and the rostrum of 
 the basisphenoid there appears an opening (fig. 44, III, YI) 
 through which the oculomotor and abducens nerves leave 
 the cranium. Further back still each is united for a short 
 space with the basisphenoid, pterygoid and quadrate, and 
 then becomes separated from the quadrate by a large foramen, 
 the foramen ovale (fig. 44, Y), through which the whole of 
 the trigeminal nerve passes out. 
 
 The dorsal portion of the parietal segment is formed by 
 the parietal (fig. 45, 4), which though double in the embryo, 
 early comes to form a single bone. It extends over the 
 posterior part of the cranial cavity, and is continuous in front 
 with the frontal, behind with the supra-occipital, and laterally 
 with the postfrontals, squamosals, alisphenoids, pro-otics and 
 epi-otics. It forms the inner boundary of a large rounded 
 vacuity on the roof of the skull, the supratemporal fossa. 
 
 The frontal segment is very imperfectly ossified, there 
 being no certain representatives of either the ventral member, 
 the presphenoid, or the lateral members, the orbitosphenoids. 
 On the dorsal side there is, however, a large development 
 of membrane bones. There is a large frontal (fig. 45, 3), 
 unpaired, except in the embryo, united behind with the 
 parietal and postfrontal, and drawn out in front into a long 
 process which is overlapped by the prefrontals and posterior 
 part of the nasals. The frontal ends off freely below, owing 
 to the orbitosphenoidal region being unossified, it forms a 
 considerable part of the roof of the cranial cavity, but takes 
 no part in the formation of the wall. 
 
 Each prefrontal (fig. 45, 14) forms part of the inner wall 
 
250 THE VERTEBRATE SKELETON. 
 
 of the orbit and sends veiitralwards a process which meets 
 the palatine. 
 
 The postfrontals (fig. 44, 6) are small bones lying at the 
 sides of the posterior part of the frontal. Each is united 
 with a number of bones, on its inner side with the frontal and 
 parietal, behind with the squamosal, and ventrally with the 
 alisphenoid. It also unites by means of a strong descending 
 process with an upgrowth from the jugal, and thus forms a 
 postorbital bar separating the orbit from the lateral tem- 
 poral fossa. The postfrontal forms also part of the outer 
 boundary of the supratemporal fossa. 
 
 2. THE SENSE CAPSULES. 
 
 Skeletal capsules occur in connection with each of the three 
 special sense organs of sight, of hearing and of smell. 
 
 The Auditory capsules and associated bones. 
 
 Three bones, the epi-otic, opisthotic and pro-otic, 
 together form the auditory or periotic capsule of each side. 
 They are wedged in between the lateral portions of the occi- 
 pital and parietal segments and complete the cranial wall in 
 this region. Their relations to the surrounding structures are 
 very complicated, and many points can be made out only in 
 sections of the skull passing right through the periotic cap- 
 sule. The relative position of the three bones is, however, 
 well seen in a median longitudinal section. The opisthotic 
 early becomes united with the exoccipital, while the epi-otic 
 similarly becomes united with the supra-occipital, the pro- 
 otic (fig. 45, 7), seen in longitudinal section to be pierced 
 by the prominent trigeminal foramen alone remaining 
 distinct throughout life. The three bones together surround 
 the essential organ of hearing which communicates laterally 
 with the deep tympanic cavity by the fenestra ovalis. 
 
 The tympanic cavity, leading to the exterior by the 
 external' auditory meatus (fig. 44, 16), is well seen in a 
 
SKELETON OF THE CROCODILE. SENSE CAPSULES. 251 
 
 side-view of the skull ; it is bounded on its inner side by the 
 periotic bones, posteriorly in part by the exoccipital, and else- 
 where mainly by the quadrate. A large number of canals 
 and passages open into it. On its inner side opening ventro- 
 anteriorly is the fenestra ovalis, opening ventro-posteriorly 
 the internal auditory meatus (fig. 45, \ T III), while dorsally 
 there is a wide opening which forms a communication through 
 the roof of the brain-case with the tympanic cavity of the 
 other side. On its posterior wall is the prominent foramen 
 through which the facial nerve passes on its way to its final 
 exit from the skull through the exoccipital, this foramen is 
 bounded by the quadrate, squamosal, and exoccipital. 
 
 The opening of the fenestra ovalis is in the fresh skull 
 occupied by the expanded end of the auditory ossicle, the 
 columella, whose outer end articulates by a concave facet 
 with a trifid extracolumellar cartilage which reaches the 
 tympanic membrane. The lower process of this extracolumella 
 passes into a cartilaginous rod which lies in a canal in the 
 quadrate and is during life continuous with Meckel's cartilage 
 within the articular bone of the mandible. 
 
 The columella and extracolumella are together homologous 
 with the chain of mammalian auditory ossicles. 
 
 The Optic capsules and associated bones. 
 
 Two pairs of bones are associated with the optic capsules, 
 viz. the lachrymals and the supra-orbitals. The lachrymal 
 (fig. 44, 3) is a fairly large flattened bone lying wedged in 
 between the maxilla, nasal, jugal, and prefrontal. It forms a 
 considerable part of the anterior boundary of the orbit, and is 
 pierced by two foramina. On the orbital edge is a large hole 
 leading into a cavity within the bone which lodges the naso- 
 lachrymal sac, and communicates with the narial passage by 
 a wide second foramen near the anterior end of the bone. 
 The supra-orbital is a very small loose bone lying in the eyelid 
 close to the junction of the frontal and prefrontal. 
 
252 THE VERTEBRATE SKELETON. 
 
 The Olfactory capsules and associated bones. 
 
 Two pairs of membrane bones, the vomers and nasals, are 
 developed in association with the olfactory organ, but the 
 mesethmoid is not ossified. 
 
 The vomers form a pair of delicate bones, each consisting of 
 a vertical plate (fig. 45, 15), which with its fellow separates 
 the two narial passages, and of a horizontal plate which forms 
 much of their roof. The vomers articulate with one another 
 and with the pterygoids, palatines, and maxillae. 
 
 The nasals (fig. 45, 2) are very long narrow bones extend- 
 ing along the middle line from the frontal almost to the 
 anterior nares. They are continuous laterally with the pre- 
 maxillae, maxillae, lachrymals and prefrontals. They form 
 the roof of the narial passages. 
 
 3. THE UPPER JAW AND SUSPENSORIAL APPARATUS. 
 
 These are enormously developed in the Crocodile and are 
 firmly united to the cranium. It will be most convenient to 
 begin by describing the bones at the anterior end of the jaw 
 and to work back thence towards the brain-case. The most 
 anterior bones are the premaxillae. The premaxillae (figs. 44 
 and 45, 1) are small bones, each bearing five pairs of teeth, 
 set in separate sockets in their alveolar borders. They con- 
 stitute almost the whole of the boundary of the anterior 
 nares, which are confluent with one another and form a 
 large semicircular opening in the roof of the skull, leading 
 into the wide narial passage. They are also partially sepa- 
 rated from one another in the ventral middle line, by the 
 small anterior palatine vacuity (fig. 43, A, 8). They form 
 the anterior part of the broad palate. The alveolar border 
 on each side between certain of the teeth is marked by pits 
 which receive the points of the teeth of the other jaw. The 
 first pair of these pits in the premaxillae are often so deep as 
 to be converted into perforations. Pits of the same character 
 occur between the maxillary and mandibular teeth. 
 
THE SKELETON OF THE CROCODILE. 253 
 
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254 THE VERTEBRATE SKELETON. 
 
 The maxillae (figs. 43, A, 2 and 44, 2) are a pair of very 
 large bones and bear the remaining teeth of the upper jaw, 
 set in sockets along their alveolar borders. On the dorsal 
 side each maxilla is continuous with the premaxilla, nasal, 
 lachrymal, and jugal, while ventrally it meets its fellow in a 
 long straight suture and forms the greater part of the long- 
 bony palate. The maxillae are separated in the middle line 
 posteriorly by processes from the palatines, while further back 
 they meet the transpalatines. The internal or nasal surface, 
 like that of the premaxilla, is excavated by a deep longitudi- 
 nal groove, the narial passage. In a ventral view of. the 
 skull a number of small openings (fig. 43, A, 21) are seen 
 close to the alveolar border, these are the openings of small 
 vascular canals which lead into the alveolar sinus, a passage 
 traversing the maxilla, and transmitting the superior max- 
 illary branch of the trigeminal nerve and certain blood-vessels. 
 This alveolar sinus opens posteriorly by the more external of 
 the two large holes in the maxilla, which lie close to the 
 anterior edge of the posterior palatine vacuity, to be described 
 immediately. The more internal of these holes, on the other 
 hand, leads into a cavity lodging the nasal sac. Behind the 
 maxillae the completeness of the palate is broken up by the 
 large oval posterior palatine vacuities (fig. 43, A, 7) ; 
 these are separated from one another in the middle line by the 
 palatines, and are bounded elsewhere by the maxillae, trans- 
 palatines, and pterygoids. 
 
 The palatines (fig. 43, A, 3) are long and rather narrow 
 bones interposed between the maxillae in front and pterygoids 
 behind. They meet one another in a long suture and form 
 much of the posterior part of the palate, while the whole length 
 of their dorsal surface contributes to the floor of the narial 
 passage. The dorsal surface of each bone is also drawn out 
 on its outer side into a prominent ridge which forms much of 
 the side and roof of the narial passage, being in contact with 
 the vomer and pterygoid, and at one point by means of a short 
 
SKELETON OF THE CROCODILE. THE SKULL. 255 
 
 ascending process with the descending process of the pre- 
 f rental. 
 
 The pterygoids (tigs. 43, A, 4, and 45, 11) are a pair of 
 large bones, each consisting of a median more or less vertical 
 part, which becomes ankylosed to its fellow in the middle 
 line early in life, and of a wide horizontal part which meets 
 the transpalatine. They completely surround the posterior 
 nares (fig. 43, A, 5) and their median portions form the whole 
 boundary of the posterior part of the narial passage, and assist 
 the palatines and vomers in bounding the middle part. 'The 
 horizontal parts form the posterior part of the secondary palate, 
 while the dorsal surface of each looks into the pterygoid fossa, 
 a large cavity lying below the quadrate and quadratojugal at 
 the side of the skull. The lateral margin adjoining the trans- 
 palatine is in the fresh skull terminated by a plate of cartilage 
 against which the mandible plays. Dorsally the pterygoid 
 articulates with the basisphenoid, quadrate, and alisphenoid. 
 
 The transpalatines (fig. 44, 11) connect the pterygoids with 
 the jugals and maxillae, articulating with each of the three 
 bones by a long pointed process. The jugal process meets also 
 a down-growth from the postfrontal. 
 
 The jugals or molars (fig. 44, 5) are long somewhat flat- 
 tened bones which are united to the lachrymals and maxillae 
 in front, while passing backwards each is united behind to the 
 quadratojugal (fig. 44, 12), the two forming the infratemporal 
 arcade which constitutes the external boundary of the orbit 
 and lateral temporal fossa. The jugal is united below to the 
 transpalatine, and the two bones together form an outgrowth, 
 which meeting that from the postfrontal forms the postorbital 
 bar, and separates the orbit from the lateral temporal fossa. 
 The quadratojugals are small bones and are united behind 
 with the quadrates. 
 
 The quadrate (figs. 43, A, 13 and 44, 8) of each side is 
 a large somewhat flattened bone firmly fixed in among the 
 other bones of the skull. It is terminated posteriorly by an 
 
256 THE VERTEBRATE SKELETON. 
 
 elongated slightly convex surface, coated with cartilage in the 
 fresh skull, by which the mandible articulates with the cranium. 
 The dorsal surface of the quadrate is flat behind, further for- 
 wards it becomes much roughened and articulates with the 
 exoccipital and squamosal ; further forwards still it becomes 
 marked by a deep groove which forms "the floor of the ex- 
 ternal auditory meatus and part of the tympanic cavity. 
 The anterior boundary of the quadrate is extremely irregu- 
 lar, it is united dorsally with the postfrontal, pro-otic, and 
 squamosal, and more ventrally with the alisphenoid. The 
 smooth ventral surface looks into the pterygoid fossa. In 
 front the quadrate forms the posterior boundary of the supra- 
 temporal fossa and foramen ovale, and is continuous with the 
 alisphenoid, while it sends down a thin plate meeting the 
 pterygoid and basisphenoid. On the inner side of the dorsal 
 surface of the quadrate near the condyle, is a small foramen 
 which leads into a tube communicating with the tympanic 
 cavity, by a foramen lying in front of and ventral to that for 
 the exit of the facial nerve. By this tube air can pass from 
 the tympanic cavity into the articular bone of the mandible. 
 
 The squamosal (fig. 44, 7) meets the quadrate and exoccipital 
 below, and forms part of the roof of the external auditory 
 meatus, while above it forms part of the roof of the skull and 
 has a pitted structure like that of the other bones of the roof. 
 It is continuous with the postfrontal in front, forming with 
 it the supratemporal arcade which constitutes the outer 
 boundary of the supratemporal fossa. It meets also the 
 parietal on its inner side, forming the post-temporal bar, the 
 posterior boundary of the supratemporal fossa. 
 
 It may be useful to recapitulate the large vacuities in the 
 surface of the Crocodile's cranium. 
 
 Dorsal surface. 
 
 1. The Supratemporal fossae. Each is bounded in- 
 ternally by the parietal, behind by the post-temporal bar 
 formed by the parietal and squamosal, and externally by the 
 
SKELETON OF THE CROCODILE. THE SKULL. 257 
 
 supratemporal arcade formed by the squamosal and post- 
 frontal. The postf rontal meets the parietal in front and forms 
 the anterior boundary of the supratemporal fossa. 
 
 2. The Lateral temporal or infratemporal fossae. 
 These lie below and to the outer side of the supratemporal 
 fossae. Each is bounded dorso-internally by the supratemporal 
 arcade ; and behind by a continuation of the post-temporal bar 
 formed by the quadrate and quadratojugal. The external 
 boundary is the infratemporal arcade formed of the quad- 
 ratojugal and jugal, while in front the fossa is separated from 
 the orbit by the postorbital bar formed by the junction of 
 outgrowths from the postf rontal and jugal. 
 
 3. The Orbits. Each is bounded behind by the post- 
 orbital bar, externally by the jugal forming a continuation of 
 the infratemporal arcade, in front by the lachrymal, and inter- 
 nally by the frontal and prefrontal. 
 
 4. The Anterior nares. These form an unpaired open- 
 ing bounded by the prem axillae. 
 
 Posterior surface. 
 
 5. The Foramen magnum. The exoccipitals form the 
 chief part of its boundary, but part of the ventral boundary 
 is formed by the basi-occipital. 
 
 6. The Pterygoid fossae. These form a pair of large 
 cavities at the sides of the occipital region of the skull. The 
 dorsal boundary is formed by the quadrate and quadratojugal, 
 the ventral by the pterygoid, the internal chiefly by the quad- 
 rate, pterygoid, alisphenoid, and basisphenoid. The trarispala- 
 tine forms a small part of the external boundary which is in- 
 complete. 
 
 Ventral surface. 
 
 7. The Posterior nares. These form a median unpaired 
 opening (fig. 43, A, 5) bounded by the pterygoids. 
 
 8. The Posterior palatine vacuities. Each is 
 bounded by the maxilla in front, the maxilla and transpalatine 
 
 R. 17 
 
258 THE VERTEBRATE SKELETON. 
 
 externally, the transpalatine and pterygoid behind, and the 
 palatine on the inner side (fig. 43, A, 7). 
 
 9. The Anterior palatine vacuity. This is unpaired 
 and is bounded by the premaxillae (fig. 43, A, 8). 
 
 (b) THE LOWER JAW OR MANDIBLE. 
 
 The mandible is a strong compact bony structure formed 
 of two halves or rami, which are suturally united at the 
 symphysis in the middle line in front. Each rainus is formed 
 of six separate bones. 
 
 The most anterior and largest of these is the dentary (figs. 
 44, 20, and 45, 18), which forms the symphysis, and greater part 
 of the anterior half of the jaw, and bears along the outer part 
 of its dorsal border a number of sockets or alveoli in which 
 the teeth are placed. Lying along the inner side of the dentary 
 is a large splint-like bone, the splenial (fig. 45, 19), which does 
 not extend so far forwards as the symphysis, and is separated 
 from the dentary posteriorly by a large cavity. Forming the 
 lower part of all the posterior half of the jaw is the large 
 angular (figs. 44, 22, and 45, 20), which underlies the posterior 
 part of the dentary in front and sends a long process below that 
 bone to the splenial. On the inner side of the jaw there is an 
 oval vacuity, the internal mandibular foramen (fig. 45, 28), 
 between the angular and the splenial ; through this pass blood- 
 vessels and branches of the inferior dental nerve. Lying 
 dorsal to the angular is another large bone, the supra-angular 
 (figs. 44, 18, and 45, 21). It extends back as far as the pos- 
 terior end of the jaw and forwards for some distance dorsal 
 to the dentary and splenial. It forms part of the posterior 
 margin of a large vacuity, the external mandibular foramen, 
 which is bordered above and in front by the dentary and below 
 by the angular ; it gives passage to the cutaneous branch of 
 the inferior dental nerve. The concave surface for articulation 
 with the mandible and much of the posterior end of the jaw is 
 formed by a short but solid bone, the articular (fig. 45, 22), 
 
SKELETON OF THE CROCODILE. THE HYOID. 259 
 
 which in young skulls rather readily becomes detached. The 
 remaining mandibular bone is the coronoid (fig. 45, 23), a very 
 small bone of irregular shape attached to the angular below, 
 and to the supra-angular and splenial above. 
 
 (c) THE HYOID. 
 
 The hyoid of the Crocodile consists of a wide flattened 
 plate of cartilage, the basilingual plate or body of the 
 hyoid, and a pair of cornua. 
 
 The basilingual plate (fig. 53, 1) is rounded anteriorly 
 and marked by a deep notch posteriorly. The cornua (fig. 
 53, 3), which are attached at a pair of notches near the middle 
 of the outer border of the basilingual plate, are partly ossified, 
 but their expanded ends are formed of cartilage. They pass 
 at first backwards and then upwards and inwards. They 
 are homologous with part of the first branchial arches of 
 Selachians. 
 
 The columella and extra-columella have been already de- 
 scribed (p. 251). 
 
 C. THE RIBS AND STERNUM. 
 
 Thoracic ribs. 
 
 The Crocodile has ten pairs of thoracic ribs, all except 
 the last one or two of which consist of three parts, a verte- 
 bral rib, an intermediate rib and a sternal rib. 
 
 Of the vertebral ribs the third may be taken as a type, 
 it consists of a curved bony rod which articulates proximal!} 7 
 with the transverse process of the vertebra by two facets. 
 The terminal one of these, the capitulum or head, articulates 
 with a notch on the side of the transverse process; the other, 
 the tuberculum, which lies on the dorsal surface a short 
 distance behind the head, articulates with the end of the trans- 
 verse process. From near the distal end an imperfectly ossified 
 uncinate process (see p. 190) projects backwards. 
 
 The intermediate ribs are short and imperfectly ossified ; 
 they are united with the sternal ribs (fig. 46, 3), which are large, 
 
 172 
 
260 THE VERTEBRATE SKELETON. 
 
 flattened, likewise imperfectly ossified structures, and articu- 
 late at their distal ends with a pair of long divergent xiphi- 
 sternal horns (fig. 46, 5), which arise from the posterior end 
 of the sternum proper. The last pair of sternal ribs are at- 
 tached to the preceding pair, not to the xiphisternal horns. 
 
 The first and second vertebral ribs differ from the others in 
 the fact that the tuberculum forms a fairly long outstanding 
 process. 
 
 Cervical ribs. 
 
 Movable ribs are attached to all the cervical as well as to the 
 thoracic vertebrae. Those borne by the atlas and axis are long, 
 narrow structures attached by a fairly broad base, and tapering 
 gradually. The ribs borne by the third to seventh cervical 
 vertebrae are shaped like a T with a double base, one limb of 
 which, corresponding to the tuberculum (fig. 41, 7), articulates 
 with a short transverse process arising from the neural arch, 
 while the other, corresponding to the capitulum, articulates with 
 a surface on the centrum. The ribs attached to the eighth and 
 ninth cervical vertebrae are intermediate in character between 
 the T-shaped ribs and the ordinary thoracic ribs. The anterior 
 limb of the T is shortened, the posterior one is drawn out, 
 forming the shaft of the rib. The distal portion of the rib of 
 the ninth cervical vertebra is unossified. 
 
 The Sacral ribs have been described in connection with 
 the sacral vertebrae. 
 
 THE STERNUM. 
 
 The sternum of Crocodiles is a very simple structure, con- 
 sisting of a plate of cartilage (fig. 46, 2) lying immediately 
 dorsal to the interclavicle, and drawn out posteriorly into a 
 pair of long xiphisternal horns (fig. 46, 5). 
 
 THE ABDOMINAL SPLINT RIBS. 
 
 Lying superficially to the recti muscles of the ventral body- 
 wall, behind the sternal ribs, are seven or eight series of 
 
SKELETON OF THE CROCODILE. THE STERNUM. 261 
 
 -2 
 
 5 
 
 .-3 
 
 FIG. 46. STERNUM AND ASSOCIATED MEMBRANE BONES OF A CROCODILE 
 (C. palustris) x $. (Brit. Mus.) 
 
 The last pair of abdominal ribs which are united with the epipubes by 
 a plate of cartilage have been omitted. 
 
 1. interclavicle. 4. abdominal splint rib. 
 
 2. sternum. 5. xiphisternal horn. 
 
 3. sternal rib. 
 
262 THE VERTEBRATE SKELETON. 
 
 slender curved bones, the abdominal ribs (fig. 46, 4). Each 
 series consists of four or more bones, arranged in a V-like 
 form with the angle of the V directed forwards. They show a 
 considerable amount of variability in number and character. 
 They are really membrane bones, and are in no way homolo- 
 gous with true ribs, but correspond rather with the more 
 posterior of the bones constituting the plastron of Chelonia. 
 
 2. THE APPENDICULAE SKELETON. 
 
 This includes the skeleton of the two pairs of limbs and 
 their respective girdles. 
 
 FIG. 47. LEFT HALF OF THE PECTORAL GIBDLE OF AN ALLIGATOB (Caiman 
 latirostris) x f . (Brit. Mus. ) 
 
 1. scapula. 3. interclavicle. 
 
 2. coracoid. 4. glenoid cavity. 
 
 THE PECTORAL GIRDLE. 
 
 The pectoral girdle of the Crocodile is less complete than is 
 that of most reptiles. It consists of a dorsal bone, the 
 
SKELETON OF THE CROCODILE. PECTORAL GIRDLE. 263 
 
 scapula, and a ventral bone, the coracoid, with a median 
 unpaired element, the interclavicle ; but there is no separate 
 representative either of the clavicle or precoracoid. 
 
 The scapula (fig. 47, 1) is a large bone, flattened and ex- 
 panded above where it is terminated by an unossified margin 
 the suprascapula, and thickened below where it meets the 
 coracoid. The scapula forms about half the glenoid cavity 
 (fig. 47, 4) for articulation with the humerus, and has the 
 lower part of its anterior border drawn out into a roughened 
 ridge. 
 
 The coracoid (fig. 47, 2) is a flattened bone, much ex- 
 panded at either end ; it bears on its upper posterior -border a 
 flattened surface which forms half the glenoid cavity, and is 
 firmly united to the scapula at its dorsal end. Its ventral end 
 meets the sternum. 
 
 The interclavicle (figs. 46, 1, and 47, 3) is a long narrow 
 blade-shaped bone lying along the ventral side of the sternum ; 
 about a third of its length projects beyond the sternum in 
 front. 
 
 THE ANTERIOR LIMB. 
 
 This is as usual divisible into three portions, the upper 
 arm, fore-arm and manus. 
 
 The upper arm or brachium contains one bone, the 
 humerus. 
 
 The humerus (fig. 48, A, 1) is a fairly long stout bone, 
 considerably expanded at either end. The proximal end or head 
 is evenly rounded and is formed by an epiphysis ossifying from 
 a centre different from that forming the shaft. It articulates 
 with the glenoid cavity. The shaft bears on the flexor surface, 
 at some little distance behind the head, a prominent rounded 
 protuberance, the deltoid ridge. The distal end or trochlea 
 is also formed by an epiphysis and is partially divided by a 
 groove into two convex surfaces ; it articulates with the two 
 bones of the fore-arm, the radius and ulna. 
 
264 
 
 THE VERTEBRATE SKELETON. 
 
 FIG. 48. 
 
 -20 
 
 A, BIGHT ANTERIOR, AND B, BIGHT POSTERIOR LIMB OF A YOUNG 
 
 ALLIGATOR (Caiman latirostris). (Brit. Mus.) 
 A x 4. B x about i. 
 
 1. humerus. 10. 
 
 2. radius. 
 
 3. ulna. 11. 
 
 4. radiale. 12. 
 
 5. ulnare. 13. 
 
 6. pisiform. 14. 
 
 7. patch of cartilage representing 15. 
 
 carpalia 1 and 2; between 
 
 it and the radiale should be 16. 
 
 another flattened patch, the 17. 
 
 centrale. 18. 
 
 8. carpalia 3, 4, and 5 (fused). 19. 
 
 9. first metacarpal. 20. 
 
 21. 
 
 proximal phalanx of second 
 digit. 
 
 second phalanx of fifth digit. 
 
 femur. 
 
 tibia. 
 
 fibula. 
 
 tibiale, intermedium and cen- 
 trale (fused). 
 
 fibulare. 
 
 tarsalia 1, 2, and 3 (fused). 
 
 tarsalia 4 and 5 (fused). 
 
 first metatarsal. 
 
 ungual phalanx of second digit. 
 
 fifth metatarsal. 
 
SKELETON OF THE CROCODILE. THE MANUS. 265 
 
 The radius and ulna are nearly equal in size and each 
 consists of a long shaft terminated at either end by an epi- 
 physis. 
 
 The radius (fig. 48, A, 2) or pre-axial bone is slightly the 
 smaller of the two. It has a straight cylindrical shaft and is 
 slightly and nearly evenly expanded at either end. The proxi- 
 mal end which articulates with the humerus is flat or slightly 
 concave, the distal end which articulates with the carpus is 
 slightly convex. 
 
 The ulna (fig. 48, A, 3) or postaxial bone is a curved bone 
 rather larger than the radius. Its proximal end is large and 
 convex, but is not drawn out into an olecranon process. 
 
 The Manus consists of the carpus or wrist, and the 
 hand. 
 
 The Carpus. This differs considerably from the more 
 primitive type met with in the Turtle. It consists of six 
 elements arranged in a proximal row of three and a distal row 
 of two, with one intervening. The bones of the proximal row 
 are the radiale, the ulnare, and the pisiform. The radiale 
 (fig. 48, A, 4) is the largest bone of the carpus : it is a some- 
 what hour-glass shaped bone, with its ends formed by flattened 
 epiphyses. It articulates by its proximal end with the whole 
 of the radius, and partly also with the ulna, and by its 
 distal end with the centrale. 
 
 The ulnare (fig. 48, A, 5) is a smaller bone, also some- 
 what hour-glass shaped ; it articulates proximally with the 
 pisiform and radiale, not quite reaching the ulna. The third 
 bone of the proximal row is the pisiform (fig. 48, A, 6), an 
 irregular bone, articulating with the ulna, radiale, and fifth 
 metacarpal. The centrale is a flattened cartilaginous element 
 applied to the distal surface of the radiale. 
 
 The distal row of carpals consists of two small structures. 
 The first of these forms a small cartilaginous patch, which is 
 wedged in between the first and second metacarpals, the 
 
266 THE VERTEBRATE SKELETON. 
 
 centrale and the bone representing carpalia 3, 4 and 5 ; this 
 cartilaginous patch represents carpalia 1 and 2 (fig. 48, A, 7). 
 The bone representing carpalia 3, 4 and 5 is a good deal 
 larger, rounded, and well -ossified ; it articulates with the 
 ulnare, the pisiform, and the third, fourth, and fifth meta- 
 carpals. 
 
 The hand. Each of the five digits consists of an elongated 
 metacarpal, terminated at each end by an epiphysis, and of a 
 varying number of phalanges. The terminal phalanx of each 
 digit has an epiphysis only at its proximal end, the others have 
 them at both ends. 
 
 The first digit, or pollex, is the stoutest, and has two 
 phalanges, the second has three, the third four, the fourth 
 three, and the fifth two. The terminal phalanx of each of the 
 first three digits is pointed and sheathed in a horny claw ; and 
 is also marked by a pair of prominent lateral grooves. 
 
 THE PELVIC GIRDLE. 
 
 The pelvic girdle of the Crocodile consists of four parts, a 
 dorsal element, the ilium, an anterior ventral element, the 
 pubis, a posterior ventral element, the ischium, and an 
 accessory anterior ventral element, the epipubis. All except 
 the epipubis take part in the formation of the acetabulum, 
 which is perforated by a prominent hole. 
 
 The ilium (fig. 49, 1) is a thick strong bone, firmly united 
 on its inner side with the two sacral ribs. Its dorsal border 
 is rounded, its ventral border bears posteriorly two irregular 
 surfaces, completed by epiphyses, which are united respectively 
 with the ischium and pubis. 
 
 The ischium (fig. 49, 2) the largest bone of the pelvis, 
 is somewhat contracted in the middle and expanded at either 
 end. Its proximal end, which is formed by an epiphysis, 
 bears two surfaces, one of which is united to the ilium, 
 while the other forms part of the acetabulum. The anterior 
 border is also drawn out dorsally into a strong process, which 
 
SKELETON OF THE CROCODILE. PELVIC GIRDLE. 26*7 
 
 is terminated by a convex epiphysis, and is united to the 
 pubis. The ventral end of the ischium forms a flattened blade, 
 meeting its fellow in a median symphysis. 
 
 The pubis (fig. 49, 3) is much smaller than either the ilium 
 or ischium ; it forms a small patch of unossified cartilage, in- 
 terposed between the anterior parts of the ilium and ischium. 
 
 FIG. 49. PELVIS AND SACBUM OF AN ALLIGATOR (Caiman latirostris) x 
 (Brit. Mus.) 
 
 1. ilium. 
 
 2. ischium. 
 
 3. true pubis. 
 
 4. epipubis (so-called pubis). 
 
 5. acetabular foramen. 
 
 6. neural spines of sacral verte- 
 
 brae. 
 
 7. symphysis ischii. 
 
 8. process bearing prezygapo- 
 
 physis. 
 
 The epipubis (fig. 49, 4) is a large bone with a thickened 
 proximal end, which is loosely articulated to the ischium, and 
 a flattened expanded distal end, which is united with its fellow, 
 and with the last pair of abdominal ribs by a large plate of 
 cartilage. This bone is generally described as the pubis. 
 
268 THE VERTEBRATE SKELETON. 
 
 THE POSTERIOR LIMB. 
 
 This is as usual divisible into three portions, the thigh, 
 the crus or shin, and the pes. 
 
 The thigh is formed by the femur (fig. 48, B, 12), a 
 moderately long stout bone, not unlike the humerus ; it arti- 
 culates with the acetabulum by a fairly prominent rounded 
 head. The distal end articulating with the tibia and fibula 
 is also expanded, and is partially divided into equal parts by 
 anterior and posterior grooves. The flexor surface bears a 
 fairly prominent trochanteric ridge. Each end of the femur 
 is formed by an epiphysis. 
 
 The cms or shin includes two bones, the tibia and 
 fibula. Both are well developed, but the tibia is considerably 
 the larger of the two. 
 
 The tibia (fig. 48, B, 13) is a strong bone with a flattened 
 expanded proximal end articulating with almost the whole of 
 the end of the femur, and a similarly expanded distal end 
 articulating with a bone representing the fused astragalus and 
 centrale. 
 
 The fibula (fig. 48, B, 14) is flattened proximally, and 
 articulates with only quite a small part of the femur, while 
 distally it is more expanded, and articulates with the fibulare 
 (calcaneum) and with a facet on the side of the fused astra- 
 galus and centrale. 
 
 The Pes consists of the tarsus or ankle, and the foot. 
 
 The Tarsus. This, like the carpus, is much reduced and 
 modified from the primitive condition. It consists of only 
 four bones, arranged in two rows of two each. The two 
 bones of the proximal row are much larger than are those of 
 the distal row. The pre-axial of them (fig. 48, B, 15) repre- 
 senting the fused astragalus (tibiale and intermedium) and 
 centrale, articulates proximally with the tibia and fibula, and 
 distally with the first metatarsal, and a small bone representing 
 the first three tarsalia. The post-axial bone, the calcaneum 
 
SKELETON OF THE CROCODILE. THE PES. 269 
 
 (fibulare) (fig. 48, B, 1 6), is drawn out into a prominent posterior 
 process forming a heel such as is almost unknown elsewhere 
 except in mammals. It articulates with the fibula, the tibiale- 
 centrale, and distally with a bone representing the fourth and 
 fifth tarsalia, and with the fifth metatarsal. 
 
 The two bones forming the distal row of tarsals are both 
 small and rounded ; one represents the first three tarsalia fused 
 together, the other tarsalia 4 and 5. 
 
 The Foot. The foot has five digits, but the fifth is much 
 reduced, consisting only of a short metatarsal. The first four 
 metatarsals are all long bones, slightly expanded at each 
 end, and terminated by small epiphyses. The first digit has 
 two phalanges, the second three, the third four, and the fourth 
 five. The terminal or ungual phalanx in each instance is 
 grooved and pointed, and in the case of the first three digits 
 bears a horny claw. The ungual phalanx progressively de- 
 creases in size from the first to the fourth. The fifth digit 
 consists only of a small, somewhat square metatarsal (fig. 48, 
 B, 21), attached to the bone representing the fused fourth and 
 fifth tarsalia. 
 
CHAPTER XVI. 
 
 GENERAL ACCOUNT OF THE SKELETON IN 
 REPTILES. 
 
 EXOSKELETON. 
 
 The exoskeleton both epidermal and dermal is exceedingly 
 well developed in reptiles. 
 
 EPIDERMAL EXOSKELETON. 
 
 This generally has the form of overlapping horny scales 
 which invest outgrowths of the dermis, and are found covering 
 the whole body in most Rhynchocephalia, Ophidia, and Lacer- 
 tilia, and many Crocodilia. In the Ophidia the ventral surface 
 of the tail is commonly covered by a double row of broad scales, 
 while the ventral surface of the precaudal part of the body is 
 covered by a single row. In the burrowing snakes (Typhlo- 
 pidae) and some sea snakes (Hydrophidae) these broad scales 
 do not occur, the scales of the ventral surface being similar to 
 those of the dorsal. 
 
 In the Chelonia with the exception of Dermochelys, Trionyx 
 and their allies there is a well-developed system of horny shields 
 having a regular arrangement which has been described in the 
 account of the Turtle's skeleton 1 . 
 
 The rattle of the rattlesnake is an epidermal structure 
 formed of several loosely articulated horny rings, produced by 
 the modification of the epidermal covering of the end of the 
 tail, which instead of being cast off when the rest of the outer 
 skin is shed is retained loosely interlocked with the adjoining 
 
 1 See pp. 214 and 215. 
 
THE SKELETON IN REPTILES. EXOSKELETON. 271 
 
 ring or joint. New rings are thus periodically added to the 
 base of the rattle, and in old animals the terminal ones wear 
 away and are lost. 
 
 Horny claws occur on the ends of some or all of the digits 
 in most living reptiles. 
 
 Owen's Chameleon bears three epidermal horns, one arising 
 from the nasal and two from the frontal region. 
 
 In the Chelonia, some of the Theromorpha such as Ude- 
 nodon and Dicynodon, probably also in the Pterosauria and 
 Polyonax among the Dinosaurs, the jaws are more or less 
 cased in horny beaks. The horny beaks of Chelonia are 
 variable ; sometimes they have cutting edges, sometimes they 
 are denticulated, sometimes they are adapted for crushing. 
 
 DERMAL EXOSKELETON. 
 
 Nearly all Crocodilia, many Dinosauria, some Rhynchoce- 
 phalia and Pythonomorpha, and some Lacertilia such as Tiliqua, 
 Scincus and Anguis have a dermal exoskeleton of bony scutes, 
 developed below and corresponding in shape to the epidermal 
 scales. Sometimes as in Caiman sclerops, Jacare and Teleo- 
 saurus, the scutes completely invest the body, being so 
 arranged as to form a dorsal and a ventral shield, and a con- 
 tinuous series of rings round the tail. In Crocodilus they are 
 confined to the dorsal surface, and in Alligator to the dorsal 
 and ventral surfaces. The scutes of some extinct forms articu- 
 late with one another by a peg and socket arrangement as in 
 some Ganoid fish. 
 
 The carapace of most Chelonia is a compound structure, 
 being partly endoskeletal and formed from the ribs and verte- 
 brae, partly from plates derived from the dermal exoskeleton. 
 The common arrangement is seen in fig. 36. All the surface 
 plates are probably exoskeletal in origin, but united with the 
 ventral surfaces of the costal and neural plates respectively are 
 the expanded ribs and neural arches of the vertebrae. 
 
 The plastron in the common genus Chelone (fig. 37) 
 
272 THE VERTEBRATE SKELETON. 
 
 includes nine plates of bone, one unpaired and four pairs ; 
 they will be referred to in connection with the ribs and pec- 
 toral girdle. 
 
 In the Leathery Turtle (Dermochelys) the carapace and 
 plastron differ completely from those of any other living 
 form. The carapace consists of a number of polygonal ossifi- 
 cations fitting closely togethei and altogether distinct from the 
 vertebrae and ribs. The plastron is imperfectly ossified, and 
 not united with the pelvis, and the whole surface of both 
 carapace and plastron is covered with a tough leathery skin, 
 without horny shields. 
 
 Some of the extinct Dinosauria have an enormously de- 
 veloped dermal exoskeleton. Thus in Stegosaurus and Omo- 
 saurus the dorsal surface is provided with flattened plates or 
 with spines reaching a length of upwards of two feet. In 
 Polacanthus the posterior part of the body is protected by a 
 bony shield somewhat recalling that of the little armadillo 
 Chlamydophorus. No exoskeleton is known in Ichthyosauria, 
 Sauropterygia, Pterosauria, many Dinosauria and Theromorpha, 
 and some Lacertilia, such as Chamadeon and Amphisbaena. 
 
 TEETH. 
 
 The teeth of reptiles are generally well developed, and in 
 the great majority of forms are simple conical structures, 
 uniform in character, generally somewhat recurved, and often 
 with serrated edges. Another common type of tooth is that 
 with a laterally compressed triangular crown provided with 
 a double cutting edge which may or may not be serrated. The 
 teeth are mainly formed of dentine, with usually an external 
 layer of enamel, and often a coating of cement on the root. 
 Vasodentine is found below the dentine in Iguanodon. The 
 teeth of reptiles never have the enamel deeply infolded, nor 
 do they have double roots. 
 
 Teeth may be present not only on the jaw-bones, but as in 
 many Squamata, also on the palatines, pterygoids or vomers. 
 
THE SKELETON IN REPTILES. THE TEETH. 273 
 
 The method by which they are attached to the bones varies 
 much. Sometimes as in Iguana and some other lizards, they 
 are pleurodont 1 , sometimes they are acrodont 1 , as in the Rhyn- 
 chocephalia, Pythonomorpha, Ophidia and some Lacertilia such 
 as Agama. Again they may be set in a continuous groove 
 as in the Ichthyosauria and young Crocodilia. Finally the 
 teeth may be thecodont or placed in distinct sockets as in the 
 Theromorpha, Sauropterygia, adult Crocodilia, Sauropoda and 
 Theropoda. In Iguanodon the teeth are set in shallow sockets 
 in a groove one side of which is higher than the other ; the 
 method of attachment thus shows points of resemblance to 
 the thecodont condition, the pleurodont condition, and that 
 met with in the Ichthyosauria. 
 
 In Ichthyosaurus the teeth are marked by a number of 
 vertical furrows, and it is from a furrow of this nature greatly 
 enlarged and converted into a tube that the channel down 
 which flows the poison of venomous snakes is derived. 
 
 In most reptiles the dentition is more or less homodont. 
 The only reptiles in which a definite heterodont dentition is 
 known are the extinct Theromorpha, and in them the teeth 
 vary greatly. Thus Udenodon is toothless, the jaws having 
 been probably cased in a horny beak. In Dicynodon the jaws 
 are likewise toothless with the exception of a pair of perma- 
 nently growing tusks borne by the maxillae. Dicynodon is the 
 only known reptile whose teeth have permanently growing 
 pulps. In Pariasaurus the teeth are uniform and very nume- 
 rous, and though placed in distinct sockets are ankylosed to 
 the jaw. In Galesaurus and Cynognathus three kinds of teeth 
 can be distinguished, slender conical incisor-like teeth, large 
 canine -like teeth, and cheek teeth with two or three cusps. 
 The teeth in Galesaurus are confined to the jaws, in Placodus 
 and its allies, however, large flat crushing teeth are attached to 
 the palatines as well as to the jaw-bones, and in Pariasaurus 
 the vomer, palatine and pterygoid all bear teeth as well as the 
 
 1 These terms are defined on p. 199. 
 B. 18 
 
274 
 
 THE VERTEBRATE SKELETON. 
 
 jaw bones. The upper jaw of Sphenodon and other Rhyn- 
 chocephalia is provided with two parallel rows of teeth, one 
 borne on the maxillae and one on the palatines, the man- 
 dibular teeth bite in a groove between these two rows. The 
 bone of the jaws in Sphenodon is so hard that when the teeth 
 get worn away, it can act as a substitute. In the young 
 Sphenodon the vomers bear teeth, as they do also in Protero- 
 saurus, 
 
 There is generally a continuous succession of teeth through- 
 out life, the new tooth coming up below, or partly at the side 
 of the one in use, and causing the absorption of part of its 
 wall or base. In this way the new tooth conies to lie in the 
 pulp cavity of the old one. This method of succession is well 
 seen in the Crocodilia. 
 
 FIG. 50. PBEPABATION OP PART OF THE BIGHT MANDIBULAB BAMUS or 
 Crocodilus palustris x \. (Brit. Mus.) 
 
 1. tooth in use. 
 
 2. fairly old germ of future 
 
 tooth. 
 
 3. symphysial surface of the 
 mandible. 
 
 Teeth have been detected in embryos of Trionyx, but 
 otherwise no teeth are known to occur in Chelonia, or in 
 Pteranodon (Pterosauria), while the anterior part of the jaw 
 is edentulous in Iguanodon, Polyonax and some other Dino- 
 saurs, and in Rliamphorhynchus. 
 
THE SKELETON IN REPTILES. VERTEBRAL COLUMN. 275 
 
 ENDOSKELETON. 
 
 VERTEBRAL COLUMN. 
 
 The vertebral column is commonly divisible into the usual 
 five regions, but in the Ophidia, Ichthyosauria, and Amphis- 
 baenidae among Lacertilia, only into caudal and precaudal 
 regions. In the Chelonia there are no lumbar vertebrae. 
 
 The form of the vertebral centra is very variable. A large 
 proportion of extinct reptiles, several entire orders, and the 
 earlier and more primitive forms in some of the other groups 
 have amphicoelous vertebrae. Vertebrae of this type occur 
 in the Theromorpha, Ichthyosauria, most Sauropterygia and 
 Rhynchocephalia,' and many Dinosauria, also in some of the 
 early Crocodilia such as Belodon, Teleosaurus and Goniopholis, 
 and the Geckonidae among Lacertilia. 
 
 The majority of living reptiles have procoelous vertebrae. 
 Thus they occur in the Lacertilia (excluding the Geckos), the 
 Ophidia, and the Crocodilia, also among extinct forms in the 
 Pterosauria and many Dinosauria. On the other hand some 
 Dinosauria such as Iguanodon have opisthocoelous cervical 
 vertebrae, while others have opisthocoelous thoracic vertebrae. 
 The vertebrae of the Ceratopsidae and some Sauropterygia, 
 the thoracic vertebrae of Iguanodon, and the sacral vertebrae 
 of Crocodilia have flat centra. The first caudal vertebra of 
 modern Crocodilia is biconvex, and in the Chelonia all types 
 of vertebral centra are found. The cervical vertebrae of 
 Sphenodon are noticeable for the occurrence of a small pro- 
 atlas, which may represent the neural arch of a vertebra in 
 front of the atlas. 
 
 In most reptiles the vertebrae are fully ossified, but in 
 some of the more primitive forms the notochord persists in 
 the centre of the vertebra (i.e. intervertebrally), this is the 
 case for instance in many of the Theromorpha and Rhyncho- 
 cephalia, and also in the Geckos. In other reptiles it persists 
 longest intravertebrally. 
 
 The centrum of each of the caudal vertebrae of most 
 
 182 
 
276 THE VERTEBKATE SKELETON. 
 
 Lacertilia is traversed by an unossified septum along which it 
 readily breaks. 
 
 Chevron bones occur below the caudal vertebrae in Lacertilia, 
 Chelonia, Ichthyosauria, many Dinosauria, and Sphenodon, 
 articulating with quite the posterior part of the centrum which 
 bears them. In Lacertilia and Orocodilia (fig. 41, 3) the axis 
 has a well-marked odontoid process. The ventral portions of 
 the intervertebral discs are sometimes ossified, forming wedge- 
 shaped intercentra, as in Geckos, and the cervical vertebrae of 
 Sphenodon. 
 
 In snakes, Theropod Dinosaurs, and the iguanas among 
 lizards, the neural arches are provided with zygosphenes, and 
 zygantra. 
 
 The neural arches are usually firmly ankylosed to the 
 centra, but in the Crocodilia and some Chelonia, Sauropterygia, 
 and Dinosauria, the suture between the centrum and neural 
 arch persists at any rate till late in life. In the Ichthyosauria 
 the neural arches were united to the centra by cartilage only. 
 
 The thoracic vertebrae of some of the Theromorpha (Dime- 
 trodon) are remarkable for the extraordinary development of 
 the neural spine, and those of Chelonia for the absence of 
 transverse processes. 
 
 In living reptiles the number of sacral vertebrae is nearly 
 always two, but in the Theromorpha, Dinosauria, and Ptero- 
 sauria, as many as five or six bones may be ankylosed together 
 in the sacral region. In Crocodiles the two halves of the pelvis 
 sometimes articulate with different vertebrae. The vertebrae 
 of some of the great Sauropoda are remarkably hollowed out, 
 having a large vacuity on each side of the centrum communi- 
 cating with a series of internal cavities. The whole structure 
 of these vertebrae shows a combination of great strength with 
 lightness. 
 
 THE SKULL. 
 
 The reptilian skull is well ossified and the bones are noticeable 
 for their density. The true cranium is often largely concealed 
 
THE SKELETON IN REPTILES. THE SKULL. 277 
 
 by a secondary or false roof of membrane bones, which is best 
 seen in the Ichthyosauria and some of the Chelonia. In other 
 reptiles the false roof is more or less broken up by vacuities 
 exposing the true cranial walls. The ethmoidal region is the 
 only one in which much of the primordial cartilaginous cranium 
 remains. The lateral parts of 'the sphenoidal region are also 
 as a rule not well ossified. 
 
 In some reptiles, such as most Lacertilia and Chelonia, the 
 orbits are separated only by the imperfect interorbital septum, 
 while in others, such as the Ophidia, Crocodilia and Amphis- 
 baenidae, the cranial cavity extends forwards between the 
 orbits. 
 
 In the occipital region all four bones are ossified. The 
 great majority of reptiles have a single convex occipital 
 coiidyle, but some of the Theromorpha such as Cynognatlius 
 have two distinct condyles as in mammals. Sometimes, as 
 in Chelonia, Ophidia and Lacertilia, the exoccipitals, as well 
 as the basi-occipital, take part in the formation of the single 
 condyle ; sometimes, as in Crocodiles, it is formed by the basi- 
 occipital alone, as in birds. The relations of the bones to the 
 foramen magnum vary considerably, in Chelonia the basi- 
 occipital generally takes no part in bounding it, and in the 
 Theromorpha, Crocodilia, and Ophidia, the supra-occipital is 
 excluded. The parietals are paired in Geckos and Chelonia 
 alone among living forms, and in the extinct Ichthyosauria 
 and some Theromorpha ; in all other reptiles they are united. 
 
 The frontals are paired in Ichthyosauria (fig. 32, 5), 
 Chelonia, Ophidia, Sphenodon (fig. 52, B, 4) and some extinct 
 crocodiles, such as Belodon. They are completely fused in 
 living Crocodilia and some Lacertilia and Dinosauria. In 
 the gigantic Polyonax they are drawn out into a pair of 
 enormous horns, and the parietals and squamosals are greatly 
 expanded behind. 
 
 An interparietal foramen occurs in the Theromorpha, the 
 Ichthyosauria (fig. 32, 10), Sphenodon, the Sauropterygia and 
 
278 THE VERTEBRATE SKELETON. 
 
 most Lacertilia. The posterior part of the skull is curiously 
 modified in some Chamaeleons, the parietal s and supra- occipitals 
 being drawn out into a backwardly-projecting sagittal crest 
 which unites with the two prolongations from the squamosals. 
 In other Chamaeleons (C. bifidus) prolongations of the pre- 
 frontals and maxillae form large forwardly-projecting bony 
 processes. 
 
 The roof of the skull is characterised by the development 
 of prefrontals and postfrontals, which lie respectively near the 
 anterior and posterior extremity of the orbit. In Theromorpha, 
 Squamata, Crocodilia, arid some Dinosauria lachrymals are 
 developed. There is a ring of bones in the sclerotic in the 
 Ichthyosauria (fig. 32, 15), the Metriorhynchidae among Croco- 
 diles and some Rhynchocephalia, Dinosauria, and Pterosauria. 
 
 The pro-otic lies in front of the exoccipital and together 
 with the opisthotic forms the hind border of the fenestra 
 ovalis. In Chelonia the opisthotic remains separate, in all other 
 living reptiles it fuses with the exoccipital. The epi-otic fuses 
 with the supra-occipital. 
 
 The parasphenoid, so important in Ichthyopsids, has very 
 often disappeared completely; it is present, however, in the* 
 Ichthyosauria, the Plesiosauridae, and a number of Squamata, 
 in many Ophidia its anterior part forming the base of the 
 interorbital septum. 
 
 In the Plesiosauridae and most Lacertilia, but not in the 
 Amphisbaenidae, a slender bone, the epipterygoid, occurs unit- 
 ing the parietal or the anterior end of the pro-otic with the 
 pterygoid. A homologous arrangement occurs in the Ichthyo- 
 sauria and some Chelonia. 
 
 In most reptiles a transpalatine occurs, connecting the 
 maxilla with the pterygoid, but this is absent in the Chelonia, 
 and some Dinosauria, and in the Typhlopidae among snakes. 
 
 The quadrate is always well developed, and except in the 
 Squamata is firmly fixed to the surrounding bones. The 
 Chamaeleons also, among the Squamata, have a fixed quadrate, 
 
THE SKELETON IN REPTILES. THE SKULL. 
 
 279 
 
 and in them too the quadratojugal is absent. Separate nasal 
 bones do not occur in any living Chelonia. 
 
 The vomers are generally paired as in Squamata, some- 
 times unpaired as in Chelonia. 
 
 FIG. 51. DOKSAL (TO THE LEFT) AND VENTRAL (TO THE RIGHT) VIEWS OF 
 THE SKULL OF THE COMMON SNAKE (Tropidinotus natrix). (After PARKER.) 
 
 1. premaxillae (fused). 
 
 2. anterior nares. 
 
 3. nasal. 
 
 4. prefrontal. 
 
 5. frontal. 
 
 6. parietal. 
 
 7. maxilla. 
 
 8. transpalatine. 
 
 9. palatine. 
 
 10. pterygoid. 
 
 11. pro-otic. 
 
 12. exoccipital. 
 
 13. supra-occipital. 
 
 14. opisthotic. 
 
 15. epi-otic. 
 
 16. quadrate. 
 
 17. parasphenoid. 
 
 18. basisphenoid. 
 
 19. basi-occipital. 
 
 20. occipital condyle. 
 
 21. splenial. 
 
 22. dentary. 
 
 23. angular. 
 
 24. articular. 
 
 25. supra-angular. 
 
 26. coronoid. 
 
 27. vomer. 
 
 28. squamosal. 
 
 IX, X foramina for the ninth 
 
 and tenth cranial nerves. 
 
280 THE VERTEBRATE SKELETON. 
 
 The disposition of the bones of the jaws is subject to 
 much modification in the Ophidia in order to adapt them for 
 swallowing very large prey. The arrangements again differ 
 greatly in the venomous and non-venomous snakes. In the 
 non-venomous snakes, such as Python and Tropidonotus, the 
 palatine is large and is fixed to the pterygoid which extends 
 outwards (fig. 51, 10) so as to be united to the quadrate, and 
 is at the same time firmly connected by the transpalatine with 
 the maxilla. The quadrate is united to the squamosal, which 
 is loosely attached to the cranium. The premaxilla is moder- 
 ately developed and bears teeth, and the maxilla forms a long 
 bar loosely connected with the rest of the skull. The rami of 
 the mandible are united only by an extremely elastic ligament. 
 It is as regards the maxillae and premaxillae that the skulls 
 of venomous and non-venomous snakes differ most. In the 
 rattlesnake (Crotalus) and other venomous snakes the pre- 
 maxilla is extremely small and toothless. The maxilla is 
 small and subcylindrical, and is movably articulated to the 
 lachrymal, which also is capable of a certain amount of motion 
 on the frontal. The maxilla is connected by means of the 
 transpalatine with the pterygoid, which in its turn is united 
 to the quadrate. When the mouth is shut the quadrate is 
 directed backwards, and carrying back the pterygoid and 
 transpalatine pulls at the maxilla and causes its palatal face, 
 to which the poison teeth are attached, to lie back along the 
 roof of the mouth. When the mouth opens the distal end 
 of the quadrate is thrust forward, and this necessitates the 
 pushing forward of the pterygoid and transpalatine, causing 
 the tooth-bearing surface of the maxilla to look downwards 
 and the tooth to come into the position for striking. 
 
 The Ophidian skull is also noticeable for the absence of the 
 jugals and quadratojugals. In poisonous snakes the place of 
 the jugal is taken by the zygomatic ligament which connects 
 the quadrate and maxilla. 
 
 The extent to which the palate is closed in reptiles varies 
 
THE SKELETON IN REPTILES. THE SKULL. 281 
 
 much. In many reptiles, such as the Squamata and Ichthyo- 
 sauria, the palate is not complete, both palatines and pterygoids 
 being widely separated in the middle line. In others, such as 
 the Crocodilia, Sauropterygia, and Chelonia, there is a more 
 or less complete bony palate. In many Chelonia this is 
 chiefly formed of the vomer, palatines, and pterygoids, the 
 posterior nares being mainly bounded by the palatines. In 
 living Crocodilia, however, outgrowths are formed from the 
 pterygoids and palatines which arch round and meet one 
 another vent rally, forming a secondary palate (fig. 43, A), 
 which completely shuts off the true sphenoidal floor of the 
 skull, and causes the posterior nares which are bounded by 
 the pterygoids to open very far back. Though this feature 
 is common to all postsecondary crocodiles, it is interesting to 
 notice that it is not found in the earlier forms, but that its 
 gradual evolution can be traced. In the Triassic Belodon, for 
 instance, the posterior nares open far forwards, and are not 
 surrounded by either the palatines or pterygoids. In the 
 Jurassic crocodile, Teleosaurus, the posterior nares lie further 
 back, being surrounded by the palatines, but the pterygoids 
 do not meet them. Finally, in the Tertiary forms the arrange- 
 ments are as in living crocodiles. 
 
 A short secondary hard palate is found also in the Therio- 
 dontia. The palatines of Ichthyosaurus are noticeable for their 
 transverse position, which recalls that in the Frog. 
 
 The various fossae or vacuities in the false roof of the 
 skull are important, and their relations may best be understood 
 by a description of their mode of occurrence in Sphenodon, a 
 form in which they are very completely developed. 
 
 In Sphenodon, then, on the dorsal surface of the skull, are 
 the large supratemporal fossae (fig. 52, 20). Their inner 
 margins are separated from one another by the parietal walls 
 of the cranium, while externally each is bounded by a bony 
 arch, the supratemporal arcade, formed of the postfrontal, 
 post-orbital, and squamosal. Posteriorly the boundary is 
 
282 
 
 THE VERTEBRATE SKELETON. 
 
 FIG. 52. SKULL OF HATTEBIA (Sphenodon punctatus). 
 A, lateral; B, dorsal; .C, ventral; D, posterior. (After VON ZITTEL.) 
 
 1. premaxilla. 
 
 2. nasal. 
 
 3. pref rental. 
 
 4. frontal. 
 
 5. postfrontal. 
 
 6. parietal. 
 
 7. squamosal. 
 
 8. quadratojugal. 
 
 9. quadrate. 
 
 10. postorbital. 
 
 11. jugal. 
 
 12. maxilla. 
 
 13. vomer. 
 
 14. palatine. 
 
 15. pterygoid. 
 
 16. transpalatine. 
 
 17. exoccipital. 
 
 18. epipterygoid. 
 
 19. basisphenoid. 
 
 20. supratemporal fossa. 
 
 21. infratemporal or lateral tem- 
 
 poral fossa. 
 
 22. orbit. 
 
 23. post-temporal fossa. 
 
 24. foramen magnum. 
 
 25. anterior nares. 
 
 26. interparietal foramen. 
 
 27. dentary. 
 
 28. supra-angular. 
 
 29. articular. 
 
THE SKELETON IN REPTILES. THE SKULL. 283 
 
 formed by a post-temporal bar, formed by the parietal and 
 squamosal. Below the supra temporal arcade is another large 
 vacuity, the infra-temporal or lateral temporal fossa (fig. 
 52, 21). This is bounded above by the supratemporal arcade, 
 and is separated from the orbit in front by the postorbital 
 bar, formed by the union of outgrowths from the jugals and 
 postorbitals. Behind it is bounded by a continuation of the 
 post-temporal bar formed of the squamosal and quadratojugal, 
 and below by an infratemporal arcade, which is chiefly com- 
 posed of the quadratojugal and jugal. 
 
 Below the post -temporal bar is a third vacuity, the 
 post-temporal fossa (fig. 52, D, 23), bounded above by 
 the post-temporal bar and below by the exoccipital and 
 opisthotic. 
 
 Sphenodon and the Crocodilia are the only living reptiles 
 with complete supratemporal and infratemporal arcades, but 
 they are both present in the extinct Pterosauria and some 
 Dinosauria. 
 
 Supratemporal fossae, bounded below by supratemporal 
 arcades, occur in all reptiles except some Chelonia, the Ophidia, 
 the Geckonidae among Lacertilia, and the Pariasauria and 
 others among Theromorpha; they are specially large in No- 
 thosaurus among the Sauropterygia, Dicynodon among the 
 Theromorpha, and many Crocodilia and Pterosauria. In some 
 Dinosaurs, such as Ceratosaurus, they are very small, while 
 the infratemporal fossae are correspondingly large. 
 
 In Elginia 1 (Theromorpha) and some Chelonia, such as 
 Chelone, there are no fossae on the surface of the skull, 
 a complete false roof being developed ; in other Chelonia, 
 such as Trionyx, the true cranium is freely visible, the only 
 part of the false roof developed being the infratemporal 
 arcade. 
 
 In many reptiles large pre-orbital vacuities occur ; they 
 
 1 E. T. Newton, Phil. Trans, vol. CLXXXIV, B, p. 431 (1893). 
 
284 THE VERTEBRATE SKELETON. 
 
 are specially large in the Pterosauria and in some of the 
 Crocodilia and Dinosauria (fig. 35, 3). In some Pterosauria 
 they are confluent with the orbits. 
 
 The premaxillae are usually separate, but sometimes, as in 
 some Ophidia (fig. 51, 1), Chelonia, Lacertilia (Agamidae), 
 and Dinosaurs (Ceratopsia) they are united. In the Dinosaur 
 Hadrosaurus they are exceedingly large and spatulate. In 
 the Rhynchocephalian Hyperodapedon they are drawn out into 
 a strongly curved beak. 
 
 As regards the mandible, sometimes, as in most Rhyncho- 
 cephalia, Ophidia and Pythonomorpha, the rami have only a 
 ligamental union ; sometimes, as in Crocodilia, the Rhyncho- 
 sauridae and the majority of Lacertilia, they are suturally 
 united. In Chelonia (fig. 28, B, 12), and apparently in Ptero- 
 sauria, the two dentaries are completely fused together. The 
 sutures between the various bones of the lower jaw usually 
 persist, but in Ophidia those between the angular, supra - 
 angular, articular and coronoid are obliterated. There are 
 sometimes large vacuities in the mandible, as in Theromorpha, 
 Crocodilia, and some Dinosauria. In Iguanodon, Polyonax, 
 Hypsilophodon and Hadrosaurus among Dinosaurs the man- 
 dible has a predentary or mento-meckelian bone which, in 
 some cases at any rate, was probably sheathed in a horny 
 beak. 
 
 The principal part of the auditory ossicular chain is formed 
 by a rod-like columella. The development of the hyoid appa- 
 ratus varies, and it often happens that the first branchial arch 
 is better developed than is the hyoid arch. In the Crocodilia 
 and Chelonia there is a large basilingual plate or body of the 
 hyoid (fig. 53, 1) ; but while in the Crocodilia the first branchial 
 forms the only well-developed arch, in the Chelonia the first 
 and second branchial s are both strongly developed, and the 
 hyoid is often fairly large. 
 
THE SKELETON IN REPTILES. THE RIBS. 
 
 285 
 
 THE RIBS. 
 
 Ribs are always present, and may be attached to any of the 
 precaudal vertebrae. In most reptiles the posterior cervical 
 vertebrae bear ribs, while the atlas and axis are ribless ; in 
 Crocodiles and Geckos, however, ribs are borne even by the 
 atlas and axis. On the other hand, in the Chelonia none of 
 
 FIG. 53. HYOIDS OF AN ALLIGATOR (Caiman latirostris) (TO THE LEFT) 
 AND OF A GREEN TURTLE (Chelone midas) (TO THE RIGHT) x f. 
 (Brit. Mus.) 
 
 The cartilaginous portions are dotted. 
 
 1. basilingual plate or body of 3. first branchial arch (anterior 
 
 the hyoid. cornu). 
 
 2. hyoid arch. 4. second branchial arch (pos- 
 
 terior cornu.) 
 
 the cervical vertebrae bear obvious ribs. In the following 
 groups the thoracic ribs have both capitula and tubercula 
 Theromorpha, Ichthyosauria, Crocodilia, Dinosauria, Ptero- 
 sauria. In the other groups each rib articulates by a single 
 
286 THE VERTEBRATE SKELETON. 
 
 head, and the position of the facet is subject to a consider- 
 able amount of variation, thus in the Squamata it lies on the 
 centrum, and in the Sauropterygia on the neural arch, while 
 in the Chelonia the rib articulates with the contiguous parts 
 of two centra instead of directly with one. 
 
 In most reptiles a greater or smaller number of ribs are 
 united ventrally with a sternum ; but in snakes a continuous 
 series of similar ribs, all articulating freely with the vertebral 
 column, extends from the third cervical vertebra to the end of 
 the trunk. The number of ribs connected with the sternum 
 varies from three or four in Lizards to eight or nine in Croco- 
 diles. Those which reach the sternum are nearly always 
 divided into vertebral, sternal, and intermediate portions, and 
 as a rule only the vertebral portion is completely ossified. In 
 Crocodiles a number of sternal ribs are connected with a 
 cartilaginous arch, which is attached to the hind end of the 
 sternum, and represents the xiphisternum. The sacral ribs 
 connecting the vertebral column with the ilia are very 
 distinct in Crocodiles; in these animals and Sphenodon the 
 vertebral ribs have backwardly-projecting uncinate processes 
 as in birds. 
 
 In the curious arboreal lizard, Draco volans, the posterior 
 ribs are long and straight, and support a parachute-like expan- 
 sion of the integument used in its long flight-like leaps. In 
 Chelonia the ribs are generally combined with the carapace. 
 
 In Ichthyosauria, Sauropterygia, Crocodilia and Sphenodon, 
 abdominal splint ribs occur ; and probably all except the first 
 of the paired ossifications forming the plastron of Chelonia are 
 of similar character. Abdominal ribs have quite a different 
 origin from true ribs, for while true ribs are cartilage bones, 
 abdominal ribs have no cartilaginous precursors, but are 
 simply the ossified tendons of the rectus abdominalis muscle. 
 
THE SKELETON IN REPTILES. THE STERNUM. 
 THE STERNUM. 
 
 287 
 
 A sternum occurs in the following groups of reptiles : 
 Rhynchocephalia, nearly all Lacertilia, Pythonomorpha, Croco- 
 dilia, and Pterosauria, and is generally more or less rhomboidal 
 or shield-shaped. In Pterosauria it is keeled and bears some 
 resemblance to that of birds. It may have been replaced by 
 membrane bone. 
 
 The sternum is absent in Sauropterygia, Ichthyosauria, 
 
 FIG. 54. VENTRAL VIEW OF THE SHOULDER-GIRDLE or STERNUM OF A 
 LIZARD (Loemanctus longipes] x 2. (After PARKER.) 
 
 1. interclavicle. 
 
 2. clavicle. 
 
 3. scapula. 
 
 4. coracoid. 
 
 5. precoracoidal process. 
 
 6. glenoid cavity. 
 
 7. sternum. 
 
 8. xiphisternum. 
 
 9. sternal rib. 
 
288 THE VERTEBRATE SKELETON. 
 
 Chelonia, Ophidia, and most of the snake-like Amphisbaenidae 
 among Lacertilia ; while it is not well known in Theromorpha 
 and Dinosauria. In the Sauropod Brontosaurus, however, two 
 rounded bones occur near the base of the coracoids, and these 
 probably represent ossified patches in a sternum, which was 
 mainly cartilaginous ; similar structures occur in Iguanodon. 
 
 The sternum frequently remains wholly cartilaginous, 
 especially in Lacertilia ; sometimes it becomes calcified, but 
 true ossification does not as a rule take place. 
 
 APPENDICULAR SKELETON. 
 
 THE PECTORAL GIRDLE. 
 
 The pectoral girdle is well developed in all groups of 
 reptiles except the Ophidia, occurring even in the limbless 
 Amphisbaenidae. It is very solid in the Theromorpha. As a 
 rule all three cartilage bones, scapula, coracoid, and precoracoid 
 are represented, and frequently also the membrane bones, 
 clavicles, and interclavicle. 
 
 The coracoids are generally flat expanded bones, which 
 sometimes, as in Sauropterygia and Ichthyosauria, meet in a 
 ventral symphysis ; sometimes, as in Lacertilia, are united with 
 the sides of the sternum. In Chelonia neither the coracoids 
 nor precoracoids meet one another, but their free ends are 
 connected by nbro-cartilaginous bands. In Lacertilia the 
 coracoids are pierced by fenestrae. 
 
 The precoracoid is generally represented, but the Thero- 
 morpha are the only reptiles in which it is separately ossified; 
 it forms a well-marked process on the coracoid in Lacertilia 
 (fig. 54, 5). It is absent in Ichthyosauria, and Dinosauria, 
 and probably in Sauropterygia. In some Lacertilia and 
 Chelonia the sternal ends of the coracoids are unossified and 
 form epicoracoids ; in some Chelonia there are also epipre- 
 coracoids ; but neither these nor the epicoracoids overlap their 
 fellows of the opposite side as they do in arciferous Anura 
 (see p. 185). In some Lacertilia with degenerate limbs the 
 
THE SKELETON IN REPTILES. THE LIMBS. 289 
 
 pectoral girdle is also much reduced, in Ophisaurus apus the 
 ventral borders of the coracoids are widely separated. 
 
 A scapula is always present, and is generally expanded 
 distally, but in the Chelonia the distal end is cylindrical. In 
 the Theromorpha it has an acromial process with which the 
 precoracoid articulates, and it is very large in Dinosauria. 
 In the Chelonia the scapula and precoracoid are ossified 
 continuously. Among the Pterosauria, Pteranodon has an 
 unique pectoral girdle; the scapula and coracoid are ankylosed 
 and the scapula articulates with the neural spines of several 
 ankylosed vertebrae. 
 
 Clavicles occur in some Theromorpha such as Pariasaurus, 
 and also in the Ichthyosauria, Sauropterygia, Rhynchocephalia, 
 and most Lacertilia. They are absent in the Pterosauria, the 
 Chamaeleons among Lacertilia, the Ophidia and the Crocodilia. 
 They are wanting too in the Chelonia, unless the first pair of 
 ossifications in the plastron are to be regarded as clavicles. In 
 the Sauropterygia bones regarded as the clavicles and inter- 
 clavicle are generally well developed. The unpaired ossification 
 in the plastron of Chelonia is an interclavicle, and a repre- 
 sentative of the same bone occurs arising from the sternum in 
 Pterosauria. A well developed T-shaped interclavicle is found 
 in Ichthyosauria, Rhynchocephalia, Lacertilia, and some Thero- 
 morpha, such as Pariasaurus. 
 
 THE LIMBS. 
 
 In most reptiles there are two pairs of pentedactylate 
 limbs provided with claws, but in nearly all Ophidia and 
 some Lacertilia (Amphisbaena, Lialis, Anguis) the limbs have 
 entirely disappeared. In a few Ophidia such as Python traces 
 of the posterior limbs occur, and in Chirotes among the Amphis- 
 baenidae there are minute anterior limbs. The Lacertilians, 
 Chalcides (Seps) and Ophisaurus (Bipes, Pseudopus) have very 
 small posterior limbs. 
 
 R. 19 
 
290 THE VERTEBRATE SKELETON. 
 
 The limbs are as a rule adapted for walking, but in Ichthyo- 
 sauria, Sauropterygia, Pythonomorpha and some Chelonia, they 
 have the form of swimming paddles, the relative size of the manus 
 and pes being increased, while that of the proximal and middle 
 portions of the limbs is reduced. This reduction is carried to its 
 furthest extent in the Ichthyosauria in which radius and ulna, 
 tibia and fibula, have the form of short polygonal bones similar 
 to those constituting the manus and pes. In the Pythono- 
 morpha the reduction of the limb bones is not quite so marked, 
 in the Sauropterygia it is less, and still less in the Chelonia. 
 In the earlier Ichthyosauria too, the limb bones are not so 
 short as they are in the later forms. The Ichthyosaurian limb 
 is also remarkable, firstly for the fact that both humerus and 
 femur are terminated by concave articulating surfaces instead 
 of by convex condyles, and secondly for the great multiplication 
 of the phalangeal bones, each digit being sometimes composed of 
 a series of over twenty. Sometimes too the number of series is 
 increased, either by the bifurcation of some of the digits or by 
 the development of marginal bones. In the Sauropterygia the 
 phalanges are likewise increased above the normal but not so 
 much as in Ichthyosauria. The humerus and femur of Sauro- 
 pterygia are noticeable for the enormous size of the terminal 
 epiphyses which form in each case by far the greater part of 
 the bone. 
 
 THE ANTERIOR LIMB. 
 
 The anterior limb is usually approximately equal in 
 length to the posterior, but in many Dinosauria it is consider- 
 ably the shorter of the two. The humerus is generally with- 
 out distinct condyles, but they are well developed in the Thero- 
 morpha, the Lacertilia and Sphenodon. 
 
 In the Therornorpha, some Rhynchocephalia, and some 
 Sauropterygia, such as Mesosaurus, the humerus has an ent-epi- 
 condylar foramen ; in Lacertilia, Chelonia and some Dinosauria 
 there is an ect-epicondylar foramen or groove ; Sphenodon 
 
THE SKELETON IN REPTILES. PELVIC GIRDLE. 291 
 
 possesses both ent- and ect-epicondylar foramina. The radius 
 and ulna are always separate. In some Chelonia, such as 
 Chelydra, the carpus has a very simple arrangement, namely, 
 a proximal row of three bones, the radiale, intermedium and 
 ulnare, and a distal row of five carpalia, with one bone, the 
 centrale, between the two rows. Many reptiles have a carpus 
 only slightly different from this. Thus the carpus in Spheno- 
 don differs mainly in having two centralia, that of most Lacer- 
 tilia, in having the centrale and intermedium fused. 
 
 Crocodiles have a much reduced carpus with the radiale 
 and ulnare considerably elongated. The manus in Chamaeleons 
 is curiously modified, having the first three digits arranged in 
 one group and turned inwards, and the fourth and fifth in 
 another group turned outwards ; carpalia 3 and 4 are united. 
 
 In the Pterosauria the anterior limbs form wings, the 
 phalanges of the fifth digit being very greatly elongated to 
 support the wing membrane. The first digit is vestigial and 
 the second, third, and fourth are clawed. 
 
 THE PELVIC GIRDLE. 
 
 The pelvic girdle is well developed in all reptiles which 
 have posterior limbs, but is absent or quite vestigial in Ophidia 
 and those Lacertilia which have no posterior limbs. The ilium 
 and ischium agree in their general characters throughout all 
 the various groups of reptiles, but that is not the case with 
 the pubis. 
 
 In many reptiles such as Chelonia, Ichthyosauria and 
 Lacertilia the ilia are small, more or less cylindrical bones 
 either directed backwards, or vertically placed as in the 
 Chamaeleons. In the Crocodilia they are larger and more ex- 
 panded, while in Dinosauria and Pterosauria they are greatly 
 elongated both in front of, and behind, the acetabulum. The 
 ischia are generally strongly developed somewhat square bones 
 meeting in a ventral symphysis. In Dinosauria the ischium 
 (fig. 35, 9) is a much elongated and backwardly-directed bone, 
 
 192 
 
292 THE VERTEBRATE SKELETON. 
 
 bearing a forwardly projecting obturator process. In Ptero- 
 sauria the ischium is fused with the ilium, and in both ptero- 
 saurs and crocodiles the ilium and ischium are the only bones 
 taking part in the formation of the acetabulum. In most 
 Lacertilia there is an unpaired structure,, the hypo-iachium or 
 os cloacae projecting back from the symphysis ischii, which is 
 usually separated from the symphysis pubis by a large space, 
 the foramen cordiforme. In some Lacertilia and Chelonia 
 there is a cartilaginous bar dividing the foramen cordiforme 
 into two obturator foramina ; in many Chelonia this bar is 
 ossified. Among Ophidia, Python, Tortrix, Typhlops and their 
 allies have a structure representing a vestigial ischio-pubis : 
 but in most Ophidia there is no trace of the pelvis. In some 
 Theromorpha all the bones of the pelvis are completely fused, 
 forming an os innominatum as in mammals ; the pubes and 
 ischia are so completely fused that sometimes as in Paria- 
 saurus even the obturator foramina are closed. 
 
 Concerning the reptilian pubis there are considerable diffi- 
 culties. Sometimes there is only a single pubic structure 
 present, sometimes there are two. The reptilian pubis is best 
 understood by comparing the arrangements met with in the 
 various other groups with that in the Orthopod Dinosaurs 
 such as Iguanodon. In Iguanodon the pubis consists of two 
 portions, viz. of a moderately broad pre-pubis directed down- 
 wards and forwards, and of a narrow greatly elongated post- 
 pubis directed backwards parallel to the ischium. The pubis 
 is united to both ilium and ischium, the acetabulum has a 
 large unossified space, and neither pre-pubes nor post-pubes 
 meet in ventral symphyses. The arrangement bears a great 
 resemblance to that of Ratite birds. In Lacertilia, Chelonia, 
 Rhynchocephalia and Ichthyosauria together with Theropod 
 and Sauropod Dinosaurs the pubis corresponds to the pre-pubis 
 of Iguanodon and is a more or less cylindrical bone expanded 
 at both ends, meeting its fellow in a ventral symphysis. In 
 Chelonia and Lacertilia the pubis bears a lateral process which 
 
THE SKELETON IN REPTILES. POSTERIOR LIMB. 293 
 
 is homologous with the post-pubis of Iguanodon. In Lacer- 
 tilia and sometimes in Chelonia there is a cartilaginous epipubis 
 attached to the anterior border of the pubic symphysis ; this is 
 well developed in the Chamaeleons and Geckos. In Crocodilia 
 there is, forming the anterior and ventral portion of the 
 acetabulum, a patch of cartilage (fig. 49, 3) which is probably 
 the true pubis homologous with that of lizards and with the 
 pre-pubis of Iguanodon. The large bone generally called the 
 pubis in Crocodiles is probably an epipubis. 
 
