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Full text of "An introduction to the study of mammals living and extinct"

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. 






AN INTRODUCTION 



TO THE 



STUDY OF MAMMALS 



^ 



AN INTEODUCTION 



TO THE STUDY OF 



MAMMALS 



LIVING AND EXTINCT 



BY 



WILLIAM HENBY FLOWEB 

C.B., F.R.S., D.C.L., LL.D., P.Z.S., F.L.S., F.G.S., &c. 

DIRECTOR OF THE NATURAL HISTORY DEPARTMENTS, BRITISH MUSEUM 



AND 

BICHABD LYDEKKEB 

B.A., F.G.S., F.Z.S., &c. 







THE Wi;iOLLY OPOSSUM 



LOXDOX: ADAM AXD CHABLES BLACK 

MDCCCXCI 



32 L I 



PREFACE 

Onp: of the greatest difficulties experienced by all who undertake a 
work of this nature, not professing to be an exhaustive treatise 
on the subject with which it deals, is to determine the amount 
of detail desirable to be introduced to meet the requirements of 
the ordinary student, without rendering it too bulky or costly 
for general use. The experience of those who endeavour to profit 
by the book can alone decide how far the authors have succeeded 
in this respect. It will be observed that in many instances certain 
better-known or more interesting members of the class have been 
described at considerable length, while it has been necessary to 
treat others with much greater brevity. 

With regard to the references to the literature of the various 
groups treated of, it has been the endeavour of the authors to 
make a selection of such memoirs and works as are likely to prove 
most valuable to the student for the amount of original informa- 
tion which they contain, and more especially of those giving 
full bibliographical data up to the time of their publication, the 
repetition of which has been considered unnecessary. 

In a few instances new generic terms have been introduced to 



vi PREFACE 



replace some -which were already occupied ; these have been pro- 
posed by Mr. Lydekker, and should be quoted as his. 

The work is based largely upon the article " Mammalia," to- 
gether with forty shorter articles, written by the senior of the two 
authors for the ninth edition of the Encyclopaedia Britannica. The 
account of the orders Rodentia, Insectivora, and Chiroptera con- 
tributed to the article "Mammalia" by Dr. G. E. Dobson, F.R.S., 
as well as the articles "Mole," "Shrew," and "Yampyre," by the 
same writer, the articles "Marmot," "Mouse," "Opossum," "Phal- 
anger," "Rat," "Squirrel," "Stoat," "Vole," and others, by Mr. 
Oldfield Thomas, and likewise the article "Ape," by Dr. St. G. 
Mivart, F.R.S., have also been made use of to a greater or less 
extent. The best thanks of the authors are due to these three 
gentlemen for freely permitting the incorporation of their own 
work in the present volume. 

Mr. Lydekker undertook the task of arranging the various 
articles in their proper sequence, selecting from these such portions 
a- seemed suitable, filling up the gaps, and adding new matter 
where necessary ; a large amount of this new matter treating of the 
extinct forms, and also of the group Artiodactyla. 

The subsequent revision, both before being sent to the printers, 
and also when passing through the press, has been made by both 
authors, who are thus jointly responsible for the whole work. 

The illustrations are to a great extent those prepared for the 
various articles in the Encyclopaedia, but many have been added 
— some drawn expressly for the work, and some borrowed from 
other publications. For most of the latter the authors take this 
opportunity of expressing their thanks to the Publication Com- 



PREFACE 



mittee of the Zoological Society of London, as well as to the 
individual writers in whose works they first appeared. 

The authors have further much pleasure in acknowledging the 
ready and obliging way in which Mr. Oldfield Thomas has, 
throughout the progress of the work, placed his extensive know- 
ledge of the group of animals of which it treats at their disposal. 



London, March 1S91. 



Corrigenda. 

Page 280, for Chaeropsis read Chceropsis. 

Page 292, for Chseropotamidae and Chaeropotanms read Chceropotamidie and 
( 'in i r< >pi itunms. 

Page 590, for Precdogale read Pcecilogale. 



CONTENTS 



CHAPTER I 

PAGE 

Introductory Remarks ..... 1 

Use of term mammals, 1 ; Characters of mammals, 2 ; De- 
velopment of young, 3 ; Size of mammals, 4 ; Uses and products 
of mammals, 4. 

CHAPTER II 

General Anatomical Characters .... 7 

I. Tegumentary Structures .... 7 

Hair, 7 ; Colour, 8 ; Scales, etc., 11 : Nails, claws, and 
hoofs, 12 ; Odour-secreting glands, 12. 

II. Dental System. . . . . .13 

Teeth, 13 ; Structure of teeth, 13 ; Development of teeth, 
15 ; Forms of teeth, 17 ; Succession of teeth, 19 ; Arrangement, 
homologies, and notation of teeth, 21 ; Dental formulae, 25 ; 
Modifications of teeth in relation to function, 28 ; Taxonomy, 
30 ; Trituberculism, 30. 

III. The Skeleton ...... 33 

Definition, 33 ; Axial skeleton, 34 ; Skull, 34 ; Vertebral 
column, 39 ; Cervical vertebra;, 41 ; Dorsal vertebra;, 42 ; 
Lumbar vertebra;, 42 ; Sacral vertebra;, 43 ; Caudal vertebra;, 
43 ; Sternum, 44 ; Ribs, 44 ; Appendicular skeleton, 46 ; 
Anterior limb, 46 ; Shoulder-girdle, 46 ; Brachium and Ante- 
brachium, 47 ; Manus, 48 ; Carpus, 48 ; Metacarpus and Phal- 
anges, 49 ; Posterior limb, 50 ; Pelvic girdle, 50 ; Thigh and 
Leg, 51 ; Pes, 52. 

IV. The Digestive System . . . . .53 

General considerations, 53 ; Mouth, 54 ; Salivary glands. 
55 ; Stomach, 57 ; Intestinal canal, 59 ; Liver, 60. 

V. Circulatory, Absorbent, Respiratory, and Urinary Systems 63 

Blood, 63 ; Heart, 63 ; Lymphatic vessels, 65 ; Ductless 
glands, 65 ; Xostrils, 66 ; Trachea, 67 ; Larynx, 67 ; Diaphragm, 
67 ; Lungs, 68 ; Air-sacs, 68 ; Urinary Organs, 69 ; Bladder, 69. 



CONTENTS 



PAGE 



VI. Nervous System and Organs of Sense . . .69 

Brain, 69; Nerves, 71; Sense of touch, 72; Taste and 
smell, 72 ; Sight, 72 ; Hearing, 73. 

VII. Reproductive Organs . . . • .74 

Testes, 74 ; Penis, 74 ; Ovaries and oviduct, 75 ; Mammary 
glands, 75 ; Secondary sexual characters, 76 ; Placenta, 76. 

CHAPTEE III 

Origin and Classification of the Mammalia . . 82 

Origin, 82 ; Classification, 84 ; Table of orders and 
families, 88. 

CHAPTER IV 

Geographical and Geological Distribution . 93 

I. Geographical Distribution . . • .93 

Zoological regions, 96 ; Palsearctic region, 97 ; Ethiopian 
region, 9S; Oriental region, 100; Celebes, 102; Nearctic region, 
102 ; Neotropical region, 103 ; Aquatic mammals, 104. 

II. Geological Distribution . . . .107 

Sequence of strata, 107 ; Mesozoic mammals, 109 ; Multi- 
tuberculata, 109 ; Polyprotodont types, 113 ; Tertiary mammals, 
115. 

CHAPTER V 

The Subclass Prototheria or Ornithodelphia . 117 

General characters, 117. Family Ornithorhynchidje, 
119; Ornithorhynchus, 119. Family Echidnidje, 124; 
Echidna, 125 ; Frocchidna, 126 ; Fossil species, 127. 

CHAPTER VI 

The Subclass Metatheria or Didelphia . . .128 

General characters, 128 ; Distribution, 131 ; Classification, 
131. 

Suborder Polyprotodontia . . . • .133 

Family Didelphyid.e, 133; Chironectes, 134; Didelphys, 
135. Family Dasyuriixe, 136 ; Subfamily Dasyurinre. 136 ; 
Thylacinus, 136; Sarcophilus, 137; Dasyurus, 138; Phascolo- 
gale, 139; Sminthopsis, 139; Antechinomys, 139; Subfamily 
Myrmecobiina?, 140; Myrmccobius, 140. Family PeramelhXE, 
141 : I'< nancies, 142; Fcragalc, 143; Chmropus, 143. 



CONTEXTS xi 



PAGE 

Snhonlr DlPROTODONTIA . . . . .144 

Family PHASCOLOMTIDJS, 144; Phascolomys, 145; Phascol- 
onus, 146. /-W/// //// Pn ai..vn<;i: km>.k, 1 17; Subfamily Tarsipedinae, 
148; Tarsipes, US; Subfamily Phalangerinse, 149 ; Phalanger, 
149; Trichosurus, 150; Pseudochirus, 151; Pctau routes, 152; 
Dactylqpsila, 152 ; I'etaunis, 153 ; Gymnobelideus, 154 ; 
Dromicia, 154 ; 1'islaeliuriis, 155 ; Acrobatcs, 155 ; Sub/amity 
Phascolarctinse, 155 ; Phascolarctus, 156. Extinct Phal- 
angeroids, 157 : Thylacoleo, 157. Family Macropodid;e, 
158 ; Subfamily Hypsiprymnodontinse, 162; Hypsiprymnodon, 
162; 2Wcfts, 162; Subfamily Potoroinse, 162; Potorous, 163; 
Bettongia, 163 ; Calqprymnus, 164 ; dSpyprymnus, 164 ; *S*«6- 
family Macropodinse, 164 ; Lagostropkus, 165 ; Dendrologies, 
165 ; Dorcopsis, 166 ; Lagorchestes, 166 ; Onychogale, 166 ; 
Petrogale, 167 ; Macropus, 167 ; Extinct genera, 170. Extinct 
Families, 171 ; Diprotodon, 171 ; Nototherium, 171. 

CHAPTER VII 

The Subclass Eutheria and the Order Edentata . . 173 

General characters and classification of Eutheria, 173. 

Order Edentata . . . . . .176 

Family Bradypodid.e, 179 ; Bradypus, 181 ; Gholcepus, 
182 ; Nothropus, 1S3. Family Megatheriid^e, 183 ; Mega- 
therium, 185 ; Scelidotherium and Mylodon, 188 ; Promega- 
therium, 189. Family Myrmecophagid^e, 190 ; Myrmecophaga, 
190; Tamandua, 192 ; Gycloturus, 193. Family Dasypodid^e, 
194 ; Subfamily Chlamydophorinse, 196 ; Chlamydophorus, 196 ; 
Subfamily Dasypodinae, 197; Dasypus, 197; Xenurus, 198; 
Priodon, 198 ; Tolypeutcs, 199 ; Subfamily Tatusiinne, 200 ; 
Tatusia, 200 ; Extinct genera, 201. Family Glyptodontid^;, 
202. Family Manid2E, 204; Manis, 204; Palceomanis, 208. 
Family Orycteropodid.e, 208 ; Orycteropus, 208. Biblio- 
graphy, 211. 

CHAPTEE VIII 

The Orders Sirenia and Cetacea . . .212 

Order Sirenia . . . . . .212 

Fa mill! Manatid.e, 215 ; Manatus, 215. Family Hali- 
COKID.E, 220 ; Halicore, 220. Family Rhytinid.e, 221 ; 
Rhytina, 221. Extinct Sirenian.s, 222 ; Halitherium, 222 ; 
Other forms, 223. Bibliography, 224. 

Order Cetacea ...... 225 

Suborder Mystacoceti ...... 234 

Family Bal^eniDjE, 234 ; Balcena, 236 ; Neobalcena, 241 ; 
Ii'hachianectes, 241 ; Megaptera, 241 ; Balcenoptero, 242 ; Extinct 
genera, 245. 



CONTENTS 



Suborder Arch^eoceti . . . . • .246 

Family Zeuglodontid.e, 246 ; Zeuglodon, 246. 

Suborder Odoxtoceti ...-•• 247 
Fa, nil, i 1'hyseterid.e, 247 ; Subfamily Physeterinse, 248 ; 
Physeter, 248 ; Cogia, 250 ; Extiuct physeteroids, 251 ; Sub- 
family Ziphiinse, 251 ; Eyperoodon, 252 ; Ziphius, 254 ; Meso- 
plodon, 254: Berardius, 256; Choneziphius, 257. Family 
Squalodoxtid.e, 257; Squalodon, 257. Family Plataxistii>.e. 
257; Platanisia,25S ; Inia,259; Pontoporia, 259; Fossil forms, 
259. Family'DmssBXSiDM t 2&(i\ Monodon,260; DelpMnapterus, 
262; Phoccena, 263 ; Cephalorhynchus, 266 ; Orcella, 267; Orca, 
267 ; Pseudorca, 268 ; Globieephalus, 26S ; Grampus, 270 ; 
Feresia, 270 ; Lagenorhynchus, 270 ; Delphinus, 271 ; Tursiops, 
271 ; Prodelphinus, 271 ; Stewo, 271 ; Sotalia, 272. Biblio- 
graphy, 272. 

CHAPTER IX 

The Order Ungulata . . ■ .273 

Ungulata Vera . . . • .275 

Suborder Artiodacttla . . . . .275 

Suina, 278. Family Hippopotamidje, 278 ; Hippopotamus, 

278. Family Suid.e, 281 ; Sus, 281 ; Babirusa, 2S7 ; Phaco- 

chcerus, 288. Family Dicotylid.e, 289 ; Dicotyles, 289 ; 

Hyotherium, etc., 291. Extinct Transitional Artiodactyles, 

292 ; Choeropotamidae, 292 ; Anthracothermhe, 292 ; Meryco- 

potamus, 293 ; Cotylopidse, 293 ; Anoplotheriidse, 293 ; Caeno- 

theriidre, 294; Dichodontidse, 294. Tylopoda, 295. Family 

Camelidjs, 295; Camelus, 296; Auehenia, 298; Extinct 

Cameloids, 303. Tragttlina, 305. Family TRAGULmae, 305; 

Tragulus, 305; Doreatherium, 306; Extinct Traguloids, 306. 

Pecora, 307; Antlers, 308; Horns, 310; Teeth, 310; Stomach, 

312. Family Cervid.£, 313 ; Subfamily Moschinse, 314 ; 

Moschus, 314 ; Subfamily Cervinse, 316 ; Plesiometacarpalia, 

316 ; Cervulus, 316 ; Elaphodus, 318 ; Ccrvus, 319 ; Telemeta- 

carpalia, 323 ; Sangifer, 324 : Alces, 326 ; Cervalces, 327 ; 

Capreolus, 327 ; Hydropotes, 328 ; Cariacus, 329 ; Pudua, 330 ; 

Extinct genera, 330. Family GlRAFFlD.dE, 330 ; Giraffa, 331 ; 

Allied extinct types, 332. Family Antilocapridje, 333 ; 

Antilocapra, 333. Family Boyid^;, 334 ; Alcelaphus, 334 ; 

Connocluctcs, 336 ; Cephalophus, 338 ; Tetraceros, 338 ; Neo- 

tragus, 338 ; Nanotragus, 339 ; Pelea, 339 ; Cobus, 339 ; Cervi- 

capra, 340 ; Antilope, 340 ; JEpyccros, 341 ; Saiga, 341 ; 

Pantholops, 341 ; Gazella, 341 ; Hippotragus, 343 ; Oryx, 343 ; 

Aiidax, 345 ; Boselaphus, 345; Tragelaphus, 346; Strepsiceros, 

347 ; Orcrts, 348 ; Extinct types, 348 ; Rwpicopra, 349 ; A'- 

rlfdus, 350 : Eaploceros, 351 ; Budorcas, 351 ; C«p-«, 352 ; 

Ovi's, 354 ; Ovt'&os, 357 ; Bos, 360. 



CONTENTS xiii 



Suborder Perissodactyla ..... 368 

Family Tai'h:ii>.k. 370 ; Tapirus, 370 ; Palceotapirus, 373. 
Family LoPHiODONTiD.fi, 373. Family 1' \i..i:< n n i.i: iid^e, 375. 
Family Equip-e, 376; Protohippus, 3S0 ; Hipparion, 380; 
Equus, 381. Family Rhinocerotid^, 402; Rhinoceros, 402; 
Extincl types, 411. Families Lamupotheriipje, Chalico- 
THERIID.fi, and TlTANOTHERHD.fi, 412. Family Macrau- 
CHBNilD.fi, 414. Family PROTEROTHERUDfi, 414. 

StTBTJNGULATA ....••• 414 

Suborder Hyracoidea ..... 415 

Family Hyracip.e, 41") ; Ilyra.r, 117 ; Dendrohyrax, 418. 

Suborder Proboscidea ...... 418 

Family ELEPHANTlDfi, 423 ; Elephas, 124 ; Mastodon, 431. 
Family DiNOTHERiiDiE, 435 ; Dinotherium, 435. 

Suborder Amblypoda ...... 436 

Uintathcrium, 436 ; Coryphodon, 437. 
Suborder Condylarthra ..... 438 

Suborder Toxodontia ...... 439 

Nesodon, 439 ; Toxodon, 439 ; Typotherium, 440. 
Group Tillodoxtia . . • • • .441 

Bibliography of Ungulates . . . . .442 

CHAPTER X 

The Order Kodentia ...... 443 

Suborder Sijiplicidentata ..... 448 

Section Sciuromorpha, 448. Family Anomalurib^e, 449 ; 
Aaomalurus, 449. Family Sciurip^:, 450; Sciurus, 450; 
Eh ith rose inrus, 452 ; Xerus, 452 ; Tamias, 452 ; Pteromys and 
Sri it ropier us, 453 ; Eupctcinrus, 454 ; Extinct genera, 454 : 
Arctomys, 454; Cynomys, 455; Spermophilus, 456; Extinct 
genera, 457. Family Haplodontid.e, 457 ; Haplodon, 457. 
Family Castoribjs, 457 ; Castor, 457. Section Myomorpha, 
459. Family aIyoxip^e, 459; Mijoxus, 459; Eliomys, 459; 
Graphiurus, 459 ; Claviglis, 460; Muscardinus, 460. Family 
LoPHlOMYlDfi, 460; Loxthiomys, 460. Family Murip^e, 461 ; 
Hydromys, 461 ; Xcromys, 461 ; Platacanthomys, 462; Gerbillus, 
162; Pachyuromys, 462 ; Mystromys, 462; Otomys&nd Dasymys, 
462 ; Molar,, mys, 462 ; Phlceomys, 462 ; Dendromys, 463 ; 
Cricetus, 463; Holochilus, 464; Sigmodon, 464; BMbhrodon 
and Oehetodon, 464 : Neotoma, 164 ; Hypogeomys, 465 ; Xesomys, 
465 ; Brachytarsomys, 465 ; Hallomys, 465 ; Fl inrus, 465 ; 
Phenacomys, 466 ; Arrimlo, 466 ; Synaptomys, 467 ; Myodes, 
467; Cuniculus, 470; lifter, 470; Neofiber, 472; Ellobius, 



xiv CONTEXTS 



PAGK 



172: Siphneus, 472; Deomys, 473; .l/c*. 173; Nesocia, 475: 
Golunda, 476; Uromys, 476; Chiruromys, 476; Hapalotis, 
476: Afastacomys, 476; Acanthomys, 176; Echinothrix, 477: 
Typhlomys, 477 ; Cricetomys and Saccostomus, 177 ; PUhechirus, 
477. Family Spalacid*, 477; Spalax, 177: Phizomys, -177: 
Bathyergus, 478; Oeorychus and Myoscalops, 478; Hetero- 
cephalus, 47*. Family Gku.myid^:, 478; Gcomys, 478; 
Thomomys, 478 : Dipodomys, 479 ; Perognathus ami //./• romys, 
479. Family Dii'oDiD-E, 479; Sminthus, 479; Zo^ks, 480; 
ZMptw, 4S0 ; Alactaga, 180 : Platycercomys, 480 ; Pcdrtcs, 480. 
,v. ,■/;,„/ Hystbicomorpha, 180. Family Octodontid.k. 480. 
Ctenodactylus, 481 ; Peetinator, 481 ; Or/,:,/,,,,, 481 ; Habrocoma, 
482; Schizodan, 482; Gtenomys, 482; Spalacopus, 482; 
Petromys, 482 ; Myopotamus, 482 ; Capromys, 482 ; Aulacodus, 
483 ; Plagiodon, 483 ; Lonchcres and Echinomys, As:', ; Mesomys, 
483 ; Dadylomys, 483 ; Ccrcomys, 483 ; Carterodon, 484 ; 
Fossil forms, 484. Family Theridhmyiile. 484. Family 
ETSTEiclDiE, 484 ; Erethizon, 484 ; Synetlicres, 485 ; Chcetomys, 
486 ; Hystrix, 4S6 ; Atherura, 4S7 ; Trichys, 487. F<>aiilij 
Chinuhillid.e, 487 ; Chinchilla, 487; Lagidiwm and Lagosto- 
mus, 488 ; Extinct genera, 488. Family Castoroidid.e, 488 ; 
Castoroides, 488. Family Dasyproctid.e, 488 ; Dasyprocta, 
488 ; Ccelogcays, 489. Family DlNOMYnxE, 489; Dinomys, 489. 
Family Cayiid.e, 489; Oc/", 489; Dolkhotis, 490; Hydro- 
clui-rns, 490 ; Extinct genera. 491. 

Suborder Duplicidextata . . . ■ .491 

Family Lagomyid^, 491 ; Lagomys, 491. Family Lepo- 
ridje, 492 ; Leims, 492. „ 



CHAPTER XI 

The Order Carxivora . . . 496 

Suborder Garni yora Vera . . . . .497 

Section tEluroidea, 501. Family FELlD.fi, 502; /'//>-. 

502; Cyncelurus, 523; Extinct genera, 523. Family Viver- 

riDjE, 525; Cryptoprocta, 525 ; l'ir,rra, 526; .Foss", 527: 

Genetta, 528 ; J J rimn„l,,,t, 530 ; Poiana, 531 ; Paradoxurus, 

532 ; Arctogalc, 533; Ilrmigalr, 53:1 : Arctictis, 531 ; Nandinia, 

534 ; Cynogale, 534; Herpcstes, 535; Heloaa/c, 537; Bilcagah:, 

537 ; Cynictis, 537 ; Rhinogalc, 537 : ' 'rossarc/n/s, 537 : Suricata, 
538; Galidictis, Gal idea, ami Hemigalidea, 538.; Eupleres, 

538 ; Extinct genera, 539. Family PROTELEEDiB, 539 ; /W< ■ 5, 
539. Family Hymsxdm, 540 ; ffycena, 5^0. Section Cynoidea, 
5 11. Family < 'anid.e, 544 ; Canis, 546 ; Lycaon, 553 ; Iclicyon, 
553; Otocyon, 554 ; Extinct genera, 555. tfec&on Arctoidea, 556. 
Family I'ksiii.k, 557 ; Crsus, 557 ; Melursus, 560 ; AElurqpus, 
560; Extinct genera, 561. Family PROCYONlDfi, 562; 
.Elm-ns, 562 : Procyon, 564 : Bassaris, 566 ; Bassaricyon, 566 ; 
Nasua, 566; Cercoleptes, 567. Fa, nil,/ M i'stelid.e, 567: 



COX/KXTS 



Lutra, 567 ; Extinct Otters, 570 ; Latax, 570 ; Mephitis, 572 ; 
patus, 574 ; Arctonyx, 571 : Mydaus, 575 ; Meles, 575 ; 
Taxidea, 576 ; Mcllivora, 576; Helictls, 578; Ictonyx, 579; 
Oalictis, 570 ; Mustela, 579 ; Extinct Mustelines, 590 ; Pcecilo- 
gale, 590 ; Lyncodon, 590 ; (thZo, 591. 

Suborder PlNNIPBDIA ...... 592 

Family OTAXIID2E, 593; Otaria, 593. Family TwCHE- 
chid.e, 596; Trkhcchus, 597. Family PHOCiDiE, 600: 
ffalichcerus, 601 ; Phoca, 601 ; Monachus, 604 ; Ogmorhinus, 

605 ; Lobodon, 605 ; Poxilophoca, 605 ; Ommatophoca, 605 ; 
OystopJbora, 605 ; Maerorhinas, 606 ; Extinct seals, 606 

Suborder Oreodoxta ..... 606 

Hya?nodontidre, 608 ; Proviverridse, 608 ; Arctocyonidre and 
Mesonychida?, 609. 

CHAPTEE XII 

The Order Ixsectivora . . . . .610 

Suborder Dermoptera . . . . . .614 

Family Galeopithecid^:, 614 ; Galeopithecus, 614. 

Suborder Insectivora Vera . . . . .616 

Family Tupaiim, 617 ; Tupaia, 617 ; Ptilocercus, 618 ; Ex- 
tinct genera, 618. Family Macroscelidid.e, 618 ; Macroscel- 
ides, 618 ; Ehyncliocyon, 618. Family Erinaceid.e, 619 ; 
Gymnura, 619 ; Erinaceus, 620 ; Extinct genera, 621 ; Family 
Soricid^:, 621 ; Sorex, 622 ; Soriculus, 624 ; Xotiosorex, 624 : 
Blarina, 624 ; Crossopus, 625 ; Myosorex, 625 ; Crocidura, 626 ; 
Diplomesodon, 626; Anurosorex, 626; Chimarrogale, 626; Necto- 
gale, 627 ; Fossil Soricidae, 627. Family Talpim:, 628 : 
Myogale, 628; Urotrichus, 629; Uropsilus, 629 ; Scalops, 630: 
Scapanus, 630 ; Condylura, 630 ; Scajptonyx, 630 ; Talpa, 630 : 
Extinct genera, 634. Family Adapisoricid^:, 634. Family 
TdTAMOGALiDiE, 634; Polamogale, 635; Geogale, 635. Family 
SoLEXODONTiDiE, 635 ; Solcnodon, 636 ; Centctes, 637 ; iZemi- 
centetes, 637 ; Ericalus, 638 ; Microgale, 638 ; Oryzorictes, 638 : 
Chrysochloris, 639. Extinct types, 640. Bibliography, 640. 

CHAPTER XIII 

The Order Chiroptera . . . . .641 

Suborder Megachiroptera ..... 650 

Family Pteropodid^e, 650 ; Epomoplborus, 650 ; Ptcropus, 
651 ; Xantharpyia, 652 ; Boneia, 653 ; Cijnoptcrus, 653 : 
Harpyia, 653 ; (Jephalotes, 653 ; Pteralopex, 654 ; Notopieris, 
654 ; Eonycteris, 654 ; Carponycteris and Melonycteris, 654 : 
Xesoaycteris, 655 ; Callinyderis, 655 ; Trygenyetcris, 655. 



CONTENTS 



Suborder Microchiroi>tera . . 655 

Section Vespertilionina, 655. Family Rhinolophuxe, 
656; Rhinolophus, 656; Hipposiderus, 657; Anihops, 657; 
Uhirumycteris and Tricenops, 658; Ccelops, 658 ; Megaderma, 
658. Family Vespertilioniixe, 660 ; Pleeotus, 660 ; Synotus, 
661; Otonyeteris, 661: Nyctophilus, 661; Antrozous, 661; 
Vesperugo, 661 ; CJialinolobus, 662; Scotqphilus, 662; Nyctice- 
jus. 663; Atalapha, 663; Harpyioeephalus, 663; Vespertilio, 
663 ; Ci //<■,,,//,/, 66 I : Natalus, 664 ; Miniopterus, 664 ; Thyrop- 
tera, 665 ; Myxopoda, 665 ; Fossil Vespertilionidse, 665. 
Jom Emballonurina, 666. Family Emballonurid^i, 666 ; 
Furipterus and ^morpAocAi7«s,666; Emballonura, 667; Coleura, 
667 : Kkyiic/ttiin/ctiTis, 667 ; Siico.ijitrrip; 667 ; Tophozou.% 667 ; 
Ijirlitlnrus, 668 ; Xudilio, 668 ; Rhinopoma, 669 ; Chiromeles, 
ijtiii : MiJnssus, 670 : Xydinomus, 670 ; Mystacops, 671. Family 
PHYLLOSTOMATID.E, 672; Chilonycteris, 672; Mormops, 672; 
Lonehorhina, Otopterus, and Dolichophyllum, 673 ; Vampyrus, 
etc., 673; Dcsmodus, 677 ; Diphylla, 678. 

CHAPTEE XIV 

The Order Primates ...... 680 

Suborder Lemuroide a . . . . . .682 

Family Lemurid^e, 683 ; Indris, 684 ; Propithecus, 684 ; 
Avakis, 686; Lemur, 687; Hapalemur, 689; Lepidolemur, 
• ;v.i ; I'/iinnjiifrns, 6S9 ; Galago, 690; Nyeticcbus, 691; Loris, 
692; Perodicticus, 693. Family Tarsiim:, 694; Tarsias. 
694. Family <Jhiromyid,e, 694 ; Chiromys, 6i>[>. Extinct 
Lemuroids, 696. 

Suborder Axthropoidea . . . . . 699 

Fa,, lily Hai'AI.idje, 709: Hapale, 710; Midas, 710. Family 
Cebid^:, 711; Mycetes, 711; Pithccia, 712; Uacaria, 712; 
Callithrix, 713; Chrysothrix, 714 ; Nyetipifhecus, 714; Ateles, 
715; Eriodes, 715; Lagothrix, 716; C'c&ks, 717. Family 
Cercopithecid^!, 718 ; Cynocephalus, 719 ; Theropithecus, 722 ; 
CynopUhecus, 722; Macacus, 722; Cercoeebus, 723; Cerco- 
pithecus, 724 ; Nasalis, 725 ; Semnopithecus, 726 ; Colobus, 

727 ; Extinct genera, 727. Family Si.miid.e, 728; Hyldbates, 

728 : Simia, 731 ; Gorilla, 734; Anthropopithecus, 736. Family 
HoMlNiD.fi, 739 : y/«//fo, 740. Classification of the varieties of 
Man, 743. 



AN INTRODUCTION" 

TO 

THE STUDY OF MAMMALS 

LIVING AND EXTINCT 
CHAPTEE I 

INTRODUCTORY REMARKS 

Mammalia (French, Mammifkres ; German, Sdugethiere) is the name 
invented by Linnaeus (from the Latin mamma), and now commonly 
used by zoologists, for one of the five great classes of vertebrated 
animals, which, though the best known and undoubtedly the most 
important group of the animal kingdom, has never received any 
generally accepted vernacular designation in our language. The 
unity of structure of the animals composing this class, and their 
definite demarcation from other vertebrates, were not recognised 
until comparatively modern times, and hence no word was thought 
of to designate what zoologists now term a mammal. The nearest 
equivalents in common use are "beast" and "quadruped," both of 
which, however, cover a different ground, since they are often used 
to include the larger four-footed reptiles, and to exclude certain un- 
doubted mammals, as Man, Bats, and AVhales. 

The limits of the class as now understood by zoologists are 
perfectly well defined, and, although certain forms still existing on 
the earth (but not those mentioned above as excluded by the popular 
idea) are of exceedingly aberrant structure, and exhibit several well- 
marked characters connecting them with the lower vertebi'ated 
groups, common consent retains them in the class with which the 
great proportion of their characters ally them, and hitherto no 
traces of any species showing still more divergent or transitional 
characters have been discovered. There is thus an interval, not 
bridged over by any known forms, between mammals and other 

1 



INTRODUCTORY 



vertebrates ; although recent discoveries have shown evidence of a 
more or less marked affinity between the most generalised mammals 
and a peculiar group of extinct reptiles known as the Anomodontia 
(or Theromora), which are themselves nearly related to the equally 
extinct Labyrinthodont amphibians of the Paheozoic and Mesozoic 
epochs. 

In the gradual order of evolution of living beings, mammals, 
taken altogether, are certainly the highest in organisation, as, with 
the possible exception of birds, they were the last to appear on 
the earth's surface. But, as in speaking of all other large and 
greatly differentiated groups, this expression must not be understood 
in too limited a sense. The tendency to gradual perfection for 
their particular station in life, which all groups manifest, leads 
to various lines of specialisation, or divergence from the common 
or general type, which may or may not take the direction of 
elevation. A too complex and sensitive condition of organisation 
may in some circumstances of life be disadvantageous, and modifi- 
cation may then take place in a retrograde direction. Thus in 
mammals, as in other classes, there are low as well as high forms, 
but by any tests that can be applied — especially those based on 
the state of development of the central nervous system — it will 
be seen that the average exceeds that of any other class ; that 
the class contains many species far excelling those of any other 
in perfection of structure, and especially one form which is un- 
questionably the culminating point yet arrived at amongst organised 
beings. 

With regard to the time of the first appearance of mammals 
upon the earth, the geological record is provokingly imperfect. At 
the commencement of the Tertiary period they were abundant, and 
already modified into most of the leading types at present existing. 
It was at one time thought that they first came into being at this 
date, but the discovery of more or less fragmentary remains of 
numerous and generally small species has revealed the existence of 
some forms of the class at various periods throughout almost the 
whole of the age of the deposition of the Secondary or Mesozoic 
rocks. This subject will be reverted to later on. 

It hardly need be said that mammals are vertebrated animals, 
and possess all the characteristics common to the members of that 
division of the animal kingdom. They are separated from the 
TcMhyopsida (fishes and amphibians), and agree with the Sawopsida 
(reptiles and birds) in the possession during their development of 
an amnion and allantois, and in never having external branchite or 
gills. They differ from reptiles and resemble birds in being warm- 
blooded, and having a heart with four cavities and a complete 
double circulation. They differ from both birds and reptiles in the 
red corpuscles of the blood being non-nucleated and, with very few 



INTRODUCTORY 



exceptions, circular in outline ; in the lungs being freely suspended 
in a thoracic cavity, separated from the abdomen by a complete 
muscular partition — the diaphragm — which is the principal agent 
in inflating the lungs in respiration ; in having but one aortic arch, 
which curves over the left bronchus ; in the skin being more or less 
clothed with hair ; in the greater perfection of the commissural 
system of the cerebral hemispheres, which has either a complete 
corpus callosum, or an incomplete one associated with a very 
large anterior commissure ; in having no syrinx or inferior vocal 
organ, but a complete larynx at the upper end of the trachea ; 
in having a mandible of which each ramus (except in very early 
developmental conditions) consists of a single bone on each side, 
articulating to the squamosal without the intervention of a quad- 
rate bone ; in having a pair of laterally placed occipital condyles 
instead of one median one ; and in the very obvious character of 
the female being provided with mammary glands, by the secretion 
of which the young (usually produced alive, although in the lowest 
forms by means of externally hatched eggs) are nourished for some 
time after birth. 

In common with all vertebrated animals, mammals never have 
more than two pairs of limbs ; as the larger number live ordinarily 
on the surface of the earth, in the great majority of the class 
both pairs are well-developed and functional, and adapted for terres- 
trial progression. Mammals are, however, by no means limited to 
this situation. Thus some species spend the greater part of their 
lives beneath the surface, their fore limbs being specially modified 
for burrowing ; others, again, are habitually arboreal, their limbs 
being fitted for climbing or hanging to boughs of trees ; some are 
as aerial as birds, the fore limbs being developed into wings of a 
special character ; while in others which are as aquatic as fishes, 
the limbs assume the form of fins or paddles. In many of the 
latter the hinder extremities are either completely suppressed, or 
present only in a rudimentary state. In no known mammal are 
the fore limbs absent. 

The hinder extremity of the axis of the body is usually prolonged 
into a tail, which may be a mere pendent appendage, or may be 
modified to perform various functions, as grasping boughs in 
climbing, or even gathering food, in the case of the prehensile- 
tailed Monkeys and Opossums, swimming in the Cetacea, and acting 
as a flap to drive away troublesome insects from the skin in the 
Ungulata. 

The state of development of the young at the time of birth 
varies greatly in the different groups. Thus among the Marsupials 
where there is no connection during infra-uterine life between the 
circulatory systems of the parent and the fcetus, the young are 
born in an exceedingly imperfectly developed condition. For their 



INTRODUCTORY 



protection the mother, in a large number of cases, has a special 
pouch enclosing the mammae, into which the young are transferred 
at birth, and in which they remain till they are well developed. 
Among the higher, or Placental types, however, where a connection 
exists between the maternal and foetal circulations previous to birth, 
the young are always born in a much more highly developed state 
than among the Marsupials, although we meet with great variations 
in this respect. In those forms which habitually live in holes, like 
many Rodents, the young are always very helpless at birth ; and 
the same is also true of many of the Carnivora, which are well able 
to defend their young from attack. In the great order of 
Ungulate, or Hoofed Mammals, where in the majority of cases 
defence from foes depends upon fleetness of foot, or upon huge 
corporeal bulk, the young are born in a very highly developed 
condition, and are able almost at once to run by the side of the 
parent. This state of relative maturity at birth reaches its highest 
development in the Cetacea, where it is evidently, associated with 
the peculiar conditions under which these animals pass their 
existence. In the Primates, however, we again find the young 
produced in a more or less helpless condition, and requiring a long- 
period before they attain their full development, this being more 
especially the case with those higher forms which approximate in 
structure to man. 