 THE POSTERIOR LIMB. 
 
 The posterior limb is entirely absent in some Lacertilia and 
 in most Ophidia, though traces occur in Python, Tortrix and 
 Typldops. In the Ichthyosauria, Sauropterygia and Pythono- 
 morpha the posterior limbs form swimming paddles and have 
 been already referred to. 
 
 The arrangement of the proximal and middle segments of 
 the limb is fairly constant in all reptiles with limbs adapted 
 for walking, and the tibia and fibula are always separate. 
 The pes is however subject to a considerable amount of varia- 
 tion, especially as regards the tarsus. In some Chelonia the 
 tarsus like the carpus has an extremely simple arrangement, 
 consisting of a proximal row of three bones, the tibiale, inter- 
 medium and fibulare, a ceiitrale, and a distal row of five tar- 
 salia. In most living reptiles, however, the tibiale and inter- 
 medium are as in mammals united, forming the astragalus. 
 In Crocodiles (fig. 48, B, 15) the centrale is also united with 
 the tibiale while the distal tarsalia are very slightly developed. 
 The calcaneum in Crocodiles is drawn out into a long process 
 forming a heel in a manner almost unique among Sauropsida. 
 In Sphenodon and Lacertilia the tibia and fibula articulate 
 with a single large bone representing the whole proximal row 
 of tarsalia. 
 
 The pes is generally pentedactylate, but in some Crocodiles 
 the fifth digit is vestigial (fig. 48, B), and in some Dinosauria 
 
294 THE VERTEBRATE SKELETON. 
 
 (fig. 35) there are only three digits. The North American Dino- 
 saurs present a continuous series ranging from a pentedactylate 
 plantigrade form like Morosaurus, to such a form as Hallopus 
 with a highly digitigrade and specialised pes reduced to three 
 functional digits, and a vestigial fifth metatarsal. The second, 
 third and fourth metatarsals in this form are nearly two- 
 thirds as long as the femur, and the calcaneum is drawn out 
 into a heel much as it is in most mammals. 
 
 In Lacertilia, Orthopoda and many Chelonia, the ankle 
 joint comes to lie between the proximal and distal row of 
 tarsals as in birds. 
 
CHAPTER XVII. 
 
 CLASS. AVES 1 . 
 
 BIRDS form a large and extremely homogeneous class of the 
 vertebrata, and are readily distinguished from all other animals 
 by the possession of an epidermal exoskeleton having the form 
 of feathers. Feathers differ from hairs in the fact that they 
 grow from papillae formed of both the horny and the Mal- 
 pighiaii layer of the epidermis, which papillae at first project 
 from the surface, and only subsequently become imbedded in 
 pits of the dermis. A dermal exoskeleton does not occur in 
 birds. 
 
 The endoskeleton is characterised by its lightness, the 
 large bones being generally hollow ; but the pneumaticity 
 does not vary in proportion to the power of flight. The 
 cervical part of the vertebral column is very long and flexible, 
 while the postcervical portion is generally very rigid, owing 
 to the fusion of many of the vertebrae, especially in the 
 lumbar and sacral regions. The vertebrae are generally with- 
 out epiphyses to their centra. The cervical vertebrae in living 
 forms have saddle-shaped articulating surfaces, and many of 
 them bear ribs. The thoracic ribs in almost all birds have 
 large unciriate processes. The sternum is very large, and the 
 ribs are always attached to its sides, not as in many reptiles 
 
 1 M. Fiirbringer, Untersuchungen zur Morphologic und Systematik der 
 Vogel, I. and II. Amsterdam, 1888. Cf. H. Gadow, Nature, xxxix. 
 1888, pp. 150 and 177. 
 
 T. H. Huxley, "On the classification of birds." P. Z. S., London, 
 1867. 
 
 E. Seleuka and H. Gadow, Vogel in Bronn's Classen und Ordnungen 
 des Thier-reichs 18691890. 
 
296 THE VERTEBRATE SKELETON. 
 
 to any backwardly-projecting process or processes. The sternum 
 ossifies from two or more centres. 
 
 The skull is extremely light, and its component bones show 
 a great tendency to fuse together completely. The facial part 
 of the skull is prolonged into a beak, chiefly formed of the pre- 
 maxillae; this beak is in all modern birds devoid of teeth, 
 and is coated externally with a horny epidermal sheath. The 
 quadrate is large and freely movable. The supratemporal 
 arcade 1 is imperfect, while the infratemporal arcade 1 is com- 
 plete. There are no postorbital or postfrontal bones. Neither 
 parotic processes nor an interparietal foramen occur. There 
 are commonly large pre-orbital vacuities. The palatines 
 and pterygoids never form a secondary bony palate as in 
 Crocodiles. Part of the floor of the skull is formed by a 
 wide basitemporal (paired in the embryo) which is continued 
 in front as a long slender rostrum ; these structures have re- 
 placed the parasphenoid of Ichthyopsids. Cartilage or bone is 
 always developed in the sclerotic. The first branchial arch is 
 well developed, the hyoid arch but slightly. The coracoids 
 are large, and the clavicles are nearly always united forming 
 ihefurc^da. There is no separate interclavicle and hardly any 
 trace of a precoracoid. 
 
 The anterior limbs form wings, and the manus is in the 
 adult always much modified, never having more than three 
 digits. The three bones of the pelvis are, except in Archaeor- 
 nithes, always ankylosed together in the adult, and the ilium 
 is greatly prolonged in front of the acetabulum, which is 
 perforated. The ilia are not connected with the sacrum by 
 ossified sacral ribs. The pubes arid ischia are directed back- 
 wards parallel to one another, and except in a very few forms 
 never meet their fellows in ventral symphyses. The fibula 
 is generally much reduced. The proximal tarsal bones are 
 always ankylosed to the tibia, and the distal tarsals to the 
 metatarsals, so that the ankle joint is intertarsal. The first 
 1 See p. 283. 
 
AVES. ARCHAEORNITHES. 297 
 
 metatarsal is nearly always free. The pes never has more than 
 four digits in the adult. 
 
 The class Aves is most conveniently divided into two sub- 
 classes : 1. Archaeornithes. 2. Neornithes. 
 
 Subclass I. ARCHAEORNITHES. 
 
 The only form referred to this subclass of extinct birds is 
 Archaeopteryx\ the earliest known bird. In this animal the 
 skeleton does not seem to be pneumatic. The cervical and 
 trunk vertebrae are generally thought to be flat, certainly 
 their articulating surfaces are not saddle-shaped. There is no 
 long compound sacrum as in modern birds. The tail is longer 
 than the whole body, the caudal vertebrae are twenty in 
 number, they gradually taper as traced away from the trunk, 
 and each bears a pair of feathers. The posterior caudal 
 vertebrae are not united together to form a pygostyle. The 
 upper jaw bears thirteen pairs of conical teeth, planted in 
 distinct sockets in the maxillae and preinaxillae, but the 
 mandible has only three pairs. The presence of these teeth 
 forms the most essential difference between the skull of 
 Archaeopteryx arid that of modern birds, and the fact that 
 they occur on the premaxillae renders it improbable that 
 a horny beak was present. There is a ring of ossifications 
 in the sclerotic. The ribs do not show uncinate processes, 
 and articulate with the vertebrae by single heads not divided 
 into capitula and tubercula. Abdominal ribs appear to have 
 been present. The furcula is large, and the scapula has a well 
 developed acromion. The sternum is unknown. The radius 
 and ulna are approximately equal in size. In the manus the 
 first, second and third digits 2 are present, each terminated by 
 
 1 E. Owen, Phil. Trans., vol. CLIII., p. 33; 1863. T. H. Huxley, 
 P. R. S., vol. xvi., p. 243; 1868. C. Vogt, Rev. Scient., ser. 2, torn. 9, 
 p. 241; 1879. C. H. Hurst, Nat. Sci., vol. in., p. 275; 1893; vol. vi., 
 pp. 112, 180, 244; 1895. W. P. Pycraft, Nat. Sci., vol. v., pp. 350 and 
 437; 1894; and vol. vm., p. 261; 1896. 
 
 2 According to Hurst the fourth and fifth digits are also present. 
 
298 THE VERTEBRATE SKELETON. 
 
 a claw. The second digit is considerably the longest, while 
 the third includes four phalanges. The three bones of the 
 pelvis probably remained distinct throughout life. The tarsals 
 are ankylosed respectively to the tibia and metatarsals as in 
 other birds. The metatarsals are ankylosed together, and the 
 pes has four digits. 
 
 Subclass II. NEORNITHES. 
 
 To this subclass may be referred all known birds except 
 Archaeopteryx. They all agree in having a short tail whose 
 component vertebrae are commonly ankylosed together form- 
 ing a pygostyle. The three metacarpals do not all remain 
 distinct. The bones of the pelvis are ankylosed together, 
 and to a large though variable number of vertebrae. There 
 are three orders, the Ratitae, Odontolcae, and Carinatae. 
 
 Order 1. RATITAE. 
 
 The Ratitae differ from Archaeopteryx and the great 
 majority of Carinatae in being flightless. The bones are 
 generally not pneumatic, containing marrow instead of air, 
 in the Ostrich however they are very pneumatic. The tail 
 is short and the posterior caudal vertebrae are generally 
 ankylosed together forming a pygostyle. The pectoral girdle 
 has comparatively a much smaller size than in Carinatae, 
 clavicles are small or absent, and the scapula and coracoid 
 lie nearly in the same straight line. The ilium and ischium 
 do not as in Carinatae unite posteriorly, and enclose a 
 foramen except in very old Rheas and Emeus. The quadrate 
 articulates with the cranium by a single head. The vomers 
 unite and form a broad plate, separating the palatines, ptery- 
 goids and basisphenoidal rostrum. 
 
 The anterior limbs are greatly reduced in size or even 
 absent, while the posterior limbs are greatly developed and 
 adapted for running. The tibia and fibula are quite distinct. 
 
AVES. RATITAE. 299 
 
 Many ornithologists agree that the various forms grouped 
 together as Ratitae are not all very closely allied to one another, 
 that they resemble one another mainly in having lost the power 
 of flight, and do not form a natural group. 
 
 The Ratitae include the following groups : 
 
 JBpyomithes 1 , huge extinct birds from Madagascar. 
 
 Apteryges, including the Apteryx of New Zealand. 
 
 Dinornithes 2 , the Moas, huge extinct birds from New 
 Zealand, and some of the neighbouring islands. 
 
 Megistanes, including the Cassowaries (Casuarius) of Aus- 
 tralia, New Guinea, and some of the neighbouring islands ; 
 and the Emeus (Dromaeus) of Australia. 
 
 Rheornithes, including the Rheas of S. America. 
 
 Struthiornithes, including the Ostriches (Struthio) now living 
 in Africa, and found fossil in N. India and Samos. 
 
 Order 2. ODONTOLCAE. 
 
 This order includes only an extinct N. American bird 
 ffesperornis 3 . The jaws are provided with a series of sharp 
 teeth placed in continuous grooves, but the premaxillae are 
 toothless, and were probably sheathed in a horny beak. The 
 rami of the mandible are not ankylosed together in front. 
 The skeleton is not pneumatic. The cervical vertebrae have 
 saddle-shaped articulating surfaces as in ordinary birds, and 
 the thoracic vertebrae are not ankylosed together. The tail 
 is comparatively long, and formed of twelve vertebrae with 
 only slight indications of a pygostyle. The ribs have uncinate 
 processes. The anterior limb is quite vestigial, being reduced 
 to a slender humerus. The posterior limb is very powerful 
 and adapted for swimming. 
 
 1 See C. W. Andrews, P. Z. S., 1894, p. 108. 
 
 2 See T. J. Parker, 2V. Zool. Soc. London, vol. xiti., pt. 2, 1895, and 
 F. W. Button, several papers in Tr. N. Zealand Inst., 1893 and 1895. 
 
 3 See 0. C. Marsh. Odontornithes. A monograph of the extinct toothed 
 birds of N. America. Newhaven, 1880. 
 
300 THE VERTEBRATE SKELETON. 
 
 Order 3. CARINATAE. 
 
 This order includes the vast majority of living birds. 
 The cervical vertebrae have saddle-shaped articulating surfaces 
 (except in the Ichthyornithiformes). The posterior caudal 
 vertebrae are ankylosed forming a pygostyle. The quadrate 
 articulates with the cranium by a double head. In all except 
 the Tinamidae the vomers are narrow behind and not inter- 
 posed between the palatines, pterygoids and basisphenoidal 
 rostrum. The sternum has a median keel, and the anterior 
 limbs are in the great majority of cases adapted for flight. 
 Clavicles are well developed, and the scapula and coracoid are 
 nearly at right angles to one another. The various groups 
 into which the Carinatae are divisible are shown in the table 
 on pp. 40 42. Their special characters will not be dealt with. 
 
 FIG. 55. Gallus barikiva var. domesticus. THE LEFT HALF OF THE SKELETON. 
 The skull, vertebral column, and sternum are bisected in the median 
 plane. (After Marshall and Hurst.) 
 
 A, acetabulum. B, cerebral fossa. CB, cerebellar fossa. CL, clavicle. CO, coracoid. 
 CR, cervical rib. C l = one, first cervical vertebra. FE, femur. HC, ventral end of clavicle. 
 HU, humerus. HY,hyoid. IF, ilio-sciatic foramen. IL, ilium. IS, ischium. L, lachrymal. 
 MC 3, postaxial metacarpal. MN, mandible. MS, xiphoid processes. MT, tarso-metatarsus. 
 MT 1, first metatarsal. N, nasal. OP, optic foramen. P, premaxilla. PB, pubis. PL, 
 palatine. PY, pygostyle. R, radius. RC, radial carpal. S, keel of sternum. SC, scapula. 
 T, tibio-tarsus. TH 4, fourth thoracic vertebra. U, ulna. UC, ulnar carpal. UP, uncinate 
 process. Z, infra-orbital bar. 1, 2, 3, 4, first, second, third and fourth digits of pes. 3, pre- 
 axial, 4, middle, and 5, postaxial digit of manus. 
 
AVES. CARINATAE. 
 
 301 
 
CHAPTER XVIII. 
 
 THE SKELETON OF THE WILD DUCK (Anas 
 boschas). 
 
 I. EXOSKELETOK 
 
 The exoskeleton of the Duck and indeed of all birds is 
 entirely epidermal in origin. Its most important part consists 
 of feathers, but it includes also the following horny struc- 
 tures : 
 
 (a) scales, which cover the toes and tarso-metatarsus ; 
 
 (b) claws, which are attached to the distal phalanges of 
 the toes and of the pollex ; 
 
 (c) the wide beak, which sheaths both upper and lower 
 jaws, and whose edges are raised into lamellae, which act as 
 strainers. 
 
 FEATHERS. 
 
 A well developed feather, such as one of the large 
 quill feathers of the wing or tail, consists of the following 
 parts : A main stem, the scapus, which forms the axis 
 running along the whole length of the feather, and is divided 
 into (1) a proximal hollow cylindrical portion, the calamus or 
 quill, and (2) a distal solid portion, the rachis or shaft, which 
 is square in section, flexible and grooved along its ventral 
 surface, and bears a number of lateral processes, the barbs. 
 The calamus which is partly imbedded in a pit in the dermis, 
 
SKELETON OF THE WILD DUCK. THE FEATHERS. 303 
 
 bears two holes : one, the inferior umbilicus, is at its 
 proximal end, and into it enters a vascular outgrowth from the 
 dermis; the other, the superior umbilicus, lies on the 
 ventral surface at the junction of the calamus and scapus. 
 
 The barbs are a series of narrow elastic plates, attached 
 by their bases to the rachis, and with their edges looking 
 upwards and downwards. The barbs are connected together 
 by a number of smaller processes, the barbules, which inter- 
 lock with one another by means of booklets, and bear the 
 same relation to the barbs that the barbs do to the rachis. 
 The barbs and barbules, together with the rachis, constitute 
 the vexillum or vane of the feather. Any feather having 
 the above type of structure is called a penna or a contour 
 feather, from the fact that it helps to produce the contour of 
 the body. 
 
 VARIETIES OF FEATHERS. 
 
 1. Pennae. There are two kinds of pennae or contour 
 feathers. 
 
 (a) The quills. These form the large feathers of the 
 wing and tail. They are divided into two groups, the 
 remiges, or wing quills, and the rectrices, or tail quills. 
 
 The remiges l include three sets of feathers, the primaries 
 or metacarpo-digitals, which are attached to the bones of 
 the manus, the secondaries or cubitals, which are attached 
 to the ulna, and the humerals, which are attached to the 
 humerus. 
 
 The primaries differ from all the other quill feathers 
 in having the posterior half of the vane much wider than the 
 anterior half. They are ten in number, and of these six, 
 the metacarpal quills (fig. 57, 14), are attached to the second 
 and third metacarpals, one, the ad-digital (fig. 57, 15), to the 
 phalanx of the third digit, two, the mid-digitals (fig. 57, 16). 
 to the first phalanx of the second digit, and two, the pre-digitals 
 
 1 See E. S. Wray, P. Z. S., 1887, p. 343. 
 
304 
 
 THE VERTEBRATE SKELETON. 
 
 (fig. 51, 17), to the second phalanx of the second digit. One 
 of the pre-digitals is very small, and is called the remicle 
 (fig. 57, 11). 
 
 FIG. 56. THE WING OF A WILD DUCK (Anas bosclias). 
 
 The upper figure shows the dorsal side of a right wing, the lower figure 
 
 the ventral side of a left wing, x ^. (Brit. Mus.) 
 
 1. scapulars. 6. metacarpo-digitals or pri- 
 
 2. tectrices marginales. maries. 
 
 3. tectrices minores. 7. tectrices mediae. 
 
 4. bastard wing. 8. cubitals or secondaries. 
 
 5. tectrices majores. 9. pennae humerales. 
 
 10. pennae axillares. 
 
 In addition, a group of three quill feathers is attached to 
 the first digit, constituting the bastard wing or ala spuria 
 (fig. 56, 4). 
 
 The secondaries or cubitals (fig. 56, 8) form a group of 
 seventeen feathers, attached to the ulna ; they are shorter than 
 
SKELETON OF THE WILD DUCK. THE FEATHERS. 305 
 
 the primaries, and do not have the posterior half of the vane 
 much wider than the anterior half. 
 
 The humerals (figs. 56, 9 and 57, 12) form a group of 
 eight small feathers, of varying length, attached to the anterior 
 half of the humerus. 
 
 B 
 
 FIG. 57. WINGS OF A WILD DUCK WITH THE COVERTS REMOVED 
 
 (Anas boschas). x -|. 
 
 A. Eight wing seen from the dorsal side. B. Left wing disarticulated 
 and seen from the ventral side. (Brit. Mus.) 
 
 1. humerus. 
 
 2. radius. 
 
 3. ulna. 
 
 4. radial carpal. 
 
 5. ulnar carpal. 
 
 6. first phalanx of first digit. 
 
 7. second metacarpal. 
 
 8. third metacarpal. 
 
 9. first phalanx of second digit. 
 
 R. 
 
 10. second phalanx of second 
 
 digit. 
 
 11. remicle. 
 
 12. pennae humerales. 
 
 13. cubitals or secondaries. 
 
 14. metacarpal quills. 
 
 15. ad-digital. 
 
 16. mid-digitals. 
 
 17. pre-digital. 
 
 20 
 
306 THE VERTEBRATE SKELETON. 
 
 (b) The tectrices or coverts are short feathers, which 
 cover over the quills of the rectrices and remiges, and clothe 
 the body generally. Their barbules are less developed than is 
 the case with the quill feathers, so that the barbs separate 
 readily from one another, especially at the base of the vane. 
 The nomenclature of the various patches of coverts on the 
 wings is seen in fig. 56. A small patch of backwardly-directed 
 feathers surrounding the external auditory opening are known 
 as the auriculars. 
 
 2. The filophimes are rudimentary feathers, consisting 
 of a minute stem and slightly developed vane. They are left 
 in the skin after the other feathers have been removed. 
 
 3. The phimulae, or down feathers, have the stem very 
 slightly developed, while the barbs are soft and free from one 
 another. They are distributed all over the body, not only 
 among the contour feathers, but also over the spaces (apteria) 
 which bear no contour feathers. 
 
 In the young bird the rudiments of the new feathers are 
 formed at the bases of the embryonic down feathers, and as 
 they grow they push them out from the skin. The embryonic 
 down feathers however remain attached to the apices of the 
 new feathers till these have reached a length of about an 
 inch; they are then shed. 
 
 II. ENDOSKELETON. 
 
 As compared with that of the Turtle or Crocodile, the 
 endoskeleton of the Duck is characterised by : 
 
 1. The great lightness of the bones, many of which con- 
 tain air cavities. 
 
 2. The tendency to become ankylosed together shown by 
 many of the bones. 
 
 3. The modification of the anterior limbs and girdle for 
 the purpose of flight. 
 
SKELETON OF THE WILD DUCK. VERTEBRAL COLUMN. 307 
 
 1. THE AXIAL SKELETON. 
 
 This, as in other vertebrates, is divisible into 
 
 A. The vertebral column. 
 
 B. The skull. 
 
 C. The ribs and sternum. 
 
 A. THE VERTEBRAL COLUMN. 
 
 The vertebral column of the duck, like that of the great 
 majority of birds, presents a number of well-marked character- 
 istics, contrasting strongly with those of the generality of 
 higher vertebrates. The centra are always without epiphyses. 
 The neck is exceedingly long, about as long as all the rest of 
 the vertebral column put together, and is remarkable for its 
 flexibility. The trunk portion of the vertebral column on the 
 other hand is characterised by extreme rigidity, and the 
 marked tendency shown by the component vertebrae to fuse 
 together into one almost continuous mass. The most rigid 
 part of the vertebral column is that to which the pelvis is 
 united, as no less than seventeen vertebrae take part in the 
 union. The tail of the duck, like that of all living birds, is 
 very short, arid the posterior caudal vertebrae are united 
 togther, forming the pygostyle. The vertebral column may 
 be divided into cervical, thoracic, lumbar, sacral, and caudal 
 regions, but the boundaries between the several regions are ill- 
 defined. 
 
 THE CERVICAL VERTEBRAE. 
 
 All the vertebrae anterior to the first one that bears a rib 
 meeting the sternum are regarded as cervical vertebrae. 
 There are therefore sixteen cervical vertebrae, the last two of 
 which bear well developed ribs. All are freely movable on 
 one another. 
 
 As a typical cervical vertebrae, any one from the fifth to 
 the ninth may be taken. The vertebra is rather elongated, 
 and is very lightly and strongly made, its most characteristic 
 
 202 
 
308 THE VEKTEBRATE SKELETON. 
 
 feature being the shape of the articulating surfaces of the 
 centra, which are generally described as saddle-shaped. The 
 anterior surface is convex from above downward, and concave 
 from side to side, while the posterior and more prominent 
 surface is concave from above downwards and convex from 
 side to side. The neural arch is low, and is drawn out into a 
 slight blade-like neural spine. Its base is deeply notched on 
 both sides posteriorly for the exit of the spinal nerves. Above 
 these notches it is drawn out into two rather prominent 
 diverging processes, which bear the postzygapophyses, 
 two flattened surfaces which look downwards and outwards. 
 The transverse processes form irregular outgrowths from 
 the anterior two-thirds of the sides of the vertebra ; each 
 projects for a short distance downwards and outwards, and 
 is terminated posteriorly by a short backwardly-projecting 
 spine. The transverse processes are shown by development 
 to ossify from separate centres, and are therefore to be 
 regarded as cervical ribs, and each is perforated at its base by 
 a canal for the passage of the vertebral artery. Above the 
 anterior end of the vertebrarterial canal are a pair of 
 thickened outgrowths, which bear upwardly and inwardly 
 directed prezygapophyses. Each transverse process is 
 perforated near its middle by a prominent foramen through 
 which passes a vein which is connected with the jugular vein. 
 
 The third and fourth cervical vertebrae resemble the suc- 
 ceeding ones in most respects, but have small hypapophyses, 
 and the neural spines are less blade-like. The posterior 
 cervical vertebrae (tenth to sixteenth) differ somewhat from 
 the middle ones. They are shorter and more massive, the 
 neural arch is much shorter, being deeply notched in the 
 middle line in front and behind. The transverse processes arise 
 from the anterior half of the vertebra only, and in the eleventh 
 vertebra each is drawn out below into a pair of rather promi- 
 nent downwardly and inwardly directed processes. In the 
 twelfth vertebra these processes have almost coalesced, and 
 
 
SKELETON OF THE WILD DUCK. VERTEBRAL COLUMN. 309 
 
 in the thirteenth vertebra they have coalesced completely, 
 forming a prominent hypapophysis. In the succeeding 
 vertebrae this hypapophysis rapidly decreases in size. 
 
 The fifteenth and sixteenth cervical vertebrae resemble the 
 succeeding thoracic vertebrae, having short thick centra and 
 prominent squarely truncated neural spines ; the sides of the 
 neural arches are very deeply notched. The fifteenth vertebra 
 has a short transverse process, perforated by a wide vertebrar- 
 terial foramen, but this foramen is absent in the sixteenth. 
 The transverse processes of the fifteenth vertebra bear two 
 facets for the articulation of the capitulum and tuberculum of 
 the rib. The sixteenth vertebra has its tubercular facet on 
 the transverse process, but the capitular facet is borne on the 
 centrum. 
 
 The second or axis vertebra is small, and has the centrum 
 drawn out into a comparatively very large hypapophysis. The 
 posterior articulating surface of the centrum is saddle-shaped, 
 the anterior nearly flat : above it the centrum is prolonged 
 into the prominent odontoid process, which is shown by 
 development to be the detached centrum of the atlas. The 
 neural arch is deeply notched in the middle line in front, and 
 at the sides behind. It is drawn out posteriorly into a wide 
 massive outgrowth, which overhangs the third vertebra and 
 bears the downwardly-directed postzygapophyses. The pre- 
 zygapophyses are situated at the sides of the anterior end of 
 the neural arch, and look directly outwards. The transverse 
 processes are very slightly developed, and are pierced by the 
 vertebrarterial canals. 
 
 The atlas vertebra is a very slight ring-like structure, 
 thickened ventrally and bearing in front a prominent concave 
 cavity for articulation with the occipital condyle of the skull. 
 Posteriorly it bears a more or less flattened surface for arti- 
 culation with the centrum of the axis. It surrounds a large 
 cavity partially divided into a larger dorsal portion, which is 
 the neural canal, and a smaller ventral portion which lodges 
 
310 THE VERTEBRATE SKELETON. 
 
 the odontoid process. The sides of the atlas are pierced by 
 the vertebra rterial canals, above which there are two slight 
 backwardly-projecting outgrowths bearing the postzygapophyses 
 on their inner faces. 
 
 THE THORACIC VERTEBRAE. 
 
 The thoracic region includes all the vertebrae bearing free 
 ribs, except the first two, viz. those whose ribs do not reach 
 the sternum. There are seven thoracic vertebrae. The first 
 four have centra with saddle-shaped articulating surfaces, but 
 are more or less firmly united together by their neural spines ; 
 the last two are completely ankylosed by their centra to the 
 lumbar vertebrae. 
 
 Each of the first five vertebrae has a prominent, vertical, 
 abruptly terminated neural spine, and straight transverse 
 processes. The zygapophyses and articulating surfaces at the 
 ends of the centra are well developed. The third, fourth, fifth, 
 and sixth vertebrae have verv prominent hypapophyses. The 
 articular facets for the ribs are well marked, those for the tu- 
 bercula lying at the free ends of the transverse processes, and 
 those for the capitula at the sides of the anterior ends of the 
 centra. The sixth and seventh thoracic vertebrae are firmly 
 fused by their centra and neural arches to one another and 
 to the lumbar vertebrae behind, and by their transverse pro- 
 cesses to the ilia. The sixth has its centrum terminated in 
 front by a saddle-shaped articulating surface, and bears a pair 
 of prominent prezygapophyses. Its transverse processes and 
 centrum bear facets for the tubercula and capitula of the ribs 
 respectively. In the seventh vertebra the tubercular facet is 
 wanting. 
 
 THE SACRUM. 
 
 The sacrum generally consists of seventeen vertebrae 
 fused with one another and with the ilia. Their number may 
 be reckoned from the number of foramina for the exit of spinal 
 nerves. The two most anterior of these vertebrae bear ribs 
 
SKELETON OF THE WILD DUCK. THE SACRUM. 311 
 
 and have been already described with the other thoracic 
 vertebrae. Their neural spines and, those of the four succeed- 
 ing vertebrae are fused together, forming a continuous crest 
 of bone completely united laterally with the ilia. The trans- 
 verse processes of all these six vertebrae are well developed, 
 
 A B 
 
 FlG. 58. A, DORSAL AND B, VENTRAL VIEW OF THE PELVIS AND SACRUM OF 
 
 A DUCK (Anas boschas). 
 
 1. ilium. 4. pectineal process. 
 
 2. ischium. 5. lumbar vertebrae. 
 
 3. pubis. 6. true sacral vertebrae. 
 
 but those of the posterior two (fig. 58, B, 5) are much the 
 stoutest. The next three vertebrae have broad centra, but 
 their transverse processes are very slightly developed and have 
 no ventral elements. These seven vertebrae belong to the 
 lumbar series. The remaining eight vertebrae have well- 
 developed transverse processes, which in the case of the first 
 three or four are divisible into dorsal and ventral elements. 
 All the dorsal elements are united to form a pair of flattened 
 plates, partially separated by a series of foramina from a 
 
312 
 
 THE VERTEBRATE SKELETON. 
 
 median plate formed by the united neural arches. Laterally 
 they are continuous with the ischia. The first two of this 
 series of vertebrae are shown by their relation to the nerves 
 to be the true sacrals (fig. 58, B, 6), the remaining six belong- 
 ing to the caudal series. 
 
 Behind them come the six free caudal vertebrae, succeeded 
 by a terminal piece, the pygostyle, formed of a number of 
 vertebrae fused together ; this bears the rectrices or tail quills. 
 
 15 
 
 18,. 
 
 FIG. 59. SKULL OF A DUCK (Anas boschas). x 1. 
 A. Dorsal view of the cranium. B. Palatal view of the mandible. 
 
 C. The Hyoid. 
 For numbers see Fig. 60. 
 B. THE SKULL. 
 
 The skull of the duck, like that of birds in general, is 
 characterised (1) by its lightness, (2) by the contrast between 
 
SKELETON OF THE WILD DUCK. 
 
 THE SKULL. 313 
 11 
 
 FIG. 60. A. Ventral view of the cranium of a Duck (Anas boschas). 
 B. Cranium and mandible seen from the left side, x 1. 
 
 1. maxilla. 22. 
 
 2. premaxilla. 23. 
 
 3. anterior nares. 24. 
 
 4. nasal process of premaxilla 
 
 (fig. 59). 25. 
 
 5. nasal. 
 
 6. frontal (fig. 59). 26. 
 
 7. lachrymal. 
 
 8. postfrontal process. 
 
 9. parietal (fig. 59). 27. 
 
 10. jugal. 
 
 11. quadratojugal. 
 
 12. quadrate. 
 
 13. condyle of mandible. 
 
 14. posterior articular process. 
 
 15. dentary at symphysis. \ 28. 
 
 16. basi-hyal. I (fig. 29. 
 
 17. uro-hyal. 59). 30. 
 
 18. basibranchial. 31. 
 
 19. vomer. I. 
 
 20. palatine. mina. 
 
 21. pterygoid. 
 
 anterior palatine foramen. 
 
 basitemporal. 
 
 foramen leading into tympanic 
 cavity. 
 
 bristle inserted into posterior 
 opening of carotid canal. 
 
 bristle inserted into posterior 
 opening of Eustachian 
 canal. 
 
 bristle emerging through an- 
 terior opening of carotid 
 canal. Close by is seen the 
 bristle emerging through 
 the anterior opening, of the 
 Eustachian canal. 
 
 fenestral recess. 
 
 maxillo-palatine. 
 
 lambdoidal crest. 
 
 rostrum. 
 
 II. IV. V. IX. X. nerve fora- 
 
314 THE VERTEBRATE SKELETON. 
 
 the bones of the cranium proper and those forming the '-rest 
 of the skull, for the bones forming the cranium proper are 
 closely fused together, the sutures between them being nearly 
 all completely obliterated in the adult, while the bones form- 
 ing the face are loosely connected with the cranium proper ; 
 
 (3) by the prolongation of the face into a long toothless beak ; 
 
 (4) by the size of the orbits, and their position entirely in 
 front of the cranium, so that they are separated from one 
 another only by a thin interorbital septum. 
 
 For purposes of description the skull may be divided into 
 
 (1) The cranial portion. 
 
 (2) The facial portion. 
 
 (3) The mandible. 
 
 (4) The hyoid. 
 
 (1) THE CRANIAL PORTION. 
 
 This is a rounded box expanded dorsally and posteriorly, 
 but tapering antero-ventrally. In the young skull the divi- 
 sional lines between the several bones can be easily seen, 
 but in the adult they are quite obliterated. 
 
 (a) The dorsal surface is rounded, expanded in front and 
 behind, but encroached upon in the middle by the cavities of the 
 orbits. There is a prominent divisional line in front, separating 
 it from the facial part of the skull. It is formed mainly by 
 the frontal (fig. 59, A, 6) and parietal bones, but the frontals 
 diverge a little anteriorly and enclose between them the ends 
 of the nasal processes (fig. 59, A, 4) of the premaxillae. Just 
 in front of the orbit the outer margins of the frontals are 
 either notched or pierced by a pair of foramina. 
 
 (b) At the posterior end of the cranium the most promi- 
 nent feature is the large, almost circular foramen magnum, 
 through which the spinal cord and brain communicate ; this in 
 young birds is seen to be bounded by four distinct bones, dor- 
 sally by the supra-occipital, ventrally by the basi-occipital, 
 and laterally by the exoccipitals. 
 
SKELETON OF THE WILD DUCK. THE SKULL. 315 
 
 The basi-occipital forms the main part of a prominent 
 convex knob, the occipital condyle, with which the atlas 
 articulates. The occipital condyle is slightly notched above, 
 and the ventral surface of the cranium is deeply pitted just 
 in front of it ; the exoccipitals also contribute slightly to its 
 formation. Slightly in front of and ventral to the foramen 
 magnum is a small foramen through which the hypoglossal 
 nerve leaves the cranial cavity. 
 
 The supra-occipital is separated from the parietal by a 
 suture line along which run a pair of prominent ridges, the 
 lambdoidal crests (fig. 60, B, 30). There are often a pair of 
 prominent vacuities in the supra-occipital dorsal to the foramen 
 magnum. The epi-otics and opisthotics become completely 
 fused with the bones of the occipital segment at a very early 
 stage. 
 
 (c) The ventral surface of the cranium is wide behind, 
 where it is formed by a broad ' transverse membrane bone, the 
 basitemporal (fig. 60, A, 23), the sides of which are fused with 
 the auditory capsules. Slightly in front of and an eighth of 
 an inch external to the hypoglossal foramen the cranial wall is 
 pierced by a pair of foramina through which the tenth or 
 pneumogastric nerves leave (fig. 60, A, X). At the sides 
 of the basitemporal are a pair of depressions, the tympanic 
 recesses, in each of which are three holes. Straight lines 
 joining these holes would form an isosceles triangle with its 
 apex directed forwards. Of the two holes at the base of the 
 triangle, the one nearer the middle line and leading into the 
 cranial cavity, is for the exit of the ninth or glossopharyngeal 
 nerve (fig. 60, A, IX), it lies just in front of the pneumogastric 
 foramen. The more external leads into the tympanic cavity, 
 while the more anterior at the apex of the triangle is the 
 posterior opening of the carotid canal (fig. 60, A, 25), 
 which traverses the base of the cranium, and during life 
 lodges the carotid artery. 
 
 The anterior end of the basitemporal is pierced near the 
 
316 THE VERTEBRATE SKELETON. 
 
 middle line by a pair of holes, the anterior openings of the 
 Eustachian canals \ while just in front of these and a little 
 further removed from the middle line are the anterior openings 
 of the carotid canals. Bristles passed in through the posterior 
 openings of the carotid canals will emerge here (fig. 60, A, 27). 
 In front of the basitemporal the base of the cranium is formed 
 by the rostrum (fig. 60, A, 31), or thickened basal portion of 
 the iiiterorbital septum ; this bears two prominent surfaces 
 with which the pterygoids articulate. In some kinds of 
 duck these surfaces are borne by well-marked basi-pterygoid 
 processes. 
 
 (d) The side of the cranium. At the base of the posterior 
 end is seen the deep tympanic cavity. The dorsal part of 
 this is divided by a vertical partition into two halves ; of these 
 the more anterior is the larger, and forms a deep funnel- 
 shaped cavity, the posterior opening of the Eustachian 
 canal (fig. 60, B, 26). A bristle passed into this opening- 
 emerges through the anterior opening of the Eustachian canal. 
 The more posterior of the two is the fenestral recess (fig. 60, 
 B, 28), and is in its turn divided by a slender horizontal bar 
 into a dorsal hole, the fenestra ovalis, and a ventral hole, 
 the fenestra rotunda. During life the fenestra ovalis lodges 
 the proximal end of the columellar chain. Lying at the 
 outer side and slightly dorsal to the tympanic cavity is a deep 
 depression, the lateral tympanic recess, and immediately 
 in front of this is the articular surface for the quadrate. 
 The tympanic cavity is bounded below by the basitemporal, 
 posteriorly by the exoccipital, and above by the squamosal, a 
 membrane bone, which roofs over a good deal of the side of 
 the cranium, and bears ventrally a prominent surface with 
 which the quadrate articulates. Just in front of this is a 
 large round hole, the trigeminal foramen (fig. 60, B, Y), 
 behind which the squamosal is drawn out into a short process. 
 
 In front of the squamosal there is a prominent forwardly- 
 projecting postfrontal process (fig. 60, 8), which ossifies 
 
SKELETON OF THE WILD DUCK. THE SKULL. 317 
 
 from a different centre from that forming the squamosal, but 
 in the adult is completely fused with it. 
 
 The orbit forms a large more or less hemispherical cavity 
 which lodges the eyeball. It is separated from its fellow of 
 the opposite side by an imperfect partition, the interorbital 
 septum. In the young skull it is seen to be bounded above by 
 the frontal, with which the lachrymal (fig. 60, 7) is fused 
 anteriorly, forming a large backwardly-projecting process \ 
 while behind it is bounded by the alisphenoid. The inter- 
 orbital septum is formed by the ossification and coalescence of 
 the mesethmoid in front, with the orbitosphenoid behind, 
 and the rostrum below. The boundary of the orbit below 
 is very imperfect, the zygomatic arch being incomplete. 
 
 The interorbital septum is pierced by the very prominent 
 optic foramen (fig. 60, B, 2), just behind which are the two 
 much smaller foramina for the exit of the oculomotor and 
 pathetic (fig. 60, B, IV) nerves, the more anterior being that 
 for the oculomotor. 
 
 Above and slightly in front of the optic foramen is a 
 median opening, the olfactory foramen. This leads into 
 the cranial cavity behind, and in front is continued forwards 
 as a groove between the interorbital septum and the frontal. 
 
 (2) THE FACIAL PART OF THE SKULL. 
 
 This includes the olfactory capsule and associated bones, 
 and the upper jaw. 
 
 The bones associated with the olfactory capsules are the 
 nasals and vomer. The nasals (figs. 59 and 60, 5) lie on the 
 dorsal surface immediately in front of the cranium, and are 
 separated from one another by the nasal processes of the pre- 
 maxillse. Each is completely fused in the adult with the 
 corresponding maxilla and premaxilla, the three bones together 
 forming the boundary of the anterior nares. The vomer (fig. 
 60, 19) is unpaired and forms a small median vertical plate 
 
318 THE A 7 ERTEBRATE SKELETON. 
 
 lying ventral to the anterior continuation of the interorbital 
 septum. 
 
 The bones of the upper jaw consist on each side of two 
 slender arcades which in front converge and are attached to 
 the large beak, while behind they diverge but are united by 
 the quadrate. 
 
 The inner arcade is formed by the pterygoid and palatine. 
 The pterygoid (fig. 60, 21) is a short flattened bone, which 
 articulates behind with the quadrate, and on its inner side 
 with a large flattened surface borne by the rostrum, in front 
 it meets the palatine, or sometimes ends freely with a long 
 antero-dorsally directed point. 
 
 The palatine (fig. 60, 20) is a slender irregular bone flat- 
 tened dorso-ventrally at its anterior end where it articulates 
 with the beak, and laterally behind. It gives off at its 
 posterior end a process, which is sometimes united with the 
 vomer, sometimes projects forwards, and meets its fellow 
 dorsal to the vomer. In the large space between it and the 
 vomer is the opening of the posterior nares. 
 
 The premaxillae (figs. 59 and 60, 2) are very large, and 
 form nearly a third of the big shovel-shaped beak. They con- 
 stitute the inner, and part of the front boundary of the an- 
 terior nares, and send back a pair of nasal processes which 
 partially separate the nasals from one another. 
 
 The outer arcade forms the slender suborbital bar, 
 and consists mainly of two rod-like bones, which in the adult 
 are completely fused together. The posterior of these is the 
 quadratojugal (figs. 59 and 60, 11) which articulates with tlie 
 quadrate, the anterior is the small and slender jugal or malar 
 (figs. 59 and 60, 10). The extreme anterior part of the bar is 
 formed by the maxilla. The main part of the maxilla how- 
 ever lies anterior to the suborbital bar, and extends forwards 
 along the side of the premaxilla forming all the lateral part of 
 the beak (figs. 59 and 60, 1); it also sends inwards a plate, 
 the maxillo-palatine (fig. 60, A, 29), which completely fuses 
 
SKELETON OF THE WILD DUCK. THE SKULL. 319 
 
 with its fellow in the middle line, and forms the posterior 
 boundary of the anterior palatine foramen. The term 
 desmognathous describes the condition of the skull in 
 which the maxillo-palatines fuse with one another in the 
 middle line in this way. 
 
 The quadrate (fig. 60, 12), which unites the two arcades 
 behind, is a stout irregular four-cornered bone forming the 
 suspensorium. It articulates by its dorso-posterior corner 
 with the squamosal, and by its antero-internal corner with the 
 pterygoid. The middle of its ventral surface forms a hemi- 
 spherical knob with which the mandible articulates, while its 
 dorso-anterior border is drawn out into a long point which 
 extends towards the interorbital septum. 
 
 (3) THE MANDIBLE. 
 
 The mandible or lower jaw consists of two rami which 
 are flattened and fused together in the middle line in front, 
 while behind they diverge from one another and articulate 
 with the quadrates. 
 
 Each ramus is composed of five bones fused together, one 
 being a cartilage bone, and the other four membrane bones. 
 The articular is the only cartilage bone of the mandible, 
 it bears the double condyle (figs. 59 and 60, 13) or concave 
 articular surface for the quadrate, and is drawn out behind 
 into a large hooked posterior articular process. The ar- 
 ticular is also drawn out into a prominent process on each 
 side of the articular surface for the quadrate, and is marked 
 by a deep pit opening posteriorly. The articular is continuous 
 in front with Meckel's cartilage which forms the original 
 cartilaginous bar of the lower jaw, and is ensheathed by the 
 membrane bones. Of these the supra-angular forms the upper 
 part of the mandible in front of the articular, its dorsal sur- 
 face is drawn out into a small coronoid process, its outer 
 surface also bearing a prominent process. The angular is 
 
320 THE VERTEBRATE SKELETON. 
 
 a small bone which underlies the articular and supra-angular 
 on the inner side of the jaw. The dentary (fig. 59, 15) forms 
 the anterior half of each ramus, and is the largest bone of the 
 mandible ; it is fused with its fellow at the symphysis in front, 
 and extends back below the supra-angular. The splenial is a 
 small bone lying along the middle half of the inner side of 
 each ramus of the mandible. 
 
 (4) THE HYOID. 
 
 With the hyoid apparatus is included the eolumella. 
 This forms a minute rod of bone, one end of which is ex- 
 panded and fits into the fenestra ovalis, while the other end,, 
 terminated by a triradiate piece of cartilage, is attached 
 to the tympanic membrane. The structure is as a whole 
 homologous with the auditory ossicles of mammals and the 
 hyomandibular of fish. 
 
 The hyoid consists of a median unpaired portion, formed 
 of two pieces of bone, the basi-hyal (fig. 59, C, 16) in front, 
 and the uro-hyal (fig. 59, C, 17) behind, the two being placed 
 end to end and terminated anteriorly by an unpaired carti- 
 laginous plate, the os entoglossum. At the posterior end 
 there come off" a pair of long posterior cornua, each of 
 which consists of two pieces, a longer basibranchial (fig. 59, 
 C, 18), and a shorter ceratobranchial. For the homology of 
 these parts see p. 336. 
 
 THE RIBS AND STERNUM. 
 
 The last two cervical vertebrae bear long movable ribs 
 which articulate by distinct capitular and tubercular processes, 
 but do not meet the sternum. The thoracic ribs are eight in 
 number, and each is divisible into a vertebral and a sternal 
 portion. The first five thoracic ribs are flattened curved bars 
 of bone, which articulate by a prominent capitulum with 
 the centrum of the corresponding vertebra, and by a tuber- 
 eulum with the transverse process. Projecting backwards 
 from each is a large hooked uncinate process. The last three 
 
SKELETON OF THE WILD DUCK. THE STERNUM. 321 
 
 ribs which are without uncinate processes, become progressively 
 more slender, and in the eighth the tubercular processes are lost. 
 The sternal portions of the ribs are imperfectly ossified 
 pieces, short and comparatively thick in the case of the anterior 
 ribs, longer and more slender in the case of the posterior ribs. 
 
 THE STERNUM 1 . 
 
 The sternum or breast bone is exceedingly large in the 
 Duck, as in all birds, and projects back far beyond the thorax over 
 much of the anterior part of the abdomen. It is an irregularly 
 oblong plate of bone, abruptly truncated behind, somewhat 
 concave dorsally, and drawn out ventrally into a prominent keel, 
 the carina, which projects for some distance forwards beyond 
 the body of the sternum, and tapers off gradually behind. 
 The point where the carina joins the body of the sternum is at 
 the anterior end drawn out into a small process, the rostrum 2 . 
 Just dorso-lateral to this are a pair of deep grooves, the 
 coracoid grooves, with which the coracoids articulate. 
 
 The sides of the sternum are drawn out in front into a 
 pair of short blunt costal processes ; and just behind these 
 are a series of seven surfaces with which the ends of the 
 sternal ribs articulate. Immediately behind these surfaces 
 the sides are produced into a pair of long backwardly-pro- 
 jecting xiphoid processes which nearly meet processes from 
 the posterior end of the sternum. 
 
 2. THE APPENDICULAR SKELETON. 
 
 This consists of the skeleton of the anterior and posterior 
 limbs and of their respective girdles. 
 
 A. THE PECTORAL GIRDLE \ 
 
 The pectoral girdle in almost all birds is strongly constructed 
 and firmly united to the sternum. It consists of three bones, 
 a dorsal element, the scapula, a posterior ventral element, the 
 coracoid, and an anterior ventral element, the clavicle. 
 
 1 Cp. fig. 63. 
 
 2 Often called the manubrium, but not homologous with the manu- 
 brium of the mammalian sternum. 
 
 R. 21 
 
322 THE VERTEBRATE SKELETON. 
 
 The scapula forms a long curved flattened bone expanded 
 at its anterior end, where it meets the coracoid, and lying 
 across the ribs at its tapering posterior end. It helps to form 
 the imperfect glenoid cavity, with which the humerus arti- 
 culates. The coracoid, a shorter but stouter bone than the 
 scapula, has its upper end or head thickened and bears on its 
 posterior border an irregular surface, with part of which the 
 scapula articulates, while the rest forms part of the glenoid 
 cavity. The inner border of the coracoid adjoining the arti- 
 cular facet for the scapula is produced into a strong process 
 which helps to complete the foramen triosseum, a space 
 lying between the adjoining ends of the scapula and coracoid, 
 through which the tendon of the second pectoral muscle passes. 
 The lower part of the coracoid, which is much flattened and 
 expanded, and abruptly truncated posteriorly, articulates 
 with the coracoid groove of the sternum. The clavicle is a 
 thickened curved membrane bone, which is fused with its 
 fellow in the middle line below, the two forming the furcula 
 or merrythought. Its dorsal end is drawn out into a process 
 which articulates with the coracoid. 
 
 THE ANTERIOR LIMB OR WING. 
 
 This consists of three parts, a proximal part, the upper arm 
 or brachium, a middle part, the fore- arm or antibrachmm, 
 and a distal part, the maims. When extended for flight the 
 parts lie almost in the same straight line, but when at rest they 
 are folded on one another in the form of a Z, the brachium and 
 manus pointing backwards, and the anti brachium forwards. 
 When extended for flight the surfaces and borders of the wing- 
 correspond in position with those of the primitive vertebrate 
 limb 1 , the pre-axial border being directed forwards and the post- 
 axial backwards, while the dorsal and ventral surfaces look 
 respectively upwards and downwards. But when the wing is 
 at rest, the humerus as it extends backwards becomes slightly 
 rotated, so that its dorsal surface looks more inwards than 
 1 See p. 28. 
 
SKELETON OF THE WILD DUCK. THE WING. 323 
 
 upwards, while the dorsal surface of the antibrachium looks 
 partially outwards and upwards, and that of the manus mainly 
 outwards. 
 
 The brachium or upper arm contains only a single bone, 
 the humerus (fig. 57, 1). This is a large nearly straight bone 
 expanded at both ends. The proximal end is specially ex- 
 panded, forming two tuberosities, and a large convex head 
 articulating with the glenoid cavity. The pre-axial tube- 
 rosity is the smaller of the two, but is continued by a 
 prominent deltoid ridge, which extends for a very short 
 distance down the shaft. The postaxial tuberosity is the 
 larger, and below it there is a very deep pit, the pneumatic 
 foramen, which leads into an air cavity in the shaft of the 
 bone. The shaft is long and straight, and at the distal end 
 of the bone is the trochlea with two convex surfaces, one 
 pre-axial with which the radius articulates, the other post- 
 axial for the ulna. 
 
 The fore-arm or antibrachium consists of two bones, 
 the radius and ulna. These are of nearly equal length, and 
 are separated from one another by a considerable space except 
 at their terminations. 
 
 The radius (fig. 57, 2), the pre-axial and smaller bone, is 
 straight and fairly stout ; its proximal end articulates with 
 the humerus by a slightly cupped surface, while its distal end, 
 which articulates with the carpus, is convex and somewhat 
 expanded. 
 
 The ulna (fig. 57, 3) is longer, stouter, and slightly curved. 
 Its proximal end is expanded, forming two surfaces which 
 articulate with the trochlea of the humerus ; behind them it 
 is drawn out into a short blunt olecranon process. Its 
 distal end is less expanded, and articulates with the carpus 
 and also with the radius. 
 
 The Manus. This includes the carpus or wrist, and the 
 hand. 
 
 The Carpus. While in the embryo the carpus consists 
 
 212 
 
324 THE VERTEBRATE SKELETON. 
 
 of five distinct elements arranged in a proximal row of two 
 and a distal row of three, in the adult only the proximal 
 bones can be clearly distinguished, the distal ones having 
 become completely ankylosed with the metacarpals to form 
 the carpometacarpus. 
 
 The two distinct carpal bones are the radial carpal and 
 the ulnar carpal. The radial carpal (fig. 57, 4) is a small 
 somewhat cubical bone, wedged in between the manus and 
 the radius and ulna. The ulnar carpal (fig. 57, 5) is a 
 somewhat larger, more irregular bone, lying adjacent to the 
 end of the ulna. It is deeply notched to receive the carpo- 
 metacarpus. 
 
 The hand. In the adult bird the hand is in a much 
 modified condition ; only the first three digits are represented, 
 and the metacarpals are all fused with one another and with 
 the distal carpalia to form the carpo-metacarpus. 
 
 The most prominent part of the carpo-metacarpus is formed 
 by the second metacarpal (fig. 57, 7), a stout, straight bone 
 expanded at both ends. The third metacarpal (fig. 57, 8) 
 is a more slender curved bone fused at both ends with the 
 second metacarpal. The first metacarpal forms simply a 
 small projection on the radial side of the proximal end of the 
 second metacarpal. 
 
 The phalanges. The first digit or pollex includes two 
 phalanges, the distal one being very small and bearing a claw. 
 
 The second digit includes three phalanges, the proximal 
 one being somewhat flattened. The third digit has a single 
 small phalanx. 
 
 THE PELVIC GIRDLE. 
 
 The bones constituting the pelvic girdle are not only as in 
 other higher vertebrates ankylosed together forming the in- 
 nominate bones, but are also ankylosed with a series of some 
 seventeen sacral and pseudosacral vertebrae. The acetabulum 
 (fig. 61, 5) with which the head of the femur articulates is 
 incompletely ossified. 
 
SKELETON OF THE WILD DUCK. PELVIC GIRDLE. 325 
 
 The ilium (figs. 58 and 61, 1) is the largest bone of the 
 pelvis. It forms a long flattened plate extending for a con- 
 siderable distance both in front of and behind the acetabulum, 
 and is fused along its whole length with the transverse pro- 
 cesses and neural spines of the sacral and pseudosacral verte- 
 brae. It forms more than half the acetabulum, above and 
 
 FIG. 61. LATERAL VIEW OF THE PELVIS AND SACRUM OF A DUCK (Anas 
 
 boschas) x 
 
 1. ilium. 
 
 2. ischium. 
 
 3. pubis. 
 
 4. pectineal process. 
 
 5. acetabulum. 
 
 6. ilio-sciatic foramen. 
 
 7. fused vertebrae. 
 
 8. antitrochanter. 
 
 behind which it is produced to form a process, the antitro- 
 chanter (fig 61, 8), with which the great trochanter of the 
 femur articulates. 
 
 The ischium (figs. 58 and 61, 2) is a flattened bone which 
 forms about one-third of the acetabulum, and lies ventral to the 
 posterior part of the ilium. Its anterior portion is separated 
 from the ilium by the large oval ilio-sciatic foramen (fig. 
 61, 6), while behind this the two bones are completely fused. 
 
 The pubis (figs. 58 and 61, 3) is a very long slender bar 
 of bone which forms only a very small part of the acetabulum 
 and runs back parallel to the ventral surface of the ischium 
 with which it is loosely connected at its posterior end. For 
 the greater part of their length the two bones are separated by 
 
326 THE VERTEBRATE SKELETON. 
 
 the long narrow obturator foramen. Behind the ischium 
 the pubis is produced into a long curved downwardly-project- 
 ing process, and in front of the acetabulum it bears a short 
 blunt pectineal or pre-pubic process (fig. 61, 4) probably 
 homologous with the pre-pubis of Orthopod Dinosaurs. The 
 remainder of the pubis is homologous with the post-pubis of 
 Orthopod Dinosaurs. 
 
 THE POSTERIOR LIMB. 
 
 The leg of the bird is somewhat differently constructed from 
 that of other vertebrates owing to the fact that there is no 
 free tarsus, the proximal tarsals having fused with the tibia, 
 and the distal with the metatarsals. 
 
 The thigh consists of a single bone, the femur. The femur 
 is a comparatively short bone with a straight shaft and ex- 
 panded ends. The proximal end bears on its inner side a 
 rounded head, which articulates with the acetabulum. On its 
 outer side is an irregular outgrowth, the great trochanter, 
 while between the two is the surface which meets the antitro- 
 chanter of the ilium. The posterior end also is expanded 
 and marked by a wide groove which lodges the patella. On 
 each side of the groove is a strong condylar ridge for articu- 
 lation with the tibia. The external condyle is deeply grooved 
 behind for articulation with the fibula. 
 
 The crus or shin consists of two separate bones, (1) the 
 tibio-tarsus, formed by the fusion of the tibia with the proxi- 
 mal row of tarsals, and (2) the fibula. 
 
 The tibio-tarsus is a thick straight bone nearly twice as 
 long as the femur. Both ends of the bone are considerably 
 expanded. The proximal end bears two slight depressions 
 which articulate with the condyles of the femur, and a third 
 depression which partly lodges the patella. The proximal end 
 of the anterior or extensor surface is drawn out into a very 
 prominent cnemial crest which bends over towards the post- 
 axial side of the bone ; a slight ridge is continued from it all 
 
SKELETON OF THE WILD DUCK. THE PES. 327 
 
 the way down the shaft. The proximal part of the shaft of 
 the tibio-tarsus bears a roughened ridge with which the fibula 
 is closely connected. The distal end is expanded and rotated 
 outwardly and forms a prominent pulley-like surface which 
 articulates with the tarso-metatarsus. 
 
 The fibula is reduced to the proximal portion only, which 
 is expanded and articulates with a depression behind the 
 external condyle of the femur. The fibula further extends 
 about a third of the way down the shaft of the tibio-tarsus. 
 The patella or knee-cap is a sesamoid bone due to an ossi- 
 fication in the tendon of the extensor muscles of the leg. 
 
 The ankle joint lies between the proximal and distal 
 tarsals which as previously mentioned fuse respectively with 
 the tibia and metatarsus. 
 
 The Pes. The pes includes four digits, and consists of the 
 tarso-metatarsus and the phalanges. The proximal tarsals 
 which are fused with the tibia also really belong to the pes. 
 
 The tarso-metatarsus is a strong straight bone nearly as 
 long as the femur, and is formed by the fusion of the distal 
 tarsals with the second, third and fourth metatarsals. The 
 proximal end of the bone is expanded and bears two facets for 
 articulation with the tibio-tarsus, and near them on the pos- 
 terior surface is a large roughened projection. The lines of 
 junction between the several metatarsals are marked along 
 the shaft by slight ridges. At the distal end of the bone the 
 three metatarsals diverge from one another arid each bears a 
 prominent convex pulley-like surface. The first metatarsal 
 is reduced to the distal end, which tapers to a point proximally, 
 and is attached by ligaments near the distal end of the tarso- 
 metatarsus. 
 
 The digits. Four digits are present, each consisting of a 
 metatarsal (already described) and a certain number of pha- 
 langes, the terminal one being in each case clawed. The first 
 digit or hallux has two phalanges, the second three, the third 
 four, and the fourth five. 
 
CHAPTER XIX. 
 
 GENERAL ACCOUNT OF THE SKELETON IN 
 BIRDS. 
 
 EXOSKELETON. 
 
 The epidermal exoskeleton of birds is very greatly de- 
 veloped, feathers constituting its most important part. 
 
 Three kinds of feathers are found, viz. (a) pennae including 
 quills and coverts, (6) down feathers or plumulae, and (c) filo- 
 plumes which are rudimentary feathers. The structure of 
 the different kinds of feathers is described on pp. 303 306. 
 
 Sometimes a fourth class of feathers, the semiplumae, is 
 recognised. They have the stems of pennae, and the downy 
 barbs and barbules of plumulae. 
 
 In most birds the pennae are riot uniformly distributed 
 over the whole surface of the body, but are confined to certain 
 tracts, the pterylae ; while the intervening spaces or apteria 
 are either bare or covered only with down feathers. In some 
 birds, however, such as the Ratitae a*nd the Penguins, pennae 
 are evenly distributed over the whole body. 
 
 In many birds the calamus or quill bears two vexilla or 
 vanes, the second of which, called the attershaft or hypo- 
 rachis, is generally much the smaller, and is attached to the 
 under surface of the main vexillum. In the Moas, Emeu and 
 Cassowary the two vexilla in the adult bird are nearly equal 
 in size ; though in the nestling Emeu one is much longer than 
 the other. The aftershaft is very small in most Passeres and 
 gallinaceous birds, but is comparatively large in Parrots, Gulls, 
 
THE SKELETON IN BIRDS. THE EXOSKELETON. 329 
 
 Herons and most birds of prey. It is absent or extremely 
 small in the Ostrich, Apteryx, Rhea, Pigeons, Owls, Anseres, 
 and others. 
 
 The quill feathers include two groups, the remiges or 
 wing quills, and the rectrices or tail quills. In most birds 
 the primary remiges, or those which are attached to the bones 
 of the manus, are ten or eleven in number, and are set in 
 grooves in the bones, being firmly attached to them. In the 
 Ostrich however the primaries are little specialised in character 
 and are as many as sixteen in number. They are also less 
 definitely attached to the bones ; as their ends do not lie in 
 grooves in the bones, but project beyond them. 
 
 The secondary quills or those attached to the ulna vary 
 much in number according to the length of the bone. The 
 large dark quills in the wings of Cassowaries are the second- 
 aries. 
 
 The wing of Penguins is very little differentiated. It 
 is covered at the margin by overlapping scales which gradually 
 merge into scale-like feathers at the proximal end. The wing 
 of the Penguin has nothing comparable to the remiges of other 
 birds. 
 
 In some birds, such as Herons (Ardea), there occur in 
 places plumulae of a peculiar kind, which grow persistently 
 and whose summits break off into fine powder as fast as they 
 are formed. These feathers are known as powder -down 
 feathers. They occur also in some Parrots and are then 
 scattered indiscriminately all over the body. 
 
 Other exoskeletal structures besides feathers are commonly 
 well developed. Thus the extremities of the jaws are sheathed 
 in horny beaks whose form varies enormously according to 
 the special mode of life. 
 
 In ducks and geese the beak with the exception of the 
 anterior end is soft, and its edges are raised into lamellae, 
 while in the Mergansers these lamellae become pointed pro- 
 cesses supported by bony outgrowths. These lamellae act as 
 
330 THE VERTEBRATE SKELETON. 
 
 strainers. In Parrots and Hawks, on the other hand, nearly 
 the whole of the beak is hard. 
 
 The toes and tarso-metatarsus are usually featherless and 
 are covered either with granular structures or with well- 
 formed scales. The toes are nearly always provided with 
 claws, and these vary in correlation with the character of the 
 beak. Claws 1 also sometimes occur on the manus. Thus 
 Archaeopteryx and some Ostriches and Rheas have claws on 
 all three digits. Most Ostriches and Rheas, and many Anseres 
 and birds of prey, have them on the first two digits, while the 
 Secretary bird (Gypogeranus) and many fowls, ducks, and birds 
 of prey, especially kestrels, have a claw only on the pollex. 
 In the Cassowary, Emeu, Apteryx and some Ostriches and 
 Rheas only the second digit is clawed. 
 
 Claws should not be confounded with spurs, which are 
 conical horny structures developed on bony outgrowths of 
 the radial side of the carpus, metacarpus, or metatarsus. 
 They occur in a number of birds, but are most commonly 
 developed in gallinaceous birds, by which they are used for 
 fighting. A single spur occurs on the metacarpus in Mega- 
 podius, in Palamedea, in Parra jacana and in ffoplopterus 
 spinosus, the Spur-winged plover. The Derbiaii Screamer, 
 Chauna derbiana, has two metacarpal spurs, borne on the 
 first and second metacarpals. The Spur-winged goose, Plec- 
 tropterus gambensis, has a carpal spur borne on the radial 
 carpal. Metatarsal spurs are quite common. 
 
 The male Solitaire (Pezophaps) has large bony excrescences 
 on the wrist which may, like spurs, have been sheathed in 
 horn and used for fighting. 
 
 Teeth do not occur in any living birds, but conical teeth 
 imbedded in separate sockets are present in Archaeopteryx 
 and Ichthyornis, while in Hesperornis similar teeth occur im- 
 planted in continuous grooves in the mandibles and maxillae, 
 the premaxillae being toothless. 
 
 1 W. K. Parker, Phil. Trans, vol. 179, p. 385, 1888 ; and Ibis, 1888, p. 124. 
 
THE SKELETON IN BIRDS. THE ENDOSKELETON. 331 
 
 Except that teeth are partly dermal in origin, a dermal 
 exoskeleton is quite unrepresented in birds. 
 
 ENDOSKELETON. 
 
 Perhaps the most striking feature of the endoskeleton of 
 birds is its pneumaticity. In the embryo all the bones con- 
 tain marrow, but as growth proceeds this becomes replaced by 
 air to a variable extent in different forms. In all birds some 
 part of the skeleton is pneumatic. Many small birds and 
 Apteryx and Penguins among larger ones have air only in the 
 skull ; in Pigeons air is present in all the bones except the 
 caudal vertebrae, the leg bones, and those of the antibrachium 
 and manus ; in Hornbills every bone contains air. 
 
 FIG. 62. THIRD CERVICAL VERTEBRA OF AN OSTRICH (Struthio camelus). 
 x 1. A anterior, B posterior, C dorsal view (A and B after MIVART). 
 
 1. neural spine. 
 
 2. neural canal. 
 
 3. prezygapophysis. 
 
 4. postzygapophysis. 
 
 5. posterior articular surface of 
 
 centrum. 
 
 6. anterior articular surface of 
 
 centrum. 
 
 7. vertebrarterial canal. 
 
 8. hypapophysis. 
 
332 THE VERTEBRATE SKELETON. 
 
 VERTEBRAL COLUMN. 
 
 The vertebral column of birds is readily divisible into a 
 very mobile cervical region, and an extremely rigid post- 
 cervical region. In most birds the vertebral centra are with- 
 out terminal epiphyses, but these structures are found in 
 Parrots. The cervical vertebrae are generally large and vary 
 in number from eight or nine to twenty -three in Swans. 
 Except in some extinct forms, such as Ichthyornis and Apa- 
 tornis, in which they are biconcave, the centra are charac- 
 terised by having saddle-shaped articulating surfaces, which 
 in front are concave from side to side and slightly convex 
 from above downwards, while posteriorly they are convex 
 from side to side and concave from above downwards. The 
 atlas is small and ring-like, and its centrum is fused with the 
 axis forming the odontoid process. Cervical ribs are often 
 well developed, and in some of the Ratitae they remain for a 
 long time distinct from the vertebrae. 
 
 The thoracic vertebrae are distinguished from the cervical 
 by the fact that their true ribs are united to the sternum 
 by means of sternal ribs. This distinction, however, though 
 convenient, is somewhat arbitrary, as it has been shown that 
 in the fowl and gannet, two pairs of ribs which in the adult 
 are free from the sternum, are connected with it in the em- 
 bryo. When, as in the Swans, the thoracic vertebrae are 
 not all fused together, they generally have saddle-shaped 
 articulating surfaces, but sometimes, as in the Penguins, Auks 
 and Plovers, the centra are convex in front and concave be- 
 hind. The trunk vertebrae generally have well-marked neural 
 spines, while in the Divers the anterior ones have peculiar 
 bifurcating hypapophyses. 
 
 The trunk vertebrae are not readily divisible into thoracic 
 and lumbar. There are two true sacral -vertebrae, but as 
 development proceeds a number of other vertebrae become 
 fused with the true sacrals, the whole forming a large com- 
 pound sacrum. These pseudosacral vertebrae generally include 
 
THE SKELETON IN BIRDS. THE SKULL. 333 
 
 the lumbar, and some of the thoracic and caudal vertebrae. 
 Sixteen to twenty vertebrae or even more may be included 
 in the compound sacrum, and sometimes the whole of the 
 trunk vertebrae are fused together. In Archaeopteryx however 
 but five vertebrae take part in the formation of the sacrum. 
 
 In Archaeopteryx there are twenty long caudal vertebrae, 
 of which the last sixteen carry a pair of feathers apiece, but 
 in all other birds the tail is short and in the great majority 
 of cases the posterior vertebrae are fused together, forming the 
 pygostyle. In the Ratitae and Tinamidae a pygostyle is rarely 
 or imperfectly developed. In Hesperornis there are twelve 
 caudal vertebrae, six or seven of which are united by their 
 centra only, forming an imperfect pygostyle. 
 
 The free caudal vertebrae are generally amphicoelous. 
 
 THE SKULL. 
 
 The skull of all birds from Archaeopteryx onwards is 
 essentially similar, differing from the skull of reptiles mainly 
 in the extent to which the cranium is arched, and its greater 
 size in proportion to the jaws. 
 
 Most of the bones of the cranium are pneumatic, and all 
 show a marked tendency to fuse together, and have their 
 outlines obliterated by the disappearance of the sutures. The 
 several bones remain longest distinguishable in the Ratitae 
 and to a less extent in the Penguins. The orbits are very 
 large and lie almost entirely in front of the cranium ; they 
 are separated by an interorbital septum which is sometimes, as 
 in Chauna and Scythrops, very complete, sometimes, as in 
 Hornbills and the Common Heron, very slightly developed. 
 As a general rule the sclerotic is cartilaginous. 
 
 The anterior nares are almost always situated far back 
 at the base of the beak near the orbits, but in Apteryx they 
 are placed right at its extremity. In Phororhacos they are 
 placed very high up on the enormous beak and are not separ- 
 ated by any bony partition. 
 
334 THE VERTEBRATE SKELETON. 
 
 The skull of Parrots has some peculiarities. In some 
 Parrots the lachrymal sends back a process which meets the 
 postorbital process of the frontal and completes the orbit. 
 In most birds the upper beak is immovably fixed, but in 
 some it is attached to the cranium, only by the nasals and 
 by flexible processes of the premaxillae, so that by this 
 means a kind of elastic joint is established and the beak is able 
 to be moved on the cranium. In the Parrots and Opisthocomus 
 there is a regular highly movable joint. 
 
 In Cassowaries the fronto-nasal region of the skull is pro- 
 duced into an enormous bony crest, and in Hornbills a 
 somewhat similar structure occurs. Although true teeth do 
 not occur in any known bird except Archaeopteryx, Hesper- 
 ornis, and Iclithyornis, another extinct bird, Odontopteryx, has 
 the margins of both jaws provided with forwardly -directed 
 tooth-like serrations, formed of part of the actual jawbone : a 
 living hawk, ffarpagus, too, has a deeply notched bill, to 
 which correspond serrations in the premaxillae. 
 
 A basipterygoid process of the basisphenoid abuts against 
 the pterygoid in Ratitae and in Tinamous, plovers, fowls, 
 pigeons, ducks and geese among Carinatae, recalling the 
 arrangement met with in many reptiles. The squamosal is 
 sometimes, as in the fowl, united with the postorbital process 
 of the frontal. In the Carinatae the quadrate articulates 
 with the cranium by a double convex surface, in the Ratitae 
 by a single one. The premaxillae are always comparatively 
 large bones, the maxillae on the contrary are small, but 
 give rise to important inwardly-projecting maxillo-palatine 
 processes. 
 
 The relations of the palatines, pterygoids, maxillae, and 
 vomers vary considerably, and on them Huxley has based a 
 classification of birds 1 . In the Ratitae and the Tinamous 
 (Tinamidae), among Carinatae the vomers unite and form a 
 large broad bone, separating the palatines and the pterygoids 
 1 See T. H. Huxley, "On the Classification of Birds," P. Z. S. 1867. 
 
THE SKELETON IN BIRDS. THE SKULL. 335 
 
 from the rostrum. Huxley uses the term Dromaeognathous 
 to describe this condition. In all other Carinatae the vomers 
 are narrow behind, and the palatines and pterygoids converge 
 posteriorly and articulate largely with the rostrum. Three 
 modifications of this condition are distinguished by Huxley, and 
 termed Schizognathous, -flSgithognathous, and Desmo- 
 gnathous. 
 
 In the Schizognathae the vomers coalesce and form a 
 narrow elongated bone, pointed in front, separating the 
 maxillo-palatine processes of the premaxillae. Waders, fowls, 
 penguins, gulls, some falcons and eagles, American vultures, 
 some herons and many owls have the Schizognathous arrange- 
 ment. In pigeons and sandgrouse there is no vomer, but the 
 other bones have the Schizognathous arrangement. 
 
 In the .flCgithognathae the arrangement is the same as in 
 the Schizognathae, except that the vomers are truncated in 
 front. Passeres, swifts, woodpeckers, humming birds, rollers, 
 hoopoes have this arrangement. 
 
 In the Desmognathae (fig. 60, A) the maxillo-palatine 
 processes approach one another in the middle line, and either 
 unite with the vomers, or unite with one another, hiding the 
 vomers. Thus a more or less complete bony roof is formed 
 across the palate. The vomers in Desmognathae are small or 
 sometimes absent. Ducks, storks, most herons, most birds of 
 prey and owls, pelicans, cormorants, parrots, and flamingoes 
 are Desmognathous. 
 
 The mandible, as in other Sauropsids, consists of a cartilage 
 bone, the articular, and a series of membrane bones, the 
 dentary, splenial, coronoid, angular, and supra-angular, de- 
 veloped round the unossified Meckel's cartilage. The dentaries 
 of the two rami are nearly always fused together, but in 
 Ichthyornis and Archaeopteryx the two rami are but loosely 
 united. There is often a fontanelle between the dentary and 
 the posterior bones, while the angle is sometimes, as in the 
 fowl, drawn out into a long curved process. 
 
336 THE VERTEBRATE SKELETON. 
 
 The hyoid apparatus (fig. 59, C) consists of a median 
 portion, and a pair of cornua. The median portion is com- 
 posed of three pieces placed end to end, and called respectively 
 the os entoglossum, the basi-hyal, and the uro-hyal. The os 
 entoglossum is shown by development to be formed by the 
 union of paired structures and is probably homologous with the 
 hyoid arch of fishes. The basihyal and the long cornua, each 
 of which is composed of two or three pieces placed end to end, 
 are homologous with the first branchial arch of fishes, while 
 the urohyal is probably homologous with the second branchial 
 arch of fishes. In Woodpeckers the cornua are enormously 
 long, and curve over the skull, extending as far forwards as 
 the anterior nares. 
 
 RIBS AND STERNUM. 
 
 Well-developed ribs are attached to the posterior cervical 
 vertebrae as well as to the thoracic vertebrae. The ribs 
 generally have uncinate processes and separate capitula and 
 tubercula, but uncinate processes are absent in Chauna Pala- 
 medea and apparently in Archaeopteryx. 
 
 The sternum (fig. 63) is greatly developed in all birds. In 
 the embryo 1 it is seen to be derived from the union of right 
 and left plates of cartilage, formed by the fusion of the ventral 
 ends of the ribs. In the Ratitae and a few Carinatae, such 
 as Stringops, it is flat, but in the great majority of birds 
 it is keeled, though the development of the keel varies greatly. 
 It is large in the flightless Penguins, which use their wings 
 for swimming. Traces of an interclavicle may occur in the 
 embryo. 
 
 PECTORAL GIRDLE. 
 
 The pectoral girdle is also strongly developed in all 
 
 Carinatae, but is much reduced in Ratitae. In some Moas 
 
 the sternum has no facet for the articulation of the coracoid, 
 
 and the pectoral girdle appears to have been entirely absent ; 
 
 1 B. Lindsay, P. Z. S. 1885, p. 684. 
 
THE SKELETON IN BIRDS. THE PECTORAL GIRDLE. 337 
 
 FIG. 63. SHOULDER-GIRDLE AND STERNUM OF 
 
 A. BLACK VULTURE (Vultur cinereus)x%. 
 
 B. PEACOCK (Pavo cristatus) x f . 
 
 C. PELICAN (Pelicanus conspic Hiatus) x ^. (All Camb. Mus.) 
 
 1. carina of the sternum. 6. surfaces for articulation with 
 
 2. coracoid. the sternal ribs. 
 
 3. scapula. 7. xiphoid processes. 
 
 4. clavicle. 8. fontanelle. 
 
 5. costal process. 
 
 R. 22 
 
338 THE VERTEBRATE SKELETON. 
 
 it is extremely small also in Apteryx. Clavicles are generally 
 well developed in the Carinatae, and small ones are found 
 also in Hesperornis, and in Emeus and Cassowaries. In the 
 other living Ratitae and in Stringops they are absent. In 
 some Parrots, Owls and Toucans they do not meet one another 
 ventrally. Clavicles are especially stout in some of the birds 
 of prey. They do not generally touch the sternum, but some- 
 times, as in the Pelican (fig. 63, C), Adjutant and Frigate bird, 
 they are fused with it. 
 
 In all Ratitae the scapula and coracoid lie almost in the 
 same straight line with one another, in the Carinatae they are 
 nearly at right angles to one another. 
 
 ANTERIOR LIMB. 
 
 In the wing of nearly all birds the ulna is thicker than the 
 radius, but in Arcliaeopteryx the two bones are equal in size. 
 In the wing of Archaeopteryx there are three long digits with 
 distinct metacarpals. In all other birds the digits are modi- 
 fied, the metacarpals being commonly fused and the phalanges 
 reduced in number. In Palamedea and some other birds the 
 metacarpus bears a bony outgrowth, which when sheathed in 
 horn forms a spur. 
 
 In most of the Ratitae and in the extinct Dodo (Didus) 
 and Solitaire (Pezophaps} the wing is very small, but the 
 .usual parts are recognisable. In Hesperornis apparently only 
 the humerus is present ; in some Moas, in which the wing is 
 imperfectly known, the presence of the humerus is indicated 
 by traces of a glenoid cavity. In most Moas the wing is 
 apparently completely absent. As compared with those in other 
 Ratitae, the wings of the Ostrich and Rhea are well developed. 
 In the Ostrich (fig. 64, B) and Rhea, as in nearly all Carinatae, 
 the manus has three digits, but in Apteryx there is only a single 
 digit, the second. The Penguins (fig. 64, A) too among Cari- 
 natae have only two digits, but in their case it is the pollex 
 which is missing. In the Ostrich the third digit has two 
 phalanges, in all other living birds it has only one phalanx. 
 
THE SKELETON IN BIRDS. THE PELVIC GIRDLE. 339 
 
 PELVIC GIRDLE. 
 
 Birds have a very large pelvis and its characters are 
 constant throughout almost the whole group. The ilium 
 
 FIG. 64. BONES OF THE EIGHT WING OF 
 
 A. A PENGUIN x ^. (Camb. Mus.) 
 
 B. OSTRICH (Stnithio camelw)x. (Partly after PARKER.) 
 
 C. GANNET (Sula alba) x ^. (Camb. Mus.) 
 
 In C the distal phalanges of the pollex and second digit have been 
 omitted. 
 1. humerus. 6. pollex. 
 
 radius. 7. second digit, 
 
 ulna. 8. cuneiform, 
 
 second metacarpal. 9. sesamoid bone, 
 
 third metacarpal. 
 
 is very large, and is united along its whole length with 
 the sacral and pseudosacral vertebrae. The ischiurn is broad 
 and extends back parallel to the ilium with which in most 
 
 222 
 
340 
 
 THE VERTEBRATE SKELETON. 
 
 FIG. 65. PELVIC GIKDLE AND SACRUM OF 
 
 A. CASSOWARY (Casuarius galeatus) x . 
 
 B. OWEN'S APTERYX (A. oweni)x%. 
 
 C. BROAD BILLED RHEA (B. macrorhyncha) x . 
 
 D. OSTRICH (Struthio camelus) x T V. (All Camb. Mus.) 
 
 1. ilium. 
 
 2. ischium. 
 
 3. pubis. 
 
 4. acetabulum. 
 
 5. pectineal process. 
 
THE SKELETON IN BIRDS. THE PELVIC GIRDLE. 341 
 
 birds it fuses posteriorly, further forward the ilio-sciatic 
 foramen separates the two bones. In Tinamus, Hesperornis, 
 Apteryx (fig. 65, B, 2), and Struthio, the ischia are separate 
 from the ilia along their whole length except at the acetabu- 
 lum ; in Phororhacos, on the other hand, the two bones are 
 fused along almost their whole length. The bone usually 
 called the pubis in birds corresponds to the post-pubis of 
 Dinosaurs and forms a long slender rod (fig. 65, 3) lying 
 parallel to the ischiurn. In many birds the ischia and pubes 
 are united at their distal ends. This is the case in the Ostrich 
 (fig. 65, D), in which the ilia and ischia are widely separated. 
 In many birds the pubis is drawn out in front into the pectineal 
 process, this is specially large in Apteryx (fig. 65, B, 5), and in 
 the embryos of many birds. It is probably homologous with the 
 pre-pubis of Dinosaurs but in some birds is formed in part by 
 the ilium. The acetabulum in birds is always perforate. 
 
 In Rhea (fig. 65, C, 2) and probably in Archaeopteryx a 
 symphysis ischii occurs, and in the ostrich alone among birds 
 there is a symphysis pubis. In Archaeopteryx all three bones 
 of the pelvis are distinct, but they are imperfectly known. In 
 Ichthyornis they are also distinct, in all other known birds 
 they are fused together to a greater or less extent. 
 
 POSTERIOR LIMB. 
 
 The tibia is always well developed and has a very strong 
 cnemial crest. The proximal tarsals are fused with its 
 distal end, the whole forming a compound bone, the tibio- 
 tarsus. There is frequently an oblique bar of bone crossing 
 the anterior face of the tibio-tarsus at the distal end, just 
 above the articular surface of the tarso-metatarsus, this is 
 absent in Ostriches and sEpyornis. The fibula though in the 
 embryo and in Archaeopteryx equal in length to the tibia, is in 
 the adult of other birds always imperfect, its proximal end 
 is often fused with the tibia, and its distal end is commonly 
 atrophied. In the Penguins however the distal end is com- 
 plete. The distal tarsals fuse with the second, third and fourth 
 
342 THE VERTEBRATE SKELETON. 
 
 metatarsals, forming a compound bone, the tarso-metatarsus. 
 The first metatarsal is nearly always free but occasionally 
 as in Phaethon it is fused with the others. No adult bird 
 has more than four digits in the pes. In the Penguins the 
 metatarsals are separate, and in many birds larger or smaller 
 gaps exist between the fused metatarsals. In most birds 
 the third metatarsal is curved so as not to lie in the same 
 plane as the others, but in the Penguins they all three lie in 
 the same plane. The metatarsals are clearly separated in 
 Archaeopteryx. In Gallinaceous birds the tarso-metatarsus 
 bears a bony outgrowth which is sheathed in horn and forms 
 a spur. 
 
 In most birds the first four toes are present while the fifth 
 is always absent. The first toe commonly has two phalanges, 
 the second three, the third four, and the fourth five. In 
 Swifts the third and fourth toes have only three phalanges. 
 Many birds, such as all Ratitae except Apteryx, have only three 
 toes, the hallux being absent ; in the Ostrich the second toe is 
 also gone with the exception of a small metatarsal, so that the 
 foot retains only the third and fourth digits, the third being 
 much the larger of the two and bearing a claw, while the 
 fourth is clawless. 
 
 In the Swifts, Cormorants, and Penguins, all four toes are 
 directed forwards. In most birds the hallux is directed back- 
 wards, and the other toes forwards. In the Owls the fourth 
 toe can be directed backwards as well as the hallux, while 
 in Parrots, Cuckoos, Woodpeckers, and Toucans the fourth toe 
 is permanently reversed. In Trogons the second toe is reversed 
 in addition to the hallux, but not the fourth. 
 
CHAPTER XX. 
 
 CLASS MAMMALIA. 
 
 THE skeleton of the members of this class, the highest of 
 the vertebrata, has the following characteristics : 
 
 Some part of the integument at some period of life is 
 always provided with hairs; these are epidermal structures 
 arising from short papillae of the Malpighiaii layer of the 
 epidermis, which at once grow inwards and become imbedded 
 in pits of the dermis. Sometimes scales or spines occur, and 
 epidermal exoskeletal structures in the form of hoofs, nails, 
 claws and horns are also characteristic. As regards the endo- 
 skeleton, the vertebral centra have terminal epiphyses except 
 in the Ornithodelphia and some Sirenia. In the skull the 
 cranial region is greatly developed as compared with that in 
 lower vertebrates, and whereas in many reptiles the true 
 cranium is largely concealed by a false roof, in mammals the 
 only relic of this secondary roof is found in the zygomatic 
 arch, and postorbital bar. In the adult all the bones except 
 the mandible, hyoid, and auditory ossicles are firmly united 
 together. The basisphenoid is well ossified, and there is no 
 parasphenoid. The pro-otic ossifies, and unites with the epi-otic 
 and opisthotic before they coalesce with any other bones. 
 
 The skull articulates with the vertebral column by means 
 of two convex occipital condyles formed mainly by the ex- 
 occipitals r and the mandible articulates with the squamosal 
 without the intervention of the quadrate. The latter is much 
 reduced, and is converted into the tympanic ring, while the 
 hyomandibular of fish is represented by the auditory ossicles 1 . 
 1 This is Gadow's view ; according to Huxley the quadrate forms the 
 
344 THE VERTEBRATE SKELETON. 
 
 The teeth are always attached to the maxillae, premaxillae 
 and mandibles, never to any of the other bones. They are 
 nearly always implanted in distinct sockets, and are hardly ever 
 ankylosed to the bone. The teeth of mammals are generally 
 markedly heterodont, four forms, incisors, canines, premolars, 
 and molars, being commonly distinguishable. Some mammals 
 are monophyodont, having only a single set of teeth, but the 
 great majority are diphyodont, having two sets, a deciduous or 
 milk dentition, and a permanent dentition. 
 
 The incisors, the front teeth, are simple, one-rooted, adapted 
 for cutting, and are nearly always borne by the premaxillae. 
 Next come the canines, one on each side in each jaw. They are 
 generally large teeth adapted for tearing or holding, and get 
 their name from the fact that they are largely developed in the 
 dog. The remaining teeth form the grinding series, the more 
 posterior of them, being the molars, which are not preceded by 
 milk teeth '. Between the molars and the canines are the pre- 
 molars, which do as a rule have milk or deciduous predecessors, 
 though very frequently the first of them is without a milk 
 predecessor. 
 
 In describing the dentition of any mammal, for the sake of 
 brevity a formula is generally made use of. Thus, the typical 
 mammalian dentition is expressed by the formula 
 .31 4 3 11 
 *3 C T^4 m <ril' 
 
 giving twenty-two teeth 011 each side, or forty-four altogether 2 . 
 The incisors are represented by i, the canines by c, the pre- 
 molars by p or pm, and the molars by m. The numbers above 
 the lines represent the teeth in the upper jaw, those below 
 
 malleus ; according to Baur it forms the zygomatic process of the squa- 
 mosal, and according to Broom the interarticular mandibular cartilage. 
 
 1 According to Leche, MorphoL Jahrb. xix. p. 502, the molar teeth 
 belong morphologically to the first series, i.e. they are milk teeth without 
 vertical successors. 
 
 2 The researches of Bateson, P. Z. S. 1892, p. 102, have shown that 
 cases of individual variation in the number of teeth are common. 
 
MAMMALIA. 345 
 
 the lines the teeth in the lower jaw. The milk dentition is 
 expressed by a similar formula with d (deciduous) prefixed to 
 the letter expressing the nature of the tooth. 
 
 The following terms are of frequent use as characterising 
 certain forms of the grinding surfaces of teeth, and it will be 
 well to define them at once. 
 
 Bunodont is a term applied to teeth with broad crowns 
 raised into rounded tubercles, e.g. the grinding teeth of Pigs 
 and Hippopotami ; 
 
 Bilophodont to teeth marked by a simple pair of trans- 
 verse ridges, with or without a third ridge running along the 
 outer border of the tooth at right angles to the other two, 
 e.g. the grinding teeth of Lopkiodon, Kangaroo, Manatee, 
 Tapir, Dinotheriu7n ; 
 
 Selenodont to teeth marked by crescentic ridges running 
 from the anterior towards the posterior end of the tooth, e.g. 
 the grinding teeth of the Ox and Sheep. 
 
 Teeth whose crowns are low so that their whole structure 
 is visible from the grinding surface are called brachydont, while 
 those with higher crowns, in which the bases of the infoldings 
 of enamel are invisible from the grinding surface are said to 
 be hypsodont. Bunodont teeth are brachydont, the teeth of the 
 Horse and Ox are hypsodont. 
 
 Passing now to the appendicular skeleton the shoulder 
 girdle differs markedly from that of Sauropsids in the fact that 
 the coracoid, except in the Ornithodelphia, is greatly reduced, 
 generally forming only a small process on the scapula. In the 
 pelvis the pubes meet in a ventral symphysis, except in some 
 Insectivora and Chiroptera. In many mammals a fourth pelvic 
 element, the acetabular bone, is distinguishable. The ankle 
 joint is cruro-tarsal, or situated between the proximal tarsal 
 bones and the tibia and fibula. Carpalia 4 and 5 are united 
 forming the unciform ; and the ulnar sesamoid bone or pisiform 
 is generally well developed. In the proximal row of tarsal ele- 
 ments there are only two bones, the calcaneum and astragalus. 
 
346 THE VERTEBRATE SKELETON. 
 
 Of these the calcaneum is the fibulare, and the astragalus is 
 generally regarded as the tibiale and intermedium fused 1 . 
 
 Subclass I. ORNITHODELPHIA OR PROTOTHERIA. 
 
 This sub-class contains only a single order, the Monotre- 
 mata, and the following characteristics are equally applicable 
 to the subclass and to the order. The vertebral centra have 
 no epiphyses, and the odontoid process remains for a long time 
 free from the centrum of the second vertebra. With the 
 exception of the atlas of Echidna the cervical vertebrae are 
 without zygapophyses. The cranial walls are smooth and 
 rounded, and the sutures between the several bones early 
 become completely obliterated as in birds. The mandible is a 
 very slight structure, with no ascending ramus, and with the 
 coronoid process (see p. 398) and angle rudimentary. The 
 auditory ossicles show a low state of development. The tuber- 
 cula of the ribs articulate with the sides of the centra of the 
 thoracic vertebrae, not with the transverse processes. Some of 
 the cervical ribs remain for a long time separate from the verte- 
 brae. Well ossified sternal ribs occur. No true teeth are present 
 in the adult. The young Ornithorhynchus has functional molar 
 teeth, but in the adult their place is taken by horny plates. 
 In the Echidnidae neither teeth nor horny plates occur. 
 
 The coracoid (fig. 66, 3) is complete and well developed, 
 and articulates with the sternum. A precoracoid (epicoracoid) 
 occurs in front of the coracoid, and there is a large interclavicle 
 (fig. 66, 6). The ridge on the scapula, corresponding to the 
 spine of other mammals, is situated on the anterior border 
 instead of in the middle of the outer surface. Epipubic bones 
 are present. In the Echidnidae, but not in Ornithorkynchus*, 
 
 1 Baur, however, suggests (Anat. Anz. vol. iv. 1889), that a tibial 
 sesamoid found in Procavia, many rodents, edentates and Ornithorhyn- 
 chus is a vestigial tibiale, and that the astragalus is the intermedium. 
 
 2 This perforation of the acetabulum in Echidna is a secondary 
 character occurring late in development, and consequently is not of 
 phylogenetic importance. 
 
MAMMALIA. ORNITHODELPHIA. 
 
 347 
 
 the central portion of the acetabulum is unossified as in birds. 
 The humerus has a prominent deltoid crest ; its ends are much 
 expanded, and the distal end is pierced by an ent-epicondylar 
 
 FIG. 66. VENTRAL VIEW OF THE SHOULDER-GIRDLE AND STERNUM OF 
 A DUCKBILL (Ornithorhynchus paradoxus) x f (after PARKER). 
 
 1 and 2. scapula. 8. presternum. 
 
 3. coracoid. 9. third segment of mesoster- 
 
 4. precoracoid (epicoracoid). num. 
 
 5. glenoid cavity. 10. sternal rib. 
 
 6. interclavicle. 11. intermediate rib. 
 
 7. clavicle. 12. vertebral rib. 
 
 foramen. The fibula has a broad proximal process resembling 
 an olecranon. The limbs and their girdles bear a striking 
 resemblance to those of some Theromorphous reptiles. 
 
 The order Monotremata includes only two living families, 
 the Echidnidae and Ornithorhynchidae. 
 
348 THE VERTEBRATE SKELETON. 
 
 MAMMALIA 1 . 
 
 It will be well here to briefly refer to certain mammals 
 of small size, the remains of which have been found in de- 
 posits of Mesozoic age. In the great majority of cases they 
 are known only by the lower jaw, or sometimes only by isolated 
 teeth. A large number of them are commonly grouped 
 together as the Multituberculata, and are sometimes, partly 
 owing to the resemblance of their teeth to those of Ornitho- 
 rhynchus, placed with the Prototheria, sometimes between the 
 Prototheria and the Metatheria. They are characterised by 
 having a single pair of large incisors in the lower jaw, and one 
 large with one or two smaller incisors in each . premaxilla. 
 The lower canines are very small or altogether wanting. The 
 incisors are separated by a diastema from the grinding teeth, 
 which are sometimes (Tritylodon) characterised by the posses- 
 sion of longitudinal rows of little tubercles separated by 
 grooves, sometimes by having the premolars provided with 
 high cutting edges, whose surfaces are obliquely grooved. 
 Some of the Mesozoic mammals found associated with the 
 Multituberculata, have however a dentition of an altogether 
 different type, with at least three lower incisors, well developed 
 canines and premolars, and numerous molars with peculiar 
 three-cusped or tritubercular grinding surfaces. These mam- 
 mals, one of the best known of which is Phascolotherium, are 
 commonly separated from the Multituberculata, and are divided 
 by Osborn into two groups, one allied to the Marsupials, and 
 one to the Insectivores. The group showing Marsupial affinities 
 is further subdivided into carnivorous, omnivorous, and herbi- 
 vorous subgroups. The members of both groups commonly 
 
 1 See K. Owen, "Monograph of the Fossil Mammalia of the Mesozoic 
 Formation," Pal. Soc. Hon. 1871. 
 
 H. F. Osborn, "Structure and Affinities of Mesozoic Mammals," 
 J. ofPhilad. Acad. 1888, vol. ix. 
 
 O. C. Marsh, "Jurassic Mammals," Amer. J. Sci. 1878 et seq. 
 
MAMMALIA. DIDELPHIA. 349 
 
 have four premolars, and six to eight molars in each mandibular 
 ramus. 
 
 Subclass IL DIDELPHIA OR METATHERIA. 
 
 This subclass, like the previous one, contains only a single 
 order, viz. the Marsupialia 1 ; but the forms referable to it are 
 far more numerous than in the case of the Monotremata. 
 
 The integument is always furry, and the teeth are always 
 differentiated into incisors, canines, premolars and molars. 
 Except in Phascolomys, the number of incisors in the upper 
 and lower jaws is never equal, and the number in the upper 
 usually exceeds that in the lower jaw. There is no such 
 regular succession and displacement of teeth as in most mam- 
 mals. Sometimes the anterior teeth are diphyoclont, and as a 
 general rule the tooth commonly regarded as the last premolar 
 is preceded by a milk tooth. The majority of the permanent 
 teeth of most Marsupials are regarded as belonging to the milk 
 series for two reasons, (1) they are developed from the more 
 superficial tissues of the jaws, (2) a second set, the permanent 
 teeth, begin to develop as outgrowths from them, but after 
 wards become aborted 2 . 
 
 The odontoid process at an early stage becomes fused with 
 the centrum of the second cervical vertebra, and the number 
 of thoraco-lumbar vertebrae is always nineteen. The skull has 
 several characteristic features. The tympanic bone remains 
 permanently distinct, and the anterior boundary of the tym- 
 panic cavity is formed by the alisphenoid. The carotid canal 
 perforates the basisphenoid, and the lachrymal canal opens 
 either outside the orbit or at its margin. There are generally 
 large vacuities in the palate. The angle of the mandible is 
 (except in Tarsipes) more or less inflected ; and as a rule the 
 jugal furnishes part of the articular surface for the mandible. 
 
 1 See Oldfield Thomas, Brit. Mus. Cat. of Marsupialia and Monotre- 
 mata (1888). 
 
 2 W. Kiikenthal, Anat. Anz. vi. p. 364, 1891. C. Rose, Anat. Anz. 
 vn. p. 639. 
 
350 THE VERTEBRATE SKELETON. 
 
 There is no precoracoid (epicoracoid) or interclavicle, and the 
 coracoid is reduced to form a mere process of the scapula, not 
 coming near the sternum. 
 
 Epipubic, or so-called marsupial bones 1 , nearly always 
 occur, and a fourth pelvic element, the acetabular bone, is 
 frequently developed. The fibula is always complete at its 
 distal end, sometimes it is fused with the tibia, but often it is 
 not only free but is capable of a rotatory movement on the 
 tibia. This is the case in the families Phascolomyidae, Didel- 
 phyidae, and Phalangeridae. 
 
 The Marsupialia can be subdivided into two main groups, 
 according to the character of the teeth : 
 
 1. POLYPROTODONTIA. 
 
 In this group the incisors are small, subequal and nume- 
 rous, not less than . The canines are larger than the 
 incisors, and the molars have sharp cusps. The members of 
 this group are all more or less carnivorous or insectivorous. 
 The group includes the families Didelphyidae, Dasyuridae, 
 Peramelidae, and Notary ctidae a . 
 
 2. DlPROTODONTIA. 
 
 In this group the incisors do not exceed , and are usually 
 f , occasionally i. The first upper and lower incisors are large 
 and cutting. The lower canines are always small or absent, 
 and so in most cases are the upper canines. The molars have 
 bluntly tuberculated, or transversely ridged crowns. The 
 group includes the families Phascolomyidae, Phalangeridae, 
 Macropodidae, and Epanorthidae. 
 
 1 These bones however have no connection with the marsupium, 
 being nearly equally developed in both male and female. They are 
 simply sesamoid bones forming ossifications in the. inner tendon of the 
 external oblique muscle, and are developed as supports for the abdominal 
 wall. Very similar structures have been independently developed in 
 various Amphibians, Reptiles and monodelphian Mammals. See W. Leche, 
 Biol. Foren. in. p. 120. 
 
 2 See H. Gadow, P. Z. S. 1892, p. 361. 
 
MAMMALIA. EDENTATA. 351 
 
 Subclass III. MONODELPHIA OR EUTHERIA. 
 
 This great group includes all the Mammalia except the 
 orders Monotremata and Marsupialia. Coming to their 
 general characteristics as in the Didelphia the odontoid 
 process and cervical ribs early become fused with the centra 
 which bear them, while the coracoid is reduced so as to form a 
 mere process on the scapula, and there is no precoracoid (epi- 
 coracoid), such as is found in Ornithodelphia. Clavicles may 
 be present or absent ; when fully developed they articulate 
 with the sternum, usually directly, but occasionally, as in some 
 Rodents and Insectivores, through the remains of the sternal 
 end of the precoracoid. There is never any interclavicle in 
 the adult, though sometimes traces of it occur during develop- 
 ment. In the pelvis the acetahula are imperforatc ; and well- 
 developed epipubic bones are never found in the adult, 
 though traces of them occur in some Carnivores and foetal 
 Ungulates. 
 
 Order 1. EDENTATA '. 
 
 Teeth are not, as the name of the order seems to imply, 
 always wanting; and sometimes they are very numerous. 
 They are, however, always imperfect, and, with very few 
 exceptions, are homodont and monophyodont. They have 
 persistent pulps, and so grow indefinitely and are never rooted. 
 In all living forms they are without enamel, consisting merely 
 of dentine and cement, and are never found in the front part of 
 the mouth in the situation occupied by the incisors of other 
 mammals. These characters derived from the teeth are the 
 only ones common to the various members of the order, 
 
 1 See W. H. Flower, "On the Mutual Affinities of the Animals com- 
 posing the order Edentata," P. Z. S. 1882, p. 358. For the fossil 
 Edentates of N. America see E. Cope, Amer. Natural. 1889; for those of 
 S. America see various papers by F. Ameghino, H. Burmeister and E. 
 Owen. Also T. H. Huxley, "On the Osteology of Glyptodon," Phil. 
 Trans. 1865. 
 
352 THE VERTEBRATE SKELETON. 
 
 which includes the living sloths, anteaters, armadillos, pangolins 
 and aard varks, together with various extinct forms, chiefly 
 found in beds of late tertiary age in both North and South 
 America, the best known being the Megatheridae and Glypto- 
 donts. 
 
 Order 2. SiRENiA 1 . 
 
 The skeleton of these animals has a general fish-like form, 
 in correlation with their purely aquatic habits. The fore limbs 
 have the form of paddles, but the number of phalanges is not 
 increased beyond the normal. There are no external traces of 
 hind limbs. 
 
 The whole skeleton and especially the skull and ribs is 
 remarkably massive and heavy. The dentition varies ; in the 
 two living genera Manatus and Halicore, incisor and molar 
 teeth are present, in one extinct genus, Rhytina, teeth are 
 entirely absent, while in another, Halitherium^ the dentition 
 is more decidedly heterodont than in living forms. In the 
 two living genera the dentition is monophyodont, but in 
 Halitherium the anterior grinding teeth are preceded by 
 milk teeth. The tongue and anterior part of the palate and 
 lower jaw are covered with roughened horny plates. The 
 skull is noticeable for the size and backward position of the 
 anterior nares, also for the absence or small size of the nasal 
 bones. There is no union of certain of the vertebrae to form 
 a sacrum, and in living forms the centra are not terminated by 
 well-formed epiphyses 2 . 
 
 The cervical vertebrae are much compressed, but they are 
 never ankylosed together. In Manatus there are only six 
 cervical vertebrae. The caudal vertebrae have well-developed 
 chevron bones. The humerus is distinctly articulated to the 
 
 1 See J. F. Brandt, Symbolae Sirenologicae, St Petersburg, 1846, 1861, 
 1868. 
 
 2 Epiphyses are fully developed in Halitherium, and traces occur in 
 Manatus. 
 
MAMMALIA. CETACEA. 353 
 
 radius and ulna, and these two bones are about equally de- 
 veloped, and are often fused together. There are no clavicles, 
 and the pelvis is vestigial, consisting of a pair of somewhat 
 cylindrical bones suspended at some distance from the ver- 
 tebral column. In living forms there is no trace of a posterior 
 limb, but in Halitherium there is a vestigial femur connected 
 with each half of the pelvis. 
 
 Order 3. CETACEA 1 . 
 
 In these mammals the general form is more fish-like than is 
 the case even in the Sirenia. The skin is generally almost 
 completely naked, but hairs are sometimes present in the neigh- 
 bourhood of the mouth, especially in the foetus. In some 
 Odontoceti vestiges of dermal ossicles have been described, and 
 in Zeuglodon the back was probably protected by dermal plates. 
 The anterior limbs have the form of flattened paddles, showing 
 no trace of nails, the posterior limb bones are quite vestigial 
 or absent, and there is never any external sign of the limb. 
 Teeth are always present at some period of the life history, but 
 in the whalebone whales they are only present during foetal 
 life, their place in the adult animal being taken by horny 
 plates of baleen. In all living forms the teeth are simple 
 and uniform structures without enamel ; they have single 
 roots, and the alveoli in which they are imbedded are often 
 incompletely separated from one another. As in some forms 
 traces of a replacing dentition have been described, it has 
 been concluded that the functional teeth of Cetacea belong to 
 the milk dentition. 
 
 The texture of the bones is spongy. The cervical vertebrae 
 are very short, and though originally seven in number, are in 
 many forms completely fused, forming one solid mass (fig. 67). 
 The odontoid process of the axis is short and blunt, or may 
 
 1 See P. J. van Beneden and P. Gervais, Osteographie des Cetaces, 
 186980. 
 
 K. 23 
 
354 
 
 THE VERTEBRATE SKELETON. 
 
 be completely wanting. The lumbar and caudal vertebrae are 
 large and numerous, and as zygapophyses are absent, are very 
 
 FIG. 67. 
 
 --3 
 
 CERVICAL VERTEBRAE OP A CA'ING WHALE (Globicephalus 
 melas) x . (Camb. Mus.) 
 
 1. centrum of seventh cervical 
 
 vertebra. 
 
 2. neural arch of seventh cer- 
 
 vical vertebra. 
 
 3. transverse process of atlas. 
 
 foramen for exit of first spinal 
 
 nerve. 
 
 transverse process of axis, 
 fused neural spines of atlas 
 
 and axis. 
 
 freely movable on one another ; zygapophyses are also absent 
 from the posterior thoracic vertebrae. The lumbar vertebrae 
 are sometimes more numerous than the thoracic. The epi- 
 physes are very distinct, and do not unite with the centra till 
 the animal is quite adult. None of the vertebrae are united 
 to form a sacrum, but the caudal vertebrae have large chevron 
 bones. 
 
 The skull is peculiarly modified; the bones forming the 
 occipital segment show a specially strong development, and 
 the cranial cavity is short, high, and almost spherical. The 
 supra-occipital is very large and rises up to meet the frontals, 
 
MAMMALIA. GETACEA. 355 
 
 thus with the interparietal completely separating the parietals 
 from one another. 
 
 The frontals are expanded, forming large bony plates, 
 which roof over the orbits. The zygomatic process of the 
 squamosal is extremely large and extends forwards to meet 
 the supra-orbital process of the frontal; the zygomatic process 
 of the jugal is on the contrary very slender. The face is 
 drawn out into a long rostrum, formed of the maxillae and 
 premaxillae surrounding the vomer and the mesethmoid 
 cartilage. The maxillae are specially large, and extend back- 
 wards so as to partially overlap the frontals. The nasals are 
 always small, and the anterior nares open upwards between 
 the cranium and rostrum. The periotics are loosely connected 
 with the other bones of the skull and the tyrnpanics are com- 
 monly large and dense. The mandible has hardly any coronoid 
 process, and the condyles are at its posterior end. 
 
 There are no clavicles, but the scapula and humerus are 
 well developed. The humerus moves freely in the glenoid 
 cavity, but all the other articulations of the anterior limb are 
 imperfect ; the various bones have flattened ends, and are 
 connected with one another by fibrous tissue, which allows of 
 hardly any movement. Frequently the carpus is imperfectly 
 ossified. 
 
 The number of digits in the manus is generally five, some- 
 times four, and when there are four digits it is the third and 
 not the first that is suppressed. The number of phalanges 
 in the second and third digits almost always exceeds that 
 which is normal in mammals, and the phalanges are also 
 remarkable for having epiphyses at both ends. The pelvis is 
 represented by two small bones which lie suspended horizon- 
 tally at some distance below the vertebral column ; in some 
 cases vestiges of the skeleton of the hind limb are attached to 
 thenl. 
 
 The Cetacea are divided into three suborders. 
 
 232 
 
356 THE VERTEBRATE SKELETON. 
 
 Suborder (1). ARCHAEOCETI. 
 
 The members of this group are extinct; they differ from 
 all living Cetacea in having the dentition heterodont and in 
 the fact that the back was probably protected by dermal 
 plates. The skull is elongated and depressed, and the brain 
 cavity is very small. The temporal fossae are large, and 
 there is a strong sagittal crest. The nasals and premaxillae 
 are a good deal larger than they are in living Cetacea, and 
 the anterior nares are usually far forward. The cervical ver- 
 tebrae are not fused with one another, and the lumbar 
 vertebrae are unusually elongated. 
 
 The limbs are very imperfectly known, but while the 
 humerus is much longer than in modern Cetaceans, it is 
 nevertheless flattened distally, indicating that the limb was 
 paddle-like, and that there was scarcely any free movement 
 between the fore-arm and upper arm. 
 
 The best known genus is Zeuglodon, which is found in 
 beds of Eocene age in various parts of Europe, and in Alabama. 
 
 Suborder (2). MYSTACOCETI or BALAENOIDEA. 
 
 These are the Whalebone Whales or True Whales. 
 
 Calcified teeth representing the milk dentition occur in the 
 foetus, but the teeth are never functional, and always dis- 
 appear before the close of foetal life. There is a definite 
 though small olfactory fossa. The palate is provided with 
 plates of baleen or whalebone. The skull is symmetrical, and 
 is extremely large in proportion to the body. The nasals are 
 moderately well developed, and the maxillae do not overlap 
 the orbital processes of the f rentals. The lachrymals are small 
 and distinct from the jugals. The tympanics are ankylosed 
 to the periotics, and the rami of the mandible do not meet in 
 a true symphysis. The ribs articulate only with the transverse 
 processes, and the capitula are absent or imperfectly deve- 
 loped. Only one pair of ribs meets the sternum, which is 
 composed of a single piece. 
 
MAMMALIA. CETACEA. 357 
 
 The group includes among others the Right whale (Balaena), 
 Humpbacked whale (Megaptera), and Rorqual (Balaenoptera). 
 
 Suborder (3). ODONTOCETI. 
 
 Teeth always exist after birth and baleen is never present. 
 The teeth are generally numerous, but are sometimes few and 
 deciduous ; the dentition is homodont (except in Squalodori). 
 The dorsal surface of the skull is somewhat asymmetrical, 
 there is no trace of an olfactory fossa, the nasals are quite 
 rudimentary, and the hind ends of the maxillae cover part of 
 the frontals ; in all these respects the skull differs from that 
 of the Mystacoceti. The lachrymal may either be united to 
 the jugal or may be large and distinct. The tympanic is 
 not ankylosed to the periotic. The rami of the mandible are 
 nearly straight and become united in a long symphysis. Some 
 of the ribs have well developed capitula articulating with the 
 vertebral centra. The sternum is almost always composed of 
 several pieces as in other mammals, and several pairs of ribs 
 are connected with it. There are always five digits to the 
 manus, though the first and fifth are usually very little 
 developed. 
 
 The suborder includes the Sperm Whale (Physeter), Nar- 
 whal (Monodon), Dolphin (Delphinus), Porpoise (Phocoena), 
 and many other living forms as well as the extinct Squalodon 
 which differs from the other members of the suborder in its 
 heterodont dentition. 
 
 Order 4. UNGULATA. 
 
 This order includes a great and somewhat heterogeneous 
 group of animals, a large proportion of which are extinct. 
 They all (except certain extinct forms) agree in having the 
 ends of the digits either encased in hoofs or provided with 
 broad flat nails. The teeth are markedly heterodont and 
 diphyodont, and the molars have broad crowns with tubercu- 
 lated or ridged surfaces. Clavicles are never present in the 
 
358 THE VERTEBRATE SKELETON. 
 
 adult except in a few generalised extinct forms such as Typo- 
 ihsrium, and it is only recently that vestigial clavicles have 
 been discovered in the embryo 1 . The scaphoid and lunar are 
 always distinct. 
 
 The order Ungulata may be subdivided into two main 
 groups, Ungulata vera and Subungulata. 
 
 Section I. UNGULATA VERA S . 
 
 The cervical vertebrae except the atlas are generally opis- 
 thocoelous. The feet are never plantigrade*. In all the 
 living and the great majority of the extinct forms the digits 
 do not exceed four, the first being suppressed. In the carpus 
 the os magnum articulates freely with the scaphoid, and is 
 separated from the cuneiform by the lunar and unciform. In 
 the tarsus the cuboid articulates with the astragalus as well as 
 with the calcaneum, and the proximal surface of the astra- 
 galus is marked by a pulley-like groove. All the bones of 
 the carpus and tarsus strongly interlock. These characters 
 with regard to the carpus and tarsus do not hold in Macrau- 
 chenia and its allies. The humerus never has an ent-epicon- 
 dylar foramen. 
 
 The group is divided into two very distinct suborders : 
 
 Suborder (1). ARTIODACTYLA. 
 
 The Artiodactyla have a number of well marked charac- 
 ters, one of the most obvious being the fact that many of the 
 most characteristic forms have large paired outgrowths on the 
 frontal bones. These may be (1) solid deciduous bony antlers, 
 or (2) more or less hollow bony outgrowths which are sheathed 
 with permanently growing horn. 
 
 1 H. Wincza, Morphol. Jahrb. xvi., p. 647. 
 
 2 See M. Pavlow, "Etudes sur 1'histoire paleontologique des Ongules." 
 Bull. Soc. Moscow, 18871890. 
 
 3 In a plantigrade animal the whole of the foot is placed on the 
 ground in walking. A digiti grade animal places only its toes on the 
 ground. An intermediate condition is distinguished by the term sub- 
 plantigrade. 
 
MAMMALIA. ARTIODACTYLA. 359 
 
 The premolar and molar teeth are usually dissimilar, the 
 premolars being one-lobed and the molars two-lobed; the last 
 lower molar of both the milk and permanent dentitions is 
 almost always three-lobed. 
 
 The grinding surfaces of the molar teeth have a tendency 
 to assume one of two forms. In the Pigs and their allies the 
 crowns are bunodont 1 , while in the more highly specialised 
 Ruminants the crowns are selenodont 1 . The nasals are not 
 expanded posteriorly, and there is no alisphenoid canal 2 . The 
 thoraco-lumbar vertebrae are always nineteen. The symphysis 
 of the ischia and pubes is very elongated, and the femur has 
 no third trochanter. The limbs never have more than four 
 digits, and are symmetrical about a line drawn between the 
 third and fourth digits ; the digits, on the other hand, are 
 never symmetrical in themselves. The astragalus has pulley- 
 like surfaces both proximally and distally, and articulates with 
 the navicular and cuboid by two nearly equal facets. The 
 calcaneum articulates with the lower end of the fibula when 
 that bone is fully developed. 
 
 In the Artiodactyla are included the following living 
 groups : 
 
 a. Suina. Pigs and Hippopotami. 
 
 b. Tylopoda. Camels and Llamas. 
 
 c. Tragulina. Chevrotains. 
 
 d. Ruminantia or Pecora. Deer, giraffes, oxen, sheep 
 and antelopes. 
 
 Suborder (2). PfiRissoDACTYLA 3 . 
 
 In this group there are never any bony outgrowths from 
 the frontals. The grinding teeth form a continuous series, 
 the posterior premolars resembling the molars in complexity, 
 and the last lower molar generally has no third lobe. The 
 
 1 See p. 345. 2 See p. 401. 
 
 3 See E. D. Cope, "The Perissodactyla," Amer. Natural, 1887. 
 
360 THE VERTEBRATE SKELETON. 
 
 cervical vertebrae with the exception of the atlas almost 
 always have markedly opisthocoelous centra, but in Macrau- 
 chenia they are flat. The nasals are expanded posteriorly, and 
 an alisphenoid canal is present. The thoraco-lumbar vertebrae 
 are never less than twenty-two in number and are usually 
 twenty-three. The femur has a third trochanter (except in 
 Chalicotherium). The third digit of the manus and pes is 
 symmetrical in itself, and larger than the others, and in some 
 cases the other digits are quite vestigial. The number of the 
 digits of the pes is always odd. The astragalus is abruptly 
 truncated distally, and the facet by which it articulates with 
 the cuboid, is much smaller than that by which it articulates 
 with the navicular. The calcaneum does not articulate with 
 the fibula, except in Macrauchenia, The group includes many 
 extinct forms, and the living families of the Tapirs, Horses 
 and Asses, and Rhinoceroses. 
 
 Section II. SUBUNGULATA. 
 
 In this group is placed a heterogeneous collection of 
 animals, the great majority of which are extinct. There is 
 really no characteristic which is common to them all, and 
 which serves to distinguish them as a group from the Ungulata 
 vera. But the most distinctive character common to the 
 greatest number of them is to be found in the carpus, whose 
 bones in most cases retain their primitive relation to one 
 another, the os magnum articulating with the lunar and some- 
 times just meeting the cuneiform, but in living forms at any 
 rate not articulating with the scaphoid. The feet frequently 
 have five functional digits, and may be plantigrade. The 
 proximal surface of the astragalus is generally flattened in- 
 stead of being pulley -like as in Ungulata vera. 
 
MAMMALIA. SUBUNGULATA. 361 
 
 Suborder (1). TOXODONTIA. 
 
 This suborder includes some very aberrant extinct South 
 American ungulates, which have characters recalling the 
 Proboscidea, both groups of Ungulata vera, and the Rodentia. 
 The limbs are subplantigrade or digitigrade, and the digits 
 are three, rarely five, in number, the third being most 
 developed. The carpus resembles that of the Ungulata vera, 
 in that the bones interlock and the magnum articulates with 
 the scaphoid. In the tarsus, however, the bones do not 
 interlock. The astragalus has a pulley-like proximal sur- 
 face (except in Astrapotherium, in which it is flat), and 
 articulates only with the navicular, not meeting the cuboid. 
 The calcaneum has a large facet for articulation with the 
 fibula, as in Artiodactyla. There is no alisphenoid canal, and 
 the orbit is confluent with the temporal fossa. Some of the 
 forms (e.g. Nesodon) referred to this group have the typical 
 mammalian series of forty-four teeth, but in others the canines 
 are undeveloped. In Toxodon all the cheek-teeth have persist- 
 ent pulps, while in Nesodon and Astrapotherium they are rooted. 
 A clavicle is sometimes present (Typotherium), and the femur 
 sometimes has a third trochanter (Typotherium and Astra- 
 potherium), sometimes is without one (Toxodon). 
 
 The remains of these curious Ungulates have been found 
 in beds of late Tertiary age in South America. 
 
 Suborder (2). CONDYLARTHRA 1 . 
 
 This group includes some comparatively small extinct 
 ungulates, which are best known from the Lower Eocene of 
 Wyoming, though their remains have also been found in 
 deposits of similar age in France and Switzerland. Their 
 
 1 See E. D. Cope, "The Condylarthra," Amer. Natural., 1884, and 
 "Synopsis of the Vertebrates of the Puerco series," Tr. Amer. Phil. Soc., 
 1888. 0. C. Marsh, "A new order of extinct Eocene Mammals (Meso- 
 dactyla)," Amer. J. Sci., 1892. 
 
362 THE VERTEBRATE SKELETON. 
 
 characters are little specialised, and they show relationship on 
 the one hand to the Ungulata vera and on the other to the 
 Hyracoidea. They also have characters allying them to the 
 Carnivora. They generally have the typical mammalian 
 series of forty-four teeth, the molars being brachydont and 
 generally bunodont. The premolars are more simple than the 
 molars. The limbs are plantigrade, and have five digits with 
 rather pointed ungual phalanges. The os magnum, as in living 
 Subungulates, articulates with the lunar, not reaching the 
 scaphoid. The astragalus has an elongated neck, a pulley-like 
 proximal and a convex distal articular surface, and does not 
 articulate with the cuboid. The humerus has an ent-epicondylar 
 foramen, and the femur has a third trochanter. The best 
 known genus is Phenacodus ; it is perhaps the most primitive 
 ungulate whose skeleton is thoroughly well known, and is of 
 special interest from the fact that it is regarded as the lowest 
 stage in the evolutionary series of the horse. Its remains 
 are found in the Lower Eocene of Wyoming. 
 
 Suborder (3). HYRACOIDEA 1 . 
 
 This group of animals is very isolated, having no very close 
 allies, either living or extinct. The digits are provided with 
 flat nails, except the second digit of the pes, which is clawed. 
 Canine teeth are absent, and the dental formula is usually 
 
 given as i -, c ^, pm -, ra ^. The upper incisors are long 
 
 and curved, and have persistent pulps as in Rodents ; their 
 terminations are, however, pointed, not chisel-shaped, as in 
 Rodents. The lower incisors have pectinated edges. The 
 grinding teeth have a pattern much like that in Rhinoceros. 
 In the skull (fig. 83) the postorbital processes of the frontal 
 and jugal almost or quite meet. The jugal forms part of the 
 
 1 See 0. Thomas, "On the species of Hyracoidea," P. Z. S., 1892, 
 p. 50. 
 
MAMMALIA. SUBUNGULATA. 363 
 
 glenoid cavity for articulation with the mandible, and also 
 extends forwards so as to meet the lachrymal. There is an 
 alisphenoid canal. There are as many as twenty-one or twenty- 
 two thoracic vertebrae, and the number of thoraco- lumbar 
 vertebrae reaches twenty-eight or thirty. There are no clavi- 
 cles, and the scapula has no acromion ; the coracoid process 
 is, however, well developed. The ulna is complete. In the 
 manus the second, third and fourth digits are approximately 
 equal in size, the fifth is smaller, and the first is vestigial. 
 The femur has a slight ridge representing the third trochanter. 
 The fibula is complete, but is generally fused with the tibia 
 proximally. There is a complicated articulation between the 
 tibia and astragalus, which has a pulley-like proximal surface. 
 In the pes the three middle digits are well developed, but there 
 is no trace of a hallux, and the fifth digit is represented only 
 by a vestigial metatarsal. 
 
 The only representatives of the suborder are some small 
 animals belonging to the genus Procavia (Hyrax), which is 
 found in Africa and Syria ; some of the species are by many 
 authors placed in a distinct genus Dendrohyrax. 
 
 Suborder (4). AMBLYPODA 1 . 
 
 This suborder includes a number of primitive extinct 
 Ungulates, many of which are of great size. Their most 
 distinguishing characteristics are afforded by the extremities. 
 In the carpus the bones interlock a little more than is the case 
 in most Subungulata, and the corner of the os magnum reaches 
 the scaphoid, while the lunar articulates partially with both 
 magnum and unciform, instead of only with the magnum. 
 In the tarsus the cuboid articulates with both the calcaneum 
 and the astragalus, which is remarkably flat. The manus and 
 pes are short, nearly or quite plantigrade, and have the full 
 number of digits. The cranial cavity is singularly small. 
 
 1 See E. D. Cope, "The Amblypoda," Amer. Natural, 1884 and 1885. 
 
364 THE VERTEBRATE SKELETON. 
 
 Canine teeth are present in both jaws, and the grinding teeth 
 have short crowns, marked by V-shaped ridges. The pelvis is 
 large, the ilia are placed vertically, and the ischia do not take 
 part in the ventral symphysis. 
 
 The best known animals belonging to this suborder are the 
 Uintatheriidae (Dinocerata) 1 , found in the Upper Eocene of 
 Wyoming. They are as large as elephants, and are charac- 
 terised by the long narrow skull drawn out into three pairs 
 of rounded protuberances, by the strong occipital crest, and 
 by the very large upper canines. 
 
 Suborder (5). PROBOSCIDEA. 
 
 This suborder includes the largest of land mammals, the 
 Elephants, and certain of their extinct allies. The limbs are 
 strong, and are vertically placed ; the proximal segment is the 
 longest, and the manus and pes are pentedactylate and sub- 
 plantigrade. The digits are all enclosed in a common integu- 
 ment, and each is provided with a broad hoof. The vertebral 
 centra are much flattened and compressed, especially in the cer- 
 vical region. The number of thoracic vertebrae is very great, 
 reaching twenty. The skull (figs. 96 and 97) is extremely large, 
 this being due to the great development of air cells, which 
 takes place in nearly all the bones of the adult skull. In the 
 young skull there are hardly any air cells, and the growth of 
 the cranial cavity does not by any means keep pace with the 
 growth of the skull in general. The supra-occipital is very 
 large, and forms a considerable part of the roof of the skull. 
 The nasals and jugals are short, and the premaxillae very 
 large. The rami of the mandible meet in a long symphysis, and 
 the ascending portion is very high. Canine teeth are absent, 
 and the incisors have the form of ever-growing tusks composed 
 mainly of dentine; in living forms they are present in the 
 upper jaw only. The grinding teeth are large, and in living 
 
 1 See 0. C. Marsh, "The Dinocerata," U. S. Geol. Survey, 1884, 
 vol. x. 
 
MAMMALIA. RODENTIA. 365 
 
 forms have a very complex structure and mode of succession. 
 In some of the extinct forms, such as Mastodon and especially 
 Dinotkerium, the teeth are much more simple. In every case 
 the teeth have the same general structure, consisting of a 
 series of ridges of dentine, coated with enamel. In the more 
 specialised forms the valleys between the ridges are filled up 
 with cement. The acromion of the scapula has a recurved 
 process, similar to that often found in rodents. Clavicles are 
 absent. The radius and ulna are not ankylosed, but are 
 incapable of any rotatory movement. All the bones of the 
 extremities are very short and thick ; the scaphoid articulates 
 regularly with the trapezoid and the lunar with the magnum. 
 The ilia are vertically placed, and are very much expanded ; 
 the ischia and pubes are small, and form a short symphysis. 
 The femur has no third trochanter, and the tibia and fibula 
 are distinct. The fibula articulates with the calcaneum, and 
 the astragalus is very flat. 
 
 Here brief reference may be made to the TiLLODONTiA 1 , a 
 group of extinct mammals found in the Eocene beds of both 
 Europe and North America. They seem to connect together 
 the Ungulata, Rodentia, and Carnivora. 
 
 The skull resembles that of bears, but the grinding teeth 
 are of Ungulate type, while the second incisors resemble those 
 of rodents, and have persistent pulps. The femur has a third 
 trochanter, and the feet resemble those of bears in being 
 plantigrade and having pointed ungual phalanges, differing, 
 however, in having the scaphoid and lunar distinct. 
 
 Order 5. RODENTIA. 
 
 The Rodents form a very large and well-defined group of 
 
 mammals easily distinguishable by their peculiar dentition. 
 
 Canines are absent, and the incisors are very large and curved, 
 
 growing from persistent pulps. They are rectangular in section 
 
 1 See 0. C. Marsh, Amer. J. Set., 1875 and 1876. 
 
366 THE VERTEBRATE SKELETON. 
 
 and are much more thickly coated with enamel on their 
 anterior face than elsewhere ; consequently, as they wear down 
 they acquire and retain a chisel-shaped (scalpriform) edge. 
 There is never more than one pair of incisors in the mandible, 
 and except in the Hares and Rabbits, there is similarly only a 
 single pair in the upper jaw. These animals are, too, the only 
 rodents which have well developed deciduous incisors. There 
 is always a long diastema separating the incisors from the 
 grinding teeth. The grinding teeth, which are arranged in a 
 continuous series, vary in number from two to six in the upper 
 jaw, and from two to five in the lower jaw. The number of 
 premolars is always below the normal, often they are altogether 
 wanting, but generally they are ^. Sometimes the grinding 
 teeth form roots, sometimes they grow persistently. 
 
 The premaxillae are always large, and the orbits always com- 
 municate freely with the temporal fossae. The condyle of the 
 mandible is elongated from before backwards, and owing to 
 the absence of a postglenoid process to the squamosal, a back- 
 ward and forward motion of the jaw can take place. The 
 zygomatic arch is complete, but the jugal is short and only 
 forms the middle of it. The palate is small, being some- 
 times, as in the hares, narrowed from before backwards, 
 sometimes as in the mole-rats (Bathyerginae) narrowed trans- 
 versely. 
 
 The thoraco-lumbar vertebrae are usually nineteen in 
 number. Clavicles are generally present, and the acromion 
 of the scapula is commonly very long. The feet are as a rule 
 plantigrade, and provided with five clawed digits. 
 
 There are two main groups of Rodentia ; the Duplici- 
 dentata, or Hares and Rabbits, which have two pairs of upper 
 incisors, whose enamel extends round to the posterior surface ; 
 and the Simplicidentata, in which there is only a single pair 
 of upper incisors, whose enamel is confined to the anterior 
 surface. This group includes all the Rodents except the 
 Hares and Rabbits. 
 
MAMMALIA. CARNIVORA. 367 
 
 Order 6. CARNIVORA. 
 
 The living Carnivora form a natural and well-marked 
 group, but as is the case with so many other groups of 
 animals, when their extinct allies are included, it becomes 
 impossible to readily define them. 
 
 The raanus and pes never have less than four well-developed 
 digits, and these are nearly always provided with more or less 
 pointed nails, generally with definite claws. The hallux and 
 pollex are never opposable. The dentition is diphyodont and 
 markedly heterodont. The teeth are always rooted, except 
 in the case of the canines of the Walrus. The incisors are 
 generally f, and are comparatively small, while the canines 
 are large, pointed, and slightly recurved. The cheek teeth are 
 variable, and are generally more or less compressed and 
 pointed ; sometimes their crowns are flattened and tuber- 
 culated, but they are never divided into lobes by deep infoldings 
 of enamel. The squamosal is drawn out into a postglenoid 
 process, and the mandible has a large coronoid process. The 
 condyle of the mandible is transversely elongated, and the 
 glenoid fossa is very deep; in consequence of this arrangement 
 the mandible can perform an up and down movement only, 
 any rotatory or back and fore movement being impossible. 
 The jugal is large, and the zygomatic arch generally strong, 
 while the orbit and temporal fossa are in most cases completely 
 confluent. The scapula has a large spine. The clavicle is 
 never complete and is often absent, this forming an important 
 distinction between the skeleton of a Carnivore and of any 
 Insectivore except Potamogale. The humerus often has an 
 ent-epicondylar foramen, and the radius and ulna, tibia and 
 fibula are always separate. The manus is often capable of the 
 movements of pronation and supination, and the scaphoid, 
 lunar and centrale are in living forms always united together. 
 
 The order Carnivora includes three suborders. 
 
368 THE VERTEBRATE SKELETON. 
 
 Suborder (1). CREODONTA 1 . 
 
 This suborder contains a number of extinct Carnivora, 
 which present very generalised characters. 
 
 The cranial cavity is very small ; and the fourth upper pre- 
 molar and first lower molar are not differentiated as carnassial 
 teeth 2 , as they are in modern Carnivora. The Creodonta also 
 differ from modern Carnivora in the fact that the scaphoid and 
 lunar are usually separate, and that the femur has a third 
 trochanter. The feet are plantigrade. 
 
 They resemble the Condylarthra, another very generalised 
 group, in having an ent-epicondylar foramen. 
 
 They occurred throughout the Tertiary period in both 
 Europe and North America, and have also been found in India. 
 One of the best known genera is Hyaenodon. 
 
 Suborder (2). CARNIVORA VERA or FISSIPEDIA. 
 
 The skeleton is mainly adapted for a terrestrial mode of 
 life, and the hind limbs have the normal mammalian position. 
 In almost every case the number of incisors is . Each jaw 
 always has one specially modified carnassial or sectorial tooth 
 which bites like a scissors blade against a corresponding tooth 
 in the other jaw. In front of it the teeth are always more 
 or less pointed, while behind it they are more or less broadened 
 and tuberculated. In the manus the first digit, and in the 
 pes the first and fifth digits are never longer than the rest, 
 and the digits of both limbs are almost invariably clawed. 
 Some forms are plantigrade, some digitigrade, some sub- 
 plantigrade. The group includes all the ordinary terrestrial 
 Carnivora, and is divided into three sections : 
 
 1 E. D. Cope, "The Creodonta," Amer. Natural., 1884. W. B. Scott, 
 "Revision of the N. American Creodonta," P. Ac. Philad., 1892. 
 
 2 See next paragraph. 
 
MAMMALIA. PINNIPEDIA. 369 
 
 JEluroidea 1 , including the cats, civets, hyaenas, and allied 
 forms. 
 
 Cynoidea, including the dog tribe. 
 
 Arctoidea, including the bears, raccoons, weasels, and allied 
 forms. 
 
 Suborder (3). PiNNiPEDiA 2 . 
 
 In this suborder the limbs are greatly modified and adapted 
 for a more or less purely aquatic life, the proximal and middle 
 segments of the limbs are shortened, while the distal segment, 
 especially in the leg, is much elongated and expanded. There are 
 always five well-developed digits to each limb, and in the pes the 
 first and fifth digits are generally larger than the others. The 
 digits generally bear straight nails instead of claws, but even 
 nails are sometimes absent. There is no carnassial tooth, and 
 the teeth in other ways differ considerably from those of Carni- 
 vora vera. The incisors are always fewer than ; while the 
 cheek teeth generally consist of four premolars and one molar, 
 all of very uniform character, being compressed with conical 
 crowns, and never more than two roots. 
 
 The suborder includes three families Otariidae (Eared 
 Seals), Trichechidae (Walrus), and Phocidae (Seals). 
 
 Order 7. INSECTIVORA 3 . 
 
 This order contains a large number of small generally ter- 
 restrial mammals. The limbs are plantigrade or subplantigrade, 
 and are generally pentedactylate. All the digits are armed 
 with claws, and the pollex and hallux are not opposable. The 
 teeth are diphyodont, heterodont, and rooted. The cheek teeth 
 
 1 St G. Mivart, The Cat, London, 1881. 
 
 2 St G. Mivart, P. Z. S., 1885. 
 
 3 St G. Mivart, "On the Osteology of Insectivora, " J. Anat. PhysioL 
 norm, path., 1867 and 1868, and P. Z. S., 1871. G. E. Dobson, Monograph 
 of the Insectivora, London, 188290. 
 
 H. 24 
 
370 THE VERTEBRATE SKELETON. 
 
 have tuberculated crowns, and there are never less than two 
 pairs of incisors in the mandible ; often the incisors, canines, 
 and premolars are not clearly differentiated from one another, 
 and special carnassial teeth are never found. The cranial cavity 
 is small, and the facial part of the skull is generally much 
 developed ; often the zygomatic arch is incomplete. Clavicles 
 are well developed (except in Potamogale), and the hum ems 
 generally has an ent-epicondylar foramen. The femur fre- 
 quently has a ridge representing the third trochanter. There 
 are two suborders : 
 
 Suborder (1). DERMOPTERA. 
 
 This suborder includes only a very aberrant arboreal genus 
 Galeopitkecus, remarkable for its greatly elongated limb bones, 
 and peculiar dentition. The incisors of the lower jaw are 
 deeply pectinated or divided by several vertical fissures, the 
 canines and outer upper incisors have two roots. Ossified 
 intercentra occur in the thoraco-lumbar region of the vertebral 
 column. 
 
 Suborder (2). INSECTIVORA VERA. 
 
 This suborder includes all the ordinary Insectivora, such as 
 moles, shrews and hedgehogs. The upper and lower incisors 
 are conical, not pectinated. 
 
 Order 8. CniROPTERA 1 . 
 
 This order is perhaps the best marked and most easily 
 defined of all the orders of mammals. The anterior limbs 
 form true wings and the whole skeleton is modified in relation 
 to flight. 
 
 The anterior limbs are vastly larger than the posterior ; 
 for all the bones except the carpals are much elongated, and 
 
 1 See G. E. Dobson, Brit. Mm. Catalogue of Chiroptera, 1878. See 
 also other papers by the same author and by Oldfield Thomas. 
 
MAMMALIA. CHIKOPTERA. 371 
 
 this applies specially to the phalanges of all the digits except 
 the pollex. 
 
 The pollex is clawed and so is sometimes the second digit ; 
 the other digits of the manus are without nails or claws. The 
 teeth are divisible into the four usual types and the series 
 
 91 33 
 
 never exceeds i ^ c -=- pm - w - x 2, total 38. The milk 
 
 O 1 DO 
 
 teeth are quite unlike the permanent teeth. The orbit is not 
 divided by bone from the temporal fossa. The vertebral 
 column is short, and in old animals the trunk vertebrae 
 have a tendency to become partially fused together. The 
 cervical vertebrae are remarkably wide, and the development 
 of spinous processes is everywhere slight. The presternum 
 has a prominent keel for the attachment of the pectoral muscles. 
 The clavicles are very long and strong, and the scapula has a 
 long spine and coracoid process. The ulna is vestigial, con- 
 sisting only of a proximal end ankylosed to the radius. All 
 the carpals of the proximal row the scaphoid, lunar and 
 cuneiform are united, forming a single bone. The pelvis is 
 very weak and narrow, and only in the Rhinolophidae do the 
 pubes meet in a symphysis. The anterior caudal vertebrae are 
 frequently united to the ischia. The fibula is generally ves- 
 tigial, and the knee joint is directed backwards instead of 
 forwards. The pes has five slender clawed digits, and the 
 calcaneum is often drawn out into a spur which helps 
 to support the membrane connecting the hind limbs with the 
 tail. 
 
 There are two suborders of Chiroptera : 
 
 1. The MEGACHIROPTERA or Flying foxes, which almost 
 always have smooth crowns to the molar teeth, and the second 
 digit of the manus clawed. 
 
 2. The MICROCHIROPTERA including all the ordinary bats 
 which have cusped molar teeth, and the second digit of the 
 manus clawless. 
 
 242 
 
372 THE VERTEBRATE SKELETON. 
 
 Order 9. PRIMATES. 
 
 The dentition is diphyodont and heterodont, the incisors 
 generally number f , and the molars, except in the Hapalidae 
 (Marmosets), are f . The cheek teeth are adapted for grind- 
 ing, and the molars are more complex than the premolars. 
 A process from the jugal meets the postorbital process of the 
 frontal completing the postorbital bar. 
 
 The clavicle is well developed, and the radius and ulna 
 are never united. The scaphoid and lunar of the carpus, 
 and commonly also the centrale, remain distinct from one 
 another. As a rule both manus and pes have five, digits, 
 but the pollex may be vestigial. The pollex is opposable to 
 the other digits, and so is the hallux except in Man; the 
 digits are almost always provided with flat nails. The hu- 
 merus has no ent-epicondylar foramen and the femur has no 
 third trochanter. 
 
 The order Primates is divisible into two suborders : 
 
 Suborder (1). LEMUROIDEA. 
 
 The skull has the orbit communicating freely with the 
 temporal fossa beneath the postorbital bar (except in Tar- 
 sius}. The lachrymal foramen is external to the margin of 
 the orbit. Both pollex and hallux are well developed. In 
 the pes the second digit is terminated by a long pointed claw, 
 and so is also the third in Tarsius. The lumbar region of 
 the vertebral column is long, sometimes including as many as 
 nine vertebrae. Besides the Lemurs the group includes the 
 aberrant Tarsius and Chiromys. 
 
 Suborder (2). ANTHROPOIDEA. 
 
 The skull has the orbit almost completely shut off from 
 the temporal fossa, and the lachrymal foramen is situated 
 within the orbit. The pollex is sometimes vestigial or absent. 
 
MAMMALIA. PRIMATES. 373 
 
 The second digit of the pes has a flattened nail except in the 
 Hapalidae, in which all the digits of the pes except the hallux 
 are clawed. 
 
 The Anthropoidea are divided into five families : 
 
 1. Hapalidae or Marmosets. 
 
 2. Cebidae or American Monkeys. 
 
 3. Cercopithecidae or Old World Monkeys. 
 
 4. Simiidae or Anthropoid Apes. 
 
 5. Hominidae or Men. 
 
CHAPTER XXI. 
 THE SKELETON OF THE DOG 1 (Canis familiaris). 
 
 I. EXOSKELETON. 
 
 The exoskeleton of the dog includes three sets of structures : 
 1. hairs, 2. claws, 3. teeth. Hairs and claws are epidermal 
 exoskeletal structures, while teeth are partly of dermal, and 
 partly of epidermal origin. 
 
 1. Hairs are delicate epidermal structures which grow 
 imbedded in little pits or follicles in the dermis. Specially 
 large hairs forming the vibrissae or whiskers grow attached 
 to the upper lip. 
 
 2. Claws are horny epidermal sheaths, one of which fits 
 on to the pointed distal phalanx of each digit. They are 
 sharply curved structures, and being in the dog non-retractile, 
 their points are commonly much blunted by friction with the 
 ground. The claws of the pollex, and of the hallux when it is 
 present, however do not meet the ground, and therefore remain 
 comparatively sharp. 
 
 3. Teeth 2 . Although as regards their mode of origin, 
 teeth are purely exoskeletal or tegumentary structures, they 
 
 1 W. Ellenberger and H. Baum, Anatomic des Hundes, Berlin, 1891. 
 
 2 T. H. Huxley, "Dental and cranial characters of the Canidae," 
 P. Z. S. 1880. 
 
THE SKELETON OF THE DOG. THE TEETH. 
 
 375 
 
 become so intimately connected with the skull that they appear 
 to belong to the endoskeleton. 
 
 Each tooth, as has been already described, consists of three 
 distinct tissues, dentine and cement of dermal origin, and 
 enamel of epidermal origin. 
 
 FIG. 68. DENTITION OF A DOG (Canis familiaris) x ^. (Camb. Mus.) 
 i 2. second incisor. pm 1, pm 4. first and fourth pre- 
 
 c. canine. 
 
 molars. 
 m 1. first molar. 
 
 The teeth of the dog (fig. 68) form a regular series arranged 
 along the margins of both upper and lower jaws, and imbedded 
 in pits or alveoli of the maxillae, premaxillae, and mandibles. 
 
376 THE VERTEBRATE SKELETON. 
 
 They are all fixed in the bone by tapering roots, and none of 
 them grow from persistent pulps. 
 
 They are divisible into four distinct groups, the incisors, 
 canines, premolars and molars. There are three incisors, 
 one canine and four premolars on each side of each jaw. 
 But while there are three molars on each side of the lower 
 jaw, the last is wanting in the upper jaw. The dentition of 
 the dog may then be represented by the formula 
 
 31 42 
 
 i^ c j pm ^ m - x 2 = 42. 
 
 In each jaw there is one large specially modified tooth 
 called the carnassial, the teeth in front of this are more or 
 less pointed and compressed, while those behind it are more or 
 less flattened and tuberculated. 
 
 Teeth of the upper jaw. 
 
 The first and second incisors are small teeth with long 
 conical roots and somewhat chisel-shaped crowns. Surround- 
 ing the base of the crown there is a rather prominent ridge, 
 terminated laterally by a pair of small cusps. This ridge, the 
 cinglllum, serves to protect the edge of the gums from injury 
 by the hard parts of food. The third incisor is a good deal 
 like the others but larger, and has the cingulum well developed 
 though not terminated by lateral cusps. All the incisors 
 are borne by the premaxillae, the remaining teeth by the 
 maxillae. 
 
 The canine is a large pointed tooth, slightly recurved and 
 with a long tapering root. 
 
 The premolars are four in number, and in all the cingu- 
 lum is fairly well seen. The first is a very small tooth with a 
 single tapering root, the second and third are larger and have 
 two roots, while the fourth, the carnassial, is much the largest 
 and has three roots. Each of the second, third and fourth pre- 
 molars has a stout blade, the middle portion of which is drawn 
 out into a prominent cone ; the posterior part of the fourth 
 
THE SKELETON OF THE DOG. THE TEETH. 377 
 
 premolar forms a compressed ridge, and at the antero-internal 
 edge of the tooth there is a small inner tubercle. 
 
 The two molar teeth are of very unequal size. The first, 
 which has two anterior roots and one posterior, is wider than 
 it is long, its outer portion being produced into two prominent 
 cusps, while its inner portion is depressed. The second molar 
 is a small tooth resembling the first in its general appearance, 
 but with much smaller outer cusps. 
 
 Teeth of the lower jaw. 
 
 The three incisors of the lower jaw have much the same 
 character as the first two of the upper jaw ; while the canine 
 is identical in character with that of the upper jaw. 
 
 The four premolars gradually increase in size from the 
 first to the last, but none are very large. The first premolar 
 is a single-rooted tooth resembling that of the upper jaw ; the 
 second, third and fourth are two-rooted, like the second and 
 third of the upper jaw, which they closely resemble in other 
 respects. 
 
 The first molar forms the carnassial (fig. 84, V), and with 
 the exception of the canine, is much the largest tooth of the 
 lower jaw ; it is a two-rooted tooth, with a long compressed 
 bilobed blade, and a posterior tuberculated talon or heel. The 
 second molar is much smaller, though likewise two-rooted, while 
 the third molar is very small and has only a single root. All 
 the teeth except the molars are preceded in the young animal 
 by temporary milk teeth. These milk teeth, though smaller, 
 are very similar to the permanent teeth by which they are 
 ultimately replaced. 
 
 II. ENDOSKELETON. 
 1. THE AXIAL SKELETON. 
 
 This includes the vertebral column, the skull, and the ribs 
 and sternum. 
 
378 THE VERTEBRATE SKELETON. 
 
 A. THE VERTEBRAL COLUMN. 
 
 This consists of a series of about forty vertebrae arranged 
 in succession so that their centra form a continuous rod, and 
 their neural arches a continuous tube, surrounding a cavity, 
 the neural canal. 
 
 The vertebrae may be readily divided into five groups : 
 
 1. The cervical or neck vertebrae. 
 
 2. The thoracic or chest vertebrae which bear ribs. 
 
 3. The lumbar vertebrae which are large and ribless. 
 
 4. The sacral vertebrae which are fused with one another 
 and united with the pelvis. 
 
 5. The caudal or tail vertebrae which are small. 
 
 Except in the sacral region the vertebrae are movably 
 articulated to one another, while their centra are separated 
 from one another by cartilaginous intervertebral discs. 
 
 GENERAL CHARACTERS OF A VERTEBRA. 
 
 Take as a type the fourth lumbar vertebra. It may 
 be compared to a short tube whose inner surface is smooth 
 and regular, and whose outer surface is thickened and drawn 
 out in a variety of ways. The basal part of the vertebra 
 is the centrum or body which forms the thickened floor of 
 the neural canal. Its two ends are slightly convex and 
 are formed by the epiphyses, two thin plates of bone which 
 are at first altogether ^distinct from the main part of the cen- 
 trum, but fuse with it as the animal grows older ; its sides are 
 drawn out into a pair of strong transverse processes, which 
 project forwards, outwards, and slightly downwards. The 
 neural arch forms the sides and roof of the neural canal, and 
 at each end just above the centrum bears a pair of interver- 
 tebral notches for the passage of the spinal nerves, the pos- 
 terior notches being considerably deeper than the anterior. The 
 neural arch is drawn out into a series of processes. Arising 
 
THE SKELETON OF THE DOG. VERTEBRAL COLUMN. 379 
 
 from the centre of the dorsal surface is a prominent median 
 neural spine or spinous process, which projects upwards 
 and slightly forwards ; its anterior edge is vertical, while its 
 posterior edge slopes gradually. At the two ends of the 
 neural arch arise the two pairs of zygapophyses or articula- 
 ting surfaces, which interlock with those of the adjacent 
 vertebrae. The anterior or prezygapophyses look inwards, 
 and are large and concave ; they are borne upon a pair of 
 large blunt outgrowths of the neural arch, the metapophyses. 
 The posterior or postzygapophyses are slightly convex and 
 look outwards and downwards ; they are borne upon back- 
 warclly projecting outgrowths of the neural arch. Lastly 
 there are a pair of minute projections arising from the 
 posterior end of the neural arch, below the postzygapophyses. 
 These are the anapophyses. In young individuals the de- 
 velopment of all the processes of the various vertebrae is less 
 marked, arid the epiphyses are obviously distinct. 
 
 FlG. 69. A, ATLAS AND B, AXIS VERTEBRA OF A DOG (CaillS 
 
 familiaris) (after VON ZITTEL). 
 
 1. transverse process of atlas. 
 
 2. vertebrarterial canal. 
 
 3. foramen for exit of spinal 
 
 nerve. 
 
 4. neural spine. 
 
 5. odontoid process. 
 
 6. anterior articulating surface 
 
 of centrum. 
 
 7. centrum. 
 
 8. transverse process of axis. 
 
 9. postzygapophysis. 
 
.380 THE VERTEBRATE SKELETON. 
 
 THE CERVICAL VERTEBRAE. 
 
 These are seven in number, as in almost all mammals. 
 They are characterised by the fact that they have small ribs 
 fused with them, forming transverse processes perforated by 
 canals through which the vertebral arteries run. 
 
 The first, or atlas vertebra (fig. 69, A), differs much from 
 all the others ; it is drawn out into a pair of wide wing-like 
 transverse processes (fig. 69, A, 1), and forms a ring surround- 
 ing a large cavity. This cavity is during life divided into 
 two parts by a transverse ligament ; the upper cavity is the 
 true neural canal, while the lower lodges the odontoid pro- 
 cess of the second vertebra, which is the detached centrum 
 of the atlas. The neural arch is broad and regular ; it has 
 no spinous process, and is perforated in front by a pair of 
 foramina for the passage of the first spinal nerves. The mid- 
 ventral portion of the atlas is rather thick, and bears a minute 
 backwardly-projecting hypapophysis. The bases of the broad 
 transverse processes .are perforated by the vertebrarterial 
 canals (fig. 69, A, 2). The atlas bears at each end a pair of 
 large articulating surfaces; those at the anterior end articulate 
 with the condyles of the skull, and are very deeply concave ; 
 those at the posterior end for articulation with the axis, are 
 nearly as large, but are flattened. The atlas ossifies from 
 three centres, one forming the mid-ventral portion, the others 
 the two halves of the remainder. 
 
 The second, or axis vertebra (fig. 69, B), also differs much 
 from the other cervicals. The long and broad centrum has 
 a very flat dorsal surface, and is produced in front into 
 the conical odontoid process (fig. 69, B, 5), and bears a 
 pair of very large convex outwardly-directed surfaces for arti- 
 culation with the atlas. At its posterior end it is drawn 
 out into a pair of small backwardly-directed spines, the 
 transverse processes ; these are perforated at their bases by 
 the vertebrarterial canals. The neural arch is deeply notched 
 in front and behind for the passage of the spinal nerves, and 
 
THE SKELETON OF THE DOG. VERTEBRAE. 381 
 
 is drawn out above into a very long compressed neural spine 
 (fig. 69, B, 4), which projects a long way forwards, and behind 
 becomes bifid and thickened, bearing a pair of flat downwardly 
 directed postzygapophyses. In the young animal the odontoid 
 process is readily seen to ossify from a centre anterior to that 
 forming the anterior epiphysis of the axis. 
 
 The remaining five cervical vertebrae, the third to the 
 seventh inclusive, have rather flattened wide centra, obliquely 
 truncated at either end. The neural spine progressively increases 
 in size as the vertebrae are followed back. The transverse 
 processes vary considerably ; those of the third are divided 
 into a thicker backwardly-, and a more slender forwardly- 
 projecting portion ; those of the fourth and fifth mainly extend 
 downwards, and that of the sixth is divided into a horizontal 
 portion and a downwardly-projecting inferior lamella. All 
 the cervical vertebrae except the seventh have the bases of the 
 transverse processes perforated by the vertebrarterial canals. 
 The prezygapophyses in each case look upwards and slightly 
 inwards, while the postzygapophyses look downwards and 
 slightly outwards. 
 
 THE THORACIC VERTEBRAE. 
 
 The thoracic vertebrae are twelve or thirteen in number, 
 and all bear movably articulated ribs. As a group they are 
 characterised by their comparative shortness, and in the case 
 of the first eight or nine by the great length of the back- 
 wardly-sloping neural spine. The posterior thoracic vertebrae 
 approach in character the succeeding lumbar vertebrae. 
 
 As type of the anterior thoracic vertebrae, take any one 
 between the second and sixth inclusive. The centrum is short, 
 and has its terminations vertically truncated. At the top of 
 the centrum, at both anterior and posterior ends on each side, 
 is a demi-facet (fig. 70, A, 4), which, together with that on the 
 adjacent vertebra, forms an articulating surface for the capitu- 
 lum of the rib. The neural arch is small and deeply notched 
 
382 
 
 THE VERTEBRATE SKELETON. 
 
 behind for the passage of the spinal nerve. It is drawn out 
 above into a very long neural spine (fig. 70, A, 1), whose base 
 extends back over the succeeding vertebra and bears the down- 
 wardly-directed postzygapophyses (fig. 70, A, 6). The summit 
 of the neural arch is deeply notched in front, and on each side 
 of the notch are the prezygapophyses, which look almost ver- 
 tically upwards. The transverse processes are short and blunt, 
 and are flattened below (fig. 70, A, 3) for the articulation of 
 the tubercula of the ribs. 
 
 B 
 
 FlG. 70. A, SECOND THORACIC, AND B, SECOND LUMBAR VERTEBRA OF A 
 
 DOG (Cants familiaris) SEEN FROM THE RIGHT SIDE (after VON ZITTEL). 
 
 1. neural spine. 4. 
 
 2. centrum. 
 
 3. transverse process bearing in 5. 
 
 A the facet for articulation 6. 
 with the tuberculum of the 
 rib. 
 
 facet for articulation with the 
 
 capitulum of the rib. 
 metapophysis. 
 postzygapophysis. 
 
 The posterior three or four thoracic vertebrae differ much 
 from the others. The centra are longer, the neural spines short 
 and not directed backwards, the articular facets for the heads 
 of the ribs are confined to the anterior end of the centrum of 
 each vertebra, not overlapping on to the preceding vertebra. 
 The transverse processes are small and irregular, and nieta- 
 pophyses and anapophyses are developed. The prezygapophyses 
 
THE SKELETON OF THE DOG. THE VERTEBRAE. 383 
 
 also look more inwards, and the postzygapophyses more out- 
 wards than in the more typical thoracic vertebrae. 
 
 THE LUMBAR VERTEBRAE. 
 
 The lumbar vertebrae are seven in number, and their 
 general characteristics have been already described. As a 
 group they are characterised by their large size, and the great 
 development of the transverse processes, inetapophyses and 
 neural spines. 
 
 THE SACRAL VERTEBRAE. 
 
 Three vertebrae are commonly found fused together, forming 
 the sacrum ; the divisions between the three being indicated 
 by the foramina for the exit of the spinal nerves. 
 