In point of size mammals vary to a greater extent than the 
existing members of any one class of animals, and include the 
largest living inhabitants of the earth. The extremes of size are 
marked on the one hand by the whale known as Sibbald's Rorqual, 
which attains a length of eighty feet and a weight of nearly as many 
tons, and on the other by the Pigmy-Shrew and the minute Harvest- 
mouse, which can climb a stem of wheat. 

Of all the living creatures inhabiting our globe, mammals are by 
far the most important in their economic uses, since, in addition to 
being the only animals capable of labour for human benefit, the}' 
furnish the greater portion of the animal food of many races of man, 
and likewise a large amount of their clothing. In these respects 
the Ungulates hold the first place. 

As regards employment for labour, with the exception of the 
Dogs used for sleighing by the Esquimaux, and those which among 
some European nations draw light carts, all the mammals in general 
use are Ungulates. Of the first importance are the Horses and 
Asses, which are employed as beasts of draught or burden over 
nearly the whole globe. Among many nations, however, cattle, as 
represented by the true Oxen, the Buftalos, and the Yaks of Tibet, 
occupy a still more important position, while in the highlands of 
Tibet Sheep are largely used for carrying burdens. In other regions, 
again, the place of the Horse and the Ass is taken by the Camels, 



INTRODUCTORY 5 



which are peculiarly fitted for traversing parched and arid deserts, 
while in the Andes Ave find the Llamas serving the same office. 
In Lapland and other parts of the northern regions the Reindeer is 
the main agent employed in draught. Lastly, we must not omit 
to mention the Indian Elephant, •which, from its vast strength, is so 
useful in transport through the wilder parts of its native country. 

As regards food, we again find the Ungulates, and more 
especially the Artiodactyle division, taking the foremost place ; and 
in this connection Ave haA r e only to mention, among animals .kept 
in a domestic condition, SAvine, Cattle, Sheep, and Goats — the three 
latter affording not only their flesh, but also milk and its resulting 
cheese and butter. To many races, however, Mares and Camels are 
the chief milk producers, Avhile the Laps make use of the milk of 
the Reindeer. The Rodents, as represented by Hares and Rabbits, 
occupy a minor position as furnishers of food. 

In relation to clothing, the Ungulates are likeAvise of paramount 
importance, as exemplified by the avooI of the Sheep, Avhich is so 
valuable on account of its peculiar property of felting. Furs, 
hoAvever, are mostly yielded by mammals of other orders, among 
Avhich the Fur-seals are perhaps the most important at the present 
day. Many other Carnivores yield valuable furs, among Avhich may 
be mentioned Bears, Foxes, Racoons, Skunks, Minks, Otters, and 
Ermines. Of less importance are certain Rodents, such as the 
Squirrels, Rabbits, Hares, etc., Avhile the hair of the Beaver Avas 
formerly much sought after for the manufacture of hats. Returning 
to the Ungulates, Ave may notice the importance of horse-hair, the 
employment of camel's hair for brushes, and the many uses of the 
bristles of the pig. Some of the Monkeys yield fur Avhich has 
been extensively used. Leather, again, is almost exclusively 
supplied by mammals, and mainly by the Ungulates. 

Three other important products, namely horn, buck's -horn, and 
ivory, are likeAvise obtained solely from the same great order. 
Horn, as we shall notice in the sequel, is the sheath covering the 
bony horn-cores of the Oxen, A\-hile buck's-horn is the commercial 
term applied to the antlers of the Deer, which are largely used for 
knife-handles and other purposes. True ivory is the product of 
the tAvo species of Elephant ; but other kinds of ivory are obtained 
from the teeth of the Sperm Whale and the tusks of the Walrus and 
Hippopotamus, the latter kind having been extensiA^ely employed 
some years ago for artificial teeth. For many purposes the place of 
ivory is taken by bone, this being mostly obtained from Ungulates. 
The bones of Camels are of an especially firm texture and good 
colour, and are largely employed in India for inlaying. Other 
important uses of bones are in the form of bone-dust as manure, 
and also as a source of phosphoric acid. The horns of the African 
Rhinoceros and the hide of the Hippopotamus are occasionally 



INTRODUCTORY 



manufactured into small canes or whips. Horns and hoofs are also 
largely employed in the manufacture of glue. 

Formerly the so-called whalebone, or more properly baleen, 
was much used, especially to form the ribs of umbrellas and in 
stiffening ladies' apparel, but the gradual destruction of the Eight 
Whales, its only source of supply, has largely restricted its use of 
late years. 

The Cetacea are also of great economical importance from the 
abundance of oil yielded by the thick layer of blubber underlying 
the skin. Large quantities of valuable oil are also furnished by 
the Walrus and the Seals. Spermaceti, which was at one time 
extensively used in the manufacture of candles, is obtained from ;i 
large cavity in the head of the Sperm Whale or Cachalot, and also 
from the Hyperoodon or Bottle-nosed Whale. 

The nature of ambergris, a peculiar substance found floating on 
the surface of the sea and employed in perfumery, was long a 
matter of controversy ; but it appears to be an intestinal concretion 
of the Sperm Whale. Other substances of more importance to the 
perfumer are musk, the product of the Musk-Deer of the Himalaya, 
and civet, which is obtained from the so-called Civet Cat and other 
allied Carnivores. A secretion of the Beaver has also been used in 
perfumery and in medicine. 



CHAPTER II 

GENERAL ANATOMICAL CHARACTERS 
I. TEGUMENTARY STRUCTURES 

Hair. — The external surface of the greater number of members of 
the class is thickly clothed with a peculiarly modified form of 
epidermis, commonly called hair. This consists of hard, elongated, 
slender, cylindrical or tapering, filiform, unbranched masses of 
epidermic material, growing from a short papilla sunk at the 
bottom of a follicle in the derm or true skin. Such hairs upon 
different parts of the same animal, or upon different animals, assume 
various forms, and are of various sizes and degrees of rigidity, — as 
seen in the delicate soft velvety fur of the Mole, the stiff* bristles 
of the Pig, and the spines of the Hedgehog and Porcupine, 
all modifications of the same structures. Each hair is composed 
usually of a cellular pithy internal portion, containing much air, 
and a denser or more horny cortical part. In some animals, as 
Deer, the substance of the hair is almost entirely composed of the 
medullary or cellular substance, and it is consequently very easily 
broken ; in others the horny part prevails almost exclusively, as in 
the bristles of the Wild Boar. In the Three-toed Sloth (Bradypus) 
the hairs have a central horny axis and a pithy exterior. Though 
generally nearly smooth, or but slightly scaly, the surface of some 
hairs is strongly imbricated, notably so in some Bats ; while in the 
Two-toed Sloth (Cholcepus) the hairs are longitudinally grooved or 
fluted. Though usually more or less cylindrical or circular in 
section, hairs are often elliptical or flattened, as in the curly-haired 
races of men, the terminal portion of the hair of Moles and Shrews, 
and conspicuously in the spines of the Rodents Xerus and Platacantho- 
mys. Hair having a property of mutual cohesion or "felting," 
which depends upon a roughened scaly surface and a tendency to 
curl, as in domestic Sheep (in which animal this property has been 
especially cultivated by selective breeding), is called " wool." 



8 GENERAL ANATOMICAL CHARACTERS 

In a large number of mammals hairs of one kind only are 
scattered pretty evenly over the surface ; but in many there are two 
kinds, one longer, stiffer, and alone appearing on the surface, and 
the other shorter, finer, and softer, constituting the under fur, 
analogous to the down of birds. This under fur, or pashm as it is 
called by the natives of Kashmir, is especially abundant in the 
mammals inhabiting the cold plateau of Tibet and the adjacent 
regions. In many cases hairs of a different character from those of 
the general surface grow in special regions, forming ridges or tufts 
on the median dorsal or ventral surface or elsewhere. The tail is 
very often completed in this way by variously disposed elongated 
hairs. The margins of the eyelids are almost always furnished with 
a special row of stifhsh hairs, called cilia or eyelashes ; and in most 
mammals specially modified hairs, constituting the vibrissa' or 
whiskers, and endowed, through the abundant nerve supply of their 
basal papillae, with special tactile powers, grow from the lips and 
cheeks. In some mammals the hairy covering is partial and limited 
to particular regions ; in others, as the Hippopotamus and the Sirenia, 
though scattered over the whole surface, it is extremely short and 
scanty ; but in none is it reduced to so great an extent as in the 
Cetacea, in which it is limited to a few small bristles confined to the 
neighbourhood of the lips and nostrils, and often only present in 
the young or even foetal condition. 

Some kinds of hairs, as those of the mane and tail of the Horse, 
appear to persist throughout the life-time of the animal ; but more 
generally, as in the case of the body hair of the same animal, they 
are shed and renewed periodically, generally annually. Many 
mammals have a longer hairy coat in winter, which is shed as 
summer comes on ; and some few, which inhabit countries covered 
in winter with snow, as the Arctic Fox, Variable Hare, and Ermine, 
undergo a complete change of colour in the two seasons, being- 
white in winter, and gray or brown in summer. The several species 
of Cape Mole (Chrysochloris), the Desmans or Water Moles (Myogale), 
and Potarnogale velox, are remarkable as being the only mammals 
whose hair reflects those iridescent tints so common in the feathers 
of tropical birds. 

The principal and most obvious purpose of the hairy covering is 
to protect the skin against external influences, especially cold and 
damp. Its function in the hairless Cetacea is supplied by the 
specially modified and thickened layer of adipose tissue beneath the 
skin, called "blubber." 

Colour. — From the consideration of hair we are easily led to 
that of colour. As a general rule, bright and primary colours are 
absent in the class ; but among the Baboons we find brilliant patches 
of scarlet or blue on some of the bare portions of the body, and one 
of the South American Monkeys (Brachyums) has its whole face of 



TEGUMEA'TARY STRUCTURES 



a bright crimson. The most general colours are various shades of 
gray, brown, and tawny, with a frequent tendency to whiteness of 
the ventral surface of the body; but among the Squirrels, and more 
especially those provided with a parachute for flying, we find brilliant 
russets, passing into orange and red. Dark brown or black is also 
not very uncommon, as in the Bears and the Sable Antelope of 
South Africa. Entirely white mammals are rare, and mostly 
characteristic of the polar regions, or of countries having a long 
and snowy winter. An entirely white Bat (Diclidurus alius) occurs, 
however, in South America. In the large majority of mammals 
that exhibit a varied coloration, the upper and most exposed parts 
of the surface present the richest and darkest colours, the under 
parts being pale or often quite white. The Katels, Gluttons, jElurus, 
Hamsters, and some others are exceptions to this rule. A large 
number of mammals having a ground colour of gray, tawny, or dun 
are marked by stripes or spots, which are generally of a darker hue 
than the ground colour, as in many Carnivora, but more rarely are 
lighter, as in the Fallow and Axis Deer and several species of Ante- 
lope. These stripes very generally run transversely to the axis of the 
body, as in the Tasmanian Thylacine, the Tiger, and the Zebra ; but 
they may be longitudinal, as in several of the Civet family. There has 
been considerable discussion as to whether the striped or the spotted 
is the more primitive type of coloration ; but no very conclusive 
arguments have been brought forward in favour of either view. It 
is, however, manifest that in several groups of mammals there is a 
tendency to lose the spots, and more rarely the stripes, and to 
assume a uniform colour. Thus the young of nearly all the species 
of Deer are spotted, whereas the adults of only the Fallow and 
Axis Deer are so marked. The same is true of most of the Pigs ; 
and the young of the Malayan and American Tapirs are marked 
by light- coloured stripes and spots on a dark ground. In like 
manner the young of the Lion and the Puma exhibit distinct spots 
which disappear with advancing age. In most of our domestic 
horses of various shades of bay and brown we may detect " dappling " 
on the under hair when the outer coat has been removed, which 
is not apparent on the surface of the latter. Many varieties of 
the Ass and the Horse also exhibit a tendency to the presence of 
stripes on the legs, which would seem to indicate a descent from a 
striped Zebra-like type. 

A peculiar feature, which is, however, common to many other 
groups of animals, is the tendency to what is known as melanism, 
or the production of black or dark individuals or races of particular 
species, due to an excess of pigment in the skin and hair. Thus Ave 
may have black Leopards and Jaguars, black Wolves, and black 
Rabbits. 

The opposite to melanism, and of more frequent occurrence, is 



io GENERAL ANATOMICAL CHARACTERS 

albinism — a condition in which the pigment or colouring matter 
usually present in the tissues constituting the external coverings of 
the body, and which gives them their characteristic hue, is absent. 
When it occurs the hair is of an opaque white, the claws, hoofs, etc., of 
a pale horn-colour, and the skin and eyes pink, in consequence of the 
colour of the blood which circulates through them being no longer 
concealed by the stronger hues of the pigments. An animal in this 
condition is called an albino. In complete albinism there is a total 
absence of pigment throughout the system. This condition occurs 
occasionally as an individual peculiarity among wild animals of 
many kinds ; but it has never been perpetuated among them in dis- 
tinct races or species. The disadvantage of absence of pigment 
in the eye, causing a certain amount of intolerance of light, is 
probably sufficient to account for this. Several races of true 
albinos, as White Ferrets, Rabbits, Rats, and Mice, have, however, 
been established under the protection of man, and in them this ab- 
normal condition is propagated from generation to generation. 

Partial albinism — a condition in which the absence of pigment 
is limited to portions of the surface, or, at all events, does not extend 
to the eyes — is much more common as an individual variation both 
in domestic and in wild animals. It is possible that the artificial 
conditions incident to domestication increase the tendency to its 
occurrence ; but, whether this be so or not, it certainly becomes 
perpetuated more frequently among domesticated than among wild 
animals. This may be accounted for partly by its proving of no 
disadvantage to them, and partly by the frequent selection by man 
of animals of such colour in preference to others. The result is that 
there is no completely domestic animal of which white races do not 
exist. On the other hand, to most wild animals even partial 
albinism seems to be a disadvantage in the struggle for existence, 
since, except in the case of species inhabiting lands continually 
covered with snow, it renders them more conspicuous objects both 
to their enemies and their prey, and hence it is rarely perpetuated. 
In northern regions, however, a large proportion of species are 
regularly and normally of a white colour, either, as the Polar Bear, 
all the year through, or, as the Ermine or Stoat, Arctic Fox, and 
Alpine Hare, during the winter season. The coloration in these 
cases is obviously protective, as it is also to a great extent in many 
other instances throughout the class. 

Among conspicuously coloured mammals, it has been observed 
that the vertical black and tawny stripes of the Tiger harmonise so 
well with the brown and green grasses of its native jungle as to 
render the animal almost invisible when lying among them ; while 
the dappled hide of the Giraffe is said to agree equally well 
with the chequered splashes of light and shade in the clumps of tall 
mimosas among which it feeds. The uniformly tawny hue of the 



TEGUMENTARY STRUCTURES n 

Lion accords well with the prevailing tint of its native desert ; and 
any one who has seen an Elephant or Buffalo in the dee}) shades of 
an Indian forest will realise how perfectly adapted is their dull, 
slaty colour to concealment in such a spot. The dun colour of the 
Wild Ass of India is equally well suited to the sandy deserts of 
Kutch ; it is also stated that the brilliant stripes of the Zebras of 
Africa are arranged in such proportion as exactly to match the pale 
tint which arid ground possesses when seen by moonlight. 1 The 
most remarkable instance of protective coloration is, however, to be 
found in the Sloths of South America, in which the coarse gray 
hairs so closely resemble a mass of lichenous growth that it is 
almost impossible to distinguish these animals when at rest from 
the gnarled and lichen-clad boughs from which they suspend them- 
selves. This resemblance is increased by the fact that the hairs 
actually develop a growth of lichens upon themselves. That the 
sombre coloration of these animals has been produced to harmonise 
with their present surroundings seems to be evident by the circum- 
stance that when the long hair is plucked off the under fur is seen 
to present a bold alternation of black and yellow stripes, which 
may probably be regarded as the original primitive coloration of 
this group. 

Scales, etc. — True scales, or flat imbricated plates of horny 
material, covering the greater part of the body, so frequently 
occurring in reptiles, are found only in one family of mammals, the 
Manidxe or Pangolins ; but these are also associated with hairs 
growing from the intervals between the scales, or on the parts of 
the skin not covered by them. Similarly, imbricated epidermic 
productions form the covering of the under surface of the tail of 
the flying Eodents of the genus Anomalurus ; and flat scutes, with 
the edges in apposition, and not overlaid, clothe both surfaces of 
the tail of the Beaver, Rats, and others of the same order, and also 
of some Insectivores and Marsupials. The Armadillos alone have 
an ossified exoskeleton, composed of plates of true bony tissue, 
developed in the derm or corium, and covered with scutes of horny 
epidermis. Other epidermic appendages are the horns of Ruminants 
and Rhinoceroses, — the former being elongated, tapering, hollow 
caps of hardened epidermis of fibrillated structure, fitting on and 
growing from conical projections of the frontal bone, and always 
arranged in pairs, while the latter are of similar structure, but 
solid and without any internal bony support, and (in all existing 
species) situated in the median line. Callosities, or bare patches 
covered with hardened and thickened epidermis, are found covering 
the pads under the soles of the feet and undersurfaces of the 
toes of nearly all mammals, upon the ischial tuberosities of many 
Apes, the sternum of Camels, on the inner side of the limbs of the 

1 Galton's South Africa, p. 187. 



12 GENERAL ANATOMICAL CHARACTERS 



Equidce, the grasping under surface of the tail of the prehensile-tailed 
Monkeys, etc. The greater part of the skin of both species of 
one-horned Asiatic Ehinoceros is immensely thickened and stiffened 
by increase of the tissue both of the derm and epiderm, con- 
stituting the well-known jointed "armour-plated" hide of those 
animals. 

Nails, Claws, and Hoofs. — With very few exceptions, the terminal 
extremities of the digits of both limbs are more or less protected or 
armed by epidermic plates or sheaths, constituting the various forms 
of nails, claws, or hoofs. These are wanting in the Cetacea alone. 
A perforated spur, with a special secreting gland in connection with 
it, is found attached to the hind leg of the males of the three genera 
of Monotremata, Ornithorhynehus, Proechidna, and Echidna. 

Odour - secreting Glands. — Besides the universally distributed 
sebaceous glands connected Avith the pilose system, most mammals 
have special glands situated in modified portions of the integument, 
often involuted to form a shallow recess or a deep sac with a narrow 
opening, situated in various parts of the surface of the body, and 
secreting odorous substances, by the aid of which individuals 
appear to recognise one another, and probably affording the princi- 
pal means by which wild animals are able to become aware of 
the presence of other members of the species, even at great dis- 
tances. Although the commencement of the modifications of 
portions of the external covering for the formation of special 
secretions may be at present difficult to understand, the principle 
of natural selection will readily explain how such organs become 
fixed and gradually increase in development in any species, especi- 
ally as there would probably be a corresponding modification and 
increased sensibility of the olfactory organs. Such individuals as 
by the intensity and peculiarity of their scent had greater power of 
attracting the opposite sex would certainly be those most likely to 
leave descendants to inherit and in their turn propagate the modi- 
fication. 

To this group of structures belong the suborbital gland or 
" crumen " of Antelopes and Deer, the frontal gland of the Muntjak 
and of Bats of the genus Hipposiderus, the submental gland of the 
Chevrotains and of Taphozous and some other Bats, the post-auditory 
follicle of the Chamois, the temporal gland of the Elephant, the 
lateral glands of the Musk-Shrew, the dorsal gland of the Peccary, 
the inguinal glands of Antelopes, the preputial glands of the Musk- 
Deer and Beaver (already alluded to in connection with the use 
made of their powerfully odorous secretion in medicine and per- 
fumery) and also of the Swine and Hare, the anal glands of Carni- 
vora, the perineal gland of the Civet (also of commercial value), the 
caudal glands of the Fox and Goat, the gland on the humeral 
membrane of Bats of the genus Saccopteryx, the post-digital gland of 



DENTAL SYSTEM 13 

the Rhinoceros, the inter-digital glands of the Sheep and many 
Ruminants, and numerous others. In some of these cases the 
glands are peculiar to, or more largely developed in, the male ; in 
others they are found equally developed in both sexes. 



II. DENTAL SYSTEM 

The dental system of mammals may be considered rather 
more in detail than space permits for some other portions of their 
structure, not only on account of the important part it plays in the 
economy of the animals of this class, out also for its interest to 
zoologists as an aid in the classification and identification of species. 
Owing to the imperishable nature of their tissues, teeth are 
preserved for an indefinite time, and in the case of extinct 
species frequently offer the only indications available from which 
to derive an idea of the characters, affinities, and habits of the 
animals to which they once belonged. Hence even their smallest 
modifications have received great attention from comparative 
anatomists, and they have formed the subject of many special 
monographs. 1 

Teeth are present in nearly all mammals, and are applied 
to various purposes. They are, however, mainly subservient 
to the function of alimentation, being used either in procuring 
food, by seizing and killing living prey or gathering and biting 
off portions of vegetable material, and more indirectly in tearing 
or cutting through the hard protective coverings of food sub- 
stances, as the husks and shells of nuts, or in pounding, crushing, 
or otherwise mechanically dividing the solid materials before 
swallowing, so as to prepare them for digestion in the stomach. 
Certain teeth are also in many animals most efficient weapons of 
offence and defence, and for this purpose alone, quite irrespective 
of subserviency to the digestive process, are they developed in the 
male sex of many herbivorous animals, in the females of which 
they are absent or rudimentary. 

Teeth belong essentially to the tegumentary or dermal system 
of organs, and, as is well seen in the lower vertebrates, pass by 
almost insensible gradations into the hardened spines and scutes 
formed upon the integument covering the outer surface of the 
body ; but in mammals they are more specialised in structure and 
limited in locality. In this class they are developed only in the 

1 L. F. E. Rousseau, Anatomic comjiaree du Systeme dentaire chez V Homme el 
chez les principaux Animaux, 2d ed., 1839 ; F. Cuvier, Des Dents des Mammiferes 
considere'es comme caracteres zoologiques, 1822-25 ; R. Owen, Odontograimy, 
1840-45 ; C. G. Giebel, OdontograpMe, 1855 ; C. S. Tomes, Manual of Dental 
Anatomy, Human and Comparative, 3d ed., 1889. 



i 4 GENERAL ANATOMICAL CHARACTERS 

giims or fibro-mucous membrane covering the alveolar borders of 
the upper and lower jaws, or, in other words, the premaxillary 
and maxillary bones and the mandible. In the process of develop- 
ment, for the purpose of giving them that support which is needful 
for the performance of their functions, they almost always become 
implanted in the bone, — the osseous tissue growing up and mould- 
ing itself around the lengthening root of the tooth, so that 
ultimately they become apparently parts of the skeleton. In no 
mammal, however, does ankylosis or bony union between the 
tooth and jaw normally take place, as in many fishes and reptiles, 
— a vascular layer of connective tissue, the alveolo-dental mem- 
brane, always intervening. 1 The presence of two or more roots, 
frequently met with in the cheek-teeth of mammals, implanted in 
corresponding distinct sockets of the jaw, is now peculiar to animals 
of this class. 2 

Structure. — The greater number of mammalian teeth when fully 
formed are not simple and homogeneous in structure, but are com- 
posed of several distinct tissues, which are enumerated below. 

The pulp, a soft substance, consisting of a very delicate 
gelatinous connective tissue, in which numerous cells are imbedded, 
and abundantly supplied with blood-vessels and nerves, constitutes 
the central axis of all the basal part- of the tooth, and affords the 
means by which the vitality of the whole is preserved. The 
nerves which pass into the pulp and endow the tooth with 
sensibility are branches of the fifth pair of cranial nerves. The 
pulp occupies a larger relative space, and performs a more important 
purpose, in the young growing tooth than afterwards, as by the 
calcification and conversion of its outer layers the principal hard 
constituent of the tooth, the dentine, is formed. In teeth which 
have ceased to grow the pulp occupies a comparatively small space, 
which in the dried tooth is called the pulp-cavity. This communi- 
cates with the external surface of the tooth by a small aperture at 
the apex of the root, through which the branches of the blood- 
vessels and nerves, by which the tooth receives its nutrition and 
sensitiveness, pass in to be distributed in the pulp. In growing 
teeth the pulp-cavity is widely open, while in advanced age it often 
becomes obliterated, and the pulp itself entirely converted into 
bone-like material. 

The dentine or ivory forms the principal constituent of the 
greater number of teeth. When developed in its most character- 
istic form, it is a very hard but elastic substance, white, with a 
yellowish tinge, and slightly translucent. It consists of an organic 

1 The lower incisors of some species of Shrews are, however, said to become 
aukyloaed to the jaw in adult age. 

- The teeth of the extinct Dinosaurian reptile Triceratqps have two distinct 
roots, placed transversely to the axis of the jaws. 



DENTAL SYSTEM 15 



matrix, something like, but not identical with, that of bone, richly 
impregnated with calcareous salts (chiefly calcium phosphate), these 
constituting in a fresh human tooth 72 per cent of its weight. 
When subjected to microscopical examination it is seen to be every- 
where permeated by nearly parallel branching tubes which run, 
in a slightly curving or wavy manner, in a general direction from 
the centre towards the free surface of the tooth. These tubes com- 
municate by open mouths with the pulp-cavity, and usually ter- 
minate near the periphery of the dentine by closed ends or loops, 
though in Marsupials and certain other mammals they penetrate 
into the enamel. They are occupied in the living tooth by soft 
gelatinous fibrils connected with the cells of the pulp. A variety 
of dentine, permeated by canals containing blood-vessels, met with 
commonly in fishes and in some few mammals, as the Megatherium, is 
called vaso-dentine. Other modifications of this tissue occasionally 
met with are called osteo-dentine and secondary dentine, — the 
latter being a dentine of irregular structure which often fills up the 
pulp-cavity of old animals. 

The enamel constitutes a thin investing layer, complete or 
partial, of the outer or exposed and working surface of the dentine 
of the crown of the teeth of most mammals. This is the hardest 
tissue met with in the animal body, containing from 95 to 97 per 
cent of mineral substances (chiefly calcium phosphate and some 
carbonate, with traces of fluoride). Its ultimate structure consists 
of prismatic fibres, placed generally with their long axes at right 
angles to the free surface of the tooth. Enamel is easily distin- 
guished from dentine with the naked eye by its clear, bluish-white, 
translucent appearance. 

The cement or crusta petrosa is always the most externally placed 
of the hard tissues of which teeth are composed, as will be under- 
stood when the mode of development of these organs is considered. 
It is often only found as a thin layer upon the surface of the root ; 
but sometimes, as in the complex-crowned molar teeth of the Horse 
and Elephant, it is a structure which plays a very important part, 
covering and filling in the interstices between the folds of the 
enamel. In appearance, histological structure, and chemical com- 
position it is closely allied to osseous tissue, containing lacuna? and 
canaliculi, though only when it is of considerable thickness are 
Haversian canals present in it. 

Development. — The two principal constituents of the teeth, the 
dentine and the enamel, are developed from the two layers of the 
mucous membrane of the jaw — the dentine from the deeper or vas- 
cular, the enamel from the superficial or epithelial layer. The latter 
dips down into the substance of the gum, and forms the enamel-organ 
or germ, the first rudiment of the future tooth, which is constantly 
present even in those animals in which the enamel is not found as a 



16 GENERAL ANATOMICAL CHARACTERS 



constituent of the perfectly-formed tooth. Below the mass of epi- 
thelial cells thus embedded in the substance of the gum, and remaining 
connected by a narrow neck of similar structure with the epithelium 
of the surface, a portion of the vascular areolar tissue becomes 
gradually separated and defined from that which surrounds it, and 
assumes a distinct form, which is that of the crown of the future 
tooth, — a single cone in the case of simple teeth, or with two or 
more eminences in the complex forms. This is called the dental 
papilla or dentine germ, and by the gradual conversion of its tissue 
into dentine the bidk of the future tooth is formed, the uncalcified 
central portion remaining as the pulp. The conversion of the 
papilla into hard tissue commences at the outer surface of the apex, 
and gradually proceeds downwards and inwards, so that the form of 
the papilla exactly determines the form of the future dentine, and 
no alteration either in shape or size of this portion of the tooth, 
when once calcified, can take place by addition to its outer surface. 
In the meanwhile, calcification of a portion of the cells of the enamel- 
organ, which adapts itself like a cap round the top of the dentinal 
papilla, and has assumed a somewhat complex structure, results in 
the formation of the enamel -coating of the crown of the tooth. 
While these changes are taking place the tissues immediately sur- 
rounding the tooth-germ become condensed and differentiated into 
a capsule, which appears to grow up from the base of the dental 
papilla, and encloses both this and the enamel-germ, constituting 
the follicle or tooth-sac. By the ossification of the inner layer of 
this follicle the cement is formed. This substance, therefore, unlike 
the dentine, increases from within outwards, and its growth may 
accordingly be the cause of considerable modification of form and 
enlargement, especially of the roots, of certain teeth, as those of 
Seals and some Cetacea. The delicate homogeneous layer coating the 
enamel surface of newly-formed teeth, in which cement is not found 
in the adult state, and known as Xasmyth's membrane, is considered 
by Tomes as probably a film of this substance, too thin to exhibit 
its characteristic structure, though by others it is believed to be 
derived from the external layer of the enamel-organ. The homology 
of the teeth Avith the dermal appendages, hairs, scales, and claws, 
has already been alluded to, and it will now be seen that in both cases 
two of the primary embryonic layers are concerned in their develop- 
ment — the mesoblast and epiblast — although in very different pro- 
portions respectively. Thus in the hair or nail the part derived from 
the epiblast forms the principal bulk of the organ, the mesoblast 
only constituting the papilla or matrix. But in the tooth the epi- 
blastic portion is limited to the enamel, and is always of relatively 
small bulk and often absent, while the dentine (the principal con- 
stituent of the tooth) and the cement are formed from the mesoblast. 
"When more than one set of teeth occur in mammals, those of 



DENTAL SYSTEM 17 



the second set are developed in a precisely similar manner to the 
first, bnt the enamel-germ, instead of being derived directly from an 
independent part of the oral epithelium, is formed from a budding 
out of the neck of the germ of the tooth succeeded. In the case of 
the true molars, which have no predecessors, the germ of the first 
has an independent origin, but that of the others is derived from the 
neck of the germ of the tooth preceding it in the series. The 
foundations of the permanent teeth are thus laid as it were almost 
simultaneously with those of their predecessors, although they 
remain in many cases for years before they are developed into 
functional activity. 

Although the commencement of their formation takes place 
at an early period of embryonic life, teeth are in nearly all mam- 
mals still concealed beneath the gum at the time of birth. The 
period of eruption, or " cutting " of the teeth as it is called, that is, 
their piercing through and rising above the surface of the mucous 
membrane, varies much in different species. In some, as Seals, the 
whole series of teeth appears almost simultaneously; but more often 
there are considerable intervals between the appearance of the 
individual teeth, the front ones usually coming into place first, and 
those at the back of the mouth at a later period. 

Farms <>f Teeth. — The simplest form of tooth may be exemplified 
on a large scale by the tusk of the Elephant (Fig. 1, I.) It is a 
hard mass almost entirely composed of dentine, of a conical shape 
at first, but during growth becoming more and more cylindrical or 
uniform in width. The enamel -covering, present on the apex in 
its earliest condition, soon disappears, but a thin layer of cement 
covers the circumference of the tooth throughout life. In section 
it will be seen that the basal portion is hollow, and contains a large 
conical pulp, as broad at the base as the tooth itself, and deeply 
imbedded in the bottom of a recess, or socket, in the maxillary 
bone. This pulp continues to grow during the lifetime of the 
animal, and at the same time is converted at its surface into dentine. 
The tooth therefore continually elongates, but the use to which the 
animal subjects it in its natural state causes the apex to wear away, 
at a rate generally proportionate to the growth at the base, other- 
wise it would become of inconvenient length and weight. Such 
teeth of indefinite growth are said to be "rootless," or to have 
"persistent pulps." 

One of the corresponding front teeth of man (Fig. 2, II. and III.) 
may be taken as an example of a very different condition. After its 
crown is fully formed by calcification of the germ, the pulp, though 
continuing to elongate, begins to contract in diameter ; a neck or 
slight constriction is formed ; and the remainder of the pulp is con- 
verted into the root (often, but incorrectly, called "fang"), a taper- 
ing conical process imbedded in the alveolar cavity of the bone, and 

2 



i8 



GENERAL ANATOMICAL CHARACTERS 



having at its extremity a minute perforation, through which the 
vessels and nerves required to maintain the vitality of the tooth enter 

the pulp -cavity, which is 




very different from the 
widely open cavity at 
the base of the growing 
tooth. When the crown 
of the tooth is broad and 
complex in character, in- 
stead of having a single root, 
it may be supported by 
two or more roots, each of 
which is implanted in a 
distinct alveolar recess or 
socket, and to the apex of 
which a branch of the com- 
mon pulp-cavity is continued 
(Fig. 1, IV.) Such teeth are 
called "rooted teeth." When 
they have once attained their 
position in the jaw, with the 
neck a little way above the 
level of the free margin of 
the alveolus, and embraced 
by the gum or tough fibro- 
vascular membrane covering 
the alveolar border, and hav- 
ing the root fully formed, 
they can never increase in 
length or alter their posi- 
tion ; if they appear to do 
so in old age, it being only 
in consequence of absorption 
and retrocession of the sur- 
alveolar 



rounding 



margins. 



Fio. 1. — Diagrammatic Sections of various forma of 
Teeth. I. Incisor or tusk of Elephant, with pulp- 
cavity persistently open at base. II. Human incisor 
during development, with root imperfectly formed, 
andpulp-cavitywidelyopenatba.se. III. Completely 

formed human incisor, with pulp-cavity contracted to Jf ? as often happens, their 
a small aperture at the end of the root. IV. Human c „____, -C^ ™r.o 

.;, , , , . t ,. ,, , r surface wears away in mas- 

molar, with broad crown and two roots. \. Molar of D »" ■"*»'« " _ J 

the Ox, with the enamel covering the crown deeply tication, it is never renewed. 

folded, and the depressions tilled up with cement. The TJjo ODen CavitV at the base 

surface is worn by use ; otherwise the enamel coating r , . . r j.i j l J 

would be continuous at the top of the ridges, in all of the imperfectly developed 

the figures the enamel is black, the pulp white, the tooth (Fig. 1, II.) Causes it 
dentine represented by horizontal lines, and the cement j._ resemble the Dersistent 
by dots. r i i 

condition of the rootless 
tooth. The latter is therefore a more primitive condition, the 
formation of the root being a completion of the process of tooth 
development. Functionally it is, however, difficult to say that the 



DENTAL SYSTEM 19 



one is a higher form than the other, since they both serve important 
and different purposes in the animal economy. 

As is almost always the case in nature, intermediate conditions 
between these two forms of teeth are met with. Thus some teeth, 
as the molars of the Horse, and of many Rodents, are for a time 
rootless, and have growing pulps producing very long crowns with 
parallel sides, the summits of which may be in use and beginning 
to wear away while the bases are still growing ; but ultimately the 
pulp contracts, forms a neck and distinct roots, and ceases to grow. 
The canine tusks of the Musk Deer and of the Walrus have 
persistent pulps, and are open at their base until the animal is of 
advanced age, when they close, and the pulp ceases to be renewed. 
The same sometimes happens in the tusks of very old Boars. 

The simplest form of the crown of a tooth is that of a cone ; 
but this may be variously modified. Thus it may be flattened, with its 
edges sharp and cutting, and pointed at the apex, as in the laterally 
compressed premolars of most Carnivora ; or it may be chisel- or 
awl-shaped, with a straight truncated edge, as in the human incisors ; 
or it may be broad, Avith a flat or rounded upper surface. Very 
often there is a more or less prominent ridge encircling the whole or 
part of the base of the crown just above the neck, called the cingu- 
lum, which serves as a protection to the edge of the gum in masti- 
cating, and is most developed in flesh -eating and insectivorous 
animals, in which the gums are liable to be injured by splinters of 
bone or other hard fragments of their food. The form of the 
crown is frequently rendered complex by the development upon its 
surface of elevations or tubercules called cusps or cones, or by 
ridges usually transverse, but sometimes variously curved or folded. 
When the crown is broad and the ridges are greatly developed, as 
in the molars of the Elephant, Horse, and Ox (Fig. 1, V.), the inter- 
spaces between them are filled with cement, which supports them 
and makes a solid compact mass of the whole tooth. When such a 
tooth wears away at the surface by friction against the opposed 
tooth of the other jaw, the different density of the layers of 
the substances of which it is composed — enamel, dentine, and 
cement — arranged in characteristic patterns, causes them to wear 
unequally, the hard enamel ridges projecting beyond the others, 
and thus giving rise to a grinding surface of great mechanical 
advantage. 