 Of these three vertebrae, the first is much the largest, 
 and is firmly united to the ilium on each side by a structure 
 formed by the transverse processes and expanded ribs. In the 
 adult this structure forms one continuous mass, but in the 
 young animal a ventral portion formed by the rib is clearly 
 distinguishable from a dorsal portion formed by the transverse 
 process. All three have low neural spines. The anterior 
 sacral vertebra bears a large pair of prezygapophyses, while 
 the posterior one bears a small pair of postzygapophyses. 
 
 THE CAUDAL VERTEBRAE. 
 
 The caudal vertebrae are about nineteen in number. 
 The earlier ones have well-developed neural arches, transverse 
 processes, and zygapophyses, but as the vertebrae are followed 
 back they gradually lose all their processes, and the neural arch 
 as well, becoming at about the thirteenth from the end reduced 
 to simple cylindrical centra. 
 
 B. THE SKULL. 
 
 The skull consists of the following three parts : (a) the 
 cranium, with which are included the skeletal sfpports of the 
 various special sense organs, and the bones of the face and 
 upper jaw ; (6) the lower jaw or mandible, which is movably 
 articulated to the cranium, and (c) the hyoid. 
 
384 THE VERTEBRATE SKELETON. 
 
 (a) THE CRANIUM. 
 
 The cranium is a compact bony box, forming the anterior 
 expanded portion of the axial skeleton. It has a longitu- 
 dinal axis, the craniofacial axis around which the various 
 parts are arranged, and this axis is a direct continuation of 
 that of the vertebral column. Similarly the cavity of the 
 cranium is a direct continuation of the spinal canal. The 
 posterior part of the craniofacial axis, which has relation^ 
 only with the cranium, is called the basicranial axis. 
 
 In the dog as in the other types previously described, the 
 skull in its earliest stages is cartilaginous, containing no bone. 
 In the adult, however, the cartilage is to a great extent 
 replaced by bone, and in addition to this cartilage bone, 
 membrane bone is largely developed, .and intimately united 
 with the cartilage bone to form one complete whole. 
 
 In the description of the dog's skeleton, as in those of the 
 previous types, the names of the membrane bones are printed 
 in italics, while those of the cartilage bones are printed in 
 thick type. 
 
 Most of the numerous foramina perforating the skull 
 walls will be described after the bones have, been dealt with. 
 
 For purposes of description the cranium may be further 
 subdivided into : 
 
 1 . The cranium proper or brain case. 
 
 2. The sense capsules. 
 
 3. The upper jaw. 
 
 1. THE CRANIUM PROPER OR BRAIN CASE. 
 
 Taking the membrane and cartilage bones together, they 
 are seen to be more or less arranged in three segments, which 
 however must not be regarded as homologous with the seg- 
 ments forming the vertebral column. 
 
 The occipital segment is the most posterior of the three, 
 and consists of four cartilage bones, which in the adult are 
 commonly completely fused together. They surround the great 
 
THE SKELETON OF THE DOG. THE SKULL. 
 
 385 
 
 
 FIG. 71, DIAGRAM OF THE RELATIONS OF THE PRINCIPAL BONES IN THE 
 MAMMALIAN SKULL (modified after FLOWER). 
 
 Cartilage is dotted. Cartilage bones are marked by dots and dashes, 
 membrane bones are left white. 
 
 1. 
 
 basi-occipital. 
 
 15. 
 
 mesethmoid. 
 
 2. 
 
 exoccipital. 
 
 16. 
 
 vomer. 
 
 3. 
 
 supra-occipital. 
 
 17. 
 
 pterygoid. 
 
 4. 
 
 basisphenoid. 
 
 18. 
 
 palatine. 
 
 5. 
 
 alisphenoid. 
 
 19. 
 
 maxilla. 
 
 6. 
 
 parietal. 
 
 20. 
 
 premaxilla. 
 
 7. 
 
 presphenoid. 
 
 21. 
 
 squamosal. 
 
 8. 
 
 orbitosphenoid. 
 
 22. 
 
 mandible. 
 
 9. 
 
 frontal. 
 
 23. 
 
 tympano-hyal. 
 
 10. 
 
 periotic, immediately below 
 
 24. 
 
 stylo-hyal. 
 
 
 which is the tympanic. 
 
 25. 
 
 epi-hyal. 
 
 11. 
 
 lachrymal. 
 
 26. 
 
 basi-hyal. Between this and 
 
 12. 
 
 ethmo-turbinal. 
 
 
 the epi-hyal is the cerato-hyal. 
 
 13. 
 
 maxillo-turbinal. 
 
 27. 
 
 thyro-hyal. 
 
 14. 
 
 nasal. 
 
 28. 
 
 jugal. 
 
 Nerve exits are indicated by Eoman numerals. 
 
 R. 
 
 25 
 
386 THE VERTEBRATE SKELETON. 
 
 foramen magnum (fig. 75, 2) through which the brain and 
 spinal cord communicate. Forming the lower margin of the 
 foramen magnum is a large flat unpaired bone, the basi- 
 occipital (fig. 75, 5). Above this on each side are the ex- 
 OCCipitals, whose sides are drawn out into a pair of down- 
 wardly-directed paroccipital processes, which are applied 
 to the tympanic bullae 1 . The inner side of each exoccipital is 
 converted into the large rounded occipital condyle (fig. 72, 
 13) by which the skull articulates with the atlas vertebra. The 
 dorsal boundary of the foramen magnum is formed by a large 
 unpaired flat bone, the supra-occipital (figs. 72 and 75, 1), 
 which is continuous with a small bone, the interparietal, pro- 
 longed forwards between the parietal bones of the next segment. 
 In old animals the interparietal forms the hind part of a 
 prominent ridge running along the mid-dorsal surface of the 
 skull and called the sagittal crest, while the junction line of 
 the occipital and parietal segments forms a prominent occi- 
 pital crest. 
 
 The plane in which the bones of the occipital segment lie 
 is called the occipital plane ; the angle that it makes with the 
 basicranial axis varies much in different mammals. 
 
 The parietal segment consists of both cartilage and 
 membrane bones. It is formed of five bones, which are in 
 contact with those of the occipital segment on the dorsal and 
 ventral surfaces, while laterally they are separated by the inter- 
 position of the auditory bones, and to some extent of the squa- 
 mosal. The basisphenoid (fig. 75, 6), an unpaired bone 
 forming the ventral member of this segment, is the direct 
 continuation of the basi-occipital. It tapers anteriorly, but is 
 rather deep vertically, its upper or dorsal surface bearing a 
 depression, the sella turcica, which lodges the pituitary body 
 of the brain. From the sides of the basisphenoid arise the 
 alisphenoids (fig. 75, 11) a pair of bones of irregular shape 
 generally described as wing-like ; each gives off from its lower 
 1 See p. 392. 
 
THE SKELETON OF THE DOG. THE SKULL. 
 
 387 
 
 19 3 
 
 FIG. 
 
 1. 
 2. 
 
 3. 
 4. 
 5. 
 6. 
 
 7. 
 
 8. 
 
 9. 
 10. 
 11. 
 12. 
 18. 
 1-1. 
 15. 
 IB. 
 17. 
 
 27 
 
 72. VEBTICAL LONGITUDINAL SECTION TAKEN A LITTLE TO THE LEFT 
 
 OF THE MIDDLE LINE THROUGH THE SKULL OF A DOG (Cants 
 
 liaris) x . (Camb. Mus.) 
 
 supra-occipital. 
 
 interparietal. 
 
 parietal. 
 
 frontal. 
 
 cribriform plate. 
 
 nasal. 
 
 mesethmoid. 
 
 maxilla. 
 
 vomer. 
 
 ethmo-turbinal. 
 
 maxillo-turbinal. 
 
 premaxilla. 
 
 occipital condyle. 
 
 basi-occipital. 
 
 tympanic bulla. 
 
 basisphenoid. 
 
 pterygoid. 
 
 18. palatine. 
 
 19. alisphenoid. 
 
 20. internal auditory meatus. 
 
 21. tentorium. 
 
 22. foramen lacerum posterius. 
 
 23. floccular fossa. 
 
 24. coronoid process. 
 
 25. condyle. 
 
 26. angle. 
 
 27. mandibular symphysis. 
 
 28. inferior dental foramen. 
 
 29. stylo-hyal. 
 
 30. epi-hyal. 
 
 31. cerato-hyal. 
 
 32. basi-hyal. 
 
 33. thyro-hyal. 
 
 XII. condylar foramen. 
 
 252 
 
388 THE VERTEBRATE SKELETON. 
 
 surface a pterygoid plate, which is united in front with the 
 palatine, and below with the pterygoid. The alisphenoids are 
 united above with a pair of large nearly square bones, the 
 parietals (fig. 73, 2), which meet one another in the mid-dorsal 
 line. The line of junction is frequently drawn out into a strong 
 ridge, which forms the anterior part of the sagittal crest. 
 
 The frontal segment, which surrounds the anterior part 
 of the brain, is closely connected along almost its whole 
 posterior border with the parietal segment. 
 
 Its base is formed by the presphenoid (fig. 75, 12), a 
 very deep unpaired bone, narrow and compressed ventrally, 
 and with an irregular dorsal surface. The presphenoid is 
 continuous with a second pair of wing-like bones, the orbito- 
 sphenoids. Each orbitosphenoid meets the alisphenoid 
 behind, but the relations of the parts in this region are 
 somewhat obscured by a number of large foramina piercing 
 the bones, and also by an irregular vacuity, the foramen 
 lacerum anterius or sphenoidal fissure, which lies between 
 the orbitosphenoid and alisphenoid, separating the lateral parts 
 of the parietal and frontal segments, in the same way as the 
 space occupied by the auditory bones separates the lateral 
 parts of the occipital and parietal segments. The orbito- 
 sphenoids pass obliquely forwards and upwards, and are united 
 above with a second pair of large membrane bones, thefrontals 
 (fig. 73, 3). The outer side of each frontal is drawn out into 
 a rather prominent rounded postorbital process (fig. 73, 10), 
 from which a ridge converges backwards to meet the sagittal 
 crest. The anterior part of the frontal is produced to form 
 the long nasal process, which is wedged in between the nasal 
 and maxilla. 
 
 The cranial cavity is continuous in front with the nasal or 
 olfactory cavities, but the passage is partially closed by a 
 screen of bone, the cribriform plate (fig. 72, 5), which is 
 placed obliquely across the anterior end of the cranial cavity, 
 and is perforated by a number of holes through which the 
 
THE SKELETON OF THE DOG. THE SKULL. 389 
 
 FIG. 73. DORSAL VIEW OF THE CRANIUM OF A DOG (Canis fami- 
 liar is) x . 
 
 1. supra-occipital. 
 
 2. parietal. 
 
 3. frontal. 
 
 4. nasal. 
 
 5. maxilla (facial portion). 
 
 6. premaxilla. 
 
 7. squamosal. 
 
 8. jugal. 
 
 10. postorbital process of frontal. 
 
 11. infra-orbital foramen. % 
 
 12. anterior palatine foramen. 
 
 13. lachrymal foramen. 
 i 1. first incisor. 
 
 c. canine. 
 
 pm 4. fourth premolar. 
 
390 THE VERTEBRATE SKELETON. 
 
 olfactory nerves pass. The plane of the cribriform plate is 
 called the ethmoidal plane, and as was the case also with 
 the occipital plane, the angle that it makes with the basi- 
 cranial axis varies much in different mammals, and is of 
 importance. The olfactory fossa in which lie the olfactory 
 lobes of the brain, is partially separated from the cerebral 
 fossa, or cavity occupied by the cerebral hemispheres, by 
 ridges on the orbitosphenoids and frontals. The presphenoid 
 is connected in front with a vertical plate formed partly of bone, 
 partly of unossified cartilage; this plate, the mesethmoid 
 (fig. 72, 7), separates the two olfactory cavities which lodge 
 the olfactory organs. Its anterior end always remains un- 
 ossified, and forms the septal cartilage of the nose. 
 
 The brain case may then, to use the words of Sir W. H. 
 Flower, be described as a tube dilated in the middle 'and com- 
 posed of three bony rings or segments, with an aperture at each 
 
 end, and a fissure or space at the sides between each of them. 
 
 i 
 2. THE SENSE CAPSULES. 
 
 Each of the three special sense organs, of hearing, of sight, 
 and of smell, is in the embryo provided with a cartilaginous 
 or membranous protecting capsule ; and two of these, the 
 auditory and olfactory capsules, become afterwards more or 
 less ossified, and intimately related to the cranium proper. 
 
 (1) Bones in relation to the Auditory capsules. 
 
 These bones lie on each side wedged into the vacuity be- 
 tween the lateral parts of the occipital and parietal segments ; 
 they are three in number, the periotic, the tympanic and the 
 squamosal. 
 
 The periotic is the most important of them, as it replaces 
 the cartilaginous auditory capsule of the embryo, and encloses 
 the essential organ of hearing. It commences to ossify 
 from three centres corresponding to the pro-otic, epi-otic and 
 opisthotic of lower skulls, such as those of the Turtle and 
 Crocodile. 
 
THE SKELETON OF THE DOG. THE SKULL. 
 
 391 
 
 These ossifications however very early combine to form a 
 single bone, the periotic, which nevertheless consists of two 
 
 FIG. 74. 
 
 DIAGRAM OF THE MAMMALIAN TYMPANIC CAVITY AND ASSOCIATED 
 PARTS (modified from LLOYD MORGAN). 
 
 1. external auditory meatus. 
 
 2. tympanic membrane. 
 
 3. malleus. 
 
 4. incus. 
 
 5. lenticular. 
 
 6. stapes. 
 
 7. fenestra ovalis. 
 
 8. fenestra rotunda. 
 
 9. Eustachian tube. 
 
 10. cavity occupied by the cochlea. 
 
 11. cavity occupied by the mem- 
 
 branous labyrinth. 
 
 portions, the petrous and the mastoid, differing considerably 
 from one another. 
 
 The petrous portion lies dorsally and anteriorly, and is 
 much the more important of the two, as it encloses the 
 essential part of the auditory organ. It forms an irregular 
 mass of hard dense bone, projecting into the cranial cavity, 
 and does not appear on the external surface at all. The 
 mastoid portion lies ventrally and posteriorly, is smaller, 
 and formed of less dense bone than is the petrous portion, 
 from which it differs also in the fact that it appears on the 
 surface of the skull, just external to the exoccipital. The 
 petrous portion bears a ridge, which together with a ridge 
 
392 THE VERTEBRATE SKELETON. 
 
 on the supra-occipital, and the tentorium (fig. 72, 21), a 
 transverse fold of the dura mater 1 , separates the large cerebral 
 fossa from the cerebellar fossa, which is much smaller than 
 the cerebral fossa and lies behind and partly beneath it. The 
 plane of the tentorium is called the tentorial plane, and the 
 angles that it makes with the basicranial axis and with the 
 occipital and ethmoidal planes vary much in different mammals. 
 
 The periotic has its inner surface marked by important 
 depressions, while both inner and outer surfaces are pierced 
 by foramina. At about the middle of its inner surface are 
 seen two deep pits, one lying immediately above the other. 
 Of these the more ventral is a foramen, the internal audi- 
 tory meatus (fig. 72, 20), through which the Vllth (facial) 
 and Vlllth (auditory) nerves leave the cranial cavity, the 
 facial nerve passing through the bone and afterwards leaving 
 the skull by the stylomastoid foramen (fig. 75, VII), while 
 the auditory passes to the inner ear. The more dorsal of the 
 two pits is not a foramen but the floccular fossa (fig. 72, 23) 
 which lodges the floccular lobe of the cerebellum. In some 
 skulls another wide and shallow but fairly prominent depres- 
 sion is seen dorsal to and slightly behind the floccular fossa, 
 this also lodges part of the cerebellum. Behind the internal 
 auditory meatus, between the periotic and exoccipital is seen 
 the internal opening of the foramen lacerum posterius 
 (fig. 72, 22). The shape of this opening varies. The ventro- 
 aiiterior border of the periotic is marked by a deep notch, the 
 sides of which sometimes unite, converting it into a foramen. 
 
 On the outer -side of the periotic, and clearly seen only 
 after the removal of the tympanic, are two holes, the fenestra 
 ovalis and the fenestra rotunda. 
 
 The tympanic (figs. 72, 15 and 75, 4) is a greatly expanded 
 boat-shaped bone, which forms the auditory bulla and lies 
 immediately ventral to the periotic ; it is separated from the 
 
 1 The dura mater is a membrane which lines the cranial cavity and 
 is formed of tough connective tissue. 
 
THE SKELETON OF THE DOG. THE SKULL. 393 
 
 periotic by the tympanic cavity into which the fenestra 
 rotunda and the fenestra ovalis open. 
 
 There are several other openings into the tympanic cavity. 
 
 (a) On the external surface is a large oval opening, the 
 external auditory meatus bounded by a thickened rim. 
 
 (6) Into the outer and anterior part of the cavity the 
 outer end of the Eustachian tube opens; while the inner 
 end passes through a foramen (fig. 75, 22) just external to the 
 foramen lacerum medium, on its way to open into the pharynx. 
 
 (c) The internal carotid artery also enters the tympanic 
 cavity by a canal which commences in the foramen lacerum 
 posterius, and passes forwards to open on the inner side of the 
 bulla. The artery then passes forwards, and barely appearing 
 on the ventral surface of the cranium, enters the brain cavity 
 through the foramen lacerum medium (fig. 75, 9). 
 
 Immediately behind the tympanic, between it and the 
 mastoid process of the periotic and the paroccipital process of 
 the exoccipital is the stylomastoid foramen (fig. 75, VIII). 
 
 Within the tympanic cavity are four small bones, the 
 auditory ossicles (cp. fig. 74), called respectively the mal- 
 leus, incus, lenticular and stapes; these together form a 
 chain extending from the fenestra ovalis to the tympanic 
 membrane. 
 
 The malleus has a somewhat rounded head (fig. 100, B, 1) 
 which articulates with the incus, while the other end of the 
 bone is drawn out into a long process, the manubrium, 
 which lies in relation to the tympanic membrane. The head 
 is also more or less connected by a thin plate of bone, the 
 lamella, to another outgrowth, the processus longus. The 
 incus (fig. 100, B, 3) is somewhat anvil-shaped, and is drawn 
 out into a process which is connected with the lenticular, a 
 nodule of bone interposed between the incus and the stapes, 
 with which it early becomes united. The stapes (fig. 100, B, 2) 
 is stirrup-shaped, consisting of a basal portion from which 
 arise two crura, which meet and enclose a space, the canal. 
 
394 THE VERTEBRATE SKELETON. 
 
 The squamosal (fig. 73, 7) is a large bone occupying much 
 of the side wall of the cranial cavity, and articulating above 
 with the parietal, and behind with the supra-occipital, while 
 in front it overlaps the frontal and alisphenoid. But though it 
 occupies so large a space on the outer wall, it forms very 
 little of the internal wall of the skull, but is really like a bony 
 plate attached to the outer surface of the cranial wall. The 
 squamosal is drawn out into a strong forward ly-directed zygo- 
 matic process which meets the jugal or malar. The ventral 
 side of the zygomatic process is hollowed out, forming the 
 glenoid fossa (fig. 75, 8), a smooth laterally elongated surface 
 with which the lower jaw articulates, while the hinder edge of 
 the glenoid fossa is drawn out into a rounded postglenoid 
 process (fig. 75, 23). The articulation is such as to allow 
 but little lateral play of the lower jaw. 
 
 (2) Bones in relation to the Optic capsules. 
 
 The only bone developed in relation to the optic capsule 
 on each side is the lachrymal. This is a small membrane 
 bone lying between the frontal and palatine behind, and the 
 maxilla and jugal in front. It is perforated by a prominent 
 lachrymal foramen (fig. 73, 13) which opens within the 
 orbit. 
 
 (3) Bones in relation to the Olfactory capsules. 
 
 In connection with the olfactory capsules, five pairs of 
 bones are developed, two pairs being membrane bones, and 
 three pairs cartilage bones. 
 
 Of membrane bones, the nasals (fig. 73, 4) are a pair of 
 long narrow bones, lying closely side by side, and forming 
 the main part of the roof of the olfactory chamber. Their 
 posterior ends overlap the froritals, and the outer margin of 
 each is in contact with the nasal process of the frontal, and 
 with the maxilla and premaxilla. 
 
 Lying immediately ventral to the nasals, and on each 
 side of the perpendicular mesethmoid, are the ethmoid or 
 
THE SKELETON OF THE DOG. THE SKULL. 395 
 
 turbinal bones, which have a curious character, being formed 
 of a number of delicate plates intimately folded on one 
 another. The posterior pair of these bones, the ethmo- 
 turbinals (fig. 72, 10), are the larger, and form a mass of 
 intricately folded lamellae attached behind to the cribriform 
 plate, and passing laterally into two thin plates of bone, 
 which abut on the maxillae. The uppermost lamella of each 
 ethmo-turbinal is larger than the others and more distinct. 
 It is sometimes distinguished as the naso -turbinal, and forms 
 an imperfect lower boundary to a canal, which is bounded 
 above by the nasals. In front of and somewhat below the 
 ethmo-turbinals, lie another pair of bones of similar character, 
 the maxillo-turbinals (fig. 72, 11). 
 
 The last bone to be mentioned in connection with the 
 olfactory capsules is a membrane bone, the vomer (fig. 72, 9). 
 This is a slender vertically-placed bone, whose anterior part lies 
 between the maxillo-turbinals, while behind it extends beyond 
 the mesethmoid, so as to underlie the anterior part of the pre- 
 sphenoid. The anterior part of the vomer forms a kind of 
 trough, while further back in the region of the ethmo-turbinals 
 it sends out a pair of strong lateral plates, each of which, 
 passing below the ethmo-turbinal, joins the side wall of the 
 nasal cavity, and forms a partition dividing the nasal 
 cavity into a lower narial passage and an upper olfactory 
 chamber. 
 
 THE JAWS. 
 
 In the embryo both upper and lower jaws are formed of 
 cartilaginous bars, but in the adult not only has the cartilage 
 entirely disappeared, but even cartilage bone is absent, the 
 jaws being formed of membrane bone. 
 
 3. THE UPPER JAW. 
 
 The bones of the upper jaw are closely connected with 
 those of the cranium proper and olfactory capsules. The most 
 
396 
 
 THE VERTEBRATE SKELETON. 
 
 22 
 
 FIG. 75. VENTRAL VIEW OF THE CRANIUM OF A DOG (Canisfami- 
 liaris) x f . (Camb. Mus. ) 
 
 anterior opening o'f carotid 
 canal. 
 
 10. postglenoid foramen. 
 
 11. alisphenoid. 
 
 12. presphenoid. 
 
 13. vomer. 
 
 1. supra-occipital. 
 
 2. foramen magnum. 
 
 3. occipital condyle. 
 
 4. tympanic bulla. 
 
 5. basi-occipital. 
 
 6. basisphenoid. 
 
 7. external auditory meatus. 14. jugal. 
 
 8. glenoid fossa. 15. pterygoid. 
 
 9. foramen lacerum medium and 16. palatal process of palatine. 
 
THE SKELETON OF THE DOG. THE SKULL. 397 
 
 17. maxilla (palatal portion). V 2 . foramen rotundum. 
 
 18. posterior palatine foramina. V 3 . foramen ovale. 
 
 19. anterior palatine foramen. VII. stylomastoid foramen. 
 
 20. premaxilla. IX, X, XI. foramen lacerum pos- 
 
 21. alisphenoid canal. terius. 
 
 22. Eustachian foramen. XII. condylar foramen. 
 
 23. postglenoid process of squa- i 2. second incisor. 
 
 mosal. c. canine. 
 
 II. optic foramen. pml, pm4. first and fourth pre- 
 
 III, IV, Vj, VI. foramen lacerum molars. 
 
 an terius. in 1. first molar. 
 
 posterior of them is the pterygoid (fig. 75, 15), a thin verti- 
 cally placed plate of bone, which articulates above with the 
 basisphenoid, the presphenoid, and the strong pterygoid pro- 
 cess of the alisphenoid. The ventral end of the pterygoid 
 is drawn out into a small backwardly-p rejecting hamular 
 process. In front the pterygoid articulates with the palatine, 
 a much larger bone, consisting of (1) a vertical portion, which 
 passes up to meet the orbitosphenoid and frontal, and sends 
 inwards a plate which meets the presphenoid and vomer, form- 
 ing much of the roof of the posterior part of the narial passage; 
 and (2) a strong horizontal portion, the palatal process (fig. 
 75, 16), which passes inwards and meets its fellow in the 
 middle line, forming the posterior part of the bridge of bone 
 supporting the hard palate. The palatal process is continuous 
 in front, with a large bone, the maxilla, which, like the pala- 
 tine, consists of vertical and horizontal portions. The vertical, 
 or facial portion (fig. 73, 5), i& the largest, and constitutes 
 the main part of the side of the face in front of the orbit, form- 
 ing also the chief part of the outer wall of the nasal cavity. 
 It is continuous in front with the premaxilla, above with the 
 nasal and frontal, and behind with the lachrymal, jugal, and 
 palatine. The horizontal, or palatal portion (fig. 75, 17), 
 forms the anterior part of the bony plate supporting the hard 
 palate, and meets its fellow in a long straight symphysis. The 
 junction line between the palatal and facial portions is called 
 
398 THE VERTEBRATE SKELETON. 
 
 the alveolar border, and along it are attached the canine, 
 premolar, and molar teeth. 
 
 The anterior part of the upper jaw on each side is formed 
 by a small bone, the premaxilla, which bears the incisor teeth. 
 It, like the maxilla, has a palatal portion (fig. 75, 20), which 
 meets its fellow in the middle line, and an ascending portion, 
 which passes backwards as the nasal process, 'tapering regu- 
 larly and lying between the nasal and the maxilla. The two 
 premaxillae form the outer and lower borders of the anterior 
 nares. The last bone to be mentioned in connection with the 
 upper jaw and face is the jugal or malar (figs. 73, 8, and 75, 14), 
 a strong bone which forms the anterior half of the zygomatic 
 arch. It is firmly united in front to the maxilla, and behind 
 meets the zygomatic process of the squamosal, being drawn 
 out dorsally into a short postorbital process at the point of 
 meeting. This process lies immediately below the postorbital 
 process of the frontal, and if the two met, as they do in some 
 mammals, they would partially shut off the orbit from a larger 
 posterior cavity, the temporal fossa. In the living animal a 
 ligament unites the two postorbital processes. 
 
 (b) THE LOWER JAW OR MANDIBLE. 
 
 This consists of two elongated symmetrical halves, the 
 rami, which are united to one another at the median 
 symphysis in front, while behind they diverge considerably, 
 and each articulates with the glenoid surface of the corre- 
 sponding squamosal. In young animals the rami are united at 
 the symphysis by fibrous tissue, but in old animals they some- 
 times become fused together. The upper or alveolar border- 
 bears the teeth, and behind them is drawn out into a high 
 laterally compressed coronoid process (fig. 72, 24), which is 
 hollowed on its outer surface. Immediately behind the coronoid 
 process is the transversely elongated condyle (fig. 72, 25), 
 which fits into the glenoid cavity in such a way as to allow 
 free up and down movement of the jaw, with but little rolling 
 motion. The posterior end of the jaw below the condyle forms 
 
THE SKELETON OF THE DOG. THE SKULL. 399 
 
 a short rounded process, the angle (fig. 72, 26). Two promi- 
 nent foramina are to be seen in the lower jaw. These are 
 firstly the inferior dental foramen (fig. 72, 28), which lies 
 on the inner surface below the coronoid process ; through it 
 an artery and a branch of the fifth nerve enter to supply the 
 teeth, and secondly the mental foramen, which lies on the 
 outer side near the anterior end, and through which a branch 
 of the same nerve emerges. 
 
 (c) THE HYOID. 
 
 The Hyoid of the dog consists of a transverse median 
 piece, the basi-hyal 1 (fig. 72, 32), from which arise two pairs of 
 cornua. The anterior cornu is much the longer of the two, 
 and consists principally of three short separate ossifications, 
 placed end to end and called respectively the cerato-hyal 1 , 
 epi-hyal, and stylo-hyal. All of them are short rods of bone, 
 contracted in the middle, and expanded at the ends, where they 
 are tipped with cartilage. The cerato-hyal (fig. 72, 3 1 ) lies next 
 to the basi hyal. The stylo-hyal is terminated by a much smaller 
 bone, the tympano-hyal, which lies in a canal between the 
 tympanic and periotic, and is ankylosed to the periotic just 
 to the anterior and inner side of the stylomastoid foramen. 
 
 The posterior cornu of the hyoid is much smaller than 
 the anterior ; it consists of a short bone, the thyro-hyal (fig. 
 72, 33), which connects the basi-hyal with the thyroid cartilage 
 of the larynx. 
 
 FORAMINA OF THE SKULL. 
 
 The foramina, or apertures perforating the walls of the 
 skull, are very numerous, arid may either be due to holes 
 actually penetrating the bone, or may be small vacuities 
 between the margins of two elsewhere contiguous bones. 
 
 They may be divided into two groups, the first including 
 
 I. The holes through which the twelve cranial nerves 
 leave the cranial cavity. 
 
 1 These are not strictly homologous with the basi-hyal and cerato-hyal 
 of the Dogfish. 
 
400 THE VERTEBRATE SKELETON. 
 
 a. The most anterior of these nerves, the olfactory, leaves 
 the skull by a number of small holes piercing the cribriform 
 plate (fig. 72, 5). 
 
 6. The second, or optic, passes out by a large hole, the 
 optic foramen (fig. 75, II) piercing the orbitosphenoid. The 
 optic foramen is the most anterior of the three prominent 
 holes seen within and immediately behind the orbit. 
 
 c. The third, fourth, and sixth nerves, i.e. those supplying 
 the eye muscles, and with them the first or ophthalmic branch 
 of the large fifth or trigeminal nerve, pass out by a large hole, 
 the foramen lacerum anterius (fig. 75, III, IY, V^VI), 
 which, as has been already mentioned, lies between the 
 orbitosphenoid and alisphenoid. 
 
 d. Immediately behind the foramen lacerum anterius, the 
 alisphenoid is perforated by a prominent round hole, the 
 foramen rotundum (fig. 75, V 2 ), through which the second 
 branch of the trigeminal nerve passes out. 
 
 e. A quarter of an inch further back there is another 
 prominent hole, the foramen ovale (fig. 75, Y 3 ), through 
 which the third branch of the trigeminal nerve leaves the 
 cranium. 
 
 f. The seventh or facial nerve, as already mentioned, 
 leaves the cranial cavity and enters the auditory capsule, 
 through an opening in the periotic called the internal 
 auditory meatus, while it finally leaves the skull by the 
 stylomastoid foramen (fig. 75, VII), which lies between 
 the tympanic bulla, the paroccipital process, and the mastoid 
 portion of the periotic. 
 
 g. The eighth or auditory nerve on leaving the cranial 
 cavity, passes with the facial straight into the auditory capsule 
 through the internal auditory meatus (fig. 72, 20). It is 
 then distributed to the organ of hearing. 
 
 h. The ninth, tenth and eleventh nerves leave the skull 
 
THE SKELETON OF THE DOG. THE SKULL. 401 
 
 through the foramen lacemm posterms (fig. 75, IX, X, 
 XI), a large space lying between the auditory bones and the 
 exoccipital. 
 
 i. Finally, the twelfth nerve, the hypoglossal, passes out 
 through the prominent condylar foramen (fig. 75, XII), 
 which perforates the exoccipital just behind the foramen 
 lacerum posterius. 
 
 II. OTHER OPENINGS IN THE SKULL. 
 
 a. The anterior narial opening lies at the anterior end 
 of the skull, and is bounded by the premaxillae and nasals. 
 In the natural condition it is divided into two by a vertical 
 partition, formed by the narial septum, the anterior un- 
 ossified j5art of the mesethmoid. 
 
 b. Penetrating the middle of the maxilla at the side of 
 the face is the rather large infra-orbital foramen (fig. 73, 11), 
 through which part of the second branch of the trigeminal 
 nerve passes out from the orbit to the side of the face. 
 
 c. Several foramina are seen perforating the anterior part 
 of the orbit. The most dorsal of these, perforating the lach- 
 rymal bone, is the lachrymal foramen (fig. 73, 13). Lying 
 below and slightly external to this is a large foramen, through 
 which part of the second branch of the trigeminal enters on 
 its way to the infra-orbital foramen and so to the side of the 
 face. Lastly, lying below these, and perforating the palatine, 
 are two closely apposed foramina, the internal orbital 
 foramina, through which part of the first or ophthalmic 
 branch of the trigeminal nerve leaves the orbit, passing into 
 the nasal cavity. 
 
 d. The anterior part of the palate between the premaxillae 
 and the maxillae is perforated by a pair of long closely apposed 
 apertures, the anterior palatine foramina (fig. 75, 19). 
 They transmit part of the trigeminal nerve. 
 
 e. Towards the posterior part of the palate are two pairs 
 of small posterior palatine foramina (fig. 75, 18). These 
 
 R. 26 
 
 f 
 
402 THE VERTEBRATE SKELETON. 
 
 perforate the palatine and transmit branches of the trigeminal 
 nerve and certain blood-vessels. 
 
 f. The posterior narial opening is bounded chiefly by 
 the palatines. 
 
 g. The alisphenoid canal (fig. 75, 21) is a short canal 
 penetrating the base of the alisphenoid bone, and transmitting 
 the external carotid artery. It lies between the foramen 
 rotundum and the foramen ovale. 
 
 h. Between the auditory bulla and the foramen ovale are 
 seen two openings. The more external of these is the opening 
 of the Eustachian canal (fig. 75, 22), which communicates 
 with the tympanic cavity. The more internal is the foramen 
 lacerum* medium (fig. 75, 9), through which the internal 
 carotid enters the cranial cavity. 
 
 i. The external auditory aperture (fig. 75, 7) is a large 
 opening with rough edges at the outer side of the tympanic bulla. 
 
 j. Between it and the glenoid surface of the squamosal is 
 the postglenoid foramen (fig. 75, 10) through which a vein 
 passes out. 
 
 k. Lastly, there is the great foramen magnum (fig. 75, 2), 
 between the occipital condyles. Through it the brain and 
 spinal cord communicate. 
 
 C. THE RIBS AND STERNUM. 
 
 These, together with the thoracic vertebrae, form the 
 skeletal framework of the thorax. Each rib is a curved rod, 
 which at its dorsal end is movably articulated to the vertebra, 
 and at its ventral end is either connected with the sternum, or 
 ends freely. In the dog there are thirteen pairs of ribs, nine 
 pairs of which are directly connected with the sternum, while 
 the remaining four end freely and are known as floating ribs. 
 Each rib is obviously divided into two parts, a dorsal or ver- 
 tebral part, and a ventral or sternal part. The vertebral 
 portion, which forms about two-thirds of the whole rib, is a 
 flattened, regularly curved rod, completely ossified. Its dorsal 
 
 
THE SKELETON OF THE DOG. THE RIBS. 
 
 403 
 
 end is rounded, forming the head or capitlllum, which 
 articulates with a concave surface furnished partly by the cor- 
 responding vertebra and partly by the vertebra next in front. 
 The last three or four however articulate with one vertebra 
 only. A short way behind the capitulum on the dorsal side of 
 the rib is a rounded outgrowth, the tubercle or tuberculum, 
 by means of which the rib articulates with the transverse 
 process. The portion of the rib between the head and the 
 tubercle is known as the neck. The sternal portion of the 
 rib (fig. 76) is a short bar of calcined or imperfectly ossified 
 cartilage, about one-third of the length of the corresponding 
 bony portion. The anterior sternal ribs are somewhat more 
 cartilaginous than the posterior ones. The vertebral portions 
 
 FIG. 76. STERNUM AND STERNAL RIBS OF A DOG (Canis familiaris) 
 
 1. presternum. 4. 
 
 2. first sternebra of mesoster- 
 
 num. 
 
 3. last sternebra of mesoster- 
 
 num. o. 
 
 xiphisternum. The flattened 
 cartilaginous plate termi- 
 nating the xiphisternum is 
 not shown. 
 
 first sternal rib. 
 
 262 
 
404 THE VERTEBRATE SKELETON. 
 
 increase in length from the first which is very stout, and has 
 the capitulum and tuberculum very distinct, to about the 
 eighth or ninth ; afterwards they gradually diminish in size. 
 The first nine to eleven have the capitula and tubercula sepa- 
 rate, afterwards they gradually merge together. 
 
 THE STERNUM. 
 
 This is an elongated cylindrical structure lying in the mid- 
 ventral wall of the thorax, and is divided into eight segments 
 or sternebrae. The anterior segment, the presternum 
 (fig. 76, 1) or manubrium sterni is expanded in front; the 
 next six segments, which, together form the mesosternum 
 are elongated, somewhat contracted in the middle and ex- 
 panded at the ends. The last segment or xiphisternum 
 (tig. 76, 4) is long and narrow, and terminates in a flattened 
 expanded plate of cartilage. The first pair of sternal ribs 
 articulate with the sides of the presternum, and the remaining 
 pairs between the successive sternebrae. Between the last 
 sternebra and the xiphisternum two pairs articulate. De- 
 velopment shows that the sternum is formed by the union 
 in the middle line of two lateral portions ; this can be well 
 seen in the presternum and xiphisternum of the puppy, but no 
 traces of this median division remain in the adult dog. 
 
 2. THE APPENDICULAR SKELETON. 
 
 The appendicular skeleton consists of the bones of the 
 anterior and posterior limbs, and of their respective supports, 
 the pectoral and pelvic girdles. 
 
 THE PECTORAL GIRDLE. 
 
 The pectoral girdle lies external to the ribs, and has no 
 bony attachment to the axial skeleton. In almost all 
 Mammalia it is, as compared with that in Sauropsids, very 
 incomplete ; and in the dog it is even more reduced than in 
 the majority of Mammalia. The dorsal portion or scapula is 
 well developed, but the ventral portion is almost entirely absent. 
 
 The scapula is somewhat triangular in shape, the apex 
 
THE SKELETON OF THE DOG. PECTORAL GIRDLE. 405 
 
 being directed downwards and forwards, and being expanded 
 to form the shallow glenoid cavity with which the head of 
 the humerus articulates. The inner surface of the scapula is 
 nearly flat, while the outer is drawn out into a very prominent 
 ridge, the spine, which, arising gradually near the dorsal end, 
 runs downwards, dividing the surface into two nearly equal 
 parts, the prescapular and postscapular fossae, and ends 
 in a short blunt process, the acromion. The anterior border 
 of the scapula is somewhat curved, and is called the coracoid 
 border ; it is terminated ventrally by a slight blunt swelling, 
 the coracoid process, which ossifies from a different centre 
 from the rest of the scapula, and is probably the sole repre- 
 sentative of the coracoid. The dorsal or suprascapular 
 border of the scapula is rounded, while the posterior or 
 glenoid border is nearly straight. The clavicle 1 or collar 
 bone, which in a large proportion of mammals is well seen, in 
 the dog is very imperfectly developed ; it is short and broad, 
 and is suspended in the muscles, not reaching either the 
 scapula or sternum. 
 
 THE ANTERIOR LIMB. 
 
 The anterior limb of the dog is divisible into the usual 
 three portions, the brachium or upper arm, the anti- 
 brachium or fore-arm, and the manus or wrist and hand. 
 
 The brachium or upper arm includes only a single bone, 
 the humerus. 
 
 The humerus is a stout elongated bone, articulating by 
 its large proximal head (fig. 77, 1) with the glenoid cavity of 
 the scapula, and at its distal end by the trochlea with the 
 bones of the fore- arm. The head passes on its inner side into 
 an area roughened for the attachment of, muscles and called 
 the lesser tuberosity (fig. 77, 2) ; while in front it is divided 
 by the shallow bicipital groove from a large roughened area, 
 the greater tuberosity (fig. 77, 3), which is continued as a 
 
 1 See note to p. 25. 
 
406 THE VERTEBRATE SKELETON. 
 
 slight roughened ridge, extending about one-third of the way 
 down the outer side of the shaft. This ridge, which in many 
 animals is much more strongly developed than it is in the dog, 
 is called the deltoid ridge. The trochlea (fig. 77, 5) at the 
 distal end of the bone is a pulley-like surface, elevated at 
 the sides and grooved in the middle. It articulates with the 
 radius and ulna of the fore-arm. On each side of it are slight 
 roughened, projections, the internal and external condyles 
 (fig. 77, 7). In the cat and many other animals there is a 
 foramen, the ent-epicondylar foramen above the internal 
 condyle, but in the dog this is not developed. Passing up 
 the shaft from the external condyle is a slight ridge, the supi- 
 nator or ectocondylar ridge ; this is better developed in 
 many mammals. Immediately above the trochlea in front 
 and behind are the deep supra-trochlear fossae, which 
 communicate with one another through the supra-trochlear 
 foramen (fig. 77, 8). The posterior of these, the olecranon 
 fossa, is much the deeper, and receives the olecranon process 
 of the ulna when the arm is extended. The head and 
 tuberosities of the humerus ossify from one centre, the shaft 
 from a second, and the trochlea and condyles from a third. 
 
 The fore-arm or antibrachium contains two bones, 
 the radius and ulna ; they are immovably articulated with 
 one another, but not fused. The pre-axial bone, the radius 
 (fig. 77, B), which lies more or less in front of the ulna, is 
 external to the ulna at its proximal end, and at its distal end is 
 internal to that bone. It articulates with the external portion 
 of the trochlea, while the ulna articulates with the internal 
 portion. It is a straight bone with its distal end slightly larger 
 than its proximal end. The proximal end articulates with the 
 trochlea, the distal ehd with the bones of the carpus. 
 
 The post-axial bone, the ulna (fig. 77, C), has the proximal 
 end much enlarged, forming the olecranon (fig. 77, 11), and 
 tapers gradually to the distal end. Near its proximal end 
 the ulna is marked by a deep sigmoid notch, which bears 
 
THE SKELETON OF THE DOG. ANTERIOR LIMB. 407 
 
 on its inner side a concave surface (fig. 77, 12) for articulation 
 with the trochlea. The pointed proximal end of the sigmoid 
 
 FIG. 77. BONES OF THE LEFT UPPER ABM AND FOKE-ABM OF A DOG 
 
 { Cam's familiaris) x \. 
 
 A, humerus (seen from the posterior side) ; B, radius, C, ulna, both seen 
 from the anterior side. 
 
 1. head. 9. proximal end of the radius. 
 
 2. lesser tuberosityJP 4W- ' 10. 
 
 3. greater tuberosity. 11. 
 
 4. shaft of the humerus. 12. 
 
 5. trochlea. 
 
 6. internal condyle. 13. 
 
 7. external condyle. 
 
 8. supra-trochlear foramen. 
 
 14. 
 
 shaft of the radius. 
 
 olecranon. 
 
 surface for articulation with 
 
 the trochlea. 
 surface for articulation with 
 
 the radius, 
 distal end of the ulna. 
 
408 THE VERTEBRATE SKELETON. 
 
 notch is called the coronoid process. Somewhat in front 
 of and below the sigmoid notch is a smaller hollow (fig. 77, 13), 
 with which the radius articulates. 
 
 In the young animal the ends of both radius and ulna are 
 seen to ossify from centres different from those forming the 
 shafts. The epiphyses forming both ends of the radius, and the 
 distal end of the ulna are large, while that at the proximal end 
 of the ulna is small, and forms only the end of the olecranon. 
 
 The Maims is divided into 
 
 a. The carpus or wrist, formed of a group of small 
 bones. 
 
 b. The hand, which includes firstly some elongated 
 bones, the metacarpals, forming what corresponds to the 
 palm of the hand, and secondly the phalanges, which form the 
 fingers. 
 
 The Carpus or wrist. The carpus of the dog consists of 
 seven small bones, arranged in a proximal row of three, and 
 a distal row of four. It differs much from the simpler type 
 met with in the newt. The largest bone of the proximal row 
 is the scapho-lunar (fig. 80, 1), formed by the fused scaphoid 
 (radiale), lunar (intermedium), and centrale ; it has a large 
 convex proximal surface for articulation with the radius, and 
 articulates distally with the trapezium, trapezoid, and magnum, 
 and internally with the cuneiform. The cuneiform (ulnare) 
 (fig. 80, 2) has a posterior rounded surface articulating with 
 the ulna ; it articulates in front with the unciform, arid in- 
 ternally with the pisiform (fig. 80, 7), which is a compara- 
 tively large sesamoid bone on the ulnar side of the carpus. 
 Frequently also there is a small sesamoid* bone on the radial 
 side of the carpus. The trapezium (carpale 1), trapezoid 
 (carpale 2), and magnum (carpale 3) (fig. 80, 5) are all small 
 bones, and support respectively the first, second, and third 
 metacarpals. The unciform (carpalia 4 and 5) (fig. 80, 6) 
 is larger, and supports the fourth and fifth metacarpals. 
 
THE SKELETON OF THE DOG. PELVIC GIRDLE. 409 
 
 The hand has five digits, each consisting of an elongated 
 metacarpal, followed by phalanges, the last of which, the 
 ungual phalanx, is pointed and curved, and bears the claw. 
 Each of the metacarpals is seen in the young animal to have 
 its distal end formed by a prominent epiphysis, and each of 
 the phalanges, except those bearing the claws, has a similar 
 epiphysis at its proximal end. 
 
 The pollex (fig. 80, A, I) is far shorter than the other digits, 
 and normally does not touch the ground in walking. It has 
 only two phalanges, while each of the other digits has three. 
 A pair of small sesamoid bones are developed on the ventral or 
 fiexor side of the metacarpo-phalangeal articulations of all the 
 digits except the pollex. Frequently similar sesamoid bones 
 occur also on the dorsal side of the phalangeal articulations. 
 
 THE PELVIC GIRDLE. 
 
 The pelvic girdle consists of two halves, which lie nearly 
 parallel to the vertebral column. 
 
 Each half is firmly united to its fellow in a ventral 
 symphysis behind, and is in front expanded and united to the 
 sacrum. Each half or innominate bone is seen in the young 
 animal to consist of four distinct parts, the ilium or dorsal 
 element, the pubis or anterior ventral element, the ischium 
 or posterior ventral element, and a small fourth part, the 
 acetabular or cotyloid bone, wedged in between the three 
 others. These parts, though all distinct in the young animal, 
 are in the adult so completely fused that their respective 
 boundaries cannot be distinguished. At about the middle of 
 the outer surface of the innominate bone is a very deep cavity, 
 the acetabulum (fig. 78, A, 1) with which the head of the 
 femur articulates ; all the bones except the pubis take part 
 in its formation. 
 
 The ilium is a rather long bone, expanded in front and 
 contracted behind ; it forms about half the acetabulum. On 
 its inner or sacral surface (fig. 78, 4) is a large roughened 
 
410 
 
 THE VERTEBRATE SKELETON. 
 
 patch for articulation with the sacrum ; its outer or gluteal 
 surface is concave. The posterior part of the bone is flattened 
 below, forming the narrow iliac surface (fig. 78, A, 5). 
 
 10- 
 
 FIG. 78. EIGHT INNOMINATE BONE, A, or A FULL-GROWN TERRIER, B, OF 
 
 A COLLIE PUPPY, x 1. 
 A is seen from the ventral side, B from the inner or sacral side. 
 
 acetabulum. 8. 
 
 thyroid foramen. 9. 
 
 supra-iliac border of ilium. 10. 
 
 sacral surface. 11. 
 
 iliac surface. 12. 
 
 acetabular border. 13. 
 
 pubic border. 14. 
 
 ischial border. 
 
 ischium. 
 
 tuberosity of ischium. 
 
 ischial symphysis. 
 
 pubis. 
 
 pubic symphysis. 
 
 cotyloid or acetabular bone. 
 
 The ischium (fig. 78, 9) is a wide flattened bone forming 
 the posterior part of the innominate bone. It meets the 
 pubis ventrally, but is separated from it for the greater part 
 of its length by the large obturator or thyroid foramen 
 (fig. 78, 2). At its posterior end externally it bears a rather 
 
THE SKELETON OF THE DOG. PELVIC GIRDLE. 411 
 
 prominent roughened ischial tuberosity (fig. 78, A, 10). 
 The ischium meets its fellow in a ventral symphysis, and 
 forms about one-third of the acetabulum. 
 
 FIG. 79. FRONT VIEW OF THE LEFT LEG BONES OF A DOG (Canis 
 
 familiaris) x ^. 
 A femur, B tibia, C fibula, D patella. 
 
 1. head of femur. 5. external condyle. 
 
 2. neck. 6. internal condyle. 
 
 3. great trochanter. 7. fabella. 
 
 4. shaft. 8. cnemial crest. 
 
 The pubis (fig. 78, 12) is smaller than either the ischium 
 or ilium ; it does not take part in the formation of the aceta- 
 bulum, and like the ischium, meets its fellow in a ventral 
 symphysis. The acetabular bone (fig. 78, B, 14) is small 
 
412 THE VERTEBRATE SKELETON. 
 
 and triangular, and is wedged in between the other three. It 
 forms about one-sixth of the acetabulum. 
 
 THE POSTERIOR LIMB. 
 
 The posterior limb, like the anterior, is divisible into three 
 parts; these are the thigh, the crus or shin, and the pes. 
 
 The thigh contains only a single bone, the femur. 
 
 The femur is a long straight bone with a nearly smooth 
 shaft and expanded ends. The proximal end bears on its 
 inner side the large rounded head (fig. 79, A, 1) which 
 articulates with the acetabulum. External to the head and 
 divided from it by a deep pit is a large rough outgrowth, 
 the great trochanter (fig. 79, 3). The deep pit is the 
 trochanteric or digital fossa. On the inner side below the 
 head is a smaller roughened surface, the lesser trochanter. 
 The lower or distal end of the bone bears two prominent 
 rounded surfaces, the condyles, which articulate with the 
 tibia. They are separated from one another by the deep 
 intercondylar notch, which is continued above and in front 
 as a shallow groove, lodging a large sesamoid bone, the patella 
 or knee-cap. At the back of the knee-joint are a pair of 
 smaller sesamoids, the fabellae (fig. 79, 7). 
 
 In the young animal there are three epiphyses to the shaft 
 of the femur, one forming the head, one the great trochanter, 
 and one the distal end. 
 
 The crus or shin contains two bones, the tibia and 
 fibula. The tibia is a fairly thick straight bone, expanded 
 at both ends, especially at the head or proximal end. The 
 proximal end is triangular in cross section, and bears two facets 
 for articulation with the condyles of the femur. The anterior 
 surface of the proximal end of the tibia is marked by the 
 strong cnemial crest (fig. 79, 8), which runs some way down 
 the shaft. The distal end of the tibia articulates with the 
 astragalus by an irregular, somewhat square surface. 
 
THE SKELETON OF THE DOG. POSTERIOR LIMB. 413 
 
 The shaft of the tibia ossifies from one centre, the distal end 
 from a second, and the proximal end from two more. 
 
 The fibula (tig. 79, C) is a distinct but very slender bone, 
 somewhat expanded at both ends. It lies external to the 
 
 FIG. 80. A, BIGHT MANUS, B, RIGHT PBS OF A DOG (Cams fami 
 liaris)x% (after VON ZITTEL). 
 
 1. bone representing the fused 
 
 scaphoid, lunar and cen- 
 trale. 
 
 2. cuneiform. 
 
 3. trapezium. 
 
 4. trapezoid. 
 
 5. magnum. 
 
 6. unciform. 
 
 7. pisiform. 
 
 9. fifth metacarpal. 
 10. astragalus, 
 calcaneum. 
 navicular. 
 middle cuneiform, 
 external cuneiform, 
 cuboid, 
 first metatarsal. 
 
 11. 
 
 12. 
 13. 
 14. 
 15. 
 16. 
 
 8. first metacarpal. 
 
 The digits are numbered with 
 Eoman numerals. 
 
414 THE VERTEBRATE SKELETON. 
 
 tibia and articulates by its proximal end with the head of the 
 tibia, and by its distal end with the calcaneum. Its shaft 
 and proximal end ossify from one centre, and its distal end 
 from a second. 
 
 The Pes. 
 
 The structure of the pes corresponds closely with that of 
 the manus. It is divided into : 
 
 a. The tarsus or ankle formed of a group of small 
 bones. 
 
 6. The foot, which includes, firstly, some elongated bones, 
 the metatarsals, forming what corresponds to the sole of 
 the foot, and secondly the phalanges, which form the toes. 
 
 The Tarsus. The tarsus of the dog consists of seven bones 
 arranged in two rows, of two and four respectively, with a 
 centrale between them. The two bones of the proximal row 
 are the astragalus and calcaneum. 
 
 The astragalus (fig. 80, 10) corresponds to the fused 
 tibiale and intermedium of the typical tarsus. Its proximal 
 end is much wider than its distal end, and forms a large 
 rounded condyle articulating with the tibia, while its pos- 
 terior end meets the navicular. It lies to the dorsal side of 
 the foot. 
 
 The calcaneum (fibulare) (fig. 80, 11), the thickest bone 
 in the pes, lies somewhat behind, and to the outer side of the 
 astragalus. It articulates with the astragalus and fibula, and 
 is drawn out behind into a long rounded process, which forms 
 the heel, and is in the young animal terminated by an epi- 
 physis. Between the proximal and distal rows of tarsals is 
 the navicular (centrale) (fig. 80, 12), a somewhat flattened 
 and square bone articulating with the astragalus. 
 
 The distal row of tarsals consists of four bones. The 
 internal cuneiform (tarsale 1) is a smooth flattened bone 
 lying to the inner side of the foot; it articulates with the 
 
THE SKELETON OF THE DOG. THE PES. 415 
 
 first metatarsal and with the navicular. The middle cunei- 
 form (tarsale 2) (fig. 80, 13) is a still smaller bone, lying 
 external to the internal cuneiform. It articulates with the 
 second metatarsal and with the navicular. The external 
 cuneiform, (tarsale 3) (fig. 80, 14) is a larger, somewhat square 
 bone lying external to the middle cuneiform. It articulates 
 with the third metatarsal and with the navicular. The cuboid 
 (tarsalia 4 and 5) (fig. 80, 15) is a considerably larger bone 
 lying to the outer side of the foot. It articulates with the 
 fourth and fifth metatarsals and with the calcaneum. 
 
 The pes has sometimes five digits, sometimes four, the 
 hallux being absent. Even when present the hallux (fig. 80, 
 B, I) is commonly much reduced, and may be quite vestigial, 
 and represented only by a small nodular metatarsal. 
 
 Each of the other digits consists of a long metatarsal, 
 which in the young animal has a prominent epiphysis at its 
 distal end, and of three phalanges. The proximal and middle 
 phalanges have epiphyses at their proximal ends, while the 
 distal phalanx is without epiphyses and is claw-shaped. 
 
CHAPTER XXII. 
 
 GENERAL ACCOUNT OF THE SKELETON IN 
 MAMMALIA. 
 
 THE EXOSKELETON AND VERTEBEAL COLUMN. 
 
 EPIDERMAL EXOSKELETON. 
 
 Hair, which forms the characteristic Mammalian exo- 
 skeleton varies much in different animals, and in different 
 parts of the same animal. A large proportion of mammals 
 have the surface fairly uniformly covered with hair of one 
 kind only. In some forms however there are two kinds of 
 hair, a longer and stiffer kind alone appearing on the surface, 
 and a shorter and softer kind forming the under fur. In 
 most mammals hairs of a special character occur in certain 
 regions, such as above the eyes, on the margins of the 
 eyelids, and on the lips and cheeks, here forming the vibrissae 
 or whiskers. 
 
 Sometimes as in Hippopotamus, Orycteropus and the Sirenia, 
 the hair, though scattered over the whole surface, is extremely 
 scanty, while in the Cetacea it is limited to a few bristles 
 in the neighbourhood of the mouth, or may even be absent 
 altogether in the adult. In most mammals the hairs are 
 shed and renewed at intervals, sometimes twice a year, before 
 and after the winter. The vibrissae or large hairs which 
 occur in many animals upon the upper lip, and the mane and 
 tail of Equidae are probably persistent. 
 
THE SKELETON IN MAMMALIA. EXOSKELETON. 417 
 
 In the hedgehogs, porcupines and Echidna certain of the 
 hairs are modified and greatly enlarged, forming stiff spines. 
 Similar spines occur in the young of Centetes, and in Acan- 
 thornys among the Muridae. 
 
 Several other forms of epidermal exoskeleton are met with 
 in mammals, including : 
 
 (a) Scales. These overlie the bony scutes of armadillos 
 and occur covering the tail in several groups of mammals, such 
 as beavers and rats. In the Manidae the body is covered by 
 flat scales which overlap. 
 
 (b) The horns of Bovine Ruminants. These, which must 
 on no account be confused with antlers, are hollow cases of 
 hardened epidermis fitting on to bony outgrowths of the frontals. 
 In almost every case they are unbranched structures growing 
 continuously throughout life, and are very rarely shed entire. 
 In the Prongbuck A ntilocapra however they are bifurcated and 
 are periodically shed. Horns are nearly always limited to a 
 single pair, but the four-horned antelope Tetraceros has two 
 pairs, the anterior pair being the smaller. 
 
 (c) The horns of Rhinoceroses. These are conical 
 structures composed of a solid mass of hardened epidermal 
 cells growing from a cluster of long dermal papillae. From 
 each papilla there grows a fibre which resembles a thick hair, 
 and cementing the whole together are cells which grow from 
 the interspaces between the papillae. These fibres differ from 
 true hairs in not being developed in pits in the dermis. 
 Rhinoceros horns may be either one or two in number, and 
 are borne on the fronto-nasal region of the skull. They vary 
 much in length, the longest recorded having the enormous 
 length of fifty-seven inches. 
 
 (d) Nails, hoofs and claws. In almost all mammals 
 except the Cetacea, these are found terminating the digits of 
 both limbs. Nails are more or less flattened structures, 
 claws are pointed and somewhat curved. In most mammals 
 
 R. 27 
 
418 THE VERTEBRATE SKELETON. 
 
 the nails tend to surround the ends of the digits much more 
 than they do in man. Sometimes the nail of one digit differs 
 from that of all the others ; thus the second digit of the pes in 
 the Hyracoidea and Lemuroidea is terminated by a long claw, 
 the other digits having flat nails. In the Felidae the claws 
 are retractile, the ungual phalanx with claw attached folding 
 back when the animal is at rest into a sheath, above, or by 
 the side of the middle phalanx. In the Sloths and Bats 
 enormously developed claws occur, forming hooks by which the 
 animals suspend themselves. In Notoryctes the third and 
 fourth digits of the manus bear claws of great size; simi- 
 lar claws occur in Chrysochloris, being correlated in each case 
 with fossorial habits. The nail at its maximum development 
 entirely surrounds the terminal phalanx of the digit to which 
 it is attached, and is then called a hoof. Hoofs are specially 
 characteristic of the Ungulata. 
 
 (e) Spurs and beaks are structures which are hardly re- 
 presented among mammals, while so characteristic of birds. 
 They are however both found in the Monotremata. In 
 both Echidna and Ornithorhynchus the male has a peculiar 
 hollow horny spur borne on a sesamoid bone articulated to 
 the tibia. The jaws in Ornithorhynchus are cased in horny 
 beaks similar to those of birds, and are provided with horny 
 pads which act as teeth. 
 
 (/) Horny plates of a ridged or roughened character 
 occur upon the anterior portion of the palate, and of the man- 
 dibular symphysis in all three genera of recent Siren ia ; also 
 upon the toothless anterior portion of the palate in Ruminants. 
 
 (g) The baleen of whales also belongs to the epidermal 
 exoskeleton. It consists of a number of flattened horny plates 
 arranged in a double series along the palate. The plates are 
 somewhat triangular in form and have their bases attached 
 to the palate at right angles to its long axis, while their apices 
 hang downwards into the mouth cavity. The outer edge 
 of each plate is hard arid smooth, while the inner edge and. 
 
THE SKELETON TN MAMMALIA. EXOSKELETON. 
 
 apex fray out into long fibres which look like hair. At the 
 inner edge of each principal plate are subsidiary smaller plates. 
 The plates are formed of a number of fibres each developed 
 round a dermal papilla in the same way as are the fibres 
 forming the horns of Rhinoceros. Baleen and Rhinoceros 
 horn likewise agree in that the fibres are bound together by 
 less hardened epithelial cells, which readily wear away and 
 allow the harder fibres to fray out. The greatest develop- 
 ment of baleen occurs in the Northern Right whale, Balaena 
 mysticetus, in which the plates number three hundred and 
 eighty or more on each side, and reach a length of ten or 
 twelve feet near the middle of the series. 
 
 DERMAL EXOSKELETON. 
 
 Mammals show two principal kinds of exoskeletal struc- 
 tures which are entirely or partially dermal in origin, viz. the 
 bony scutes of armadillos, and teeth. 
 
 The bony scutes of armadillos are quadrate or polygonal 
 in shape and are in general aggregated together, forming 
 several shields protecting various re'gions of the body. The 
 head is generally protected by a cephalic shield, the anterior 
 part of the body by a scapular, and the posterior by a pelvic 
 shield. The tail is also generally encased in bony rings, and 
 scutes are irregularly scattered over the surface of the limbs. 
 The mid-body region is protected by a varying number of 
 bands of scutes united by soft skin, so as to allow of move- 
 ment. Corresponding to each dermal scute is an epidermal 
 plate. In Chlamydophorus the scutes are mainly confined to 
 the posterior region where they form a strong vertically-placed 
 shield which coalesces with the pelvis. The anterior part of 
 the body is mainly covered by horny epidermal plates with 
 very little ossification beneath. In the gigantic extinct 
 Glyptodonts the body is covered with a solid carapace 
 formed by the union of an immense number of plates, and 
 there are no movable rings. The top of the head is defended 
 
 272 
 
420 THE VERTEBRATE SKELETON. 
 
 by a similar plate, the tail is generally encased in an unjointed 
 bony tube, and there is commonly a ventral plastron. 
 
 In Phocaena phocaenoides the occurrence of vestigial dermal 
 ossicles has been described, and in Zeuglodon the back was 
 probably protected by dermal plates. 
 
 TEETH 1 . 
 
 Teeth are well developed in the vast majority of mammalia, 
 and are of the greatest morphological and systematic import- 
 ance, many extinct forms being known only by their teeth. 
 Mammalian teeth differ from those of lower animals in various 
 well-marked respects. (1) They are attached only to the 
 maxillae, premaxillae and mandible, never to the palatines, 
 pterygoids or other bones. (2) They frequently have more 
 than one root. (3) They are always, except in some Odon- 
 toceti, placed in distinct sockets. (4) They are hardly ever 
 ankylosed to the bone. (5) They are in most cases markedly 
 heterodont. (6) They are commonly developed in two sets, 
 the milk dentition and permanent dentition. 
 
 It sometimes happens that teeth after being formed are 
 reabsorbed without ever cutting the gum. This is the case, 
 for instance, with the upper incisors of Ruminants. 
 
 The form of mammalian teeth varies much, some are simple 
 conical structures comparable to those of most reptiles, and 
 these may either have persistent pulps, as in the case of the 
 upper canines of the Walrus and the tusks of Elephants, or 
 may be rooted as in most canine teeth. Some teeth have chisel- 
 shaped edges, and this may be their original form, as in the 
 
 1 See W. H. Flower, "Remarks on the homologies and notation of the 
 teeth in Mammalia," J. Anat. and Physiol. norm, path., Vol. iii., p. 262; 
 R. Owen, Odontography, London, 1840 45; C. S. Tomes, Manual of 
 Dental Anatomy, London, 1876. See also H. F. Osborn, "Recent re- 
 searches on succession of teeth in Mammals," Amer. Natural., xxvu., 
 p. 493, and "Rise of Mammalia in N. America," Stud. Biol. Lab. Columb. 
 Coll, Zool. i., no. 2. 
 
THE SKELETON IN MAMMALIA. THE TEETH. 
 
 421 
 
 human incisors, or may, as in those of Rodents, be brought 
 about by the more rapid wearing away of the posterior edge, 
 the anterior edge being hardened by a layer of enamel. 
 
 m.c 
 
 m 2 
 
 pnr4 
 
 FIG. 81. SKULL OF A YOUNG INDIAN EHINOCEBOS (R. unicornis), 
 
 SHOWING THE CHANGE OF THE - DENTITION X \. (Brit. MllS.) 
 
 1. nasal. 
 
 2. frontal. , 
 
 3. parietal. 
 
 4. zygomatic process of squa- 
 
 mosal. 
 
 5. jugal. 
 
 wiJT milk incisor. 
 
 inc. milk canine. 
 
 mpm r milk premolar. 
 
 I r first incisor. 
 
 c. canine. 
 
 pm 2 , pm s , pm^. 2nd, 3rd and 
 
 4th premolars. 
 ?!, w 2 . first and second molars. 
 
 Then, again, the crown may, as in the majority of grinding 
 teeth, be' more or less flattened. The various terms used in 
 describing some of the forms of the surface of grinding teeth 
 are denned on page 345. 
 
 The teeth of the Aard Varks are compound, and differ 
 completely from those of all other mammals (see p. 425). 
 
 As a rule, the higher the general organisation of an anima] 
 
422 THE VERTEBRATE SKELETON. 
 
 the better are its milk teeth developed, and the more do they 
 form a reproduction on a small scale of the permanent set. 
 This fact is well seen in the Primates, Carnivora and Ungu- 
 lata. The method of notation by which the dentition of any 
 mammal can be briefly expressed as a formula has been already 
 described. The regular mammalian arrangement of teeth for 
 each side is expressed by the formula 
 
 i - c - pm - m x 2 ; total, 44. 
 o 1 4 o 
 
 MONOTEEMATA. Iii Echidna teeth are quite absent. In 
 the young Ornithorhynchus 1 functional molar teeth of a multi- 
 tubercular type resembling those of some Mesozoic mammalia 
 are present, but in the adult they disappear, their office being 
 discharged by horny plates. 
 
 MARSUPiALiA 2 have a heterodont dentition, which has 
 generally been regarded as almost monophyodont, the only 
 tooth which has an obvious deciduous predecessor being the 
 last premolar. The researches of Rose 3 and Kiikenthal 4 tend 
 to show that the teeth of Marsupials are developed in the 
 same way as in other mammals, and are diphyodont. In 
 the case of the premolars, teeth which are homologous with 
 the permanent teeth of other mammals begin to develop as 
 lateral outgrowths from the milk teeth, but afterwards be- 
 come absorbed, so that the teeth which actually persist belong 
 to the milk series. The last premolar, however, does as 
 a rule develop and replace its milk predecessor; sometimes, 
 however, as in Didelphys, it takes its place among the milk 
 molars without replacing one of them. 
 
 1 See E. B. Poulton, P. R. S., Feb. 1888, and Quart. J. Micr. Sci., 
 Vol. xxix. 1889; also Oldfield Thomas, P. E. S., XLVI. (1889). 
 
 2 W. H. Flower, Phil. Trans., vol. 156, pp. 631 641, 1867 ; also 
 Oldfield Thomas, Phil. Trans., pp. 443462, 1887. 
 
 3 C. Rose, Anat. Anz. vn., p. 639. 
 
 4 W. Kiikenthal, Anat. Anz. vi., p. 364. 
 
THE SKELETON IN MAMMALIA. THE TEETH. 423 
 
 The types of dentition characteristic of the different groups 
 of placental mammals may mostly be paralleled among 
 the Marsupials. Thus among the polyprotodont forms the 
 Didelphyidae or opossums, and some of the Dasyuridae, such 
 as Sarcophilus and Thylacinus, have a typical carnivorous 
 dentition with small incisors, large canines, and molars with 
 pointed compressed crowns. The dental formula of Tkylacinus, 
 
 41 34 
 is i c T pin ^m -, total 46. 
 o 1 o 4 
 
 In Myrmecobius five or six molar teeth occur on each side, 
 and the total number of teeth reaches fifty-two or fifty-six. 
 The teeth bear rows of tubercles, and resemble those of the 
 Multituberculate mesozoic Mammals 1 , more than do those of 
 any other living form. Calcified teeth have recently been 
 described 2 in Myrmecobius earlier than the functional or milk 
 set. This would relegate the milk teeth of mammals in general 
 
 to a second series, and the permanent teeth to a third. In 
 
 31-24 
 Notary ctes the dental formula 3 is given as i ^ c ^ pm ^ m ^ , 
 
 total 40. The canines are small, and the anterior molars 
 have strongly developed cusps, and much resemble those of 
 Chrysochloris (Insectivora). 
 
 Among the diprotodont types the Phascolomyidae, or 
 Wombats, have a dentition recalling that of the Rodents. All 
 the teeth grow from persistent pulps, and the incisors have 
 enamel only on the anterior surface as in Rodents. The dental 
 
 formula is i | c |j pm ^ m^ , total 24. There are indications 
 
 of a vestigial second pair of incisors. 
 
 The Macropodidae, or Kangaroos, have a herbivorous 
 
 O /A 1 \ 9 A 
 
 dentition with the formula i - c ^ Q ' pm^m-^. The incisors 
 are sharp and cutting, and are separated by a long diastema or 
 
 i See p. 348. 2 W. Leche, Morph. Jahrb. xx., pp. 113142 (1893). 
 3 E. C. Stirling, P. Z.S. 1891, p. 327. 
 
424 THE VERTEBRATE SKELETON. 
 
 gap from the molars, which have their crowns marked by ridges 
 or cusps. There are indications of several vestigial incisors. 
 
 Coenolestes, a remarkable form recently described from 
 America, belongs to the diprotodont section, and is the only 
 living member of the section known outside the Australian 
 region 1 . An exceptional dentition is seen in the case of the 
 extinct Thylacoleo, in which the functional teeth are reduced 
 to two pairs; one pair of large cutting incisors and one of 
 compressed sharp-edged premolars. 
 
 EDENTATA. Some Edentata, viz. the anteaters (Myrme- 
 cophagidae) are, as far as is known, absolutely toothless at all 
 stages of their existence ; being the only mammals except 
 Echidna in which no tooth germs have been discovered ; 
 others, viz. the Manidae, though showing foetal tooth germs, 
 are quite toothless in post-foetal life ; others, viz. some of 
 the armadillos, have the largest number of teeth met with in 
 land mammals. The teeth are homodont except in the Aard 
 Yarks, and grow from persistent pulps. In the sloths (Brady- 
 podidae) and the Megatheriidae, there are five pairs of teeth in 
 the upper and four in the lower jaw. The teeth of sloths consist 
 of a central axis of vasodentine, surrounded firstly by a thin coat- 
 ing of hard dentine, and secondly by a thick coating of cement. 
 
 In no living Edentate have the teeth any enamel; it has, 
 however, been described as occurring in certain early Mega- 
 theroid forms from S. America 2 , and an enamel organ has 
 also been discovered in an embryo Dasypus*. In the Arma- 
 dillos (Dasypodidae) the number of teeth varies from f or \ in 
 Tatusia, to upwards of f J- in Priodon, which therefore may have 
 upwards of a hundred teeth, the largest number met with in any 
 land mammal. In Tatusia all the teeth except the last are 
 
 1 0. Thomas, P. Z. S., 1895, p. 870. 
 
 2 .Ameghino,Bull.Ac. Argen.xu. p. 437. According to H. Burmeister, 
 Annal. Mus. Buenos Aires, in. 401 (1891), enamel does not occur, osteo- 
 dentine having been mistaken for it. 
 
 3 E. Ballowitz, Arch. Mikr. Anat. XL. p. 133. 
 
THE SKELETON IN MAMMALIA. THE TEETH. 425 
 
 preceded by two-rooted milk teeth. The Aard Varks are 
 diphyodont, and milk teeth are also known in a species of 
 Dasypus, but with these exceptions Edentates are, as far as is 
 known, monophyodont. In Glyptodon the teeth are almost 
 divided into three lobes by two deep grooves on each side. 
 
 The Aard Varks (Orycteropodidae) are quite exceptional 
 as regards their teeth, which are cylindrical in shape, and 
 are made up of a number of elongated denticles fused to- 
 gether. Each denticle contains a pulp cavity from which a 
 number of minute tubes radiate outwards. These teeth are 
 diphyodont and somewhat heterodont, eight to ten pairs occur 
 in the upper jaw and eight in the lower, but they are not all in 
 place at one time. The last three teeth in each jaw are not 
 preceded by milk teeth 1 . 
 
 SIRENIA. The teeth of Sirenia show several very distinct 
 types, the least modified being that of the extinct Hali- 
 theriidae, which have large incisors in the upper jaw, and five 
 or six pairs of tuberculated grinding teeth in each jaw, the 
 anterior ones being preceded by milk teeth. 
 
 In both the living genera the dentition is monophyodont. 
 
 9 11 
 
 In Afanatus the dentition is i -^ pm and m . The incisors are 
 , 2 
 
 vestigial, and disappear before maturity. The grinding teeth 
 have square enamelled crowns marked by transverse tuber- 
 culated ridges. They are not all present in the jaw at the same 
 time. In Halicore the upper jaw bears a pair of straight tusk- 
 like incisors ; in the male these have persistent pulps and 
 project out of the mouth; in the female they soon cease to 
 grow and are never cut. They are separated by a long 
 diastema from the grinding teeth which have tuberculated 
 crowns and are 4- or in number, but are not all in place at 
 once. Several other pairs of slender teeth occur in the young 
 animal, but are absorbed or fall out before maturity. In 
 Rhytina teeth are altogether absent. 
 
 1 See Oldfield Thomas, P. R. S. t vol. XLVII., p. 246 (1890). 
 
426 THE VERTEBRATE SKELETON. 
 
 CETACEA. 
 
 ARCHAEOCETI. Zeuglodon has the following dentition, 
 
 31 5 
 
 i ^ c - pm and m -=, total 36. The incisors and canines are 
 31 5 
 
 simple and conical ; the cheek teeth are compressed and have 
 serrated cutting edges like those in some seals. 
 
 In the MYSTACOCETI, or whalebone whales, calcified tooth 
 germs probably belonging to the milk dentition are present 
 in the embryo, but they are never functional, and are al- 
 together absent in the adult. The anterior of these germs 
 are simple, the posterior ones are originally complex, but 
 subsequently split up into simple teeth like those of the 
 anterior part of the jaw. Hence according to Kukenthal, 
 who described these structures, the Cetacean dentition was 
 originally heterodont. 
 
 In the living ODONTOCETI the dentition is homodont and 
 monophyodont. In some cases traces occur of a replacing 
 dentition which never comes to maturity, and renders it pro- 
 bable that the functional teeth of the Odontoceti are really 
 homologous with the milk teeth of other mammals. Some of 
 the dolphins afford the apparently simplest type of mammalian 
 dentition known. The teeth are all simple, conical, slightly 
 recurved structures, with simple tapering roots and without 
 enamel. The dentition is typically piscivorous, being adapted 
 for seizing active slippery animals such as fish. The prey is 
 then swallowed entire without mastication. Sometimes the 
 teeth are excessively numerous, reaching two hundred or more 
 (fifty to sixty on each side of each jaw) in Pontoporia. This 
 multiplication of teeth is regarded by Kukenthal as due to the 
 division into three parts of numbers of trilobed teeth similar to 
 those of some seals. 
 
 In the Sperm whale, Physeter, the lower jaw bears a series 
 of twenty to twenty-five stout conical recurved teeth, while in 
 the upper jaw the teeth are vestigial and remain imbedded in 
 the gum. An extinct form, Physodon, from the Pliocene of 
 
THE SKELETON IN MAMMALIA. THE TEETH. 427 
 
 Europe and Patagonia is allied to the Sperm whale, but has 
 teeth in both jaws. In the Grampus Orca, the teeth number 
 about ^|, and are very large and strong. In some forms the 
 teeth are very much reduced in number ; thus in Mesoplodon 
 the dentition consists simply of a pair of conical teeth borne 
 in the mandible. In the Narwhal Monodon the dentition is 
 practically reduced to a single pair of teeth, which lie horizon- 
 tally in the maxilla, and in the female normally remain perma- 
 nently in the alveoli. In the male the right tooth remains 
 rudimentary, while the left is developed into an enormous 
 cylindrical tusk marked by a spiral groove. Occasionally both 
 teeth develop into tusks, and there is reason for thinking that 
 two-tusked individuals are generally or always female. In the 
 extinct Squalodon the dentition is decidedly heterodorit, and 
 the molars have two roots. The dental formula is 
 
 i =- c pm m -= , total 60. 
 