Succession. — The dentition of all mammals consists of a definite 
set of teeth, almost always of constant and determinate number, 
form, and situation, and, with few exceptions, persisting in a 
functional condition throughout the natural term of the animal's 
life. In many species these are the only teeth which the animal 
ever possesses, — the set which is first formed being permanent, or, if 
accidentally lost, or decaying in extreme old age, not being replaced 



2o GENERAL ANATOMICAL CHARACTERS 

by others. These animals are called Monophyodont. But in the 
larger number of mammals, certain of the teeth are preceded by 
others, which may be only of a very transient, rudimentary, and 
functionless character (being in the Seals, for example, shed either 
before or within a few days after birth), or may be considerably 
developed, and functionally occupy the place of the permanent teeth 
for a somewhat lengthened period, during the growth and develop- 
ment of the latter and of the jaws. In all cases these teeth 
disappear (by the absorption of their roots and shedding of the 
crowns) before the frame of the animal has acquired complete 
maturity, as evidenced by the coalescence of the epiphyses of the 
osseous system. As these teeth are, as a general rule, present 
during the period in which the animal is nourished by the milk of 
the mother, the name of "milk-teeth" (French dents cle lait, 
German milchztihne) has been commonly accorded to them, although 
it must be understood that the epoch of their presence is by no 
means necessarily synchronous with that of lactation. Animals 
possessing such teeth are called Diphyodont. No mammal is known 
to have more than two sets of teeth ; and the definite and orderly 
replacement of certain members of the series is a process of quite a 
different nature from the indefinite succession which takes place in 
all the teeth continuously throughout the lifetime of the lower 
vertebrates. 

AVhen the milk-teeth are well developed, and continue in place 
during the greater part of the animal's growth, as is especially the 
case with the Ungulata, and, though to a less degree, with the 
Primates and Carnivora, their use is obvious, since taken all together 
they form structurally a complete epitome on a small scale of the 
more numerous and larger permanent set (see Fig. 3), and, con- 
sequently, are able to perform the same functions, while time is 
allowed for the gradual maturation of the latter, and especially 
while the jaws of the growing animal are acquiring the size and 
strength sufficient to support the permanent teeth. Those animals, 
therefore, that have a well-developed and tolerably persistent set of 
milk-teeth may be considered to be in a higher state of development, 
as regards their dentition, than those that have the milk-teeth 
absent or rudimentary. 

It is a very general rule that individual teeth of the milk and 
permanent set have a close relationship to one another, being 
originally formed, as mentioned above, in exceedingly near proximity, 
and with, at all events so far as the enamel-germ is concerned, a 
direct connection. Moreover, since the latter ultimately come to 
occupy the position in the alveolar border temporarily held by the 
former, they are spoken of respectively as the predecessors or suc- 
cessors of each other. But it must be understood that milk-teeth 
may be present which have no successors in the permanent series, 



DENTAL SYSTEM 21 



and, what is far more general, permanent teeth may have no pre- 
decessors in the milk series. 

The complete series of permanent teeth of most mammals forms 
a complex machine, with its several parts adapted for different 
functions, — the most obvious structural modification for this purpose 
being an increased complexity of the individual components of the 
series from the anterior towards the posterior extremity of such 
series. Since, as has just been said, the complete series of the milk 
teeth often presents structurally and functionally a similar machine, 
but composed of fewer individual members, and the anterior of which 
are as simple, and the posterior as complex as those occupying 
corresponding positions in the permanent series, — and since the 
milk-teeth are only developed in relation to the anterior or lateral, 
never to the most posterior of the permanent series, — it follows 
that the hinder milk-teeth are usually more complex than the teeth 
of which they are the predecessors in the permanent series, and 
represent functionally, not their immediate successors, but those 
more posterior permanent teeth which have no direct predecessors. 
This character is clearly seen in those animals in which the various 
members of the molar series are well differentiated from each other 
in form, as the Carnivora, and also in Man. 

In animals which have two sets of teeth the number of those 
of the permanent series which are preceded by milk-teeth varies 
greatly, being sometimes, as in Marsupials and some Rodents, as 
few as one on each side of each jaw, and sometimes including the 
larger portion of the series. 

Although there are difficulties in some cases in arriving at a 
satisfactory solution of the question, it is, on the whole, safest to 
assume that when only one set of teeth is present, this corresponds 
to the permanent teeth of the Diphyodonts. When this one set 
is completely developed, and remains in use throughout the 
animal's life, there can be no question on this subject. When, on 
the other hand, the teeth are rudimentary and transient, as in the 
Whalebone Whales, it is possible to consider them as representing 
the milk series ; but there are weighty reasons in favour of the 
opposite conclusion. 1 

Arrangement, Homologies, and Notation of Teeth.— The teeth of 
the two sides of the jaws are always alike in number and character, 

1 This and other questions concerning the homologies, notation, and suc- 
cession of the teeth of mammals are more fully developed in two memoirs hy one 
of the present writers : — " Remarks on the Homologies and Notation of the Teeth 
of the Mammalia," in the Journal of Anatomy and Physiology, vol. iii. p. 262, 
1869; and "Notes on the First or Milk Dentition of the Mammalia," in the 
Tnnis. Odontological Society of Great Britain, 1871. See also an important 
memoir by Oldfield Thomas on the "Homologies and Succession of the teeth 
in the Dasyuridse," Phil. Trans. 1887, pp. 443-462. 



22 



GENERAL ANATOMICAL CHARACTERS 



except in cases of accidental or abnormal variation, and in the one 
remarkable instance of constant deviation from bilateral symmetry 
among mammals, the tusks of the Narwhal (Monodon), in which 
the left is of immense size, and the right rudimentary. In cer- 
tain mammals, such as the Dolphins and some Armadillos, which 
have a very large series of similar teeth, not always constant in 
number in different individuals, there may be differences in the two 
sides ; but, apart from these, in describing the dentition of any 
mammal, it is quite sufficient to give the number and characters 
of the teeth of one side only. Since the teeth of the upper and the 
lower jaws work against each other in masticating, there is a general 
correspondence or harmony between them, the projections of one 
series, when the mouth is closed, fitting into correspondingdepressions 
of the other. There is also a general resemblance in the number, 
characters, and mode of succession of both series, so that, although 
individual teeth of the upper and lower jaws may not be in any 
strict sense of the term homologous parts, there is a great con- 
venience in applying the same descriptive terms to the one as are 
used for the other. 

The simplest dentition as a whole is that of many species of 
Dolphin (Fig. 2), in which the crowns are single-pointed, slightly 




Fio. 2.— Upper and Lower Teeth of one side of the Mouth of a Dolphin (Lagenorhynchus) as an 
example of the homodont type of dentition. The bone covering the outer side of the roots of 
the teeth has been removed to show their simple character. 

curved cones, and the roots also single and tapering, and all alike in 
form from the anterior to the posterior end of the series, though it 
may be with some slight difference in size, those at the two extremities 
of the series being rather smaller than the others. Such a dentition 
is called Homodont, and in the case cited, as the teeth are never 
changed, it is also Monophyodont. Such teeth are adapted only 
for catching slippery living prey, as fish. 

In a very large number of mammals the teeth of different 
parts of the series are more or less differentiated in character, 
and have different functions to perform. The front teeth are 
simple and one-rooted, and are adapted for cutting and seizing. 
They are called " incisors." The back- or cheek-teeth have broader 
and more complex crowns, tuberculated or ridged, and are sup- 



PF.XTAL SYSTEM 



23 



ported on two or more roots. They crush or grind the food, and 
are hence called "molars." Many animals have, between these 
two sets, a tooth at each corner of the mouth, longer and more 
pointed than the others, adapted for tearing or stabbing, or for 
fixing struggling prey. From the conspicuous development of 
such teeth in the Carnivora, especially the Dogs, they have received 
the name of "canines." A dentition with its component parts so 
differently formed that these distinctive terms are applicable to 
them is called Heterodont. In most cases, though by no means 
invariably, animals with Heterodont dentition are also Diphyodont. 

This general arrangement is extremely obvious in a considerable 
number of mammals; and closer examination shows that, under 
very great modification in detail, there is a remarkable uniformity 
of essential characters in the dentition of a large number of 
members of the class belonging to different orders and not otherwise 
closety allied ; so much so indeed that it has been possible (chiefly 
through the researches of Sir Richard Owen) to formulate a common 
plan of dentition from which the others have been derived by the 
alteration of some and suppression of other members of the series, 
and occasionally, but very rarely, by addition. The records of 
palaeontology fully confirm this view, as by tracing back many 
groups now widely separated in dental characters we find a 
gradual approximation to a common type. In this generalised form 
of mammalian dentition (which is best exemplified in the genera 
Anoplotherium and Homalodontotherium) the entire number of teeth 
present is 44, or 11 above and 11 below on each side. Those of 
each jaw are placed in continuous series without intervals between 
them ; and, although the anterior teeth are simple and single- 
rooted, and the posterior teeth complex and with several roots, 
the transition between the two kinds is gradual. 

In dividing and grouping such teeth for the purpose of descrip- 
tion and comparison, more definite characters are required than 
those derived merely from form or function. The first step towards 
a classification has been made by the observation that the upper 
jaw is composed of two bones, the j)remaxilla and the maxilla, 
and that the suture between these bones separates the three 
anterior teeth from the others. These three teeth, then, which are 
implanted by their roots in the premaxilla, form a distinct group, 
to which the name of ".incisor " is applied. This distinction is, 
however, not so important as it aj)pears at first sight, for, as 
mentioned when speaking of the development of the teeth, their 
connection with the bone is only of a secondary nature, and, although 
it happens conveniently for our purpose that in the great majority 
of cases the segmentation of the bone coincides with the interspace 
between the third and fourth tooth of the series, still, when it does 
not happen to do so, as in the case of the Mole, we must not give 



24 GENERAL ANATOMICAL CHARACTERS 

too much weight to this fact, if it contravenes other reasons for 
determining the homologies of the teeth. The eight remaining 
teeth of the upper jaw offer a natural division, inasmuch as the 
posterior three never have milk-predecessors ; and, although some 
of the anterior teeth may be in the same case, the particular one 
preceding these three always has such a predecessor. These three 
then are grouped apart as the " molars," or, since some of the teeth 
in front of them often have a molariform character, " true molars." 
Of the five teeth between the incisors and molars the most anterior, 
or that which is usually situated close behind the premaxillary 
suture, almost always, as soon as any departure takes place from 
the simplest and most homogeneous type, assumes a lengthened 
and pointed form, and is the tooth so developed as to constitute 
the " canine " or " laniary " tooth of the Carnivora, the tusk of the 
Boar, etc. It is customary therefore to call this tooth, whatever 
its size or form, the " canine." The remaining four are the " pre- 
molars " or "false molars." This system of nomenclature has been 
objected to as being artificial, and in many cases not descriptive, 
the distinction between premolars and canine especially being 
sometimes not obvious ; but the terms are now in such general use, 
and are so practically convenient — especially if, as it is best to do 
in all such cases, we forget their original signification and treat 
them as arbitrary signs — that it is not likely they will be super- 
seded by any that have been proposed as substitutes for them. 

AVith regard to the lower teeth the difficulties are greater, 
owing to the absence of any suture corresponding to that which 
defines the incisors above ; but since the number of the teeth is 
the same, the corresponding teeth are preceded by milk-teeth, and 
in the large majority of cases it is the fourth tooth of the series 
which is modified in the same way as the canine (or fourth tooth) 
of the upper jaw, it is quite reasonable to adopt the same divisions 
as with the upper series, and to call the first three, which are 
implanted in the part of the mandible opposite to the premaxilla, 
the incisors, the next the canine, the next four the premolars, and 
the last three the molars. It may be observed that when the 
mouth is closed, especially when the opposed surfaces of the teeth 
present an irregular outline, the corresponding upper and lower 
teeth are not exactly opposite, otherwise the two series could not 
fit into one another ; but as a rule the points of the lower teeth 
shut into the interspaces in front of the corresponding teeth of the 
upper jaw. This is seen very distinctly in the canine teeth of the 
Carnivora, and is a useful guide in determining the homologies of 
the teeth of the two jaws. Objections have certainly been made 
to this view, because, in certain rare cases, the tooth which, accord- 
ing to it, would be called the lower canine has the form and 
function of an incisor (as in Ruminants and Lemurs), and on the 



DENTAL SYSTEM 25 



other hand (as in Cotylops,axi extinct Ungulate from North America) 
the tooth that would thus he determined as the first premolar has 
the form of a canine ; hut it should not he forgotten that, as in all 
such cases, definitions derived from form and function alone are 
quite as open to objection as those derived from position and 
relation to surrounding parts, or still more so. 

lh iit<tl formula'. — For the sake of brevity the complete dentition, 
arranged according to these principles, is often described by the 
following formula, the numbers above the line representing the 

teeth of the upper, those below the line those of the lower jaw : — 

. . 3-3 • 1-1 , 4-4 , 3-3 11-11 

incisors — , canines - — -, premolars - — 7 . molars r — - = — — — : 

3-3 1 - 1 L 4-4 3-3 11-11 

total 44. Since, however, initial letters may be substituted for 
the names of each group, and it is quite unnecessary to give more 
than the numbers of the teeth on one side of the mouth, the 
formula may be conveniently abbreviated into — 

* f » c h P b m f = tt J total 44 - 
The individual teeth of each group are always enumerated from 
before backwards, and by such a formula as the following — 
i 1, i 2, i 3, c, p 1, p 2, p 3, p 4, m 1, m 2, m 3 
i 1, i 2, i 3, c, p 1, p 2, p 3, p 4, m 1, m 2, in 3 

or more briefly — 

. 1, 2, 3 1_ 1, 2, 3, 4 1, 2, 3 
1 1, 2, 3' C 1' P 1, 2, 3, 4' m 1, 2, 3' 

A special numerical designation is thus given by which each one 
can be indicated. In mentioning any single tooth, such a sign as Hi 
will mean the first upper molar, ^n the first lower molar, and so on. 
The use of such signs saves much time and space in description. 1 

It was part of the view of the founder of this system of dental 
notation that, at least throughout the group of mammals whose 
dentition is derived from this general type, each tooth has its 
strict homologue in all species, and that in those cases in which 
fewer than the typical number are present (as in all existing 
mammals except the genera Sus, Gymnura, Talpa, and Myogale), the 
teeth that are missing can be accurately defined. According to 
this view, when the number of incisors falls short of three it is 
assumed that the absent ones are missing from the outer and 
posterior end of the series. Thus, when there is but one incisor 
present, it is i 1 ; when two, they are i 1 and i 2. Further- 
more, when the premolars and the molars are below their typical 
number, the absent teeth are missing from the fore part of the 
premolar series, and from the back part of the molar series. If 
this were invariably so, the labours of those who describe teeth 

1 By many writers the letters indicating the different kinds of teeth are 
printed in capitals, as /, C, P, and M ; while very frequently the symbol Pin is 
employed in place of p. 



26 



GENERAL ANATOMICAL CHARACTERS 



Avould be greatly simplified ; but there are so many exceptions that 
a close scrutiny into the situation, relations, and development of a 
tooth is required before its nature can be determined, and in some 
cases the evidence at our disposal is scarcely sufficient for the 
purpose. In other instances, however, as among the Polyprotodont 
Marsupials, we have decisive evidence to show that the missing 
premolar teeth are not those at the extremity of the series. 

The milk -dentition is expressed by a similar formula, d 
for deciduous or m for milk being commonly prefixed to the 



-p.A- 



17L.\ jji.z 




(Zzf'i.a.3 



JT 
dm.\ dms. clm.z 




m 2 m.z 



Fio. 3. — Milk and Permanent Dentition of Upper (I.) and Lower (II.) Jaw of the Dog (Canis 
familiaris), with the symbols by which the different teeth are commonly designated. The third 
upper molar (m.3) is the only tooth wanting in this animal to complete the typical heterodont 
mammalian dentition. 



letter expressive of the nature of the tooth. Since the three 
molars, and almost invariably the first premolar of the permanent 
series, have no predecessors, the typical milk-dentition would be 
expressed as follows — di §, dc \, dm 3, = -f, total 28. In a few 
Ungulates, however, such as the Hyrax and Tapir, and in some 
instances the Rhinoceros and the extinct Palceotherkun, the whole of 
the four premolars are preceded by milk-teeth ; when we have the 
fullest development of cheek-teeth in the whole of the Eutheria. The 
teeth which precede the premolars of the permanent series are all 
called molars in the milk-dentition, although as a general rule, in 



DENTAL SYSTEM 17 



form and function they represent in a condensed form the whole 
premolar and molar series of the adult. When there is a marked 
difference between the premolars and molars of the permanent 
dentition, the first milk-molar resembles a premolar, while the last 
has the characters of the posterior true molar. 

The dentition of all the members of the orders Primates, 
Carnivora, Insectivora, Chiroptera, and Ungulata can clearly be 
derived from the above -described generalised type. The same 
may be said of the Rodents, and even the Proboscidea, though 
at least in the existing members of the order with greater modi- 
fication. It is also apparent in certain extinct Cetacea, as 
Z< uglodon and Squalodon, but it is difficult to find any traces of 
it in existing Cetacea, Sirenia, or any of the so-called Edentata. 
All the Marsupials, different as they are in their general structure 
and mode of life, and variously modified as is their dentition, 
present in this system of organs some deep-lying common characters 
which show their unity of origin. The generalised type to which 
their dentition can be reduced presents considerable resemblance 
to that of the placental mammals, yet differing in details. It is 
markedly heterodont, and susceptible of division into incisors, 
canines, premolars, and molars upon the same principles. The 
whole number is, however, not limited to forty-four. The incisors 
may be as numerous as five on each side above, and they are 
almost always different in number in the upper and the lower jaw. 
The premolars and molars are commonly seven, as in the placental 
mammals, but their arrangement is reversed, as there are four 
true molars and three premolars. 

The larger number of incisive and molar teeth among the 
Marsupials suggests that their additional teeth have disappeared 
in the Eutheria, 1 and Mr. 0. Thomas has endeavoured to construct 
a generalised dental formula from which both the Marsupial and 
Eutherian modifications may have been derived by the suppression 

of particular teeth. Thus the hypothetical formula i ' 2 ' ' — — 5 > 

C 1' & 1 *>' 3' 4 ' m 1 i 3' *~5» ky the loss of the fifth lower incisor, 
and of the second premolars (which we know to be those which 
disappear in the Marsupials) and the fifth molars, will give 

* i; I i, X o > 4 ^mHH' ?n BHH' or the formula of the 

Opossum (Didelphys), usually written i |, c \, p § , m £ . Again, 
in the same formula the loss of the fourth and fifth incisors in 

.12 3 1 

both jaws, and also of the fourth molars, gives us i ' ' ' ' n , c -> 

12 3 4 12 3 ^' 

p ' ,7 ' , m ' ' ' or the formula of a typical Eutherian, like the 

1, -, o, 4 1, Z, 

1 According to Mr. G. E. Dobson there are four upper incisors in some of 
the Soricidce. 



28 GENERAL ANATOMICAL CHARACTERS 

Pig, which we generally write as i %, c \, p f, m|. Such a 
generalised formula will admit of modification into that of all 
existing, and a large number of fossil Marsupials, but it is possible 
that some of the Mesozoic types may have had more than four 
premolars, although there is no absolutely decisive evidence that 
such was the case. The presence of seven or eight true molars in 
some Mesozoic forms merely entails the addition of two or three 
additional figures to the ideal generalised formula. 

The milk-dentition of all known Marsupials, existing or extinct, 
is (if not entirely absent) limited to a single tooth on either side of 
each jaw, this being the predecessor of the last permanent premolar. 
And if the view that the milk -dentition is an additional series 
grafted upon the original permanent series be correct, it is evident 
that we have in this single replacement the first stage of this 
additional development. 

In very few mammals are teeth entirely absent. Even in the 
Whalebone Whales their germs are formed in the same manner 
and at the same period of life as in other mammals, and even 
become partially calcified, but they never rise above the gums, 
and completely disappear before the birth of the animal. In some 
species of the order Edentata, the true Anteaters and the Pangolins, 
no traces of teeth have been found at any age. The adult 
Monotremata are likewise devoid of teeth of the same structure 
as those of ordinary mammals ; but well-developed molars occur in 
the young Ornithorhynchus, although no traces of teeth have hitherto 
been detected in Echidna. 

Modifications of the Teeth in Relation to their Functions. — The 
principal functional modifications noticed in the dentition of 
mammalia may be roughly grouped as piscivorous, carnivorous, 
insectivorous, omnivorous, and herbivorous, each having, of course, 
numerous variations and transitional conditions. 

The essential characters of a piscivorous dentition are best 
exemplified in the Dolphins, and also (as modifications of the 
carnivorous type) in the Seals. This type consists of an elongated, 
rather narrow mouth, wide gape, with numerous subequal, conical, 
sharp-pointed, recurved teeth, adapted simply to rapidly seize, but 
not to divide or masticate, active, slippery, but not powerful prey. 
All animals which feed on fish as a rule swallow and digest them 
entire, a process which the structure of prey of this nature, especially 
the intimate interblending of delicate, sharp-pointed bones with the 
muscles, renders very advantageous, and for which the above- 
described type of dentition is best adapted. 

The carnivorous type of dentition is shown in its most specialised 
development among existing mammals in the Felidce. The function 
being here to seize and kill struggling animals, often of large size 
and great muscular power, the canines are immensely developed, 



DENTAL SYSTEM 29 



trenchant, and piercing, and are situated wide apart, so as to give 
the firmest hold when fixed in the victim's body. The jaws are as 
short as is consistent with the free action of the canines, so that no 
power may be lost. The incisors are very small, so as not to 
interfere with the penetrating action of the canines, and the 
crowns of the molar series are reduced to scissor-like blades, with 
which to pare oft' the soft tissues from the large bones, or to divide 
into small pieces the less dense portions of the bones for the sake of 
nutriment afforded by the blood and marrow they contain. The 
gradual modification between this and the two following types will 
be noticed in their appropriate places. 

In the most typical insectivorous animals, as the Hedgehogs 
and Shrews, the central incisors are elongated, pointed, and project 
forwards, those of the upper and lower jaw meeting like the blades 
of a pair of forceps, so as readily to secure small active prey, quick 
to elude capture, but powerless to resist when once seized. The 
crowns of the molars are covered with numerous sharp edges and 
points, which, working against each other, rapidly cut up the hard- 
cased insects into little pieces fit for swallowing and digestion. 

The omnivorous type, especially that adapted for the con- 
sumption of soft vegetable substances, such as fruits of various 
kinds, may be exemplified in the dentition of Man, of most 
Monkeys, and of the less modified Pigs. The incisors are moderate, 
subequal, and cutting. If the canines are enlarged, it is usually 
for other purposes than those connected with food, and only in the 
male sex. The molars have their crowns broad, flattened, and 
elevated into rounded tubercles. The name Bunodont, or hillock- 
toothed, has been proposed for molars of this type, and will 
frequently be found convenient. 

In the most typically herbivorous forms of dentition, as seen in the 
Horse and Kangaroo, the incisors are well developed, trenchant, and 
adapted for cutting off the herbage on which the animals feed ; the 
canines are rudimentary or suppressed ; the molars are large, with 
broad crowns, which in the simplest forms have strong transverse 
ridges, but may become variously complicated in the higher degrees 
of modification which this type of tooth assumes. 

Various forms of teeth of this type will be noticed among the 
Ungulates and Rodents. 

The natural groups of mammals, or those which in our present 
state of knowledge we have reason to believe are truly related to 
each other, may each contain examples of more than one of these 
modifications. Thus the Primates have both omnivorous and 
insectivorous forms. The Carnivora show piscivorous, carnivorous, 
insectivorous, and omnivorous modifications of their common type 
of dentition. The Ungulata and the Rodentia have among them 
the omnivorous and various modifications, both simple and complex, 



30 GENERAL ANATOMICAL CHARACTERS 



of the herbivorous type. The Marsupialia exhibit examples of 
all forms, except the purely piscivorous. Other orders, more 
restricted in number or in habits, as the Proboscidea and Cetacea, 
naturally do not show so great a variety in the dental structure of 
their members. 

Taxonomy. — In considering the taxonomic value to be assigned to 
the modifications of teeth of mammals, two principles, often 
opposed to each other, which have been at work in producing these 
modifications, must be held in view: — (1) the type, or ancestral 
form, as we generally now call it, characteristic of each group, 
which in most mammals is itself derived from the still more 
generalised type described above ; and (2) variations which have 
taken place from this type, generally in accordance with special 
functions which the teeth are called upon to fulfil in particular 
cases. These variations are sometimes so great as completely to 
mask the primitive type, and in this way the dentition of many 
animals of widely different origin has come to present a remarkable 
superficial resemblance, as in the case of the Wombat (a Marsupial), 
the Aye- Aye (a Lemur), and the Eodents, or as in the case of the 
Thylacine and the Dog. In all these examples indications may 
generally be found of the true nature of the case by examining the 
earlier conditions of dentition ; for the characters of the milk- 
teeth or the presence of rudimentary or deciduous members of the 
permanent set will generally indicate the route by which the 
specialised dentition of the adult has been derived. It is perhaps 
owing to the importance of the dental armature to the well-being 
of the animal in procuring its sustenance, and preserving its life 
from the attacks of enemies, that great changes appear to have 
taken place so readily, and with such comparative rapidity, in the 
forms of these organs — changes often accompanied with but little 
modification in the general structure of the animal. Of this 
proposition the Aye-Aye (Chiromyx) among Lemurs, the Walrus 
among Seals, and the Narwhal among Dolphins form striking- 
examples ; since in all these forms the superficial characters of their 
dentition would entirely separate them from the animals with which 
all other evidence (even including the mode of development of their 
teeth) proves their close affinity. 

Trituberculism. — Recent researches, and more especially those of 
Professors Cope and Osborn, tend to show that almost all of the 
extremely different forms of tooth-structure found among Mammals 
may be traced to one common type, in Avhich the crown of each 
tooth carried three cusps, and hence termed the tritubercular type ; 
these three cusps being arranged in a triangle, with the apex 
directed inwardly in the upper teeth (Fig. 4, e), and outwardly in 
the lower ones (Fig. 4, 7). It is further probable that this 
tritubercular type was itself derived from a type of dentition in 



DENTAL SYSTEM 



3i 



which the teeth were in the form of almost a quite simple cone ; 
such a presumably primitive type of dentition being apparently 
retained among some existing Edentates, like the Armadillos, while 
it is possible that we should regard the dentition of the existing 
Cetacea (Fig. 2) as a reversion to the same primitive type. None of 
the Mesozoic mammals at present known exhibit this simple 
conical type of teeth, although we have an approximation to it in 
the extremely generalised genus Dromatheriiou. Starting then 





\ 





7a 




hy- 



/2 






/J 




Fig. 4. — Molar teeth of Mesozoic Mammals (enlarged). Triconodont type — 1, Dromatherium ; 
2, M icrocoiiodon ; 3, Amphilestes ; 4, Phascolotherium ; 5, Triconodon. Tritubercular type — 0, 7, 
Spalacotherium ; 10, Asthenodon. Tubercular sectorial type — S, Amphitherium ; 9, Peramus ; 11- 
13, Amblotherium ; 14 (?) Amblotherium. pr, Protocone ; hy, hypocone ; pa, paracone ; me, 
metacone, in the upper teeth ; and protoconid, hypoconid, paraconid, and metaconid in the 
lower. 6 and 15 are upper molars, and the rest lower molars. (After Osborn.) 

from this presumed simple cone it appears that the teeth of Droma- 
therium (Fig. 4, i) present the first stage towards trituberculism, the 
crown of each tooth having one main cone, with minute lateral 
cusps, and the root being grooved. In the next or true Tricon- 
odont stage (Fig. 4, 3-5) the crown has become elongated antero- 
posteriorly, and consists of one central and two lateral cones or 
cusps, while the root is divided. From this the transition is easy to 
the tritubercular type, in which the three cusps, instead of being- 
placed in a line, are arranged in a triangle ; the upper teeth (Fig. 



32 



GENERAL ANATOMICAL CHARACTERS 



4, 6) having one inner and two outer cusps, while the reverse 
condition obtains in those of the lower jaw (Fig. 4, 7). These 
three cusps of the simple tritubercular tooth are collectively desig- 
nated as the primitive triangle ; in the upper tooth the inner cusp 
is termed the protocone, the antero-external one the paracone, and 
the postero-external the metacone ; the corresponding cusps of the 
lower tooth being named protoconid, paraconid, and metaconid — 
the protoconid being here on the outer side of the crown. 

It is thus apparent that in the first, or haplodont type, as well 
as in the triconodont type, the upper and lower molars are alike ; 
while in the simple tritubercular type they have a similar pattern, 
but with the arrangement of the cusps reversed. This simple 
tritubercular type occurs in the Mesozoic genus Spalacotherium 
(Fig. 4, 6 and 7), and apparently in the existing Chrysochhris ; but 
in the majority of tritubercular forms, while this primitive triangle 
forms the main portion of the crown, other secondary cusps are 
added, the homologies of which in the upper and lower teeth are 
somewhat doubtful. At the same time that we have the addition 
of these secondary cusps we also find trituberculism differentiating 
into a secodont and a bunodont series, according as to whether the 
dentition becomes of a cutting or a crushing type. 

Thus in the lower molars (Fig. 4, s and 9) we very frequently 
find the three cusps of the primitive triangle elevated and connected 
by cross crests, while there is an additional low posterior heel or 
talon, which may be termed the hypoconid. This tubercular- 
sectorial sub-type, as it is termed, is found in the lower molars of 
many Polyprotodont Marsupials and Insectivores, and it also occurs 
in the lower carnassial teeth of the true Carnivora. The presence 

of two cusps (inner and 




outer) to the talon con- 
verts this modification 
into a quinquetubercular 
form ; while, by the sup- 
pression of one of the 
three primitive cusps, it 
develops into the quadri- 
tubercular type of the 
bunodont series. 

In the upper molars 
the primitive triangle in 
the secodont series may 
remain purely tricuspid ; 
but the addition of in- 
termediate cusps, both in the secodont and bunodont series, may give 
rise to a quinquetubercular type ; these intermediate cusps being 
respectively designated as the protoconule and metaconule (Fig. 5, 



Fig. 5. — Diagram of two upper and two lower left 
quadritubercular molars in mutual apposition. The cusps 
and ridges of the upper molars in double lines, and those 
of the lower in black lines. The lower molars are looked 
at from below, as if transparent, pr, Protocone ; hy, hypo- 
cone ; pa, paracone ; me, metacone ; ml, protoconule ; pi, 
metaconule ; prd, protoconid ; hyd, hypoconid ; pad, para- 
conid ; med, metaconid ; end, entoconid. (After Osborn.) 



THE SKELETON 33 



ml, pi). Finally, in the bunodont scries, the addition of a postero- 
internal cusp (Fig. 5, h>i), termed the hypocone, forms the sextuber- 
cular molar. 

The following table exhibits, in a collective form, the names 
and relations of all the above-mentioned cusps, and the letters by 
which they are indicated in the figures : — 

Upper Molars. 

Antero-intemal cusp =protocone =pr. 

Postero „ or 6th cusp = hypocone = hy. 

Antero-external cusp =paracone = pa. 

Postero ,, „ = metacone = me. 

Anterior intermediate cusp = protoconule = ml. 

Posterior „ „ =metaconule —pi. 

Lower Molars. 

Antero-external cusp =protoconid = 2ird. 

Postero „ ,, =hypoconid =hyd. 

Antero-internal or 5th cusp =paraconid =pad. 

Intermediate (or in quadritubercular 

molars antero-internal) cusp. = metaconid = med. 

Postero-internal cusp =entaconid = end. 

The common occurrence of trituberculism in the mammals of 
the earlier geological epochs is, as remarked by Osborn, very 
significant of the uniformity of molar origin. Thus, among the 
Mesozoic mammals (with the exception of the group known as 
Multituberculata, in which the molars are constructed on a different 
type), trituberculism occurs in the great majority of the genera; 
while out of 82 species, belonging to five different suborders from 
the Lowest or Puerco Eocene of the United States, all but four 
exhibit this feature ; and the same holds good for the mammals of 
the corresponding European horizon. At the present day trituber- 
culism persists in the Lemuroidea, Insectivora, Carnivora, and Mar- 
supialia. In the Carnivora there is a tendency to lose the meta- 
conid, while in the bunodont molars of the Ungulata it is the 
paraconid that disappears. 



III. THE SKELETON. 

Definition. — The skeleton is a system of hard parts, forming a 
framework which supports and protects the softer organs and 
tissues of the body. It consists of dense fibrous and cartilaginous 
tissues, portions of which remain through life in this state, but the 
greater part is transformed during the growth of the animal into 
bone or osseous tissue. This is characterised by a peculiar 

3 



34 GENERAL ANATOMICAL CHARACTERS 

histological structure and chemical composition, being formed 
mainly of a gelatinous basis, strongly impregnated with salts of 
calcium, chiefly phosphate, and disposed in a definite manner, con- 
taining numerous minute nucleated spaces or cavities called lacuna?, 
connected together by delicate channels or canaliculi, which radiate 
in all directions from the sides of the lacuna?. Parts composed of 
bone are, next to the teeth, the most imperishable of all the organs 
of the body, often retaining their exact form and internal structure 
for ages after every trace of all other portions of the organisation 
has completely disappeared, and thus, in the case of extinct animals, 
affording the only means of attaining a knowledge of their characters 
and affinities. 1 

In the Armadillos and their extinct allies alone is there an 
ossified exoskeleton, or bony covering developed in the skin. In 
all other mammals the skeleton is completely internal. It may be 
described as consisting of an axial portion belonging to the head 
and trunk, and an appendicular portion belonging to the limbs. 
There are also certain bones called splanchnic, being developed 
Avithin the substance of some of the viscera. Such are the os cordis 
and os penis found in some mammals. 

It is characteristic of all the larger bones of the mammalia that 
their ossification takes its origin from several distinct centres. One 
near the middle of the bone, and spreading throughout its greater 
portion, constitutes the diaphysis, or "shaft," in the case of the long 
bones. Others near the extremities, or in projecting parts, form 
the epiphyses, which remain distinct during growth, but ultimately 
coalesce with the rest of the bone. 

Axial skeleton. — The axial skeleton consists of the skull, the 
vertebral column (prolonged at the posterior extremity into the 
tail), the sternum, and the ribs. 

Skull. — In the skull of adult mammals, all the bones, except the 
lower jaw, the auditory ossicles, and the bones of the hyoid arch, 
are immovably articulated together, their edges being in close con- 
tact, and often interlocking by means of fine denticulations project- 
ing from one bone and fitting into corresponding depressions of the 
other ; they are also held together by the investing periosteum, or 
fibrous membrane, which passes directly from one to the other, 
and permits no motion, beyond perhaps a slight yielding to external 
pressure. In old animals there is a great tendency for the different 
bones to become actually united by the extension of ossification 
from one to the other, with consequent obliteration of the sutures. 

1 See for the principal modifications of the skeleton of the class, the large 
and beautifully illustrated Ost6ographie of De Blainville, 1835-54 ; the section 
devoted to the subject in Bronn's Klasscn und Ordnungen des Thicr-Rcichs, by 
Giebel, 1874-79 ; and An Introduction to the Osteology of the Mammalia, by 
W. II. Flower, 3d ed., 1885. 



THE SKELETON 



o 



The cranium, thus formed of numerous originally independent 
ossifications, which may retain throughout life more or less of their 
individuality, or be all fused together, according to the species, the 
age, or even individual peculiarity, consists of a brain-case, or bony 
capsule for enclosing and protecting the brain, and a face for the 
support of the organs of sight, smell, and taste, and of those concerned 
in seizing and masticating the food. The brain-case articulates 
directly with the anterior cervical vertebra, by means of a pair 
of oval eminences, called condyles, placed on each side of the large 
median foramen which transmits the spinal cord. It consists of a 
basal axis, continuous serially with the axes or centra of the 



Pa 



IJP 



jcO 




Fig. 6. — Longitudinal and vertical section of the skull of a Dog (Canis famillaris), with 
mandible and hyoid arch, an, Anterior narial aperture ; MT, maxillo-turbinal bone ; ET, ethmo- 
turbinal ; Na, nasal ; ME, ossified portion of the mesethmoid ; CE, cribriform plate of the 
ethmo-turbinal : Fr, frontal ; Pa, parietal ; IP, interparietal ; SO, supraoccipital ; ExO, ex- 
occipital ; BO, basioccipital ; Per, periotic ; BS, basisphenoid ; Pt, pterygoid ; AS, ali- 
sphenoid ; OS, orbitosphenoid ; PS, presphenoid ; PI, palatine ; VO, vomer ; Mx, maxilla ; 
PMx, premaxilla ; sh, stylohyal ; eh, epihyal ; ch, ceratohyal ; bh, basihyal ; th, thyrohyal ; 
s, symphysis of mandible ; cp, coronoid process ; cd, condyle ; a, angle ; id, inferior dental 
canal. The mandible is displaced downwards, to show its entire form ; the * indicates the 
part of the cranium to which the condyle is articulated. 1 

vertebra?, and of an arch above, roofing over and enclosing the 
cavity which contains the cephalic portion of the central nervous 
system (see Fig. 6). The base with its arch is composed of three 
segments placed one before the other, each of which is comparable 
to a vertebra with a greatly expanded neural arch. The hinder or 

1 This and many of the following figures in this chapter are taken from Flower's 
Osteology of the Mammalia. 



tf GENERAL ANATOMICAL CHARACTERS 



j 



occipital segment consists of the basioccipital, exoccipital, and 
supraoccipital bones ; the middle segment of the basisphenoid, ali- 
sjmenoid, and parietal bones ; and the anterior segment of the 
presphenoid, orbitosphenoid, and frontal bones. The axis is 
continued forwards into the mesethmoid, or septum of the nose, 
around which the bones of the face are arranged in a manner 
so extremely modified for their special purposes that anatomists 
Avho have attempted to trace their serial homologies with the more 
simple portions of the axial skeleton have arrived at very diverse 
interpretations. The characteristic form and structure of the face 
of mammals is mainly dependent upon the size and shape of (1) the 
orbits, a pair of cup-shaped cavities for containing the eyeball and 
its muscles, which may be directed forwards or laterally, placed 
near together or wide apart, and may be completely or only partially 
encircled by bone ; (2) the nasal fossa?, or cavities on each side of 
the median nasal septum, forming the passage for the air to pass 
between the external and the internal nares, and containing in their 
upper part the organ of smell ; (3) the zygomatic arch, a bridge of 
bone for the purpose of muscular attachment, which extends from 
the side of the face to the skull, overarching the temporal fossa ; 
(4) the roof of the mouth, with its alveolar margin for the implanta- 
tion of the upper teeth. The face is completed by the mandible, or 
lower jaw, consisting of two lateral rami, articulated by a hinge 
joint with the scpiamosal (a cranial bone interposed between the 
posterior and penultimate segment of the brain-case, where also the 
bony capsule of the organ of hearing is placed), each being composed 
of a single solid piece of bone, and the two united together in the 
middle line in front, at the symphysis, — which union may be per- 
manently ligamentous or become completely ossified. Into the 
upper border of the mandibular rami the lower teeth are implanted. 
In addition to the bones already mentioned as entering into the 
formation of the cranium, there are many others, the most import- 
ant of which may be briefly noticed. The anterior extremity of the 
skull is formed by the premaxillse (Figs. 6, 7, PMx), which carry the 
incisors ; behind them are the maxilla?, in which all the remaining 
upper teeth are implanted. Both the premaxillse and maxilla? meet 
in a median suture on the palate, where they form a floor to the nasal 
passage ; this floor being continued backwards by the plate-like pala- 
tines, at the hinder extremity of which the posterior nares are usually 
situated. In a few instances, however, as in certain Edentates and 
Cetaceans, the small pair of bones forming the posterior continuation 
of the lateral borders of the palatines, and known as the pterygoids 
(Fig. 6, Pt), likewise meet in the middle line below the nasal passage, 
and thus cause the aperture of the posterior nares to be situated 
near the occiput. On the upper, or frontal aspect of the cranium the 
paired nasals roof over the nasal passage and fill the interval left 



THE SKELETON 



37 



VJSls 




Per 



Fig. 7. — Side view of skull of Cape Jumping Hare (Pedetes 
caffer). xj. PMx, Premaxilla ; Mr, maxilla; Ma, jugal or 
malar ; Fr, frontal ; L, lachrymal ; Pa, parietal ; Na, nasal ; 
Sq, squamosal ; Ty, tympanic ; ExO, exoccipital ; AS, alisphen- 
oid ; OS, orbitosphenoid ; Per, mastoid bulla. 



between the premaxilla and maxilla of either side. Behind the nasals 
and maxilla 1 , the anterior part of the brain-case is formed by the 
large paired frontals (Figs. 6, 7, Fr), behind which are the parietals, 
which ma) T be of still 
larger size, and form 
the great it part of 
the brain -case. A 
median interparietal 
ossification (Fig. 6, 
IP) may divide the 
parietals posteriorly, 
and is itself articu- 
lated with the supra- 
occipital, to the lat- 
eral borders of Avhich 
the parietals are also 
joined. The squam- 
osal (Fig. 7, Sq) forms 
the lateral wall of 
the hinder part of 
the brain -case, and 
articulates superiorly with the parietal, and posteriorly with the 
exoccipital. The glenoid cavity (Fig. 8), for the reception of the 
articular condyle of the mandible, is formed by the inferior portion 
of the squamosal, at the point where it gives off the zygomatic 
process to form the hinder portion of the zygomatic arch. The 
middle portion of that arch is formed by the jugal, or malar bone 
(Fig. 7, Ma), which articulates posteriorly with the zygomatic process 
of the squamosal, and anteriorly Avith the maxilla. The jugal (as 
in Fig. 7) may also articulate with a small bone situated on the 
anterior border of the orbit known as the lachrymal. It is im- 
portant to observe that the zygomatic or temporal arch is a 
squamoso-maxillary one, and that an arcade thus composed is found 
elsewhere only among the extinct Anomodont reptiles, which have 
already been mentioned as showing signs of mammalian affinity. 
The relative position occupied by the orbito- and alisphenoid is 
sufficiently indicated in Fig. 7. 

Wedged in between the squamosal and the bones of the occipital 
and basisphenoidal region are the bones connected with the organ 
of hearing, known as the periotic and tympanic. The position of 
the periotic, which encloses the labyrinth or essential organ of 
hearing, is shown in Fig. 6. The periotic is divided into a very 
dense antero-internal moiety known as the petrosal, and a postero- 
external or mastoid portion (Fig. 8), which appears on the outer Avail 
of the brain-case. The tympanic is produced horizontally outwards 
to form the external auditory meatus or tube of the ear, Avhile the 



38 



GENERAL ANATOMICAL CHARACTERS 



inner and under surface is frequently dilated into a shell-like 
auditory bulla (Fig. 8). The small bones of the internal ear known 
as the malleus, incus, and stapes are contained in the membranous 

tympanic cavity, 
which is situated in 
a space left among 
this group of bones. 
Further mention of 
these bones is made 
below under the 
head of the sense 



C2J- 




organs. 



In the Carni- 
vora and some other 
groups the foram- 
ina on the base of 
the skull for the 
passage of blood- 
vessels and nerves 
are of considerable 
taxonomic import- 
ance. The position 
of the more im- 
portant of these 
foramina is indi- 
cated in Fig. 8 ; 
but for details the 
reader may refer to 
the work on the 
Osteology of theMam- 
malia already men- 
tioned. Attention 
may, however, be 
particularly di- 
rected tO the SO- 
sphenoid canal ; P, paroccipital process of exoccipital ; m, mastoid ,, , ,. , .-. 
process of periotic ; am, external auditory meatus ; g, glenoid for- Called allspnenOlCl 
amen, below which is the glenoid cavity for the condyle of the man- canal, the position 
dible. (Flower, Proc. Zool. Soc, 1869, p. 25.) _£ -lylijf;^ jg shown 

in Fig. 8, since this is a feature of some importance in the classifica- 
tion of the Carnivora. This canal is a short channel running hori- 
zontally forward from near the foramen ovale through the alisphenoid, 
and opening anteriorly with the foramen rotundum ; it is traversed 
by the external carotid artery. 

Only in those species, as Man and the smaller kinds of the 
Primates and some other orders, in which the brain holds a large 
relative proportion to the rest of the body, does the external form 



Fig. 8.— The right half of the hinder part of the base of the 
cranium of the Wolf (Canis lupus), c, Condyloid foramen ; I, fora- 
men lacerum posticum ; car, carotid canal ; e, eustachian canal ; 
o, foramen ovale ; a, posterior, and a', anterior aperture of ali 



THE SKELETON 39 



of the skull receive much impress from the real shape of the cavity 
containing the brain. The size and form of the mouth, and the 
modifications of the jaws for the support of teeth of various shape 
and number, the ridges and crests on the cranium for the attachment 
of the muscles necessary to put this apparatus in motion, and out- 
growths of bone for the enlargement of the external surface required 
for the support of sense organs or of weapons, such as horns or 
antlers (which outgrowths, to prevent undue increase of weight, are 
filled with cells containing air), cause the principal variations in the 
general configuration of the skull. These variations are, however, 
only characteristically developed in perfectly adult animals, and are 
in many cases more strongly marked in the male than the female 
sex. Throughout all the later stages of growth up to maturity the 
size and form of the brain-case remain comparatively stationary, 
while the accessory parts of the skull rapidly increase and assume 
their distinctive development characteristic of the species. 

The hyoidean apparatus in mammals (Fig. 6) supports the tongue 
and larynx, and consists of an inferior median portion termed the 
basihyal, from which two pairs of half arches, or cornua, extend up- 
wards and outwards. The anterior is the more important, being 
connected with the periotic bone of the cranium. It may be almost 
entirely ligamentous, but more often has several ossifications, the 
largest of which is usually the stylohyal. The posterior cornu 
(thyrohyal) is united at its extremity with the thyroid cartilage of 
the larynx, which it suspends in position. The median portion, 
or basihyal, is sometimes, as in the Howling Monkeys, enormously 
enlarged and hollowed, admitting into its cavity an air-sac connected 
with the organ of voice. 

Vertebral Column. — The vertebral column consists of a series of 
distinct bones called vertebra?, arranged in close connection with 
each other along the dorsal side of the neck and trunk, and in the 
median line. 1 It is generally prolonged posteriorly beyond the 
trunk, to form the axial support of the appendage called the tail. 
Anteriorly it is articulated with the occipital region of the skull. 
The number of distinct bones composing the vertebral column 
varies greatly among the Mammalia, the main variation being 
due to the degree of elongation of the tail. Apart from this, in 
most mammals the number is not far from thirty, though it may 
fall as low as twenty-six (as in some Bats), or rise as high as 
forty (Hyrax and Cholcepus). The different vertebrse, with some 
exceptions, remain through life quite distinct from each other, 
though closely connected by means of fibrous structures which 
allow of a certain, but limited, amount of motion between them. 
The exceptions are the following: — (1) near the posterior part 

1 For the sake of uniformity, in all the following descriptions of the vertebral 
column, the long axis of the body is supposed to be in the horizontal position. 



4o 



GENERAL ANATOMICAL CHARACTERS 



of the trunk, in nearly all mammals which possess completely 
developed hinder limbs, two or more vertebra? become ankylosed 
together to form the " sacrum," or portion of the vertebral column 
to which the pelvic girdle is attached ; (2) in some species of 
Whales and Armadillos there are constant ossific unions of certain 
vertebrae of the cervical region. 

Although the vertebrae of different regions of the column of the 
same animal or of different animals present great diversities of 
form, yet there is a certain general resemblance among them, or a 
common plan on which they are constructed, which is more or less 
modified by alteration of form or proportions, or by the addition or 
suppression of parts to fit them to fulfil their special purpose in the 
economy. An ordinary or typical vertebra consists, in the first 
place, of a solid piece of bone, termed the body or centrum (Fig. 
9, c), of the form of a disk or short cylinder. The bodies of con- 




az 




JJZ 



Fio. 9. — Anterior surface of Human 
thoracic vertebra (fourth), c, Body or 
centrum ; nc, neural canal ; p, pedicle, 
and I, lamina of the arch ; t, transverse 
process ; az, anterior zygapophysis. 



Fig. 10. — Side view of the first lum- 
bar vertebra of a Dog (Canis familiaris). 
s, Spinous process ; az, anterior zygapo 
physis ; pz, posterior zygapophysis ; m, 
metapophysis ; a, anapophysis ; t, trans- 
verse process. 



tiguous vertebrae are connected together by a very dense, tough, and 
elastic material called the " intervertebral substance," of peculiar and 
complex arrangement. This substance forms the main, and in some 
cases the only, union between the vertebrae. Its elasticity provides 
for the vertebrae always returning to their normal relation to each 
other and to the column generally, Avhen they have been disturbed 
therefrom by muscular action. A process (p) arises on each side 
from the dorsal surface of the body. These processes, meeting in 
the middle line above, form an arch, surmounting a space or short 
canal (nc). Since it contains the posterior prolongation of the 
great cerebro-spinal nervous axis, or spinal cord, this space is called 
the neural canal, and the arch the neural arch, in contradistinction 
to another arch on the ventral surface of the body of the verte- 
brae, called the haemal arch. The latter is, however, never formed 



THE SKELETON 41 



in mammals by any part of the vertebra itself, but by certain 
distinct bones placed more or less in apposition to it, namely the 
ribs in the thoracic, and the " chevron bones " in the caudal region. 
In most cases the arch of one vertebra is articulated with that of 
the next by distinct surfaces with synovial joints, placed one on 
each side, called "zygapophyses " (az, pz), but these are often entirely 
wanting when flexibility is more needed than strength, as in the 
greater part of the caudal region of long-tailed animals. In addition 
to the body and the arch, there are certain projecting parts called 
processes, chiefly serving for the attachment of the numerous 
muscles which move the vertebral column. Of these two are single 
and median, viz. the spinous process, neural spine, or neurapophysis 
(s), arising from the middle of the upper part of the arch, and the 
hypapophysis from the under surface of the body. The latter, how- 
ever, is as frequently absent as the former is constant. The other 
processes are paired and lateral. They are the transverse processes 
(/), of which there may be two, an upper and a lower, in which case 
the former .is called, in the language of Owen (to whom we are 
indebted for the terminology of the parts of vertebrae in common 
use), " diapophysis," and the latter " parapophysis." Other processes 
less constantly present are called respectively " metapophyses " (m) 
and " anapophyses " (a). 

The vertebral column is divided for convenience of description 
into five regions — the cervical, thoracic or dorsal, lumbar, sacral, and 
caudal. This division is useful, especially as it is not entirely 
arbitrary, and in most cases is capable of ready definition ; but at 
the contiguous extremities of the regions the characters of the 
vertebra of one are apt to blend into 
those of the next region, either normally 
or as peculiarities of individual skeletons. 

Cervical Vertebrae. — The cervical region 
constitutes the most anterior portion of f^^^^^^p^^xaz 

the column, or that which joins the 
cranium. The vertebra which belong to 
it are either entirely destitute of movable 
ribs, or if they have any these are small, 
and do not join the sternum. As a general 
rule they have a considerable perforation 
through the base of the transverse process 
(the vertebrarterial canal, Fig. 11, v) ; or, 
as it is sometimes described, they have s , spinous process ; az, anterior 

two transverse processes, superior and zygapophysis ; v, vertebrarterial 




Fig. 11. — Anterior surface of 
sixth cervical vertebra of Dog. 



canal ; t, transverse process ; t', its 

inferior, which meet at their extremities inferior lamella . 

to enclose a canal. This, however, rarely 

applies to the last vertebra of the region, in which only the upper 

transverse process is usually developed. The transverse process, 



42 GENERAL ANATOMICAL CHARACTERS 

moreover, very often sends down near its extremity a more or 
less compressed plate (inferior lamella), which, being considered 
serially homologous with the ribs of the thoracic vertebra? (though 
not developed autogenously), is often called the " costal " or 
" pleurapophysial " plate. This is usually largest on the sixth, and 
altogether wanting on the seventh vertebra. The first and second 
cervical vertebrae, called respectively "atlas" and "axis," are 
specially modified for the function of supporting and permitting 
the free movements of the head. They are not united together 
by the intervertebral substance, but connected only by ordinary 
ligaments and synovial joints. 

The cervical region in mammals presents the remarkable 
peculiarity that, whatever the length or flexibility of the neck, the 
number of vertebrae is the same, viz. seven, with the exception of 
the Manatee and Hoffman's Two-toed Sloth (Cholospus hoffmanni), 
which both have but six, and the Three-toed Sloth (Bradyjms 
tridactylus), which has nine, though in this case the last two usually 
support movable ribs, which are not sufficiently developed to reach 
the sternum. 

According to Parker there may occasionally be eight cervicals 
in the Pangolins (Manis). 

Dorsal Vertebral. — The dorsal (or, as it would be more correctly 
termed, thoracic) region consists of the vertebrae succeeding those 
of the neck, which have ribs movably articulated to them. These 
ribs arch round the thorax — the anterior one, and usually the 
greater number of those that follow, being attached below to the 
sternum. 

Lumbar Vertebrce. — The lumbar region consists of those vertebrae 
of the trunk in front of the sacrum which bear no movable ribs. 
It may happen that, as the ribs decrease in size posteriorly (the 
last being sometimes more or less rudimentary), the step from the 
thoracic to the lumbar region may be gradual and rather undeter- 
mined in a given species ; but most commonly this is not the 
case, and the distinction is as well defined here as in any other 
region. As a general rule there is a certain relation between the 
number of the thoracic and lumbar vertebrae, the whole number 
being tolerably constant in a given group of animals, and any 
increase of the one being at the expense of the other. Thus in all 
known Artiodactyle Ungulata there are 1 9 dorso-lumbar vertebrae ; 
but these may consist of 1 2 dorsal and 7 lumbar vertebrae, or 1 3 
dorsal and 6 lumbar, or 14 dorsal and 5 lumbar. The smallest 
number of dorso-lumbar vertebrae in mammals occurs in some 
Armadillos, which have but 14. The number found in Man, 
the higher Apes, and most Bats, viz. 17, is exceptionally low; 
19 prevails in the Artiodactyla, nearly all Marsupials, and very 
many Rodents; 20 or 21 in Carnivora and most Insectivora ; 



THE SKELETON 



43 



and 23 in Terissodactyla. The highest and quite exceptional 
numbers are in the Two-toed Sloth (Choke/pus) 27, and the Hyxax 
30. The prevailing number of rib-bearing vertebra? is 12 or 13, 
any variation being generally in excess of these numbers. 

Sacral Vertebra*. — The sacral region offers more difficulties o. 
definition. Taking the human " os sacrum " as a guide for 
comparison, it is generally defined as consisting of those vertebras 
between the lumbar and caudal regions which are ankylosed 
together to form a single bone. It happens, however, that the 
number of such vertebras varies in different individuals of the 
same or nearly allied species, especially as age advances, when a 
certain number of the tail vertebras generally become incorporated 
with the true sacrum. Other suggested tests — as those vertebras 
which have a distinct additional (pleurapophysial) centre of ossifica- 
tion between the body and the ilium, those to which the ilium is 
directly articulated, or those in front of the insertion of the ischio- 
sacral ligaments — being ecpially unsatisfactory or unpractical, the 
old one of ankylosis, as it is found to prevail in the average 
condition of adults in each species, is used in the enumeration of 
the vertebras in the following pages. The Cetacea, having no iliac 
bones, have no part of the vertebral column modified into a 
sacrum. 

Caudal Vertebra}. — The caudal vertebras are those placed behind 
the sacrum, and terminating the vertebral column. They vary 
in number greatly — being reduced to 5, 4, or even 3, in a most 
rudimentary condition, in Man 
and in some Apes and Bats, and 
being numerous and powerfully 
developed, with strong and com- 
plex processes, in many mammals, 
especially among the Edentata, 
Cetacea, and Marsupialia. The 
highest known number, 46, is 
possessed by the African Long- 
tailed Pangolin. Connected with 
the under surface of the caudal 
vertebras of many mammals which 
have the tail well developed are 
certain bones formed more or less 
like an inverted arch, called chev- 
ron bones, or by the French os en 
V. These are always situated 
nearly opposite to an interverte- 
bral space, and are generally artic- 
ulated both to the vertebra in front and the vertebra behind, but 
sometimes chiefly or entirely either to one or the other. 




Fig. 12. — Anterior surface of fourth 
caudal vertebrae of Porpoise (Phoccena com- 
munis), s, Spinous process ; m, metapophy- 
sis ; t, transverse process ; h, chevron bone. 



44 



GENERAL ANATOMICAL CHARACTERS 



ms' 



In some of the Anomodont Keptiles and Labyrintkodont 
Amphibians these chevrons are attached to the intercentra — or 
imperfect disks alternating with the true centra — which suggests 
that they are primarily intercentral elements which have been trans- 
ferred to the edges of the centra by the disappearance of the inter- 
centra. 

Sternum. — The sternum of mammals is a bone, or generally a 
series of bones, placed longitudinally in tke mesial line, on tke 
inferior or ventral aspect of tke tkorax, and connected on eack side 

Avitk tke vertebral column by a series 
of more or less ossified bars called 
" ribs." It is present in all mammals, 
but varies muck in ckaracter in tke 
different groups. It usually consists 
of a series of distinct segments placed 
one before tke otker, tke anterior 
being called tke presternum or " manu- 
brium sterni " of kuman anatomy, and 
tke posterior tke xipkisternum, or 
xipkoid or ensiform process, wkile tke 
intermediate segments, Avkatever tkeir 
number, constitute tke mesosternum 
or " body." In tke Wkalebone Wkales 
tke presternum alone is developed, and 
but a single pair of ribs is attacked 
to it. 

Bibs. — Tke ribs form a series of 
long, narrow, and more or less flattened 
bones, extending laterally from tke 
sides of tke vertebral column, curving 
downwards towards tke median line 
of tke body below, and mostly joining 
tke sides of tke sternum. Tke posterior 
ribs, kowever, do not directly articulate 
witk tkat bone, but are eitker attacked by tkeir extremities to 
tke edges of eack rib in front of tkem, and tkus only indirectly 
join tke sternum, or else tkey are quite free below, meeting no part 
of tke skeleton. Tkese differences kave given rise to tke division 
into " true " and " false " ribs (by no means good expressions), signi- 
fying tkose tkat join tke sternum directly and tkose tkat do not ; 
and of tke latter, tkose tkat are free below are called " floating " 
ribs. Tke portion of eack rib nearest tke vertebral column and 
tkat nearest tke sternum differ in tkeir ckaracters, tke latter being 
usually but imperfectly ossified, or remaining permanently cartila- 




Fig. 13. -Human sternum and 
sternal ribs, ps, Presternum ; ms, 
mesosternum ; xs, xiphisterimm ; c, 
point of attachment of clavicle ; 1 to 
10, the cartilaginous sternal ribs. 



Tkese are called " costal cartilages," or wken ossified 



" sternal ribs." 



THE SKELETON 



45 



In the anterior part of the thorax the vertebral extremity of 
each rib is divided into two parts, " head " or " capitnlum," and 
"tubercle"; the former is attached to the side of the body of the 
vertebra, the latter to its 
transverse process ; the 
former attachment corre- 
sponds to the interspace 
between the vertebra?, the 
head of the rib commonly 
articulating partly with 
the hinder edge of the 
body of the vertebra ante- 
cedent to that which bears 
its tubercle. Hence the 
body of the last cervical 
vertebra usually supports 
part of the head of the first 
rib. In the posterior part 
of the series the capitular 
and tubercular attach- 
ments commonly coalesce, 
and the rib is attached 
solely to its corresponding 
vertebra. The number of pairs of ribs is of course the same as that 
of the thoracic vertebrae. 

The circumstance that in some of the Anomodont reptiles and 




Fig. 14.— Sternum and strongly ossified sternal ribs 
of Great Armadillo (Priodon gigas). j>s, Presternum; 
xs, xiphisternum. 




Fig. 15. — Skeleton of Lion (Felis ho), cd, Caudal vertebrae ; cp, carpus ; cr, coraeoid process 
of scapula ; cv, cervical vertebrae ; d, dorsal vertebra; ; fb, fibula ; fm, femur ; h, humerus ; il, 
ilium ; isch, ischium ; I, lumbar vertebras ; m, metatarsus ; mc, metacarpus ; p, patella ; pb, pubis ; 
ph, phalanges ; pv, pelvis ; r, radius ; s, sacral vertebrae ; sc, scapula ; sk, skull ; tb, tibia ; ts, 
tarsus ; v., ulna ; zy, zygomatic arch. 

Labyrinthodonts the capitula of the ribs articulate with the inter- 
central elements of the vertebral column has suggested, as in the 



46 GENERAL ANATOMICAL CHARACTERS 

instance of the chevron bones, that the intercentral capitular articu- 
lation of the ribs of mammals is a feature directly inherited 
from those extinct types by the gradual disappearance of the 
intercentra. 

Appendicular Skeleton. — The appendicular portion of the frame- 
work consists, when completely developed, of two pairs of limbs, 
anterior and posterior (Fig. 15). 

Anterior Limb. — The anterior limb is present and fully developed 
in all mammals, being composed of a shoulder girdle and three seg- 
ments belonging to the limb proper, viz. the upper arm or brachium, 
the fore-ai'm or antebrachium, and the hand or manus. 

Shoulder-girdle. — The shoulder or pectoral girdle'm the large majority 
of mammals is in a rudimentary or rather modified condition, com- 
pared with that in which it exists in other vertebrates. In the Mono- 
tremata (Ornithorhynchus and Echidna) alone is the ventral portion, or 
coracoid, complete and articulated with the sternum below, as in the 
Sauropsida ; and in this group alone do we find an anterior ventral 
element, apparently corresponding with the precoracoid of the Anom- 
odont reptiles, although generally known as the epicoracoid. In all 
other mammals the coracoid, though ossified from a distinct centre, 
forms only a process, sometimes a scarcely distinct tubercle, projecting 
from the anterior border of the glenoid cavity of the scapula. The 
last-named cavity, which in the Monotremes is formed jointly by 
the scapula and coracoid, receives the head of the humerus, or 
arm-bone. The scapula is always well developed, and generally 
broad and flat (whence its vernacular name " blade bone "), with a 
ridge called the " spine " on its outer surface, which usually ends in 
a free curved process, the "acromion." As the scapula affords 
attachment to many of the muscles which act upon the anterior 
limb, its form and the development of its processes are greatly 
modified according to the uses to which the member is put. Thus it 
is most reduced and simple in character in those animals whose limbs 
are mere organs of support, as the Ungulates ; and most complex 
when the limbs are also used for grasping, climbing, or digging. 
The development or absence of the clavicle or " collar-bone," an 
accessory bar which connects the sternum with the scapula and 
steadies the shoulder-joint, has a somewhat similar relation, though 
its complete absence in the Bears shows that this is not an invariable 
rule. A complete clavicle is found in Man and all the Primates, in 
Chiroptera, all Insectivora (except Potaniogale), in many Rodents, in 
most Edentates, and in all Marsupials, except Perameles. More or 
less rudimentary clavicles (generally suspended freely in the muscles) 
are found in the Cat, Dog, and most Carnivora, Myrmecophaga, and 
some Rodents. Clavicles are altogether absent in most of the I Wsidce, 
all the Pinnipedia, Manis among Edentates, the Cetacea, Sirenia, 
Ungulates, and some Rodents. 



THE SKELETON 



47 



ig 



a T-shaped 

the sternum, 



The Monotremcs are peculiar in possessin 
interclavicle like that of many reptiles, lying upon 
and articulating superiorly with the clavicles. 

Brachiv/m and Antebrachium. — The proximal segment of the 
anterior or pectoral limb proper contains a single bone, the humerus, 
and the second segment two bones, the radius and the ulna, placed 
side by side, and articulating with the humerus at their proximal, 
and with the carpus at their distal extremity (Fig. 15). In their 
primitive and unmodified condition these bones may be considered as 
placed one on each border of the limb, the radius being preaxial or 
anterior, and the ulna postaxial or posterior, when the distal or free 
end of the limb is directed outwards, or away from the trunk. This 
is their position in the earliest embryonic condition, and is best 
illustrated among adult mammals in the Cetacea, where the two 
bones are fixed side by side and parallel to each other. In the 
greater number of mammals the bones assume a very modified and 
adaptive position, usually crossing each other in the forearm, the 
radius in front of the ulna, so that the preaxial bone (radius), 
though external (in the ordinary position of the limb) at the upper 
end, is intei'nal at the lower end ; and the hand, being mainly fixed 
to the radius, also has its preaxial border internal. In the large 
majority of mammals the bones are fixed in this position, but in 
some few, as in Man, a free movement of crossing and uncrossing — 
or pronation and supination, as it is termed — is allowed between 
them, so that they can be placed in their primitive parallel condition, 
when the hand (which moves with the radius) 
is said to be supine, or they may be crossed, 
when the hand is said to be prone. 

The humerus frequently has a foramen 
piercing the inner border of the distal 
extremity, known as the entepicondylar 
foramen, which corresponds with a similar 
one found in the Anomodont reptiles. The 
hollow in the head of the ulna for the recep- 
tion of the head of the humerus is known 
as the greater sigmoid cavity, and that for 
the head of the radius as the lesser sigmoid 
cavity (Fig. 16). The term olecranon is 
applied to that process of the ulna which 
forms the prominence of the elbow. 

In most mammals Avalking on four limbs, 
in which the hand is permanently prone, the 
ulna is much reduced in size, and the radius 
increased, especially at the upper end ; so 
that the articular surface of the latter, instead of being confined to 
the external side of the trochlea of the humerus, extends all across 




Fig. 16. — Outer aspect of 
the proximal extremity of the 
right ulna of a Bear (Ursus). 
a, Anterior tubercle ; ol, 
olecranon ; 6, greater sigmoid 
cavity ; c, lesser do. 



4 8 



GENERAL ANATOMICAL CHARACTERS 



its anterior surface, and the two bones, instead of being external 
and internal, are anterior and posterior. In many hoofed or Ungu- 
late mammals, and in Bats, the ulna is reduced to little more than 
its upper articular extremity, and firmly ankylosed to the radius 
— stability of these parts being more essential than mobility. 

Manas. — The terminal segment of the anterior limb is the hand 
or maims. Its skeleton consists of three divisions : (1) the 
" carpus," a group of small, more or less rounded or angular bones 
with flattened surfaces applied to one another, and, though arti- 
culating by synovial joints, having scarcely any motion between 
them ; (2) the " metacarpus," a series of elongated bones placed side 
by side, with their proximal ends articulating by almost immovable 
joints with the carpus; (3) the "phalanges" or bones of the digits, 
usually three in number to each, articulating to one another by freely 
movable hinge- joints, the first being connected in like manner to 
the distal end of the metacarpal bone to which it corresponds. 

Carpus. — To understand thoroughly the arrangement of the 
bones of the carpus in mammals, it is necessary to study their 
condition in some of the lower vertebrates. Fig. 17 represents 
the manus in one of its fullest and at the same time most 

generalised forms, as seen in one of the 
Water Tortoises (Chelydra serpentina). The 
carpus consists of two principal rows of 
bones. The upper or proximal row con- 
tains three bones, to which Gegenbaur 
has applied the terms radiate (r), inter- 
medium (i), and uhiare (u), the first being 
on the radial or preaxial side of the limb. 1 
The lower or distal row contains five 
bones, called carpale 1, 2, 3, 4, and 5 
respectively, commencing on the radial 
side. Between these two rows, in the 
middle of the carpus, is a single bone, 
the centrate (c). In this very symmetrical 
carpus it will be observed that the radiate 
supports on its distal side two bones, 
carpale 1 and 2 ; the intermedium is in a 
line with the centrate and carpale 3, which 
together form a median axis of the hand, 
while the ulnare has also two bones articu- 
lating with its distal end, viz. carpale 4 
and 5. Each of the carpals of the distal 
row supports a metacarpal. 

1 The opinion has recently been expressed by Baur that the bone termed 
radiale in Fig. 17 is really a second centrale, and that the radiale is represented 
by a minute bone generally known as the radial sesamoid. The mammalian 




Fio. 17.— Dorsal surface of the 
right inarms of a Water Tortoise 
(Chelydra serpentina). After Ge- 
genbaur. U, Ulna ; R, radius ; u, 
ulnare ; i, intermedium ; r, radiale ; 
c, centrale ; 1-5, the five bones of 
the distal row of the carpus ; mi- 
ni 5 , the five metacarpals. 



THE SKELETON 49 



In the carpus of the Mammalia there are usually two additional 
bones developed in the tendons of the flexor muscles, one on each 
side of the carpus, which may be called the radial and ulnar 
sesamoid bones ; the latter, which is the more constant and generally 
larger, is commonly known as the pisiform bone. The fourth and 
fifth carpals of the distal row are always united into a single bone, 
and the centrale is very often absent. As a general rule all the 
other bones are present and distinct, though it not unfrequently 
happens that two may have coalesced to form a single bone, or 
one or more may be altogether suppressed. 

The following table shows the principal names in use for the 
various carpal bones, — those in the second column being the terms 
generally employed by English anatomists : — 

Radiale — Scaphoid = Naviculars 
Intermedium = Lunar = Semilunare, Lunatum. 

Ulnare = Cuneiform = Triquetrum, Pyramidale. 

Centrale = Central = Intermedium (Cuvier). 

Carpale 1 = Trapezium = Multangulum majus. 

Carpale 2 = Trapezoid = Multangulum minus. 

Carpale 3 = Magnum = Capitatum. 



Carpale 4 
Carpale 5 



Unciform = Hamatum, Uncinatum. 



The radial and ulnar sesamoids are regarded by Bardeleben l as 
the rudiments of a prepollex and a postminimus digit ; the primitive 
number of digits being thus supposed to have been seven. These 
bones have been observed in all orders of mammals having five 
complete digits. Occasionally, as in Peclctes caffer, the so-called 
prepollex consists of two bones, of which the distal one bears a 
distinct nail -like horny covering. In Bathyergus maritimus the 
pisiform, or postminimus, is likewise double ; the two elements 
being regarded by their describer as representing the carpal and 
metacarpal of the presumed seventh digit. 

Similarly in the posterior limb the tibial sesamoid, and a fibular 
ossification corresponding to the pisiform, are regarded as represent- 
ing a prehallux and a postminimus. 

Metacarpus and Phalanges. — The metacarpal bones, with the 
digits which they support, are never more than five in number, and 
are described numerically — first, second, etc., counting from the 
radial towards the ulnar side. The digits are also sometimes named 
(1) the pollex, (2) index, (3) medius, (4) annularis, (5) minimus. 

scaphoid is accordingly also regarded as a second centrale. In the same com- 
munication, Dr. Baur expresses his disbelief in the existence of remnants of a 
prepollex and of a seventh digit in mammals and other vertebrates. (See Anat. 
Anzeiger, vol. iv. pp. 49-52, 1889.) 

1 On the Prsepollex and Pramallux, etc., Proc. Zool. Soc. 1889, pp. 259-262. 

4 



50 GENERAL ANATOMICAL CHARACTERS 

One or more may be in a rudimentary condition, or altogether 
suppressed. If one is absent, it is most commonly the first. 
Excepting the Cetacea, no mammals have more than three phalanges 
to each digit, but they may occasionally have fewer by suppression 
or ankylosis. The first or radial digit is an exception to the usual 
rule, one of its parts being constantly absent, since, while each of the 
other digits has commonly a metacarpal and three phalanges, it has 
only three bones altogether ; whether the missing one is a meta- 
carpal or one of the phalanges is a subject which has occasioned 
much discussion, and has not yet been satisfactorily decided. The 
terminal phalanges of the digits are usually specially modified to 
support the nail, claw, or hoof, and are called " ungual phalanges." 
In walking, some mammals (as the Bears) apply the whole of the 
lower surface of the carpus, metacarpus, and phalanges to the 
ground ; to these the term " plantigrade " is applied. Many others 
(as nearly all the existing Ungulata) only rest on the last one or two 
phalanges of the toes, the first phalanx and the metacarpals being 
vertical and in a line with the fore-arm. These are called " digiti- 
grade." Intermediate conditions exist between these two forms, to 
which the terms " phalangigrade " (as the Camel) and " subplanti- 
grade " (as in most Carnivora), are applied. When the weight is 
borne entirely on the distal surface of the ungual phalanx, and the 
horny structures growing around it, as in the Horse, the mode of 
progression is called " unguligiade." 

In the Chiroptera the digits are enormously elongated, and 
support a cutaneous expansion constituting the organ of flight. In 
the Cetacea the manus is formed into a paddle, being covered by 
continuous integument, which conceals all trace of division into 
separate digits, and shows no sign of nails or claws. In the Sloths 
the manus is long and very narrow, habitually curved, and terminat- 
ing in two or three pointed curved claws in close apposition with 
each other, and incapable, in fact, of being divaricated ; so that it is 
reduced to the condition of a hook, by which the animal suspends 
itself to the boughs of the trees among which it lives. These are 
only examples of the endless modifications to which the distal 
extremity of the limb is subjected in adaptation to the various 
purposes to which it is applied. 

Posterior Limb. — The posterior limb is constructed upon a plan 
very similar to that of the anterior extremity. It consists of a 
pelvic girdle and three segments belonging to the limb proper, viz. 
the thigh, the leg, and the foot or pes (Fig. 15). 

Pelvic Girdle. — The pelvic girdle is present in some form in all 
mammals, though in the Cetacea and the Sirenia it is in an exceed- 
ingly rudimentary condition. In all mammals except those be- 
longing to the two orders just named, each lateral half of the pelvic 
girdle consists essentially, like the corresponding part of the anterior 



THE SKELETON 51 



limb, of a flattened rod of bone crossing the long axis of the trunk, 
having an upper or dorsal and a lower or ventral end. The upper 
end diverges from that of the opposite side, but the lower end 
approaches, and, in most cases, meets it, forming a symphysis, 
without the intervention of any bone corresponding to the sternum. 
The pelvic girdle differs from the shoulder girdle in being firmly 
articulated to the vertebral column, thus giving greater power to 
the hinder limb in its function of supporting and propelling the 
body. Like the shoulder girdle, it bears on its outer side, near 
the middle, a cup-shaped articular cavity (" acetabulum "), into 
which the proximal end of the first bone of the limb proper is 
received. Each lateral half of the girdle is called the "os 
innominatum," or innominate bone, and consists originally of three 
bones which unite at the acetabulum. The "ilium" or upper bone 
is that which articulates with the sacral vertebrae. Of the two 
lower bones the anterior or " pubis " unites with its fellow of 
the other side at the symphysis; the posterior is the "ischium." 
These lower elements form two bars of bone, united above and 
below, but leaving a space between them in the middle, filled only 
by membrane, and called the " thyroid " or " obturator " foramen. 
The whole circle of bone formed by the two innominate bones 
and the sacrum is called the pelvis. In the Monotremata 
and Marsupialia, a pair of thin, flat, elongated ossifications 
called epipubic or marsupial bones are attached to the fore part 
of the pubis, and project forward into the muscular wall of the 
abdomen. 