 It is probable that the homodont condition of modern Odonto- 
 ceti is not primitive, but due to retrogressive evolution. 
 
 UNGULATA. 
 
 Just as in the Cetacea a piscivorous dentition is most 
 typically developed, so the Ungulata are, as a group, the most 
 characteristic representatives of a herbivorous dentition in its 
 various forms. 
 
 UNGULATA VERA. 
 
 ARTIODACTYLA. As regards the living forms, the Artio- 
 dactyla can be readily divided into two groups, namely those 
 with bunodont and those with selenodont teeth. It has, how- 
 ever, been shown that selenodont teeth always pass through 
 an embryonic bunodont stage 1 . The bunodont type is best seen 
 
 in Pigs and Hippopotami and such extinct forms as Hyotherium. 
 
 /2 3\ } 43 
 
 In Hippopotamus the dental formula is i , - -=* c - pm 7^0- 
 
 (1 o) 1 4 o 
 
 1 J. Taeker, " Fur Kenntniss der Odontogenese bei Ungulaten."- Dorpat, 
 1892. 
 
428 THE VERTEBRATE SKELETON. 
 
 The incisors and canines of Hippopotamus are very large 
 and grow continuously. The genus Sus, which affords a good 
 instance of an omnivorous type of dentition, has the regular 
 
 unmodified Mammalian dental formula i - c - pin j m - , total 
 
 o 1 4 o 
 
 44. The canines, specially in the male, are large and have 
 persistent pulps, and the upper canines do not have the usual 
 downward direction but pass outwards and upwards. In the 
 Wart Hog, Phacochaerus, they are enormously large, but a 
 still more extraordinary development of teeth is found in 
 Babirussa. In the male Babirussa the canines, which are with- 
 out enamel, are long, curved and grow continuously. Those of 
 the upper jaw never enter the mouth, but pierce the skin of 
 the face and curve backwards over the forehead. The dental 
 
 21 23 
 formula of Babirussa is i J c ^pm -m^, total 34. 
 
 1 Jo 
 
 The Wart Hog has a very anomalous dentition, for as 
 age advances all the teeth except the canines and last molars 
 show signs of disappearing ; both pairs of persisting teeth are 
 however very large. 
 
 Various extinct Uiigulata such as Anoplotherium have 
 teeth which are intermediate in character between the bun- 
 odont and selenodont types. Anoplotherium has the regular 
 mammalian series of forty -four teeth. The crowns of all the 
 teeth are equal in height, and there is no diastema an 
 arrangement found in no living mammal but man. 
 
 We come now to the selenodont Artiodactyla. 
 
 The Tylopoda camels (Camelidae) and Llamas (Auchenii- 
 dae) when young have the full number of incisors, but in the adult 
 the two upper middle ones are lost. The molars are typically 
 selenodont and hypsodont 1 . In the Camel the dental formula 
 
 11 33 
 
 is i c ^pm ^m^, total 34. The upper incisors, canines and 
 o 1 2i o 
 
 first premolars of the Camel are very small teeth, and the 
 
 1 See p. 345. 
 
THE SKELETON IN MAMMALIA. THE TEETH. 429 
 
 first premolar is separated by a long diastema from the 
 others. 
 
 The Tragulina or Chevrotains have no upper incisors, while 
 the canines are largely developed, especially in the male. 
 
 The Ruminantia or Pecora are very uniform as regards 
 their dentition. The upper incisors are always absent, for 
 though their germs are developed they are reabsorbed without 
 ever becoming visible, and as a rule the upper canines are 
 absent too, while the lower canines are incisiform. The 
 grinding teeth are typically selenodont, and in the lower jaw 
 form a continuous series separated by a wide diastema from 
 the canines. The dental formula is usually 
 
 .0 01 3 3 
 
 The canines are largely developed in the male Muskdeer 
 (Moschus) and in Hydropotes. 
 
 PERISSODACTYLA. The premolars and molars have a very 
 similar structure and form a continuous series of large 
 square teeth with complex crowns. The crowns are always 
 constructed on some modification of the bilophodont 1 plan, as 
 is easily seen in the case of the forms with brachydont teeth, 
 but in animals like the Horse, in which the teeth are very 
 hypsodont, this arrangement is hard to trace. All four pre- 
 molars in the upper jaw are preceded by milk teeth, while in 
 Artiodactyla the first has no milk predecessors. 
 
 In the Tapiridae the grinding teeth are brachydont and 
 the lower ones are typically bilophodont. The last two upper 
 molars have the transverse ridges united by an outer longi- 
 
 31 43 
 
 tudinal ridge. The dentition is i ^ c =- pm -m-^, total 42. 
 
 o 1 o o 
 
 In some of the extinct Perissodactyles such as Lophiodon 2 , 
 
 1 See p. 345. 
 
 2 According to H. F. Osborn, Amer. Natural., xxvi. p. 763, a number of 
 not very closely allied forms have been included under Lophiodon. 
 
430 THE VERTEBRATE SKELETON. 
 
 the dentition is brachydont and bilophodont, the grinding 
 teeth in general resembing the posterior upper molars of the 
 Tapir. The same type of brachydont tooth is seen in Palaeo- 
 therium but the transverse ridges are crescentic instead of 
 straight, and are separated from one another by shallow 
 valleys without cement. Some of the Palaeotheridae have the 
 regular series of forty-four teeth. 
 
 A complete series of forms is known showing how from the 
 simple brachydont teeth of the Palaeotheridae, were derived 
 the complicated hypsodont teeth of the Equidae. The increase 
 in depth of the tooth was accompanied by increase in the 
 depth and complexity of the enamel infoldings, and of the 
 cement filling them. 
 
 Both upper and lower grinding teeth of the Equidae are 
 much complicated by enamel infoldings, but their derivation 
 from the bilophodont type can still be recognised. The 
 diastema in front of the premolars is longer in the living 
 Equidae than in their extinct allies. In the adult horse the 
 
 31 33 
 
 dental formula is i - c -pm-m-, total 40, with often a 
 o 1 66 
 
 vestigial first upper premolar (fig. 82, pm 1). The last molar is 
 not more complex than the others, and in the female the canine 
 is quite vestigial. The incisors are large and adapted for cutting 
 and have the enamel curiously folded in forming a deep pit. 
 
 30 3 
 
 The milk dentition is di -= dc - dpm - , total 24. The last 
 
 o 6 
 
 milk premolar is not more complex than the premolar that 
 succeeds it. The horse affords an excellent instance of a 
 typically herbivorous type of dentition, the cutting incisors, 
 reduced canines and series of large square flat-crowned grinding 
 teeth being most characteristic. 
 
 In Rhinoceros the grinding teeth are much like those of 
 Lophiodon, having an outer longitudinal ridge from which two 
 crescentic transverse ridges diverge. The upper premolars are 
 as complex as the molars, and there are no canines ; in some 
 
THE SKELETON IN MAMMALIA. THE TEETH. 431 
 
 ,-7 
 
 1.1 
 
 FIG. 82. PALATAL ASPECT OF THE CRANIUM AND MANDIBLE OF A 
 DONKEY (Equus asinus) x i. (Camb. Mus.) 
 
 1. supra-occipital. 
 
 2. occipital condyle. 
 
 3. basi-occipital. 
 
 6. glenoid surface. 
 
 7. vomer. 
 
 i 1, i 3. first and third incisors. 
 
 4. vacuity representing the con- c. canine. 
 
 fluent foramen lacerum pml,pm2. first and second pre 
 posterius and foramen la- molars, 
 
 cerum medium. m 1. first molar. 
 
 5. auditory bulla. 
 
432 THE VERTEBRATE SKELETON. 
 
 species incisors also are absent. The dental formula is 
 . (02) 43 
 
 ^0=T) C (0=l)^4 m 3- 
 
 Among the Titanotheriidae Palaeosyops 1 has very brachy- 
 dont teeth whose crowns have been described as buno-selenodont, 
 the inner pair of columns being bunodont, the outer, seleno- 
 dont. Similar grinding teeth occur in Chalicotherium. Some 
 of the Titanotheriidae have the regular mammalian series of 
 forty -four teeth. 
 
 SUBUNGULATA. 
 
 TOXODONTIA. Nesodon has the regular dental formula ; 
 its grinding teeth are rooted and the upper ones resemble those 
 of Rhinoceros. The second upper and third lower incisors 
 form ever-growing tusks. There is a marked difference between 
 the deciduous arid permanent dentition. Astrapotherium like- 
 wise has large rooted cheek teeth of a rhinocerotic type, and 
 each jaw bears a pair of permanently growing tusks, those 
 of the lower jaw being the canines. The dental formula is 
 
 10 23 
 i -z c - pm - m , total 28. 
 o I L o 
 
 In Toxodon the upper incisors and molars are large and curved 
 and all the teeth have persistent pulps. In Typotherium there 
 are no tusks, but the upper incisors are chisel-like, recalling 
 those of Rodents. 
 
 The CONDYLARTHRA have brachydont, generally bunodont 
 teeth, with the premolars simpler than the molars. They 
 generally have the regular dental formula. 
 
 HYRACOIDEA. The dental formula of Procavia is usually 
 
 given as i^ c -pm-m-, total 34; in young individuals how- 
 ever there occur a second pair of upper incisors which early 
 fall out. The upper incisors resemble those of Rodents in 
 being long and curved and growing from persistent pulps. 
 
 1 C. Earle, J. Ac. Philad., vol. ix., 1892, p. 267. 
 
THE SKELETON IN MAMMALIA. THE TEETH. 433 
 
 They are however triangular in transverse section, not rect- 
 angular, having two antero-lateral faces covered with enamel 
 and a posterior face without enamel. Their terminations 
 are pointed, not chisel-shaped as in Rodents. The lower in- 
 cisors (fig. 83, i 1) are pectinate or partially divided by vertical 
 fissures, and the grinding teeth are of the rhinocerotic type. 
 
 2 
 
 6 
 
 -h-\A 
 
 1.1 
 
 FIG. 83. SKULL OF Procavia (Dendrohyrax) dorsalisx%. (Camb. Mus.) 
 
 1. nasal. 5. jugal. 
 
 2. parietal. 6. lachrymal foramen. 
 
 3. external auditory meatus. i 1. first incisor. 
 
 4. paroccipital process of the 
 
 exoccipital. 
 
 AMBLYPODA. Two of the best known forms belonging to 
 this extinct group differ much as regards dentition. For while 
 Coryphodon has the regular dental formula, and the canines 
 of both jaws of moderate size, in Uintatherium the dentition 
 is very specialised, there are no upper incisors, and the upper 
 canines form a pair of enormous tusks. The grinding teeth 
 form a continuous series marked by V-shaped ridges and the 
 
 01 33 
 
 dental formula is i ^ c -- pm m total 34. 
 o 1 o o 
 
 PROBOSCIDEA. The incisors are composed entirely of den- 
 tine and have the form of conical tusks projecting greatly 
 R. 28 
 
434 THE VERTEBRATE SKELETON. 
 
 from the mouth. In living forms they are confined to the 
 upper jaw, in some species of the extinct Mastodon however 
 they occur in the lower jaw also. In Dinotherium they are 
 probably absent from the upper jaw, but form a pair of 
 downwardly and backwardly-directed tusks growing from the 
 elongated symphysis of the mandible. 
 
 The grinding teeth in the various Proboscidea show a very 
 remarkable series of modifications. In Dinotherium they are 
 bilophodont or else are marked by three straight transverse 
 
 . ? 23 
 ridges. I he dental tormula is * c -pm-?n~ , and the 
 
 teeth have the normal method of succession. In Masto- 
 don as in Dinotherium the grinding teeth are marked by 
 transverse ridges, but the ridges are subdivided into conical or 
 mammillary cusps, and similar cusps often occur between 
 the ridges. These cusps are covered with very thick enamel 
 and the spaces between them are not filled up with cement. 
 There are six of these grinding teeth for each side of each 
 jaw but only three are in place at once. The first three are 
 milk teeth as they may be succeeded vertically by others. 
 
 In the true Elephants the number and depth of the enamel 
 folds is much increased, and the spaces between the folds are 
 filled up with cement. A very complete series of extinct 
 forms is known with teeth intermediate in character between 
 those of Mastodon and those of the Mammoth and living 
 elephants. The dental formula of Elephas is 
 ,.1.1 7 34 3 
 d *0 % e dm 3=4 m 3' 
 
 Sir W. H. Flower describes 1 the mode of succession of teeth 
 in Elephants as follows : " As regards the mode of succession 
 that of modern Elephants is as before mentioned very peculiar. 
 During the complete lifetime of the animal there are but six 
 molar teeth on each side of each jaw with occasionally a rudi- 
 mentary one in front, completing the typical number of seven. 
 1 Encyclopedia Britannica, article Mammalia, p. 424. 
 
THE SKELETON IN MAMMALIA. THE TEETH. 435 
 
 The last three represent the true molars of ordinary mammals, 
 those in front appear to be milk molars which are never re- 
 placed by permanent successors, but the whole series gradually 
 moves forwards in the jaw, and the teeth become worn away 
 and their remnants cast out in front while development of 
 others proceeds behind. The individual teeth are so large 
 and the processes of growth and destruction by wear take 
 place so slowly, that not more than one or portions of two 
 teeth are ever in place and in use on each side of each jaw 
 at one time, and the whole series of changes coincides with 
 the usual duration of the animal's life. On the other hand 
 the Dinotherium, the opposite extreme of the Proboscidean 
 series, has the whole of the molar teeth in place and use at 
 one time, and the milk molars are vertically displaced by pre- 
 molars in the ordinary fashion. Among Mastodons trans- 
 itional forms occur in the mode of succession as well as in 
 structure, many species showing a vertical displacement of 
 one or more of the milk molars, and the same has been ob- 
 served in one extinct species of Elephant (E. planifrons) as 
 regards the posterior of these teeth." 
 
 In the TILLODONTIA the grinding teeth are of Ungulate 
 type, while the second incisors are large and grow from per- 
 sistent pulps, so as to resemble those of Rodents. 
 
 BODKNTIA have a most characteristic and very constant 
 dentition, the common dental formula being 
 
 * r G l pm (=1) m l> total 18 or 2a 
 
 The incisors always have chisel-like edges and persistent 
 pulps, and are separated by a wide diastema from the 
 premolars. Canines are always absent, and there are ge- 
 nerally three grinding teeth not preceded by milk teeth ; 
 their surface may be grooved, or may be bunodont. Teeth 
 are most numerous in the Duplicidentata (Hares and Rabbits), 
 
 9 A 33 
 in which the formula is i y c -pm-m^, total 28, and fewest 
 
 282 
 
436 
 
 THE VERTEBRATE SKELETON. 
 
 in Hydromys and certain other forms, in which the formula is 
 
 .10 02 
 
 i y c -: pm - m - , total 1 2. The hares and rabbits are the 
 
 VI 
 
 FIG. 84. CABNASSIAL OR SECTOEIAL TEETH OF CARNIVORA (from 
 FLOWER). 
 
 Upper sectorial teeth of I. Felts, II. Cams, III. Ursus. 1. anterior, 
 2. middle, 3. posterior cusp of blade, 4. inner lobe supported on distinct 
 root, 5. inner lobe posterior in position and without distinct root, 
 characteristic of the Ursidae. 
 
 Lower sectorial teeth. 1. Fells, 2. Cauls, 3. Herpestes. 1. anterior, 
 2. posterior lobe of blade, 3. inner tubercle, 4. heel. 
 
THE SKELETON IN MAMMALIA. THE TEETH. 437 
 
 only rodents which have Avell developed deciduous incisors, 
 though a vestigial milk incisor has been described in the 
 Mouse (Mus musculus). The last upper molar of Hydrochaerus 
 is very complicated, its structure approaching that of the teeth 
 of Elephants. 
 
 CARNIVORA have the teeth rooted and markedly diphyodont 
 and heterodont. The canines are greatly developed, and the 
 incisors are small. 
 
 In CARNIVORA VERA the incisors are almost always . The 
 fourth upper premolar and first lower molar are differentiated 
 as carnassial teeth (see p. 436), and retain fundamentally the 
 same characters throughout the suborder. The upper car- 
 nassial (fig. 84, I. II. III.) consists of a more or less compressed, 
 commonly trilobed blade borne on two roots, with an inner 
 tubercle borne on a third root. The lower carnassial has only 
 two roots ; its crown consists of a bilobed blade with generally 
 an inner cusp, and a heel or talon (fig. 84, 4) behind the blade. 
 
 The most thoroughly carnivorous type of dentition is seen 
 in the ^luroidea, and especially in the cat tribe (Felidae). In 
 
 31 31 
 the genus Felis the dental formula is i = c = pm - m - , total 30. 
 
 The incisors are very small, so as not to interfere with the 
 action of the large canines, the lower carnassial is reduced to 
 simply the bilobed blade (fig. 84, IV), and the cheek teeth are 
 greatly subordinated to the carnassial. The extinct Machae- 
 rodus has the upper canines comparable in size to those of the 
 Walrus. 
 
 The Civets and Hyaenas have a dentition allying them 
 closely to the cats. The hyaena-like Proteles has, however, 
 the grinding teeth greatly reduced. 
 
 .31 4 2 
 
 In the Cynoidea 1 the general dentition is i = c = pm - m -= , 
 
 o 1 4 o 
 
 total 42. This differs from the regular mammalian dentition 
 
 1 See T. H. Huxley, "The dental and cranial characters of the 
 Cauidae," P. Z. S., 1880, p. 238. 
 
438 
 
 THE VERTEBRATE SKELETON. 
 
 only in the absence of the last upper molar. The upper 
 carnassial tooth (fig. 84, II.) consists of a larger middle and 
 smaller posterior lobe with hardly any trace of an anterior 
 lobe. The lower carnassial (fig. 84, V.) is typical, consisting 
 of a bilobed blade with inner cusp and posterior talon. 
 
 The dentition of the Cynoidea is most closely linked with 
 that of the Arctoidea by means of fossil forms. 
 
 In the Arctoidea the dentition is not so typically carnivorous 
 
 FIG. 85. MANDIBLE OF ISABELLINE BEAR (Ursus isabellinus) x 
 (Camb. Mus.) 
 
 1. condyle. m 1. 
 
 2. coronoid process. 
 i 1. first incisor. 
 
 first molar. The dotted 
 line is pointing to the pos- 
 terior half of the tooth. 
 
 c. canine. 
 
 pm 1, pm 2. first and second pre- 
 molars. 
 
 This specimen has only 
 three premolars, there 
 should be four. 
 
THE SKELETON IN MAMMALIA. THE TEETH. 439 
 
 as in the ^Eluroidea and Cynoidea. In the bears, Ursidae, 
 the molars have broad flat tuberculated crowns (fig. 85). The 
 
 31 42 
 dental formula in Ursus is i - c pm ra , total 42. The 
 
 upper carnassial (fig. 84, III.) differs from that of the 
 roidea and Cynoidea in having no inner lobe supported on a 
 third root. In the large group of Mustelidae there are gene- 
 rally two molars in the lower and one in the upper jaw. The 
 grinding teeth commonly have large, flattened, more or less 
 tuberculated crowns, and the upper molar may be as large or 
 much smaller than the carnassial. 
 
 In the CREODONTA there are no specially differentiated 
 carnassial teeth. 
 
 pm1 
 
 3 
 
 FIG. 86. LEFT MANDIBULAR RAMUS OF THE SEA LEOPARD (Ogmorhinus 
 leptonyx) WITH THE ROOTS OF THE TEETH EXPOSED x . (Ckmb. Mus.) 
 
 1. condyle. pml, ^w4. first and fourth pre- 
 
 2. coronoid process. molars. 
 i 3. third incisor. m. molar. 
 
 c. canine. 
 
 In the PINNIPEDIA the dentition differs considerably from 
 that of the Garni vora vera. The milk dentition is always 
 vestigial, and the teeth are frequently absorbed before birth. 
 There are four premolars and one molar, forming an uniform 
 series of cheek teeth, all of which except in the Walrus have 
 compressed and pointed, never flattened, crowns. There is 
 no special carnassial tooth, and the incisors are always fewer 
 than jj . In Otaria the dentition is 
 
 * 9 c T P m 7 m - > tot&l 34 or 36. 
 
440 THE VERTEBRATE SKELETON. 
 
 In the Walrus the upper canines form immense tusks. The 
 other teeth are all small and one-rooted, and the molars have 
 flat crowns. In the true seals the dentition is strikingly pis- 
 civorous, the cheek teeth often having accessory cusps (fig. 86). 
 
 The INSECTIVORA are diphyodont and heterodont, having 
 well-developed rooted teeth. The canines are usually weak, 
 the incisors pointed, and those of the two jaws often meet 
 like a pair of forceps. The crowns of the molars are charac- 
 teristically studded with short cusps. Some genera, such as 
 Gymnura and the mole, Talpa, have the regular mammalian 
 dentition. In the hedgehog, Erinaceus, the dentition is 
 
 i - c ^ pm - m -, total 36. 
 
 In the genus Sorex (Shrews) the teeth differ in the following 
 two marked respects from those of most other Monodelphia, 
 (1) they are monophyodont, (2) the lower incisors sometimes 
 become fused to the jaws. Most Insectivora have square molar 
 teeth, but in Potamogale, Chrysochloris, Solenodon and the 
 Centetidae the molar teeth are triangular in section. Four 
 molars occur in Centetes. 
 
 In the aberrant genus Galeopithecus the dentition is 
 91 23 
 i ^ c = pm - m K , total 34. The upper incisors are placed at 
 
 G 1 2i O 
 
 some distance from the anterior end of the jaw, and the outer 
 upper incisors and canines of both jaws have two roots, a 
 very unusual character. The lower incisors are deeply grooved 
 or pectinated in the same way as are the lower incisors of Pro- 
 cavia. The upper incisors and canines of both jaws bear many 
 cusps, and are very similar in appearance to the cheek teeth of 
 some Seals. 
 
 The dentition of the CHIEOPTERA is diphyodont and hetero- 
 dont, and the dental formula never exceeds 
 
 21 33 
 i g c - pm g m 3 ' total 38 - 
 
THE SKELETON IN MAMMALIA. THE TEETH. 441 
 
 The milk teeth are very slender and have sharp recurved cusps; 
 they are quite unlike the permanent teeth. The permanent 
 teeth are of two types. In the Insectivorous forms the molar 
 teeth are cusped, and resemble those of Insectivora. In the 
 blood-sucking Vampire bat Desmodus, the teeth are peculiarly 
 modified ; the canines and the single pair of upper incisors are 
 much enlarged and exceedingly sharp, while all the other 
 teeth are much reduced in size. 
 
 In the Frugivorous bats the molar teeth have nearly always 
 smooth crowns. The dental formula in the chief genus Pteropus 
 
 9 1 32 
 
 is i - c pm - m - , total 34. 
 2 1 o 5 
 
 The PRIMATES have a diphyodont and heterodont dentition, 
 generally of an omnivorous type, with cheek teeth adapted for 
 grinding. The incisors are generally -|, and the molars, except 
 in the Hapalidae, are . In the Lemurs the upper canines 
 are large, and the lower incisors slender and directed almost 
 horizontally forwards. The Aye Aye, Chiromys, has the follow- 
 ing singular dentition : i - c ^ pm - m ~ , total 18. The in- 
 
 1 U U o 
 
 cisors much resemble those of rodents having persistent pulps, 
 and enamel only on the anterior face. 
 
 In Man and in the Anthropoid and Old World Apes 
 
 21 23 
 the dental formula is always i - c - pm - m ^ , total 32. 
 
 In the Cebidae there is an extra premolar in each jaw 
 bringing the number up to 36. In the Hapalidae, as in the 
 Cebidae, there is a third premolar, but the molars are reduced 
 to f . Man is the only Primate that has the teeth arranged 
 in a continuous series. In all the others there is a gap or 
 diastema of larger or smaller size between the incisors and 
 canines. In all except man also the canines are enlarged, 
 especially in the males. 
 
442 THE VERTEBRATE SKELETON. 
 
 The Exoskeletal structures of mammals may be summarised 
 in the following table : 
 
 I. Epidermal exoskeletal structures. 
 
 1. Hairs (a) ordinary hair, 
 
 (6) vibrissae and bristles, 
 
 (c) spines of hedgehog, porcupine, Echidna, 
 Centetes, Acanthomys. 
 
 . ( of Manidae, 
 
 2. Scales \ , 
 
 [ on tails of rats, beavers, &c. 
 
 3. Horns of Rhinoceros. 
 
 4. Horns of Bovine Ruminants. 
 
 5. Nails, claws, hoofs. 
 
 6. Spurs of male Ornithorhynchus and Echidna. 
 
 7. Horny beak and teeth of Ornithorhynchus. 
 
 8. Horny pads on jaws of Sirenians and Ruminants. 
 
 9. Baleen of whales. 
 10. Enamel of teeth. 
 
 II. Dermal exoskeletal structures. 
 
 1. Dentine and cement of teeth. 
 
 2. Bony scutes of Armadillos. 
 
 ENDOSKELETOK 
 
 VERTEBRAL COLUMN. 
 
 CERVICAL VERTEBRAE. 
 
 The cervical vertebrae of all mammals have certain cha- 
 racters in common. However long the neck may be, the 
 number of cervical vertebrae, with very few exceptions, is 
 seven. Movable ribs are generally absent, and if present 
 are small and do not reach the sternum. The transverse 
 processes are generally wide but not long, and are perforated 
 near the base by the vertebrarterial canals, through which 
 the vertebral arteries pass ; they generally bear downwardly- 
 directed inferior lamellae which are sometimes as in the seventh 
 human cervical seen to ossify from centres distinct from those 
 
THE SKELETON IN MAMMALIA. VERTEBRAL COLUMN. 443 
 
 forming the rest of the transverse process, and are really of 
 the nature of ribs. The atlas and axis always differ much 
 from the other vertebrae. 
 
 We may pass now to the special characters of the cervical 
 vertebrae in the different groups. In MONOTREMES and MAR- 
 SUPIALS the number of cervical vertebrae is always seven. With 
 the exception of the atlas of Echidna the cervical vertebrae 
 of Monotremes are without zygapophyses. In. Monotremes the 
 transverse processes ossify from centres distinct from that form- 
 ing the body, and remain suturally connected with the rest of 
 the vertebra until the adult condition is reached. The method 
 of the ossification of the atlas in Marsupials varies considerably, 
 thus in some forms such as the Wombats (Phascolomys) there is 
 an unossified gap in the middle of the inferior arch of the atlas, 
 which may remain permanently open ; in Thylacinus this gap 
 is filled up by a distinct heart-shaped piece of bone, while in 
 Didelphys and Perameles the atlas is ossified below in the same 
 way as in other mammals. In Notoryctes the second to sixth 
 cervical vertebrae are ankylosed together. 
 
 The cervical vertebrae of the EDENTATA have some remark- 
 able peculiarities. In the three-fingered Sloth, Bradypus, 
 there are nine cervical vertebrae, all except the last of which 
 have their transverse processes perforated by the vertebrar- 
 terial canals. In a two-fingered sloth, Choloepus hqffmanni, 
 there are only six cervical vertebrae. In the Megatheriidae, 
 Anteaters (Myrmecophagidae), Pangolins (Manidae), and Aard 
 Varks (Orycteropodidae), the cervical vertebrae are normal, 
 but in the Armadillos (Dasypodidae), and still more in the 
 Glyptodonts, several of them are commonly fused together. 
 The fusion affects not only the centra, but also the neural 
 arches, so that the neural canals form a continuous tube. 
 
 In the Glyptodonts there is a complex joint at the base of 
 the neck to allow the partial retraction of the head within the 
 carapace. This arrangement recalls that in Tortoises. 
 
 As a rule the SIRENIA possess seven short cervical vertebrae, 
 
444 
 
 THE VERTEBRATE SKELETON. 
 
 not fused together and not presenting any marked peculiarities. 
 In Manatus however there are only six cervical vertebrae and 
 they are very variable. 
 
 In the CETACEA there are invariably seven cervical verte- 
 brae, but they are always very short and are frequently even 
 before birth fused together by their centra into one continuous 
 mass (see fig. 67). Sometimes the last one or two are free. In 
 the Rorquals (Balaenoptera) however, the cervical vertebrae are 
 
 1- 
 
 FIG. 87. CERVICAL VERTEBRAE OF A YOUNG FIN WHALE (Balaenoptera 
 
 musculus) x T V (Camb. Mus.) 
 1. 
 
 surface on the atlas for arti- 
 culation with the occipital 
 condyle of the skull. 
 
 2. foramen for exit of the first 
 
 spinal nerve. 
 
 3. upper transverse process. 
 
 4. lower transverse process. 
 
 In the fresh specimen these two 
 transverse processes are united by 
 cartilage, in adult individuals the 
 whole transverse process is ossified. 
 
 5. epiphyses of centrum. 
 
 6. neural spine. 
 
 quite separate and distinct (fig. 87), and in the fluviatile Odon- 
 toceti, Platanista, Inia, and Pontoporia, and also in Beluga 
 and Monodon, though very short they are free. In Physeter 
 the first vertebra is free while the others are fused. An 
 odontoid process is not commonly present even in Cetaceans 
 with free cervical vertebrae, but a very short one occurs in 
 the Rorquals. The cervical vertebrae of Rorquals give off 
 on each side two transverse processes (fig. 87, 3 and 4) which 
 
THE SKELETON IN MAMMALIA. VERTEBRAL COLUMN. 445 
 
 enclose between them a wide space. These processes are not 
 completely ossified till the animal is adult. 
 
 In all UNGULATA the number of cervical vertebrae is seven. 
 Among the Artiodactyla two forms of the odontoid process of 
 the axis occurs ; in the Suina and Tragulina it is conical, in 
 the Ruminantia and Tylopoda it is spout-like (fig. 88, 4). The 
 atlas in the Suina and to a less extent in the Ruminantia has 
 
 B fe.- 
 
 FIG. 88. 
 
 A 
 
 ATLAS (B) AND AXIS (A) VEBTEBRAE OF AN Ox (Bos 
 taurus) x %. (Camb. Mus. ) 
 
 8. 
 
 7. 
 
 anterior opening of the verte- 
 
 brarterial canal, 
 foramen for the exit of the 
 
 second spinal nerve, 
 neural spine, 
 postzygapophysis. 
 
 1. neural canal. 
 
 2. transverse process. 
 
 3. surfaces for articulation with 
 
 the occipital condyles of 
 the skull. 
 
 4. spout-like odontoid process. 
 
 5. hypapophysis. 
 
 long flattened transverse processes, and the remaining cervical 
 vertebrae are opisthocoelous. Those of the Giraffe and Llama 
 (fig. 103) are noticeable for their great length. In the Tylo- 
 poda the posterior half of the vertebrarterial canal is confluent 
 with the neural canal. 
 
 The Perissodactyla have remarkably opisthocoelous cervical 
 vertebrae. Those of Macrauchenia have the posterior half of 
 the vertebrarterial canal confluent with the neural canal as in 
 Tylopoda. In the Proboscidea they are short flattened discs 
 slightly opisthocoelous ; the axis and seventh vertebra and to 
 a less extent the sixth have high neural spines. 
 
446 THE VERTEBRATE SKELETON. 
 
 In the RODENTIA the atlas generally has broad wing-like 
 transverse processes, and the axis a large and long neural spine, 
 while the odontoid process is much developed. In the Jerboas 
 (Dipus) all the cervical vertebrae except the atlas are fused 
 together, a condition recalling that in armadillos. 
 
 In the CARNIVORA the wings of the atlas are well developed 
 (tig. 69, A, 1), and it is deeply cupped for articulation with 
 the condyles of the skull. The axis has a long odontoid process 
 and a high compressed neural spine (fig. 69, B, 4). The third 
 to sixth cervical vertebrae have large transverse processes with 
 prominent perforated inferior lamellae, whose ventral margins 
 in the third and fourth vertebrae diverge as they pass back- 
 wards, while in the fifth they are parallel and in the sixth 
 convergent. The transverse processes of the seventh vertebra 
 have no inferior lamellae and are not perforated. Metapo- 
 physes are often developed. 
 
 In the INSECTIVORA the cervical vertebrae vary considerably. 
 The neural spines except in the case of the axis are generally 
 very small and in the Shrews and Moles the neural arches 
 ^re exceedingly slender. 
 
 In the CHIROPTERA all the cervical vertebrae are broad and 
 short with slender neural' arches. 
 
 PRIMATES. In Man the cervical vertebrae have short blunt 
 transverse processes and small often bifid neural spines. The 
 neural and vertebrarterial canals are large. The atlas forms 
 a ring surrounding a large cavity, and has a very slender 
 inferior arch and small transverse processes. Traces of a pro- 
 atlas have been described in Macacus and Cynocephalus. The 
 axis has a prominent spine and odontoid process and short 
 transverse processes. In most Primates the cervical vertebrae 
 are very similar to those of man, but the inferior lamellae of 
 the transverse processes are better developed. In the Anthro- 
 poid Apes the neural spines are as a rule much elongated. 
 
THE SKELETON IN MAMMALIA. VERTEBRAL COLUMN. 447 
 
 THORACO-LUMBAR, OR TRUNK VERTEBRAE. 
 
 In the MONOTREMATA there are nineteen thoraco-lumbar 
 vertebrae, sixteen (Echidna) or seventeen (Ornithorhynchus) 
 of which bear ribs. The transverse processes are very short 
 and do not articulate with the ribs, which are united to the 
 centra only. 
 
 In the MARSUPIALIA there are always nineteen thoraco- 
 lumbar vertebrae, thirteen of which generally bear ribs. The 
 lumbar vertebrae frequently have large metapophyses and 
 anapophyses, these being specially well seen in the Kangaroos 
 and Koala (Phascolarctus). 
 
 The EDENTATA are very variable as regards their trunk 
 vertebrae. The two genera of Sloths differ much as regards 
 the number, for while Bradypus has only nineteen, fifteen or 
 sixteen of which bear ribs, Choloepus has twenty-seven, twenty- 
 four of which are thoracic, and bear ribs. In Bradypus a 
 small outgrowth from the transverse process articulates with 
 the neural arch of the succeeding vertebra. In both genera 
 the neural spines are all directed backwards. 
 
 In the Megatheriidae as in the sloths the neural spines 
 are all directed backwards, and in the lumbar region additional 
 articulating surfaces occur, better developed than are those in 
 Bradypus. 
 
 In the anteaters (Myrmecophagidae) there are seventeen 
 or eighteen thoraco-lumbar vertebrae, all of which except two 
 or three bear ribs. The posterior thoracic and anterior lumbar 
 vertebrae articulate in a very complex fashion, second, third, and 
 fourth pairs of zygapophyses being progressively developed in 
 addition to the ordinary ones, as the vertebrae are followed back. 
 
 In the Armadillos the lumbar vertebrae have long meta- 
 pophyses which project upwards and forwards and help to 
 support the carapace. In Glyptodon almost all the thoraco- 
 lumbar vertebrae are completely ankylosed together. 
 
 In the Manidae there are no additional zygapophyses but 
 the normal ones of the lumbar and posterior thoracic regions 
 
448 THE VERTEBRATE SKELETON. 
 
 are very much developed, the postzygapophyses being semi- 
 cylindrical and fitting into the deep prezygapophyses of the 
 succeeding vertebra. 
 
 In the SIRENIA the number of lumbar vertebrae is very 
 small ; in the dugong there are nineteen thoracic and four 
 lumbar, and in the manatee seventeen thoracic arid two lumbar. 
 
 In the CETACEA the number of thoracic vertebrae varies from 
 nine in Hyperoodon to fifteen or sixteen in Balaenoptera, and 
 the number of lumbar vertebrae from three in Inia to twenty- 
 four or more in Delphinus. The lumbar vertebrae are often 
 very loosely articulated together and the zygapophyses some- 
 times as in the Dolphins are placed high up on the neural 
 spines. The centra are large, short in the anterior region but 
 becoming longer behind. The epiphyses are prominent, and 
 so are the neural spines and to a less extent the metapophyses. 
 The transverse processes are well developed, anteriorly they 
 arise high up on the neural arch, but when the vertebral 
 column is followed back they come gradually to be placed lower 
 down, till in the lumbar region they project from the middle of 
 the centra. This can be well traced in the Porpoise (Phocaena). 
 In the Physeteridae the transverse processes of the anterior 
 thoracic vertebrae are similar to those of most Cetacea, but 
 when followed back, instead of shifting their position on the 
 vertebrae, they gradually disappear, and other processes 
 gradually arise from the point where the capitulum of the rib 
 articulates. 
 
 UNGULATA. In the Ungulata vera the thoraco-lumbar 
 vertebrae are slightly opisthocoelous. The anterior thoracic 
 vertebrae commonly have exceedingly high backwardly-pro- 
 jecting neural spines (fig. 89,1) ; but those of the lumbar and 
 posterior thoracic vertebrae often point somewhat forwards 
 so that the spines all converge somewhat to a point called the 
 centre of motion (cp. fig. 101). In the Artiodactyla there are 
 always nineteen thoraco-lumbar vertebrae, and in the Perisso- 
 dactyla twenty-three. 
 
THE SKELETON IN MAMMALIA. VERTEBRAL COLUMN. 449 
 
 Procavia sometimes has thirty thoraco-lumbar vertebrae, a 
 greater number than occurs in any other terrestrial mammal ; 
 
 FIG. 89. 
 
 1. neural spine. 
 
 2. neural canal. 
 
 3. prezygapophysis. 
 
 4. facet for articulation with the 
 
 tuberculum of the rib. 
 
 FlEST AND SECOND THORACIC VERTEBRAE OF AN Ox (BOS 
 
 taunts) x . (Camb. Mus. ) 
 
 5. facet for articulation with the 
 
 capitulum of the rib. 
 
 6. postzygapophysis. 
 
 7. foramen for exit of spinal 
 
 nerve. 
 
 twenty-two of these are thoracic and eight lumbar. In Phe- 
 nacodus the convergence of the neural spines to a centre of 
 motion is well seen. 
 
 In the Proboscidea there are twenty-three thoraco-lumbar 
 vertebrae, of which nineteen or twenty bear ribs. 
 
 In the RODKNTIA there are generally nineteen thoraco- 
 lumbar vertebrae but occasionally the number rises as high as 
 twenty-five. In the Hares (Leporidae) the number is nineteen, 
 R. 29 
 
450 THE VERTEBRATE SKELETON. 
 
 twelve or thirteen of which are thoracic. The anterior 
 thoracic vertebrae have short centra and high backwardly- 
 directed neural spines, the lumbar vertebrae have large for- 
 wardly- and downwardly-directed transverse processes with 
 expanded ends. Metapophyses, anapophyses and hypapophyses 
 are all present. In the Agouti (Dasyprocta) the convergence 
 of the neural spines to a centre of motion is very strongly 
 marked. 
 
 In the CARNIVORA the trunk vertebrae are nearly always 
 twenty or twenty-one in number; in the genera Felis and 
 Canis thirteen of these are thoracic and seven lumbar. The 
 anterior thoracic vertebrae have long back wardly-p rejecting 
 neural spines, while the posterior thoracic and lumbar vertebrae 
 have shorter and thicker neural spines which project slightly 
 forwards. In the Pinnipedia there is no change in the direc- 
 tion of the neural spines, and anapophyses are but little deve- 
 loped. 
 
 In the INSECTIVORA the number of trunk vertebrae varies 
 much from nineteen thirteen thoracic and six lumbar in 
 Tupaia, to twenty-four nineteen thoracic and five lumbar 
 in Centetes. The development of the various processes varies 
 in accordance with the habits of the animals, being great in 
 the active forms, slight in the slowly moving or burrowing 
 forms. In Talpa and Galeopithecus the inter vertebral discs 
 of the thoraco-lumbar region instead of being cartilaginous 
 have ossified forming intercentra, a condition met with in 
 very few mammals. 
 
 In the CHIROPTERA there are seventeen or eighteen thoraco- 
 lumbar vertebrae, eleven to fourteen of which may bear ribs. 
 The development of processes is slight. 
 
 Among PRIMATES the number of trunk vertebrae is gene- 
 rally nineteen, of which twelve to fourteen bear ribs ; in man 
 and the Gorilla and Chimpanzee the number is, however, 
 seventeen, and in the Orang (Simia) sixteen. In some of the 
 Lemuroidea there are as many as twenty-three or twenty-four. 
 
THE SKELETON IN MAMMALIA. VERTEBRAL COLUMN. 451 
 
 In most cases the neural spines converge more or less to a 
 centre of motion, and this is especially marked in some of the 
 Lemurs ; it does not occur in man and the anthropoid apes. 
 
 SACRAL AND CAUDAL VERTEBRAE. 
 
 At the posterior end of the trunk in all mammals a 
 certain number of vertebrae are found fused together forming 
 the sacrum. But of these only two or three answer to the 
 definition of true sacral vertebrae in being united to the ilia 
 by small ribs. The others which belong to the caudal series 
 may be called pseudosacral vertebrae. In different individuals 
 of the same species it sometimes happens that different 
 vertebrae are attached to the pelvis and form the sacrum. 
 Sometimes even different vertebrae are attached to the pelvis 
 at successive periods in the life history of the individual. This 
 is owing to a shifting of the pelvis and has been especially 
 well seen in man. In young human embryos the pelvis is 
 at a certain stage attached to vertebra 30, but as develop- 
 ment goes on it becomes progressively attached to the twenty- 
 ninth, twenty-eighth, twenty-seventh, twenty-sixth and twenty- 
 fifth vertebrae. As the attachment to these anterior vertebrae 
 is gained, the attachment to the posterior ones becomes 
 lost, so that in the adult the pelvis is generally attached 
 to vertebrae 25 and 26. But there are no absolutely pre- 
 determined sacral vertebrae, as sometimes the pelvis does not 
 reach vertebra 25, remaining attached to vertebrae 26 and 27; 
 sometimes it becomes attached even to vertebra 24. This 
 shifting of the pelvis is seen in Choloepus in a more marked 
 degree even than in man. 
 
 Of the MONOTREMATA, Omithorhynclius has two sacral verte- 
 brae ankylosed together, while Echidna has three or four 1 . 
 
 In MARSUPIALIA as a rule only one vertebra is directly 
 united to the ilia, but one or two more are commonly fused 
 to the first. In the Wombats there may be as many as four 
 
 1 G. B. Howes, Journ. of Anat. and Phys. xxvu., p. 544. 
 
 292 
 
452 THE VERTEBRATE SKELETON. 
 
 or five vertebrae fused together in the sacral region. In 
 Notary ctes there is extensive fusion in the sacral region, six 
 vertebrae, owing mainly to the great development of their 
 metapophyses, being united with one another, and with the 
 ilia, and the greater part of the ischia. 
 
 In most EDENTATA there is an extensive fusion of verte- 
 brae in the sacral region. This is especially marked in the 
 Armadillos and Megatheriidae, and to a less extent in the 
 Sloths and Aard Yarks. 
 
 In the SIRENIA the vestigial pelvis is attached by ligament 
 to the transverse processes of a single vertebra, which hence 
 may be regarded as sacral. 
 
 In CETACEA there is no sacrum, the vestigial pelvis not 
 being connected with the vertebral column. 
 
 In most UNGULATA the sacrum consists of one large ver- 
 tebra united to the ilia, and having a varying number of 
 smaller vertebrae fused with it behind. 
 
 The same arrangement obtains in most RODENTIA, but in 
 the Beavers (Castoridae) all the fused vertebrae are of much 
 the same size, the posterior ones having long transverse 
 processes which nearly meet the ilia. 
 
 In CARNTVORA there may be two sacral vertebrae as in the 
 Hyaena, three as in the Dog, four or five as in Bears and 
 Seals. 
 
 In INSECTIVORA from three to five are united, while in 
 many CHIROPTERA all the sacral and caudal vertebrae have 
 coalesced. Among PRIMATES, in Man and Anthropoid Apes 
 there are usually five fused vertebrae forming the sacrum, 
 but of these only two or three are connected to the ilia by ribs. 
 In most of the other Anthropoidea there are two or three 
 fused vertebrae, and in the Lemuroidea two to five. 
 
 FREE CAUDAL VERTEBRAE. The free caudal vertebrae 
 vary greatly in number and character. When the tail is well 
 developed, the anterior vertebrae are comparatively short and 
 broad, with well-developed neural arches and zygapophyses ; 
 
THE SKELETON IN MAMMALIA. VERTEBRAL COLUMN. 453 
 
 but as the tail is followed back, the centra gradually 
 lengthen and become cylindrical, and at the same time the 
 neural arches and all the processes gradually become reduced 
 and disappear, so that the last few vertebrae consist of simple 
 rod-like centra. Chevron bones are frequently well-developed. 
 
 Of the MONOTREMES Echidna has twelve caudal vertebrae, 
 two of which bear irregular chevron bones. In Ornitho- 
 rhynchus there are twenty or twenty-one caudal vertebrae with 
 well-developed hypapophyses, but no chevron bones. 
 
 In MARSUPIALS there is great diversity as regards the tail. 
 In the Wombat and Koala the tail is small and without 
 chevron bones. In most other Marsupials it is very long, 
 having sometimes as many as thirty-five vertebrae in the 
 prehensile-tailed opossums. In the Kangaroos the tail is very 
 large and stout. Chevron bones are almost always present, and 
 in Notoryctes are large and expanded. 
 
 Most EDENTATES have large tails with well -developed 
 chevron bones. The length of the tail varies greatly from the 
 rudimentary condition in Sloths to that in the Pangolins, one 
 of which has forty-six to forty-nine caudal vertebrae the 
 largest number in any known mammal. Chevron bones are 
 much developed, sometimes they are Y-shaped, sometimes as in 
 Priodon, they have strong diverging processes. The caudal 
 vertebrae of Glyptodonts, though enclosed in a continuous 
 bony sheath, have not become ankylosed together. 
 
 The SIRENIA have numerous caudal vertebrae with wide 
 transverse processes. In the CETACEA also the tail is much 
 developed, and the anterior vertebrae have large chevron 
 bones and prominent straight transverse processes ; the pos- 
 terior caudal vertebrae, which in life are enclosed in the hori- 
 zontally expanded tail fin, are without transverse processes. 
 
 In UNGULATA the tail is simple, formed of short cylindrical 
 vertebrae, which in living forms are never provided with 
 chevron bones. The number of caudal vertebrae varies from 
 four, sometimes met with in Procavia, to thirty-one in the 
 
454 THE VERTEBRATE SKELETON. 
 
 Elephant. The tail is exceedingly long in Anoplotherium and 
 in Phenacodus, in which there are thirty caudal vertebrae. 
 
 In RODENTIA the tail is variable. In the Hares, Guinea 
 pig (Cavia) and Capybara it is very small, in Pedetes and the 
 Beaver it is very long and has well-developed chevron bones. 
 
 Most of the CARNIVORA except the Bears and Seals have 
 very long tails, the greatest number of vertebrae, thirty-six, 
 being met with in Paradoxurus. Bears have only eight to 
 ten caudal vertebrae. Chevron bones are not often much 
 developed. 
 
 In INSECTIVORA the tail is very variable as regards length, 
 the number of vertebrae varying from eight in Centetes to 
 forty-three in Microgale. 
 
 In CHIROPTERA the tail is sometimes quite rudimentary, 
 and as in Pteropus, composed of a few coalesced vertebrae, 
 sometimes it is formed of a large number of slender ver- 
 tebrae. 
 
 In PRIMATES also the tail is very variable. In Man all 
 the four caudal vertebrae are rudimentary and are fused 
 together, forming the coccyx. In the Anthropoid apes, too, 
 there are only four or five caudal vertebrae. In many 
 monkeys of both the eastern and western hemispheres the 
 tail is very long, having thirty-three vertebrae in Ateles, in 
 which genus it is also prehensile. Chevron bones are present 
 in all Primates with well-developed tails. In the Lemuroidea 
 the number of caudal vertebrae varies from seven to twenty- 
 nine. 
 
CHAPTER XXIII. 
 
 GENERAL ACCOUNT OF THE SKELETON IN 
 MAMMALIA (CONTINUED). 
 
 THE SKULL AND APPENDICULAK SKELETON. 
 
 THE SKULL. 
 
 MONOTREMATA. In both genera the cranium is thin -walled, 
 has a fairly large cavity, and is very smooth and rounded ex- 
 ternally. The sutures between many of the bones early become 
 obliterated in a manner comparable to that in birds, and the 
 facial portion of the skull is much prolonged. 
 
 In Echidna the face is drawn out into a gradually tapering 
 rostrum, formed mainly by the premaxillae, maxillae and nasals. 
 The zygomatic arch is very weak, and the palate extends very 
 far back. The tympanic forms a slender ring. The mandible 
 is extremely slight, with no ascending portion, and but slight 
 traces of the coronoid process and angle. The hyoid has a 
 wide basi-hyal and stout thyro-hyals, while the anterior cornua 
 are slender, and include ossified epi-hyals and cerato-hyals. 
 
 In Ornithorhynchus the zygomatic arch is much stouter 
 than in Echidna. The face is produced into a wide beak, 
 mainly supported by the premaxillae, between whose diverging 
 anterior ends there is a dumb-bell-shaped bone. The maxillae 
 
456 
 
 THE VEKTEBEATE SKELETON. 
 
 are flattened below, and each bears a large horny tooth, which 
 meets a corresponding structure borne on a surface near the 
 middle of the mandible. The mandible is considerably stouter 
 than in Echidna, but the angle and coronoid process are but 
 little developed. The infra-orbital foramen and the inferior 
 dental and mental foramina of the mandible are all very large. 
 
 Fro. 90. HALF FKONT viEW 1 OF THE SKULLS OF A TASMANIAN WOLF (Thy- 
 lacinus cynocephalus) (to the left) x f ; AND OF A HAIKY-NOSED 
 WOMBAT (Phascolomys latifrons) (to the right) xf. (Camb. Mus.) 
 
 7. coronoid process of the man- 
 
 dible. 
 
 8. lachrymal foramen. 
 
 i. 1. first upper incisor. 
 C. canine. 
 
 premaxilla. 
 
 nasal. 
 
 frontal. 
 
 infra-orbital foramen. 
 
 lachrymal. 
 
 jugal. 
 
 MARSUPIALIA. The skulls of the various types of the 
 Marsupials frequently bear a strong superficial resemblance to 
 those of some of the different groups of placental mammals. 
 Thus the skull of the Dasyuridae resembles that of the Carni- 
 vora, the resemblance being most marked between the skulls of 
 
 1 The figure was drawn from a photograph and the size of the jaws 
 relatively to the cranium is exaggerated. 
 
THE SKELETON IN MAMMALIA. THE SKULL. 457 
 
 Thylacinus and the dog. The skull of Notoryctes is strongly sug- 
 gestive of that of an Insectivore, and that of other Marsupials 
 such as the wombat, recalls equally the characteristic features 
 of a Rodent's skull. But, however much they may differ from 
 one another, the skulls of all Marsupials agree in the following 
 respects. (1) The brain cavity, and especially the cerebral 
 fossa, has a very small comparative size. (2) The nasals are 
 always large, and the mesethmoid is extensively ossified, and 
 terminated by a prominent vertical edge. (3) Processes from 
 the jugal and frontal in living forms never meet and enclose 
 the orbit, but the zygomatic arch is always complete. (4) The 
 jugal always extends back to form part of the glenoid fossa. 
 (5) The lachrymal canal opens either external to or upon the 
 margin of the orbit, and the nasal processes of the premaxillae 
 never quite reach the f rentals. (6) The posterior part of the 
 palate is commonly pierced by large oval vacuities. (7) The 
 tympanic is small and never fused to the bones of the 
 cranium. (8) The carotid canal perforates the basisphenoid 
 and not the tympanic bulla. (9) The optic foramen and 
 sphenoidal fissure are confluent. (10) In every case except 
 Tarsipes the angle of the mandible is more or less inflected. 
 
 The skull of the extinct Thylacoleo differs from that of all 
 other Marsupials in the fact that the postorbital bar is com- 
 plete. The hyoid is constructed on much the same plan in all 
 Marsupials. It consists of a small basi-hyal, a pair of broad 
 cerato-hyals, and a pair of strong thyro-hyals. The epi-hyals 
 and stylo-hyals are generally unossified. 
 
 EDENTATA. In Sloths (Bradypodidae) the sutures become 
 early obliterated, the cranial portion of the skull is rather 
 high, and the facial portion very short. The lachrymal is very 
 small, and its canal opens outside the orbit. The zygomatic 
 arch is incomplete, and the jugal (fig. 91, 5) is curiously forked, 
 but in a manner differing in the two genera. The premaxillae 
 are very small, in Bradypus quite vestigial. The mandible is 
 well developed, the angle being specially marked in Bradypus. 
 
458 THE VERTEBRATE SKELETON. 
 
 In Choloepus the symphysial part is drawn out in a somewhat 
 spout-like manner (fig. 91, 6). In both genera the thyro-hyals 
 are ankylosed with the basi-hyal. 
 
 5 
 
 FIG. 91. SKULL OF A TWO-FINGERED SLOTH (Choloepus didactylus) x \. 
 (Camb. Mus.) 
 
 1. anterior nares. 4. angle of the mandible. 
 
 2. postorbital process of the 5. jugal. 
 
 frontal. 6. spout-like prolongation of the 
 
 3. coronoid process. mandible. 
 
 In Megatherium the general appearance of the skull is 
 distinctly sloth-like, but the facial portion is more elongated, 
 partly owing to the development of a prenasal bone, and the 
 zygomatic arch is complete. The mandible is very deep in the 
 middle, and is drawn out into a long spout-like process in front. 
 
 Anteaters (Myrmecophagidae) have a much modified skull, 
 and this is especially the case in the Great Anteater, Myrme- 
 cophaga. The skull is smooth and evenly-rounded, in these 
 respects recalling that of Echidna, but it is longer and tapers 
 much more gradually than in Echidna. The occipital condyles 
 are remarkably large. The premaxillae are small, and the 
 long rostrum is chiefly composed of the maxillae and nasals 
 with the mesethmoid and vomer. The zygomatic arch is 
 incomplete, and there is no trace of a separation between the 
 orbit and the temporal fossa. The palate is much elongated, 
 
THE SKELETON IN MAMMALIA. THE SKULL. 459 
 
 the ptery golds meeting in the middle line just like the pala- 
 tines. The mandible is very long and slender, there being no 
 definite coronoid process, and a short and slight symphysis. 
 The hyoid arch is noticeable for the length of the anterior 
 cornu. 
 
 In the Armadillos (Dasypodidae) the skull varies a good 
 deal in shape, but the facial portion is always tapering and 
 depressed. The zygomatic arch is complete. In Dasypus and 
 Chlamydophorus the tympanic bulla is well ossified. 
 
 In the Glyptodontidae the skull is very short and deep ; 
 the zygomatic arch is complete, and has a long downwardly 
 projecting maxillary process. The mandible is massive, and 
 has a very high ascending portion. 
 
 In the Manidae the skull is smooth and rounded, the zygo- 
 matic arch is incomplete, and the orbit is inconspicuous. The 
 palate is long and narrow, but the pterygoids do not take part 
 in its formation. The mandible is slightly developed and has 
 no angle or coronoid process. 
 
 In Orycteropus the zygomatic arch is complete, and there 
 is a small postorbital process to the frontal. The mandible is 
 well-developed, having a coronoid process and definite ascending 
 portion, and the hyoid is well ossified. 
 
 SIRENIA. The skull, and especially the brain case of all 
 Sirenia, is remarkable for the general density of the component 
 bones, which, though often very thick, are without air sinuses. 
 It is noticeable also for the roughness of the bones, and the 
 irregular manner in which they are united together. 
 
 The cranial cavity is decidedly small, the reduction being 
 specially noticeable in the cerebral fossa, which is not much 
 larger than the cerebellar fossa. The foramen magnum is 
 large, and the dorsal surface of the cranium narrow. The 
 zygomatic arch is very strongly developed, the squamosal (fig. 
 92, 4) being especially prominent, and being drawn-out not only 
 into the zygomatic process, but also into a large post- tympanic 
 process which articulates with the exoccipital. At the side 
 
460 
 
 THE VERTEBRATE SKELETON. 
 
 of the skull between the squamosal, supra-occipital and exocci- 
 pital, there is a wide vacuity in the cranial wall, partially filled 
 
 .-5 
 
 FIG. 92. LATEBAL VIEW OF THE SKULL OF Rhytina stelleri x % 
 (Brit. Mus.) 
 
 7. 
 
 frontal, 
 parietal, 
 zygomatic process 
 
 squamosal. 
 squamosal. 
 exoccipital. 
 occipital condyle. 
 
 pterygoid process of the ali- 
 
 sphenoid. 
 of the 8. jugal. 
 
 9. premaxilla. 
 
 10. angle of the mandible. 
 
 11. maxilla. 
 
 up by the very large periotic, which is aiikylosed to the tym- 
 panic, but is not united to any other bones of the skull. The 
 foramen lacerum medium is confluent with the foramen lacerum 
 anterius, and the two together form an enormous vacuity on 
 the floor of the skull, bounded chiefly by the exoccipital, basi- 
 occipital, alisphenoid and squamosal. The jugal (fig. 92, 8) is 
 large and in Manatus sends up a strong process, which nearly 
 or quite meets the postorbital process of the frontal, completing 
 the orbit. In the other Sirenia the orbit is completely confluent 
 with the very large temporal fossa. The lachrymal in Manatus 
 is very small, but is larger in Halicore. The premaxillae (fig. 
 92, 9) are large, but smaller in Manatus than in the other 
 
THE SKELETON IN MAMMALIA. THE SKULL. 461 
 
 genera, in all of which they are curiously bent down in front. 
 Their upper margin forms the anterior border of a very large 
 aperture lying high on the roof of the skull and extending 
 back for a considerable distance. This aperture is formed by 
 the union of the two anterior nares. The nasals are quite 
 vestigial or absent, and the iiarial aperture is bounded above 
 by the frontals; in its floor are seen the slender vomer and 
 large mesethmoid. The palate is long and narrow, and formed 
 mainly by the maxillae ; behind it there is a large irregular 
 process formed by the union of the palatine, pterygoid, and 
 pterygoid plate of the alisphenoid. The mandible is very 
 massive and has a very high ascending portion, a rounded 
 angle (fig. 92, 10), and a prominent coronoid process ; the two 
 rami are firmly ankylosed together. The hyoid consists prin- 
 cipally of the broad flat basi-hyal ; the anterior cornua are but 
 slightly ossified, while the thyro-hyals are not ossified at all. 
 
 CETACEA. The skull in all Getacea, especially in the Odon- 
 toceti, is a good deal modified from the ordinary mammalian 
 type. 
 
 In the ARCHAEOCETI this modification is less marked than 
 in either of the other suborders. The nasals and premaxillae 
 are a good deal larger than they are in living forms, and the 
 anterior nares are placed further forward. The maxillae do 
 not extend back over the frontals, and there is a well-marked 
 sagittal crest. 
 
 In the MYSTACOCETI the skull is always quite bilaterally 
 symmetrical, and is not so much modified from the ordinary 
 mammalian type as in the Odontoceti. The parietals are not, 
 as in the Odontoceti, separated by a wide interparietal, but 
 meet ; they are, however, hidden under the very large supra- 
 occipital. The nasals are developed to a certain extent, and 
 the nares, though placed very far back and near the top of the 
 head, terminate forwardly-directed narial passages. Turbinal 
 bones are also developed to some extent ; this fact, and the 
 occurrence of a definite though small olfactory fossa constituting 
 
462 THE VERTEBRATE SKELETON. 
 
 important distinctions from the Odontoceti. The maxillae are 
 large, but do not extend back to cover the frontals as in the 
 Odontoceti. The zygomatic process of the squamosal is very 
 large. The mandibular rami are riot compressed, but are 
 rounded and arched outwards, and never meet in a long 
 symphysis. 
 
 ODONTOCETI. The skull departs widely from the ordinary 
 mammalian type. The following description will apply to any 
 of the following genera of the Delphinidae, Phocaena, Globi- 
 cephalus, Lagenorhynchus, Delphinus, Tursiops, Proddphinus, 
 Sotalia. 
 
 The upper surface of the skull is more or less asymmetrical. 
 The cerebral cavity is high, short and broad ; and formed mainly 
 by the cerebral fossa, the olfactory fossa being entirely absent. 
 The supra-occipital (fig. 93, 3) is very large, and forms much 
 of the posterior part of the roof of the skull. It has the 
 interparietal (fig. 93, 7) fused with it, and completely separates 
 the two parietals. The frontal (tig. 93, 10)- is large and late- 
 rally expanded, forming the roof of the orbit, but is almost 
 completely covered by an extension of the maxilla. The 
 zygomatic arch is very slender, and is mainly formed by a 
 rod-like process from the jugal (fig. 93, 15), the zygomatic 
 process of the squamosal being short and stout. 
 
 The nasal passages are peculiarly modified, instead of 
 passing horizontally forwards above the roof of the mouth, 
 they pass upwards and even somewhat backwards towards 
 the top of the skull (fig. 93, 23). They are bounded laterally 
 by two processes from the premaxillae, the left of which is 
 shorter than the right. The nasal cavities are narrow and 
 without turbinals and the nasals (fig. 93, 19) are almost as 
 much reduced as in Sireriia. 
 
 In front of the nasal openings the face is prolonged as a 
 narrow beak or rostrum of varying length, formed by the 
 maxillae and premaxillae surrounding the vomer and large 
 mesethmoid (fig. 93, 11), which sends forwards a long partially 
 
THE SKELETON IN MAMMALIA. THE SKULL. 463 
 
 21 
 
 18 
 
 FIG. 93. A, LATERAL VIEW, AND B, LONGITUDINAL SECTION or THE SKULL 
 OF A YOUNG CA'ING WHALE (Globicephalus melas) x . (Brit. Mus. 
 
 1. basi-occipital. 13. periotic. 
 
 2. exoccipital. 14. squamosal. 
 
 3. supra-occipital. 15. jugal. 
 
 4. basispbenoid. 16. vomer. 
 
 5. alisphenoid. 17. palatine. 
 
 6. parietal. 18. pterygoid. 
 
 7. interparietal. 19. nasal. 
 
 8. presphenoid. 20. maxilla. 
 
 9. orbitospbenoid. 21. premaxilla. 
 
 10. frontal. 22. mandible. 
 
 11. mesethmoid. 23. anterior nares. 
 
 12. tympanic. 
 
464 THE VERTEBRATE SKELETON. 
 
 cartilaginous process, and is fused behind with the presphenoid 
 (fig. 93, 8). The basi-occipital (fig. 93, 1) too is fused with 
 the basisphenoid. The foramen rotundum is confluent with 
 the sphenoidal fissure, and the foramen ovale with the foramen 
 lacerum medium and the foramen lacerum posterius. The 
 palate is mainly formed by the maxillae ; the premaxillae and 
 palatines (fig. 93, 17), though both meet in symphyses, forming 
 very little of it. The pterygoids vary in size in the different 
 genera, sometimes as in Lagenorhynchus and Delphinus meet- 
 ing in the middle line, sometimes as in Phocaena and Globi- 
 cephalus (fig. 93, 18) being widely separated. The tympanic 
 and periotic are not fused together, and the periotic has 
 generally no bony union with the rest of the skull. The 
 mandible is rather slightly developed, with the rami straight, 
 compressed and tapering to the anterior end. The condyle is 
 not raised at all above the edge of the ramus ; the angle is 
 rounded and the coronoid process is very small. Platanista has 
 a curiously modified skull ; the rostrum and mandible are 
 exceedingly long and narrow, and arising from the maxillae 
 are two great plates of bone which nearly meet above. 
 
 In the Physeteridae the skull is raised into a very promi- 
 nent crest at the vertex behind the nares. In front of this 
 in Hyperoodon a pair of ridges occur, formed by outgrowths 
 from the maxillae. In the old male these ridges reach an 
 enormous size and almost meet in the middle line. In Phy 
 seter, the Sperm whale, these ridges are not developed ; the 
 maxillae and premaxillae unite with the other bones of the 
 crest enclosing an enormous half basin-shaped cavity, at the 
 base of which are the very asymmetrical anterior narial aper- 
 tures. 
 
 In all living Cetacea the hyoid has the same general shape, 
 consisting firstly of a crescentic bone formed by the fusion 
 of the thyro-hyals with the basi-hyal, and secondly of the 
 anterior cornu formed principally by the strong stylo-hyal. 
 
 UNGULATA. None of the distinctive characters separating 
 
THE SKELETON IN MAMMALIA. THE SKULL. 465 
 
 the Ungulata from the other groups of mammals are drawn 
 from the skull. But in the Ungulata vera as opposed to the 
 Subungulata a distinguishing feature is found in the fact that 
 the lachrymal and jugal form a considerable part of the side 
 of the face, and that the jugal always forms the anterior part 
 of the zygomatic arch, the maxilla taking no part in it. 
 
 UNGULATA VERA. 
 
 ARTIODACTYLA. The skull in Artiodactyla differs from that 
 in Perissodactyla in the fact that the posterior end of the 
 nasal is not expanded and there is no alisphenoid canal. 
 
 The skulls in the different groups of Artiodactyla differ 
 considerably from one another. 
 
 The skull of the Pig 1 will be described as illustrative of the 
 skull in the Suina. In the Pig as in most Artiodactyla the 
 face is bent sharply down on the basicranial axis, the com- 
 mencement of the vomer being situated below the mesethmoid 
 instead of in front of it as in most skulls. The occipital region 
 of the skull is small, and the line of junction of the supra-occi- 
 pital and parietals is raised into a prominent occipital crest. 
 The parietal completely fuses at an early stage with its fellow, 
 and the exoccipital is drawn out into a long paroccipital process 
 (fig. 94, A, 8). The frontal is large and broad and drawn out 
 into a small postorbital process. The lachrymal too is large and 
 takes a considerable part in forming the side of the face in front 
 of the orbit, as does also the jugal, though to a less extent. 
 The face is long and tapers much anteriorly. The nasals are 
 long and narrow, as are the nasal processes of the premaxillae, 
 which do not however reach the frontals. A prenasal ossicle 
 is developed in front of the mesethmoid. The palate is long 
 and narrow, the pterygoid (fig. 94, A, 10) is small, but the 
 pterygoid process of the alisphenoid is prominent. The 
 squamosal is small and has the tympanic fused with it ; the 
 tympanic is dilated below, forming a bulla (fig. 94, A, 9) filled 
 
 1 See W. K. Parker, "On the Structure and Development of the Skull 
 in the Pig." Phil. Trans, pp. 289336, 1874. 
 
 R. 30 
 
466 
 
 THE VERTEBRATE SKELETON. 
 
 1.1 
 
 FIG. 94. A, CRANIUM AND 
 
 1. jugal. 
 
 2. postorbital process of 
 
 frontal. 
 
 3. zygomatic process of 
 
 squamosal. 
 
 4. supra-occipital. 
 
 5. glenoid cavity. 
 
 6. occipital condyle. 
 
 7. foramen magnum. 
 
 8. paroccipital process of 
 
 exoccipital. 
 
 9. tympanic bulla. 
 10. pterygoid. 
 
 J3, MANDIBLE OF A PlG (SUS SCTOfa)xi. 
 
 (Camb. Mus.) 
 
 11. anterior palatine foramen, 
 the 12. palatal plate of maxilla. 
 
 13. coronoid process, 
 the 14. mandibular condyle. 
 
 i 1, i 2, i 3. first, second, and third 
 
 incisors, 
 c. canine. 
 
 pm 1, pm 2, pm 3, pm 4. first, 
 second, third, and fourth 
 the premolars. 
 
 ml, ?w2, ra3. first, second, and 
 third molars. 
 
THE SKELETON IN MAMMALIA. THE SKULL. 467 
 
 with cancellous bone, and above forms the floor of a long up- 
 wardly-directed auditory meatus. The mandible has a high 
 ascending portion and a small coronoid process (fig. 94, B, 13). 
 The hyoid differs from that of most Ungulates, the stylo-hyal 
 being very imperfectly ossified. 
 
 In Hippopotamus the skull though essentially like that of 
 the pig is much modified in detail. The brain cavity is very 
 small, while the jaws are immensely developed. The face con- 
 tracts in front of the orbits and then expands again greatly, 
 to lodge the enormous incisor and canine teeth. The postorbital 
 bar is complete or nearly so, and the orbits project curiously 
 outwards and slightly upwards ; the lachrymal is thin and 
 
 FIG. 95. MANDIBLE OF A HIPPOPOTAMUS (H. amphibius) x f . 
 (Camb. Mus.) 
 
 The second incisor of the left side is missing and the crowns of the 
 grinding teeth are much worn. 
 
 1. condyle. c. canine. 
 
 2. coronoid process. pm 3. third premolar. 
 
 3. mental foramina. m 1, m 3. first and third molar. 
 il, 1 2. first and second incisors. 
 
 302 
 
468 THE VERTEBRATE SKELETON. 
 
 much dilated. The squamosal is drawn out into a postglenoid 
 process, and the hamular process of the pterygoid is prominent. 
 The tympanic bulla is filled with cancellous bone. The mandible 
 is enormously large, the symphysis is long, the angle much 
 expanded and drawn out into a process which projects outwards 
 and forwards. 
 
 Among extinct forms related to the Suina, Gyclopidius is 
 noticeable for having large vacuities in the lachrymo-nasal 
 region, while Cotylops has the postorbital bar complete ; both 
 these forms are from the North American Miocene. 
 
 In the Tylopoda and Tragulina the skull resembles in most 
 respects that of the Ruminants, shortly to be described ; but it 
 is allied to that of the Suina in having the tympanic bulla filled 
 with cancellous bone. The tympanic bulla is better developed 
 in the Tragulina than in most Ungulates. 
 
 Among Ruminants, the Bovidae, that large group includ- 
 ing the Oxen, Sheep, and Antelopes, as a rule have the face 
 bent on the basicranial axis much as in the Suina. The 
 parietals are generally small and early coalesce, the frontals 
 are large and are usually drawn out into horn cores, which are 
 however absent in the skulls of some domestic varieties of sheep 
 and oxen, and also in some of the earlier extinct forms of Bo- 
 vidae. These horn cores are formed internally of cancellous 
 bone, and on them the true epidermal horns are borne. In 
 young animals there is a distinct interparietal, but this early 
 fuses with the supra-occipital, and in the oxen also with the 
 parietals. The occipital crest is generally well marked, but 
 in the genus Bos becomes merged in a very prominent straight 
 ridge running between the two horn cores ; this ridge, which 
 contains air cells communicating with those in the horn cores, is 
 not nearly so well marked in Bison. There is often, as in Gazella, 
 a vacuity on the side of the face between the nasal, frontal, 
 lachrymal, and maxilla, but this is not found in oxen or sheep. 
 The prem axillae are small, the nasals are long and pointed, 
 and the turbinals are much developed. The Saiga antelope 
 
THE SKELETON IN MAMMALIA. THE SKULL. 469 
 
 has a curiously specialised skull ; the nasals are absent or 
 have coalesced with the frontals and the anterior nares are 
 enormously large. In all Ruminants the lachrymal is large 
 and forms a considerable part of the side of the face ; it often 
 bears a considerable depression, the suborbital or lachrymal 
 fossa, well seen in most of the smaller antelopes. The post- 
 orbital bar is complete, and the orbit is prominent and nearly 
 circular. The palatines and pterygoids are moderately large, 
 and the pterygoids have a back wardly-projec ting hamular pro- 
 cess. The squamosal is small, but has a postglenoid process. 
 The tympanic is not fused to the periotic and has a small bulla 
 not filled with cancellous bone. There is a large paroccipital 
 process to the exoccipital and the mandible has a long slender 
 coronoid process. 
 
 In the Cervidae and Giraffidae the face is not bent down 
 on the basicranial axis as it is in the Bovidae. The frontals are 
 drawn out, not into permanent horn cores as in the Bovidae, 
 but into short outgrowths, the pedicels, upon which in the 
 Cervidae long antlers are annually developed. These antlers are 
 outgrowths of bone, and are covered during development by 
 vascular integument, which dries up and peels off when growth 
 is complete. Every year they are detached, by a process of 
 absorption at the base, and shed. They may occur in both sexes, 
 as in the Reindeer, but as a rule they are found only in the 
 male. They are generally more or less branched, and are some 
 times of enormous size and weight, as in the extinct Cervus mega- 
 ceros. In young animals they are always simple, but become 
 annually more and more complicated as the animal grows older. 
 
 In the Giraffe the frontals bear a small pair of bony cores, 
 which are at first distinct, but subsequently become fused to 
 the skull. In the allied Sivatherium, a very large form from 
 the Indian Pliocene, the skull bears two pairs of bony out- 
 growths, a pair of short conical outgrowths above the orbits, 
 and a pair of large expanded outgrowths on the occiput. 
 
 The opening of the lachrymal canal is commonly double 
 
470 THE VERTEBRATE SKELETON. 
 
 and the lachrymal fossa is large in the Cervidae and the Griraf- 
 fidae except Sivatherium. The vacuity between the frontal, 
 lachrymal, maxilla, and nasal is specially large. 
 
 The hyoid of Ruminants is noticeable for the development 
 of the anterior cornua, which include stout and short cerato- 
 hyals and epi-hyals, long and strong stylo-hyals and large 
 tympano-hyals which are more or less imbedded in the tym- 
 panics. 
 
 PERISSODACTYLA. In the skull of Perissodactyles an ali- 
 sphenoid canal is found and the nasals are expanded behind. 
 Among the living animals belonging to this group the skull least 
 modified from the ordinary type is that in Rhinoceros. In this 
 form the skull is considerably elongated, the facial portion being 
 very large. The occipital region is elevated, but the cranial 
 cavity is small, the boundary line between the occipital and 
 parietal regions being drawn out into a prominent crest, which 
 is occupied by air cells. There is no postorbital process to the 
 frontal, and the orbit is completely confluent with the temporal 
 fossa. The nasals are fused together and are very strongly 
 developed, extending far forwards, sometimes considerably 
 beyond the premaxillae. In some extinct species, such as Elas- 
 motherium and the Tichorhine Rhinoceros, R. antiquitatis, the 
 mesethmoid is ossified as far forwards as the end of the nasals. 
 The nasals are arched and bear one or two roughened surfaces 
 to which the great nasal horns are attached. The premaxillae 
 are very small and the pterygoids are slender. The palate is 
 long, narrow, and deeply excavated behind. The postglenoid 
 process of the squamosal is well developed, and generally 
 longer than the paroccipital process of the exoccipital. The 
 tympanic and periotic are both small and are fused together. 
 The condyle of the mandible is very wide, the angle rounded, 
 and the coronoid process moderately developed. 
 
 In the Titanotheriidae, a family of extinct Perissodactyla 
 from the Miocene of North America, the occipital region is much 
 elevated, as is also the fronto-nasal region, the nasals (perhaps 
 
THE SKELETON IN MAMMALIA. THE SKULL. 471 
 
 only in the male) bearing a pair of blunt bony outgrowths, 
 Between these two elevated regions the skull is much de- 
 pressed. The cranial, cavity is very small, the orbit confluent 
 with the temporal fossa, and the zygomatic arch massive. 
 
 In Tapirus the orbit and temporal fossa are confluent. 
 The nasals are small, wide behind and pointed in front, and 
 are supported by the mesethmoid ; the anterior nares are 
 exceedingly large and their lateral boundaries are entirely 
 formed by the maxillae. The postglenoid and post-tympanic 
 processes of the squamosal are large. The periotic is not fused 
 to the squamosal or to the small tympanic. The mandible is 
 large and has the angle much developed and somewhat inflected. 
 
 Palaeotherium, which lived in early Tertiary times, has a 
 skull much like that of the Tapir, especially as regards the 
 nasal bones. 
 