Thigh and Leg. — The first segment of the limb proper has one 
bone, the femur, corresponding with the humerus of the anterior 
limb. The second segment has two bones, the tibia and fibula, corre- 
sponding with the radius and ulna. These bones always lie in their 
primitive unmodified position, parallel to each other, the tibia on 
the preaxial and the fibula on the postaxial side, and are never 
either permanently crossed or capable of any considerable amount 
of rotation, as in the corresponding bones of the fore limb. In the 
ordinary walking position the tibia is internal, and the fibula ex- 
ternal. In many mammals the fibula is in a more or less rudi- 
mentary condition, and it often ankyloses with the tibia at one or 
both extremities. The patella or " knee-cap," which is found in an 
ossified condition in all mammals, with the exception of some of 
the Marsupialia, is a large sesamoid bone developed in the tendon 
of the extensor muscles of the thigh, where the tendon passes over 
the front of the knee-joint, to which it serves as a protection. 
There are frequently smaller ossicles, one or two in number, situated 
behind the femoral condyles, called "fabelke." The processes for 
the attachment of muscles near the upper end of the femur are 
termed trochanters ; and the third trochanter, found on the hinder 



52 GENERAL ANATOMICAL CHARACTERS 

aspect of the shaft of this bone in many forms is of considerable 
taxonomic importance. 

Pes. — The terminal segment of the hind limb is the foot or pes. 
Its skeleton presents in many particulars a close resemblance to that 
of the manus, being divisible into three parts: (1) a group of 
short, more or less rounded or square bones, constituting the 
tarsus ; (2) a series of long bones placed side by side, forming the 
metatarsus; and (3) the phalanges of the digits or toes. 

The bones of the tarsus of many of the lower Vertebrata closely 
resemble both in number and arrangement those of the carpus, as 
shown in Fig. 1 7. They have been described in their most general- 
ised condition by Gegenbaur under the names expressed in the first 
column of the following table. The names in the second column are 
those by which they are generally known to English anatomists, 
while in the third column some synonyms occasionally employed 
are added. 

Tibialei?) ) =Agt lugl =Talus 

Intermedium J 

Fibula/re = Calcaneum = Os calcis. 

Centrale = Navicular = Scaphoideum. 

Tarsale 1 = Internal cuneiform = Entocunciforme. 

Tarsale 2 = Middle cuneiform = Mesocuneiforme. 

Tarsale 3 = External cuneiform = Ectocuneiforme. 

Tarsale 4 \ _ p i • j 

Tarsale 5 J 

The bones of the tarsus of mammals present fewer diversities of 
number and arrangement than those of the carpus. The proximal 
row (see Fig. 18) always consists of two bones, namely the astra- 
galus (a), which probably represents the coalesced scaphoid and lunar 
of the hand, and the calcaneum (c). The former is placed more to 
the dorsal side of the foot than the latter, and almost exclusively 
furnishes the tarsal part of the tibio-tarsal or ankle-joint. The cal- 
caneum, placed more to the ventral or " plantar " side of the foot, is 
elongated backwards to form a more or less prominent tuberosity, 
the " tuber calcis," to which the tendon of the great extensor muscles 
of the foot is attached. The navicular bone (?i) is interposed between 
the proximal and distal row on the inner or tibial side of the foot, 
but on the outer side the bones of the two rows come into contact. 
The distal row, when complete, consists of four bones, which, be- 
ginning on the inner side, are the three cuneiform bones, internal 
(c 1 ), middle (c 2 ), and external (c 3 ), articulated to the distal surface 
of the navicular, and the cuboid (cb), articulated with the calcaneum. 
Of these the middle cuneiform is usually the smallest in animals 

1 Cope and Baur consider that the astragalus corresponds only with the inter- 
medium, and that the tihiale may exist as a distinct element. 



THE DIGESTIVE SYSTEM 



53 



in which all five digits arc developed ; but when the hallux is 
wanting the internal cuneiform may be rudimentary or altogether 
absent. The three cuneiform bones sup- 
port respectively the first, second, and third 
metatarsals, and the cuboid supports the 
fourth and fifth ; they thus exactly corre- 
spond with the four bones of the distal row 
of the carpus. 

In addition to these constant tarsal 
bones, there may be supplemental or 
sesamoid bones : one situated near the 
middle of the tibial side of the tarsus, 
largely developed in many Carnivora and 
Rodentia ; another, less frequent, on the 
fibular side ; and a third, often developed 
in the tendons of the plantar surface of 
the tarsus, is especially large in Armadillos. 
There is also usually a pair of sesamoid 
bones on the plantar aspect of each meta- 
tarso-phalangeal articulation. In the young 
of the carnivorous genus Cryptoprocta there 
may be a second centrale, which usually 
coalesces with the ectocuneiform. 

The metatarsal bones never exceed five 
in number, and the phalanges follow the 
same numerical rule as in the manus, never 
exceeding three in each digit. Moreover, 
the first digit, counting from the tibial side, 
or hallux, resembles the pollex of the hand 
in always having one segment less than 
the other dibits. As the function of the 
hind foot is more restricted than that of the hand the modifica- 
tions of its structure are less striking. In the Cetacea and the 
Sirenia it is entirely wanting, though in some existing members of 
the first-named order rudiments of the bones of both the first and 
second segments of the limb have been detected, and a femur is 
present in the Miocene Sirenian Halitherium. 




Fio. 18.— Bones of the right 
Human foot. T, Tarsus ; M, 
metatarsus ; Ph, phalanges ; c, 
calcaneum ; a, astragalus ; cb, 
cuboid ; n, navicular ; c 1 , inter- 
nal cuneiform ; c-, middle cunei- 
form ; c3, external cuneiform. The 
digits are indicated by Roman 
numerals, counting from the 
tibial to the fibular side. 



IV. THE DIGESTIVE SYSTEM. 



General Considerations. — The search after the purpose which 
every modification of structure subserves in the economy is always 
full of interest, and, if conducted with due caution and sufficient 
knowledge of all the attendant circumstances, may lead to important 
generalisations. It must always be borne in mind, however, that 



54 GENERAL ANATOMICAL CHARACTERS 

adaptation to its special function is not the only cause of the 
particular form or structure of an organ, but that this form, having 
in all probability been arrived at by the successive and gradual 
modification of some other different form from which it is now to a 
greater or less degree removed, has other factors besides use to be 
taken into account. In no case is this principle so well seen as in 
that of the organs of digestion. These may be considered as 
machines which have to operate upon alimentary substances in very 
different conditions of mechanical and chemical combination, and to 
reduce them in every case to the same or precisely similar 
materials ; and Ave might well imagine that the apparatus required 
to produce flesh and blood out of coarse fibrous vegetable substances 
would be different from that which had to produce exactly the 
same results out of ready-made flesh or blood ; and in a very broad 
sense we find that this is so. Thus, if we take a large number of 
carnivorous animals, belonging to different fundamental types, and 
a large number of herbivorous animals, and strike a kind of average 
of each, we shall find that there is, pervading the first group, a 
general style, if we may use the expression, of the alimentary organs, 
different from that of the others. That is to say, there is a specially 
carnivorous and a specially herbivorous modification of these parts. 
But, if function were the only element which has guided such 
modification, it might be inferred that, as one form must be supposed 
to be best adapted in its relation to a particular kind of diet, that 
form would be found in all the animals consuming such diet. But 
this is far from being the case. Thus the Horse and the Ox, for 
instance — two animals whose food in the natural state is precisely 
similar — are most different as regards the structure of their ali- 
mentary canal, and the processes involved in the preparation of that 
food. Again, the Seal and the Porpoise, both purely fish-eaters, 
which seize, swallow, and digest precisely the same kind of prey, in 
precisely the same manner, have a totally different arrangement of the 
alimentary canal. If the Seal's stomach is adapted in the best conceiv- 
able manner for the purpose it has to fulfil, why is not the Porpoise's 
stomach an exact facsimile of it, and vice versa ? We can only answer 
that the Seal and Porpoise belong to different natural groups of 
animals, formed either on different primitive types, or descended 
from differently constructed ancestors. On this principle only can 
we account for the fact that, whereas, owing to the comparatively 
small variety of the different alimentary substances met with in 
nature, few modifications would appear necessary in the organs of 
digestion, there is really endless variety in the parts devoted to 
this purpose. 

Mouth. — The digestive apparatus of mammals, as in other ver- 
tebrates, consists mainly of a tube with an aperture placed at or 
near either extremity of the body, — the oral and the anal orifice, — 



THE DIGESTIVE SYSTEM 55 

and furnished with muscular walls, the fibres of which are so 
arranged as by their regular alternate contraction and relaxation to 
(hive onwards the contents of the tube from the first to the second 
of these apertures. The anterior or commencing portion of this 
tube and the parts around it are greatly and variously modified in 
relation to the functions assigned to them of selecting and seizing 
the food, and preparing it by various mechanical and chemical 
processes for the true digestion which it has afterwards to undergo 
before it can be assimilated into the system. For this end the tube 
is dilated into a chamber or cavity called the mouth, bordered 
externally by the lips, which are usually muscular and prehensile, 
and supported by a movable framework carrying the teeth ; the 
structure and modifications of which have been already described. 
The roof of the mouth is formed by the palate, terminating behind 
by a muscular, contractile arch, having in Man and some few other 
species a median projection called the uvula, beneath which the 
mouth communicates with the pharynx. The anterior part of the 
palate is composed of mucous membrane tightly stretched over the 
flat or slightly concave bony lamina separating the mouth from 
the nasal passages, and is generally raised into a series of trans- 
verse ridges, which sometimes, as in Ruminants, attain a con- 
siderable development. In the floor of the mouth, between the 
rami of the mandible, and supported behind by the hyoidean 
apparatus, lies the tongue ; an organ the free surface of which, 
especially in its posterior part, is devoted to the sense of taste, but 
which also, by its great mobility (being composed almost entirely 
of muscular fibres), performs important mechanical functions 
connected with masticating and procuring food. Its modifications 
of form in different mammals are very numerous. Between the 
long, extensile, vermiform tongue of the Anteaters, which is 
essential to the peculiar mode of feeding of those animals, and the 
short, sessile, and almost functionless tongue of the Porpoise, every 
intermediate condition is found. Whatever the form, the upper 
surface is always covered with numerous fine papilla?, in which 
the terminal filaments of the gustatory nerve are distributed. 

Salivary Glands. — The fluid known as the saliva is secreted by 
an extensive and complex system of glands discharging into the 
cavity of the mouth (buccal cavity), the position and relation of 
some of which are exhibited in the woodcut on the next page 
(Fig. 19). 

This apparatus consists of small glands embedded in the mucous 
membrane or submucous tissue lining the cavity of the mouth, 
which are of two kinds (the follicular and the racemose), and of 
others in which the secreting structure is aggregated in distinct 
masses removed some distance from the cavity ; other tissues besides 
the lining membrane being usually interposed, and pouring their 



56 



GENERAL ANATOMICAL CHARACTERS 



secretion into the cavity by a distinct tube or duct, which traverses 
the mucous membrane. To the latter alone the name of " salivary 
glands " is ordinarily appropriated, although the distinction 
between them and the smaller racemose glands is only one of 
convenience for descriptive purposes, their structure being more or 
less nearly identical ; and, since the fluids secreted by all become 
mixed in the mouth, their functions are, at all events in great part, 
Under the name of salivary glands are commonly 



common. 



MSP 







Fig. 19. — Salivary Glands of the Genet. A, Right side of the head dissected ; p, parotid 
gland ; d, Steno's duct ; sm, submaxillary gland, traversed by the jugular veins (jv) ; o, aperture 
of Steno's duct. B, Part of the head with the lip drawn up to show (st.d) aperture of 
Steno's duct ; z.gl, zygomatic gland ; o, aperture of do. ; z, zygomatic arch. (Mivart, Proo. 
Zool. Soc. 1882, p. 504.) 

included — (1) the "parotid" (p), situated very superficially on the 
side of the head, below or around the cartilaginous external 
auditory meatus, and the secretion of which enters the mouth by 
a duct (often called Steno's or Stenson's) which crosses the masseter 
muscle and opens into the upper and back part of the cheek 
(Fig. 19); and (2) the "submaxillary" (sm), situated in the neck, 
near or below the angle of the mandible, and sending a long duct 



THE DIGESTIVE SYSTEM 57 

(Wharton's) forwards to open on the fore-part of the floor of the 
cavity of the month, below the apex of the tongue. These are the 
most largely developed and constant of the salivary glands, being- 
met with in various degrees of development in almost all animals 
of the class. Next in constancy are (3) " the sublingual," closely 
associated with the last-named, at all events in the locality in which 
the secretion is poured out ; and (4) the " zygomatic " (z.gl), found 
only in some animals in the cheek, just under cover of the anterior 
part of the zygomatic arch, its duct entering the buccal cavity near 
that of the parotid. 

The most obvious function common to the secretion of these 
various glands, and to that of the smaller ones placed in the mucous 
membrane of the lips, the cheeks, the tongue, the palate, and fauces, 
is the mechanical one of moistening and softening the food, to 
enable it the more readily to be tasted, masticated, and swallowed, 
though each kind of gland may contribute in different manner 
and different degree to perform this function. The saliva is, 
moreover, of the greatest importance in the first stage or introduc- 
tion to the digestive process, as it dissolves or makes a watery 
extract of all soluble substances in the food, and so prepares them 
to be further acted on by the more potent digestive fluids met with 
subsequently in their progress through the alimentary canal. In 
addition to these functions it seems noAv well established by experi- 
ment that saliva serves in Man and many animals to aid directly 
in the digestive process, particularly by its power of inducing the 
saccharine transformation of amylaceous substances. As a general 
rule, in mammals the parotid saliva is more watery in its 
composition, while that of the submaxillaries, and still more the 
sublingual, contains more solid elements and is more viscid ; — so 
much so that some anatomists consider the latter, together with the 
small racemose glands of the cheeks, lips, and tongue, as mucous 
glands, retaining the name of salivary only for the parotid. These 
peculiar properties are sometimes illustrated in a remarkable 
degree, as, for example, the great secretion of excessively viscid 
saliva which lubricates the tongue of the Anteaters and Armadillos, 
associated with enormously developed submaxillary glands ; while, 
on the other hand, the parotids are of great size in those animals 
which habitually masticate dry and fibrous food. 

Stomach. — After the preparation which the aliment has under- 
gone in the mouth, — the extent of which varies immensely in 
different forms, being reduced almost to nothing in such animals as 
the Seals and Cetaceans, which, to use the familiar expression, 
" bolt " their food entire, and most fully carried out in the Rumin- 
ants, Avhich " chew the cud," — it is swallowed, and carried along 
the oesophagus by the action of its muscular coats into the stomach. 
In the greater number of mammals this organ is a simple saccular 



58 



GENERAL ANATOMICAL CHARACTERS 



dilatation of the alimentary canal, as in Figs. 20, 21, but in others 
it undergoes remarkable modifications and complexities. The lining 
of the stomach is thickly beset with tubular glands, which are 
generally considered to belong to two different forms, recognisable 
by their structure, and different in their function — the most 
numerous and important secreting the gastric juice (the active 
agent in stomachic digestion), and hence called " peptic " glands, 
while the others are concerned only in the elaboration of mucus. 
The relative distribution of these glands in different regions of the 
Avails of the stomach varies greatly in different animals, and in 
many species there are large tracts of the mucous membrane which 
do not secrete a fluid having the properties of gastric juice, but 
often constitute more or less distinct cavities devoted to storing 




Fig. 20. — Stomach and pancreas of the Genet. Posterior or dorsal surface, a', (Esophagus ; 
s, pancreas ; pd, pancreatic duct ; bd, biliary duct from the liver. (From Mivart, Proc. Zool. 
Soc. 1882, p. 305.) 

and perhaps softening or otherwise preparing the food for digestion. 
Sometimes there is a great aggregation of glands forming distinct 
thickened patches of the stomach wall, as in the Beaver and Koala, 
or even collected in pyriform pouches with a common narrow 
opening into the cavity, as in the Manatee and the curious African 
Rodent Lophiomi/s. The action of the gastric fluid is mainly 
exerted upon the nitrogenous elements of the food, which it 
dissolves and modifies so as to render them capable of undergoing 
absorption, effected partly by the blood-vessels of the stomach, 
although the greater part passes through the pylorus, an aperture 
surrounded by a circular muscular valve, into the intestinal canal. 
Here it comes in contact with the secretion of a vast number of 
small glands called the crypts of Lieberkuhn, somewhat similar 
to those of the stomach ; and also of several special glands of a 
different character, namely, the small racemose, duodenal, or 



THE DIGESTIVE SYSTEM 



59 



Brunner's glands, the pancreas, and the liver ; the position of the 
ducts of the two latter organs being indicated in Fig. 20. 

Intestinal Canal. — The intestinal canal varies greatly in relative 
length and capacity in different animals, and it also offers manifold 
peculiarities of form, being sometimes a simple cylindrical tube of 
nearly uniform calibre throughout, but more often subject to altera- 
tions of form and capacity in different portions of its course, — the 
most characteristic and constant being the division into an upper 
and narrower, and lower and wider portion, called respectively the 
small and the large intestine, the former being divided quite arbi- 
trarily and artificially into duodenum, jejun- 
um, and ileum, and the latter into colon and 
rectum. One of the most striking peculiari- 
ties of this part of the alimentary canal is 
the frequent presence of a diverticulum or 
blind pouch, the caput ccecurn coli, as it was 
first called, a name generally abbreviated into 
" caecum," situated at the junction of the 
large and the small intestine, a structure pre- 
senting an immense variety of development, 
from the smallest bulging of a portion of the 
side wall of the tube to a huge and complex 
sac, greatly exceeding in capacity the whole 
of the remainder of the alimentary canal. It 
is only in herbivorous animals that the caecum 
is developed to this great extent, and among 
these there is a curious complementary re- 

,,.,., ,, . x , i ■, Fig- 21. — Diagrammatic 

lationship between the size and complexity plan of the gen erai arrange- 

Of this Organ and that of the Stomach, ment of the alimentary canal 

Where the latter is simple the caecum is * a *>'P ical / I f nmal - °- 

r CEsophagus ; st, stomach ; p, 

generally the largest, and vice versa. Both the py i rus ; s, s, small intestine 

caecum and colon are often sacculated, a dis- (abbreviated) ; e, caecum ; i, i, 

position caused by the arrangement of the Jjj^^^Sj rectum? 1011 ' "*" 
longitudinal bands of muscular tissue in their 

vails ; but the small intestine is always smooth and simple-walled 
externally, though its lining membrane often exhibits various 
contrivances for increasing the absorbing surface "without adding to 
the general bulk of the organ, such as the numerous small villi by 
which it is everywhere beset, and the more obvious transverse, 
longitudinal, or reticulating folds projecting into the interior, met 
with in many animals, of Avhich the " valvulae conniventes " of Man 
form well-known examples. , 

Besides the crypts of Lieberkuhn found throughout the in- 
testinal canal, and the glands of Brunner confined to the duodenum, 
there are other structures in the mucous membrane, about the 
nature of which there is still much uncertainty, called " solitary " and 




60 GENERAL ANATOMICAL CHARACTER 

" agminated " glands ; the latter being more commonly known by the 
name of "Peyer's patches." These were formerly supposed to be 
secretory organs, which discharged some kind of fluid into the 
intestine, but are now more generally considered to belong to that 
group of structures of somewhat mysterious function of which the 
lymphatic and lacteal glands are members. The solitary glands are 
found scattered irregularly throughout the whole intestinal tract ; 
the agminated, on the other hand, are always confined to the small 
intestine, and are most abundant in its lower part. They are 
subject to great variation in number and in size, and even 
in different individuals of the same species, and also differ in 
character at different periods of life, becoming atrophied in old 



age. 



Liver. — The distinct glands situated outside the walls of the 
intestinal canal, but which pour their secretion into it, are the 
pancreas and the liver. The latter is the more important on 
account of its size, if not on account of the direct action of its 
secretion in the digestive process. This large gland, so complex in 
structure and function, is well developed in all mammals, and its 
secreting tube, the bile-duct, always opens into the duodenum, or 
that portion of the canal which immediately succeeds the stomach. 
It is situated on the riskt side of the abdomen in contact with the 
diaphragm and the stomach, but varies greatly in relative size, and 
also in form, in different groups of mammals. In most mammals a 
gall-bladder, consisting of a pyriform diverticulum from the bile- 
duct, is present, but in many this appendage is wanting, and it is 
difficult to find the rationale of its presence or absence in relation 
to use or any other circumstance in the animal economy. 

The descriptions of the livers of various animals to be met 
with in treatises or memoirs on comparative anatomy are very 
difficult to understand for want of a uniform system of nomencla- 
ture. The difficulty usually met with arises from the circumstance 
that this organ is divided sometimes, as in Man, Ruminants, and 
the Cetacea, into two main lobes, which have been always called 
respectively right and left, and in other cases, as in the lower 
Monkeys, Carnivora, Insectivora, and several other orders, into a 
larger number of lobes. Among the latter the primary division usu- 
ally appears at first sight tripartite, the whole organ consisting of a 
middle, called " cystic " or " suspensory " lobe, and two lateral lobes, 
called respectively right and left lobes. This introduces confusion 
in describing livers by the same terms throughout the whole series 
of mammals, since the right and left lobes of the Monkey or Dog, 
for instance, do not correspond Avith parts designated by the same 
names in Man and the Sheep. There are, moreover, conditions 
where neither the bipartite nor the tripartite system of nomencla- 
ture will answer, so that we should have considerable difficulty in 



THE DIGESTIVE SYSTEM 



61 



describing them without some more general system. In order to 
arrive at such a system it appears desirable to consider the liver in 
all cases as primarily divided by the umbilical vein (see Fig. 22, u) 
into two segments, right and left. This corresponds with its 
development and with the condition characteristic of the organ in 
the inferior classes of vertebrates. The situation of this division 
can almost always be recognised in adult animals by the persistence 
of some traces of the umbilical vein in the form of the round 
ligament, and by the position of the suspensory ligament. 

When the two main parts into Avhich the liver is thus divided 
are entire, as in Man, the Ruminants, and Cetacea, they may be 
spoken of as the right and left lobes ; when fissured, as the right 
and left segments of the liver, reserving the term lobe for the sub- 




Fig. 22. — Diagrammatic plan of the inferior surface of a multilobed liver of a Mammal. 
The posterior or attached border is uppermost, u, Umbilical vein of the fcetus, represented by 
the round ligament in the adult, lying in the umbilical fissure ; dv, the ductus venosus ; vc, 
the inferior vena cava ; p, the vena portas entering the transverse fissure ; llf, the left lateral 
fissure ; rlf, the right lateral fissure ; c/, the cystic fissure ; 11, the left lateral lobe ; Ic, the left 
central lobe ; re, the right central lobe ; rl, the right lateral lobe ; s, the Spigelian lobe ; c, the 
caudate lobe ; g, the gall-bladder. 

divisions. This will involve no ambiguity, for the terms right and 
left lobe will no longer be used for divisions of the more complex 
form of liver. In the large majority of mammals each segment is 
further divided by a fissure, more or less deep, extending from 
the free towards the attached border, which are called right and 
left lateral fissures (Fig. 22, rlf and llf). When these are more 
deeply cut than the umbilical fissure (u), the organ has that 
tripartite or trefoihlike form just spoken of, but it is easily seen 
that it is really divided into four regions or lobes, those included 
between the lateral fissures being the right and left central (re and 
Ic) separated by the umbilical fissure, and those beyond the lateral 
fissures on each side being the right and left lateral lobes (rl and 11). 



62 GENERAL ANATOMICAL CHARACTERS 

The essentially bipartite character of the organ and its uniformity 
of construction throughout the class are thus not lost sight of, even 
in the most complex forms. The left segment of the liver is rarely 
complicated to any further extent, except in some cases by minor 
or secondary fissures marking off small lobules, generally inconstant 
and irregular, and never worthy of any special designation. On 
the other hand, the right segment is usually more complex. The 
gall-bladder, when present, is always attached to the under surface 
of the right central lobe, sometimes merely applied to it, in other 
cases deeply embedded in its substance. In many instances the 
fossa in which it is sunk is continued to the free margin of the 
liver as an indent, or even a tolerably deep fissure (cf). The 
portal fissure (p), through which the portal vein and hepatic artery 
enter and the bile-duct emerges from the liver, crosses the right 
central lobe transversely, near the attached border of the liver. 
The right lateral lobe always has the great vena cava (yc) either 
grooving its surface or tunnelling through its substance near the 
inner or left end of its attached border ; and a prolongation of this 
lobe to the left, between the vein and the portal fissure, sometimes 
forming a mere flat track of hepatic substance, but more often 
a prominent tongue-shaped process, is the so-called "Spigelian lobe" 
(s). From the under surface of the right lateral lobe a portion is 
generally partially detached by a fissure, and called the " caudate 
lobe " (c). In Man this lobe is almost obsolete, but in most 
mammals it is of considerable magnitude, and has very constant 
and characteristic relations. It is connected by an isthmus at the 
left (narrowest or attached) end to the Spigelian lobe, behind which 
isthmus the vena cava is always in relation to it, channelling 
through or grooving its surface. It generally has a pointed apex, 
and is deeply hollowed to receive the right kidney, to the upper 
and inner side of which it is applied. 

Considerations derived from the comparatively small and simple 
condition of the liver of the Ungulata, compared with its large 
size and complex form in the Carnivora, have led to the perhaps 
too hasty generalisation that the first type is related to a herbivorous 
and the latter to a carnivorous diet. The exceptions to such a 
proposition are very numerous. The fact of the great difference 
between the liver of the Cetacea and that of the Seals cannot 
be accounted for by difference of habits of life, though it perhaps 
may be by difference of origin. 1 

1 For further details of these modifications, see Flower's "Lectures on the 
Comparative Anatomy of the Organs of Digestion of the Mammalia," Medical 
Times and Gazette, Feb. -Dec. 1872. 



CIRCULATORY AND RESPIRATORY SYSTEMS 63 



V. CIRCULATORY, ABSORBENT, RESPIRATORY, AND URINARY 

SYSTEMS. 

Blood. — The blood of mammals is always red, and during the 
life of the animal hot, having a nearly uniform temperature, 
varying within a few degrees on each side of 100° Fahr. The 
corpuscles are, as usual in the vertebrates, of two kinds : ( 1 ) 
colourless, spheroidal, nucleated, and exhibiting amoeboid move- 
ments ; while (2) the more numerous, on which depends the 
characteristic hue of the fluid in which they are suspended, are 
coloured, non -nucleated, flattened, slightly biconcave discs, Avith 
circular outline in all known species except the Camels and Llamas, 
where they have the elliptical form characteristic of the red 
corpuscles of nearly all the other vertebrates, though adhering to 
the mammalian type in the absence of nucleus and relatively small 
size. As a rule they are smaller as well as more numerous than in 
other classes, but vary considerably in size in different species, and 
not always in relation to the magnitude of the animal ; a Mouse, 
for instance, having as large corpuscles as a Horse. Within the 
limits of any natural group there is, however, very often some such 
relation, the largest corpuscles being found among the large species 
and the smallest corpuscles among the small species of the group, 
but even to this generalisation there are many exceptions. The 
transverse diameter of the red corpuscles in Man averages -32V0 of 
an inch, which is exceptionally large, and only exceeded by the 
Elephant { z fa s ), and by some Cetacea and Edentata. They are 
also generally large in Apes, Rodents, and the Monotremata, and 
small in the Artiodactyles, least of all in the Chevrotains (Tragulus), 
being in T. javanicus and meminna not more than x^stts- 1 

Heart. — The heart of mammals consists of four distinct cavities, 
two auricles and two ventricles. Usually the ventricular portion is 
externally of conical form, with a simple apex, but in the Sirenia it 
is broad and flattened, and a deep notch separates the apical portion 
of each ventricle. A tendency to this form is seen in the Cetacea 
and the Seals. It is characteristic of mammals alone among verte- 
brates that the right auriculo-ventricular valve is tendinous like the 
left, consisting of flaps held in their place by fibrous ends (chordce 
tendinice) and arising from projections of the muscular walls of 
the ventricular cavity (riiusculi papUlares). In the Monotremata a 
transition between this condition and the simple muscular flap of 
the Sauropsida is observed. In most of the larger Ungulates a dis- 
tinct but rather irregular ossification (os cordis) is developed in the 
central tendinous portion of the base of the heart. 

Blood-vessels. — The orifices of the aorta and pulmonary artery are 

1 G. Gulliver, Proc. Zool. Soc., 1862, p. 91. 



64 GENERAL ANATOMICAL CHARACTERS 

each guarded by three semilunar valves. The aorta is single, and 
arches over the left bronchial tube. After supplying the tissues of 
the heart itself with blood by means of the coronary arteries, it 
gives off large vessels ("carotid") to the head and ("brachial") to the 
anterior extremities. The mode in which these vessels arise from 
the aorta varies much in different mammals, and the study of their 
disposition affords some guide to classification. In nearly all cases 
the right brachial and carotid have a common origin (called the 
"innominate artery" in anthropotomy). The other two vessels 
may come off from this, as is the rule in Ungidates, the common 
trunk constituting the " anterior aorta " of veterinary anatomy ; or 
they may be detached in various degrees, both arising separately 
from the aorta, as in Man, or the left carotid from the innominate 
and the left brachial from the aorta, a very common arrangement ; 
or the last two from a common second or left innominate, as in 
some Bats and Insectivores. The aorta, after giving off the inter- 
costal arteries, passes through the diaphragm into the abdomen, and, 
after supplying the viscera of that cavity by means of the gastric, 
hepatic, splenic, mesenteric, renal, and spermatic vessels, gives off 
in the lumbar region a large branch (iliac) to each of the hinder 
extremities, which also supplies the pelvic viscera, and is continued 
onwards in the middle line, greatly diminished in size, along the 
under surface of the tail as the caudal artery. In certain mammals, 
arterial plexuses, called retia mirabilia, formed by the breaking up 
of the vessel into an immense number of small trunks, which may 
run in a straight course parallel to one another (as in the limbs of 
►Sloths and Slow Lemurs), or form a closely packed network, as in 
the intracranial plexuses of Ruminants, or a sponge-like mass of 
convoluted vessels, as in the intercostals of Cetaceans, are 
peculiarities of the vascular system the meaning of which is 
not in all cases clearly understood. In the Cetacea they are ob- 
viously receptacles for containing a large quantity of oxygenated 
blood available during the prolonged immersion, with consequent 
absence of respiration, to which these animals are subject. 

The vessels returning the blood to the heart from the head and 
upper extremities usually unite, as in Man, to form the single vena 
cava superior or precaval vein, but in some Insectivores, Chiroptera, 
and Rodents, in the Elephant, and all Marsupials and Monotremes, 
the two superior caval veins enter the right auricle without uniting, 
as in birds. In Seals and some other diving mammals there is a 
large venous sinus or dilatation of the inferior vena cava immediately 
below the diaphragm. In the Cetacea the purpose of this is supplied 
by the immense abdominal venous plexuses. As a rule the veins 
of mammals are furnished with valves, but these are said to be 
altogether wanting in the Cetacea, and in the superior and inferior 
cava, subclavian and iliac veins, the veins of the liver (both portal 



ABSORBENT SYSTEM 65 

and hepatic), heart, lungs, kidneys, brain, and spinal cord of other 
mammals. Many of the veins within the cranium are included in 
spaces formed by the separation of the laminae of the dura mater, 
and do not admit of being dilated beyond a certain size ; these are 
termed sinuses. The portal circulation in mammals is limited to 
the liver, the portal vein being formed by the superior and inferior 
mesenteric, the splenic, the gastroepiploic, and the pancreatic veins. 
The kidney is supplied solely by arterial blood, and its veins empty 
their contents only into the inferior cava. 

Lymphatic Fessels.—The absorbent or lymphatic system of vessels is 
very fully developed in the Mammalia. Its ramifications extend 
through all the soft tissues of the body, and convey a colourless 
fluid called lymph, containing nucleated corpuscles, and also, 
during the process of digestion, the chyle, a milky fluid taken up 
by the lymphatics (here called lacteals) of the small intestine, and 
pour them into the general vascular system, where they mix with 
the venous blood. The lymphatic vessels of the hinder extremities, 
as well as those from the intestinal canal, unite in the abdomen to 
form the "thoracic duct," the hinder end or commencement of 
which has a dilatation called the receptacvlum chyli. This duct, 
which is of irregidar size and sometimes double, often dividing and 
uniting again in its course, or even becoming plexiform, passes for- 
wards close to the bodies of the thoracic vertebrae, and empties itself, 
by an orifice guarded by a valve, into the great left brachio-cephalic 
vein, having previously received the lymphatics from the thorax and 
the left side of the head and left anterior extremity. The lymph- 
atics from the right side of the head and right anterior limb usually 
enter by a small distinct trunk into the corresponding part of the 
right brachio-cephalic vein. The duct, and also the principal lymph- 
atic vessels, are provided with valves. 

Lymphatic glands, rarely met with in the Sauropsida, are usually 
present in mammals, both in the general and in the lacteal system ; 
the latter being called " mesenteric glands." They are round or oval 
masses, situated upon the course of the vessels, which break up in 
them and assume a plexiform arrangement, and then reunite 
as they emerge. No structures corresponding to the pulsating 
" lymphatic hearts " of the lower vertebrates have been met with in 
mammals. 

Ductless Glands. — Associated with the vascular and lymphatic 
systems are certain bodies (the functions of which are not properly 
understood), usually, on account of their general appearance, 
grouped together under the name of "ductless glands." The 
largest of these is the " spleen," which is single, and always 
placed in mammals in relation to the fundus or left end of the 
stomach, to which it is attached by a fold of peritoneum. It is dark- 
coloured and spongy in substance, and has a depression or " hilus " 

5 



66 GENERAL ANATOMICAL CHARACTERS 

on one side, into which the splenic artery, a branch of the coeliac 
axis of the abdominal aorta, enters, and from which the vein joining 
the portal system emerges. The spleen varies much in size and form 
in different mammals, being relatively very small in the Cetacea. 
It is sometimes almost spherical, but more often flattened, oval, 
triangular, or elongated, and occasionally, as in Monotremes and 
most Marsupials, triradiate. The "suprarenal bodies" or "adrenals" 
are two in number, each situated either in contact with, or at a 
short distance in front of the anterior extremity of the kidney. 
They are abundantly supplied with nerves, and are much larger re- 
latively in early than in adult life. The "thyroid bodies," of which 
there are generally two, though in Man and some other species 
they are connected by an isthmus passing across the middle line, 
are constant in mammals, though only met with in a rudimentary 
condition, if at all, in other vertebrates. They are situated in the 
neck, in contact with the sides of the anterior extremity of the 
trachea. The " thymus " lies in the anterior part of the thorax, 
between the sternum and the great vessels at the base of the heart, 
and differs from the thyroid in being median and single, and having 
a central cavity. It attains its greatest development during the 
period in which the animal is nourished by its mother's milk, and 
then it diminishes, and generally disappears before full growth is 
attained. 

Nostrils. — Mammals breathe occasionally through the mouth, 
but usually, and in many cases exclusively, through the nostrils or 
tmres. These are apertures, always paired (except in the toothed 
Cetacea, where they unite to form a single external opening), and 
situated at the fore part of the face, generally at or beneath the 
end of the muzzle, a median prominence above the mouth. This is 
sometimes elongated to form a proboscis, to the extremity of which 
the nostrils are carried, and which attains its maximum of develop- 
ment in the Elephant. In the Cetacea the nostrils are situated at 
a considerable distance behind the anterior end of the face, upon 
the highest part of the head, and are called " blow-holes," from the 
peculiar mode of respiration of those animals. The nostrils are 
kept open by means of cartilages surrounding their aperture, 
which many animals have the power of moving so as to cause 
partial dilatation or contraction. In diving animals, as Seals and 
Cetacea, they can be completely closed at will so as to prevent the 
entrance of water when beneath the surface. The passage to which 
the nostrils lead is in most mammals filled by a more or less 
complex sieve -like apparatus, formed of the convoluted turbinal 
bones and cartilages, over which a moist, vascular, ciliated mucous 
membrane is spread, which intercepts particles of dust, and also 
aids in warming the inspired air before it reaches the lungs. In 
the Proboscidea, in which these functions are performed by 



RESPIRATORY SYSTEM 67 

the walls of the long tubular proboscis, this apparatus is entirely 
wanting. 