 In the Horse and its allies (Equidae) the facial portion of 
 the skull is very large as compared with the cranial portion, 
 the nasals and nasal cavities being specially large. In the 
 living species of the genus Equus there is no fossa between the 
 maxilla and lachrymal, but it occurs in some extinct species. 
 The lachrymal and jugal form a considerable part of the side 
 of the face ; and the orbit though small is complete and pro- 
 minent. The postorbital bar is formed by a strong outgrowth 
 from the frontal, which unites with a forward extension of the 
 squamosal. The squamosal may extend forwards and form 
 part of the wall of the orbit, a very unusual feature, as in most 
 mammals the squamosal stops before the postorbital bar. The 
 palate is narrow and excavated behind as in Rhinoceros ; the 
 palatines take very little part in its formation. The glenoid 
 surface for the articulation of the mandible is very wide. The 
 squamosal gives rise to small postglenoid and post-tympanic 
 processes, and the exoccipital to a large paroccipital process. 
 The tympanic and periotic are ankylosed together, but not to 
 any other bones. 
 
 In the SUBUNGULATA, the lachrymal and jugal do not form 
 
472 THE VERTEBRATE SKELETON. 
 
 any considerable part of the side of the face, and the maxilla 
 commonly takes part in the formation of the zygomatic arch. 
 
 TOXODONTIA. The skull in the Toxodontia shows several 
 Artiodactyloid features, while the manus and pes are of a more 
 Perissodactyloid type. The Artiodactyloid features are (1) the 
 absence of an alisphenoid canal, (2) the fact that the palate is 
 not excavated behind, and that the palatines form a consider- 
 able part of it, and (3) the fusion of the tympanic to the 
 squamosal and exoccipital, forming the floor of an upwardly 
 directed auditory meatus. The frontal has a fairly well deve- 
 loped postorbital process, but the orbit is confluent with the 
 temporal fossa. The premaxilla is well developed, as is the par- 
 occipital process of the exoccipital, especially in Typotherium. 
 The mandible has a rounded angle and a coronoid process of 
 moderate size. In Typotherium the ascending portion is very 
 massive. 
 
 C ONDYLARTHRA. As far as is known the skull of these 
 generalised Ungulates is depressed, and is frequently marked 
 by a strong sagittal crest. The cranial cavity is small, the 
 cerebral fossa in Phenacodus being exceptionally small. The 
 orbit is completely confluent with the temporal fossa. 
 
 HYRACOIDEA. The skull of Procavia resembles that of 
 Perissodactyles more than that of any other Ungulates, but 
 differs strongly in the comparatively small size of its facial 
 portion. The posterior portion of the cranium is rather high, 
 the occipital plane being nearly vertical. There is a small 
 interparietal. The nasals are wide behind, and the zygomatic 
 arch is strongly developed, its most anterior part being formed 
 by the maxilla. The jugal and parietal give rise to post- 
 orbital processes which sometimes meet, but as a rule the orbit 
 is confluent with the temporal fossa; it is very uncommon 
 for the parietal to give rise to a postorbital process, and even 
 in Procavia the frontal often forms part of the process. The 
 alisphenoid canal, and postglenoid and paroccipital processes 
 are well developed. The tympanic bulla is large and the 
 
THE SKELETON IN MAMMALIA. THE SKULL. 473 
 
 periotic and tympanic are fused together, but not as a rule 
 to the squamosal. The ascending portion of the mandible is 
 very high and broad, the angle rounded and the coronoid 
 process moderate in size. The hyoid is singular, there is a 
 large flat basi-hyal prolonged laterally into two broad flattened 
 thyro-hyals. Articulating with its anterior end are two large 
 triangular cerato-hyals, which are drawn out into two processes 
 meeting in the middle line. 
 
 AMBLYPODA. In the Uintatheriidae (Dinocerata) the skull 
 has a very remarkable character, being long and narrow and 
 drawn out into three pairs of rounded protuberances, a small 
 pair on the nasals, a larger pair on the maxillae in front of the 
 orbits, and the largest pair on the parietals. The cranial cavity, 
 and especially the cerebral fossa, is extraordinarily small. The 
 orbit is not divided behind from the temporal fossa. The 
 mandible has a prominent angle, and a long curved coronoid 
 process ; its symphysial portion bears a curious flattened out- 
 growth to protect the great upper canines. 
 
 In Coryphodon the skull is of a more normal character, 
 being without the conspicuous protuberances. The cranial 
 cavity though very small is not so small as in Uintatherium. 
 
 PROBOSCIDEA. The character of the skull in the young ele- 
 phant differs much from that in. the old animal. In very young 
 individuals the skull is of a normal character, and the cranial 
 cavity is distinctly large in proportion to the bulk of the skull. 
 But as the animal gets older, while its brain does not grow 
 much, the size of its trunk and especially of its tusks increases 
 greatly ; and consequently the skull wall is required to be of 
 very great superficial extent in order to afford space for the 
 attachment of the muscles necessary for the support of these 
 heavy weights. This increase in superficial extent is brought 
 about without much increase in weight of bone by the develop- 
 ment of an enormous number of air cells in nearly all the 
 bones of the skull ; sometimes, as in the case of the frontal, 
 separating the inner wall of the bone from the outer, by as 
 
474 
 
 THE VERTEBRATE SKELETON. 
 
 much as a foot. This development of air cells is accompanied 
 by the obliteration of the sutures between the various bones. 
 The most noticeable point with regard to the cranial cavity 
 is the comparatively large size of the olfactory fossa. The 
 supra-occipital (figs. 96 and 97, 9) is large exceedingly large 
 in the adult skull ; the parietals (figs. 96 and 97, 2) are also 
 very large. The frontals send out small postorbital processes, 
 but these do not meet processes from the small jugal, which 
 
 14 
 
 -11 
 
 ml 
 
 FIG. 96. SKULL OF A YOUNG INDIAN ELEPHANT (Elephas indicus), SEEN 
 
 FROM THE RIGHT SIDE, THE ROOTS OF THE TEETH HAVE BEEN EXPOSED. 
 
 x . (Camb. Mus. ) 
 1. exoccipital. 
 
 2. parietal. 
 
 3. frontal. 
 
 4. squamosal. 
 
 5. jugal. 
 
 6. premaxilla. 
 
 7. maxilla. 
 
 9. supra-occipital. 
 
 13. basi-occipital. 
 
 14. postorbital process of the 
 
 frontal. 
 
 15. lachrymal. 
 
 16. pterygoid process of the ali- 
 
 sphenoid. 
 i 1. incisor. 
 mm 3., mm 4. third and fourth 
 
 milk molars. 
 m 1. first molar. 
 
THE SKELETON IN MAMMALIA. THE SKULL. 
 
 475 
 
 forms only the middle part of the slender zygomatic arch, the 
 anterior part being formed by the maxilla. The lachrymal 
 (fig. 96, 15) is small and lies almost entirely inside the orbit. 
 The anterior narial aperture (fig. 97, 8) is wide and directed 
 upwards, opening high on the anterior surface of the skull. It 
 is bounded above by the short thick nasals and below by the 
 premaxillae. The narial passage is freely open, maxillo-tur- 
 binals not being developed. The palatine is well developed, 
 the pterygoid is small and early fuses with the pterygoid 
 
 17 
 
 8--. 
 
 mm4 
 
 FIG. 97. LONGITUDINAL SECTION TAKEN RATHER TO THE RIGHT OF THE 
 
 MIDDLE LINE OF THE SKULL OF A YOUNG INDIAN ELEPHANT (E. 
 Indicus) x ^ . (Camb. Mus.) 
 
 anterior nares. 12. pterygoid. 
 
 periotic. 17. nasal, 
 
 palatine. Other numbers as in Fig. 96. 
 
 8. 
 10. 
 11. 
 
 process of the alisphenoid. The tympanic is united with the 
 periotic but not with the squamosal, and forms a large auditory 
 
476 THE VERTEBRATE SKELETON. 
 
 bulla. There are no paroccipital or postglenoid processes. 
 The exoccipital is not perforated by the condylar foramen, a 
 very exceptional condition. 
 
 The mandible has a high ascending portion, is rounded off 
 below and has no angle. The symphysial portion is long, 
 narrow, and spout-like, and the coronoid process is small. 
 The thyro-hyals are ankylosed with the basi-hyal, which is 
 connected with the large forked stylo-hyals by ligament only. 
 
 RODENTIA. The cranial cavity is depressed, elongated, and 
 rather small, and the cerebral fossa lies entirely in front of the 
 cerebellar fossa. The occipital plane is vertical or directed 
 somewhat backwards, and the supra-occipital does not form 
 much of the roof of the cranium. The paroccipital processes 
 of the exoccipitals are generally of moderate size ; in the 
 Capybara (Hydrochaerus), however, they are very long, and 
 are laterally compressed and directed forwards. The parietals 
 are small, and often become completely fused together ; there 
 is sometimes a small interparietal. The frontals in most genera 
 have no trace of a postorbital process ; in Squirrels, Marmots 
 and Hares, however, one occurs, but in no case does it meet a 
 corresponding process from the zygomatic arch, so the orbit 
 and temporal fossa are completely confluent. In Hares the 
 postorbital process of the frontal is much flattened, and has 
 an irregular margin. The temporal fossa is always small, and 
 in LopJiiomys is arched over by plates arising respectively 
 from the parietal and jugal ; a secondary roof is thus partially 
 developed in a manner unique among mammals, but carried 
 to a great extent in many Chelonia. The nasal bones and 
 cavities are large, attaining their maximum development in 
 the Porcupines (fig. 98, 1). The premaxilla is always very 
 large, and sends back a long process which meets the frontal. 
 The vomer is occasionally found persisting in two separate 
 halves, a feature recalling the arrangement in Sauropsids. In 
 many Rodents there is an enormous vacuity at the base of the 
 maxillary portion of the zygomatic arch. It is sometimes as 
 
THE SKELETON IN MAMMALIA. THE SKULL. 477 
 
 large as the orbit, and attains its maximum development in 
 the Capybara and other Hystricomorpha ; in the Marmots, 
 Beavers, and Squirrels (Sciuromorpha), and in the Hares it is 
 undeveloped. In Lagostomus the maxilla bears an upwardly 
 directed plate of bone, shutting off from this vacuity a space 
 which is the true infra-orbital foramen. 
 
 The zygomatic arch is always complete, and in many cases 
 the jugal extends back to form part at least of the glenoid 
 
 1 
 
 2- 
 
 FIG. 98. HALF FRONT VIEW OF THE SKULL OF A PORCUPINE 
 (Hystrix cristata)x%. (Camb. Mus.) 
 
 1. nasal. 5. premaxilla. 
 
 2. maxillo-turbinals. 6. jugal. 
 
 3. infra-orbital vacuity. i 1. upper incisor. 
 
 4. maxilla. 
 
 surface for articulation with the mandible. In Coelogenys the 
 jugal and maxillary portion of the zygomatic arch is greatly 
 expanded and roughened, and the maxillary portion encloses a 
 large cavity. The palate in Rodents is narrow, and the space 
 between the incisor and molar teeth passes imperceptibly 
 into the sides of the face. The anterior palatine foramina 
 form long, rather narrow slits in this region. The bony 
 palate between the grinding teeth is sometimes as in the Hares 
 
478 THE VERTEBRATE SKELETON. 
 
 very short, sometimes as in the Capybara very long. The 
 maxilla extends back beneath the orbit to unite with the 
 squamosal. The pterygoid is always small, but sometimes 
 has a well-marked hamular process which in Hystrix, Lagos- 
 tomus, and some other genera unites with the tympanic bulla. 
 The periotic is large, and fused with the tympanic, which 
 forms a prominent bulla, and is generally drawn out into a 
 tubular meatus. The bulla attains its maximum development 
 in Chinchilla and Dipus. 
 
 The mandible is narrow and rounded in front, the two 
 halves meeting in a long symphysis. The angle is generally 
 drawn out into a long backwardly-projecting process, which is 
 often pointed and directed upwards. In the Hares the angle 
 is rounded. The coronoid process is never large. 
 
 There are a number of points in which the skull of the 
 Duplicidentata (Hares and Rabbits) differs from that of other 
 Rodents, (a) The sutures between the basi-occipital and 
 basisphenoid, and between the basisphenoid and presphenoid 
 remain open throughout life. (6) Much of the maxilla forming 
 the side of the face in front of the orbit is fenestrated. (c) The 
 optic foramina are united to form a single hole, much as in 
 birds, (d) The coronoid process is slightly differentiated from 
 the ascending portion of the mandible. The first two of these 
 points have been thought to indicate degradation of the 
 hares and rabbits as compared with higher mammals. 
 
 CARNivoRA 1 . It is characteristic of the skull in Carnivora 
 that the glenoid fossa is deep, and the postglenoid process 
 (fig. 75, 23) well developed. The condyle of the mandible is 
 much elongated transversely. The orbit and temporal fossa 
 in the great majority of forms communicate freely, the post- 
 orbital bar being incomplete. 
 
 CARNIVORA VERA. The axis of the facial portion of the 
 skull is a direct continuation of that of the cranial portion. 
 
 1 See W. H. Flower, "On the value of the characters of the base of the 
 -cranium in the classification of the order Carnivora." P. Z. S. 1869, p. 5. 
 
THE SKELETON IN MAMMALIA. THE SKULL. 479 
 
 The cranial cavity though rather depressed is large, and 
 generally long, though in Cats it is comparatively short and 
 wide. The occipital plane is nearly vertical, and the exocci- 
 pitals are developed into fairly prominent paroccipital processes. 
 The interparietal is commonly distinct, and the parietals unite 
 in a long sagittal suture, which is often developed into a crest. 
 The nasals (fig. 73, 4) are well developed, especially in Cats, and 
 the nasal processes of the premaxillae do not nearly reach the 
 frontals. A considerable part of the palate is formed by the 
 palatine, and the maxillary portion is pierced by rather long 
 anterior palatine foramina. The pterygoid has a hamular 
 process. The zygomatic arch is strong, especially in Cats. 
 Postorbital processes are developed on the frontal (fig. 73, 
 10) and jugal, but never form a complete postorbital bar. A 
 carotid canal is well seen in the Ursidae, and to a less extent 
 in the Felidae ; in the Canidae there is an alisphenoid canal 
 (fig. 75, 21). 
 
 The auditory bulla differs a good deal in the different 
 groups. In the Bears (Ursidae) it is not much inflated, and 
 is most prominent along its inner border ; it is not closely con- 
 nected with the paroccipital process. In the Cats it is very 
 prominent, and its cavity is almost divided by a septum into 
 two parts, the inner of which contains the auditory ossicles. 
 The paroccipital process is closely applied to the bulla. In the 
 Dogs the bulla is intermediate in character between that of 
 the Cats and that of the Bears ; it is partially divided by a 
 septum, and is moderately expanded. 
 
 The mandible is well developed with a prominent angle 
 (fig. 72, 26), and a large coronoid process. The hyoid consists 
 of a broad basi-hyal, a long many-jointed anterior cornu and 
 short thyro-hyals (fig. 72, 33). 
 
 The skull in the CREODONTA is in most respects allied to 
 that of the Canidae, but presents some ursine affinities. The 
 tympanic bulla is fairly prominent, but has no well-developed 
 septum. The cranial cavity is very small and narrow, the 
 
480 THE VERTEBRATE SKELETON. 
 
 zygomatic arch standing away from it. The temporal fossa is 
 of great size. 
 
 In the PINNIPEDIA the cranial cavity is large and rounded. 
 The skull is much compressed in the interorbital region, and 
 in correlation with this compression the ethmo-turbinals are 
 little developed, while the maxillo-turbinals are large. The 
 orbit is large, and the temporal fossa smaller than in the 
 Carnivora vera. In the Walrus (Trichechus) the anterior part 
 of the face is distorted by the development of the huge canines. 
 The Otariidae have an alisphenoid canal. The tympanic bulla 
 is small in Otaria, large in the Phocidae, and flattened in the 
 Walrus. The hyoid is similar to that in Carnivora vera. 
 
 INSECTIVORA. The skull varies much in the different mem- 
 bers of the order Insectivora, but the following points of 
 agreement are found. The cranial cavity is of small size, and 
 is never much elevated. The facial part of the skull is generally 
 considerably elongated, and the nasals and premaxillae are 
 well developed. The zygomatic arch is usually slender or 
 incomplete, and the coronoid process and angle of the mandible 
 are commonly prominent. 
 
 In some Insectivora, such as Galeopithecus, Tupaia, and 
 Macroscelides, the skull shows a higher type of structure 
 than is met with in most members of the order. In these 
 genera the cranial cavity is comparatively large, and the 
 occipital plane is nearly vertical. The zygomatic arch is fairly 
 strong, and the frontal and jugal give rise to postorbital pro- 
 cesses which nearly or quite (Tupaia) meet. The tympanic 
 bulla is well developed, and produced into a tubular auditory 
 meatus, this being specially well marked in Macroscelides. 
 
 In the other Insectivora the cranial cavity is of smaller 
 comparative size, and the orbit and temporal fossa are com- 
 pletely confluent, often without any trace of a postorbital 
 bar. The occipital plane commonly slopes forwards. In 
 the Hedgehogs (Erinaceidae) and Centetidae the tympanic is 
 very slightly developed, forming a small ring. The zygomatic 
 
THE SKELETON IN MAMMALIA. THE SKULL. 481 
 
 arch of Hedgehogs and Gymnura is very slender, the jugal 
 being but little developed and the squamosal and maxilla 
 meeting one another; in the Centetidae the jugal is absent 
 and the arch is incomplete. 
 
 The Moles (Talpidae) have an elongated, depressed and 
 rounded skull with a very slender zygomatic arch formed by 
 the squamosal and maxilla. The nasals are fused together, 
 and the mesethmoid is ossified very far forwards. In the 
 Shrews (Soricidae) there is no zygomatic arch ; the tympanic 
 is ring-like, and the angle of the mandible is very prominent. 
 The hyoid has a transversely extended basi-hyal, a long 
 anterior cornu with three ossifications, and thyro-hyals which 
 are sometimes fused to the basi-hyal. 
 
 CHIROPTERA. In the frugivorous Flying Foxes (Ptero- 
 pidae) the skull is elongated, and the cranial cavity is large 
 and arched, though considerably contracted in front. There 
 are commonly strong sagittal and supra-orbital crests. The 
 parietals take a great part in the formation of the walls of 
 the cranial cavity, the supra-occipital and f rentals being small. 
 The frontal is drawn out into a long postorbital process, but 
 the zygomatic arch, which is slender, and formed mainly by 
 the squamosal and maxilla, gives rise to only a small post- 
 orbital process, so that the orbit and temporal fossa are con- 
 fluent. There is no alisphenoid canal, and the tym panics are 
 very slightly connected with the rest of the skull. The man- 
 dible has a large coronoid process, a rounded angle, and a trans- 
 versely expanded condyle. 
 
 In Insectivorous Bats the skull is generally shorter and 
 broader than in the Pteropidae. The cranial cavity is large 
 and rounded, and has thin smooth walls. The zygomatic 
 arch is slender, and postorbital processes are not generally 
 well developed. The premaxilla is generally small, sometimes 
 absent. The tympanics are ring-like and are not connected with 
 the surrounding bones. The angle of the mandible is distinct. 
 The hyoid in most respects resembles that of the Insectivora. 
 
 K. 31 
 
482 THE VERTEBRATE SKELETON. 
 
 PRIMATES. The characters of the skull differ greatly in 
 the two suborders of Primates, the Anthropoidea and the 
 Lemuroidea. 
 
 In the LEMUROIDEA the general relative proportions of the 
 cranium and face are much as in most lower mammals, and the 
 occipital plane forms nearly a right angle with the basicranial 
 axis. The postorbital processes of the frontals are commonly 
 continued as a pair of ridges crossing the roof of the cranium 
 and meeting the occipital crest. Though the postorbital bar 
 is complete, the orbit and temporal fossa communicate freely 
 below it. The lachrymal canal opens outside the orbit, and the 
 lachrymal forms a considerable part of the side of the face. 
 The tympanic is developed into a large bulla. The hyoid 
 apparatus much resembles that of the Dog. 
 
 In the ANTHROPOIDEA the skull differs greatly from that in 
 the Lemuroidea. The cranial portion of the skull is very 
 large as compared with the facial portion, though the 
 comparative development varies, some monkeys, such as the 
 baboons (Cynocephali) having the facial portion relatively large. 
 The comparative size of the jaws does not vary inversely with 
 the general development of the animal, some of the Cerco- 
 pithecidae having comparatively larger jaws than some of the 
 Cebidae. The great size of the cranial part of the skull is 
 mainly due to the immense development of the cerebral fossa, 
 which commonly completely overlaps the olfactory fossa in 
 front, and the cerebellar fossa behind. This development also 
 has the effect of making the ethmoidal and occipital planes lie, 
 not at right angles to the basicranial axis, but almost in the 
 same straight line with it. This is, however, not always the 
 case, as the Howling Monkey (Mycetes) and also some of the 
 very highest monkeys, the Gibbons (Hylobates\ have the occi- 
 pital plane nearly vertical to the basicranial axis. In adult 
 Man the basi-occipital, exoccipitals and supra-occipital coalesce, 
 forming the so-called occipital bone ; while the basisphenoid, 
 presphenoid, alisphenoids, orbitosphenoids and pterygoids form 
 
THE SKELETON IN MAMMALIA. THE SKULL. 483 
 
 the sphenoid bone. The roof of the skull is partly formed 
 by the large supra-occipital and frontals, but mainly by the 
 parietals (fig. 99, 1), which in Man are of enormous extent. 
 
 In Man and in most monkeys, at any rate when young 
 (fig. 99, B), the roof of the skull is smooth and rounded, but 
 in many forms, such as the Baboons, in the adult the supra- 
 orbital and occipital ridges are much developed. In the Gorilla 
 this is also the case with the sagittal crest (fig. 99, A, 2). The 
 
 FIG. 99. HALF FRONT VIEW OF THE SKULLS, A OF AN OLD, B OF A 
 YOUNG GORILLA (Gorilla savagei) x. (Camb. Mus.) 
 
 1. parietal. 5. squamosal. 
 
 2. sagittal crest. 6. maxilla. 
 
 3. frontal. 7. external auditory meatus. 
 
 4. supra-orbital ridge. 
 
 bones of the upper surface of the cranium interlock with wavy 
 outlines. The nasals vary much in length, being much shorter 
 in man than in most monkeys ; they commonly become early 
 fused together, as do also the frontals. The vomer is well 
 developed, and the ethmo-turbinal always forms part of the 
 boundary of the orbit. There are frequently, as in many 
 Lemuroidea, a pair of more or less well-marked ridges, cross- 
 ing the roof of the skull from the postorbital processes of the 
 
 312 
 
484 THE VERTEBRATE SKELETON. 
 
 f rentals to the occipital crest. The orbit is completely encircled 
 by bone, and the alisphenoid assists the jugal and frontal in 
 shutting it off from the temporal fossa, leaving however a 
 communication between the two as the sphenomaxillary fissure. 
 In most cases the frontals meet one another in the middle line 
 between the mesethmoid and orbitosphenoid, but in Man, Simia, 
 and some Cebidae this does not take place. In nearly all 
 Cebidae the parietal and jugal meet one another, separating 
 the frontal and alisphenoid on the skull wall ; in Man and all 
 Old World monkeys, on the other hand, the alisphenoid and 
 frontal meet and separate the jugal and parietal. The pre- 
 maxillae nearly always send back processes which meet the 
 nasals. The palate is rather short and both the palatine and 
 the premaxilla take a considerable part in its formation. The 
 pterygoid plate of the alisphenoid is decidedly large, and there 
 is no alisphenoid canal. There is never any great develop- 
 ment either of the paroccipital process of the exoccipital, or 
 of the postglenoid process of the squamosal. The periotic 
 and tympanic are always fused together ; in Cebidae they 
 form a small bulla, but a bulla is not developed in any Old 
 World forms. The periotic is large, especially the mastoid 
 portion, which forms a distinct portion of the skull wall be- 
 tween the squamosal and exoccipital. In Man and still more 
 in Old World monkeys, the external auditory meatus is drawn 
 out into a definite tube, whose lower wall is formed by the 
 tympanic ; in the Cebidae the tympanic is ring-like. The 
 perforation of the periotic by the carotid canal is always 
 conspicuous. 
 
 The mandible is rather short and broad, and the angle 
 formed by the meeting of the two rami is more obtuse than in 
 most mammals. The coronoid process is fairly well developed, 
 and the angle is more or less rounded. In most Primates the 
 condyle is considerably widened, but this is not the case in 
 Man. In Mycetes the mandible is very large, its ascending 
 portions being specially developed. The hyoid of Primates is 
 
THE SKELETON IN MAMMALIA. AUDITORY OSSICLES. 485 
 
 remarkable for the large expanded basi-hyal, which is generally 
 concave above and convex below. The anterior cornu is never 
 well ossified, but the thyro-hyal is always strong. In Mycetes 
 the basi-hyal is enormously large, forming a somewhat globular 
 thin-walled capsule. 
 
 AUDITORY OSSICLES. 
 
 There are in mammals four auditory ossicles forming a 
 chain extending from the fenestra ovalis to the tympanic 
 membrane. Three of these, the malleus, incus and stapes, 
 are always distinct, while the fourth, the lenticular, is smaller 
 
 FIG. 100. MALLEUS, STAPES AND INCUS OF 
 A. MAN. B. DOG. C. RABBIT. (After DOBAN) x 1. 
 
 1. head of malleus. 5. manubrium of malleus. 
 
 2. canal of stapes. 6. processus brevis. 
 
 3. incus. 7. lamella. 
 
 4. processus longus (or gracilis). 
 
 than the others and is sometimes not distinct. The names are 
 derived from human anatomy and indicate in the case of the 
 first three a more or less fanciful resemblance respectively to a 
 hammer, an anvil, and a stirrup. The ossicles are homologous 
 
486 THE VERTEBRATE SKELETON. 
 
 as a whole to the hyomandibular of fishes and to the columellar 
 chain of Sauropsids and Amphibians. The malleus is homo- 
 logous to the extracolumella of Crocodiles and the stapes 
 to the columella. The malleus when typically developed 
 consists of a rounded head (fig. 100, 1) which bears a surface 
 articulating with the incus, and a short neck continued into a 
 process, the manubrium (fig. 100, 5), which comes into relation 
 with the tympanic membrane. From the junction of the neck 
 and manubrium two processes are given off, a processus longus 
 or gracilis (fig. 100, 4), which in the embryo is continuous 
 with Meek el's cartilage, and a processus brevis (fig. 100, 6). 
 The incus generally consists of a more or less anvil-shaped 
 portion which articulates with the malleus, and of a process 
 which is connected with the stapes by the small lenticular. 
 The stapes is generally stirrup shaped, consisting of a basal 
 portion from which arise two crura separated by a space the 
 canal through which a branch of the pharyngeal artery runs 
 The lenticular is frequently cartilaginous and sometimes is 
 not developed at all. 
 
 The above is the arrangement of the auditory ossicles met 
 with in the higher Mammalia, but in the lower Mammalia 
 the characters approach more nearly to those met with in 
 Sauropsids. 
 
 In MONOTREMES the ossicles, though distinctly mammalian 
 in character, show a very low type of development. The incus 
 is articulated, or often fused, with an outgrowth from the 
 head of the malleus. The stapes is very much like a reptilian 
 columella, having a single crus with no perforation. 
 
 In MARSUPIALS the ossicles are of a low type, but not so 
 low as the rest of the skeleton might have led one to expect, 
 and all or almost all the points showing a low grade of de- 
 velopment may be paralleled among the Monodelphia. The 
 lowest Marsupials as regards the ossicles are the Peramelidae, 
 whose ossicles are of a frail papery consistence. The Didel- 
 phyidae on the other hand have the most highly developed 
 
THE SKELETON IN MAMMALIA. AUDITORY OSSICLES. 487 
 
 ossicles, the malleus much resembling that of many Insectivores, 
 and the stapes having two definite crura separated by a canal. 
 
 In EDENTATES the character of the ossicles varies much. 
 In Sloths the stapes approaches that of Sauropsids in its 
 narrowness and the slight trace of a canal ; this character 
 is however still more marked in Manis, whose stapes is as 
 Sauropsidan as that of Monotremes, and consists of a nearly 
 circular basal plate bearing a column which does not show any 
 sign of division into crura. The stapes of other Edentates, 
 such as anteaters, aard varks, and most armadillos, is of a high 
 type and has well-developed crura. Priodon has a lower type 
 of stapes than Dasypus and Tatusia. 
 
 The ossicles of the SIRENIA differ widely from those of all 
 other mammals in their great density and clumsy form. 
 
 In CETACEA the ossicles are solid, though not so solid as in 
 Sirenia, and their details vary much. The malleus is always 
 firmly fused to the tympanic by means of the processus longus, 
 and the manubrium is very little if at all developed. The 
 incus has the stapedial end greatly developed, and the stapes 
 has very thick crura with hardly any canal. The ossicles of 
 the Mystacoceti are apparently less specialised than are those 
 of the Odontoceti. 
 
 The auditory ossicles of the UNGULATA do not present any 
 characters common to all the members of the group. 
 
 Among Ruminants they are chiefly remarkable for the 
 development of a broad lamellar expansion between the head 
 and the processus longus of the malleus. In some cases the 
 malleus of the foetus differs strikingly from that of the adult. 
 Among Perissodactyla the Rhinoceros and Tapir have the 
 malleus of a low type, recalling those of Marsupials ; while in 
 the Horse the head is well developed, and the malleus is of 
 a higher type. 
 
 The ossicles of Procavia, which recall those of the Equidae, 
 are chiefly remarkable for the small size of the body of the 
 incus. In Elephants the ossicles are large and massive. 
 
488 THE VERTEBRATE SKELETON. 
 
 In the RODENTIA (fig. 100, C) the malleus is generally 
 characterised by a very broad manubrium. In many genera 
 such as Batfiyergus, and most of the Hystricomorpha such as 
 Hystrix, Chinchilla and Dasyprocta, the malleus and incus are 
 ankylosed together. 
 
 CARNIVORA. In Carnivora vera the most striking feature 
 of the malleus is the occurrence of a broad lamellar expan- 
 sion between the head and neck and the processus longus. 
 This however does not occur in some Yiverridae. In the 
 Carnivora vera the incus and stapes are small as compared 
 with the malleus, but in the Pinnipedia they are large. In 
 the Pinnipedia the auditory ossicles have a very dense 
 consistence, and except in the Otariidae are very large. The 
 stapes frequently has no canal, or only a very small one. 
 
 In INSECTIVORA the characters of the auditory ossicles are 
 very diverse. Many forms such as shrews, moles, hedgehogs, 
 and the Centetidae have a low type of malleus resembling that 
 of Edentates. Chrysochloris has very extraordinary auditory 
 ossicles. The head of the malleus is drawn out into a great 
 club-shaped process, the incus is long and narrow, and differs 
 much from the ordinary type. 
 
 In CHIROPTERA the ossicles and especially the malleus much 
 resemble those of shrews. The stapes is always normal in 
 character, never becoming at all columelliform. 
 
 PRIMATES. In Man and the Anthropoid Apes the malleus 
 has a rounded head, a short neck, and the manubrium, a 
 processus longus and a processus brevis. The incus consists of 
 an anvil-shaped portion from which arises a long tapering 
 process. The stapes has diverging crura and consequently a 
 wide canal. The crura in other monkeys do not diverge so 
 much as in man and anthropoid apes. The New World monkeys 
 have no neck to the malleus. 
 
THE SKELETON IN MAMMALIA. THE STERNUM. 489 
 THE STERNUM 1 . 
 
 In MONOTREMES and most MARSUPIALS the sternum does 
 not present any characters of special importance. The pre- 
 sternum is strongly keeled in Notoryctes. 
 
 The sternum in EDENTATES is very variable : in the Sloths 
 it is very long, the mesosternum of Choloepus having twelve 
 segments. In the anteaters and armadillos the presternum 
 is broad and sometimes as in Priodon strongly keeled. In 
 Manis macrura the xiphisternum is drawn out into a pair of 
 cartilaginous processes about nine inches long. 
 
 In the SIRENIA the sternum is simple and elongated, and 
 of fairly equal width throughout, in the adult it shows no sign 
 of segmentation. Its origin from the union of two lateral 
 portions can be well seen in Manatus. 
 
 Two distinct types of sternum are met with in the CETACEA. 
 In the Odontoceti the sternum consists of a broad presternum 
 followed by three or four mesosternal segments, but with no 
 xiphisternum. Indications of the original median fissure can 
 be traced, and are very evident in Hyperoodon. In the 
 Mystacoceti, on the other hand, the sternum consists simply 
 of a broad flattened presternum which is sometimes more or 
 less heart-shaped, sometimes cross-shaped. Only a single pair 
 of ribs are united to it. 
 
 The sternum in UNGULATA is generally long and narrow and 
 formed of six or generally seven segments. The presternum 
 is as a rule small and compressed, often much keeled, especially 
 in the horse and tapir. The segments of the mesosternum 
 gradually widen as followed back and the xiphisternum is 
 often terminated by a cartilaginous plate. 
 
 In the RODENTIA the sternum is long and narrow and 
 generally has a large presternum, and a xiphisternum termi- 
 nated by a broad cartilaginous plate. 
 
 1 See W. K. Parker, Monograph of the shoulder-girdle and sternum 
 of the Vertebrata, Ray Soc. 1868. 
 
490 THE VERTEBRATE SKELETON. 
 
 In the GARNI VORA, too, the sternum (fig. 76) is long and 
 narrow and formed of eight or nine pieces, all of nearly the 
 same size. The xiphisternum generally ends in an expanded 
 plate of cartilage. 
 
 In INSECTIVORA the sternum is well developed but variable. 
 The presternum is commonly large and is sometimes as in the 
 Hedgehog (Erinaceus) bilobed in front, sometimes as in the 
 Shrew (Sorex) trilobed. It is especially large in the Mole 
 (Talpa) and is expanded laterally and keeled below. 
 
 In the CHIROPTERA the presternum is strongly keeled and 
 so is sometimes the mesosternum. 
 
 Among PRIMATES, in Man and the Anthropoid Apes the 
 sternum is rather broad and flattened ; the mesosternum 
 consists of four segments which are commonly fused together 
 and the xiphisternum is imperfectly ossified. 
 
 THE RIBS. 
 
 Free ribs are borne as a rule only by the thoracic ver- 
 tebrae ; ribs may be found in other regions, especially the 
 cervical and sacral, but these are almost always ankylosed to 
 the vertebrae. As a general rule the first thoracic rib 
 joins the presternum, while the succeeding ones are attached 
 between the several segments of the mesosternum. Some 
 of the posterior ribs frequently do not reach the sternum; 
 they may then be attached by fibrous tissue to the ribs in 
 front, or may end freely (floating ribs). There are generally 
 thirteen pairs of ribs, and in no case do they have uncinate 
 processes. 
 
 In MONOTREMES (fig. 102, B) each rib is divided not into 
 two but into three parts, an intermediate portion being inter- 
 posed between the vertebral and sternal parts. The sternal 
 ribs are well ossified, and some are very broad and flat. The 
 intermediate portions are unossified, those of the anterior ribs 
 are short and narrow, but they become longer and wider 
 further back. 
 
THE SKELETON IN MAMMALIA. THE RIBS. 491 
 
 In MARSUPIALS there are almost always thirteen pairs 
 of ribs, whose sternal portions are very imperfectly ossified. 
 Notoryctes has fourteen pairs of ribs, eight of which are float- 
 ing: the first rib is very stout, and is abruptly bent on itself 
 to join the sternum. It has no distinct sternal portion. All 
 the other ribs are slender. 
 
 Of the EDENTATES the Sloths have very numerous ribs ; 
 twenty-four pairs occur in C/ioloepus, and half of these reach 
 the sternum. In the Armadillos there are only ten or twelve 
 pairs of ribs, but the sternal portions are very strongly ossified. 
 The first rib is remarkably broad and flat, and is not divisible 
 into vertebral and sternal portions. 
 
 In the SIRENIA there are a very large number of ribs 
 noticeable for their great thickness and solidity, but not 
 more than three are attached to the sternum. 
 
 CETACEA. In the Whalebone whales the ribs are remark- 
 able for their very loose connection both with the vertebral 
 column and with the sternum. The capitula are scarcely 
 developed, and the attachment of the tubercula to the trans- 
 verse processes is loose. The first rib is the only one connected 
 with the sternum. In the Toothed whales the anterior ribs 
 have capitula articulating with the centra, as well as tubercula 
 articulating with the transverse processes ; in the posterior 
 ones, however, only the tubercula remain. Seven pairs of 
 well-ossified sternal ribs generally meet the sternum. In the 
 Physeteridae most of the ribs are connected to the vertebrae 
 by both capitula and tubercula. 
 
 In the UNGULATA the ribs are generally broad and flattened, 
 and this is especially the case in the genera Bos and Bubalus 
 (fig. 101, 6). The anterior ribs are short and nearly straight, 
 and sternal ribs are well developed. The Artiodactyla have 
 twelve to fifteen pairs of ribs, the Perissddactyla eighteen or 
 nineteen, and Procavia twenty to twenty-two. The Elephant 
 has nineteen to twenty-one pairs, seven of which may be float- 
 ing ribs. 
 
492 
 
 THE VERTEBRATE SKELETON. 
 
 CM 
 
THE SKELETON IN MAMMALIA. PECTORAL GIRDLE. 493 
 
 FIG. 101. SKELETON OF A CAPE BUFFALO (Bubalus coffer). 
 The left scapula is omitted for the sake of clearness x T y. (Brit. Mus.) 
 
 1. premaxilla. 7. femur. 
 
 2. nasal. 8. patella. 
 
 3. orbit. 9. tibia. 
 
 4. neural spine of first thoracic 10. metatarsals. 
 
 vertebra. 11. radius. 
 
 5. scapula. 12. metacarpals. 
 
 6. rib. 
 
 In the RODENTIA there are generally thirteen pairs of ribs, 
 which do not present any marked peculiarities. 
 
 The CARNIVORA have thirteen to fifteen pairs of ribs, 
 whose vertebral portions are slender, nearly straight and 
 subcylindrical, while their sternal portions are long and 
 imperfectly ossified (fig. 76, 5). There is nothing that calls 
 for special remark about the ribs, in either INSECTIVOKA or 
 CHIROPTERA. 
 
 PRIMATES. In Man and the Orang (Simia) there are ge- 
 nerally twelve pairs of ribs ; in the Gorilla and Chimpanzee 
 (Antkropopithecus), and Gibbons (Hylobates), there are thirteen, 
 in the Cebidae twelve to fifteen, and in the Lemuroidea twelve 
 to seventeen pairs. The first vertebral rib is shorter than the 
 others, and the sternal ribs generally remain cartilaginous 
 throughout life, though in man the first may ossify. 
 
 APPENDICULAR SKELETON. 
 
 THE PECTORAL GIRDLE. 
 
 By far the most primitive type of the pectoral or shoulder 
 girdle is found in the MONOTREMATA. The scapula (fig. 102, 
 A, 1) is long and recurved, and has only two surfaces, one 
 corresponding to the prescapular 1 fossa, the other to the post- 
 scapular 1 and subscapular 1 fossae. The coracoid is a short bone 
 attached above to the scapula and below to the presternum ; 
 it forms a large part of the glenoid cavity. In front of the 
 coracoid there is a fairly large flattened epicoracoid (fig. 102, 6); 
 
 1 See p. 405. 
 
494 
 
 THE VERTEBRATE SKELETON. 
 
 there is also a large T-shaped interdavicle (fig. 102, 4), 
 which is expanded behind and rests on the presternum. The 
 clavicles rest on and are firmly united to the anterior border 
 of the interclavicle. This shoulder girdle differs greatly from 
 that of any other mammals, and recalls that of some Lacertilia. 
 In MARSUPIALS, as in all mammals except the Monotremes, 
 the shoulder girdle is much reduced ; there are no epicoracoids 
 
 A. B 
 
 FIG. 102. A, SIDE VIEW, B, DORSAL VIEW OF THE SHOULDER GIRDLE AND 
 
 PART OF THE STERNUM OF THE SPINY ANTEATER (Echidna 
 
 x 1. (After PARKER.) 
 
 1. scapula. 6. epicoracoid. 
 
 2. suprascapula. 7. 
 
 3. clavicle. 8. 
 
 4. interclavicle. 9. 
 
 5. coracoid. 10. 
 
 glenoid cavity, 
 presternum. 
 second sternal rib. 
 second vertebral rib. 
 
 and interclavicle, and the coracoid forms simply a small process 
 on the scapula, ossifying from a centre separate from that 
 giving rise to the rest of the bone. The scapula has a long 
 acromion, and a clavicle is always present except in Perameles. 
 Unossified remains of the precoracoids are found at either end 
 of the clavicle. The scapula of Notoryctes has a very high 
 
THE SKELETON IN MAMMALIA. PECTORAL GIRDLE. 495 
 
 overhanging spine, and there is a second strong ridge running 
 along the proximal part of the glenoid border. 
 
 The shoulder girdle of the EDENTATA shows some very 
 curious variations. In Orycteropus the scapula is of very 
 normal form and the clavicle is well developed. In the Pan- 
 golins and Anteaters the scapula is very broad and rounded ; 
 there is no clavicle in the Pangolins, and generally only a 
 vestigial one in Anteaters. In Armadillos, Sloths, and Mega- 
 theriidae, the acromion is very long and the clavicle is well 
 developed. In the Sloths, Megatherium, and Myrmecophaga, a 
 connection is formed between the coracoid, which is unusually 
 large, and the coracoid border of the scapula, converting the 
 coraco-scapula notch into a foramen. In Bradypus the 
 clavicle is very small, and is attached to the coracoid, which 
 sometimes forms a distinct bone 1 . 
 
 In the SIRENIA the scapula is somewhat narrow and curved 
 backwards : the spine, acromion, and coracoid process are 
 moderately developed, and there is no clavicle. 
 
 CETACEA. In nearly all the Odontoceti the scapula is 
 broad and somewhat fan-shaped ; the prescapular fossa is much 
 reduced, and the acromion and coracoid process form flattened 
 processes, extending forwards nearly parallel to one another. 
 Some of the Mystacoceti, such as Halaenoptera, have a broad, 
 fan-shaped scapula, with a long acromion and coracoid process, 
 extending parallel to one another. Others, such as Balaena, 
 have a higher and narrower scapula, with a smaller coracoid 
 process. 
 
 In UNGULATA the scapula is always high and rather narrow, 
 and neither acromion nor coracoid process is ever much deve- 
 loped. In no adult Ungulate except Typotherium is there any 
 trace of a clavicle, but a vestigial clavicle has been described 
 in early embryos of sheep 2 . 
 
 UNGULATA VERA. In the Ruminantia the suprascapular 
 
 1 See R. Lydekker, P. Z. S. 1895, p. 172. 
 
 2 See H. Wincza, Morph. Jahr. xvi. p. 647, 1890. 
 
496 
 
 THE VERTEBRATE SKELETON. 
 
 region (fig. 103, 5) is very imperfectly ossified, and when this 
 is removed the upper border of the scapula is very straight 
 (fig. 101, 5). The spine is prominent, and generally has a 
 
 FIG. 103. SKELETON OF A LLAMA (Auchenia glama) x 
 (Brit. Mus.) 
 
 hyoid. 6. 
 
 atlas vertebra. 7. 
 
 seventh cervical vertebra. 8. 
 
 scapula. 9. 
 
 imperfectly ossified supra- 10. 
 scapula. 
 
 olecranon process of ulna. 
 
 metacarpals. 
 
 ilium. 
 
 patella. 
 
 calcaneum. 
 
 fairly well-marked acromion. In Hippopotamus the acromion 
 is fairly prominent, but in the other Suina, though the spine 
 is prominent, the acromion is not developed. The Perisso- 
 dactyla have no acromion, but while the Equidae and Hyra- 
 cotherium have the scapula long and slender, with the spine 
 very slightly developed, the other living Perissodactyla have 
 the spine prominent and strongly bent back at about the 
 middle of its length. 
 
THE SKELETON IN MAMMALIA. SHOULDER GIRDLE. 497 
 
 SUBUNGULA.TA. Typotherium (Toxodontia) differs from all 
 other known Ungulates in having well-developed clavicles ; 
 its scapula has a strong backwardly-projecting process, much 
 like that in Rhinoceros. 
 
 Phenacodus (Condylarthra), has a curiously rounded 
 scapula, with the coracoid and suprascapular borders passing 
 imperceptibly into one another. The scapula resembles that 
 of a carnivore more than does that of any existing Ungulate. 
 
 Procavia has a triangular scapula with a prominent spine 
 and no acromion ; there is a large unossified suprascapular 
 region. 
 
 The scapula in the Proboscidea has a large rounded supra- 
 scapular border and a narrow, slightly concave glenoid border. 
 The spine is large, and has a prominent process projecting 
 backwards from about its middle. The spine lies towards 
 the front end of the scapula, so that the postscapular fossa is 
 much larger than the prescapular fossa. 
 
 In RODENTIA the shoulder girdle is of a rather primitive 
 type. The scapula is generally high and narrow, somewhat 
 as in Ruminantia; it differs, however, from the Ruminant 
 scapula in having a high acromion, which is often, as in the 
 Hares and Rabbits, terminated by a long metacromion. The 
 development of the clavicle varies, and sometimes it is alto- 
 gether absent. It is frequently connected by cartilaginous 
 bands or ligaments (fig. 104, 7 and 9), on the one hand with 
 the scapula, and on the other with the sternum. These un- 
 ossified bands are remains of the precoracoid. Epicoracoidal 
 vestiges of the sternal ends of the coracoids (fig. 104, 11) are 
 also often present. 
 
 In the CARNIVORA VERA the scapula is large, and generally 
 has rather rounded borders. The spine and acromion are well 
 developed, and the prescapular and postscapular fossae are 
 nearly equal in size. The coracoid is very small, and the 
 clavicle is never completely developed, being often absent, as 
 in the Bears and most of their allies. In the Seals (Phocidae) 
 R. 32 
 
498 
 
 THE VERTEBRATE SKELETON. 
 
 the scapula is elongated and curved backwards, and has a very 
 concave glenoid border. In the Eared Seals (Otariidae) the 
 scapula is proportionally much larger and wider, the pre- 
 scapular fossa being specially large, and being traversed by a 
 ridge, which converges to meet the spine. 
 
 FIG. 104. DORSAL VIEW OF THE STERNUM AND RIGHT HALF OF THE 
 SHOULDER-GIRDLE OF Mus sylvaticus x 4. (After PARKER.) 
 
 1. postscapular fossa. 
 
 2. prescapular fossa. 
 
 3. spine. 
 
 4. suprascapular border unossi- 
 
 fied. 
 
 5. coracoid process. 
 
 6. acromion. 
 
 7. cartilaginous vestige of pre- 
 
 coracoid at scapular end of 
 clavicle. 
 
 8. clavicle. 
 
 9. cartilaginous vestige of pre- 
 
 coracoid at sternal end of 
 clavicle. 
 
 10. omosternum. 
 
 11. epicoracoid. 
 
 12. presternum. 
 
 13. first segment of mesosternnm. 
 
 14. xiphisternum. 
 
 15. cartilaginous termination of 
 
 xiphisternum. 
 
 16. 2nd sternal rib. 
 
 17. 1st vertebral rib. 
 
SKELETON IN MAMMALIA. UPPER ARM AND FORE- ARM. 499 
 
 In the INSECTIVORA the shoulder girdle is well developed 
 and, as in Rodents, remains are met with of various parts not 
 generally seen in mammals. In the Shrews the scapula is 
 long and narrow, and has a well-marked spine, whose end 
 bifurcates, forming the acromion and metacromion. The 
 clavicle is long and slender, and is connected with the sternum 
 and acromion by vestiges of the precoracoid. Considerable 
 remains of the sternal end of the coracoid are also found. In 
 Potamogale, however, there are no clavicles. In the Mole the 
 shoulder girdle is greatly developed, and of very remarkable 
 form. The scapula is high and very narrow, with the spine 
 and acromion very little developed. The other shoulder girdle 
 element is an irregular bone, which articulates with the 
 humerus and presternum, and is connected by ligaments with 
 the scapula. This bone appears to represent both the coracoid 
 and the clavicle, being formed partly of cartilage bone, partly 
 of membrane bone. 
 
 In the CHIROPTERA the scapula is large and oval, and has 
 a moderately high spine and a large acromion. The coracoid 
 process is well developed and is often forked. The clavicles are 
 also well developed, and vestiges of the precoracoid and of the 
 sternal end of the coracoid are often found. 
 
 In PRIMATES the clavicle and coracoid process are always 
 well developed. In Man and the Gorilla the scapula has a 
 long straight suprascapular border, a well-developed coracoid 
 process and spine, and a large curved acromion. Vestiges of 
 the precoracoid occur at each end of the clavicle. The shape 
 of the scapula varies much iri the lower Primates. 
 
 THE UPPER ARM AND FORE-ARM. 
 
 In the MONOTREMATA the humerus is short, very broad at 
 each end and contracted in the middle. The radius and ulna 
 are stout and of nearly equal size, while the ulna has a greatly 
 expanded olecranon. 
 
 In the MARSUPIALIA the humerus is generally a strong bone, 
 
 322 
 
500 
 
 THE VERTEBRATE SKELETON. 
 
 broad at the distal end and having well marked deltoid and 
 supinator ridges, which are specially large in Notoryctes. An 
 
 FIG. 105. ANTERIOB SUKFACE OF THE BIGHT HUMEKUS OF A WOMBAT 
 
 (Phascolomys latifrons). (After OWEN.) 
 
 head. 6. 
 
 greater tuberosity. 7. 
 
 lesser tuberosity. 8. 
 
 deltoid ridge. 9. 
 
 ent-epicondylar (supracondy- 10. 
 lar) foramen. 
 
 supinator ridge, 
 external condyle. 
 internal condyle. 
 articular surface for radius, 
 articular surface for ulna. 
 
 ent-epicondylar or supracondylar foramen (fig. 105, 5) is almost 
 always present except in Notoryctes. The radius and ulna are 
 always distinct and well developed, and a certain amount of 
 rotation can take place between them. The ulna of Notoryctes 
 has an enormous hooked olecranon which causes the bone to 
 be nearly twice as long as the radius. 
 
 EDENTATA. The Sloths have long slender arm bones ; the 
 humerus is nearly smooth and has a very large ent-epicondylar 
 foramen in Choloepus, but not in Bradypus. The radius 
 
SKELETON IN MAMMALIA. UPPER ARM AND FORE-ARM. 501 
 
 and ulna can be rotated on one another to a considerable 
 extent. The humerus in all other Edentates is very strong and 
 has the points for the attachment of muscles much developed, 
 especially in the Armadillos and Megatheriidae. An ent- 
 epicondylar foramen is found in all living forms. The radius 
 and ulna are well developed, but are not capable of much 
 rotation. 
 
 In the SIRENIA the humerus is well developed and of a 
 normal character. It is expanded at each end and has a 
 prominent internal condyle, a small olecranon fossa, and no 
 ent-epicondylar foramen. In the Dugong and Rhytina there 
 is a bicipital groove and the tuberosities are distinct, but in 
 the Manatee there is no bicipital groove, and the tuberosi- 
 ties coalesce. The radius and ulna are about equally developed 
 and ankylosed together at both ends. 
 
 In the CETACEA the arm bones are very short and thick. 
 The humerus has a globular head, and a distal end terminated 
 by two equal flattened surfaces to which the radius and ulna 
 are united. There is no bicipital groove, and the tuber- 
 osities coalesce. The radius and ulna are flat expanded bones 
 fixed parallel to one another, but the ulna has a definite ole- 
 cranon. Scarcely any movement can take place between 
 them and the humerus, and in old animals the three bones are 
 often ankylosed together. 
 
 In the UNGULATA VERA the humerus is stout and rather 
 short. The great tuberosity is always large and often overhangs 
 the bicipital groove, it is especially large in Titanotherium 
 (Brontops], There is never an ent-epicondylar foramen. The 
 radius is always large at both ends, but the condition of the 
 ulna is very variable. Sometimes, as in Tapirus, Rhinoceros, 
 Macrauchenia, Suina and Tragulina, the ulna is well developed, 
 and quite distinct from the radius ; but in most forms, although 
 complete, it is much reduced distally, and is fused to the 
 radius. Sometimes, as in the Horse and Giraffe, it is reduced 
 to the olecranon and to a very slender descending process 
 
502 THE VERTEBRATE SKELETON. 
 
 which does not nearly reach the carpus. In the Tylopoda, 
 though the ulna is complete and its distal end is often distinct, 
 it has coalesced with the radius throughout its whole length ; 
 the olecranon is generally very large. 
 
 SUBUNGULATA. In the large Condylarthra the humerus 
 has an ent-epicondylar foramen, and the radius and ulna are 
 stout bones nearly equal in size. 
 
 In Procavia the humerus is rather long, and has a very 
 prominent greater tuberosity, and a large supratrochlear fossa, 
 but no ent-epicondylar foramen. 
 
 In the Proboscidea the humerus is marked by a greatly 
 developed supinator ridge, and is very long, longer than the 
 radius and ulna. The ulna has a remarkable development, 
 having its distal end larger than that of the radius, it has 
 also a larger articular surface for the humerus than has the 
 radius. 
 
 In RODENTIA the humerus varies much in its development 
 according to the animal's mode of life. In the Hares it is long 
 and straight, with a small distal end, and a slight deltoid ridge. 
 In the Beaver on the other hand the deltoid and supinator 
 ridges are considerably developed. There is generally a large 
 supratrochlear fossa, but no ent-epicondylar foramen. 
 
 CARNIVORA. In the Carnivora vera the humerus has large 
 tuberosities, a prominent deltoid ridge and a deep olecranon 
 fossa. The shaft is generally curved, and an ent-epicondylar 
 foramen is often found, though not in the Canidae, Hyaenidae, 
 and Ursidae. The radius and ulna are never united. The 
 radius (fig. 77, B) has a very similar development throughout 
 its whole length, while the ulna has a large olecranon (fig. 
 77, C, 11) and a shaft tapering somewhat towards the distal 
 end. 
 
 In the Pinniped ia the arm bones are very strongly de- 
 veloped. The humerus has a very prominent deltoid ridge, 
 and the proximal end of the ulna and distal end of the 
 radius are much expanded. 
 
THE SKELETON IN MAMMALIA. THE MANUS. 503 
 
 In the INSECTIVORA the arm bones are well developed, and 
 the radius and ulna, though sometimes united, are generally 
 distinct ; as a rule there is an ent-epicondylar foramen, but this 
 is absent in the Hedgehog. The Mole has an extraordinary 
 humerus, very short and curved, and much flattened and ex- 
 panded at both ends. It articulates both with the scapula 
 and coraco-clavicle. The ulna has a greatly developed ole- 
 cranon. 
 
 In the CHIROPTERA both humerus and radius are exceed- 
 ingly long and slender ; the ulna is reduced to little more than 
 the proximal end and is fused to the radius. There is no ent- 
 epicondylar foramen. 
 
 All PRIMATES have the power of pronation and supination 
 of the fore-arm, by the rotation of the distal end of the radius 
 round that of the ulna. 
 
 In Man and the Anthropoid Apes the humerus is long and 
 straight, and has a globular head ; neither of the tuberosities, 
 nor the deltoid nor supinator ridges are much developed. The 
 olecranon fossa is deep and there is no ent-epicondylar fora- 
 men. The radius is curved and has a narrow proximal, and 
 expanded distal end, the ulna is straighter than the radius 
 and has the distal end much smaller than the proximal ; the 
 olecranon is not much developed. 
 
 In the lower Primates, although the radius and ulna are 
 always quite separate, the power of pronation and supination 
 is not nearly so great as in the higher forms. In most of the 
 Cebidae and Lemurs an ent-epicondylar foramen occurs. 
 
 THE MANUS. 
 
 The Manus is divisible into two parts, viz. the carpus or 
 wrist, and the hand which is composed of the metacarpals and 
 phalanges. The carpal bones are always modified from their 
 primitive arrangement, sometimes more, sometimes less. One 
 modification however is always found in mammals, viz. the 
 
504 THE VERTEBRATE SKELETON. 
 
 union of carpalia, 4 and 5 to form the unciform bone. Two 
 sesamoid bones are commonly developed, one on each side of 
 the carpus, the pisiform or one on the ulnar side being much 
 the larger and more constant : it has been suggested that 
 these represent respectively vestiges of a prepollex and a post- 
 minimus digit 1 . 
 
 One or more of the five digits commonly present may be 
 lost, and sometimes all are lost except the third. The terminal 
 or ungual phalanges of the digits are commonly specially 
 modified to support nails, claws, or hoofs. There are as a rule 
 two small sesamoid bones developed on the ventral or flexor 
 side of the metacarpo-phalangeal articulations, and sometimes 
 similar bones occur on the dorsal or extensor side. 
 
 MONOTREMATA. In Echidna the carpus is broad, the sca- 
 phoid and lunar are united and there is no centrale. The 
 pisiform is large and several other sesamoid bones occur. Each 
 of the five digits is terminated by a large ungual phalanx. In 
 OrnithorhyncTius the man us is more slender, but the general 
 arrangement is the same as in Echidna. 
 
 MARSUPIALIA. The carpus has no centrale and the lunar 
 is generally small or absent. Five digits are almost always 
 present. In Choeropus however the only two functional digits 
 are the second and third, which have very long closely apposed 
 metacarpals ; the fourth digit is vestigial, but has the normal 
 number of phalanges, while the first and fifth are absent. The 
 manus in Notoryctes is extraordinarily modified, the scaphoid 
 and all the distal carpalia are apparently fused, the first, 
 second, and fifth digits are very small, the third and fourth, 
 though having only one phalanx apiece, bear each an enormous 
 claw. Lying on and obscuring the ventral surface of the manus 
 is a large bone, probably a sesamoid. 
 
 Among the EDENTATA there is a great diversity in the 
 structure of the manus, the centrale is however always want- 
 ing, and except in Manis the scaphoid and lunar are distinct. 
 1 See K. Bardeleben, P. Z. S., 1889, p. 259. 
 
THE SKELETON IN MAMMALIA. THE MANUS. 505 
 
 In the Sloths the manus is very long, narrow, and curved, 
 and terminated by two or three long hooked claws, borne 
 by the second and third, or the second, third and fourth 
 digits. The fifth digit is absent, and the fourth is represented 
 only by a small metacarpal. In the Anteaters the third digit 
 is greatly developed and bears a long hooked claw. In Myr- 
 mecophaga all five digits are fairly well though irregularly 
 developed, in Cydoturus the first, fourth, and fifth, are vesti- 
 gial. In the Armadillos the manus is broad, and has strongly 
 developed ungual phalanges. The digits, though almost always 
 five in number, vary much in their relative arrangement. In 
 Dasypus they are regular, but are remarkably irregular in 
 Priodon. The pollex is absent in Glyptodonts and in Mega- 
 therium. In Megatherium the fifth digit is clawless while the 
 second, third, and fourth bear enormous claws. In the Manidae 
 the scaphoid and lunar are united; five digits are present, 
 the third and fourth being very large, and all being terminated 
 by deeply cleft ungual phalanges. In Orycteropus the pollex is 
 absent, while the other digits are terminated by pointed un- 
 gual phalanges. 
 
 In SIRENIA the general structure of the manus is quite of 
 the ordinary mammalian type. In Manatus most of the bones 
 of the carpus are distinct, but in Halicore many, especially 
 those of the distal row, have coalesced. The digits are always 
 five in number and have the normal number of flattened 
 phalanges. 
 
 In the CETACEA, on the other hand, the manus is much 
 modified by the fact that the number of phalanges may be 
 greatly increased above the normal number of three, thirteen 
 or fourteen sometimes occurring in each digit. These are 
 believed to be duplicated epiphyses. In the Mystacoceti the 
 manus remains largely cartilaginous, in the Odontoceti it is 
 better ossified, and the phalanges commonly have epiphyses at 
 both ends. In Physeter the carpal bones also have epiphyses. 
 The carpus generally consists of six bones arranged in two 
 
506 THE VERTEBRATE SKELETON. 
 
 rows of three each. Five digits are generally present, but 
 sometimes as in Balaenoptera musculus, there are four, the 
 third being suppressed. Their relative development varies 
 much. The Sperm Whale which till recently was placed in the 
 entrance hall of the Natural History Museum at South Ken- 
 sington has one phalanx to the first digit, four to the second, 
 five to the third, four to the fourth, and three to the fifth. 
 Generally the manus is short and broad, but sometimes, as in 
 Globicephalus, it is much elongated owing to the great develop- 
 ment of the second and third digits. 
 
 UNGULATA 1 . The manus of the members of this great 
 order is of very great classificatory and morphological impor- 
 tance. All the members agree in having the scaphoid and 
 lunar distinct, and in almost every case the ends of the digits 
 are either encased in hoofs or provided with broad flat nails. 
 It is by means of characters derived from the manus and pes 
 that the group is subdivided into the Ungulata vera and 
 the Subungulata. 
 
 In the UNGULATA VERA the manus is never plantigrade, 
 and there are not more than four digits, the pollex being almost 
 always completely suppressed : in Cotylops among extinct Artio- 
 dactyla however a vestigial pollex is found. The centrale is 
 absent, and the magnum articulates freely with the scaphoid, 
 and is separated from the cuneiform by the unciform and lunar. 
 A1J the bones of the carpus interlock strongly, and the axis of 
 the third digit passes through the magnum and between the 
 scaphoid and lunar. 
 
 There is a very strong distinction between the manus of 
 the suborders Artiodactyla and Perissodactyla. In the Artio- 
 dactyla the axis of the manus passes between the third and 
 fourth digits, which are almost equally developed arid, except in 
 the Hippopotami and some extinct forms such as Anoplotherium, 
 
 1 See E. Cope, " The origin of the foot structures of Ungulata," Journ. 
 ofPhilad. Acad. 1874. H. F. Osborn, "The evolution of the Ungulate 
 foot," T. Amer. Phil. Soc. 1889. 
 
THE SKELETON IN MAMMALIA. THE MANUS. 507 
 
 have their ungual phalanges flattened on their contiguous 
 surfaces. 
 
 In all ARTIODACTYLA the third and fourth digits are large, but 
 a gradual reduction in the second and fifth can be well traced. 
 Thus in the Suina the second and fifth digits, though smaller 
 than the third and fourth, are well developed and all four 
 metacarpals are distinct. In the Tragulina too all four meta- 
 carpals are developed, and in Dorcatherium the third and fourth 
 commonly remain distinct as in the Suina. In the other Artio- 
 dactyla however the third and fourth metacarpals are almost 
 always united, though indications of their separate origin 
 remain. In some Ruminantia, such as many Deer, the second 
 and fifth digits are reduced to minute splint bones attached 
 to the proximal end of the fused third and fourth metacarpals, 
 and to small hoof-bearing phalanges, sometimes attached to 
 splint-like distal vestiges of the metacarpals, sometimes alto- 
 gether unconnected with any other skeletal structures. In 
 some other Ruminants, such as the Sheep and Oxen, the only 
 remnants of the second and fifth digits are nodules of bone 
 supporting the hoofs, and in others, such as the Giraffe, Ano- 
 plotherium commune, some Antelopes and the Tylopoda, all 
 traces of these digits have disappeared. The Camels differ 
 from all living Ungulata vera in not having the distal pha- 
 langes completely encased in hoofs, and from all except the 
 Hippopotami in placing a considerable amount of the manus 
 on the ground in walking. 
 
 While the manus of the Artiodactyla is symmetrical about 
 a line drawn between the third and fourth digits, that of the 
 PERISSODACTYLA is symmetrical about a line drawn through the 
 middle of the third digit, which is larger than the others and 
 has its ungual phalanx evenly rounded and symmetrical in 
 itself. The most reduced manus in the whole of the mam- 
 malia is found in the Horse and its allies, in which the third 
 digit, terminated by a very wide ungual phalanx, is the only 
 one functional. Small splint bones representing the second and 
 
508 
 
 THE VERTEBRATE SKELETON. 
 
 fourth metacarpals are attached to the upper part of the third 
 metacarpal. In Hipparion 1 and other early horse-like animals 
 the second and fourth digits, though very small and function- 
 less, are complete and are terminated by small hoofs. In Rhi- 
 noceros the second and fourth digits are equally developed 
 and nearly as large as the third, and reach the ground in 
 
 JT 
 
 FIG. 106. MANUS OF PERISSODACTYLES. 
 
 A. LEFT MANUS OF Tapirus. (After VON ZITTEL.) 
 
 B. EIGHT MANUS OF Titanotherium. (After MARSH.) 
 
 G. LEFT MANUS OF Chalicotherium gigantium. (After GERVAIS.) 
 
 scaphoid. 
 
 lunar. 
 
 cuneiform. 
 
 trapezoid. 
 
 magnum. 
 
 6. unciform. 
 
 7. trapezium. 
 
 II, III, IV, V. second, third, 
 fourth and fifth digits. 
 
 walking, a vestige of the fifth is also present. In the -Tapir 
 
 1 See 0. C. Marsh, various papers including "Fossil horses in 
 America," Amer. Natural. 1874 ; " Polydactyl horses," Amer. J. Sci. 1879 
 and 1892. M. Pavlow, "Le de>eloppement des Equides," Bui. Soc. 
 Moscou, 1887, and subsequent papers in the same. Osborn and Wortman, 
 " On the Perissodactyls of the White Eiver beds," Bull. Amer. Mus. Dec. 
 23rd, 1895. 
 
THE SKELETON IN MAMMALIA. THE MANUS. 509 
 
 (fig. 106, A) and Hyracotherium the fifth digit is fully de- 
 veloped but is scarcely functional. In Titanotherium (Er on- 
 tops] (fig. 106, B) it is nearly as well developed as any of the 
 others, and there is little or no difference between the relative 
 development of the third and fourth digits. 
 
 The Chalicotheriidae l , though distinctly Perissodactyles in 
 various respects such as their cervical vertebrae and teeth, 
 differ not only from all other Perissodactyles, but from almost 
 all other Ungulates, in the very abnormal character of their 
 manus. For while the carpus and metacarpus are like those 
 of ordinary Perissodactyles, the phalanges resemble those of 
 Edentates, each second phalanx having a strongly developed 
 trochlea, and each distal one being curved, pointed and deeply 
 cleft at its termination (fig. 106, C). 
 
 The Macraucheniidae, while agreeing with Perissodactyles 
 in having only three digits, with the limb symmetrical about 
 a line drawn through the middle of the third, have a carpus 
 which approaches closely to the subungulate condition, the 
 magnum articulating regularly with the lunar, and only to a 
 slight extent with the scaphoid. 
 
 In the SUBUNGULATA the manus sometimes has five func- 
 tional digits, and a considerable part of it rests on the ground 
 in walking. The bones of the carpus retain their primitive 
 relation to one another, the magnum articulating with the 
 lunar, but not with the scaphoid. This character does not 
 however hold in the Toxodontia, for in most of the animals 
 belonging to this group the magnum does articulate with the 
 scaphoid. The corner of the scaphoid just reaches the magnum 
 also in Amblypoda. 
 
 As far as is known the TOXODONTIA generally have three, 
 sometimes five digits to the manus, and the third is symme- 
 trical in itself a Perissodactyloid feature. 
 
 In Phenacodus (fig. 107, B) (CONDYLARTIIRA) all five digits 
 
 1 See H. F. Osborn, Clialicotherium and Macrotherium, Amer. Natural. 
 188991-92. 
 
510 
 
 THE VERTEBRATE SKELETON. 
 
 are well developed, the pollex being the smallest. The carpal 
 bones retain their primitive arrangement, the magnum articu- 
 
 FIG. 107. LEFT MANUS OF 
 
 A. Coryphodon hamatus. (After MAKSH.) xi. 
 
 B. Phenacodus primaevus. (After COPE. ) x J . 
 
 C. Procavia (Dendrohyrax) arboreus. (After VON ZITTEL.) 
 
 1. scaphoid. 
 
 2. lunar. 
 
 3. cuneiform. 
 
 4. trapezium. 
 
 5. trapezoid. 
 
 6. magnum. 
 
 7. unciform. 
 
 8. centrale. 
 
 9. pisiform. 
 
 I, II, III, IV, V. first, second, 
 third, fourth and fifth 
 digits respectively. 
 
 lating with the lunar and not with the scaphoid. There is no 
 separate centrale. 
 
 In the HYRACOIDEA (fig. 107, C) the manus is very similar 
 to that in Phenacodus, but a centrale is present and the pollex 
 is much reduced. 
 
 The manus of the AMBLYPODA, such as Coryphodon (fig. 
 107, A) and Uintatherium, is short and broad, with five well- 
 
THE SKELETON IN MAMMALIA. THE MANUS. 511 
 
 developed digits and large carpal bones. The carpals however 
 interlock to a slight extent, and the corner of the magnum 
 reaches the scaphoid. 
 
 In the PROBOSCIDEA the manus is very short and broad, with 
 large somewhat cubical carpals which articulate by very flat 
 surfaces and do not interlock at all. .All five digits are present, 
 and none of them are much reduced in size. The manus in 
 Proboscidea and in Coryphodon is subplantigrade. 
 
 In the Tillodontia the manus is plantigrade and has pointed 
 ungual phalanges, in this respect approaching the Carnivora. 
 It differs however from that of all living Carnivora in having 
 the scaphoid and lunar distinct. 
 
 In RODENTIA the manus nearly always has five digits with 
 the normal number of phalanges : the pollex may however be 
 very small as in the Rabbit, or absent as sometimes in the 
 Capybara. The scaphoid and lunar are generally united, and 
 a centrale may be present or absent. In Pedetes coffer the 
 radial sesamoid is double and the distal bone bears a nail-like 
 horny covering. In Bathyergus the pisiform is double. It is 
 upon these facts that the contention for the former existence 
 of prehallux and post-minimus digits has partly been based. 
 
 In living CARNIVORA the scaphoid, lunar and centrale are 
 always united, forming a single bone. All five digits are 
 present, but as a rule in Carnivora vera the pollex is small, and in 
 Hyaena is represented only by a small metacarpal. Sometimes, 
 as in Cats and Dogs, the manus is digitigrade, sometimes, as in 
 Bears, plantigrade. The ungual phalanges are large and point- 
 ed, and in forms like the Cats, whose claws are retractile, they 
 can be folded back into a deep hollow on the ulnar side of the 
 middle phalanx ; a small radial sesamoid is often present. 
 
 In Pinniped ia the manus is large and flat and the digits 
 are terminated by ungual phalanges which are blunt (sea lions 
 and walrus), or slightly curved and pointed (seals). The pollex 
 is nearly or quite as long as the second digit, and as a rule 
 the digits then successively diminish in size. 
 
512 THE VERTEBRATE SKELETON. 
 
 The Creodonta differ from living Carnivora in the fact that 
 the scaphoid and lunar are usually separate. 
 
 In INSECTIVORA the scaphoid and lunar are sometimes 
 united, sometimes separate, and a separate centrale is usually 
 present. There are generally five digits, but sometimes the 
 pollex is absent. In the Mole the manus is greatly developed 
 and considerably modified. It is very wide, its breadth being 
 increased by the great development of the radial sesamoid 
 which is very large and sickle-shaped. The ungual phalanges 
 are also large and are cleft at their extremities. 
 
 In the CHIROPTERA the manus is greatly modified for the 
 purpose of flight. The pollex is short and is armed with a 
 rather large curved claw, the other digits are enormously 
 elongated, the elongation in the case of the Insectivorous bats 
 being mainly due to the metacarpals, and in the Frugivorous 
 bats to the phalanges. In the Frugivorous bats the second 
 digit is clawed as well as the pollex, in other bats this claw is 
 always absent, and so is often the ungual phalanx, the middle 
 phalanx then tapering gradually to its termination. 
 
 In PRIMATES as a rule the manus is moderately short and 
 wide. The carpus has the scaphoid and lunar distinct, and 
 generally also the centrale : sometimes however, as in Man, 
 the Gorilla, Chimpanzee, and some Lemurs, the centrale has 
 apparently fused with the scaphoid. There are almost always 
 five well-developed digits, but in the genera Colobus and A teles 
 the pollex is vestigial. 
 
 The magnum in man is the largest bone of the carpus. The 
 pisiform also is well developed, but there is no radial sesamoid. 
 In Man, the Gorilla, Chimpanzee, and Orang, the carpus arti- 
 culates only with the radius, in most Primates it articulates 
 also with the ulna. The third digit of the Aye- Aye (Chiromys) 
 is remarkable for its extreme slenderness. 
 
 THE PELVIC GIRDLE. 
 
 The pelvic girdle in all mammals except the Sirenia and 
 
THE SKELETON IN MAMMALIA. PELVIC GIRDLE. 513 
 
 Cetacea consists of two halves, usually united with one another 
 at the symphysis in the ID id-ventral line, and connected near 
 their upper ends, with the sacral vertebrae. Each half forms 
 one of the innominate bones, and includes at least three separate 
 elements, a dorsal bone, the ilium, and two ventral bones, the 
 ischium and pubis. Very often a fourth pelvic element, the 
 acetabular or cotyloid bone, occurs. 
 
 In the MONOTREMATA the pelvis is short and broad, and the 
 pubes and ischia meet in a long symphysis. The acetabulum 
 is perforated in Echidna as in birds, but not in Ornithorhynchus. 
 A pair of elongated slender bones project forwards from the 
 edge of the pubes near the symphysis ; these are sesamoid bones 
 formed by ossifications in the tendons of the external oblique 
 abdominal muscles, and are generally called marsupial bones. 
 
 In the MARSUPIALIA the ilia are generally very simple, 
 straight, and narrow, while the pubes and ischia are well de- 
 veloped and meet in a long symphysis. Marsupial bones are 
 nearly always prominent, but are not developed in Thylacinus 
 or Notoryctes. The ischium often has a well-marked tuberosity 
 and in Kangaroos the pubis bears a prominent pectineal 
 process on its anterior border close to the acetabulum. The 
 pelvis in Notoryctes differs much from that in all other Marsu- 
 pials, the ilium and ischium being ankylosed with six vertebrae 
 in a manner comparable to that of many Edentates. 
 
 In the EDENTATA the pelvis is generally well developed, but 
 the symphysis is very short. In the Sloths the pelvis is rather 
 weak and slender, the obturator foramina are very large and 
 the ischia do not meet in a symphysis. In the Megatheriidae 
 the pelvis is exceedingly wide and massive, and is firmly 
 ankylosed with a number of vertebrae. In the Armadillos, 
 Glyptodonts, Anteaters, and Pangolins it is much developed 
 and firmly united to the vertebral column by both the ilia and 
 the ischia. In Orycteropus however the ischium does not 
 become united to the vertebral column, and the pubis generally 
 has a strongly developed pectineal process. 
 
 a. 33 
 
514 THE VERTEBRATE SKELETON. 
 
 In the SIRENIA the pelvis is quite vestigial. In the Dugong 
 it consists on each side of two slender bones, one of which 
 represents the ilium and the other the ischium and pubis ; the 
 two bones are placed end to end and are commonly fused 
 together. The ilium is attached by ligament to the transverse 
 process of one of the vertebrae. In the Manatee each half 
 of the pelvis is represented by a triangular bone connected by 
 ligaments with its fellow and with the vertebral column. In 
 neither Manatee nor Dugong is there any trace of an aceta- 
 bulum but one can be made out in Halitherium. 
 
 In the CETACBA the pelvis is even more vestigial than in 
 the Sirenia, consisting simply of a pair of small straight bones 
 which probably represent the ischia, and lie parallel to and 
 below the vertebral column at the point where the develop- 
 ment of chevron bones commences. 
 
 In UNGULATA VERA the pelvis is generally rather long and 
 narrow. The ilium is flattened and expanded in front (fig. 
 103, 8), but becomes much narrower and more cylindrical 
 before reaching the acetabulum. Both pubis and ischium 
 contribute to the symphysis which is often very long. The 
 ischia are large and have prominent tuberosities, especially in 
 Artiodactyles. In most Ruminantia there is a deep depression, 
 the supra-acetabular fossa above the acetabulum, but this is 
 not found in the Suina or Tylopoda. 
 
 SUBUNGULATA. In Procavia the pelvis is long and narrow, 
 and bears resemblance to that in Artiodactyles. 
 
 The Proboscidea have a very large pelvis set nearly at 
 right angles to the vertebral column ; the ilium is very wide, 
 having expanded iliac 1 and gluteaP surfaces, and a narrow 
 sacral 1 surface. The pubes and ischia are rather small, but 
 both meet their fellows in the symphysis. Uintatherium (sub- 
 order Amblypoda) also has a large and vertically placed pelvis 
 (fig. 108) with a much expanded ilium. The pelvis however 
 
 1 See p. 409. 
 
THE SKELETON IN MAMMALIA. PELVIC GIRDLE. 515 
 
 differs from that of the Proboscidea in the fact that the ischia 
 do not meet in a ventral symphysis. 
 
 In many RODENTIA the ilia have their gluteal, iliac, and 
 sacral surfaces of nearly equal extent ; in the Hares, however, 
 the gluteal and iliac surfaces are confluent. The pubes and 
 ischia are always well developed and sometimes, as in the 
 Hares, the acetabular bone also. In these animals the pubis 
 does riot take part in the formation of the acetabulum, and 
 the ischium bears on its outer side a well-marked ischial 
 tuberosity. 
 
 In the CARNIVORA the pelvis is long and narrow. The 
 iliac surfaces (fig. 78, A, 5) are very small and the sacral large ; 
 the crest or supra-iliac border is formed by the union of the 
 sacral and gluteal surfaces. The symphysis is long and includes 
 part of both pubis and ischium. The ischial tuberosity (fig. 
 78, A, 10) is often well marked, and sometimes as in Viverra 
 the acetabular bone is distinct. In the Pinnipedia the pelvic 
 symphysis is little developed, or sometimes not developed at 
 all, and the obturator foramina are remarkably large. 
 
 In some INSECTIVORA such as Galeopithecus, there is a long 
 pelvic symphysis, in others such as Erinaceus and Centetes, it is 
 very short, in others again such as Talpa and Sorex, there is no 
 pelvic symphysis. The acetabular bone is exceptionally large 
 in Talpa and Sorex. 
 
 In CHIROPTERA. the pelvis is small and narrow, and in the 
 great majority of cases the two halves do not meet in a ventral 
 symphysis. The pubis has a strongly developed pectineal 
 process, which occasionally unites with a process from the 
 ilium enclosing a large pre-acetabular foramen. 
 
 PRIMATES. In Man and the Anthropoid Apes the pelvis is 
 very large and wide, and the ilium has much expanded iliac 
 and gluteal surfaces. The symphysis is rather short and formed 
 by the pubis alone. The acetabulum is deep and the obturator 
 foramen large, and there is frequently a well-marked ischial 
 tuberosity. In the lower Anthropoidea the ilium is long and 
 
 332 
 
516 
 
 THE VERTEBRATE SKELETON. 
 
 1 
 
 FIG. 108. LEFT ANTEBIOB AND POSTEBIOB LIMB AND LIMB GIBDLE OF 
 ' Uintatherium mirabile. The anterior limb is to the left, the posterior 
 to the right x T V (From casts, Brit. Mus.) 
 
 1. ilium. 4 - Patella. 
 
 2. head of femur. 5. fibula. 
 
 3. great trochanter. 6. tibia. 
 
THE SKELETON IN MAMMALIA. THIGH AND SHIN. 517 
 
 7. second digit of pes. 14. radius. 
 
 8. ungual phalanx of fifth digit 15. ulna. 
 
 of pes. 17. unciform. 
 
 9. calcaneum. 18. cuneiform. 
 
 10. postscapular fossa. 20. lunar. 
 
 11. prescapular fossa. 21. first metacarpal. 
 
 12. coracoid process. 22. fifth metacarpal. 
 
 13. humerus. 
 
 narrow and has a small iliac surface. The ischial tuberosities 
 are large in the old world monkeys. 
 
 THE THIGH AND SHIN. 
 
 In the MONOTREMATA the femur is short, rather narrow in 
 the middle, and expanded at each end. The great and lesser 
 trochanters are large and about equally developed, but there is 
 no third trochanter. The fibula is very large and is expanded 
 at its proximal end, forming a flattened plate much resembling 
 an olecranon. The patella is well developed. 
 
 In the MARSUPIALIA there is no third trochanter to the 
 femur, the fibula is well developed but not the patella as a 
 general rule. Notoryctes has a femur with a prominent ridge 
 extending some little way down the shaft from the great tro- 
 chanter ; the tibia has a remarkably developed crest, and the 
 fibula has its proximal end much expanded and perforated; 
 there is an irregularly shaped patella closely connected with 
 the proximal end of the tibia. 
 
 EDENTATA. In the Sloths the leg bones are all long and 
 slender. The femur has no third trochanter, and the fibula is 
 complete and nearly equal in size to the tibia. In the Mega- 
 theriidae the leg bones are extraordinarily massive, the cir- 
 cumference of the shaft of the femur in Megatherium equalling 
 or exceeding the length of the bone. There is no third tro- 
 chanter in Megatherium. In most of the remaining Edentata 
 the leg bones are strongly developed. The femur in the Arma- 
 dillos and Aard Yarks has a strong third trochanter, and the 
 
518 
 
 THE VERTEBRATE SKELETON. 
 
 tibia and fibula are both large and are commonly ankylosed 
 together at either end. The limb bones are very massive also 
 in the Glyptodonts. 
 
 SIRENIA. In no living Sirenian is there any trace of a 
 hind limb, but in Halitherium a vestigial femur is found, 
 which articulates with the pelvis by a definite acetabulum. 
 
 ...4 
 
 FIG. 109. LEFT FEMUR OF AN Ox (Bos taurus) (to the left) ANI> OF 
 A SUMATEAN RHINOCEROS (E. sumatrensis) (to the right), x ^ . 
 (Camb. Mus.) 
 
 1. head. 
 
 2. great trochanter. 
 
 3. lesser trochanter. 
 
 third trochanter. 
 
 shaft. 
 
 condyles. 
 
 In the Mystacoceti among the CETACEA small nodules of 
 bone or cartilage occur connected with the vestigial pelvis, 
 and may represent the femur and tibia. No trace of the 
 skeleton of the hind limb is known in the Odontoceti. 
 
THE SKELETON IN MAMMALIA. THIGH AND SHIN. 519 
 
 In the UNGULATA VERA the femur is noticeable for the size 
 of the great trochanter (fig. 109, 2) ; there is no definitely 
 constricted neck separating the head from the rest of the 
 bone, and the lesser trochanter (fig. 109, 3) is not very promi- 
 nent. All Perissodactyles except the Chalicotheriidae show 
 a strongly marked third trochanter, but this is absent in all 
 known Artiodactyles. The development of the fibula in general 
 corresponds to that of the ulna. In Rhinoceros, Jlfacrauchenia, 
 Tapirus and the Suina it is distinct and fairly well developed ; 
 in the Tragulina on the other hand it is vestigial, being reduced 
 to the proximal end only. In the Rumiriantia and Tylopoda 
 also, it is much reduced forming merely a small bone attached 
 to the distal end of the tibia, sometimes as in the Red deer 
 a slender vestige of the proximal end also is preserved quite 
 detached from the distal portion ; in the Horse this proximal 
 portion is all that there is found of the fibula. The progressive 
 diminution of the fibula can be well seen in the series of forms 
 that are regarded as the ancestors of the Horse. The patella 
 of the Ungulata vera is well ossified, but fabellae 1 are not 
 usually found. 
 
 SUBUNGULATA. Of the Toxodontia, Toxodon has no third 
 trochanter while Typotherium and Astrapotherium have one. 
 In the Condylarthra the femur has well-marked lesser and 
 third trochanters, and the fibula and patella are well developed. 
 In the Hyracoidea there is a slight ridge on the femur in the 
 place of the third trochanter, the fibula is complete, but is 
 generally fused to the tibia at its proximal end. 
 
 Of the Amblypoda, Coryphodon has a third trochanter, but 
 Uintatherium has none ; in this respect, in the vertical position 
 and general appearance (fig. 108) of the limb, and in the 
 articulation of the fibula with the calcaneum, the leg of 
 Uintatherium closely approaches that of the Proboscidea. 
 
 In the Proboscidea the femur is very long and straight, 
 
 1 See p. 412. 
 
520 THE VERTEBRATE SKELETON. 
 
 the development of trochanters is slight, and the fibula though 
 slender is complete and articulates with the calcaneum. 
 
 A third trochanter is found in the Tillodontia. 
 
 In RODENTIA the femur is variable, the great trochanter is 
 generally large and so sometimes is the third as in the Hares. 
 In most Rodents as in the Beaver the fibula is distinct, some- 
 times as in the Hares it is united distally with the tibia. The 
 patella is well developed, and so too are the fabellae as a 
 general rule. 
 
 GARNI VORA. In the Garni vora vera the femur (fig. 79, A) 
 is generally rather straight and slender, and has a very distinct 
 head. The fibula (fig. 79, C) is always distinct and there is 
 generally a considerable interval between it and the tibia. 
 Fabellae (fig. 79, 7) are commonly present. 
 
 In the Pinnipedia the femur is short, broad and flattened, 
 having a prominent great trochanter. The fibula is nearly as 
 large as the tibia, and the two bones are generally ankylosed 
 together at their proximal ends. 
 
 The Creodonta differ from all living Carnivores in having 
 a femur with a third trochanter. 
 
 In the INSECTIVORA a third trochanter is sometimes 
 developed. The fibula is sometimes distinct, sometimes fused 
 distally with the tibia, thus differing from that of a Carnivore. 
 
 In CHIROPTERA the femur is straight, slender and rather 
 short, with a small but well-developed head. The fibula may 
 be well developed or quite vestigial or absent. Owing to the 
 connection of the hind limb with the wing membrane the knee 
 joint is directed backwards. 
 
 In PRIMATES the femur is rather long and slender, having 
 a nearly spherical head and large great trochanter. The tibia 
 and fibula are always distinct and well developed. Fabellae 
 are not found in the highest forms but are generally present 
 in the others. 
 
THE SKELETON IN MAMMALIA. THE PES. 521 
 
 THE PES. 
 
 The skeleton of the pes is in most respects a counterpart 
 of that of the manus. Just as in the manus if one digit is 
 absent it is the pollex, so in the pes it is the hallux. But 
 while in the manus the third digit is always well developed, 
 however much the limb may be modified, in the pes any of the 
 digits may be lost. In all mammals the tibiale and inter- 
 medium fuse to form the astragalus, and the fourth and fifth 
 tarsalia to form the cuboid. Sesamoid bones are considerably 
 developed. In almost every case the phalanges and first meta- 
 tarsal have epiphyses only on their proximal ends, while the 
 remaining four metatarsals have epiphyses only on their distal 
 ends. 
 
 In the MONOTREMATA all the usual tarsal bones are distinct, 
 and the five digits have the normal number of phalanges. 
 Several sesamoid bones are developed, the most important one, 
 found only in the male, being articulated to the tibia and bearing 
 the curious horny spur. The ungual phalanges of the pes like 
 those of the manus, are deeply cleft at their extremities. In 
 the Echidnidae the pes is turned outwards and backwards in 
 walking. 
 
 In the MARSUPIALIA the pes is subject to great modifica- 
 tions, but in every case the seven usual tarsal bones are dis- 
 tinct. In the Didelphyidae the foot is broad, all five digits are 
 well developed, and the hallux is opposable to the others. 
 In the Dasyuridae the foot is narrow, and the hallux may be 
 very small, or as in Thylacinus completely absent. In Noto- 
 ryctes the pes is much less abnormal than the manus, and 
 all five digits have the usual number of phalanges. The fifth 
 metatarsal has a curious projecting process, and there is a 
 large sesamoid above the hallux. In the Wombats (Phascolo- 
 myidae) the foot is short and broad, the digits are all distinct, 
 arid the hallux is divaricated from the others. 
 
 In the remaining marsupials the second and third meta- 
 carpals and digits are very slender, and are enclosed within a 
 
522 THE VERTEBRATE SKELETON. 
 
 common integument. This condition is known as syndactylism, 
 and its effect is to produce the appearance of one toe with two 
 claws. In the Kangaroos (Macropodidae) the pes is very long 
 and narrow, owing to the elongation of the metacarpals. The 
 fourth digit is greatly developed, the fifth moderately so, 
 while the hallux is absent, and the second and third digits 
 are very small. The Peramelidae have the foot constructed 
 on the same plan as in the Kangaroos, and in one genus 
 Choeropus the same type of foot is carried to a greater 
 extreme than even in the Kangaroos. Thus the fourth digit 
 is enormously developed, the second and third are small, and 
 the fifth smaller still, while the hallux is absent. In the 
 Phalangers and Koalas though the second and third toes are 
 very slender, the hallux is well developed and opposable. 
 
 EDENTATA. In the Sloths the pes much resembles the 
 manus, being long and narrow, but in both genera the second, 
 third and fourth digits are well developed. Most of the other 
 Edentates have a but little modified pes with the normal 
 number of tarsal bones and the complete series of digits. In 
 Cycloturus however the hallux is vestigial and it is absent 
 in Glyptodonts. Megatherium has a greatly modified pes, the 
 hallux is absent, and the second digit vestigial, while the 
 third is very large, having an enormous ungual phalanx. The 
 calcaneum too is abnormally large. 
 
 No trace of the pes occurs in either SIRENIA or CETACEA. 
 
 In the UNGULATA the pes like the manus is subject to 
 much variation and is of great morphological importance. 
 
 In the UNGULATA VERA the pes is never plantigrade and 
 never has more than four digits, the hallux being absent. 
 The cuboid always articulates with the astragalus, and the 
 tarsal bones strongly interlock. As was the case also with the 
 manus, the pes is formed on two well-marked types character- 
 istic respectively of the Artiodactyla and Perissodactyla. 
 
 ARTIODACTYLA. Just as in the manus, the third and 
 fourth digits are well and subequally developed ; their ungual 
 
THE SKELETON IN MAMMALIA. THE PES. 523 
 
 phalanges have the contiguous sides flat, and the axis of the limb 
 passes between them, and between the cuboid and navicular. 
 The astragalus has both the proximal and distal surfaces 
 pulley-like, and articulates with the navicular and cuboid by 
 two facets of nearly equal size. The calcaneum articulates 
 with the lower end of the fibula if that bone is fully developed. 
 
 In the Suina four toes are developed, and though in the 
 Peccaries the third and fourth metatarsals are united, they 
 are all distinct in most members of the group, as are all 
 the tarsal bones. In the Hippopotami the four digits are of 
 approximately equal size, and the middle ones do not have 
 the contiguous faces of their ungual phalanges flattened. 
 
 In the Tragulina the cuboid, navicular, and two outer cunei- 
 forms are united forming a single bone ; all four metatarsals 
 are complete and the two middle ones are united. In the 
 Tylopoda and Anoplotherium commune only the third and 
 fourth digits are developed, their metatarsals are free distally, 
 but are elsewhere united. In the Ruminantia the cuboid and 
 navicular are always united and so are the second and third 
 cuneiforms, while in Cervulus all four bones are united 
 together. The third and fourth metatarsals in Ruminants 
 are always united in the same way as are the third and fourth 
 metacarpals, while the second and fifth are always wanting. 
 In Deer the second and fifth digits are usually each repre- 
 sented by three small phalanges, but in the Giraffe and most 
 Bovidae the bones of these digits are wanting. 
 
 In the PERISSODACTYLA the pes like the manus is symme- 
 trical about a line drawn through the third digit; this line 
 when continued passes through the external cuneiform, navi- 
 cular and astragalus. The astragalus has its distal portion 
 abruptly truncated, and the facet by which it articulates with 
 the cuboid is much smaller than that by which it articulates 
 with the navicular. The calcaneum does not articulate with 
 the fibula. The tarsus in Macrauckenia like the carpus 
 differs from that of other Perissodactyles and resembles that 
 
524 
 
 THE VERTEBRATE SKELETON. 
 ,1 
 
 FIG. 110. ^4. LEFT PES OF A TAPIR (Tapirus americanus). x. 
 
 .B. RIGHT PES OF A RHINOCEROS (E. sumatrensis). xf. 
 
 C. (CAST OF) BIGHT PES OF Hipparion gracile, xf. 
 
 D. RIGHT PES OF A HOUSE (Equus caballus). x^-. (All Camb. Mus.) 
 
 1. calcaneum. 5. external cuneiform. 
 
 2. astragalus. 6. middle cuneiform. 
 
 3. iiavicular. 7. internal cuneiform. 
 
 4. cuboid. 
 
THE SKELETON IN MAMMALIA. THE PES. 525 
 
 of Subungulates in having the bones arranged in lines with 
 little or no interlocking. The calcaneum resembles that of 
 Artiodactyles in having a small facet for articulation with the 
 fibula. Tapirus (fig. 110, A), Rhinoceros (fig. 110, B) and 
 Titanotherium have a short and broad foot with the usual 
 tarsal bones and three well-developed digits, a number never- 
 exceeded by any Perissodactyle. From this tridactylate limb 
 a series of stages is exhibited by various extinct forms leading 
 gradually to the condition met with in the Horse (fig. 110, D) 
 in which the third toe is greatly developed, while the second 
 and fourth are reduced to slender metatarsals attached to the 
 proximal half of the third metatarsal. 
 
 In Chalicotherium and Agriochoerus the pes has the same 
 abnormal characters as the manus, the digits being clawed and 
 the ungual phalanges in Chalicotherium deeply cleft. 
 
 In the SUBUNGULATA the pes is sometimes plantigrade and 
 pentedactylate, the cuboid sometimes does not articulate with 
 the astragalus, and the tarsal bones sometimes do not inter- 
 lock. 
 
 In Typotherium (TOXODONTIA) the hallux is absent and the 
 other four digits are well developed ; in Toxodon and Nesodon 
 the pes is tridactylate. The tarsal bones have the regular Sub- 
 ungulate arrangement, the cuboid not articulating with the 
 astragalus. The calcaneum articulates with the fibula as in 
 Artiodactyles. The astragalus in most forms, but not in 
 Astrapotherium, resembles that of the Ungulata vera in having 
 a grooved proximal surface. 
 
 In Phenacodus (CONDYLARTHRA) the tarsus is very little 
 modified, five digits are present, the first and fifth being small 
 and not reaching the ground. 
 
 In Procavia only the three middle digits are present with 
 a vestige of the fifth metacarpal. 
 
 In the AMBLYPODA the pes (fig. 108) is very short and 
 broad, all five digits are functional, and at any rate in 
 Coryphodon plantigrade, the hallux being the smallest. The 
 
526 THE VERTEBRATE SKELETON. 
 
 astragalus is very flat, and the tarsals interlock to a slight 
 extent, the cuboid articulating with both calcaneum and 
 astragalus. 
 
 The pes in the PROBOSCIDEA much resembles that in the 
 Amblypoda, but differs in that the astragalus does not arti- 
 culate with the cuboid, the tarsals not interlocking at all. 
 
 In the RODENTIA the structure of the foot is very variable. 
 In Beavers the foot is very large, all five digits being well 
 developed ; the fifth metatarsal articulates with the outer side 
 of the fourth metatarsal, and not with the cuboid, and there 
 is a large sesamoid bone on the tibial side of the tarsus. In 
 the Rats, Porcupines and Squirrels, there are five digits, in the 
 Hares only four, and in the Capybara and some of its allies 
 only three. In the Jerboa (Dij)us) a curious condition of the 
 pes is met with, as it consists of three very long metatarsals 
 fused together and bearing three short toes, each formed of 
 three phalanges. Lophiomys differs from all other Rodents 
 in having the hallux opposable. 
 
 CARNIVORA. In the Carnivora vera the pes is regular and 
 shows little deviation from the normal condition. All the 
 usual tarsal bones are present, but sometimes as in the Dogs, 
 Cats, and Hyaenas, the hallux is vestigial. Sometimes as in 
 the Bears the pes is plantigrade, sometimes as in the Cats and 
 Dogs it is digitigrade. In this respect and in the character 
 of the ungual phalanges, the pes closely corresponds with 
 the manus. In the Sea Otter (Latax) the foot is large and 
 flattened and approaches in character that of the Pinni- 
 pedia. 
 
 In the Pinnipedia the pes differs much from that in the 
 Carnivora vera. In the Seals in which the foot cannot be 
 used for walking, and is habitually directed backwards, the 
 first and fifth digits are much longer and stouter than any 
 of the others. In the Sea Lions which can use the pes for 
 walking, the digits are all of nearly the same length, and 
 in the Walrus the fifth is somewhat the longest. 
 
THE SKELETON IN MAMMALIA. THE PES. 527 
 
 In the INSECTIVORA the pes is almost always normal, and 
 provided with five digits. 
 
 In the CHIROPTERA the pes is pentedactylate, and the digits 
 are terminated by long curved ungual phalanges. In some 
 genera the toes have only two phalanges. The calcaneum is 
 sometimes produced into a long slender process which helps 
 to support the membrane between the leg and the tail. 
 
 Among the PRIMATES Man has the simplest form of pes. 
 In Man all five digits are well developed, the hallux being 
 considerably the largest. Sesamoid bones occur only under 
 the metatarso-phalangeal joint of the hallux. 
 
 In the other Primates the internal cuneiform has a saddle- 
 shaped articulating surface for the hallux, which is obliquely 
 directed to the side of the foot and opposable to the other 
 digits. Two sesamoid bones are usually developed below 
 each metatarso-phalangeal joint, and one below the cuboid. 
 The second digit in Lemurs, and all except the hallux in 
 Ckiromys have pointed ungual phalanges ; in all other cases 
 the ungual phalanges are flat. In some of the Lemuroidea, 
 especially Tarsius, the tarsus is curiously modified by the 
 elongation of the calcaneum and navicular. 
 
LIST OF AUTHORS REFERRED TO. 
 
 Abbott, E. C., 112 
 
 Ameghino, F., 351, 424 
 
 Andrews, C. W., 299 
 
 Balfour, F. M., 16 
 
 Ballowitz, E., 424 
 
 Bardeleben, K., 504 
 
 Bateson, W., 50, 344 
 
 Baum, H., 374 
 
 Baur, G., 27, 189, 190, 344, 346 
 
 Beneden, P. J. van, 353 
 
 Benham, W. B., 51 
 
 Bettany, G. T., 16. 87, 154 
 
 Boulenger, G. A., 169 
 
 Brandt, J. F., 352 
 
 Bridge, T. W., 123 
 
 Briihl, C. B., 210 
 
 Burmeister, H., 351, 424, 
 
 Cope, E. D., 135, 199, 204, 351; 
 
 359, 361, 363, 368 
 Credner, H., 135 
 Dean, B., 63, 104 
 Dobson, G. E. , 369, 370 
 Earle, C., 432 
 Ecker, A., 151 
 Ellenberger, W., 374 
 Flower, W. H., 28, 42, 351, 420, 
 
 422, 434 
 Fritsch, A., 135 
 Fiirbringer, M., 295 
 Gadow, H., 40, 112, 190, 295, 343, 
 
 350 
 
 Gegenbaur, C., 127 
 Gervais, P. , 353 
 Giinther, A. C. L. G., 70, 104 
 Haslam, G., 151 
 Hasse, C., 112, 113 
 Haswell, W. A., 127 
 
 R. 
 
 Hertwig, 0., 169 
 
 Hoffmann, C. K., 190, 202, 210 
 
 Howes, G. B., 164, 451 
 
 Hubrecht, A. A. W., 104 
 
 Hulke, J. W., 192, 204 
 
 Hurst, C. H., 71, 297 
 
 Hutton, F. W., 299 
 
 Huxley, T. H., 11, 13, 133, 135, 191, 
 
 210, 295, 297, 334, 343, 351, 374, 
 
 437 
 
 Kirkaldy, J. W., 51 
 Klein, E., 11 
 Kolliker, A., 9 
 Ktikentbal, W., 349, 422 . 
 Lankester, E. Bay, 51 
 Leche, W., 344, 423 
 Lindsay, B., 336 
 
 Lydekker, E., 36, 42, 190, 195, 495 
 Macbride, E. W., 50 
 Marsh, 0. C., 204, 209, 299, 348, 
 
 361, 364, 365, 508 
 Marshall, A. M., 71, 151 
 Masterman, A. T., 51 
 Meyer, H. v., 135 
 Miall, L. C., 135, 243 
 Mivart, St G., 369 
 Morgan, C. Lloyd, 11 
 Newton, E. T., 283 
 Osborn, H. F., 348, 420, 429, 508 
 Owen, E., 191, 204, 210, 297, 348, 
 
 351, 420 
 
 Parker, T. J., 83, 96, 299 
 Parker, W. K., 16, 24, 53, 87, 154, 
 
 173, 200, 243, 465, 489 
 Pavlow, M., 358, 508 
 Pollard, H. B., 119 
 Poulton, E. B., 422 
 
 34 
 
530 LIST OF AUTHORS REFERRED TO. 
 
 Pycraft, W. P., 297 Thomas, 0., 349, 362, 370, 422, 
 
 Ridewood, W. G., 106, 164 424, 425 
 
 Rose, C., 422 Tomes, C. S., 420 
 
 Sagemehl, M., 104 Traquair, R. H., 55, 58 
 
 Schafer, E., 11 Vogt, C., 297 
 
 Scott, W. B., 368 Wiedersheim, R., 25, 134, 136 
 
 Seeley, H. G., 191, 212 Wincza, H., 358, 495 
 
 Selenka, E., 40, 295 Woodward, A. Smith, 34, 54, 58, 
 
 Shufeldt, R., 123 62, 127, 210 
 
 Smith, E. Noble, 11 Wortman, J. L., 508 
 
 Stirling, E. C., 423 Wray, R. S., 303 
 
 Swirski, G., 103 Zittel, K. A. v., 36, 205, 212 
 
 Taeker, J., 427 
 
INDEX. 
 
 Every reference is to the page : words in italics are names of genera or 
 species; figures in italics indicate that the reference relates to syste- 
 matic position ; figures in thick type refer to an illustration ; /. = and 
 in following page or pages; n. = note. 
 
 Aard Vark 44, 352; femur 517; 
 
 sacrum 452 ; teeth 425 ; see 
 
 Orycteropus 
 
 Aard wolf 48 ; see Proteles 
 Abdominal ribs, crocodile 260 ; 
 
 reptiles 286 
 
 Abdominal shield, turtle 215 
 Acanthias 32 ; calcification of ver- 
 tebrae 114 ; pectoral fins 130 
 Acanthodes 32, 64 
 Acanthodii 32 ; general characters 
 
 64 ; spines 106 
 Acanthomys 47 ; spines 417 
 Acanthopterygii 34 
 Accipitres 41 
 Acetabular bone 25, 513 ; dog 409 f.; 
 
 frog 165 
 Acetabulum 25 ; crocodile 266 ; 
 
 dog 409; duck 324; frog 165; 
 
 newt 149 ; turtle 235 
 Acipenser 32, 117 ; exoskeleton 67 ; 
 
 distribution 66 ; pectoral fins 
 
 131 ; plates 104 ; skull 121, 122 ; 
 
 spinal column 112 
 Acipenseridae 32 
 Acrodont, defined 199; teeth of 
 
 reptiles 273 
 Acrodus 32 ; teeth 109 
 Acromion, dog 405 
 Actinotrocha 30 ; organ regarded as 
 
 double notochord 51 
 
 Ad-digital quill, duck 303 
 Adjutant 41 ; clavicles 338 
 ^Egithognathous 335 
 ^Eluroidea 48, 369 ; teeth 437 
 ^Epyornis 40 ; tibio-tarsus 341 
 ^Epyornithes 40, 299 
 Aftershaft 328 
 Agama 38 ; teeth 273 
 Agamidae 38 ; premaxillae 284 
 Aglossa 36 
 
 Agouti 48 ; see Dasyprocta 
 Agriochoeridae 45 
 Agriochoerus 45 ; pes 525 
 Ala spuria, duck 304 
 Alcidae 42 ; see Auks 
 Alisphenoid 19 ; crocodile 247 ; duck 
 
 317 ; dog 386 
 Alligator 39, 210, 212 ; hyoid 285 ; 
 
 limbs 264 ; pectoral girdle 262 ; 
 
 pelvis and sacrum 267 ; scutes 
 
 271 ; skull 245, 248, 253 
 Alligatoridae 39 
 Alytes 36; fronto-parietal fontanelle 
 
 179 ; vertebrae 172 
 Amblypoda 47 ; general characters 
 
 363 ; manus 510 ; pes 525 ; skull 
 
 473 ; teeth 433 ; thigh and shin 
 
 519 
 
 Amblystoma 35; skull 175 
 American monkeys 373; see Ce- 
 
 bidae 
 
 342 
 
532 
 
 INDEX. 
 
 American vultures 41 ; vomers 335 
 Amia 33 ; distribution 66 ; exo- 
 
 skeleton 67; pectoral fin 131; 
 
 scales 105; skull 123; tail 115, 
 
 117 ; vertebrae 114 
 Amiidae 33 
 Ammocoetes 31, 55 
 Amphibia 35 ; anterior limb 185 ; 
 
 exoskeleton 168 ; general charac- 
 ters 133 ; hyoid apparatus 180 ; 
 
 pectoral girdle 184 ; pelvic girdle 
 
 187 ; posterior limb 188 ; ribs 
 
 182; skull 173; sternum 182; 
 
 teeth 169 ; vertebral column 170 
 Amphicoelous, defined 14 
 Amphioxus 30; skeleton 51 f. ; spinal 
 
 column 112 
 Amphisbaena 38, 272 ; loss of limbs 
 
 289 
 Amphisbaenidae 38, 200; pectoral 
 
 girdle 288; skull 277; vertebral 
 
 column 275 
 Amphitheriidae 43 
 Amphiuma 35, 135 ; manus 187 ; pes 
 
 188 ; skull 174 
 Amphiumidae 35 
 Anacanthini 33 
 Anal shield, turtle 215 
 Anas 41 ; A. boschas, see Duck 
 Ankylosis, defined 12 
 Angel fish 32 
 
 Angler, attachment of teeth 107 
 Anguidae 38 
 Anguilla 33; see Eel 
 Anguis 38 ; loss of limbs 289 ; scutes 
 
 271 
 Angular 22 ; cod 100 ; crocodile 
 
 258; duck 319; salmon 94; turtle 
 
 231 
 
 Angulo-splenial, frog 161 
 Ankle joint, duck 327 ; reptiles 294 
 Anomodontia 36 
 Anoplotheriidae 45 
 Anoplotherium 45; manus 506; pes 
 
 523; tail 454; teeth 428 
 Anser 41 
 Anseres 41; aftershaft 329; claws 
 
 330 
 
 Anseriformes 41 
 Anteaters 352; absence of teeth 
 
 424 ; manus 505 ; pectoral girdle 
 
 495; pelvis 513; skull 458; tho- 
 
 raco -lumbar vertebrae 447 ; Spiny 
 
 43 ; Great and Two -toed 
 44 
 
 Antelope 359; manus 507; Four- 
 horned A. 46 
 
 Anterior limb 26 ; Amphibia 185 ; 
 birds, 338; crocodile 263; dog 
 405 ; duck 322 ; frog 164 ; newt 
 147; reptiles 290; turtle 232 
 
 Anthropoid apes 373; arm-bones 
 503; pelvis 515 
 
 Anthropoidea 49 ; general charac- 
 ters 372 ; sacrum 452 ; skull 482 ; 
 teeth 441 
 
 Anthropopithecus 49 ; ribs 493 
 
 Antiarcha 31 ; general characters 55 
 
 Antibrachium, see fore-arm 
 
 Antilocapra 46 ; horns 417 
 
 Antilocapridae 46 
 
 Antitrochanter, duck 325 
 
 Antlers 8, 358 ; Cervidae 469 
 
 Antorbital process 18 
 
 Anura 36 ; general characters 136 ; 
 hyoid apparatus 180 ; pelvis 187 ; 
 posterior limb 188; skull 179: 
 sternum 182; vertebrae 172 
 
 Apatornis 40 ; vertebrae 332 
 
 Apteria 328 
 
 Apteryges 40 
 
 Apteryx 40, 299 ; aftershaft 329 ; 
 anterior nares 333 ; claws 330 ; 
 foot 342 ; manus 338 ; pectineal 
 process 341 ; pectoral girdle 338 ; 
 pneumaticity of skeleton 331 ; A. 
 owenl, pelvic girdle and sacrum 
 34O 
 
 Aqueductus vestibuli, dogfish 74 
 
 Arcade: infratemporal , crocodile 
 255; Sphcnodon 283; inner , 
 duck 318 ; outer , duck 318 ; 
 supratemporal , crocodile 257 ; 
 reptiles 281 
 
 Archaeoceti 44 ; general characters 
 356 ; skull 461 ; teeth 426 
 
 Archaeopteryx 40, 297 ; claws 330 ; 
 fibula 341 ; mandible 335 ; meta- 
 tarsals 342 ; pelvis 341 ; ribs 
 336; sacrum 333; skull 333; 
 tail 333 ; teeth 330 ; wing 338 
 
 Archaeornitb.es 40 ; characters 297 
 
 Archegosaurus 35, 136; palatines 
 177 
 
 Archipterygium, Ceratodus 127 ; 
 Ichthyotomi 62 
 
INDEX. 
 
 533 
 
 Arcifera 36, 185 
 
 Arctoidea 48, 369 ; teeth 438 
 
 A rdea 41 ; see Heron 
 
 Ardeae 41 
 
 Arm, see fore-arm and upper arm 
 
 Armadillo 44, 352 ; cervical verte- 
 brae 443 ; femur 517 ; humerus 
 501 ; lumbar vertebrae 447 ; ma- 
 nus 505 , pectoral girdle 495 ; 
 pelvis 513 ; ribs 491 ; sacrum 
 452 ; scales 417 ; scutes 419 ; 
 skull 459 ; teeth 424 
 
 Armour plates 8 
 
 Arthrodira 34 ; characters 70 
 
 Articular 22 ; cod 100 ; crocodile 
 258; duck 319; newt 144; sal- 
 mon 94 ; turtle 231 
 
 Avtiodactyla 45 ; characters 358 ; 
 manus 506 ; odontoid process 
 445 ; pes 522 ; ribs 491 ; skull 
 465 ; teeth 427 ; thoraco-lumbar 
 vertebrae 448 
 
 Asses 360 
 
 Asterolepis 31, 55 
 
 Asterospondyli 114 
 
 Astragalus 27 ; crocodile 268 ; dog 
 414 ; mammals 521 
 
 Astrapotheriidae 46 
 
 Astrapotherium 46, 361 ; dental 
 formula 432 : femur 519 ; pes 
 525 
 
 Ateles 49 ; pollex 512 ; tail 454 
 
 Atlantosauridae 38 
 
 Atlas 15; crocodile 240 ; dog 379, 
 380 ; duck 309 ; ox 445 ; turtle 
 219 
 
 Attachment of teeth 4 ; in fish 107 
 
 Auchenia 45 ; see Llama 
 
 Auditory aperture or meatus : ex- 
 ternal , crocodile 250 ; dog 402 ; 
 turtle 228 ; internal , crocodile 
 246, 251 ; dog 392 ; turtle 228 
 
 Auditory capsule 20 ; cod 96 ; cro- 
 codile 250 ; dog 390 ; dogfish 74; 
 frog 156 ; newt 143 ; turtle 227 
 
 Auditory ossicles, crocodile 251 ; 
 dog 393; duck 320; mammals 
 485 f . ; turtle 228 
 
 Auks 42 ; thoracic vertebrae 332 
 
 Autostylic 61, 119 
 
 Aves 40 ; characters 295 ; see Birds 
 
 Axial skeletal rods 50 
 
 Axial skeleton, crocodile 239 ; cod 
 
 83 ; dog 377 ; dogfish 72 ; duck 
 
 307 ; frog 152 ; newt 138 ; turtle 
 
 218 
 Axis vertebra, crocodile 241 ; dog 
 
 380 ; duck 309 ; turtle 220 
 Axolotl 35 ', see Siredon 
 Aye Aye 49 ; see Chiromys 
 
 Babirussa 45 ; dental formula 428 
 
 Baboon 49 ; see Cynocephalus 
 
 Balanoglossus 30, 50 
 
 Balaena 44, 357; scapula 495; 
 B. mysticetus baleen 419 
 
 Balaenidae 44 
 
 Balaenoidea 44 ; general characters 
 356 
 
 Balaenoptera 44, 357 ; manus 506 ; 
 thoracic vertebrae 448; scapula 
 495 ; B. musculus, cervical verte- 
 brae 444 
 
 Baleen 3, 418 
 
 Balistes 33 ; teeth 111 
 
 Balistidae 33 
 
 Ball and socket joints 13 
 
 Bandicoot 43 
 
 Barb 302 
 
 Barbule 303 
 
 Barramunda 34 ; see Ceratodus 
 
 Basalia, dogfish 79 
 
 Basi-branchial, dogfish 78 ; cod 101 ; 
 duck 320 ; newt 145 ; salmon 95 
 
 Basi-branchiostegal, cod 101; sal- 
 mon 95 
 
 Basicranial axis 19 ; dog 384 
 
 Basidorsalia, dogfish 72 
 
 Basi-hyal, dogfish 78 ; dog 399 ; 
 duck 320 
 
 Basilar plate 17 
 
 Basilingual plate, Anura 180 ; cro- 
 codile 259 ; frog 161 ; turtle 231 
 
 Basi-occipital 19 ; crocodile 246 ; 
 cod 97; dog 386; duck 315; 
 salmon 89 ; turtle 224 
 
 Basipterygium, cod 103 ; dogfish 82 
 
 Basisphenoid 19 ; crocodile 247 ; 
 dog 386 ; salmon 91 ; turtle 225 
 
 Bastard wing, duck 304 
 
 Bathyerginae, palate 366 
 
 Bathyergus 47 ; auditory ossicles 
 488 ; manus 511 
 
 Batoidei 32, 64 
 
 Batraclioseps 35 ; teeth 169 
 
534 
 
 INDEX. 
 
 Bats, claws 418 ; Horseshoe bats 
 49 ; see Chiroptera 
 
 Bdellostoma 31, 55 ; teeth 57 
 
 Beak 3 ; birds 329 ; duck 302 ; 
 Siren 168 ; tadpoles of Anura 
 168 ; turtle 215 
 
 Bears 48, 369 ; maims 511 ; pes 
 526 ; sacral vertebrae 452 ; skull 
 479 ; Isabelline mandible 438 
 
 Beaver 47 ; fibula 520 ; humerus 
 502 ; pes 526 ; sacrum 452 ; tail 
 454 
 
 Belodon 39, 211; frontals 277; 
 palate 281 ; vertebrae 275 
 
 Bichir 33 ; see Polypterus 
 
 Bicipital groove, dog 405 
 
 Bilophodont, defined 345 ; teeth of 
 Tapiridae 429 
 
 Bipes 38 ; limbs 289 
 
 Birds, anterior limb 338 ; endo- 
 skeleton 331f.; exoskeleton 328f.; 
 general characters 295 ; hyoid 
 336 ; pectoral girdle 336 ; pelvic 
 girdle 339 ; posterior limb 341 ; 
 ribs 336 ; skull 333 ; sternum 336 ; 
 teeth 330 ; vertebral column 332 
 
 Bison 46 ; occipital crest 468 
 
 Blind snake 38 ; see Typhlops 
 
 Blind worm 38 ; see Anguis 
 
 Boidae 38 
 
 Bombinator 36 ; vertebrae 172 
 
 Bone, development of 10 f. 
 
 Bone cells 10 
 
 Bony Ganoids, fins 105 ; pelvic fin 
 132 ; ribs 126 ; skull 123 ; verte- 
 bral column 114 ; see Holostei 
 
 Border: alveolar , of dog's jaw 
 398 ; coracoid, glenoid, and supra- 
 scapular of dog's scapula 405 
 
 Bos 46 ; occipital crest 468 ; ribs 
 491 ; see Ox 
 
 Bottlenose 44 ; see Hyperoodon 
 
 Bovidae 46 ; pes 523 ; skull 468 
 
 Bow-fin 33 ; see Amia 
 
 Brachial ossicles, cod 103 
 
 Brachium ; see upper arm 
 
 Brachydont, defined 345 ; teeth of 
 Ungulates 429 f. 
 
 Brachycephalus 36 ; bony plates of 
 168 
 
 Brain case, crocodile 245 ; dog 384 ; 
 duck 314 ; frog 154 ; newt 140 ; 
 turtle 224 
 
 Bradypodidae 43 ; see Sloths 
 Brady pus 43 ; cervical vertebrae 
 
 443; pectoral girdle 495; skull 
 
 457 ; thoraco-lumbar vertebrae 
 
 447 
 Branchial arches, Amphibia 180 f . ; 
 
 cod 101 ; dogfish 78 ; fish 120 f. ; 
 
 newt 145; salmon 95 ; basket, 
 
 Marsipobranchii 38 ; skeleton, 
 
 Amphioxus 52 ; Balanoglossus 
 
 50 
 Branchiosaurus 35 ; branchial 
 
 arches 180 
 
 Branchiostegal rays, cod 100 
 Brontops 46 ; see Titanotherium 
 Brontosaurus 38, 207 ; sternum 288 
 Bubalus 46 ; ribs 491 ; see Buffalo 
 Buccal skeleton, Amphioxus 52 
 Buceros 42 ; see Hornbill 
 Buckler, of Labyrinthodonts 168, 
 
 184 
 Buffalo 46; Cape , skeleton of 
 
 492 
 Bufo 36; hyoid 182; jaws 169; 
 
 B. viridis, carpus 186 
 Bufonidae 36 
 Bunodont, defined 345 ; teeth of 
 
 Ungulata 427 f. 
 Buno-selenodont, defined 432 
 
 Caeciliidae 35 
 
 Caiman 39 ; C. latirostris hyoid 
 285, limbs 264, lateral view of 
 skull 248, palatal view of cra- 
 nium and mandible 245, longi- 
 tudinal section of skull 253, 
 pectoral girdle 262, pelvic girdle 
 and sacrum 267 ; C. sclerops, 
 scutes 271 
 
 Ca'ing whale 45 ; see Globicephalus 
 
 Calamoichthys 33 ; distribution 66 
 
 Calamus 302 
 
 Calcaneum 27 ; crocodile 268 ; dog 
 414 
 
 Calcar, of frog 167 
 
 Callorhynchus 32, 66 ; teeth 110 
 
 Camel 45, 359 ; manus 507 ; teeth 
 428 
 
 Camelidae 45 
 
 Camelus 45 ; see Camel 
 
 Camptosauridae 39 
 
 Canal: alisphenoid , dog 402; ca- 
 rotid , duck 315 ;Eustachian , 
 
INDEX. 
 
 535 
 
 crocodile 247 ; dog 402 ; duck 
 316; interorbital , dogfish 76 
 
 Canaliculi 10 
 
 Canidae 48 ; humerus 502 ; skull 
 479 ; see Dog 
 
 Canine 344 ; dog 376 f. 
 
 Canis 48 ; thoraco-lumbar verte- 
 brae 450 ; see Dog 
 
 Capitosaurus 35 ; skull 176 
 
 Capybara 48; maims 511 ; pes 526 ; 
 skull 476 ; tail 454 
 
 Carapace, Chelonia 271 ; Dcrmo- 
 chelys 272 ; Glyptodoiits 419 ; 
 Green turtle 215 ; Loggerhead 
 turtle 216 
 
 Carcharidae 32 
 
 Carina sterni, duck 321 
 
 Carinatae 40 ; general characters 
 300 ; quadrate 334 
 
 Carnassial teeth, 368 ; carnivora 
 436 ; dog 376 f. 
 
 Carnivora 48 ; arm bones 502 ; 
 auditory ossicles 488 ; cervical 
 vertebrae 446 ; general characters 
 367 ; manus 511 ; pelvis 515 ; 
 pes 526 ; ribs 493 ; sacral verte- 
 brae 452 ; skull 478 ; sternum 
 490; tail 454; teeth 437; thigh 
 and shin 520 ; thoraco-lumbar 
 vertebrae 450 
 
 Carnivora vera 48 ; general charac- 
 ters 368 ; scapula 497 
 
 Carp 33 ; pharyngeal teeth 111 
 
 Carpo-metacarpus, duck 324 
 
 Carpus 26 ; crocodile 265 ; dog 408 ; 
 duck 323 ; frog 164 ; newt 147 ; 
 turtle 233 
 
 Cartilage, structure of 10 
 
 Cartilaginous ganoids, cranium 
 121 ; pelvic fin 132 ; spinal 
 column 112 ; see Chondrostei 
 
 Cassowary 40, 299 ; aftershaft 328 ; 
 bony crest 334 ; claAvs 330 ; pel- 
 vic girdle and sacrum 34 O ; 
 secondaries 329 
 
 Castor 47 ; see Beaver 
 
 Castoridae 47 
 
 Casuarius 40 ; see Cassowary 
 
 Cataphracti 34 
 
 Cat 48, 369 ; hallux 526 ; manus 
 511; skull 479 
 
 Cat-fish 33 
 
 Cathartae 41 
 
 Cathartes 41 ; see American vulture 
 
 Caudal fin, Cetacea 453 ; fish 116 ; 
 
 vertebrae, crocodile 243 ; 
 
 cod 85; dog 383; duck 312; 
 
 general characters 16; newt 140; 
 
 turtle 222 
 Cavia 48 ; tail 454 
 Caviidae 48 
 Cebidae 49, 373 ; ribs 493 ; skull 
 
 484 ; teeth 441 
 Coenolestes 43, 424 
 Cement 5 
 Centetes 49 ; caudal vertebrae 454 ; 
 
 pelvic symphysis 515 ; spines 
 
 417 ; teeth 440 ; thoraco-lumbar 
 
 vertebrae 450 
 Centetidae 49 ; auditory ossicles 
 
 488; skull 480 
 
 Centrale 27 ; see Carpus and Tarsus 
 Centre of motion 448 
 Centrum 14 
 Cephalaspis 31, 55 
 Cephalic shield, armadillos 419 
 Cephalochordata 30, 51 
 Cephalodiscus 30, 50 
 Ceratodus 34,70 ; branchial arches 
 
 124; cranium 125; skeleton 
 
 128; skull 117, 124; spinal 
 
 column 113 ; teeth 111 
 Cerato-branchial, cod 101 ; dogfish 
 
 78 ; duck 320 ; salmon 95 
 Cerato-hyal 23 ; cod 100 ; dog 399 ; 
 
 dogfish 78 ; salmon 95 
 Ceratophrys 36 ; bony plates of 
 
 168 ; teeth 170 
 Ceratops 39 ; see Polyonax 
 Ceratopsia 39 ; characters 209 ; 
 
 premaxillae 284 
 Ceratopsidae 39 
 
 Ceratosaurus 38, 208 ; supra- 
 temporal fossae 283; C. nasi- 
 
 cornis, skeleton 2O6 
 Cercopithecidae 49, 373 
 Cervical ribs, crocodile 260; rep- 
 tiles 285 
 Cervical vertebrae, crocodile 239 ; 
 
 dog 380; duck 307; general 
 
 characters 15 ; mammals 442 ; 
 
 turtle 219 
 
 Cervidae 46 ; skull 469 
 Cervulus 46 ; pes 523 
 Cervus 46 ; C. megaceros, antlers 
 
 469 
 
536 
 
 INDEX. 
 
 Cestracion 32 ; calcification of 
 vertebrae 114 ; external bran- 
 chial arches 121 ; pectoral fin 
 130; skull 118; suspensorium 
 119 ; teeth 109 ; vertebral column 
 114 
 
 Cestraciontidae 32 
 
 Cetacea 44, 522 ; arm bones 501 ; 
 auditory ossicles 487 ; caudal ver- 
 tebrae 453 ; cervical vertebrae 
 444; characters 353; exoskeleton 
 416 f. ; hind limb 518 ; manus 
 505 ; pectoral girdle 495 ; pelvis 
 514 ; position of limbs 28 ; ribs 
 491 ; skull 461 f. ; sternum 489 ; 
 teeth 426 ; thoraco-lumbar ver- 
 tebrae 448 
 
 Cetiosauridae 38 
 
 Chalcides 38 ; limbs 289 
 
 Chalicotheriidae 46 ; femur 519 ; 
 manus 509 
 
 Chalicotherium 46 ; femur 360 ; pes 
 5O8, 525 ; teeth 432 
 
 Chamaeleon 38, 199 f. ; epipubis 
 293 ; ilia 291 ; manus 291 ; skull 
 278 
 
 Chamaeleonidae 38 
 
 Charadriidae 42 
 
 Charadriiformes 42 
 
 Chauna 41 ; interorbital septum 
 333 ; ribs 336 ; C. derbiana, spurs 
 330 
 
 Chelone37, 194 ; plastron 271, 218 ; 
 see Turtle 
 
 Chelonia 37', beaks 271; carapace 
 271 ; general characters 193 ; 
 humerus 290 ; limbs 290 ; palate 
 281 ; pectoral girdle 288 ; pelvic 
 girdle 291 ; skull 277 f. ; tarsus 
 293 ; vertebrae 275 f. 
 
 Chelonidae 37 
 
 Chelydae 37 
 
 Chelydra 37 ; carpus 26, 291 
 
 Chelydridae 37 
 
 Chelys 37, 195 
 
 Chersidae 37 
 
 Chevron bones 16 ; crocodile 243 ; 
 mammals 453 f. ; reptiles 276 
 
 Chevrotain 45, 359 ; teeth 429 
 
 Chimaera 32, 66 ; attachment of 
 fins 130 ; pelvic girdle 127 ; skull 
 65 ; teeth 110 
 
 Chimaeridae 32 
 
 Chimaeroidei, general characters 65 
 
 Chimpanzee 49 ; carpus 512 ; ribs 
 493 ; thoraco-lumbar vertebrae 
 450 
 
 Chinchilla 47 ; auditory ossicles 
 488 
 
 Chinchillidae 47 
 
 Chiromyidae 49 
 
 Chiromys 49, 372 ; manus 512 ; pes 
 527 ; teeth 441 
 
 Chiroptera 49 ; auditory ossicles 
 488 ; arm bones 503 ; cervical 
 vertebrae 446 ; general characters 
 370 ; manus 512 ; pelvis 515 ; 
 pes 527 ; sacrum 452 ; shoulder 
 girdle 499; skull 481; sternum 
 490 ; tail 454 ; teeth 440 ; thigh 
 and shin 520 ; thoraco-lumbar 
 vertebrae 450 
 
 Chirotes 38 ; limbs 289 
 
 Chlamydophorus 44, 272 ; scutes 
 419 ; skull 459 
 
 Chlamydoselache 31 ; branchial 
 arches 121 
 
 Choeropus 43 ; manus 504 ; pes 
 522 
 
 Gholoepus 43 ; ribs 491 ; shifting of 
 pelvis 451 ; skull 458 ; sternum 
 489 ; thoraco-lumbar vertebrae 
 447 ; C. hoffmanni cervical verte- 
 brae 443 
 
 Chondrocranium, salmon 87 
 
 Chondroid tissue, Balanoylossus 50 
 
 Chondrostei 32 ; fins 105 ; general 
 characters 67 ; teeth 110 ; see 
 Cartilaginous ganoids 
 
 Chordal sheath, Amphioxus 52 
 
 Chrysochloridae 49 
 
 Chrysochloris 49 ; auditory ossicles 
 488 ; claws 418 ; teeth 440 
 
 Ciconia 41 ; see Stork 
 
 Ciconiiformes 41 
 
 Cingulum 376 
 
 Civet 48, 369 ; teeth 437 
 
 Cladoselache 31, 63; fin 129 
 
 Clasper 132 ; dogfish 82 
 
 Clavicle 25; birds 338; cod 102; 
 duck 322; dog 405; fish 126; 
 frog 163 ; mammals 494 f. ; rep- 
 tiles 289 
 
 Claws 3 ; birds 330 ; crocodile 237 ; 
 dog 374 ; duck 302 ; mammals 
 417 ; turtle 215 
 
INDEX. 
 
 537 
 
 Clupeidae 33 
 
 Clupeus 33 
 
 Cnemial crest, dog 412 ; duck 326 
 
 Coccosteus 34, 70 ' 
 
 Coccyx, man 454 
 
 Cochliodontidae 31 
 
 Cochliodus 31 ; dental plates 109 
 
 Cod 33 ; appendicular skeleton 
 101 f. ; cranium 96 ; mandibular 
 and hyoid arches 99 ; median 
 fins 86 ; pectoral girdle and fin 
 102; ribs 86; skull 96 f.; verte- 
 bral column 83 f. 
 
 Coelofjenys 48 ; zygomatic arch 
 477 
 
 Coenolestes 43, 424 
 
 Coffer-fish 33 ; see Ostracion 
 
 Colobus 49 ; pollex 512 
 
 Colubridae 38 
 
 Columbae 42 
 
 Columbidae 42 
 
 Columella, crocodile 251 ; duck 
 320 ; frog 157 ; turtle 228 
 
 Columella cranii, 200 n. ; see epi- 
 pterygoid 
 
 Colymbi 40 
 
 Colymbiformes 40 
 
 Compsognathidae 38 
 
 Compsognathus 38, 208 
 
 Condylar ridge, duck 326 
 
 Condyle of humerus, dog 406 ; of 
 mandible, dog 398 
 
 Condylarthra 47 ; femur 519 ; 
 general characters 361 ; manus 
 509 ; skull 472 ; teeth 432 
 
 Contour feather, duck 303 
 
 Copula 23 
 
 Coracias 42 ; see Holier 
 
 Coraciae 42 
 
 Coraciiformes 42 
 
 Coracoid 25 ; cod 103 ; crocodile 
 263 ; duck 322 ; frog 163 ; Mono- 
 tremata 493 ; newt 147 ; reptiles 
 288 ; turtle 232 
 
 Coracoid groove, duck 321 
 
 Cormorant 41 ; foot 342 ; skull 335 
 
 Cornu, see hyoid 
 
 Cornua trabeculae 18 
 
 Coryphodon 47 ; femur 519 ; manus 
 510 ; pes 525 ; skull 473 ; teeth 
 433 ; G. hamatua, manus 51O 
 
 Coryphodontidae 47 
 
 Costal plate, turtle 215 ; process, 
 
 duck 321; - shield, turtle 
 214 
 
 Cotyloid bone, 25, 513 ; see Ace- 
 tabular bone 
 
 Cotylopidae 45 
 
 Cotylops 45 ; pollex 506 ; skull 468 
 
 Coverts 306, 328 
 
 Cranium 18 ; cod 96 f. ; crocodile 
 244 f. ; development of 16 f . ; dog 
 384 f . ; dogfish 73 f. ; duck 314 ; 
 frog 154 f. ; newt 140 f. ; turtle 
 222 f. 
 
 Cranio-facial axis, dog 384 
 
 Creodonta 48 ; carpus 512 ; femur 
 520 ; general characters 368 ; 
 skull 479 ; teeth 439 
 
 Cribriform plate, dog 388, 400 
 
 Crocodile 210, 212; anterior limb 
 263; exoskeleton 237; pectoral 
 girdle 262 ; pelvic girdle 266 ; 
 posterior limb 268 ; ribs and 
 sternum 259 ; skeleton 237 f. ; 
 skull 243 f. ; tarsus 293; teeth 
 238 ; vacuities in surface of cra- 
 nium 256 ; vertebral column 239 
 
 Crocodilia 39 ; general characters 
 of 210 ; palate 281 ; skull 277 f.; 
 succession of teeth 274 ; teeth 
 273 
 
 Crocodilidae 39 
 
 Crocodilus 39 ; C. palustris, sternum 
 and associated bones 261 ; late 
 thoracic and first sacral verte- 
 brae 242 ; C. vulgaris, cervical 
 vertebrae 239 
 
 Crossopterygii 33 ; general charac- 
 ters 68 
 
 Crotalidae 38 
 
 Crotalus 38 ; jaws 280 ; see Rattle- 
 snake 
 
 Crows 42 
 
 Crura of stapes, dog 393 
 
 Cruro-tarsal, ankle joint 345 
 
 Crus, 26 ; crocodile 268 ; dog 412 ; 
 duck 326; frog 166; neVt 149; 
 turtle 235 
 
 Crusta petrosa 5 
 
 Cryptobranchus 35, 135 ; skull 175 ; 
 C. lateralis, sacral vertebrae 171 
 
 Cryptodira 37 ; characters 194 
 
 Ctenoid scales 8, 60, 105 
 
 Cubitals 303 f . 
 
 Cuboid 27 ; dog 415 
 
538 
 
 INDEX. 
 
 Cuckoo, foot 342 
 
 Cuculi 42 
 
 Cuculiformes 42 
 
 Cuneiform bones 27 ; dog 414 f. 
 
 Cyclodus 38 ; see Tiliqua 
 
 Cycloid scales 8, 60, 105 ; cod 83 
 
 Cyclopidhis 45 ; skull 468 
 
 Cyclospondyli 114 
 
 Cyclostomata 31 ; general charac- 
 ters 53 
 
 Cycloturus 44 ; hallux 522 ; manus 
 505 
 
 Cygnus 41 ; see Swan 
 
 Cynoceplialus 49 ; cervical vertebrae 
 446 ; skull 482 
 
 Cynoidea 48, 369 ; dental formula 
 437 
 
 Cynognathus 36 ; occipital condyle 
 277 ; teeth 273 
 
 Cyprinidae 33 
 
 Cyprinus 33 ; see Carp 
 
 Cypseli 42 
 
 Cypselidae 42 ; see Swifts 
 
 Cystignathidae 36 
 
 Dactylopterus 34 ; pectoral fins 131 
 
 Dasypodidae 44 
 
 Dasyprocta 48 ; auditory ossicles 
 488 ; thoraco-lumbar vertebrae 
 450 
 
 Dasyproctidae 48 
 
 Dasypus 44 ; manus 505 ; skull 
 459 ; stapes 487 ; teeth 424 
 
 Dasyuridae 43, 350 ; dentition 423 ; 
 pes 521 ; skull 456 
 
 Deer 359 ; manus 507 ; pes 523 ; 
 Chinese water 46, see Hydro- 
 potes ; Musk 46, see Muschus ; 
 Bed fibula 519 
 
 Delphi nidae 45 
 
 Delphinus 45, 357 ; lumbar verte- 
 brae 448 ; skull 462 f . 
 
 Deltoid ridge, crocodile 263 ; dog 
 406 ; frog 164 
 
 Dendrohyrax 363 
 
 Dental formula, regular 344, 422 ; 
 Anthropoidea 441 ; Astrapothe- 
 rium 432 ; Babirussa 428 ; Camel 
 428 ; Chiromys 441 ; Chiroptera 
 (many) 440 ; Cynoidea 437 ; 
 Dinotherium 434 ; Dog 376 ; Du- 
 plicidentata 435 ; Elephas 434 ; 
 Erinaceus 440 ; Felis 437 ; Galeo- 
 
 pithecus 440 ; Hippopotamus 427 ; 
 
 Horse 430; Hydromys 436; 
 
 Hyracoidea 362; Macropodidae 
 
 423 ; Manatus 425 ; Notary cte* 
 
 423; Otorm439; Procavia 432 ; 
 
 Pteropus 441 ; Kodentia (most) 
 
 435 ; Kuminantia 429 ; Squalo- 
 
 don 427 ; Sus 428 ; Tapiridae 
 
 429 ; Thylacinus 423 ; Uinta- 
 
 therium 433; Ursus 439; Zeug- 
 
 lodon 426 
 Dentary 22 ; crocodile 258 ; cod 
 
 100 ; duck 320 ; frog 161 ; newt 
 
 144 ; salmon 94 ; turtle 230 
 Dentine 5 
 
 Derbian Screamer, spurs 330 
 Dermal exoskeletou, crocodile 237 ; 
 
 fish 105; mammals 419 ; reptiles 
 
 271 ; turtle 215 
 Dermo-supra-occipital,Labyrintho- 
 
 dontia 177 ; Polypterus 122 
 Dermochelydidae 37 
 Dermochelys 37, 194, 214, 270 ; 
 
 carapace and plastron 272 
 Dermoptera 48 ; general characters 
 
 370 
 
 Derotremata 35 
 Desmodus 49 ; teeth 441 
 Desmognathous 319, 335 
 Development of bone 10 ; of 
 
 cranium 16 ; of teeth 7 
 Dicynodon 36, 192 ; beak 271 ; 
 
 supratemporal fossa 283 ; teeth 
 
 273 
 Didelphia 43 ; general characters 
 
 349 
 Didelphyidae 43, 350 ; auditory 
 
 ossicles 486 ; pes 521 ; teeth 423 
 Didelphys 43 ; atlas 443 ; teeth 422 
 Didus 42 ; see Dodo 
 Digitigrade, defined 358 n. 
 Digits 26 ; see Manus and Pes 
 Dimetrodon 36 ; thoracic vertebrae 
 
 276 
 
 Dinichthys 34, 70 
 Dinocerata 364 ; see Uintatheriidae 
 Dinornithes 40, 299 ; see Moas 
 Dinosauria 38 ; general characters 
 
 204 ; humerus 290 ; ischium 291 ; 
 
 pectoral girdle 288 ; pes 293 ; 
 
 pre-orbital vacuity 284 ; ribs 
 
 285 ; vertebrae 275 f. 
 Dinotheriidae 47 
 
INDEX. 
 
 539 
 
 Dinotherium 47, 365 ; dental for- 
 mula 434 ; teeth 345 
 
 Diodon 33 ; beaks 111, I), hystrix, 
 scales 105 
 
 Diphycercal tail 60, 116 
 
 Diphyodont, defined 7, 344 
 
 Diplacanthus 32, 64 
 
 Dipneumona 34 
 
 Dipnoi 34 ; general characters 69 ; 
 pelvic fins 131 ; skull 124 ; spinal 
 column 113 ; tail 116 ; teeth 111 
 
 Dipodidae 47 
 
 Diprotodont 423 
 
 Diprotodontia 43 ; characters 350 
 
 Dipteridae 34, 70 ; cranium 124 ; 
 tail 117 ; teeth 111 
 
 Dipus 47 ; cervical vertebrae 446 ; 
 pes 526 
 
 Discoglossidae 36 
 
 Discoglossus 36 ; ribs 182 ; verte- 
 brae 172 
 
 Distal, defined 23 n. 
 
 Divers 40 ; thoracic vertebrae 332 
 
 Docidophryne 36 ; shoulder girdle 
 and sternum 183 
 
 Dodo 42 ; wing 338 
 
 Dog 48; arm bones 4O7 ; an- 
 terior limb 405 ; atlas and axis 
 379; cranium 384, 389, 396; 
 dentition 375 ; innominate bone 
 41O; leg bones 411; manus 
 408, 413, 511; pectoral girdle 
 404; pelvic girdle 409; pes, 413, 
 414 ; posterior limb 412 ; ribs 402 ; 
 second lumbar vertebra 382; 
 second thoracic vertebra 382; 
 skull 383, 387; sternum 4O3, 
 404 ; vertebral column 378 
 
 Dogfish 64 ; cranium 73 ; exoskele- 
 ton 71 ; median tins 79 ; pectoral 
 girdle and fin 79; pelvic girdle 
 81 ; pelvic fin 81 ; ribs 73 ; skull 
 73, 75 ; vertebral column 72 ; 
 visceral skeleton 77 ; Spotted and 
 Spiny 32 
 
 Dolphin 45, 357; lumbar vertebrae 
 448; Gangetic 45, see Pla- 
 tanista 
 
 Donkey, skull 431 
 
 Dorcaiherium 45 ; manus 507 
 
 Dorsal vertebra 16 
 
 Dorsal shield, crocodile 238 
 
 Down feathers 306 
 
 Draco 38; ribs 286 
 Dromaeognathous 335 
 Dromaeus 40, 299; see Emeu 
 Duck 41, 334; beak 329; claws 
 330; cranium 313; exoskeleton 
 302; pectoral girdle 321; pelvic 
 girdle 324, 311, 325; pes, 327; 
 posterior limb 326; ribs 320; 
 skull 312, 312, 313; sternum 
 
 321, vertebral column 307 ; wing 
 
 322, 304, 305 
 
 Duckbill 43; see Ornithorhynchus 
 Dugong 44 ; humerus 501 ; pelvi 
 
 514; thoraco-lumbar vertebrae 
 
 448 ; see Halicore 
 Duplicidentata 48, 366; dental 
 
 formula 435 ; skull 478 
 
 Eagles 335 
 
 Eared Seals 369; scapula 498; see 
 Otariidae 
 
 Echidna 43; caudal vertebrae 453; 
 manus 504; pelvis 513; sacral 
 vertebrae 451; shoulder-girdle and 
 sternum 494 ; skull 455 ; spines 
 417 ; spur 418 ; thoraco-lumbar 
 vertebrae 447 
 
 Echidnidae 43; pes 521 
 
 Ectethmoid 21 n. 
 
 Ectocondylar ridge, dog 406 
 
 Edentata 43 ; auditory ossicles 487 ; 
 arm bones 500; caudal vertebrae 
 453 ; cervical vertebrae 443 ; ma- 
 nus 504 ; pectoral girdle 495 ; pes 
 522; pelvis 513; ribs 491; sa- 
 crum 452; skull 457; sternum 
 489; teeth 424; thigh and shin 
 517; thoraco-lumbar vertebrae 
 447 
 
 Eel 33 ; scales 105 
 
 Elasmobranchii 31 ; cranium 118 f. ; 
 clasper 132 ; general characters 
 61; pelvic fins 131; ribs 125; 
 teeth 109; vertebral column 113 f. ; 
 visceral arches 120 
 
 Elasnwtherium 46 ', mesethmoid 470 
 
 Elephant 47 ; auditory ossicles 487; 
 caudal vertebrae 453 ; ribs 491 ; 
 skull 473 f., 474 and 475 ; tusks 
 420 ; see also Proboscidea 
 
 Elephantidae 47 
 
 Elephas47, 364; dental formula 434; 
 E. plantfron* 435 ; see Elephant 
 
540 
 
 INDEX. 
 
 Elginia 36; skull 191, 283 
 
 Embolomerous 172 
 
 Emeu 40, 299; aftershaft 328; 
 claws 330 
 
 Enamel 4 ; cap 7 ; organ 7 
 
 Endochondral ossification 11 
 
 Endoskeleton, Amphibia 170; birds 
 331 f. ; cod 83 f. ; crocodile 239 f. ; 
 dog 377 f. ; dogfish 71 f . ; duck 
 306 f.; fish 112f. ; frog 151 f.; 
 mammals 442 f. ; newt 138 f. ; 
 reptiles 275 f. ; turtle 218 f . 
 
 Engystomatidae 36 
 
 Entoplastron, turtle 217 
 
 Epanorthidae 43, 350 
 
 Epi-branchial, cod 101 ; dogfish 78 ; 
 salmon 94 
 
 Epicoracoid 25 ; frog 163 ; turtle 
 232 ; Monotremes 493 ; vestiges 
 of in Kodentia 497 
 
 Epicrium 35 ; orbit 179 
 
 Epidermal exoskeleton, birds 328; 
 crocodile 237; dog 374; duck 
 302 ; mammals 416 ; reptiles 
 270; turtle 214 
 
 Epi-hyal, cod 100 ; dog 399; salmon 
 94 
 
 Epi-otic 20 ; cod 96 ; crocodile 250 ; 
 Labyrinthodontia 177; reptiles 
 278 ; salmon 89 ; turtle 227 
 
 Epiphysis 11 
 
 Epiplastron, turtle 217 
 
 Epiprecoracoid, Amphibia 184 ; 
 turtle 232 
 
 Epipterygoid, Lacertilia 200; rep- 
 tiles 278 
 
 Epipubis, crocodile 267 ; newt 149 ; 
 turtle 235 
 
 Episternum 217; frog 163 
 
 Equidae 46; mane 416; scapula 
 496; skull 471 
 
 Equus 46; see Horse 
 
 Erinaceidae 49 
 
 Erinaceus 49 ; dental formula 440 ; 
 pelvic symphysis 515; prester- 
 num 490 ; see Hedgehog 
 
 Esocidae 33 
 
 Esox 33; attachment of teeth 107 
 
 Ethmoid 394 ; see median ethmoid 
 
 Ethmoidal plane 390 ; region 21 
 
 Ethmo-palatine ligament, dog- 
 fish 77 
 
 Ethmo-turbinal, dog 395 
 
 Euchirosaurus 35; vertebrae 171 
 Eustachian canal; see Canal 
 Eusuchia 39; general characters 
 
 212 
 
 Eutheria 43; general characters 351 
 Exocaetus 33; pectoral fins 131 
 Exoccipital 19; cod 97; crocodile 
 246; dog 386; duck 314; frog 
 154; newt 141; salmon 89; 
 turtle 224 
 
 Exoskeleton 2 ; Amphibia 168 ; birds 
 328; crocodile 237; dog 374; 
 dogfish 71; duck 302; fish 104; 
 ganoids 66 ; mammals 442 ; rep- 
 tiles 270 ; turtle 214 
 Extensor side, defined 29 
 Extra-branchial, dogfish 79 
 Extra-columella, crocodile 251 ; 
 turtle 228 
 
 Fabella, dog 412 
 
 Falco 41 
 
 Falcon 41, 335 
 
 Falconiformes 41 
 
 Feathers 3, 328; duck 302 
 
 Felidae 48 ; claws 418 
 
 Felis 48; dental formula 437; tho- 
 
 raco-lumbar vertebrae 450 
 Femoral shield, turtle 215 
 Femur 26; crocodile 28; dog 412; 
 
 duck 326; frog 166; mammals 
 
 517 f.; newt 149; ox and rhino- 
 ceros 518; turtle 235 
 Fenestra ovalis, crocodile 250 f. ; 
 
 dog 392; duck 316; frog 157; 
 
 turtle 228 ; rotunda, dog 392; 
 
 duck 316 
 
 Fenestral recess, duck 316 
 Fibula 26 ; crocodile 268 ; dog 412 ; 
 
 duck 327; frog 166; newt 149; 
 
 turtle 235 
 
 Fibulare 27 ; see Tarsus 
 File-fish 33 ; see Batistes 
 Filoplume 306 
 Finches 42 
 Fins, fish 115; caudal , Cetacea 
 
 453; cod 87; fish 116; Ichthyo- 
 
 sauria 195; median , cod 86; 
 
 dogfish 79; pectoral , cod 103; 
 
 dogfish 79; pelvic , cod 103; 
 
 dogfish 81 
 Fin-rays 105, 115; cod 83, 103; 
 
 dogfish 79 
 
INDEX. 
 
 541 
 
 Firmisternia 36, 185 
 
 Fish, appendicular skeleton 126; 
 endoskeleton 112 f. ; exoskeleton 
 104; general characters 60 f. ; 
 paired fins 127 f. ; ribs 125 f. ; 
 skull 117 f. ; spinal column 112 f. ; 
 teeth 106 f. 
 
 Fissipedia 48', general characters 
 368 
 
 Flamingo 335 
 
 Flexor side, defined 29 
 
 Floating ribs, dog 402; mammals 
 490 
 
 Flower, Sir W. H., on succession of 
 teeth in elephants 434 
 
 Flying-fish 33; fox 49, 371, skull 
 481, see Ptcropux ; gurnard 34, 
 see Dactyloptvrus; lemur 48, 
 see Galeopithecus; lizard 38, 
 see Draco 
 
 Fontaiielle, salmon 89 ; anterior , 
 dogfish 74 ; frog 154 ; posterior , 
 frog 154 
 
 Foot, crocodile 269 ; dog 414 ; frog 
 167 ; newt 149 f. ; turtle 236 
 
 Foramen : anterior palatine , dog 
 401 ; condylar , dog 401 ; cor- 
 diforme, reptiles 292; ect-epicon- 
 dylar , Sphenodon 290 ; ent-epi- 
 coudylar 191 n. ; Carnivora 
 vera 502; Cebidae 503; Choloe- 
 pus 500; Condylarthra 362, 502; 
 Creodonta 368 ; Insectivora 503 ; 
 Lemurs 503 ; Marsupials 500 ; 
 reptiles 290 ; external mandibular 
 , crocodile 258 ; inferior dental 
 , dog 399 ; infra-orbital , dog 
 401; Kodents 477 ; ilio-sciatic , 
 duck 325 ; internal mandibular 
 , crocodile 258 ; internal orbital 
 , dog 401; interparietal , 
 Labyrinthodontia 173, 177; rep- 
 tiles 277; lacerum anterius, 
 dog 388, 400; lacerum me- 
 dium, dog 402; lacerum pos- 
 terius, dog 392, 401; lachrymal 
 , dog 394, 401; magnum, 
 cod 97; crocodile 257; dog 386, 
 402; dogfish 76; duck 314; frog 
 154; newt 141; salmon 89; 
 turtle 224; mental , dog 399; 
 obturator , duck 326; dog 410; 
 ophthalmic , dogfish 74; optic 
 
 , dog 400 ; dogfish 74 ; orbi- 
 tonasal , dogfish 74; ovale, 
 crocodile 249; dog 400; pneu- 
 matic , duck 323; pneumo- 
 gastric , dogfish 76; posterior 
 palatine , dog 401 ; post- glenoid 
 , dog 402; pre-acetabular , 
 Chiroptera 515; rotundum, 
 dog 400; stylomastoid , dog 
 392 f., 400; thyroid , dog 410; 
 trigeminal , duck 316 ; tri- 
 osseum, duck 322 
 
 Fore-arm 26; crocodile 265; dog 
 406; duck 323; frog 164; newt 
 147 ; turtle 233 
 
 Fossa : cerebellar , dog 392 ; cere- 
 bral , dog 392 ; digital , dog 
 412 ; floccular , dog 392 ; infra- 
 temporal , see lateral temporal 
 , lachrymal , Kuminants 
 469; lateral temporal , croco- 
 dile 257 ; Sphenodon 283 ; ole- 
 cranon , dog 406; prescapular 
 , dog 405 ; postscapular , dog 
 405; post-temporal , Spheno- 
 don 283; pterygoid , crocodile 
 257; suborbital , Kuminants 
 469; supra-acetabular , Kumi- 
 nants 514; supra-temporal , 
 crocodile 249, 256; reptiles 283; 
 supra-trochlear , dog 406 ; tem- 
 poral , dog 398; trochanteric 
 , dog 412 
 
 Fowl 41, 335; claws 330; skeleton 
 301 
 
 Fox 48 
 
 Frigate bird 41 ; clavicles 338 
 
 Frog, anterior limb 164; cranium 
 155, 157 ; hyoid apparatus 161 ; 
 pelvic girdle 165 ; posterior limb 
 166; shoulder - girdle and ster- 
 num 183; skull 154 f., 155, 
 159; teeth 151; vertebral co- 
 lumn 152; Common , Edible 
 , Fire-bellied , Green-tree 
 , Horned , Midwife , 
 Painted and Toad 36 
 
 Frontal 19; cod 96; crocodile 249; 
 dog 388; duck 314; newt 141; 
 salmon 91; turtle 225; seg- 
 ment, crocodile 249; dog 388; 
 turtle 225 
 
 Fronto-parietal, frog 156 
 
542 
 
 INDEX. 
 