Trachea. — The narial passages have the organ of smell situated 
in their upper part, and communicate posteriorly with the 
pharynx, and through the glottis Math the " trachea " or windpipe, 
a tube by which the air is conveyed to and from the lungs. The 
permanent patency of the trachea during the varied movements of 
the neck is provided for by its walls being stiffened by a series of 
cartilaginous rings or hoops, which in most mammals are incomplete 
behind. Having entered the thorax, the trachea bifurcates into the 
two bronchi, one of which enters, and, dividing dichotomously, 
ramifies through each lung. In some of the Cetacea and 
Artiodactyla a third bronchus is given off from the lower 
part of the trachea, above its bifurcation, and enters the right 
lung. 

Larynx. — The upper end of the trachea is modified into the 
organ of voice or " larynx," the air passing through which to and 
from the lungs is made use of to set the edges of the " vocal cords," 
or fibrous bands stretched one on each side of the tube, into vibra- 
tion. The larynx is composed of several cartilages, stich as the 
"thyroid," the "cricoid," and the " arytenoid " which are moved 
upon one another by muscles, and suspended from the hyoidean arch. 
By alteration of the relative position of these cartilages the cords 
can be tightened or relaxed, approximated or divaricated, as 
required to modulate the tone and volume of the voice. A median 
tongue-shaped fibro-cartilage at the top of the larynx, the "epiglottis," 
protects the " glottis," or aperture by which the larynx communi- 
cates with the pharynx, from the entry of particles of food during 
deglutition. The form of the larynx and development of the vocal 
cords present many variations in different members of the class, 
the greatest modification from the ordinary type being met with in 
the Cetacea, where the arytenoid cartilages and epiglottis are united 
in a tubular manner, so as to project into the nasal passage, and, 
being grasped by the muscular posterior margin of the palate, pro- 
vide a direct channel of communication from the lungs to the 
external surface. An approach to this condition is met with in the 
Hippopotamus and some other Ungulates; it is indeed so general 
as an abnormality, that Howes suggests that an internarial epi- 
glottis may have been a primitive feature common throughout the 
class. Nearly all mammals have a voice, although sometimes it is 
only exercised at seasons of sexual excitement. Some Marsupials 
and Edentates appear to be quite mute. In no mammal is there 
an inferior larynx, or " syrinx," as in birds. 

Diaphragm. — The thoracic cavity of mammals differs from that 
of the Sauropsida in being completely separated from the abdomen 
by a muscular partition, the " diaphragm," attached to the vertebral 



68 GENERAL ANATOMICAL CHARACTERS 

column, the ribs, and the sternum. This is much arched, with the 
convexity towards the thorax, so that when its fibres contract and 
it is flattened the cavity of the thorax is increased, and when they 
are relaxed the cavity is diminished. 

Lungs. — The lungs are suspended freely in the thorax, one on 
each side of the heart, being attached only by the root, which 
consists of the bronchus or air-tube and pulmonary arteries and 
veins by which the blood is passed backwards and forwards between 
the heart and the lungs. The remaining part of the surface of 
each lung is covered by serous membrane, the "pleura"; and what- 
ever the state of distension or contraction of the chest-wall, is 
accurately in contact with it. Inspiration is effected by the con- 
traction of the diaphragm and by the intercostal and other muscles 
elevating or bringing forward the ribs, and thus throwing the 
sternum farther away from the vertebral column. As the surface 
of the lung must follow the chest-wall, the organ itself is expanded, 
and air rushes in through the trachea to fill all the minute cells in 
which the ultimate ramifications of the bronchi terminate. In 
ordinary expiration very little muscular power is expended, the 
elasticity of the lungs and surrounding parts being sufficient to 
cause a state of contraction and thus drive out at least a portion of 
the air contained in the cells, when the muscular stimulus is with- 
drawn. The lungs are sometimes simple externally, as in the 
Sirenia (where they are greatly elongated) and the Cetacea, but are 
more often divided by deep fissures into one or more lobes. The 
right lung is usually larger and more subdivided than the left. It 
often has a small distinct lobe behind, wanting on the left side, and 
hence called lobulus azygos. 

Air-sacs. — Most mammals have in connection with the air passages 
certain diverticuli or pouches containing air, the use of which is 
not always easy to divine. The numerous air sinuses situated 
between the outer and inner tables of the bones of the head, 
represented in Man by the antrum of Highmore and the frontal and 
sphenoidal sinuses, and attaining their maximum of development 
in the Indian Elephant, are obviously for the mechanical purpose 
of allowing expansion of the osseous surface without increase of 
weight. They are connected with the nasal passages. The Eusta- 
chian tubes pass from the back of the pharynx to the cavity of the 
tympanum, into which and the mastoid cells they allow air to pass. 
In the Equiclce there are large post-pharyngeal air-sacs in connection 
with them. The Dolphins have an exceedingly complicated system 
of air-sacs in connection with the nasal passages just within the 
nostrils, and the Tapirs, Rhinoceroses, and Horses have blind sacs 
in the same situation. In the males of some Seals (Cystophora and 
Macrorhinus) large pouches, which the animal can inflate with air, 
and which are not developed in the young animal or the female, 



URIXARY SYSTEM 69 



arise from the upper part of the nasal passages, and lie immediately 
under the skin of the face. These appear analogous, although not 
in the same situation, to the gular pouch of the male Bustard. 
The larynx frequently has membranous pouches in connection 
with it, into which air passes. These may be lateral and opening 
just above the vocal cords, when they constitute the saccull laryngis, 
found in a rudimentary state in Man, and attaining an enormous 
development, so as to reach to the shoulders and axilla?, in some 
of the Anthropoid Apes ; or they may be median, opening in 
front either above or below the thyroid and cricoid cartilages, as in 
the Howling and other Monkeys, and also in the Whalebone 
Whales and Great Anteater. 

Urinary Organs. — The kidneys of mammals are more compact 
and definite in form than in other vertebrates, being usually more 
or less oval, with an indent on the side turned towards the middle 
line, from and into which the vessels and ducts pass. They are 
distinctly divided into a cortical secretory portion, composed 
mainly of convoluted tubes, and containing the so-called Malpighian 
bodies ; and a medullary excreting portion, formed of straight tubes 
converging towards a papilla, embraced by the commencement of 
the ureter or duct of the organ. The kidneys of some mammals, 
as most Monkeys, Carnivores, Rodents, etc., are simple, with a 
single papilla into which all the renal tubuli enter. In others, as 
Man, there are many pyramids of the medullary portion, each with 
its papilla, opening into a division (calyx) of the upper end of the 
ureter. Such kidneys, either in the embryonic condition only, or 
throughout life, are lobulated on the surface. In some cases, as in 
Bears, Seals, and especially the Cetacea, the lobulation is carried 
further, the whole organ being composed of a mass of renules, 
loosely united by connective tissue, and with separate ducts, which 
soon join to form the common ureter. 

Bladder. — In all mammals except the Monotremes the ureters 
terminate by slit-like valvular openings in the urinary bladder. 
This receptacle when filled discharges its contents through the 
single median urethra, which in the male is almost invariably 
included in the penis, and in the females of some species of Rodents, 
Insectivores, and Lemurs has a similar relation to the clitoris. In 
the Monotremes, though the bladder is present, the ureters do not 
enter into it, but join the urino-genital canal some distance below 
it, with the orifice of the genital duct intervening. 



VI. NERVOUS SVSTEM AND ORGANS OF SENSE. 

Brain. — The brain of mammals shows a higher condition of 
organisation than that of other vertebrates. The cerebral hemi- 



70 GENERAL ANATOMICAL CHARACTERS 

spheres have a greater preponderance compared with other parts, 
especially to the so-called optic lobes, or corpora quadrigemina, 
which are completely concealed by them. The commissural system 
of the hemispheres is much more complex, both fornix and corpus 
callosum being present in some form ; and when the latter is 
rudimentary, as in Marsupials and Monotremes, its deficiency is 
made up for by the great size of the anterior commissure. The 
lateral lobes of the cerebellum, wanting in loAver vertebrates, are 
well developed and connected by a transverse commissure, the pons 
Varolii. The whole brain, owing especially to the size of the 
cerebral hemispheres, is considerably larger relatively to the bulk 
of the animal than in other classes, but it must be recollected that 
the size of its brain depends upon many circumstances besides the 
degree of intelligence which an animal possesses, although this is 
certainly one. Man's brain is many times larger than that of all 
other known mammals of equal bulk, and even three times as large 
as that of the most nearly allied Ape. Equal bulk of body is here 
mentioned, because, in drawing any conclusions from the size of 
the brain compared with that of the entire animal, it is always 
necessary to take into consideration the fact that in every natural 
group of closely allied animals the larger species have much smaller 
brains relatively to their general size than the smaller species, so 
that, in making any effective comparison among animals belonging 
to different groups, species of the same size must be selected. It 
may be true that the brain of a Mouse is, as compared with the 
size of its body, larger than that of a Man, but, if it were possible 
to reduce an animal having the general organisation of a Man to the 
size of a Mouse, its brain would doubtless be very many times larger ; 
and conversely, as shown by the rapid diminution of the relative 
size of the brain in all the large members of the Kodent order, a 
Mouse magnified to the size of a Man would, if the general rule 
were observed, have a brain exceedingly inferior in volume. Al- 
though the brain of the large species of Whales is, as commonly 
stated, the smallest in proportion to the bulk of the animal of any 
mammal, this does not invalidate the general proposition that the 
Cetacea have very large brains compared with terrestrial mammals, 
like the Ungulata, or even the aquatic Sirenia, as may be proved 
by placing the brain of a Dolphin by the side of that of a Sheep, a 
Pig, or a Manatee of equal general weight. It is only because the 
universally observed difference between the slower ratio of increase 
of the brain compared with that of the body becomes so enormous 
in these immense creatures that they are accredited with small 
brains. 

The presence or absence of " sulci " or fissures on the surface 
of the hemisphere, dividing it into " convolutions " or " gyri," and 
thus increasing the superficies of the cortical gray matter, as well 



AEE VO US S 1 r J> TEM 



7i 



as allowing the pia mater with its nutrient blood-vessels to pene- 
trate into the cerebral substance, follow somewhat similar rules. 
The sulci are related partly to the high or low condition of organis- 



a great degree to the size of 



tlie 



ation of the species, but also in 
cerebral hemispheres. In 
very small species of all 
groups, even the Primates, 
they are absent, and in the 
largest species of groups so 
low in the scale as the Mar- 
supials and Edentates they 
are found. They reach their 
maximum of development in 
the Cetacea. 

The accompanying wood- 
cut (Fig. 23) shows the prin- 
cipal parts of a mammalian 
brain, as seen from the 
superior, lateral, and inner 
surfaces. The sylvian fissure 
(>;/) is one of the most con- 
stant of the sulci found in 
the hemispheres. 

The researches of Palae- 
ontologists, founded upon 
studies of casts of the in- 
terior of the cranial cavity 
of extinct forms, have shown 
that, in many natural groups 
of mammals, if not in all, 
the brain has increased in 
size, and also in complexity 
of surface foldings, with the 
advance of time, — indicating 
in this, as in so many other 
respects, a gradual progress 
from a lower to a higher type 
of development. 

Nerves. — The twelve pairs of cranial nerves generally recognised 
in vertebrates are usually all found in mammals, though the 
olfactory nerves are excessively rudimentary, if not altogether 
absent, in the Toothed Whales. The spinal cord, or continuation 
of the central nervous axis, lies in the canal formed by the neural 
arches of the vertebra?, and gives off the compound double-rooted 
nerves of the trunk and the extremities, corresponding in number 
to the vertebrae, through the interspaces between which they pass 




Fig. 23. — Brain of the Genet (Genetta tigrlna). A, 
From above ; B, from the right side ; C, inner sur- 
face of right hemisphere ; cc, corpus callosum ; 
c.m.s, calloso-marginal sulcus ; c, notch represent- 
ing crucial sulcus of other forms ; d, depression on 
superior lateral gyrus of hemisphere ; hg, hippo- 
cam pal gyrus ; i, inferior lateral gyrus of hemi- 
sphere ; m, middle lateral gyrus of do. ; s, superior 
lateral gyrus of do. ; os, supraorbital sulcus of do. ; 
sf, sylvian fissure of do. ; 61, olfactory lobes. The 
deeply convoluted part behind the cerebral hemi- 
sphere is the cerebellum, below which lies the 
medulla oblongata, or commencement of the spinal 
cord. (Mivart, Proc. Zool. Soc. 1882, p. 516.) 



72 GENERAL ANATOMICAL CHARACTERS 

out to their destination. The cord is somewhat enlarged at the two 
points where it gives off the great nerves to the anterior and the 
posterior extremities, which, from their interlacements soon after 
their origin, are called respectively the brachial and lumbar plexuses. 
The ganglionic or sympathetic portion of the nervous system is well 
developed, and presents few modifications. 

Sense of Touch. — The sense of touch is situated in the skin 
generally, but is most acute in certain regions more or less 
specialised for the purpose by the presence of tactile papilla?, such 
as portions of the face, especially the lips and end of the snout, and 
the extremities of the limbs when these are used for other purposes 
than mere progression, and the under surface of the end of the tail 
in some Monkeys. The " vibrissa? " or long stiff bristles situated 
on the face of many mammals are rendered extremely sensitive to 
touch by the abundant supply of branches from the fifth nerve to 
their basal papilla?. In Bats the extended wing membranes, and 
probably also the large ears and the folds and prominences of skin 
about the face of some species, are so sensitive as to receive 
impressions even from the different degrees of resistance of the air, 
and so enable the animals to avoid coming in contact with obstacles 
to their nocturnal flight. 

Taste and Smell. — The organs of the other special senses are 
confined to the head. Taste is situated in the papilla? scattered on 
the dorsal surface of the tongue. The organ of smell is present in 
all mammals except the Toothed "Whales. It consists of a ramifica- 
tion of the olfactory nerves over a plicated, moist, mucous 
membrane, supported by folded plates of bone, placed on each side 
of the septum nasi in the roof, or often in a partially distinct upper 
chamber, of the nasal passage, so arranged that, of the air passing 
into the lungs in inspiration, some comes in contact with it, causing 
the perception of any odorous particles with which it may be 
charged. Many mammals possess intense powers of smelling 
certain odours which others are quite unable to appreciate, and the 
influence which this sense exercises over the well-being of many 
species is very great, especially in indicating the proximity of others 
of the same kind, and giving warning of the approach of enemies. 
The development and modification of the sense of smell is probably 
associated with that of the odorous secretion of the cutaneous 
glands. 

Sight. — The organ of sight is quite rudimentary, and even 
concealed beneath the integument, in some burrowing Rodents and 
Insectivores, and is most imperfectly developed in the Platanista, or 
Freshwater Dolphin of the rivers of India. In all other mammals 
the eyeball has the structure characteristic of the organ in the 
higher Vertebrata, consisting of parts through which the rays of 
light are admitted, regulated, and concentrated upon the sensitive 



ORGANS OF SENSE 73 

expansion of the optic nerve lining the posterior part of the ball. 
A portion of the fibro-vascular and highly pigmented layer, the 
choroid, which is interposed between the retina and the outer 
sclerotic coat, is in many mammals modified into a brilliantly- 
coloured light-reflecting surface, the tapetum lucidum. There is 
never a pecten or marsupium like that of the Sauropsida, nor is 
the sclerotic ever supported by a ring of flattened ossicles, as is so 
frequently the case in the lower vertebrated classes. The eyeball 
is moved in various directions by a series of muscles — the four 
straight, two oblique, and, except in the higher Primates, a pos- 
terior retractor muscle called choanoid. The superior oblique muscle 
passes through a tendinous pulley fastened to the roof of the orbit, 
which is a feature not found beyond the limits of the mammalian 
class. The eye is protected by the lids, generally distinctly separated 
into an upper and a lower movable flap, which, when closed, meet 
over the front of the eye in a more or less nearly horizontal line ; 
but sometimes, as in the Sirenia, the lids are not distinct, and the 
aperture is circular, closing to a point. In almost all mammals 
below the Primates, except the Cetacea, a " nictitating membrane " 
or third eyelid is placed at the inner corner of the eyeball, and 
works horizontally across the front of the ball within the true lids. 
Its action is instantaneous, being apparently for the purpose of 
cleaning the front of the transparent cornea ; — a function unneces- 
sary in animals whose eyes are habitually bathed in water, and which 
in Man and his nearest allies is perforaied by winking the true 
eyelids. Except in Cetacea the surface of the eye is kept moist by 
the secretion of the lachrymal gland, placed under the upper lid at 
its outer side, and the lids are lubricated by the Harderian and 
Meibomian glands, the former being situated at the inner side of 
the orbit, and especially related to the nictitating membrane, the 
latter in the lining membrane of the lids. 

Hearing. — The organ of hearing is inclosed in a bony capsule 
(periotic) situated in the side of the head, intercalated between the 
posterior (occipital) and the penultimate (parietal) segment of the 
skull. It has, in common with other vertebrates, three semicircular 
canals and a vestibule, but the cochlea is more fully developed than 
in the Sauropsida, and, except in the Monotremes, spirally con- 
voluted. The tympanic cavity is often dilated below, forming a 
smooth rounded prominence on the base of the skull, the auditory 
bulla (Fig. 8). The three principal ossicles, the "malleus," " incus," 
and " stapes," are always present, but variable in characters. In 
the Sirenia, Cetacea, and Seals they are massive in form, being in 
the first-named order of larger size than in any other mammals. In 
the Cetacea the malleus is ankylosed to the tympanic ; but in other 
mammals it is connected only with the membrana tympani. The 
stapes in the lower orders — Edentates, Marsupials, and Monotremes 



74 GENERAL ANATOMICAL CHARACTERS 

— has a great tendency to assume the columnar form of the 
corresponding bone in Sauropsida, its two rami entirely or partially 
coalescing. 1 The tympanic membrane (drum of the ear) forms the 
outer wall of the cavity. In the foetal state it is level with the 
external surface of the skull, and remains so permanently in a few 
mammals, as the American Monkeys ; but commonly, by the growth 
of the squamosal bone, it becomes deeply buried at the bottom of a 
bony tube {meatus auditorus externus), which is continued to the sur- 
face of the skin in a fibrous or fibrocartilaginous form. In Whales, 
owing to the thickness of the subcutaneous adipose tissue, this 
meatus is of great length, and is also extremely narrow. In most 
aquatic and burrowing animals it opens upon the surface by a simple 
aperture, but in the large majority of the class there is a projecting 
fold of skin, strengthened by fibro- cartilages, called the pinna, 
auricle, or " external ear," of very variable size and shape, generally 
movably articulated on the skull, and provided with muscles to 
vary its position ; this pinna helping to collect and direct the vibra- 
tions of sound into the meatus. 



VII. REPRODUCTIVE ORGANS. 

Testes. — In the male the testes retain nearly their primitive or 
internal position throughout life in the Monotremata, Sirenia, 
Cetacea, most Edentata, Hyracoidea, Proboscidea, and Seals, 
but in other groups they either periodically (as in Rodentia, 
Insectivora, and Chiroptera) or permanently pass out of the 
abdominal cavity through the inguinal canal, forming a projection 
beneath the skin of the perineum, or becoming suspended in a 
distinct pouch of integument called the scrotum. All the Marsupials 
have a pedunculated scrotum, the position of which differs from 
that of other mammals, being in front of, instead of behind, the 
preputial orifice. As regards the presence, absence, or comparative 
size and number of the accessory generative glands — prostate, vesi- 
cular, and Cowper's glands, as they are called — there is much 
variation in different groups of mammals. 

Penis. — The penis is almost always completely developed, 
consisting of two corpora cavernosa attached to the ischial bones, 
and of a median corpus spongiosum enclosing the urethra, and 
forming the glans at the distal portion of the organ. In Marsupials, 
Monotremes, and the Sloths and Anteaters, the corpora cavernosa 
are not attached directly to the ischia, and in the last-named the 
penis is otherwise of a very rudimentary character, the corpus 

1 The modifications of these bones are fully described by A. Doran, "Morpho- 
logy of the Mammalian Ossicula auditus," Trans. Linn. Soc. ser. 2, vol. i. pp. 
371-497, pi. lviii.-lxiv. (1878). 



REPRODUCTIVE ORGANS 75 

spongiosum not being present. In many Marsupials the glans penis 
is bifurcated. In most Primates, Carnivora, Kodentia, Insectivora, 
and Chiroptera, but in no other orders, an os penis is present. 

Ovaries and Oviduct. — In the female, the ovaries permanently retain 
their original abdominal position, or only descend a short distance 
into the pelvis. They are of comparatively smaller size than in 
other vertebrates, have a definite flattened oval form, and are 
enclosed in a more or less firm " tunica albigenia." The oviduct 
has a trumpet-like, and usually fimbriated abdominal aperture, and 
is more or less differentiated into three portions : — (1) a contracted 
upper part, called in Man and the higher mammals the " Fallopian 
tube "; (2) an expanded part Avith muscular walls, in which the 
ovum undergoes the changes by which it is developed into the 
fcetus, called the " uterus "; (3) a canal, the " vagina," separated 
from the last by a valvular aperture, and terminating in the urino- 
genital canal, or common urinal and genital passage, which in 
higher mammals is so short as scarcely to be distinct from the vagina. 
The complete distinction of the oviducts of the two sides through- 
out their whole length, found in all lower vertebrates, only occurs 
in this class in Monotremes ; a prevailing mammalian characteristic 
being their more or less perfect coalescence in the middle line to form 
a single median canal. In the Marsupials this union only includes 
the lower part of the vagina ; but in most Placentals it extends to the 
whole vagina and a certain portion of the uterus, which cavity is 
then described as "bicornuate." In the higher mammals, as in 
Man, and also in some of the Edentates, the whole of the uterus is 
single, the contracted upper portion of the oviducts or Fallopian 
tubes, as they are then called, entering its upper lateral angles by 
small apertures. In certain lower forms the urino- genital canal 
opens with the termination of the rectum into a common cloaca, 
as in other vertebrates ; but it is characteristic of the majority 
of the class that the two orifices are more or less distinct exter- 
nally. 

Mammary Glands. — Mammary glands secreting the milk by 
which the young are nourished during the first portion of their 
existence after birth, are present in both sexes in all mammals, 
though usually only functional in the female. In the Monotremes 
alone their orifices are mere scattered pores in the skin, but in all 
other forms they are situated upon the end of conical elevations, 
called mammillae or teats, which, taken into the mouth of the 
young animal, facilitate the process of sucking. These are always 
placed in pairs upon some part of the ventral surface of the body, 
but vary greatly in number and position in different groups. In 
the Cetacea, where the prolonged action of sucking would be incom- 
patible with their subaqueous life, the ducts of the glands are 
dilated into large reservoirs from which the contents are injected 



76 GENERAL ANATOMICAL CHARACTERS 

into the mouth of the young animal by the action of a compressor 
muscle. 

Secondary Sexual Characters. — Secondary sexual characters, or 
modifications of structure peculiar to one sex, but not directly 
related to the reproductive function, are very general in mammals. 
They almost always consist of the acquisition or perfection of some 
character by the male as it attains maturity, which is not found in 
the female or the young in either sex. In a large number of cases 
these clearly relate to the combats in which the males of many 
species engage for the possession of the females during the breeding- 
season ; others are apparently ornamental, and of many it is still 
difficult to apprehend the meaning. Many suggestions on this 
subject will, however, be found in the chapters devoted to it in 
Darwin's work on The Descent of Man and Selection in Relation to Sex, 
where most of the best-known instances are collected. Superiority 
of size and strength in the male of many species is a well- 
marked secondary sexual character related to the purpose indicated 
above, being probably perpetuated by the survivors or victors in 
combats transmitting to their descendants those qualities which 
gave them advantages over others of their kind. To the same 
category belong the great development of the canine teeth of the 
males of many species which do not use these organs in procuring 
their food, as the Apes, Swine, Musk and some other Deer, the tusk 
of the male Narwhal, the antlers of Deer, which are present in most 
cases only in the males, and the usual superiority in size and 
strength of the horns of the Bovidw. Other secondary sexual 
characters, the use of which is not so obvious, or which may only 
relate to ornament, are the presence of masses or tufts of long hair 
on different parts of the body, as the mane of the male Lion and 
Bison, the beards of some Ruminants and Bats (as Taphozous melano- 
fogoii), Monkeys, and of Man, and all the variations of coloration 
in the sexes, in which, as a general rule, the adult male is darker 
and more vividly coloured than the female. Here may also be 
mentioned the presence or the greater development of odoriferous 
glands in the male, as in the Musk Deer, and the remarkable 
perforated spur with its glands and duct, so like the poison-tooth 
of the venomous serpents, found in the males of both Ornithorhynchns 
and Echidna, the use of which is at present unknown. 

Placenta. — The development of the mammalian ovum, and the 
changes which the various tissues and organs of the body undergo 
in the process of groAvth, are too intricate subjects to be explained 
without entering into details incompatible with the limits of this 
work, especially as they scarcely differ, excepting in their later 
stages, from those of other vertebrates, upon which, owing to the 
greater facilities these present for examination and study, the 
subject has been more fully worked out. There are, however, 



REPRODUCTIVE ORGANS 77 

some points -which require notice, as peculiar to the mammalian 
class, and as affording at least some hints upon the difficult subject 
of the affinities and classification of the members of the group. 

The nourishment of the foetus during intra-uterine life takes 
place through the medium of certain structures, partly belonging 
to the foetus itself and partly belonging to the inner parietes of the 
uterus of the parent. These in their complete form constitute the 
complex organ called the "placenta," serving as the medium of 
communication between the mother and foetus, and in which the 
physiological processes that are concerned in the nutrition of the 
latter take place ; but, as "we shall see, though a placenta, in the 
usual acceptation of the term, is peculiar to the mammalian class, it is 
not in all of its members that one is developed. The structures to 
which we shall have especially to refer are the outer tunic of the 
ovuni, to which, however formed, the term " chorion " is commonly 
applied, and two sac-like organs connected with the body-cavity of 
the embryo, both formed from the splanchnic mesoblast, lined by a 
layer of the hypoblast. These are the " umbilical vesicle " or " yolk- 
sac" and the "allantois." 

The umbilical vesicle is a thin membrane enclosing the yolk, 
which by the doubling in of the ventral walls of the embryo becomes 
gradually formed into a distinct sac external to the body, with a 
pedicle (the omphalo-enteric duct) by which for a time a communica- 
tion is maintained between its cavity and the intestinal canal. In 
the walls of this sac blood-vessels (omphalo-meseraic or vitelline) 
are developed in connection with the vascular system of the embryo, 
through which, either by their contact with the outer surface of the 
walls of the ovum, or by the absorption through them of the 
contents of the yolk-sac, the nutrition of the embryo in the lower 
vertebrates chiefly takes place. In mammals the umbilical ves- 
icle plays a comparatively subordinate part in the nourishment 
of the foetus, its function being generally superseded by the 
allantois. 

The last-named sac commences at a very early period as a 
diverticulum from the hinder end of the alimentary tract of the 
embryo. Its proximal portion afterwards becomes the urinary 
bladder, the contracted part between this and the cavity of the 
allantois proper constituting the urachus, which passes out of the 
body of the foetus at the umbilicus together with the vitelline duct. 
The mesoblastic tissue of the walls of the allantois soon becomes 
vascular ; its arteries are supplied with foetal blood by the two 
hypogastric branches of the iliacs, or main divisions of the abdominal 
aorta, and the blood is returned by venous trunks uniting to 
form the sinerle umbilical vein which runs to the under surface of 
the liver, where, part of it joining the portal vein and part entering 
the vena cava directly, it is brought to the heart. These are 



73 GENERAL ANATOMICAL CHARACTERS 



the vessels which, with their surrounding membranes, consti- 
tute the umbilical cord — the medium of communication between 
the foetus and the placenta, when that organ is fully de- 
veloped. 

The egg membranes of the Monotremes present many points of 
agreement with those of the ovum of the Marsupials, 1 and differ 
from those of the Placental types. Thus Monotremes and Marsu- 
pials agree in having a vitelline membrane, which appears between 
the young ovum and the follicular epithelium, persisting in the 
one ^ case until the time of hatching, and in the other till a late 
uterine stage. There are also several other common features fully 
described in Mr. Caldwell's memoir, but which cannot be detailed 
in this work. 

In the Marsupialia the observations made many years ago by 
Sir R. Owen upon the development of the Kangaroo have been 
confirmed by those of Dr. H. C. Chapman, 2 while Dr. Selenka, 3 and 
Professor H. F. Osborn 4 have contributed important evidence as to the 
structure and relations of the foetal membranes of the Opossums 
and others. It thus appears that up to the period of the very 
premature birth of these animals the outer covering of the ovum, 
or false chorion, is free from persistent villi, and .not adherent 
to the epithelium of the uterine walls ; for, although fitting into 
the folds of the latter, it is perfectly and readily separable in its 
entire extent from them. The umbilical vesicle or yolk-sac is large, 
vascular, and adherent to a considerable portion of the false chorion 
or subzonal membrane, while the allantois is relatively small, and 
although the usual blood-vessels can be traced into it, it does not 
appear to contract any connection with the false chorion, and, there- 
fore, much less with the Avails of the uterus, of such a nature as to 
constitute a placenta. In some forms, however, such as the 
Opossums, the umbilical vesicle or yolk-sac develops temporary 
villi, Avhich unite with the subzonal membrane, or false chorion, to 
form a disc -like area closely attached to the cells covering the 
utricular glands of the uterine epithelium, and thus forming a 
so-called yolk-sac placenta. The function of this organ is considered 
to be the transmission of the secretions of the utricular glands to 
the embryo by means of the umbilical vesicle ; the function of the 
allantois being either respiratory or the absorption of the fluid 
secreted in the uterine cavity by the utricular glands. 

While in the uterus the nourishment of the foetus seems, there- 
fore, to be derived from the umbilical vesicle, as in reptiles and 

1 See B. H. Caldwell— "The Embryology of Monotremata and Marsupialia," 
Phil. Trans, for 1887, p. 463. 

2 Proc. Acad. Nat. Sci. Philadelphia, 1881, p. 468. 

3 " Studienueber Entivickelungeschichtc dcr Thierc," pt. 4, Wiesbaden, 1886. 

4 Journal of Morphology, vol. i. p. 373 (1887). 



REPRODUCTIVE ORGANS 79 

birds, rather than from the uterine Avails by means of the allantoic 
vessels, as in the higher mammals. The latter vessels, in fact, play 
oven a much less important part in the development of these 
animals, not only than in the placental mammals, but even than in 
the Sauropsida, for they can scarcely have the respiratory function 
assigned to them in that group: pulmonary respiration and the 
lacteal secretion of the mother very early superseding all other 
methods of providing the due supply both of oxygen and of food 
required for the development and growth of the young animal. 
in this sense the Marsupials may be looked upon as the most 
typically " mammalian " of the whole class. In no other group do 
the milk -secreting glands play such an important part in pro- 
viding for the continuity of the race. 

In the third primary division of the Mammalia, the so-called 
Placentalia, the umbilical vesicle generally does not quite unite 
with the chorion, and disappears as development proceeds, so that 
no trace of it can be seen in the membranes of an advanced 
embryo ; but it may persist until the end of the intra-uterine life 
as a distinct sac in the umbilical cord, or lying between the 
allantois and amnion. The disappearance or persistence of the 
umbilical vesicle does not, according to our present knowledge, 
appear to be correlated with a higher or lower general grade of de- 
velopment, as might be presupposed. It is stated to have been 
found in Man even up to the end of intra-uterine life, and also in 
the Carnivora, while in the Ungulata and Cetacea it disappears at 
an earlier age. In many, if not all, of the Rodentia, Insectivora, 
and Chiroptera, it plays a more important part, becoming adherent 
to a considerable part of the inner surface of the chorion, to which 
it conveys blood-vessels, although villi do not appear to be developed 
from the surface of this part, as they are on the portion of the 
chorion supplied by the allantoic vessels. These orders thus 
present to a certain extent a transitional condition from the Mar- 
supials, although essentially different, in possessing the structures 
next to be described. 

The special characteristic of the whole of the placental mammals 
constituting the majority of the class, is that the allantois and its 
vessels become intimately blended with a smaller or greater part of 
the parietes of the ovum, forming a structure on the outer surface of 
which villi are developed, and which, penetrating into corresponding 
cavities of the " decidua," or soft, vascular, hypertrophied lining 
membrane of the uterus, constitutes the placenta. This organ may 
be regarded, as Sir William Turner says, both in its function and in 
the relative arrangement of its constituent textures, as a specially 
modified secreting gland, the ducts of which are represented by the 
extremities of the blood-vessels of the foetal system. The passage 
of material from the maternal to the foetal system of vessels is not 



So GENERAL ANATOMICAL CHARACTERS 

a simple percolation or diffusion through their walls, but is oc- 
casioned by the action of a layer of cells derived from the maternal 
or uterine structures, and interposed between the blood-vessels of 
the maternal part of the placenta and those of the villi covering 
the chorion, in which the embryonic vessels ramify. 

The numerous modifications in the details of the structure of 
this organ relate to augmenting the absorbing capacity of the vessels 
of the chorion, and are brought about either by increasing the com- 
plexity of the foetal villi and maternal crypts over a limited area, 
or by increasing the area of the part of the chorion covered by the 
placental villi, or by various combinations of the two methods. 

The first class of variations has given rise to a distinction into 
two principal kinds of placenta: (1) simple or non-deciduate, and 
(2) deciduate. In the former the foetal villi are received into corre- 
sponding depressions of the maternal surface, from which at the 
period of parturition thej r are simply withdrawn. In the second, 
or more complex form, the relation is more intimate, a layer of 
greater or less thickness of the lining membrane of the uterus, 
called " decidua," becoming so intimately blended with the chorion 
as to form part of the placenta proper, or that structure which is 
cast off as a solid body at parturition. In other words, in the one 
case the line of separation between the placenta and uterus at birth 
takes place at the junction of the foetal and maternal structures, in 
the other through the latter, so that a portion of them, often of con- 
siderable thickness, and containing highly organised structures, is 
cast off with the former. It was once thought that the distinction 
between these two forms of placentation is so important as to con- 
stitute a sufficiently valid basis for a primary division of the pla- 
cental mammals into two groups. It has, however, been shown 
that the distinction is one rather of degree than of kind, as inter- 
mediate conditions may exist, and it is probable that in different 
primary groups the simpler, non-deciduate form may have become 
developed independently into one or other of the more complex 
kinds. 

Apart from its intimate structure, the placenta may be met with 
of very varied general form. It may consist of villi scattered more 
or less regularly over the greater part of the surface of the chorion, 
the two extremities or poles being usually more or less bare. This 
form is called the " diffused placenta." It is probably a primitive 
condition, from which most of the others are derived, although its 
existence must presuppose the absence of the umbilical vesicle as a 
constituent of the chorionic wall. It is found at present in the 
Manis among Edentates, the Cetacea, the Perissodactyle Ungulates, 
and the Camels, Pigs, and Chevrotains among the Artiodactyles. 
Such placentae are always non-deciduate. Kecent observations by 
Sir W. Turner on the placentation of the Dugong show that the 



REPRODUCTIVE ORGANS Si 

Sironia present the peculiarity of having a zonary placenta, which is 
either entirely or in great part non-deciduate, and is, therefore, 
transitional between the diffused and the true zonary type. 

In the true Ruminants or Pecora, among the Artiodactyle 
Ungulates, the villi are aggregated in masses called cotyledons, 
with bare spaces between. Such a placentation is called "poly- 
cotyledonary." In another modification the villi are collected in a 
more or less broad band encircling the chorion, leaving a very large 
portion of the two poles bare, constituting the "zonary placenta," 
characteristic of the Carnivora, and also occurring in the Elephant, 
Hyrax, and Orycteropus. The fact of the form of the placenta of 
these three last-named animals agreeing together, and with that of 
the Carnivora, does not, however, necessitate the ascription of 
zoological affinities, as the same ultimate form may have been 
attained by different processes of development. 

In another form one pole only of the chorion is non-vascular, 
the placenta assuming a dome or bell shape, as in the Lemurs and 
the Sloths. The transition from this, by the gradual restriction of 
the vascular area, is easy to the oval or discoidal form of placenta 
of the Anteaters, Armadillos, and higher Primates. The discoidal 
placenta of the Rodents, Insectivores, and Chiroptera, though show- 
ing so much superficial resemblance to that of the last-named order 
as to have led to the inclusion of all these forms in one primary 
group, is now known to be developed in another manner, not by the 
concentration of villi from a diffused to a limited area, but by 
retaining the area to which it was originally restricted in con- 
sequence of the large surface of the chorion occupied, as before 
mentioned, by the umbilical vesicle. To compensate for the small- 
ness of area, the complex or deciduate structure has been developed. 
Among some Rodents there is evidence to show that the discoidal 
placenta has been derived from a zonary one, of which distinct 
vestiges have been detected in the Mouse. We may conclude 
that, although the characters and arrangement of the foetal structures 
may not have that extreme importance which has been attributed 
to them by some zoologists, they will form, especially when more 
completely understood, valuable aids in the study of the natural 
affinities and evolution of the Mammalia. 1 

1 For a full exposition of the present state of knowledge on this subject, see 
the various memoirs of Sir "William Turner, also F. M. Balfour's Treatise on 
Comparative Embryology, vol. ii. (1881), and J. A. Ryder in American Naturalist, 
vol. xxi. p. 780 (1887). 