 Frugivorous bats, manus 512 ; see 
 
 Pteropidae 
 
 Fulcra 67; Polypterus 106 
 Furcula296; duck 322 
 
 Gadidae 33 
 
 Gadus 33 ; see Cod 
 
 Galeopithecidae 48 
 
 Galeopithecus 48, 370; dental for- 
 mula 440 ; iutercentra 450 ; pel- 
 vic sympliysis 515 ; skull 480 
 
 Galesaurus 36, 192 ; teeth 273 
 
 Galeus, 32; occipital joint 118 
 
 Clalli 41 
 
 Gallif ormes 41 
 
 Gallus 41 ; G. bankiva skeleton 3O1 
 
 Gannet, 41 ; wing 339 
 
 Ganoid scales 8, 60, 104 
 
 Ganoidei 32; general characters 
 and distribution 66; pectoral 
 girdle 126 ; pelvic fins 132 ; teeth 
 110; skull 121 f. ; spinal column 
 112 and 114 
 
 Garialidae 39 
 
 Garialis 39, 212 
 
 Garial 210 
 
 Gar pike 33 ; see Lepidosteus 
 
 Gavialis 39 
 
 Gazella 46 
 
 Gazelle4<S; skull 468 
 
 Geckonidae 37 ; see Gecko 
 
 Gecko 37; epipubis 293; parietals 
 277; supra-temporal fossa 283; 
 vertebrae 275 
 
 Gibbon 49; ribs 493; skull 482 
 
 Gill-rays, dogfish 78 ; salmon 95 
 
 Giraffa 46 
 
 Giraffe 46, 359; cervical vertebrae 
 445 ; manus 507 ; pes 523 ; ulna 
 501 
 
 Giraffidae 46 ; skull 469 
 
 Girdle bone, frog 156 
 
 Glenoid cavity 25; crocodile 263; 
 dog 405; duck 322; frog 162; 
 newt 146; turtle 232; fossa, 
 dog 394 
 
 Globe-fish 33 
 
 GloNcephalus 45; cervical vertebrae 
 354 ; manus 506 ; skull 463 
 
 Gluteal surface of ilium, dog 410 
 
 Glyptodon 44; carapace 419; cervi- 
 cal vertebrae 443 ; caudal verte- 
 brae 453 ; mauus 505 ; pelvis 513 ; 
 
 pes 522; teeth 425; thoraco- 
 
 lumbar vertebrae 447 
 Glyptodontidae 44, 352 ; skull 459 ; 
 
 see also Glyptodon 
 Gnathostomata 31, 59 
 Golden mole 49 ; see CJirysochloris 
 Goniopholidae 39 
 Goniopholis 39 ; vertebrae 275 
 Goose 334 ; beak 329 ; Spur-winged 
 
 41 
 Gorilla 49 ; carpus 512 ; ribs 493 ; 
 
 scapula 499; skull 483; thoraco- 
 
 lurnbar vertebrae 450 
 Gruidae 41 ; see Cranes 
 Gruiformes 41 
 Guinea-pig 48; tail 454 
 Gular shield, turtle 215 
 Gulls 42, 335 ; aftershaft 328 
 Gymnodontidae 55; beaks 111 
 Gymnophiona 35 ; branchial arches 
 
 180 ; general characters 136 ; ribs 
 
 182; scales 168; skull 177; teeth 
 
 169 ; vertebrae 172 
 Gymnura 49 ; teeth 440 ; zygomatic 
 
 arch 481 
 
 Gypogeranus 41 ; claws 330 
 Gyrinophilus 35; vertebral column 
 
 171 
 
 Haddock 55 
 
 Hadrosauridae 39 
 
 Hadrosaurus 39 ; skull 284 
 
 Hag or hag-fish 31, 54 f. 
 
 Hair 3 ; dog 374 ; mammals 416 
 
 Halicore 44, 352 ; manus 505 ; skull 
 
 460 ; teeth 425 ; see Dugong 
 Halicoridae 44 
 Halitheriidae 44 
 Halitherium 44, 352 ; femur 518 ; 
 
 pelvis 514 ; teeth 425 
 Hallux 26; dog 415; duck 327; 
 
 frog 167 
 
 Hamular process, dog 397 
 Hand, crocodile 266; dog 408 f.; 
 
 duck 324; frog 165; newt 147; 
 
 turtle 233 
 Hapale 49 
 
 Hapalidae 49, 372 f. ; teeth 441 
 Hare 48, 366 ; acetabular bone 
 
 515 ; dental formula 435 ; femur 
 
 520 ; humerus 502 ; pelvis 515 ; 
 
 scapula 497; skull 476; tail 
 
 454 ; thoraco-lumbar vertebrae 
 
INDEX. 
 
 543 
 
 449; Cape jumping 47', see 
 Pedetea 
 
 H(irp<t(/ux 41 ; serrated beak 334 
 
 Harriotta 32, 66 
 
 Hatter ia 37, 197; see Sphenodon 
 
 Haversian canals 10; system 
 10 
 
 Hawks, beak of 330 
 
 Hedgehog 49, 370 ; auditory ossicles 
 488 ; humerus 503 ; presteriium 
 490 ; skull 480 ; spines 417 ; see 
 Erinaceut 
 
 Hemichordata 30, 50 
 
 Hi'ptanchiis 31 ; branchial arches 
 63, 120; vertebrae 114 
 
 Herbivorous dentition 427, 430 
 
 Heron 41, 335; inter-orbital sep- 
 tum 333 ; powder down feathers 
 329 
 
 Herring 33 
 
 Hesperornis 40, 299 ; caudal ver- 
 tebrae 333 ; clavicles 338 ; teeth 
 330 ; wing 338 
 
 Heterocercal tail 60, 116 
 
 Heterodont 7 
 
 Heterostraci 31 ; general character 
 54 
 
 Hexanchus 31 ; branchial arches 
 63, 121 
 
 Hinge joint 13 
 
 Hipparion 46 ; manus 508 ; pes 
 524 
 
 Hippopotamidae 45 
 
 Hippopotamus 45, 359; dental for- 
 mula 427 ; hair 416 ; mandible 
 467; manus 506; pes 523; sca- 
 pula 496 ; skull 467 ; teeth 345 
 
 Hoatzin 41 ; see Opisthocomus 
 
 Holocephali 32, 65, 104; clasper 
 132; spinal column 113; tail 116; 
 teeth 109 
 
 Holoptychiidae 33 
 
 Holopty chins 33 ; scales 105 
 
 Holostei 33; general characters 68 ; 
 teeth 110 ; see Bony Ganoids 
 
 Hominidae 49, 373 
 
 Homo 49 ; see Man 
 
 Homocercal tail 60, 69, 117; codfish 
 87 
 
 Homodont, defined 7 
 
 Hoofs 3 ; 418 
 
 Hoopoe 42, 335 
 
 Hoplopterus, spur 330 
 
 Hornbill 42, 331 ; bony crest 334 ; 
 interorbital septum 333 
 
 Horns 3, 417 
 
 Horny plates on palate 418; - 
 teeth, Lampreys 4; Myxinoids 
 57 ; Ornithorhynchm 4 
 
 Horse 46, 360 ; fibula 519 ; malleus 
 487 ; manus 507 ; pes 524 ; skull 
 471 ; teeth 345, 430 ; ulna 501 
 
 Howling monkey 49 ; see Mycetes 
 
 Humerals, duck 303 f. 
 
 Humeral shield, turtle 215 
 
 Humerus 26 ; crocodile 263 ; dog 
 405; duck 323; frog 164; newt 
 147 ; turtle 232 ; wombat 5OO 
 
 Humming-birds 42, 335 
 
 Humpbacked whale 44, 357 
 
 Hyaena 48, 369 ; hallux 526 ; pol- 
 lex 511; sacral vertebrae 452; 
 teeth 437 
 
 Hyaenidae 48; humerus 502 
 
 Hyaenodon 48, 368 
 
 Hyaenodontidae 48 
 
 Hyaline cartilage 10 
 
 Hydrochaerus 48 ; teeth 437 ; see 
 Capybara 
 
 Hydromys 47 ; dental formula 436 
 
 Hydrophidae 38 ; scales 270 
 
 Hydropotes 46 ; canines 429 
 
 Hyla 36; fronto-parietal fontanelle 
 179 ; sternum 184 
 
 Hylidae 36 
 
 Hylobates 49 ; ribs 493 ; skull 482 
 
 Hyoid 21 ; alligator 285 ; Amphibia 
 180 ; birds 336 ; cod 100 ; croco- 
 dile 259; dogfish 77; dog 399; 
 duck 320; frog 161; newt 144; 
 reptiles 284; salmon 94; turtle 
 231, 285 
 
 Hyomandibular 23 ; cod 100 ; dog- 
 fish 78 ; salmon 94 
 
 Hyomoschus 45 
 
 Hyoplastron, turtle 217 
 
 Hyostylic 61, 119 
 
 Hyotherium 45; teeth 427 
 
 Hyperodapedon 37, 198 ; premaxillae 
 284 
 
 Hyperoodon 44 ; skull 464 ; sternum 
 489 ; thoracic vertebrae 448 
 
 Hypo-branchial, cod 101; dogfish 
 78 
 
 Hypo-hyal, cod 100 ; salmon 95 
 
 Hypo-ischium, Lacertilia 292 
 
544 
 
 INDEX. 
 
 Hypoplastron, turtle 217 
 
 Hyporachis 328 
 
 Hypsilophodon 39 ; predentary bone 
 284 
 
 Hypsodont, defined 345, 429 
 
 Hypural bone, cod 85 
 
 Hyracidae 47 
 
 Hyracoidea 47 ; femur 519 ; general 
 characters 362 ; manus 510 ; nails 
 418 ; skull 472 ; teeth 432 
 
 Hyracotherium 46; manus 508; 
 scapula 496 
 
 Hyrax 47, 363; see Procavia 
 
 Hystricidae 47 
 
 Hystricomorpha 47; auditory os- 
 sicles 488 
 
 Hystrix, 47 '; auditory ossicles 488; 
 see Porcupine 
 
 Ichthyodorulites 106 
 
 Ichthyoidea 35 ; general characters 
 
 134 
 Ichthyopsida3jf ; general characters 
 
 59 
 
 Ichthyopterygium 130 
 Ichthyornis 40 ; mandible 335 ; 
 
 pelvis 341 ; teeth 330 ; vertebrae 
 
 332 
 
 Ichthyornithiformes 40, 300 
 Ichthyosauria 37; general charac- 
 ters 195 ; ribs 285 
 Ichthyosauridae 37 
 Ichthyosaurus 37,197; limbs 290; 
 
 palatines 281 ; pectoral girdle 
 
 288 ; position of limbs 28 ; skull 
 
 196 ; teeth 273 ; vertebral column 
 
 275 
 Ichthyotomi 31 ; general characters 
 
 62; fins 1 30 f.; tail 116 
 Iguana 38 ; teeth 273 
 Iguanidae 38; zygosphenes 200, 
 
 276 
 Iguanodon 39, 208 f.; jaws 292; 
 
 predeutary 284 ; sternum 288 ; 
 
 teeth 272 f. ; vertebrae 275 
 Iguanodontidae 39 
 Iliac surface of ilium, dog 410 
 Ilium 25 ; crocodile 266 ; dog 409 ; 
 
 duck 325; frog 165; mammals 
 
 513 f. ; newt 149 ; reptiles 291 ; 
 
 turtle 235 
 Incisors, dog 376 f. ; mammals 
 
 344 
 
 Incus, dog 393; man, dog and 
 rabbit 485 
 
 Infra-marginal shield, turtle 215 
 
 Infra-pharyngeal bone, cod 101 
 
 Inia 45 ; cervical vertebrae 444 ; 
 lumbar vertebrae 448 
 
 Innominate bone, dog 409 ; mam- 
 mals 513 
 
 Insectivora 48 ; arm bones 503 ; 
 auditory ossicles 488 ; cervical 
 vertebrae 446 ; general characters 
 369 f. ; manus 512 ; pelvis 515; 
 pes 527 ; sacrum 452 ; shoulder- 
 girdle 499; skull 480; sternum 
 490; tail 454; teeth 440; thigh 
 and shin 520 ; thoraco-lumbar 
 vertebrae 450 
 
 Insectivora vera 49; general cha- 
 racters 370 
 
 Intercentra 15 ; Galeopithecus 370 ; 
 Ichthyosauria 195; Labyrintho- 
 dontia 172 ; Sphenodon 198 ; 
 Talpa 450 
 
 Interclavicle 25 ; crocodile 263 ; 
 Monotremata 494 ; reptiles 289 
 
 Intercondylar notch, dog 412 
 
 Intergular shield, turtle 215 
 
 Interhyal, cod 100 
 
 Intermedium 27; see Carpus and 
 Tarsus 
 
 Intermuscular bones, cod 86 
 
 Internasal septum, dogfish 76 
 
 Interorbital septum, birds 333 ; 
 crocodile 247 ; duck 317 ; reptiles 
 277 
 
 Interspinous bones, cod 86 
 
 Intertarsal ankle joint 190 
 
 Intervertebral discs 15, 378 
 
 Ischial tuberosity, dog 411 
 
 Ischium 25 ; crocodile 266 ; dog 
 410 ; duck 325 ; frog 165 ; newt 
 149 ; turtle 235 
 
 Ischyodus 32, 66 
 
 Ivory 5 
 
 Jacana 42 ; see Parra 
 Jacare 39; scutes 271 
 Jaws 21 ; cod 98 f. ; crocodile 252 f. ; 
 
 dog 395f . ; dogfish 77 ; duck 317 f .; 
 
 frog 158 f. ; newt 143 f. ; salmon 
 
 93 f . ; turtle 229 f. 
 Jerboa 47; cervical vertebrae 446; 
 
 pes 526 
 
INDEX. 
 
 545 
 
 Joints, kinds of 13 
 
 Jugal 22 ; crocodile 255 ; dog 398 ; 
 
 duck 318 ; turtle 229 
 Jugulares 132 
 
 Kangaroo 43 ; dental formula 423 ; 
 
 lumbar vertebrae 447 ; pectineal 
 
 process 513; pes 522; tail 453; 
 
 teeth 345 
 Kestrel, claws 330 
 Killer 45 ; see Orca 
 Kiwi 40; see Apteryx 
 Knee-cap, see patella 
 Koala 43 ; lumbar vertebrae 447 ; 
 
 pes 522; tail 453 
 Kiikentbal, W., on teeth of Cetacea 
 
 426 ; on teeth of Marsupials 422 
 
 Labial cartilage, dogfish 77; Squa- 
 tina 119 
 
 Labridae 33 
 
 Labrus 33 ; see Wrasse 
 
 Labyrinthodontia 35 ; buckler 168 ; 
 general characters 135 ; inter- 
 parietal foramen 173 ; pelvis 187; 
 ribs 182 ; skull 176 ; teeth 169 
 
 Lacertilia 37 ; general characters 
 199 ; pectoral girdle 288 ; skull 
 277 ; vertebrae 275 
 
 Lachrymal 20; cod 97; crocodile 
 251 ; dog 394 ; duck 317 ; salmon 
 93 
 
 Lacunae 10 
 
 Lagenorhynchus 45 ; skull 462 
 
 Lagostomus 47 ; maxilla 477 
 
 Lambdoidal crest, duck 315 
 
 Lamella of malleus, dog 393 
 
 Lamuidae 32 
 
 Lamprey 31, 55 f. 
 
 Lancelot 30 ; see Amphioxus 
 
 Laridae 42 ; see Gulls 
 
 Larks 42 
 
 Larvacea 30 ; notochord 51 
 
 Latax 48 ; pes 526 
 
 Lateral ethmoid 21 ; cod97; salmon 
 89 f. 
 
 Leathery turtle 37 ; see Derrno- 
 chelys 
 
 Lemuroidea 49; caudal vertebrae 
 454 general characters 372 ; 
 nails 418 ; ribs 493 ; sacrum 452 ; 
 skull 482 ; thoraco-lumbar verte- 
 brae 450 ; see Lemurs 
 
 E. 
 
 Lemurs, carpus 512 ; pes 527 ; 
 teeth 441 ; see Lemuroidea 
 
 Lenticular 485 ; dog 393 
 
 Lepidosiren 34, 70; branchial 
 arches 125 ; fins 130 
 
 Lepidosteidae 33 
 
 Lepidosteus 33; attachment of 
 teeth 108 ; distribution 66 ; pec- 
 toral fins 131 ; scales 67, 104 ; 
 skull 123 ; tail 117 ; vertebrae 68 
 
 Lepidotus 33 ; teeth 110 
 
 Leporidae 48 
 
 Lepospondyli 35 
 
 Lepus 48 ; see Hare 
 
 Leptoptilus 41 ; see Adjutant 
 
 Lialis 37 ; 289 
 
 Limbs, general account 26 ; modifi- 
 cations in position of 28 ; rep- 
 tiles 289 
 
 Llama 45, 359 ; cervical vertebrae 
 445 ; skeleton 496 ; teeth 428 
 
 Limicolae 42 
 
 Lingual apparatus, lampreys 58 ; 
 myxinoids 57 
 
 Lion 48 
 
 Loemanctus longipes, shoulder girdle 
 and sternum 287 
 
 Loggerhead turtle, carapace 216 
 
 Lophiodon 46 ; teeth 345, 429 
 
 Lophiodontidae 46 
 
 Lophiomyidae 47 
 
 Lophiomys 47 ; pes 526 ; skull 476 
 
 Lophius, attachment of teeth 107 
 
 Lower jaw ; see Mandible 
 
 Lumbar vertebrae 16 ; crocodile 
 242 ; dog 378 f. ; duck 311 
 
 Lunar 27 ; dog 408 
 
 Macacus 49 ; cervical vertebrae 446 
 Machaerodus 48; upper canines 437 
 Macrauchenia 46, 358 ; calcaneum 
 
 360 ; cervical vertebrae 445 ; 
 
 fibula 519; tarsus 523 ; ulna 501 
 Macraucheniidae 46, 509 
 Macropodidae 43, 350; dental 
 
 formula 423 ; pes 522 
 Macropus 43 ; see Kangaroo 
 Macroscelidae 49 
 Macroscelides 49 ; skull 480 
 Magnum 27 ; see Carpus 
 Malar 22 ; see jugal 
 Malleus, dog 393 ; man, dog and 
 
 rabbit 485 
 
 35 
 
546 
 
 INDEX. 
 
 Mammalia 42; auditory ossicles 
 485 ; cervical vertebrae 442 ; exo- 
 skeleton 416 ; general characters 
 343; manus 503; Mesozoic 348 ; 
 pectoral girdle 493 ; pelvic girdle 
 512 ; pes 521 ; ribs 490 ; sacral 
 and caudal vertebrae 451 ; skull 
 455 ; sternum 489 ; thigh and 
 shin 517 ; thoraco -lumbar verte- 
 brae 447 
 
 Man 49 ; arm bones 503 ; auditory 
 ossicles 488 ; caudal vertebrae 
 454 ; cervical vertebrae 446 ; pel- 
 vis 515 ; pes 527 ; ribs 493 ; 
 scapula 499 ; skull 483 ; sternum 
 490 ; teeth 441 
 
 Manatee 44 ; see Manatus 
 
 Manatidae 44 
 
 Manatus 44 ; cervical vertebrae 444 ; 
 dental formula 425 ; humerus 
 501 ; manus 505 ; pelvis 514 ; 
 skull 460 ; sternum 489 ; teeth 
 345 ; thoraco-lumbar vertebrae 
 448 
 
 Mandible, birds 335 ; cod 100 ; 
 crocodile 258 ; dog 398 ; duck 
 319 ; frog 160 ; Hippopotamus 
 467 ; Isabelline bear 438 ; newt 
 144 ; salmon 94 ; turtle 230 
 
 Manidae 44 ; see Manis 
 
 Manis 44 ; auditory ossicles 487 ; 
 manus 504 ; scales 3, 417 ; skull 
 459 ; M. macrura xiphisternum 
 489 ; see Pangolin 
 
 Manubrium of malleus 486 ; dog 
 393 ; sterni, dog 404 
 
 Manus 26; crocodile 265 ; dog 408, 
 413; duck 323 ; frog 164 ; mam- 
 malia 503 ; newt 147 ; Perisso- 
 dactyles 5O8 ; turtle 233 
 
 Marginal plate, turtle 21 6 ; ray 
 131 ; shield, turtle 214 
 
 Marmoset 49, 372 f. 
 
 Marmot, frontals 476 
 
 Marsipobranchii 31, 53; spinal 
 column 56 
 
 Marsupial bones 513 
 
 Marsupial mole 43 ; see Notoryctes 
 
 Marsupialia 43 ; arm bones 499 ; 
 auditory ossicles 486; cervical 
 vertebrae 443 ; caudal vertebrae 
 453 ; general characters 349 ; 
 manus 504 ; pectoral girdle 494 ; 
 
 pelvis 513 ; pes 521 ; ribs 491 ; 
 sacral vertebrae 451 ; skull 456 ; 
 teeth 422 ; thigh and shin 517 ; 
 thoraco-lumbar vertebrae 447 
 
 Mastodon 47, 365 ; teeth 434 
 
 Mastodonsaurus 35, 136 ; pelvis 187 
 
 Mastoid portion of periotic, dog 
 391 
 
 Maxilla 22 ; cod 98 ; crocodile 254; 
 dog 397 ; duck 318 ; frog 159 ; 
 newt 144 ; turtle 229 
 
 Maxillo-mandibular arch 21 
 
 Maxillo-palatine, duck 318 
 
 Maxillo-turbinal, dog 395 
 
 Meatus, external auditory , cro- 
 codile 250 ; dog 393 ; turtle 228 ; 
 internal auditory , crocodile 
 251 ; dog 392, 400 ; turtle 228 
 
 Meckel's cartilage 22 ; cod 100 ; 
 dogfish 77 ; salmon 94 
 
 Median ethmoid 21 ; cod 98 ; Gym- 
 nophiona 179 ; salmon 91 ; - 
 fin, Amphibia 52 ; cod 86 ; dog- 
 fish 79 
 
 Megachiroptera 49 ; general charac- 
 ters 371 
 
 Megalobatrachus 35, 135 ; carpus 
 186 ; skull 175 
 
 Megalosauridae 38 
 
 Megalosaurus 38, 208 
 
 Megapodius, spur 330 
 
 Megaptera 44, 357 
 
 Megatheriidae 44, 352 ; humerus 
 501 ; leg bones 517 ; pelvis 513 ; 
 sacrum 452 ; teeth 424 ; thoraco- 
 lumbar vertebrae 447 
 
 Megatherium 44 ; femur 517 ; ma- 
 nus 505 ; pectoral girdle 495 ; 
 pes 522 ; skull 458 
 
 Megistanes 40, 299 
 
 Membranous cranium 17 
 
 Menobranchidae 35 
 
 Menobranchus 35, 135 ; carpus 185 ; 
 pes 188 ; skull 174 ; teeth 169 
 
 Menopoma 35 ; see Cryptobranchu* 
 
 Mento-meckelian 22 ; frog 161 ; 
 reptiles 284 
 
 Merganser 41 ; beak 329 
 
 Mergus 41 
 
 Merrythought, duck 322 
 
 Mesethmoid 20; dog 390; duck 
 317 
 
 Mesoplodon 44 ; teeth 427 
 
INDEX. 
 
 547 
 
 Meso-pterygium 79 
 
 Mesosauridae 37 
 
 Mesosaurus 37 
 
 Mesosternum, dog 404 
 
 Metacarpal quill, duck 303 
 
 Metacarpo-digital, duck 303 
 
 Metacarpus 20 ; see Manus 
 
 Metacromion, hares and rabbits 
 497 
 
 Meta-pterygium 79 
 
 Metatarsus 26 ; see Pes 
 
 Metatheria 43 ; general characters 
 349 
 
 Metriorhynchus 39, 278 
 
 Microchiroptera 49 ; general cha- 
 racters 371 
 
 Microgale 49 ; caudal vertebrae 454 
 
 Mid-digital quill, duck 303 
 
 Milk-teeth 344 ; dog 377 ; horse 
 430 
 
 Moa 40, 299 ; aftershaft 328 ; pec- 
 toral girdle 336 ; wing 338 
 
 Molar teeth 344 ; dog 376 f. 
 
 Mole 49, 370 ; auditory ossicles 
 488 ; cervical vertebrae 446 ; 
 humerus 503 ; manus 512 ; pre- 
 sternum 490 ; shoulder girdle 
 499 ; skull 481 ; teeth 440; Golden 
 49 ; see Chrysochloris ; Mar- 
 supial 43 ; see Notoryctes 
 
 Molge 35, 135 ; see Newt 
 
 Monitor 38 ; see Varanus 
 
 Monkey 49, 373; see under Pri- 
 mates 
 
 Monodelphia 43 ; characters of 351 
 
 Monodon 45, 357 ; see Narwhal 
 
 Monophyodont, defined 7 ; 344 
 
 Monopneumona 34 
 
 Monotremata 42 ; arm bones 499 ; 
 auditory ossicles 486 ; caudal 
 vertebrae 453 ; cervical vertebrae 
 443 ; general characters 346 ; 
 manus 504 ; pectoral girdle 493 ; 
 pelvis 513 j pes 521 ; ribs 490 ; 
 sacral vertebrae 451 ; skull 455 ; 
 sternum 489 ; teeth 422 ; thigh 
 and shin 517 ; thoraco-lumbar 
 vertebrae 447 
 
 Morosaurus 38, 207 ; pes 294 
 
 Mosasaurus 38, 204 
 
 Moschus 46 ; canines 429 
 
 Mouse 47 ; teeth 437 ; see lft/.s 
 
 Mud-fish 34 
 
 Multituberculata 43, 348 
 
 Muntjac 46; see Gervulus 
 
 Muraenidae 33 
 
 Muridae 47 
 
 Mus 47; M. musculus, teeth 437 ; M. 
 
 sylvaticus, sternum and shoulder 
 
 girdle 498 
 
 Musk deer 46 ; canines 429 
 Mustelidae 48 ; teeth 439 
 Mycetes 49 ; hyoid 485 ; mandible 
 
 484 ; skull 482 
 Myliobatidae 32 ; teeth 109 
 Myomorpha 47 
 Mynnecobius, teeth 423 
 MyrmecopJiaga 44 ; manus 505 ; 
 
 pectoral girdle 495 ; skull 458 
 Myrmecophagidae 44, 424 ; see 
 
 Anteaters 
 Mystacoceti 44 ; general characters 
 
 356 ; hind limb 518 ; manus 
 
 505 ; pectoral girdle 495 ; skull 
 
 461 ; teeth 426 
 Myxine 31, 55 ; fins 115 ; noto- 
 
 chordal sheath 9 
 Myxinoidei 31, 55 
 
 Nails 3 ; Amphibia 168 ; mammals 
 417 
 
 Nares: anterior , crocodile 252, 
 257; dog 401 ; duck 317; newt 143; 
 turtle 225, 229 ; posterior , cro- 
 codile 257 ; dog 402 ; duck 318 ; 
 frog 158 ; newt 143 ; turtle 230 
 
 Narial cavity, salmon 89 ; pas- 
 sage, crocodile 254 ; dog 395; 
 septum, dog 401 
 
 Narwhal 45, 357 ; teeth 427 
 
 Nasal 21 ; crocodile 252 ; dog 394 ; 
 duck 317 ; frog 158 ; newt 143 ; 
 turtle 228; capsule 20; cod 97 ; 
 crocodile 252 ; dog 394 ; dogfish 
 74 ; frog 158 ; newt 143 ; turtle 
 228 ; cavity, dog 388 ; fossae, 
 salmon 89 ; horns, rhinoceros 3 
 
 Navicular 27 ; dog 414 
 
 Neornithes 40 ; general characters 
 298 
 
 Nesodon 46, 361 ; pes 525 ; teeth 
 432 
 
 Nesodontidae 46 
 
 Neural arch 14 ; plate, turtle 
 215 ; spine 14 
 
 Neuromere, defined 112 
 
 352 
 
548 
 
 INDEX. 
 
 Newt 35 ; anterior limb 147 ; hyoid 
 apparatus or visceral arches 144, 
 181 ; pelvic girdle 149 ; ribs 
 145 ; shoulder girdle 146 ; skull 
 140 ; sternum 145 ; vertebral 
 column 138 
 
 Notidanidae 31 ; calcification of 
 vertebrae 114; pectoral fins 130; 
 vertebral column 113 ; visceral 
 arches 63, 119 f. 
 
 Notochord, Amphioxus 52 ; Balano- 
 glossusSO; dogfish 72; Tunicates 
 51 
 
 Nothosaurus 37, 193; supratemporal 
 fossae 283 
 
 Nothosauridae 37 
 
 Notoryctes 43 ; arm bones 500 ; 
 caudal vertebrae 453 ; cervical 
 vertebrae 443 ; claws 418 ; dental 
 formula 423 ; manus 504 ; pelvis 
 513 ; pectoral girdle 494 ; pes 
 521; ribs 491; sacrum 452; 
 skull 457 ; sternum 489 ; thigh 
 and shin 517 
 
 Notoryctidae 43, 350 
 
 Nuchal plate, turtle 215 ; shield, 
 crocodile 238 ; turtle 214 
 
 Nyrania 35] palatines 177 
 
 Occipital condyle, crocodile 246 ; 
 dog 386; duck 315; frog 154; 
 turtle 224 ; crest, dog 386 ; 
 
 segment, crocodile 246; dog 
 384 ; turtle 224 
 
 Odontaspis 32 ; succession of teeth 
 
 1O7 
 
 Odontoblast 7 
 Odontoceti 44; general characters 
 
 357 ; manus 505 ; pectoral girdle 
 
 495; skull 462; sternum 489; 
 
 teeth 426 
 Odontolcae 40 ; general characters 
 
 299 
 
 Odontopteryx 40; jaws 334 
 Ogmorhinus 48; mandibular ramus 
 
 439 
 Olecranon process, dog 406; duck 
 
 323 ; frog 164 
 Olfactory capsule, see nasal capsule ; 
 
 cavity, dog 388 ; chamber, 
 dog 395 ; fossa, dog 390 
 
 Omosaurus, exoskeleton 272 
 
 Omosternum, frog 163 
 
 Onychodactyliix 35 ; nails 168 
 
 Operculum, cod 101 ; salmon 95 
 
 Ophidia 38 ; general characters 202 ; 
 jaw bones 280 ; scales 270; skull 
 277 f. ; vertebral column 275 
 
 Opliisaurus 38; limbs 289; pectoral 
 girdle 289 
 
 Opisthocoelous, defined 14 
 
 OpistJiocomus 41 ; skull 334 
 
 Opisthotic 20 ; cod 96 ; crocodile 
 250 ; salmon 89 f. ; turtle 227 
 
 Opossum 43; caudal vertebrae 453; 
 teeth 423 
 
 Optic capsule 20 ; crocodile 251 ; 
 dog 394 ; turtle 228 
 
 Orang 49; carpus 512; ribs 493; 
 thoraco-lumbar vertebrae 450 
 
 Orbit, crocodile 257 ; dogfish 74 ; 
 duck 317 
 
 Orbital ring, cod 97 ; salmon 93 
 
 Orbitosphenoid 19 ; dog 388 ; duck 
 317 ; newt 141 
 
 Orca 45 ; teeth 427 
 
 Oreodon 45 ; see Cotylops 
 
 Ornithodelphia 42 ; general charac- 
 ters 346 
 
 Ornithosauria 212 
 
 Ornithorhynchidae 43 
 
 Ornithorhynchus 43; beak 3, 418; 
 caudal vertebrae 453 ; manus 
 504; pelvis 513; sacral vertebrae 
 451; shoulder girdle 347; skull 
 455 ; spur 418 ; tarsus 27 n. ; teeth 
 4, 346, 422 ; thoraco-lumbar ver- 
 tebrae 447 
 
 Ornithopoda 39 ; general characters 
 209 
 
 Orthopoda 39 ; general characters 
 208 ; pubes 292 
 
 Orycteropodidae 44 ; teeth 425 
 
 Orycteropus 44 ; hair 416 ; manus 
 505 ; pectoral girdle 495 ; pelvis 
 513; skull 459 ; see Aard Vark 
 
 Osborn, H. F., on Mesozoic Mam- 
 mals 348 
 
 Os entoglossum, duck 320 
 
 Osteoblast 11 
 
 Osteoclast 11 
 
 Osteodentine 108 
 
 Osteostraci 31 ; general characters 
 54 
 
 Ostracion 33, 69 ; plates 105 
 
INDEX. 
 
 549 
 
 Ostracionidae 33 
 
 Ostracodermi 31 ; general charac- 
 ters 54 
 
 Ostrich 40, 299 ; aftershaft 329; 
 cervical vertebrae 331; claws 
 330; foot 342; manus 338 ; pelvic 
 girdle and sacrum 34O ; pubis 
 341 ; tibio-tarsus 341 ; wing 
 339 
 
 Otaria 48; dentition 439; tym- 
 panic bulla 480 
 
 Otariidae 48, 369 ; auditory ossicles 
 488 ; scapula 498 ; skull 480 
 
 Owen's apteryx, pelvic girdle and 
 sacrum 34 O 
 
 Owen's chameleon, epidermal horns 
 271 
 
 Owls 42, 335 ; aftershaft 329 ; foot 
 342 
 
 Owl-parrot 42 ; see Stringops 
 
 Ox 46, 359; atlas and axis 445; 
 three cervical vertebrae 15 ; fe- 
 mur 518; manus 507; teeth 
 345 ; two thoracic vertebrae 449 
 
 Paca 48 
 Paired fins 127 
 Palaeoniscidae 32 
 Palaeoniscus 32 ; scales 67 
 Palaeospondylidae 31 
 Palaeospondylns 31, 58 
 Palaeosyops 46 ; teeth 432 
 Palaeotheriidae 46 
 Palaeotherium 46 ; skull 471 ; teeth 
 
 430 
 
 Palamedea 41 ; spur 330, 338 
 Palamedeae 41 
 Palate, reptiles 280 f. 
 Palatine, cod 98; crocodile 254; 
 
 dog 397; duck 318; frog 160; 
 
 salmon 93 ; turtle 230 
 Palato - pterygo - quadrate bar 22; 
 
 dogfish 77; fish 120 f.; salmon 
 
 93 
 
 Palm civet 48 
 Pangolin 44 ; pectoral girdle 495 ; 
 
 pelvis 513 ; caudal vertebrae 453 ; 
 
 see Mania 
 Parachordals 17 
 Paradoxurus 48; tail 454 
 Parasphenoid 21 ; cod 97 ; frog 
 
 156 ; newt 141 ; reptiles 278 ; 
 
 salmon 93 
 
 Parasuchia 39 ; general characters 
 211 
 
 Parethmoid 21 n. 
 
 Pariasauria 36 
 
 Pariasaurus 36, 192; pectoral girdle 
 289 ; pelvis 292 ; supratemporal 
 fossa 283 ; teeth 273 
 
 Parietal 19 ; cod 96 ; crocodile 
 247; dog 386; duck 314; newt 
 141 ; salmon 91 ; turtle 225 ; - 
 segment, crocodile 247 ; dog 386 ; 
 turtle 225 
 
 Paroccipital process, dog 386 
 
 Parr a 42 ; spur 330 
 
 Parrots 335; aftershaft 328; beak 
 330; epiphyses of centra 332; 
 foot 342 ; powder-down feathers 
 329 ; skull 334 
 
 Parrot fish 33 ; see Scans 
 
 Passeres, aftershaft 328 
 
 Passeriformes 42 
 
 Patella, dog 412 ; duck 327 
 
 Pavo 41 ; P. cristatus, shoulder 
 girdle and sternum 337 
 
 Peacock 41 ; see Pavo 
 
 Peccary, pes 523 
 
 Pecora 46, 359 ; teeth 429 
 
 Pectinated incisors, Galeopjthecus 
 370, 440 ; Procavia 362 
 
 Pectineal process, duck 326 
 
 Pectoral fins, cod 103 ; dogfish 79 ; 
 girdle 24; Amphibia 184; 
 birds 336; cod 101; crocodile 
 262; dog 404; dogfish 79; duck 
 321; fish 126; frog 162; mam- 
 malia 493; newt 145; reptiles 
 288 ; turtle 231; shield, turtle 
 215 
 
 Pedetes 47; manus 511; tail 454 
 
 Pelican 41, 335 ; clavicles 338 
 
 Pelicanus 41 ; P. conspicillatus 
 shoulder girdle and sternum 
 337 
 
 Pelobates 36; vertebrae 172; P. 
 cultripes teeth 169 
 
 Pelobatidae 36 
 
 Pelvic tins, cod 103; dogfish 82; 
 fish 131 ; girdle 25 ; Amphi- 
 bia 187 ; birds 339 ; crocodile 266 ; 
 dog 409; dogfish 81; duck 324; 
 fish 127 ; frog 165 ; mammals 
 512; newt 149; Eatitae 34O; 
 Reptilia 291 ; turtle 235 
 
550 
 
 INDEX. 
 
 Penguin 40 ; distribution of feathers 
 328 ; fibula 341 ; foot 342 ; manus 
 338; metatarsus 342; pneuma- 
 ticity of skeleton 331; skull 333; 
 sternum 336 ; thoracic vertebrae 
 332 ; wing 329, 339 
 
 Penna, duck 303 
 
 Pentedactylate, denned 26 
 
 Perameles 43; atlas 443; pectoral 
 girdle 494 
 
 Peramelidae 43, 350; auditory os- 
 sicles 486; pes 522 
 
 Perca 34 
 
 Perch 34 pelvic fin 132 ; urostyle 
 117 
 
 Percidae 34 
 
 Perennibranchiata 35', characters 
 135 
 
 Perichondrium 10 
 
 Perichordal sheath 16 
 
 Periosteal ossification 10 
 
 Periosteum 10 
 
 Periotic, dog 390; capsule, see 
 Auditory capsule 
 
 Perissodactyla 46; cervical verte- 
 brae 445; general characters 
 359 ; manus 507 ; pes 523 ; ribs 
 491; scapula 496; skull 470; 
 teeth 429 ; thoraco-lumbar ver- 
 tebrae 448 
 
 Persistent pulps 5 
 
 Pes 26; crocodile 268; dog 413, 
 414 ; duck 327 ; frog 166 ; mam- 
 mals 521; reptiles 293; turtle 
 236 ; of Tapir, Ehinoceros, Hip- 
 parion and Horse 524 
 
 Petromyzon 31, 55 f. ; notochordal 
 sheath 9 
 
 Petromyzontidae 31, 55 
 
 Petrous portion of periotic, dog 
 391 
 
 Pezophaps 42; see Solitaire 
 
 Phacochaerus 45 ; teeth 428 
 
 Phaethon 41 ; metatarsals 342 
 
 Phalacrocorax 41 
 
 Phalangeridae 43, 350 
 
 Phalanges 26 ; see Manus and 
 Pes 
 
 Phaneroglossa 36 
 
 Pharyngo-branchial, cod 101 ; dog- 
 fish 78 ; salmon 95 
 
 Pharyngognathi 33 
 
 PJiascolarctus 43 ; see Koala 
 
 Phascolomyidae 43, 350 
 
 Phascolomys 43, 349 ; see Wombat 
 
 Phascolotherium 43, 348 
 
 Phenacodontidae 47 
 
 Phenacodus 47, 362 ; caudal ver- 
 tebrae 454; manus 51O; pes 
 525 ; scapula 497 ; skull 472 ; 
 thoraco-lumbar vertebrae 449 
 
 Phocaena 45, 357; skull 462; tho- 
 raco-lumbar vertebrae 448 ; P. 
 phocaenoides, ossicles 420 
 
 Phocidae 48, 369; scapula 497; 
 tympanic bulla 480 
 
 Phoronis 30, 50 f . 
 
 Phororhacos 41 ; anterior nares 
 333; ischia 341 
 
 Physeter 44 ; cervical vertebrae 
 444; manus 505; skull 464; teeth 
 426 
 
 Physeteridae 44; ribs 491; thoraco- 
 lumbar vertebrae 448 
 
 Physodon 44 ; teeth 426 
 
 Physodontidae 44 
 
 Physostomi 33 
 
 Phytosauridae 39 
 
 Phytosaurus 39; see Belodon 
 
 Pici 42 
 
 Picus 42; see Woodpecker 
 
 Pig 45, 359; skull 465 f., 466; 
 teeth 345, 427 
 
 Pigeons 42, 334 f. ; aftershaft 329 ; 
 pneumaticity of skeleton 331 
 
 Pike 33; pelvic fin 132; teeth 107, 
 110 
 
 Pinnipedia 48; arm bones 502; 
 auditory ossicles 488 ; general 
 characters 369 ; manus 511 ; 
 pelvis 515; pes 526; skull 480; 
 teeth 439 ; thigh and shin 520 ; 
 thoraco-lumbar vertebrae 450 
 
 Pipa 36 ; hyoid apparatus 182 ; 
 jaws 169; skull 180; sternum 
 184 ; vertebrae 172 
 
 Pipidae 36 
 
 Pisces 31 ; general characters 60 
 
 Piscivorous dentition 426, 440 
 
 Pisiform 345, 504; crocodile 265; 
 dog 408 ; turtle 233 
 
 Pituitary fossa, crocodile 247 ; 
 space 17 
 
 Placodontia 36 
 
 Placodus 36, 192; teeth 273 
 
 Placoid scale 4, 60, 104 
 
INDEX. 
 
 551 
 
 Plantigrade, defined 358 n. 
 
 Plastron, Dermochelys 272; Che- 
 lone midas 217, 218, 271 
 
 Platanistidae 45 
 
 Platanista 45, cervical vertebrae 
 444 ; skull 464 
 
 Plectognathi 33 ; vertebrae 115 
 
 Plectroptertis 41 ; P. gambensis, 
 spur 330 
 
 Plesiosauridae 37; limbs 193 ; para- 
 sphenoid 192 ; skull 278 
 
 Plesiosaurus 37, 193 ; position of 
 limbs 28 
 
 Pleuracanthidae 63 ; fins 115 
 
 Pleurodira 37-, general characters 
 195 
 
 Pleurodont, 159, 199, 273 
 
 Pleuronectidae 33 
 
 Pleuropterygii 31, 63 
 
 Pliosaurus 37, 193 
 
 Plovers, 42, 334 ; thoracic verte- 
 brae 332 
 
 Pneumaticity of bird's skeleton 331 
 
 Polacanthus 39', exoskeleton 272 
 
 Pollex 26 ; see Manus 
 
 Polyodoji 32, 104 ; distribution 66 ; 
 pectoral fins 131; skull 122; 
 spinal column 112 ; teeth 110 
 
 Polyodontidae 32 
 
 Polyonax 39, 209; beak 271; 
 frontals 277; jaw 274 ; predentary 
 284 
 
 Polyprotodont 423 
 
 Polyprotodontia 43', general cha- 
 racters 350 
 
 Polypteridae 33 
 
 Polypterus 33, 68 ; distribution 66 ; 
 exoskeleton 67; pectoral fins 
 131 ; pelvic fins 132 ; pelvis 
 127 ; scales 104 ; skull 122 ; tail 
 116 
 
 Pontoporia 45; cervical vertebrae 
 444; teeth 426 
 
 Porcupine 47; pes 526; skull 476, 
 477 ; spines 417 
 
 Porpoise 45, 357; thoraco-lumbar 
 vertebrae 448 
 
 Postaxial 28 
 
 Posterior cornu, duck 320; turtle 
 231; limb 26; Amphibia 188; 
 birds 341 ; dog 412 ; duck 326 ; 
 frog 166; newt 149, 148 ; reptiles 
 293; turtle 235, 234 
 
 Postfrontal 21 ; crocodile 250 ; 
 turtle 225 
 
 Postorbital bar, crocodile 250, 
 255 f.; Hatteria 283; groove, 
 dogfish 76 
 
 Post-temporal, cod 102 ; reptiles 
 283 ; bar, crocodile 256 ; Hat- 
 teria 283 
 
 Potamogale 49, 367, 370; shoulder 
 girdle 499; teeth 440 
 
 Potamogalidae 49 
 
 Powder-down feathers 329 
 
 Pre-axial 28 
 
 Precoracoid 25 ; frog 163 ; newt 147 ; 
 reptiles 288 ; turtle 232 
 
 Predentary, reptiles 284 
 
 Predigital quill, duck 303 
 
 Prefrontal 21 ; crocodile 249 ; rep- 
 tiles 278 ; turtle 225 
 
 Prefronto-lachrymal, newt 141 
 
 Prehallux, frog 167 f. 
 
 Premaxilla 22; cod 98; crocodile 
 252; dog 398; duck 314, 318; 
 frog 158; newt 143; salmon 94; 
 turtle 230 
 
 Premolar, dog 370, 377; mammals 
 344 
 
 Prenasal process, frog 158 
 
 Pre-orbital vacuity, reptiles 283 
 
 Presphenoid 19 ; dog 388 
 
 Prespiracular ligament, dogfish 77 
 
 Presternum, dog 404 
 
 Primaries, duck 303 
 
 Primates 49; arm bones 503; au- 
 ditory ossicles 488 ; cervical ver- 
 tebrae 446; general characters 
 372; manus 512; pelvis 515; 
 pes 527; ribs 493; sacrum 452; 
 shoulder girdle 499 ; skull 482 f . ; 
 sternum 490 ; tail 454 ; teeth 
 441 ; thigh and shin 520 ; thora- 
 co-lumbar vertebrae 450 
 
 Priodon 44 ; caudal vertebrae 453 ; 
 manus 505 ; stapes 487 ; sternum 
 489 ; teeth 424 
 
 Pristidae 32 
 
 Pristis 32; snout or rostrum 109, 
 119 
 
 Proboscidea 47; arm bones 502; 
 cervical vertebrae 445 ; general 
 characters 364 ; femur 519 ; ma- 
 nus 511; pelvis 514; pes 526; 
 scapula 497; skull 473; teeth 
 
552 
 
 INDEX. 
 
 433; 
 449 
 
 thoraco-lumbar vertebrae 
 
 Procavia 47, 363; auditory ossicles 
 487; caudal vertebrae 453; dental 
 formula 432 ; humerus 502; ma- 
 nus 51O; pelvis 514; pes 525; 
 ribs 491 ; scapula 497 ; skull 
 433, 472; tarsus 27; thoraco- 
 lumbar vertebrae 449 
 
 Process, alinasal , firog 158 ; 
 basi-pterygoid , birds 334 ; 
 coracoid , dog 405; coronoid 
 
 (of mandible), dog 398; duck 
 319; coronoid (of ulna), dog 
 408 ; pectineal , duck 326 ; post- 
 frontal , duck 316; postgle- 
 noid , dog 394 ; postorbital 
 (of frontal), dog 388; postorbital 
 
 (of jugal), dog 398; posterior 
 articular , duck 319; zygo- 
 matic , dog 394 
 
 Processus brevis, 486; gracilis 
 
 486; longus, 486; dog 393 
 Procoelous, defined 14 
 Prodelphinus 45; skull 462 
 Proganosauria 37 
 Prone position 29 
 Prongbuck 46 ; horns 417 
 Pro-otic 20; frog 157; turtle 227 
 Pro-pterygium, dogfish 79 
 Proteidae 35 
 Proteles 48; teeth 437 
 Protelidae 48 
 Proterosauridae 37 
 Proterosaurus 37; teeth 198, 274; 
 
 vertebrae 197 
 Proteus 35, 135, 182; branchial 
 
 arches 180 ; digits 187 ; pes 188 ; 
 
 skull 174 
 Protoptervs 34, 70. 117; branchial 
 
 arches 121, 124; fins 130; skull 
 
 124; vestigial gill on pectoral 
 
 girdle 129 
 Prototheria 42; general characters 
 
 346 
 
 Proximal, defined 23 n. 
 Psephurus, distribution 66 
 Pseudopus 38 ; limbs 289 
 Psittaci 42; see Parrots 
 Pteranodon 39, 274 ; pectoral girdle 
 
 289 
 
 Pteranodontidae 39 
 Pteraspis 31, 54 
 
 Pterichthys 31, 55 
 
 Pterocles 42 ; see Sandgrouse 
 
 Pteroclidae 42 
 
 Pterodactylidae 39 
 
 Pterodactylus 39, 213 
 
 Pteropidae 49; skull 481 
 
 Pteropus 49; dental formula 441; 
 
 tail 454 ' 
 Pterosauria 39; general characters 
 
 212; ischia 292; limbs 291; pre- 
 
 orbital vacuity 284; ribs 285; 
 
 sternum 287 ; vertebrae 275 f. 
 Pterotic 20; cod 96; salmon 90 f. 
 Pterygoid, cod 98; crocodile 255; 
 
 dog 397; duck 318; frog 160; 
 
 newt 144 ; salmon 93 ; turtle 230 ; 
 
 fossa, crocodile 255 ; plate, 
 
 dog 388 
 Pterylae 328 
 Pubis 25; crocodile 266 f.; duck 
 
 325; dog 411; frog 165; newt 
 
 149; reptiles 292 ; turtle 235 
 Pygal plate, turtle 217 ; shield, 
 
 turtle 214 
 Pygopodidae 37 
 Pygostyle, duck 307, 312 
 Python 38; ischio-pubis 292; jaws 
 
 280 ; vestiges of limbs 289, 293 
 Pythonomorpha 38; general cha- 
 racters 204; limbs 290; teeth 
 
 273 
 
 Quadrate 22; cod 98; crocodile 
 255; duck 319; frog 160; newt 
 144 ; salmon 93 ; turtle 229 
 
 Quadratojugal 22 ; crocodile 255 ; 
 duck 318; frog 160; turtle 229 
 
 Quill, duck 302 
 
 Babbit 48, 366; pollex 511 
 Kaccoon 369 
 Eachis, duck 302 
 Kachitomous, defined 171 
 Eadiale 27 ; see Carpus 
 Eadialia 115; dogfish 79 f. 
 Eadio-ulna, frog 164 
 Eadius 26; crocodile 265; dog 406; 
 
 duck 323 ; newt 147 ; turtle 233 
 Raia 32 ; calcification of vertebrae 
 
 114 
 
 Eaiidae 32 
 Eana 36 ; see Frog 
 Eanidae 36; shoulder girdle 185 
 
INDEX. 
 
 553 
 
 Eat, pes 526 
 
 Eatitae 40; caudal vertebrae 333; 
 clavicles 338; foot 342; general 
 characters 298; skull 333; ster- 
 num 336 ; vomers 334 ; wing 338 
 
 Eattlesnake 38; rattle 3, 270 
 
 Eay, pectoral fin 130; Eagle , 
 Electric and Sting , 32 
 
 Eectrices, 303, 329 
 
 Eeed-fish 33 
 
 Eeindeer, antlers 469 
 
 Eemicle, duck 304 
 
 Eemiges, 303, 329 
 
 Eeptiles, anterior limb 290; exo- 
 skeleton 270; fossae in skull 281 ; 
 pectoral girdle 288 ; pelvic girdle 
 291; posterior limb 293; ribs 
 285; skull 276; sternum 287; 
 teeth 272 ; vertebral column 275 
 
 Eeptilia 36 ; general characters 190 ; 
 see Eeptiles 
 
 Rhabdopleura 30, 50 
 
 Rhamphastos 42; see Toucan 
 
 Ehamphorhynchidae 39 
 
 Rhamphorhynchus 39, 213, 274 
 
 Rhea 40] aftershaft 329; claws 
 330; ischia341; manus 338; R. 
 macrorhyncha, pelvic girdle and 
 sacrum 34 O 
 
 Eheornithes 40 
 
 Rhina 32 ; see Squatina 
 
 Ehinal process, frog 158 
 
 Rhinoceros 46, 360, 419; femur 
 518; fibula 519; malleus 487; 
 manus 508; nasal horns 3, 417; 
 pes 525; skull 421, 470; teeth 
 430; ulna 501; R. antiquitatis 
 470 
 
 Ehinocerotidae 46 
 
 Ehinolophidae 49 
 
 Ehiptoglossa 38 
 
 Ehizodontidae 33 
 
 Rhizodus 33; teeth 110 
 
 Ehynchocephalia 37; general cha- 
 racters 197 ; humerus 290 ; teeth 
 273 f. ; vertebrae 275 
 
 Ehynchosauridae 37 ; maxillae 198 
 
 Rhytina 44, 352, 425; humerus 
 501 ; skull 460 
 
 Ehytinidae 44 
 
 Eibs 23; Amphibia 182; birds 336; 
 cod 86 ; crocodile 259 ; dog 402 ; 
 dogfish 73 ; duck 320 ; fish 125 ; 
 
 frog 153; mammalia 490; newt 
 145 ; reptiles 285 
 
 Eidge, supra-orbital andsuborbital, 
 dogfish 74 
 
 Eodentia 47 ; auditory ossicles 488 ; 
 cervical vertebrae 446 ; dental 
 formula 435 ; general characters 
 365 ; pelvis 515 ; pes 526 ; hume- 
 rus 502; manus 511; ribs 493; 
 sacrum 452; shoulder girdle 497 ; 
 skull 476; sternum 489; tail 
 454; teeth 421; thigh and shin 
 520 ; thoraco-lumbar vertebrae 
 449 
 
 Eoller 42, 335 
 
 Eooted teeth, defined 5 
 
 Eorqual 44, 357 ; cervical vertebrae 
 444 
 
 Eostrum, crocodile 247; dogfish 
 74; duck 316; Prai119; of 
 sternum, duck 321 
 
 Eose, C., on teeth of Marsupials 
 422 
 
 Euminantia 46, 359; auditory os- 
 sicles 487; fibula 519; horny 
 plates on palate 418; hyoid 470; 
 manus 507 ; odontoid process 
 445 ; pes 523 ; scapula 495 ; teeth 
 420, 429 
 
 Sabre-toothed lion 48, see Machac- 
 rodus 
 
 Sacral ribs, crocodile 243 ; sur- 
 face of ilium, dog 409 ; verte- 
 brae 16; crocodile 243; dog 383; 
 duck 312; frog 153; newt 140; 
 turtle 222 
 
 Sacrum, duck 310 ; see Sacral ver- 
 tebrae 
 
 Sagittal crest, dog 386 
 
 Saiga, skull 468 
 
 Salamander 35 
 
 Salamandra 35, 135; antibrachium 
 and manus of larva 186 ; manus 
 of larva 185 ; tarsus 27 
 
 Salamandrina 35, 135 ; skull 175 ; 
 sternum 182 
 
 Salmo 33 
 
 Salmon 33 ; branchial arches 95 ; 
 chondrocranium 87 ; opercular 
 bones 95; pectoral fins 131 ; skull 
 87 
 
 Salmonidae 33 
 
554 
 
 INDEX. 
 
 Sandgrouse 42, 335 
 Sarcophilus 43 ; teeth 423 
 Sauropoda 38; general characters 
 
 205 ; teeth 273 ; vertebrae 276 
 Sauropsida 36 ; general characters 
 
 189 
 
 Sauropterygia 37-, general charac- 
 ters 192; limbs 290; palate 281; 
 
 pectoral girdle 288; vertebrae 
 
 276 
 
 Saw-fish 32 ; see Pristis 
 Scales, cod 83; crocodile 237; 
 
 ctenoid 8 ; cycloid 8 ; duck 302 ; 
 
 ganoid 8 ; Gymnophiona 168 ; 
 
 mammals 417 
 Scale-foot 37 
 Scalpriform 366 
 
 Scaphirhynchus 32, 104 ; distribu- 
 tion 66; exoskeleton 67; spinal 
 
 column 112 
 
 Scaphoid 27 ; mammals 504 f. 
 Scapho-lunar, dog 408 
 Scapula 25 ; cod 103; crocodile 263 ; 
 
 dog 404; duck 322; frog 162; 
 
 newt 146 ; turtle 232 
 Scapular shield, armadillo 419 
 Scapus, duck 302 
 Scarus 33; beaks 111 
 Scelidosauridae 39 
 Schizognathous, defined 335 
 Scincidae 38 
 Scincus 38 ; scutes 271 
 Sciuromorpha 47 
 Sclerotic, turtle 228 
 Screamer 41 ; spurs 330 
 Scutes, armadillos 419 ; crocodile 
 
 237 ; reptiles 271 
 Scylliidae 32 
 
 Scyllium 32; calcification of ver- 
 tebrae 114 ; pectoral fins 130 ; 
 
 suspensorium 119 ; see Dogfish 
 Scymnus 32, 118; calcification of 
 
 vertebrae 114 ; mandibular arch 
 
 120 ; pectoral fins 130 
 Scythrops 42 ; interorbital septum 
 
 333 
 Sea leopard 48 ; see Ogmorhinus ; 
 
 lion 48; manus 511 ; pes 526 ; 
 
 position of limbs 29 ; otter 
 
 48; pes 526 
 Seal 369; manus 511; pes 526; 
 
 sacral vertebrae 452 ; scapula 
 
 497 
 
 Secondaries, duck 303 f. 
 Secretary-bird 41 ; claws 330 
 Selachii 31 ; general characters 63 ; 
 
 teeth 108 
 
 Selenodont, defined 345, 428 
 Sella turcica, crocodile 247 ; dog 
 
 386 
 
 Semionotidae 33 
 Semiplumae 328 
 Sense capsules, see Auditory, Nasal 
 
 and Optic capsule 
 Seps 38 ; limbs 289 
 Shagreen 61 
 Shaft of feather 302 
 Shark 64; Frill-gilled 31\ see 
 
 Chlamydoselache ; Port Jackson 
 
 32 ; see Cestracion 
 Sheep 359 ; manus 507 ; teeth 345 
 Shields of turtle 214 
 Shin 26 ; see Crus 
 Shoulder girdle, see Pectoral girdle 
 Shrew 49, 370; auditory ossicles 
 
 488 ; cervical vertebrae 446 ; pre- 
 
 sternum 490; skull 481; teeth 
 
 440 
 
 Sigmoid notch, dog 406 
 Siluridae 33 ; plates 105 
 Simla 49 ; ribs 493 ; skull 484 
 
 thoraco-lumbar vertebrae 450 
 Simiidae 49, 373 
 Simplicidentata 47, 366 
 Siphonops 35; S. annulatus, skull 
 
 178 
 Siredon 35 ; skull 175 ; teeth 169 ; 
 
 visceral arches 181 
 Siren 35, 135, 188; beaks 168; 
 
 branchial arches 180 ; digits 187 
 
 skull 174 ; teeth 169 
 Sirenia 44, 522 ; arm bones 501 ; 
 
 caudal vertebrae 453 ; cervical 
 
 vertebrae 443 ; general characters 
 
 352 ; hair 416 ; horny plates 418 ; 
 
 manus 505 ; pectoral girdle 495 ; 
 
 pelvis 514 ; ribs 491 ; skull 459 ; 
 
 sternum 489 ; teeth 425 ; thoraco- 
 lumbar vertebrae 448 
 Sirenidae 35 
 Sirenoidei 34; general characters 
 
 70 
 
 Sivatherium 46 ; skull 469 
 Skate 32 
 Skeletogenous layer 14, 16; Amphi- 
 
 oxus 52, 112 
 
INDEX. 
 
 555 
 
 Skeleton, defined 1 ; Cape Buffalo 
 492 ; Ceratodu* 128 ; cod 83 f. ; 
 crocodile 237 f . ; dog 374 f . ; duck 
 302 f. ; frog 151 f. ; llama 496 ; 
 newt 138 f. ; turtle 214 f. 
 
 Skink 38 ; see Tiliqua 
 
 Skull 16 f. ; Amphibia 173 f . ; Anura 
 179 f.; birds 333 f.; cod 96 f.; 
 crocodile 243 f. ; diagram of 
 Mammalian 385 ; Dipnoi 124 ; 
 dog 383 f. ; dogfish 73 f. ; donkey 
 431 ; duck 312 f. ; fish 117; frog 
 154 f., 159 ; Globicephalus 463 ; 
 Gymnophiona 177; Indian ele- 
 phant 474 ; Mammalia 455 ; 
 Marsipobranchii 57; pig 466; 
 Procavia 433 ; reptiles 276 f. ; 
 Ehinoceros 421 ; Rhytina 46O ; 
 sloth 458 ; Tasmanian wolf 
 456 ; Teleostei 124; turtle 222 f.; 
 wombat 456 
 
 Sloth 43, 352 ; auditory ossicles 
 487 ; arm bones 500 ; claws 418 ; 
 leg bones 517; manus 505; pec- 
 toral girdle 495 ; pelvis 513 ; pes 
 522; ribs 491; sacrum 452; skull 
 457; sternum 489; teeth 424; 
 thoraco-lumbar vertebrae 447 
 
 Snake 38 ; see Ophidia 
 
 Sole 33 
 
 Solea 33 
 
 Solenodon 49 ; teeth 440 
 
 Solenodontidae 49 
 
 Solitaire 42, 330 ; wing 338 ; wrist 
 330 
 
 Sorex 49; pelvis 515; see Shrew 
 
 Soricidae 49 ; skull 481 
 
 Spalacidae 47 
 
 Spatularia 32 ; distribution 66 
 
 Spelerpes 35 ; branchial arches 180 ; 
 ribs 182 ; S. belli teeth 169 
 
 Sperm whale 44, 357 ; see Physeter 
 
 Sphargis 37; see Dermochelys 
 
 Sphenethmoid, frog 156 
 
 Sphenisci 40 ; see Penguins 
 
 Sphenisciformes 40 
 
 Sphenodon 37, 197 f. ; carpus 291 ; 
 cervical vertebrae 275 ; fossae in 
 skull 281; humerus 290; inter- 
 parietal foramen 277; ribs 286; 
 skull 282; tarsus 293; teeth 
 274 
 
 Sphenodontidae 37 
 
 Sphenoidal fissure, dog 388 
 
 Sphenotic 20 ; cod 97 ; salmon 
 89 
 
 Spider monkey 49; see Ateles 
 
 Spinacidae 32 
 
 Spinal column 13 ; Dipnoi 113 ; 
 fish 112 ; Holocephali 113 ; Mar- 
 sipobranchii 56 
 
 Spines, Elasmobranchs 61 ; mam- 
 mals 417 
 
 Spiny anteater 43 ; see Echidna ; 
 mouse 47 ; see Acanthomys 
 
 Splenial 22; crocodile 258; duck 
 320 ; turtle 231 
 
 Spurs, birds 330; Monotremata 
 418 
 
 Spur- winged goose 330 ; plover 
 330 
 
 Squalidae 31, 64 
 
 Squalodon 45, 357 \ dental formula 
 427 
 
 Squalodontidae 45 
 
 Squamata 37; general characters 
 198 ; position of teeth 272 ; skull 
 278 
 
 Squamosal 21 ; crocodile 256 ; dog 
 394; duck 316; frog 160; newt 
 144 ; turtle 229 
 
 Squatina 32 ; calcification of ver- 
 tebrae 114; labial cartilages 119; 
 tail 63 ; vertebral column 114 
 
 Squatinidae 32 
 
 Squirrels, frontals 476 ; pes 526 
 
 Stapes, dog 393; frog 157; man, 
 dog, rabbit 485 ; newt 141 
 
 Steganopodes 41 
 
 Stegosauria 39 ; general characters 
 209 
 
 Stegosauridae 39 
 
 Stegosaurus 39, 208 f. ; exoskeleton 
 272 
 
 Steller's sea-cow 44 ; see Rhytina 
 
 Stereornithes 41 
 
 Stereospondyli 35 
 
 Sternal ribs, crocodile 259 ; dog 
 402 ; duck 320 ; mammals 490 f. 
 
 Sternebra, dog 404 
 
 Sternum 24 ; Amphibia 182 ; birds 
 336; crocodile 260, 261; dog 
 403 ; duck 321 ; frog 163 ; 
 Mammalia 489; newt 145; rep- 
 tiles 287 
 
 Stork 335 ; White 41 
 
556 
 
 INDEX. 
 
 Striges 42 ; see Owls 
 
 Stringops 42 ; sternum 336 
 
 Struthio 40, 299 ; see Ostrich 
 
 Struthiornithes 40, 299 
 
 Sturgeon 32 ; see Acipenser 
 
 Stylo-hyal, dog 399 
 
 Suborbital bar, duck 318 ; ridge, 
 
 dogfish 76 
 
 Subplantigrade, defined 358 n. 
 Subungulata 46; arm bones 502; 
 
 general characters 360 ; manus 
 
 509; pelvis 514; pes525; shoulder 
 
 girdle 497 ; skull 471 ; teeth 432 ; 
 
 thigh and shin 519 
 Suidae 45 
 Suina 45, 358 f. ; fibula 519 ; manus 
 
 507; odontoid process 445 ; pelvis 
 
 514; pes 523; ulna 501 
 Sula 41 ; see Gannet 
 Supinator ridge, dog 406 
 Supine position, defined 29 
 Supra-angular 22 ; crocodile 258 ; 
 
 duck 319 ; turtle 230 f. 
 Supracaudal shield, turtle 214 
 Supraclavicle, cod 102 
 Supra- occipital 19; crocodile 247; 
 
 dog 386 ; duck 315 ; turtle 224 
 Supra-orbital 20 ; crocodile 251 
 Suprapharyngeal bone, cod 101 
 Suprascapula, crocodile 263 ; frog 
 
 162 
 Supratemporal arcade, crocodile 
 
 256 ; reptiles 281 
 Surinam toad 36 ; see Pipa 
 Sus 45; dental formula 428; see 
 
 Pig 
 
 Suspensorium, Amphibia 173; dog- 
 fish 78 ; duck 319 ; frog 160 ; newt 
 
 144 ; Pisces 61 
 Sutures 12 
 Swan 41; cervical and thoracic 
 
 vertebrae 332 
 Swift 42, 335 ; foot 342 
 Symplectic, cod 100 ; salmon 94 
 
 Tails, fish 60 
 
 Talpa 49; pelvis 515; see Mole 
 
 Talpidae 49 
 
 Tapir 46, 360; malleus 487; pes 
 
 524, 525 ; teeth 345 ; see Tapirus 
 Tapiridae 46 ; dental formula 429 
 Tapirus 46 ; fibula 519 ; manus 
 
 508 ; skull 471 ; see Tapir 
 
 Tarsier 49 
 
 Tarsiidae 49 
 
 Tarsipes 43, 349 ; mandible 457 
 
 Tarsius, 49, 372 ; pes 527 
 
 Tarso-metatarsus, duck 327 
 
 Tarsus 26 f. ; crocodile 268 ; dog 
 414; frog 166; newt 150; turtle 
 236 
 
 Tasmanian devil, 43; see Sarco- 
 pliilus; wolf 43; see Thylacinus 
 
 Tatusia 44 ; stapes 487 ; teeth 424 
 
 Tectospondyli 114 
 
 Tectrices, duck 306 
 
 Teeth 6 ; Amphibia 169 ; birds 330; 
 cod 83; crocodile 238; develop- 
 ment 7 ; dog 374 f. ; fish 106 f. ; 
 frog 158 f. ; horses 5 ; mammals 
 344, 420 f. ; pharyngeal 8 ; rep- 
 tiles 272 f . ; structure 4 ; succes- 
 sion 7 
 
 Teleosauridae 39 
 
 Teleosaurus 39 ; palate 281 ; scutes- 
 271 ; vertebrae 275 
 
 Teleostei 33 ; general characters 
 69; ribs 126; skull 124; tail 
 117; teeth 110; vertebral column 
 115 
 
 Temnospondyli 35 
 
 Tenrec 49; see Centetex 
 
 Tentorium, dog 392 
 
 Terrapin 37 
 
 Testudo 37, 194 
 
 Tetraceros 46 ; horns 417 
 
 Thalassochelys, carapace 216 
 
 Thecodont, defined 273 
 
 Theriodontia 36 
 
 Theromorpha 36; general charac- 
 ters 191; humerus 290; pectoral 
 girdle 288; ribs 285; skull 278; 
 teeth 273 ; vertebral column 275 f . 
 
 Theropoda 38; general characters 
 207 ; teeth 273 
 
 Thoracic ribs, crocodile 259; see 
 Bibs ; vertebrae 16 ; crocodile 
 241, 242; dog 381, 382; duck 
 310; turtle 221 
 
 Thoraco- lumbar vertebrae, mam- 
 mals 447 f. 
 
 Thornback skate 104 
 
 Thylacinus 43; atlas 443; dental 
 formula 423; pelvis 513; pes. 
 521 ; skull 456 
 
 Thylacoleo 43; skull 457 
 
INDEX. 
 
 557 
 
 Thyro-hyal, dog 399 
 
 Tibia 26; crocodile 268; dog 412; 
 
 newt 149 ; turtle 235 
 Tibiale 27; see Tarsus 
 Tibio-fibula, frog 166 
 Tibio-tarsus, duck 326 
 Tichorhine Khinoceros 470 
 Tiger 48 
 
 Tiliqua 38; scutes 200, 271 
 Tillodontia 47, 365; femur 520; 
 
 manus 511 ; teeth 435 
 Tinamidae 300; caudal vertebrae 
 
 333 ; vomers 334 
 Tinamiformes 41 
 Tinamus 41 ; ischia 341 
 Titanotheriidae46; skull 470; teeth 
 
 432 
 Titanotherium 46; humerus 501; 
 
 manus 5O8 ; pes 525 
 Toad 36 ; shoulder girdle 185 
 Tope 32 
 
 Torpedinidae 32 
 Torpedo 32, 104 
 
 Tortoise 37; position of limbs 28 
 Tortrix, ischio-pubis 292; traces 
 
 of posterior limb 203 
 Toucan 42; foot 342 
 Toxodon 46, 361; femur 519; pes 
 
 525 ; teeth 432 
 Toxodon tia 46; general characters 
 
 361 ; manus 509; skull 472; teeth 
 
 432 
 
 Toxodontidae 46 
 Trabeculae 11; cranii 17 
 Tragulidae 45 
 Tragulina 45, 359; fibula 519; 
 
 manus 507 ; odontoid process 
 
 445; pes 523; skull 468; teeth 
 
 429; ulna 501 
 
 Transpalatine, crocodile 255; rep- 
 tiles 278 
 
 Trapezium 27 ; dog 408 
 Trapezoid 27 ; dog 408 
 Trichechidae, 48, 369 
 Trichechus 48; see Walrus 
 Triouychia 37 ; general characters 
 
 194 
 
 Trionychidae 37 
 Triomjx 37, 193 f. ; exoskeleton 
 
 214, 270; skull 283; vestiges of 
 
 teeth 274 
 
 Trixaolepi* 32; scales 104 
 Tritylodon 43 ; teeth 348 
 
 Trochanter, dog 412 ; duck 326 
 
 Trochilidae 42 ; 5 see Humming-birds 
 
 Trochlea, crocodile 263; dog 405 f.; 
 duck 323 ; turtle 232 
 
 Trogon, 42 ; foot 342 
 
 Trogonidae 42 
 
 Tropidouotus 38; jaws 280; skull 
 279 
 
 Trunk vertebrae, cod 84; see tho- 
 racic and lumbar vertebrae 
 
 Trygon 32; calcification of verte- 
 brae 114 ; caudal spine 106 
 
 Trygonidae 32 
 
 Tuberosities of humerus, dog 405 ; 
 of ischium, dog 411 
 
 Tunicata 30, 51 
 
 Tupaia, skull 480; thoraco-lumbar 
 vertebrae 450 
 
 Turbinals, dog 395 
 
 Tursiops 45 ; skull 462 
 
 Turtle 37 ; anterior limb 232, 234 ; 
 cranium 222 f., 226; hyoid 231, 
 285; mandible 230; pectoral 
 girdle 231; pelvic girdle 235; 
 pes 236; plastron 217, 218; pos- 
 terior limb 234, 235; sense cap- 
 sules 227; skull 222; vertebral 
 column 219 ; Leathery , see 
 Dermochelys ; Snapping , see 
 Trionyx 
 
 Tylopoda 45, 359 ; fibula 519 ; ma- 
 nus 507 ; odontoid process 445 ; 
 pelvis 514; pes 523; skull 468; 
 teeth 428 ; ulna 502 
 
 Tympanic, dog 392 ; - - cavity, 
 crocodile 250; diagram of mam- 
 malian 391; dog 393; duck 
 315 f.; turtle 228; recess, 
 duck 315 
 
 Tympano-hyal, dog 399 
 
 Typhlopidae 38; scales 270; skull 
 278 
 
 Typhlops 38; ischio-pubis 292; 
 traces of posterior limb 293 
 
 Typotheriidae 46 
 
 Typotherium 46, 358, 361; clavicle 
 495, 497; femur 519; pes 525; 
 skull 472 ; teeth 432 
 
 Udenodon 36, 192 ; beak 271 
 Uintatheriidae 47; skull 364 
 Uintatherium 47; dental formula 
 433; leg 519; limbs and limb 
 
558 
 
 INDEX. 
 
 girdles 516; manus 510 ; pelvis 
 
 514; skull 473 
 Ulna 26; crocodile 265; dog 406; 
 
 duck 323; frog 164; newt 147; 
 
 turtle 233 
 
 Ulnare 27 ; see Carpus 
 Umbilicus, inferior and superior, 
 
 duck 303 
 Unciuate process 190; crocodile 259; 
 
 duck 320 
 
 Unciform 27, 345, 504; dog 408 
 Ungulata 45 ; auditory ossicles 487 ; 
 
 caudal vertebrae 453; cervical 
 
 vertebrae 445 ; general characters 
 
 357 ; manus 506 ; pectoral girdle 
 
 495 ; pes 522 ; ribs 491 ; sacrum 
 
 452; skull 464 f.; sternum 489; 
 
 teeth 427 f. ; thoraco-lumbar ver- 
 tebrae 448 
 Ungulata vera 45 ; arm bones 501 ; 
 
 general characters 358; manus 
 
 506; pelvis 514; thigh and shin 
 
 519 
 Upper arm 26 ; crocodile 263 ; dog 
 
 405; duck 323; frog 164; newt 
 
 147 ; turtle 232 
 Upupa 42 ; see Hoopoe 
 Urochordata 30, 51 
 Urodela 35] general characters 
 
 134; pelvis 187; ribs 182; skull 
 
 174 
 
 Urohyal, cod 101 ; duck 320 
 Urostyle, Anura 172; cod 85; frog 
 
 153 ; Teleostei 117 
 Ursidae 48 ; humerus 502 
 Ursus 48 ; dental formula 439 ; see 
 
 Bears 
 
 Vacuities, anterior palatine , cro- 
 codile 252, 258 ; in reptilian 
 skull 281 ; posterior palatine , 
 crocodile 254, 257; pre-orbital 
 , reptiles 283 f. 
 
 Vampire 49; teeth 441 
 
 Vane, of feather 303 
 
 Varanidae 38 
 
 Varanus 38 ; shoulder girdle 2O2 ; 
 skull 201 
 
 Vasodentine 108, 272 
 
 Vertebral column 14; Amphibia 
 170; birds 332; cod 83; croco- 
 dile 239; dog 378; duck 307; 
 Elasmobranchs 113; frog 152; 
 
 mammals 442 ; newt 138 ; turtle 
 
 219 ; ribs, crocodile 259 ; dog 
 
 402 ; duck 320 ; shield, turtle 
 
 214 
 
 Vertebrata, general characters 53 
 Vexillum, of feather 303 
 Vibrissae, dog 374 
 Viscacha 47 
 Visceral skeleton 21; dogfish 77; 
 
 Elasmobranchs 119 f. 
 Viverra 48; acetabular bone 515 
 Viverridae 48 
 Vomer 21; cod 98; crocodile 252; 
 
 dog 395; duck 317; frog 158; 
 
 salmon 93 ; turtle 229 
 Vomero-palatine, newt 143 
 Vultur 41 
 Vulture 41; Black , shoulder 
 
 girdle and sternum 337 
 
 Waders 335 
 
 Walrus 48, 367, 369; canines 420; 
 manus 511; pes 526; position 
 of limbs 29; skull 480; teeth 
 440 
 
 Warblers 42 
 
 Wart hog 45 ; teeth 428 
 
 Weasel 369 
 
 Whale, baleen 3, 418; Ca'ing - 
 45, see Globicephalus ; Hump- 
 backed 44, 357 ; Right 44, 
 357 ; Sperm 44, 357, see Phy- 
 seter; True or Whalebone 356 
 
 Whiting 33 
 
 Wild duck 41 ; see Duck 
 
 Wing, duck 322 ; Gannet, Ostrich, 
 and Penguin 339 
 
 Wolf 48 
 
 Wombat 43; atlas 443; pes 521; 
 sacrum 451; skull 456; tail 
 453 ; teeth 423 
 
 Woodpecker 42, 335; foot 342; 
 hyoid 336 
 
 Wrasse 33 ; teeth 111 
 
 Xenacanthus 31 ; pectoral fins 130 
 
 Xenopidae 36 
 
 Xenopus 36; branchial arches 182; 
 
 nails 168 ; pelvis 188 ; ribs 182 
 Xiphiplastron, turtle 217 
 Xiphisterual horn, crocodile 260 
 Xiphisternum, dog 404 ; frog 163 
 Xiphoid process, duck 321 
 
INDEX. 559 
 
 Zeuglodon 44, 353, 356 ; dental 240 f . ; dog 379 f. ; duck 308 f. ; 
 
 formula 426 ; dermal plates 420 frog 152 f. ; newt 139 ; turtle 
 
 Zeuglodontidae 44 219 f. 
 
 Zygantra, denned 199 n. ; reptiles Zygosphene, denned 199 n.; reptiles 
 
 276 276 
 Zygapophyses, cod 84; crocodile 
 
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UNIVERSITY OF CALIFORNIA MEDICAL SCHOOL LIBRARY 
 
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Arnolds. 3. 
 R46 The vertebrate 
 
 keleton. 
 
 9 1 109^'OV 1 1 1924 
 
 APR 4 - 1929 
 
 ./APR 18 192bAPR 20 1929 
 
 -fllpR 30 194S 
 
 University of CaUfornia Medical School Library