CHAPTEE III 

ORIGIN AND CLASSIFICATION OF THE MAMMALIA 

Origin. — Although, as stated in the first chapter, the mammalian 
class, as at present known either by existing or extinct forms, is 
completely isolated from all other groups of the animal kingdom, 
yet it is impossible to refrain from speculating as to its origin and 
nearest affinities. In arranging the classes of vertebrates in a linear 
series it is customary to place them in the following order — Pisces, 
Amphibia, Reptilia, Aves, Mammalia, — an order which probably 
indicates the relative degree of elevation to which the mos 
highly developed members of each class has attained. Such 
an arrangement appears to express the true relationship of the first 
four classes to one another, but it is quite clear that the Mammalia 
have no sort of affinity with the Aves. Writing in 1879, Professor 
Huxley l came to the conclusion that, in looking among vertebrates 
for the progenitors of the Mammalia, we must pass over all known 
forms of birds and reptiles, and go straight clown to the Amphibia. 
In addition to the characters derived from the conformation of the 
pelvis upon which the argument was primarily based, the following 
reasons were given for this conclusion : " The Amphibia are the 
only air-breathing Vertebrata which, like mammals, have a dicon- 
dylian skull. It is only in them that the articular element of the 
mandibular arch remains cartilaginous, while the quadrate ossifica- 
tion is small, and the squamosal extends down over it to the osseous 
elements of the mandible, thus affording an easy transition to the 
mammalian condition of those parts. The pectoral arch [girdle] of 
the Monotremes is as much amphibian as it is sauropsidian ; the 
carpus and the tarsus of all Sauropsida, except the Chelonia, are 
modified away from the Urodele type, while those of the mammal 
are directly reducible to it. Finally, the fact that in all Sauropsida 
it is a right aortic arch which is the main conduit of arterial blood 
leaving the heart, while in mammals it is a left aortic arch which 

1 Proceedings of the Royal Society of London, vol. xxviii. p. 395 (1879). 



ORIGIN 83 



performs this office, is a great stumbling-block in the way of the 
derivation of the Mammalia from any of the Sauropsida. But, if 
we suppose the earliest forms of both the Mammalia and the Saur- 
opsida to have had a common Amphibian origin, there is no difficulty 
in the supposition that, from the first, it was a left aortic arch in 
the one series, and the corresponding right aortic arch in the other, 
which became the predominant feeder of the arterial system." 
Subsequently Professor E. D. Cope l in a suggestive paper called 
attention to the remarkable resemblances to the Monotremes pre- 
sented by the skeleton of that group of early secondary reptiles 
which he then designated the Theromorpha, but which may be 
included in the Anomodontia of Sir R. Owen, and came to the 
conclusion that in that group we have the true ancestors of the 
Mammalia. This conclusion was, however, disputed by Dr. Baur, 2 
who considered that the Anomodontia were too specialised to have 
been the actual progenitors of the Mammalia, and that they should 
rather be regarded as a divergent branch of the stem which had given 
origin to the Mammalia. Since that date observations made on 
the structure of the South African Anomodonts have shown such 
an intimate connection between that group and the Labyrinthodont 
Amphibians, that there can be no hesitation in regarding the one 
as the direct descendant of the other ; and we may probably regard 
the Mammalia as having originated from the same ancestral stock 
at the time the Amphibian type was passing into the Reptilian. 
From this point of view, some of the mammalian features found in 
the more specialised Anomodonts may probably be regarded as 
having been acquired during a parallel line of development. 

Both the Anomodontia and the Mammalia differ from the 
Amphibians in the loss of the splint- like parasphenoid which 
underlies the basisphenoid axis of the skull, and by the ossification 
of that axis ; but while the former have become monocondylic by 
the participation of the basioccipital in the support of the cranium, 
the latter retain the Amphibian dicondylic plan. The skull of the 
Anomodonts presents mammalian resemblances not found in any 
other Reptiles, this being especially noticeable in the region of the 
squamosal ; and it is only in this group and mammals that the 
temporal or zygomatic arch is a squamoso-maxillary one (see p. 
37). The resemblance between the pectoral and pelvic girdles 
of the Anomodonts and those of the Monotreme Mammals is 
noticed under the head of the latter, where reference is also made 
to the similarity in the structure of the humerus in the two groups. 

1 " The Relations between the Theromorphous Reptiles and the Monotreme 
Mammalia," Proceedings of the American Association for the Advancement of 
Science, vol. xxxiii. p. 471 (1885). 

- "On the Phylogenetic Arrangement of the Sauropsida," Journal of 
Morphology, vol. i. pp. 93-104 (1887). 



84 ORIGIN AND CLASSIFICATION 

The pes of the Amphibia and Anomodontia agree in having a 
distinct intermedium, tibiale, fibulare, and centrale, whereas in 
other Reptiles these bones are not generally distinct ; in Mammals 
the intermedium, fibulare, and centrale are distinct, and according 
to Cope's interpretation there may be a distinct tibiale. 

Classification. — In the present condition of the world, mammals 
have become so broken up into distinct groups by the extinction of 
intermediate forms, that a systematic classification is perfectly 
practicable. Most of the associations of species, which Ave call 
" orders," and even the " suborders " and " families," are natural 
groups. In isolating, defining, and naming them, we are really 
dealing with facts of nature of a totally different order from the 
artificial and fanciful divisions formed in the infancy of zoological 
science. 

When, however, we pass to the extinct world, all is changed. 
In many cases the boundaries of our groups become enlarged until 
they touch those of others. New forms are discovered which 
cannot be placed within any of the existing divisions. As the 
horizon of our vision is thus expanded, the principles upon which a 
scheme of classification is constructed must be altogether changed. 
Our present divisions and terminology are no longer sufficient for 
the purpose ; and some other method will have to be invented to 
show the complex relationships existing between different animal 
forms when viewed as a whole. The present time, pre-eminently 
distinguished by the rapidly changing and advancing knowledge of 
extinct forms, is scarcely one in which this can be done with any 
satisfactory result ; so that all attempts to form a classification 
embracing even the already known extinct species must be only 
of a provisional and temporary nature. 

In systematic descriptions in books, in lists, and catalogues, and 
in arranging collections, the objects dealt with must be placed in a 
single linear series. But by no means whatever can such a series 
be made to coincide "with natural affinities. The artificial character 
of such an arrangement, the constant violation of all true relation- 
ships, are the more painfully evident the greater the knowledge of 
the real structure and affinities. But the necessity is obvious ; and 
all that can be done is to make such an arrangement as little as 
possible discordant with facts. 

The following table contains a list of the orders, suborders, and 
families of existing mammals as recognised by the authors, and placed 
in the order in which they will be treated of in this work. The 
more important of the groups containing only extinct forms are 
added in a different type, being interpolated, as near as may be, 
among those that appear to be their existing relatives. 

A few explanatory remarks upon the mutual relations of some 
of the principal groups mentioned in the table may be useful here, 



CLA SSIFICA TION 8 5 



but the subject will be more fully developed in treating separately 
of each division. 

One of the most certain and fundamental points in the classifica- 
tion of the Mammalia is, that all the animals now composing the 
class can be grouped primarily into three natural divisions, which, 
presenting very marked differential characters, and having no exist- 
ing, or yet certainly demonstrated extinct, intermediate, or trans- 
itional forms, may be considered as subclasses of equal value, tax- 
onomically speaking, though very different in the numbers and 
importance of the animals at present composing them. These three 
groups are often called by the names originally proposed for them 
by Blainville — (1) Ornithodelphia, (2) Didelphia, (3) Monodelphia — 
the first being equivalent to the order Monotremata, the second 
to the Marsupiidia, and the third including all the remaining 
members of the class. Although actual pala?ontological proof is 
wanting, there is much reason to believe that each of these, as now 
existing, are survivors of distinct branches to which the earliest 
forms of mammals have successively given rise, and for which 
hypothetical branches Professor Huxley has proposed the names of 
Prntotheria, Metatheria, and Eutheria, names which, being far less 
open to objection than those of Blainville, are here used as equiva- 
lents of the latter. 

The only known existing Prototheria, although agreeing in 
many important characters, evidently represent two very divergent 
stocks, perhaps as far removed as are the members of some of the 
accepted orders of the Eutheria. It would, however, be merely 
encumbering zoological science with new names to give them any 
other than the ordinarily known family designations of Ornitho- 
rhynchidce and Echidnidce. 

Similarly with regard to the Metatheria, although the great 
diversity in external form, in anatomical characters, and in mode of 
life of the various animals of this section might lead to their 
division into groups equivalent to the orders of the Eutheria, we do 
not think it advisable to depart from the usual custom of treating 
them all as forming one order, called Marsupialia, the limits of 
which are equivalent to those of the subclass. The characters of the 
six families which compose the group are extremely well ma/rked 
and easily defined ; and since they form a regular gradation between 
two extreme types, they can be satisfactorily arranged in a serial 
order. A marked distinction in the dentition enables us to divide 
them into primary groups or suborders. 

The remaining mammals are included in the Eutheria, Placen- 
talia, or Monodelphta. Their affinities with one another are so 
complex that it is impossible to arrange them serially with any 
regard to natural affinities. Indeed each order is now so isolated 
that it is almost impossible to say what its affinities are ; and none 



86 ORIGIN AND CLASSIFICATION 

of the hitherto proposed associations of the orders into larger groups 
stand the test of critical investigation. All serial arrangements of 
the orders are therefore perfectly arbitrary ; and although it would 
be of very great convenience for reference in books and museums 
if some general sequence, such as that here proposed, were generally 
adopted, such a result can scarcely be expected, since equally good 
reasons might be given for almost any other combination of the 
various elements of which the series is composed. In fact, we have 
already seen reason to depart in some respects from that used in the 
" Encyclopedia." 

The Edentata, Sirenia, and Cetacea stand apart from all the 
rest in the fact that their dentition does not conform to the general 
heterodont, diphyodont type to which that of all other Eutheria 
can be reduced, and which is such a close bond of union between 
them. In all three orders, however, some indications may be traced 
of relationship, however distant, with the general type. 

With regard to the Edentata, reasons will be given for believing 
that both the Sloths and Anteaters are nearly related, and that the 
Armadillos, though much modified, belong to the same stock, but 
that the Pangolins and the Aard-varks represent very isolated 
forms. 

There is no difficulty about the limits of the order Sirenia, com- 
prising aquatic, vegetable-eating animals, with complete absence of 
hind limbs, and low cerebral organisation, represented in our present 
state of knowledge only by two existing genera, Halicore and Mana- 
tus, and a few extinct forms, which, though approaching a more 
generalised mammalian type, show no special characters allying 
them to any of the other orders. The few facts as yet collected 
relating to the former history of the Sirenia leave us as much in 
the dark as to the origin and affinities of this peculiar group of 
animals as we were when Ave only knew the living members. 
They lend no countenance to their association with the Cetacea ; 
and, on the other hand, their supposed affinity with the Ungulata 
receives no very material support from them. 

Another equally well-marked and equally isolated, though far 
more numerously represented and diversified order, is that of the 
Cetacea, placed simply for convenience next to the Sirenia ; with 
Avhich, except in their fish-like adaptation to aquatic life, they have 
little in common. The old association of these orders in one group 
can only be maintained either in ignorance of their structure or 
in an avowedly artificial system. Among the existing members of 
the order, there are two very distinct types, the toothed Whales or 
Odontoceti, and the Baleen Whales or Mystacoceti, which present 
as many marked distinguishing structural characters as are found 
between many other divisions of the Mammalia usually reckoned 
as orders. Since the extinct Zeuglodonts, so far as their characters 



CLASSIFICATION 87 



are known, do not fall into either of these groups, but are in some 
respects annectant forms, we have placed them provisionally, at 
least, in a third group by themselves, named Arclneoceti. There 
is nothing known at present to connect the Cetacea with any 
other order of Mammals ; but it is quite as likely that they are 
offsets of a primitive Ungulate as of a Carnivorous type, or perhaps 
of a still more generalised mammalian stock. 

The remaining Eutherian mammals are clearly united by the 
characters of their teeth, being all heterodont and diphyodont, with 
their dental system reducible to a common formula. 

Although older views of, the relationship of Ungulate mammals 
expressed by the terms Pachydermaia, Ruminantia, and so forth, still 
linger in some corners of zoological literature, no single point in 
zoological classification can be considered so firmly established as the 
distinction between the Perissodactyle and Artiodactyle Ungulates ; 
both being in the existing fauna of the world perfectly natural 
and distinctly circumscribed groups. The breaking-up of the latter 
into four equivalent sections, the Pecora, Tylopoda, Tragulina, and 
Suina, is equally in accordance with all known facts. Less certain, 
however, is the association of the Proboscidea and the Hyracoidea 
with the true Ungulates. By many zoologists they are each, 
although containing so very few existing species, made into distinct 
orders ; and much is to be said in favour of this view. The 
discovery, however, of a vast number of extinct species of Ungu- 
lates which cannot be brought under the definition of either Perisso- 
dactyla or Artiodactyla, and yet are evidently allied to both, and 
to a certain extent bridge over the interval between them and the 
isolated groups just mentioned, make it necessary either to intro- 
duce a number of new and ill-defined ordinal divisions, or so to 
widen the scope of the original order as to embrace them all, 
considering the Elephants and the Hyraces as representing sub- 
orders equivalent to the great Perissodactyle and Artiodactyle groups. 
It is the latter alternative that we have adopted. 

The Rodentia, although generally presenting a low grade of 
development, are a very specialised and distinct group. The 
position here assigned to them would accord with apparent relation- 
ships with the Ungulates, through the Elephant on the one hand 
and the extinct Tijpotherium on the other. 

In the present state of the fauna of the earth, the Carnivora 
form a very distinct order, though naturally subdivided into two 
groups, the members of the one being more typical, while those of 
the other (the Pinnvpedia) are aberrant, having the whole of their 
organisation specially modified for living habitually in the water. 

The Insectivora comprise various lowly organised and generalised 
forms, exhibiting considerable divergence of character, and ap- 
parently connected through transitional extinct species with the 



88 ORIGIN AND CLASSIFICATION 

Carnivora. As no other order can claim the family Galeopithecidce, 
it is placed here, but rather for convenience than for any other 
consideration, since it has but little if any relationship with any of 
the other members. Its isolated position is indicated by assigning 
it a distinct subordinal rank. 

The Chiroptera have always been placed near the Insectivora ; 
but they are really a highly specialised group, as much isolated 
from all other mammals by the modification of their anterior limbs 
in adaptation to aerial locomotion, as the Cetacea and the Sirenia, 
by the absence of hind limbs, are specially adapted for an aquatic 
life. 

Lastly, the Primates, which in any natural system must be 
placed at the head of the series, are divisible into two very distinct 
groups — one containing the various forms of Lemurs (Lemuroidea), 
and the other the Monkeys and Man (Anthropoidea). Whether 
the Lemuroidea should form part of the Primates (according to the 
traditional view), or a distinct order altogether removed from it, 
is as yet an undetermined question, for both sides of which there 
is much to be said. There can, however, be no doubt that the 
Anthropoidea form a perfectly natural group, presenting a series 
of tolerably regular gradations from the Marmosets {Hapxdc) to 
Man. Certain breaks in the series, however, enable us to divide 
it into five distinct families : — Hapalida' or Marmosets ; Cebiclce or 
American Monkeys, with three premolar teeth on each side of each 
jaw ; Cercopithecidce, containing the majority of Old-world Monkeys ; 
Simiidce, consisting of the genera Hylobates, Simia, Gorilla, and 
Anthropopithecus, the true Man -like Apes; and, lastly, LTominida; 
containing the genus Homo alone. 

Subclass I. Prototheria. 
Order i. Monotremata — Monotremes. 

Fam. 1. OrnithorhynchidcB — Duck-bill. 
2. Echidnidce — Spiny Anteater. 

Group. MULTITUBERCULATA. 1 

Fam. 1. Plagiaulacidse — Plagiaulax. 

2. Polymastodontidae — Polymastodon. 

3. Tritylodontidse — Tritylodon. 

Subclass II. Metatheria. 
Order ii. Marsupialia — Marsupials. 

Suborder 1. Polyprotodontia — Polyprotodonts. 

1 The names of the groups containing only extinct forms are printed in heavier 
type than those which contain species still existing. 



CLASSIFICATION 89 



Fain. 1. Dromatheriidae — Dromatherium. 

■1. Amphitheriidae — AmpMtherium, etc 

3. Spalacotheriidae — Spnlacotherium. 

4. Tritylodontidae — Tritylodon. 

5. Dideljihyidiv — Opossums. 

I!. Dasyuridce — Thylacine and Dasyures. 

7. l'cramelidcc — Bandicoots. 

Suborder 2. Diprotodontia — Diprotodonts. 
Fam. 8. Phascolomyidce — Wombats. 
9. PhalangeridoB — Phalangers. 

1 0. Diprotodontidse— Diprotodon. 

11. Nototheriidae — Notothere. 

1 2. Macropodidce — Kangaroos. 

Subclass III. EUTHEKIA. 

Order iii. Edentata — Edentates. 

Fam. 1. Bradypodidce — Sloths. 

2. Megatheriidae — Ground Sloths. 

3. Myrmecophagidce — Anteaters. 

4. Dasypodidce — Armadillos. 

5. Glyptodontidae — Glyptodonts. 
G. Manidce — Pangolins. 

7. Oryeteropodidoe — Aard-varks. 

Order iv. SlRENlA — Sirenians. 

Fam. 1. Manatidce — Manatees. 

2. Rhytinidae — Rhytina. 

3. Halicoridce — Dugongs. 

4. Halitheriidae — Halithere. 

Order v. Cetacea — Cetaceans. 

Suborder 1. Mystacoceti — Baleen Whales. 
Fam. 1. Balcenidce — Greenland Whale, etc. 

Suborder 2. ARCILEOCETI. 

Fam. 2. Zeuglodontidae — Zeuglodonts. 

Suborder 3. Odontoceti — Toothed Whales. 
Fam. 3. Physeteridce — Sperm Whale. 

4. Platanistidce — Freshwater Dolphins. 

5. Delphinidce — Dolphins, Porpoises, etc. 

Order vi. Ungulata — Hoofed Mammals. 
Suborder 1. Artiodactyla — Artiodactyles. 
Section A. Suina — Pig-like Artiodactyles. 
Fam. 1. Hippopotamidce — Hippopotamus. 
2. Suidce — Pigs and Peccaries. 



9o ORIGIN AND CLASSIFICATION 



1 h\ 



3. Choeropotamidae — Chceropotamus. 

4. Anthracotheriidae — Anthracothere. 

5. Merycopotamidae — Merycopotainus. 

6. Cotylopidse — Oreodonts. 

7. Anoplotheriidae — Anoplothere. 

8. Dichodontidae — Dichodon. 

Tragulina — Chevrotains. 
TragulidoB — Clievrotains. 

Tylopoda — Camels. 

Camelidce — Camels and Llamas. 

Poebrotheriidae — Poebrotherium. 

Pecora — True Ruminants. 
Cervidce — Deer. 
Giraffidce — Giraffe. 
Antilocapridce — Prong-buck. 
Bovidce — Sbeep, Cattle, etc. 

Perissodactyla — Perissodactyles. 
Tapiridee — Tapirs. 
Lophiodontidae — Loplnodonts. 
Palaeotheriidae — Palieotheres. 
Eqwidce — Horses. 
Rhinocerotidce — Rhinoceroses. 
Lambdotheriidae — Palaeosyops. 
Chalicotheriidae — Chalicothere. 
Titanotheriidae — Titanotbere. 
Macraucheniidae — Macrauchenia. 

TOXODONTIA— Toxodonts. 
Toxodontidae — Toxodon. 
Typotheriidas — Typothere. 

Suborder 4. CONDYLARTHRA 

Fam. 27. Periptychidae — Periptychus. 

28. Phenacodontidae — Phenacodus. 

29. Meniscotheriidae — Meniscothere. 

Suborder 5. Hyracoidea — Hyraces. 
Fam. 30. Hyracidce — Hyrax. 

Suborder 6. AMBLYPODA. 

Fam. 31. Pantolambdidae — Pantolambda. 

32. Coryphodontidas — Coryphodon. 

33. Uintatheriidae — Uintathere. 

Suborder 7. Proboscidea — Proboscideans. 

Fam. 34. Dinotheriidae — Dinotbere. 
35. Elephantidce — Elephants. 



Section B. 


9. 


Section C. 


10. 


11. 


Section D. 


12. 


13. 


14. 


15. 


Suborder 2. 


Fam. 16. 


17. 


18. 


19. 


20. 


21. 


22. 


23. 


24. 


Suborder 3. 


Fam. 25. 


26. 



CLA SSIFICA TION 9 1 



Group. TILLODONTIA— Tillodonts. 

Fam. Anchippodontidae — Anchippodus. 
Calamodontidae — Calamodon. 

Order vii. Eodentia — Kodents. 
Suborder 1. Simplicidentata. 

Fam. 1. Anomaluridcc — Auomalurus. 

2. Sciurida? — Squirrels and Marmots. 

3. Haplodontidcc — Haplodon. 

4. Ischyroniyidae — Ischyromys. 



6. Myoxidce — Dormice. 

7. Lophiomyidre — Lophiomys. 

8. Muridce — Rats, Mice, and Voles. 

9. Spalacidcc— Mole-rats. 

TO. Geomyida; — Pouched Rats. 

1 1 . Dipodidce — Jerboas. 

1 2. Theridomyidae — Theridomys. 

13. Octodontidce — Spiny Mice. 

1 4. Oastoroididae — Castoroides. 

1 5. Hystricidic — Porcupines. 

1 6. Chinchillidce — Chinchillas. 

17. Dinomyidce — Dinomys. 

1 8. Caviidce — Cavies. 

1 9. Dasyproctidre — Agouties. 

Suborder 2. Duplicidentata. 

Fam. 20. Lagomyidce — Picas. 

21. Leporidce — Hares and Rabbits. 

Order viii. Carnivora — Carnivores. 

Suborder 1. Carnivora Vera — Fissipedes. 

Fam. 1. Felidce — Cats. 

2. Hycewidce — Hyaenas. 

3. Proteleidce — Earth-wolf. 

4. Viverridce — Civets and Ichneumons. 

5. Canidce — "Wolves and Foxes. 

6. Vr&idM — Bears. 

7. Mustelidce — -Weasels and Otters. 

8. P?-ocyonidce — Racoons and Cat-bear. 

Suborder 2. Pinnipedia — Pinnipedes. 

Fam. 9. Otariidce — Eared Seals. 

1 0. Trichechidce — Walrus. 

1 1 . Phocidos — Seals. 

Suborder 3. CREODONTA — Creodonts. 

Fam. 12. Hyaenodontidae — Hycenodon. 

1 3. Proviverridae — Proviverra. 

14. Arctocyonidae — Arctocyon. 

1 5. Mesonychidae — Mesonyx. 



92 ORIGIN AND CLASSIFICATION 



Order ix. Insectivora — Insectivores. 
Suborder 1. Insectivora Vera. 
Fam. 1. Tupaiidce — Tupaias. 

2. Macroscelididce — Elephant-Shrews. 

3. Erinaceidce — Hedgehogs. 

4. Soricidce — Shrews. 

5. TalpidoB — Moles. 

6. Potamogalidce — Potamogale. 

7. Solenodontidce — Solenodon. 

8. Centetidce — Centetes. 

9. Chrysochloridce — Golden Moles. 
Suborder 2. Dermoptera. 

Fam. 10. GaleopithecidcB — Galeopithecus. 

Order x. Chiroptera — Bats. 

Suborder 1. Megachiroptera — Frugivorous Bats. 

Fain. 1. Pteropodidce — Flying Foxes. 
Suborder 2. Microchiroptera — Insectivorous Bats. 

Fam. 2. Vespertilionidce — Common Bats. 

3. Nycteridce — Nycteris. 

4. Rhinolophidce — Leaf-nosed Bats. 

5. Emhallommdce — Emballonura. 

6. Phyllostomatidce — Vampy res. 

Order xi. Primates. 

Suborder 1. Lemuroidea — Lemuroids. 
Fam. 1. Hyopsodontidae — Hyopsodus. 

2. Chiromyidce — Aye-Aye. 

3. Tarsiidce — Tarsier. 

4. Lemuridce — Lemurs. 

Suborder 2. Anthropoidea — Anthropoids. 
Fam. 5. Hapalidce — Marmosets. 

6. Cebidce — American Monkeys. 

7. Cercopithecidce — Old World Monkeys. 

8. Simiidce — Gibbons and Man-like Apes. 

9. Hominidce. — Man. 

The distinctive character of these subclasses and orders, with an 
account of their subdivisions and the principal forms contained in 
each, will be given in subsequent chapters. 



CHAPTER IV 



GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION 
I. GEOGRAPHICAL DISTRIBUTION. 1 

In considering the present distribution of mammals over the 
globe, Ave may, in the first place, direct our attention to terrestrial 
or land types, reserving the consideration of aerial types, like the 
Bats, and aquatic forms, as exemplified by the Cetaceans, Sirenians, 
and Seals, to separate sections. 

Among terrestrial forms each species has a certain definite area 
of distribution in space, which may be of very wide extent, or may 
be confined to a restricted region. This distributional area is, 
however, always connected, or continuous ; that is to say, that 
although we may have a single species inhabiting two continents, 
like the Lion in Asia and Africa, or dwelling both on a continent 
and adjacent continental islands, like the Javan Rhinoceros of India, 
Java, and Borneo, yet we shall always find that such areas, if not 
still connected, show evident signs of having been so connected 
in comparatively late geological epochs ; and we never find 
instances of the same species inhabiting totally disconnected areas, 
such as India and South America. As examples of mammals 
with a wide distribution we may mention the Lion and the 
Leopard, Avhich are now found throughout Africa, and also occur 
in India, as well as in the intervening areas of Arabia and Persia. 
In the case of the former species, palaeontology further teaches us 
that its distribution in the last geological epoch was even more 
extensive, since we have good evidence to show that it formerly 
ranged over the greater part of Europe, including the British Isles. 
The Jackal affords another well-known instance of a species common 

1 On this subject see A. Murray, Geographical Distribution of Mammals, 1866 ; 
and especially A. R. Wallace, The Geographical Distribution of Animals, 2 vols., 
1876, and Island Life, 1881 ; also A. Heilprin, The Geographical and Geological 
Distribution of Animals, 1887. 



94 GEOGRAPHICAL DISTRIBUTION 



to India and Africa. The American Puma, again, may be cited as 
an example of a mammal having a very wide range in latitude, 
since it is found from Patagonia in the south to Canada in the 
north. As instances of wide range in the opposite direction we 
have only to mention the Reindeer and the Elk or Moose, found 
in the northern regions of both the Old and New Worlds, which 
are only separated from one another by the narrow channel of 
Behring Strait. 

Of mammals with extremely restricted distributional areas, we 
may mention many of the Insectivora, such as the Desman of the 
Pyrenees, and some of the Madagascar types of this order, the 
Lemurs from the same island, some of the species of Marmots, the 
remarkable bear dike Mbir&pus of Eastern Tibet, one species of Zebra, 
and other Ungulates from Africa. 

The distribution of a genus (except of course when the genus is 
represented only by a single form) is very generally more exten- 
sive than that of a species ; and this may be markedly the case 
when there are only some two or three species in a genus. In 
genera, moreover, we meet with what is known as discontinuous 
distribution, that is, where the distributional area of one or 
more species is totally separated from that of others. The best 
instance of this occurs in the case of the Tapirs, where we find 
one species inhabiting the Malayan Peninsula, and no others 
anywhere in the world, with the exception of South America. The 
explanation of such an apparently anomalous feature in distribution 
is to be found in the past history of the globe, which shows us that 
Tapirs once existed in China, Europe, and North America, and, 
therefore, indicates that the existing isolated species are the sole 
survivors of a group once spread over a large portion of the earth's 
surface. In regard to generic distribution it must, however, be 
mentioned that this depends to a great extent on the limits which 
we are disposed to assign to genera themselves. 

As the distributional area of a genus generally exceeds that of 
a species, so that of a family, or group of genera, is larger than that 
of a single genus ; and similarly the distribution of an order, or 
assemblage of families, usually occupies a larger area than that of 
a single family. Thus, for instance, the genus Thi/lacimis, re- 
presented only by the so-called Tasmanian Wolf or Thylacine, is 
now entirely restricted to Tasmania ; but the family Dasyuridte, to 
which that genus belongs, ranges all over Australia, while the order 
Marsupialia, which includes the Dasynridce, is found both in Aus- 
tralia and America, and in past epochs was probably spread over 
the entire globe. 

A remarkable feature in connection with the distribution of the 
terrestrial Mammalia is the circumstance that, with the exception of 
certain species introduced by human agency, and small forms which 



TERRESTRIAL DISTRIBUTION 95 

can easily have been transported on floating timber or other similar 
means, they are totally absent from what are known as oceanic 
islands — that is islands arising from great depths in the ocean, 
mainly composed of coral or volcanic rocks, and showing no signs 
of having ever been connected with the existing continents, or the 
larger and so-called continental islands. The obvious explanation 
of this feature is, that from their total isolation these islands 
have never been able to receive a mammalian fauna from the 
great continental areas on which mammalian life was probably 
first developed. 

As an intermediate step between these islands which are 
practically void of mammalian life and the continents which teem 
with such a variety of forms, are certain larger islands and portions 
of continents containing a mammalian fauna more or less markedlj' 
distinct from that of the whole of the other regions of the globe. 
The best instance of this is Australia, which, with the exception of 
one dog — the Dingo — and certain Muridce and Bats, has no mammals 
except Monotremes and Marsupials. The latter are, moreover, per- 
fectly distinct from those of America, which, if we exclude the islands 
in the neighbourhood of Australia, is the only other region which now 
possesses any Marsupials at all. Here also we have a ready and full 
explanation which accords with all the facts ; since it is evident 
that Australia has been isolated from the Asiatic continent from 
some very remote geological epoch, at which period it is probable 
that Monotremes and Marsupials were the dominant if not the sole 
representatives of the Mammalia then existing. Consequently 
Australia has never been able to receive an influx of the Eutherian 
orders, which have probably swept away all the Marsupials except 
the small American Opossums from the rest of the globe. Again, 
the large island of Madagascar, which has a fauna of an African type, 
but still very markedly different from that of the mainland, may 
be considered to have been connected with the latter at a time 
when the Eutheria had become the dominant forms, but has been 
separated for a sufficiently long period to have enabled a large 
number of its species and genera to have become distinct from those 
of the adjacent continent. Similarly, there is evidence to show 
that South America was probably cut off for a considerable period 
from the northern half of the American continent, in consequence 
of which its lowly organised fauna of Edentates were enabled to 
attain such a remarkable development in the later geological 
periods. 

In contrast to the mammalian fauna of islands of the preceding- 
type is, or rather was, that of the British Islands, Avhich in the 
early historic and prehistoric periods was identical with that of 
the Continent. This leads to the inference that at a comparatively 
late epoch there was a direct land communication between Britain 



96 GEOGRAPHICAL DISTRIBUTION 

and the Continent, which is shown by geological evidence to have 
actually been the case. 

The above instances are sufficient to show what an important 
influence the date of separation of islands from the adjacent 
continents has had upon their existing mammalian fauna, and how 
largely the present distribution of mammalian life is bound up with 
the past history of our globe. We must, however, not omit to 
mention another very important agency of past times which has 
likewise had great influence on the present distribution of the 
various faunas of the northern hemisphere. This is the so-called 
glacial epoch, Avhich took place immediately before the establish- 
ment of the present condition of things, and appears to have been 
the cause of the extinction of many of the larger mammalian types 
which formerly inhabited Europe, and whose retreat to the warmer 
regions of the south was apparently cut oft' by the Mediterranean. 

Zoological Regions. — Zoologists are now generally agreed in dividing 
the land surfaces of the globe into a number of zoological regions or 
provinces, characterised by a more or less distinctly marked general 
fades of their fauna as a whole. Some of these regions are much more 
distinctly defined than the others ; and in the majority of cases 
there is a kind of neutral ground or No-man's land at the junction 
between any two of these regions. It must also be remembered 
that in the Old World proper as we go back in time we find a 
gradual assimilation in the mammalian faunas of the different 
regions, indicating that originally there was one large fauna of 
a generally similar type occupying the greater portion of this 
area. Thus we find that Hippopotami, Giraffes, Kudus, Elands, 
and other types of Antelopes now restricted to Africa, formerly 
extended to Europe and India, while there is also evidence to show 
that the group of large anthropoid Apes, now found only in Africa 
and the Bornean region, were likewise spread over a large part of 
the south-western half of the Old World. Moreover, while at the 
present day there is a marked connection between. the mammals of 
the northern regions of both the Old and New Worlds, in the 
Tertiary period it appears that the fauna of the whole of North 
America was much more nearly allied to that of the central regions 
of the Old World than is now the case. Thus in the Tertiary 
rocks of America we meet with remains of what we are accustomed 
to regard as such essentially Old AVorld genera as Horses and 
Khinoceroses. On the other hand there are no traces in America 
of the existence at any period of Apes, Giraffes, Hippopotami, or 
Hyaenas, while that continent has yielded evidence of groups of 
Ungulates totally unrepresented in the eastern hemisphere. 

The chief zoological regions of the globe, proposed by Mr. Sclater 
in 1857, and now recognised by the majority of authorities, are 
six in number, and are named as follows. Firstly, the Palaearctic 



ZOOLOGICAL REGIONS— PALAZARCTIC 97 

region, embracing the whole of Europe, Persia, Northern Arabia, 
and all of Asia northward of the line of the Himalaya proper, 
Japan, that part of Africa lying northward of the Sahara Desert, 
and the oceanic islands of the North Atlantic. Secondly, the 
Ethiopian region, which comprises all Africa lying to the south 
of the Sahara, the southern part of Arabia, Madagascar, and the 
Mascarene Islands. Thirdly, the Oriental or Indian region, which 
is taken to include India south of the Himalaya, and to the 
north-west as far as Beluchistan, the Malay peninsula, southern 
China, Sumatra, Java, Borneo, and the Philippines. Fourthly, 
the Australasian region, Avhich is usually defined as being bounded 
to the north-west by the deep sea channel lying between Borneo and 
Celebes known as Wallace's line, and is taken to include Celebes, 
Lumbok, New Guinea, Australia, Tasmania, New Zealand, and the 
host of oceanic islands in the South Pacific. Several writers, how- 
ever, prefer to regard Celebes and some of the adjacent islands as 
representing a transitional Austro- Malayan region. Fifthly, the 
Nearctic region, comprising Greenland and North America as far 
south as the north of Mexico. And, sixthly, the Neotropical 
region, which embraces the remaining portion of the American 
continent and the West Indies. 

Various minor modifications of this scheme have been proposed. 
Thus some writers are disposed to raise India to the rank of a 
distinct primary region, while others propose the same for New 
Zealand. The Palaearctic and Nearctic regions have a large number 
of common types, more especially among the mammals, and Dr. A. 
Heilprin l has expressed his opinion that they should be regarded 
as a single primary region under the name of the Holarctic. The 
same writer would also separate the South Pacific Islands as con- 
stituting a Polynesian region. 

Minor divisions or sub-regions have also been marked out, but it 
will be unnecessary to indicate their limits in the present work. 
We may, however, mention the Mediterranean sub-region of the 
Palaearctic, which includes the peninsular portion of southern 
Europe, North Africa, Asia Minor, Persia, Afghanistan, Beluchistan, 
and Northern Arabia, as a good instance of the transition from one 
region to another, since its fauna has a mingling of Palaearctic, 
Ethiopian, and Oriental types, the former being, however, the 
predominant ones. 

• Of the chief mammalian types characteristic of these various 
regions only a brief sketch can be given in this work. 

Pahrardic Region. — The Palaearctic region is of enormous extent, 
and includes countries varying greatly in their flora, climate, and 
elevation. Thus it embraces the Arctic plains of Siberia, the warm 
regions of Italy, Southern France, and Northern Africa, the forest- 

1 Distribution of Animals. 

7 



9 8 GEOGRAPHICAL DISTRIBUTION 

clad slopes of the outer Himalaya, and the lofty arid plains of Turk- 
estan and Tibet, scorched by a burning sun in summer and chilled by 
a still more terrible cold in winter. Its extreme limits in the west 
are marked by the Canaries and Azores, and in the east by distant 
Japan ; and yet throughout this vast expanse we find a great uni- 
formity of life, as exemplified by the large number of British genera 
which occur also in Japan. The mammals which are on the whole 
the most characteristic of this region are the Sheep and Goats, forming 
a section of the great family of Bovidce, nearly all the species of which 
are Palsearctic, although we meet with one Goat (Capra) in the 
Nilgherries of Southern India, and a Sheep (Ovis) in the Nearctic 
region. The Musk Ox (Ovibos) is characteristic of the Palsearctic 
and Nearctic regions. At least one species of Camel is characteristic 
of this region, and it is not improbable that the second may also 
have originated in it. There are a few characteristic types of 
Antelopes, such as the Alpine Chamois (Bupicapra), the Saiga of 
Tartary, and the Chiru (Panthokps) of Tibet, each of which is 
represented by only a single species ; and we miss the host of 
Antelopes so characteristic of the Ethiopian region. Deer (Cervus) 
are abundant, although by no means confined to this region ; and 
the Musk Deer (Moschus), the sole representative of the subfamily 
Moschince, is exclusively Palsearctic. Monkeys, as a rule, are absent, 
although we meet with one species of Macacus in Northern 
Africa and at Gibraltar, and some other types on the southern 
border of Tibet. The Moles (Talpa) are mainly Palsearctic, 
although one species enters Northern India, while the Desmans 
(Myogale) of the Pyrenees and Southern Russia are unknown 
beyond the limits of this region. The Water-shrew (Nectogale) is 
likewise a peculiar eastern Palsearctic type. Among the Rodents, 
the Picas or Tailless Hares (Lagomys) and the Dormice (Mi/oxus) 
are essentially Palsearctic forms, only one species of each being found 
beyond the limits of the region, and the one extra-Palsearctic species 
of Lagomys occurring in the cognate Nearctic region. The Mice and 
Rats are represented by the typical genus Mus and other types, 
and Hares (Lepus) and one species of Squirrel (Sciarus) are common. 
The Carnivora include two species of Bears (Ursus), Wolves and 
Foxes (Canis), a Lynx and a few species of Cats (Felis), as well as 
numerous weasels (Mustela), and some other types. 

Ethiopian Region. — The Ethiopian region is of great interest to 
the student of mammals, since it is inhabited by a number of forms 
remarkable for their large size. A considerable portion of the area 
consists of desert, especially in the north ; but there is also a Avide 
extent of grassy plains (veltd), as well as vast tracts of equatorial 
forests of great density. Perhaps the most striking feature in the 
Ethiopian fauna is the number of Ungulates, both of the Artio- 
dactyle and Perissodactyle sections. In the former section we have 



ETHIOPIAN REGION 99 

the Giraffes (Jjiraffa) represented by one species, which is the type 
of a family, and is unknown elsewhere. Equally characteristic are 
the Hippopotami, which likewise form the type of a family, while 
the Pigs are represented by the Wart-hogs (Phticochozrus) and the 
River-hogs, forming an aberrant group of the genus Sus. The Oxen 
(Bos) are represented by Buffaloes, but there are no species of true 
Oxen or Bison. The Antelopes attain an extraordinary develop- 
ment, the number of species being estimated at from eighty to ninety, 
which are referred to a large number of genera, although several of 
these are more or less ill defined. Most of these genera are peculiar 
to this region, but the Gazelles (Gazdla) are also found in the desert 
regions of other parts of the Old World, and Oryx ranges into Arabia 
and Persia. In contrast to this abundance of Antelopes is the total 
absence of the Deer family, or Cerridiv, which are so characteristic 
of the Palaearctic and Oriental regions. The Chevrotains or 
TragvlidcB are, however, represented by Dorcatherium. 1 In the 
Perissodactyle section we may notice the presence of two species 
of Rhinoceros, both furnished with two horns, and distinguished from 
those of the Oriental region by the absence of incisor and canine 
teeth. The Horse family (Equidce) is also represented by several 
species, and includes the peculiar group of Zebras, characterised 
by their beautifully striped skins. Of other Ungulates the Ele- 
phants, which, like the Ehinoceroses, are now peculiar to the 
Ethiopian and Oriental regions, have one species, which is widely 
different from its Indian congener. The Hyraces are mainly 
characteristic of this region, although one species occurs in Syria 
and Palestine. The Carnivora include some forms like the Lion, 
Leopard, and Jackal, common to the Oriental region, but likewise 
include certain peculiar types like the Earth-wolf (Proteles), which 
may be regarded as the type of a distinct family, and two species 
of Hyaenas, which are referred by some authorities to a distinct genus 
(Crocuta). There is also the Hunting-dog (Lycaon), and the peculiar 
group of Foxes known as the Fennecs, together with Otocyon. Bears, 
Wolves, and true Foxes are absent ; but Civets, etc., are abundant, 
although not characteristic of the region. The Primates yield several 
very characteristic types, such as the Gorilla and the Chimpanzee 
(Anthropopithecus) among the Simiidcr, which, Avith the exception of 
the Orangs of Borneo, are the only existing large man-like Apes, 
and the group of Dog-faced Baboons (Cijnoceplialus) in the Cereopithe- 
cidce. The genus Colobus is also a group of the latter family, 
absolutely characteristic of the region. Lemurs, again, occur on 
the continent of Africa, but the great development of this group 
is in the adjacent island of Madagascar, where several peculiar 
genera occur, and where the larger Carnivora and Ungulata are 

1 Generally known as Hyomoschus, but first described as an extinct form 
under the above name. 



ioo GEOGRAPHICAL DISTRIBUTION 



absent. These peculiarities of the fauna of Madagascar apparently 
point, as previously mentioned, to its separation from the mainland 
before the latter was overrun by the larger types, and at a time 
when its chief mammals were Lemurs and Insectivores. There 
are two genera of Edentates, the Pangolins (Manis), and the Aard- 
vark (Orycterqpus), the latter being peculiar. 

Although the foregoing groups of mammals are now so 
characteristic of the Ethiopian region, it cannot be too strongly 
insisted that their restriction to this region is, so to speak, merely 
a feature of the present day, and that at a late geological epoch 
nearly all the peculiar genera Avere represented in India, and many 
of them also in Europe. 

Oriental Region. — The third or Oriental region is likewise of very 
considerable extent, and is the only one, in addition to the Ethiopian, 
which is the home of huge Ungulates, like Elephants and 
Rhinoceroses, and the large man-like Apes. A large proportion of 
this extensive area is occupied by tropical and subtropical forests 
and swamps ; these being especially abundant in Burma, Southern 
China, Siam, and the southern ridges of the Himalaya, collectively 
constituting the Indo-Chinese sub-region, and also in the Indo- 
Malayan sub-region of the Malay peninsula and adjacent islands. 
In the third or Indian sub-region, comprising peninsular India, with 
the exception of the Carnatic, there are large tracts of open country, 
including some of the hottest regions in the world, parts of which 
form plains more or less covered with vegetation during the cooler 
and rainy seasons, while others are barren rocky table-lands, as in 
the Deccan, or arid deserts like those of parts of the Punjab and 
Sind. Finally, in the fourth or Cingalese sub-region, represented 
by the Carnatic and the island of Ceylon, we find vast areas of 
luxuriant forest and jungle. In the north-western desert area of 
the Indian sub-region the fauna includes a mixture of Palasarctic and 
Ethiopian forms, Avith those characteristic of the Oriental region. 

Among the chief features of the mammalian fauna "of this 
region we may notice the absence of Hippopotami and Giraffes, the 
greatly diminished number of Antelopes, as compared with those 
of Africa, and the abundance of Deer and true Pigs. The Antelopes 
comprise the two peculiar genera Boselaphus (Nilghai) and the 
typical Antilo'pe (Black-buck), each of which is represented by only 
a single species, while the Deer belong to the so-called Rusine 
group, which is markedly different from that to which the 
Palsearctic Red Deer belongs. True Chevrotains (Tragidus) are 
peculiar to this region. The Oxen include the true Buffalo, 
differing in many respects from the African species of the same 
group, and also certain species of true Oxen, such as the Gaour and 
Banting, belonging to the Bibovine group, which is confined to this 
region. In the Perissodactyla Horses (Equus) are represented 



ORIENTAL REGION 101 

only by a single species in the desert area of the Indian sub-region, 
while the two species of Rhinoceros diner from those of Africa 
in being furnished with canines and incisors. The Malayan 
Tapir is the only Old World species of its genus. The Indian 
Elephant differs, moreover, so markedly from its African ally that 
some writers regard the two as types of distinct genera. The 
Carnivora include the Lion, Leopard, Jackal, and Hunting-Leopard, 
which are common to Africa ; but the Tiger is very characteristic 
of this region, although extending northwards into the Palsearctic. 
Civets are abundant, comprising some peculiar genera, of which it 
will suffice to mention the well known Paradoxurus. Wolves closely 
allied to the Palaearctic species occur in Northern India, and there 
are also Foxes related to the typical species. The Dog-like animals 
which hunt in packs, and are separated by some writers from Canis 
under the name of Cyon, occur in the present and the Palsearctic 
region. The striped Hyaena is the Indian representative of its genus. 
Ratels are common to this and the Ethiopian region, and constitute 
the genus Mellivora. The most striking feature in the Carnivorous 
fauna of this region, as distinguished from the Ethiopian, is, however, 
the presence of Bears, some of which belong to the typical genus 
Ursus, while one species is usually generically separated under the 
name of Melursus. Among the Rodents we may especially notice 
the abundance of the Muridce and Sciuridce. In the former family 
Ave have numbers of true Mice (Mus), and also the peculiar genus 
Xesocia (Bandicoot-Rat), while in the latter both the true Squirrels 
(Sciu rus) and the Flying-Squirrels (Pteromys) attain great develop- 
ment. The genus {Pteromys) is, indeed, mainly characteristic of this 
region, although in Kashmir and Japan it enters the Palsearctic. 
The Bats ai*e very numerous, being represented by all the families, 
with the exception of the Phyllostomatidce, or Vampyres, of South 
America. Among the Insectivora the genera Tujxiia and Galeo- 
pithecus (Flying Lemur) are peculiar to this region, although not 
found in India. Finally, in the Primates we have the genera 
Macacus and Semnopithems very abundantly represented, although 
both also enter the Palsearctic region ; but the Anthropoid types 
are confined to the south-eastern half of the region, and include the 
Orangs (Simla) of Borneo, and the smaller long-armed Gibbons 
(Hylobates), which are abundant in the Malay peninsula, both 
genera not being found beyond this region. The Lemurs are much 
less abundant than in the Ethiopian region, but they include the 
peculiar Tarsier of Sumatra, Borneo, and Celebes (Austro-Malayan 
region), which differs so markedly in dentition and structure of 
the feet from all other forms that it has been made the type of 
a separate family. The Edentates, so poorly represented in the 
Old World, include only Pangolins (Manis), which, as we have 
already seen, also occur in the Ethiopian region. 



102 GEOGRAPHICAL DISTRIBUTION 

Australasian Region. — With the fourth or Australasian region we 
come to a mammalian fauna so peculiar that we have no difficulty 
whatever in defining it from all the other regions of the globe, 
although it should be observed that in the Austro-Malayan islands 
Ave have a partial mingling of the Australasian and Malayan faunas. 
If we exclude Celebes from this region we find that, with the 
exception of a Pig in New Guinea, of the Dingo in Australia, of 
numerous Mice and Rats (Mv/ridce), and Bats, there are no Eutherian 
mammals throughout the area. The mammals of this region are 
restricted to the Australian mainland, the island of Tasmania, New 
Guinea, and the Aru islands, the whole area of New Zealand 
having been totally devoid of mammalian life until introduced by 
man. The whole of the Monotremata, constituting the subclass 
Prototheria, and all the Marsupials, exclusive of the few outlying 
forms ranging into the transitional Austro-Malayan area, and with 
the exception of the American family of the OjDossums (Did elphy idee), 
are absolutely confined to this region. 

Celebes. — The mammals of Celebes — the typical representative 
of the Austro-Malayan transitional region or sub-region — include the 
peculiar Ape known as Cynopithecus, Tarsius (also Oriental), the 
Anoa, and the single species of Babirusa. Several other types of 
placental mammals are found in this transitional area, while the 
Marsupials are represented by Phalanger and Petaurus. 

Neardie Region. — The two remaining regions we have to consider 
are comprised in the New World. The first of these is the 
Nearctic, which, as already mentioned, has a fauna showing such a 
strongly marked relationship to that of the Palasarctic region, that 
it has been proposed to unite the two regions. Among types 
common to these two regions we may mention closely allied species 
of true Deer (Cervus) as exemplified by the Red Deer and the 
Wapiti ; the allied Bisons of the two regions ; the Reindeer and Elk 
common to both ; as well as nearly related, and in some cases 
identical, species of Cats, Lynxes, Bears, Wolves, Foxes, Beavers, 
Squirrels, Marmots, and Hares. The Glutton or Wolverene, and the 
Musk Ox is also common to the Arctic portions of the two regions. 
The Ungulates are very poorly represented, but Ave have, in addition 
to the forms already mentioned, one species of the Palaearctic genus 
Ovis, namely the Big-horn, and the Prong-buck (Antilocapra), Avhich 
is quite peculiar. There are, hoAvever, no Perissodactyla. The 
Racoons and Coatis (Procyonidce) constitute a family represented out 
of the NeAV World only by the aberrant Cat-Bear (jEIutus) of Nipal. 
The characteristic American feline knoAAm as the Puma extends over 
this region ; but there are no Edentates, and the Marsupials are 
represented only by a single species of Opossum. Rodents are ex- 
tremely numerous, and comprise several characteristic types, Avhich 
alone would tell us what part of the globe Ave Avere visiting. The 



NEOTROPICAL REGION 103 

most distinctive are the Pouched Rats {Geomyidce), and the Beaver-like 
rodents known as the Hajolodontidce. True Rats and Mice (Mus), 
which are represented throughout the Old World, are totally wanting 
in the New, where they are replaced by the Vesper-mice, which may 
be included in the European genus Oricettis, although often separated 
as Hesperomys. This feature alone would seem to justify the dis- 
tinction of the Nearctic from the Palsearctic region. The Musquash 
(Fiber) is a genus of Nearctic rodents unknown in the Old World. 
Among other characteristic genera we may mention, in the Carnivora, 
the Skunk (Mephitis) and the American Badger (Tazidea). Primates 
are absent from the entire region. 

Neotropical Region. — The last of the six main regions is the 
Neotropical, including Mexico, South America, and the West Indies. 
A very large extent of this area is occupied by forests, which are 
described as being denser and more luxuriant than those of any 
other part of the globe. Alternating with these forest areas are 
the vast grassy plains known in different regions as llanos, savannas, 
and pampas. The back-bone of the region is formed by the great 
chain of the Andes. Next to the Australasian, this region is 
perhaps better characterised by its mammalian fauna than any of 
the others. Commencing with the Ungulates, we find a total 
absence of Antelopes, Sheep, and Oxen, and also of all Perissodac- 
tyles except Tapirs. Deer are, however, represented, although by 
peculiar forms (Cariacus) unknown beyond the New World. The 
Peccaries (Dicotyles), Avhich are often made the type of a distinct 
family, take the place of the Old World Pigs, while the Llamas and 
Alpacas (Auchenia) are the substitutes for the Palsearctic Camels. 
The Carnivora include several Cats (Felis), among which the Puma 
and the Jaguar are the most noticeable ; and there are also Racoons, 
Coatis, Foxes, and one species of Bear. Insectivora are totally 
wanting ; but the Bats are characterised by the presence of the 
Vampyres (Phyllostomatidce), which are almost restricted to this 
region. The Rodents likewise include three families unknown 
elsewhere, namely the Chinchillas and Viscacha (Chinchillidce), the 
Agouties (Dasyproctidce), and the Cavies (Caviidce) ; while a large 
number of the Octodontidce are Neotropical, all the other forms 
being Ethiopian. In the Primates, again, we have all the forms 
quite peculiar to this region, and constituting two families, viz. the 
Cebidce or Prehensile -tailed Monkeys, and the Hapalidce, or Mar- 
mosets, both of which differ decidedly in their dentition, as well 
as in other features, from the Old World Monkeys. Lemuroids 
are unknown. Perhaps, however, the mammals which may be 
considered as most characteristic of the Nearctic region are the 
numerous Edentates, which form three families, mostly confined to 
it. These comprise the Bradypodidce or Sloths, which solely 
inhabit the forest region ; the Myrmecopliagidce or Anteaters ; and 



104 GEOGRAPHICAL DISTRIBUTION 

the Dasj/podidce or Armadillos, of which one species has crept 
northward as far as Texas. Almost equally characteristic are the 
numerous Opossums, the majority of which belong to the genus 
Didelplujs. Finally, it should be observed that the West Indies are 
distinguished from the rest of the region by the absence of Primates, 
Carnivora, and Edentates. 

Aquatic Mammals. — Many mammals grouped for the present 
purpose as terrestrial pass a great portion of their lives in brooks, 
lakes, or rivers, and, being dependent upon such waters for ob- 
taining their subsistence, are necessarily confined to their vicinity ; 
but the truly aquatic mammals, or those living constantly in the 
water, and unable to move their quarters from place to place by 
land, are the orders Cetacea and Sirenia, with which may also be 
grouped the Seals, forming the Pinniped division of the order 
Carnivora. 

For the marine Cetacea, animals mostly of large size and 
endowed with powers of rapid locomotion, there are obviously no 
barriers to universal distribution over the surface of the earth 
covered by sea, except such as are interposed by uncongenial 
temperature or absence of suitable food. Nevertheless it was 
thought some years ago that the fact of a Whale or a Dolphin 
occurring in a sea distant from that in which it had usually been 
found was sufficient justification for considering it as a distinct 
species and imposing a new name upon it. There are now, 
however, so many cases known in which Cetaceans from the 
northern and southern seas, from the Atlantic and Pacific Oceans, 
present absolutely no distinguishing external or anatomical charac- 
ters upon which specific determination can be based that the 
opposite view is gaining ground ; and, since some species are un- 
doubtedly very widely distributed, being in fact almost cosmopolitan, 
there seems little reason why many others should not be included in 
the same category. The evidence is satisfactory enough in those 
instances in which the intermediate regions are inhabited by the same 
forms ; — the cases of " continuous areas " of distribution. In those in 
which the areas of distribution are apparently discontinuous, there 
may be more room for doubt ; but it must not be forgotten that the 
negative evidence is here of much less value than in the case of 
land animals, since the existence of Cetaceans in any particular part 
of the ocean may be easily overlooked. The great Sperm Whale 
(Physet&r macrocephalus) is known to be almost cosmopolitan, in- 
habiting or passing through all the tropical and temperate seas, 
although not found near either pole. At least three of the well- 
known species of Korqual (Bahenoptera) of the British coasts are 
represented in the North Pacific, on the South American shores, 
and near New Zealand, by species so closely allied that it is difficult 
to point out any valid distinctive characters, though it may perhaps 



AQUATIC MAMMALS 105 



be desirable to wait for a more exhaustive examination of a large 
series of individuals before absolutely pronouncing them to be 
specifically identical There is nothing yet known by which we can 
separate the "Humpback Whales" (Megaptera) of Greenland, the 
Cape of Good Hope, and Japan. The same may be said of the 
common Dolphin of the European seas (Delphinus ddphis) and the 
so-called D. bairdi of the North Pacific and D. forsteri of the 
Australian seas. The Pilot Whale (Globicephalus melas) and the 
Psmdorca of the North Atlantic and of New Zealand are also, 
so far as present knowledge enables us to judge, respectively alike. 
Many other similar cases might be given. Captain Maury collected 
much valuable evidence about the distribution of the larger Cetacea, 
and, finding Right Whales (Bidcena) common in both northern and 
southern temperate seas, and absent in the intermediate region, laid 
down the axiom that " the torrid zone is to the Right Whale as a sea 
of fire, through which he cannot pass." Hence all cetologists have 
assumed that the Right Whale of the North Atlantic (B. biscayensis), 
that of the South Seas (B. australis), and that of the North Pacific (B. 
japonka), are necessarily distinct species. The anatomical structure 
and external appearance of all are, however, so far as yet known, 
marvellously alike, and, unless some distinguishing characters can 
be pointed out, it seems scarcely justifiable to separate them from 
geographical position alone ; as, though the tropical seas may be 
usually avoided by them, it does not seem impossible, or even 
improbable, that some individuals of animals of such size and rapid 
powers of swimming may have at some time traversed so small a 
space of ocean as that which divides the present habitual localities 
of these supposed distinct species. If identity or diversity of 
structural characters is not to be allowed as a test of species in 
these cases, as it is usually admitted to be in others, the study of 
their geographical distribution becomes an impossibility. 

Although many species are thus apparently of such wide dis- 
tribution, others are certainly restricted ; thus the Arctic Right 
Whale (Bakrna mysticetus) has been conclusively shown to be limited 
in its range to the region of the northern circumpolar ice, and no 
corresponding species has been met with in the southern hemisphere. 
In this case, not only temperature, but also the peculiarity of its 
mode of feeding, may be the cause. The Narwhal and the Beluga 
have a very similar distribution, though the latter occasionally 
ranges farther south. The common Hyperoodon is restricted to 
the North Atlantic, never entering, so far as is yet known, the 
tropical seas. Other species are exclusively tropical or austral in 
their range. One of the true Whalebone Whales (Neobalcem 
in ■trginata) has only been met with hitherto in the seas round 
Australia and New Zealand ; and a large Ziphioid (Berardius 
arneuxi) only near the last-named islands. 



io6 GEOGRAPHICAL DISTRIBUTION 



The Cetacea are not limited to the ocean, or even to salt water, 
some entering large rivers for considerable distances, and others 
being exclusively fluviatile. One species of Platanista is extensively 
distributed throughout nearly the whole of the river systems of the 
Ganges, Brahmaputra, and Indus, ascending as high as there is 
water enough to swim in, but apparently never passing out to sea. 
The individuals inhabiting the Indus and the Ganges must therefore 
have been for long ages isolated without developing any definite 
distinguishing anatomical characters ; for those by which the sup- 
posed P. indi was formerly separated from P. gangetica have been 
shown by Anderson to be of no constant value. Orcella fluminalis 
appears to be limited to the Irawaddy river, and at least two distinct 
species of Dolphin belonging to different genera are found in the 
waters of the upper Amazon. A Neomeris has been found in the 
great Chinese river, the Yang-tsi-Kiang, nearly a thousand miles 
from the sea. It is remarkable, however, that none of the great 
lakes or inland seas of the world are, according to our present 
knowledge, inhabited by Cetaceans. A regular seasonal migration 
has been observed in many of the oceanic Cetacea, especially those 
inhabiting the North Atlantic, but further observations upon this 
subject are still much needed. 

The great difference in the manner of life of the Sirenia, as 
compared with that of the Cetacea, causes a corresponding difference 
in their geographical distribution. Slow in their movements, and 
feeding exclusively upon vegetable substances, water-grasses, or fuci, 
the Sirenia are confined to rivers, estuaries, or coasts where these 
grow, and are not denizens of the open sea, although of course there 
is a possibility of accidental transport by the assistance of oceanic 
currents across considerable distances. Of the three genera exist- 
ing within historic times, one (Manatus) is exclusively confined to 
the shores of the tropical Atlantic and the rivers entering into it, 
individuals scarcely specifically distinguishable being found both on 
the American and the African side of the ocean. The Dusons 
(Halicore) is distributed in different colonies, at present isolated, 
throughout the Indian Ocean from Arabia to North Australia. 
The Bhytina or Northern Sea-Cow was, for some time before its 
extinction, limited to a single island in the extreme north of the 
Pacific Ocean. 

The Pinnipeds, although capable of traversing long reaches of 
ocean, are less truly aquatic than the last two groups, always 
resorting to the land or to extensive ice-floes for the purpose of 
breeding. The geographical range of the various species is generally 
more or less restricted, usually according to climate, as they are 
mostly inhabitants either of the Arctic or Antarctic seas and adjacent 
temperate regions, very few being found within the tropics. For this 
reason the northern and the southern species are for the most part 



GEOLOGICAL DISTRIBUTION 107 

quite distinct In fact, the only known exception is the case of a 
colony of the Sea-Elephant (Macrorhinus leoninvs), the general range 
of which is in the southern hemisphere, inhabiting the coast of 
California. Even in this case a different specific name has been 
given to the northern form ; but the characters by which it is 
distinguished are not of great importance, and probably, except for 
the abnormal geographical distribution, would never have been 
noticed. The most remarkable circumstance connected with the 
distribution of the Pinnipeds is the presence of members of the 
suborder in the three isolated great lakes or inland seas of Central 
Asia — the Caspian, Aral, and Baikal ; these forms, notwithstanding 
their long isolation, having varied but slightly from species now 
inhabiting the Polar Seas. 

II. GEOLOGICAL DISTRIBUTION. 

Geological Sequence. — In order to understand the geological 
distribution, or in other words the distribution in time of mammals, 
it is necessary to be acquainted with the chief divisions, or time- 
periods, of the strata constituting the crust of the globe. These are 
shown in the following table, which commences with the uppermost 
or most recent beds and ends with the lowest and oldest. 

I. Cainozoic or Tertiary — 

1. Pleistocene — River alluvia, etc. 

2. Pliocene — Suffolk Crag. 

3. Miocene — Hempstead Beds of Hampshire. 

4. Eocene — Paris Gypsum and London Clay. 

II. Mesozoic or Secondary — 

1. Cretaceous — Chalk, Greensands, etc. 

2. Jurassic — Oolites and Lias. 

3. Triassic — Red Marls, Dolomites, etc. 

III. Palaeozoic or Primary — 

1. Permian — Beds overlying the Coal. 

2. Carboniferous — Coal-measures, etc. 

3. Devonian — Old Red Sandstone. 

4. Silurian — Wenlock Limestone, etc. 

5. Cambrian — Llanberis Slate, etc. 

6. Archaean — Gneiss and other schists. 

The names in the first column indicate the primary divisions or 
life-periods, while those in the second column are the great systems, 
each of which is again divided into minor groups, the popular 
names of a few of these minor groups being given in the third 
column. There are at present no means of arriving at any satis- 
factory conclusion as to the absolute length of time indicated by 



108 GEOLOGICAL DISTRIBUTION 

either the primary or secondary divisions ; but there is little doubt 
that the whole of the Tertiary period is only equal to a fraction of 
the Mesozoic as regards its duration, while it is probable that 
the duration of the Mesozoic epoch was largely exceeded by that 
of the Palaeozoic. 

Mesozoic Mammals. — The earliest date at which mammals are at 
present known is in the upper part of the Triassic period, which 
forms the base of the great Mesozoic epoch ; and from this date they 
are represented more or less abundantly in various horizons of the 
Jurassic and Cretaceous. 

The very rapid advances in our knowledge of these forms which 
have been made in the last few years, especially in consequence of 
the explorations of rich fossiliferous beds in North America, have 
not only completely changed the present aspect of the science, but 
give such promise for the future, that any sketch which we may 
now attempt of this branch of the subject can only be regarded 
as representing a transient phase of knowledge. It will be well, 
however, to gather together in this place the leading facts now 
ascertained with regard to the most ancient forms, as, owing to the 
uncertainty of their relationship with any of the existing orders, 
they will be most conveniently treated of separately, while the 
ascertained facts relating to the geological history of the forms 
more nearly allied to those now living will be more appropriately 
described under the account of the different groups into which the 
class may now be divided. 

The remains of mammals which existed anterior to the Tertiary 
period hitherto discovered nearly all belong to creatures of very 
small size, many of the largest scarcely exceeding the common Pole- 
cat or Squirrel. Some are known only by a few isolated teeth, 
others by nearly complete sets of these organs, and the majority by 
more or less nearly perfect specimens of the rami of the lower jaw. 
It is a very curious circumstance that this part of the skeleton 
alone has been preserved in such a large number of instances. 
Only very rarely has a nearly complete cranium been found ; and 
there is no satisfactory evidence of the structure of the vertebral 
column of any single individual, and only one known case of a com- 
plete limb. 1 The species already described from European strata 
are numerous, although the number of genera and species has lately 
been reduced. Of these by far the greater number have been found 
at a single spot near Swanage in Dorsetshire, in a bed of calcareous 
mud only forty feet long, ten feet wide, and averaging five inches in 
depth. The marvellous results obtained by the exploration by Mr. 
S. H. Beckles of this small fragment of the earth's surface show by 
what accidents, as it were, our knowledge of the past history of life 

1 The fore limb from S. Africa described as Theriodcsmus, which appears to 
be mammalian, and may belong to Tritylodon. 



MESOZOIC MAMMALS 



109 



has been gained, and what may still remain in store where little 
thought of at present. A bed, apparently equally rich, has been 
discovered in the Jurassic of Wyoming, North America, the contents 
of which have been made known by Professor Marsh, while another 
fertile source of these remains occurs in the Laramie beds of the 
Upper Cretaceous of the United States. 1 

jNl The whole of the Mesozoic mammals at present known may be 
divided into two great groups, the one characterised by a type of 
dentition more or less clearly resembling that found among the 
existing Polyprotodont Marsupials, while the other presents an 
altogether peculiar modification, recalling in some respects that of 
the Diprotodont Marsupials, although differing so decidedly as to 





Fig. 24. —Frontal and oral aspects of tlie cranium of Tritylodon longcevus ; from tlie Karoo 
system of Basuto-land, South Africa. § natural size. (After Owen.) 

show that the owners of this form of dentition cannot be included 
in that group. 

MuUituberculata. — The name Multituberculata has been proposed 
for the group exhibiting the type of dentition last mentioned, and 
is generally adopted, although the term Allotheria has been also 
suggested. The essential characteristic of the dentition of this group 
is the presence of a single scalpriform incisor on each side of the 

1 The subjects referred to under this heading are mostly described and figured 
in detail in Owen's "Monograph of the Fossil Mammalia of the Mesozoic Forma- 
tions," Palxontographical Society's Publications, 1871 ; and in various papers by 
Marsh, in the American Journal of Science and Arts, 1878-89. Important con- 
tributions to our knowledge of these forms have also been made by Professors Cope 
and Osborn, and the reader should especially consult the memoir by the latter 
writer on the "Structure and Affinities of the Mesozoic Mammals," published in 
the Journal of the Philadelphia Academy (1888), vol. ix. 



no 



GEOLOGICAL DISTRIBUTION 



c 

■■■\ 



lower jaw (Fig. 25) and of one larger incisor, and in some instances 
of one or two smaller ones in each premaxilla (Fig. 24). These 
incisors are separated by an interval or diastema from the first of 
the premolars. The true molars, and in some instances the pre- 
molars (Fig. 24), are 
characterised by having 
longitudinal rows of 
tubercles separated by 
one or more grooves ; 
there being either two 
or three of these rows 
in the upper molars of 
those forms in Avhich 
these teeth are known, 
Avhile there are, at least 
usually, only two in 
those of the lower jaw. In other cases the premolars are of a 
secant type, with a highly convex cutting-edge, and usually either 
serrated or obliquely grooved (Figs. 25, 26). From a certain 
resemblance between these secant premolars and those of some of 
the smaller Macropoclidce it was at one time considered that we had 
in these mammals representatives of Diprotodont Marsupials. The 
great difference in the structure of the molar teeth of these forms, 




Fig. 25. — The right ramus of the mandible of Plagiaulax 
beklesi; from the Purbeek of Swanage. Twice natural size. 
i, Incisor ; m, molar ; b, coronoid process ; c, condyle. (After 
Owen.) 





Fio. 26. — The imperfect right ramus of the 
mandible of Plagiaulax minor ; from Swanage. 
Four times natural size, p, Premolars ; m, 
molars. (After Lyall.) 



Fig. 27. — Stereognathus oblithicus. Frag- 
ment of jaw with three teeth (a, b, c), in 
matrix ; from the Stonesfleld Slate. Natu- 
ral size. (After Owen.) 



coupled with the circumstance that when the number of upper 
incisors is reduced below three it is the second in place of the first 
which becomes enlarged and opposed to the incisor of the lower 
jaw, seems to prevent the acceptation of this view. Moreover, in 
their peculiar structure the molars seem, on the whole, to make a 
nearer approximation to the teeth of Ornithorhynchus than to any 
other known mammal ; and it has accordingly been suggested that 
the Multitubercnlata may really represent an order of Prototheria. 
Some support is afforded to this suggestion by certain fragmentary 
bones from the Cretaceous of the United States, which are regarded 



MESOZOIC MAMMALS in 

by Marsh as parts of a coracoid and interclavicle. The peculiar 
character of the whole dentition of these forms indicates that if 
they are really Prototherians they cannot be regarded as primitive 
and ancestral types. 

It would be beyond the scope of the present work to describe 
in detail, or even to mention the names of all the members of 
this group, and it will therefore suffice to refer to a few of the 
principal types. Of the forms with tubercular premolars the best 
known is the genus Tritylodon (Fig. 24), which occurs typically 
in beds of Lower Mesozoic in South Africa, but is also known from 
the Trias of Stuttgart. In the Stonesfield Slate, near Oxford, 
which belongs to the lower part of the Jurassic system, and is 
separated from the Trias by the intervening Lias, a fragmentary jaw 
with three teeth (Fig. 27) appears to indicate an allied type, the 
teeth having three longitudinal ridges separated by grooves. In 
the Purbeck beds of Dorsetshire, forming the top of the Jurassic 
system, we find another member of this group, which has been 
described as Buhxlon, closely allied to which is Allodun of the 
Upper Jurassic of the United States. 

The first discovery of the remains of Mesozoic mammals was 
made in the Keuper or Upper Trias of the Rhastian Alps in 
Bavaria. In 1847 Professor Pleininger of Stuttgart, while sifting 
some sand from the Keuper of Diegerloch and Steinenbronn, 
found, among an immense mass of teeth, scales, and unrecog- 
nisable fragments of skeletons of fish and saurians, two minute 
teeth, each with well- defined, enamelled, tuberculated crowns 
and distinct roots, plainly showing their mammalian character. 
These were considered by their discoverer to indicate a predaceous 
and carnivorous animal of very small size, to which he gave the name 
of Microlestes antiquus. Subsecpiently Mr. C. Moore discovered in a 
bone bed of Rhaatic (topmost Trias) age, filling a fissure in the 
Mountain Limestone at Holwell, near Frome in Somersetshire, 
various isolated teeth with their crowns much worn, but apparently 
including both upper and lower molars and a canine, which are 
assigned by Sir R. Owen to Pleininger's genus Microlestes, and 
described specifically as M. moorei. Under the name of Hypsi- 
prymnopsis rhceticus, Professor Boyd Dawkins described a single tooth 
with two roots discovered in the Rhaatic Marlstone at "Watchet in 
Somersetshire. Sir R. Owen referred the latter tooth to Microlestes, 
and if its describer is right in regarding it as a much worn premolar 
of the type of those of Plagiaulax (Fig. 25) there would be evidence 
that Microlestes was closely allied to the latter, from the molars 
of which those of Microlestes are scarcely distinguishable. 

Plagiaulax, of the Dorsetshire Purbeck (Figs. 24, 25), is at once 
distinguished from Tritylodon by its secant premolars, which, as already 
mentioned, recall those of some of the Macropodidce, although readily 



U2 GEOLOGICAL DISTRIBUTION 



distinguished by the convexity of the cutting edge and their oblique 
grooving. This remarkable and highly specialised type has been the 
occasion of one of the most interesting discussions on the inferences 
which may be drawn as to the affinities and habits of an otherwise 
unknown animal from the structure of a small portion of its organisa- 
tion which occurs in the annals of natural history — a discussion 
carried on with great ability, ingenuity, and wealth of illustration 
on both sides. Dr. Falconer maintained that it was more nearly 
allied to the Rat-Kangaroo (Potorous or Hypsiprymnus) than to any 
other existing form, and that, as it is known that these animals 
feed upon grass and roots, " it may be inferred of Plagiaulax that 
the species were herbivorous or frugivorous. I can see nothing in 
the character of their teeth," he adds, " to indicate that they were 
either insectivorous or omnivorous." Sir R. Owen, on the other 
hand, from the same materials came to the conclusion that "the 
physiological deductions from the above-described characteristics of 
the lower jaw and teeth of Plagiaulax are that it was a carnivorous 
Marsupial. It probably found its prey in the contemporary small 
insectivorous mammals and Lizards, supposing no herbivorous form 
like Stereognathus to have co- existed during the Upper Oolitic 
period." 

It is impossible here to give at any length the arguments by 
which these opposing views are respectively supported, but it may 
be indicated that the first-mentioned is strongly countenanced by 
the consideration of the following facts : (1) all existing Marsupials 
may be divided, so far as their dentition is concerned, into two 
groups — (a) those which have a pair of large more or less procumbent 
incisors close to the symphysis of the lower jaw, and rudimentary 
or no canines (diprotodont dentition), and (b) those which have 
numerous small incisors and large pointed canines (polyprotodont 
dentition) ; (2) the vast majority of the former group are purely 
vegetable feeders, and almost all of the latter are carnivorous or 
insectivorous ; and (3) Plagiaulax, so far as its structure is known, 
shows an analogy with the former group ; and, as we have no sure 
basis for inferences as to the habits of an unknown animal, but the 
knowledge of the habits of such as are known, we have no grounds 
for supposing that its habits differed from those forms having an 
analogous type of dental structure. 1 

Allied types, such as Ctenacodon, are also met with in the Upper 

1 The whole discussion is contained in the following memoirs : (1) H. 
Falconer, " Description of Two Species of the Fossil Mammalian genus 
Plagiaulax, from Purbeck," Quart. Journ. Geol. Soc. vol. xiv. 1857 ; (2) R. Owen, 
art. " Paleontology," Encyclopaedia Britannica, 8th ed., 1859 ; (3) H. Falconer, 
"On the Disputed affinity of the Mammalian genus Plagiaulax," Quart. Journ. 
Gcol. Soc. vol. xviii. 1862; (4) R. Owen, "Monograph of the Fossil Mammalia 
of the Mesozoic Formation," Palxontographical Society, 1S71. 



MESOZOIC MAMMALS u 



Jurassic of North America ; and the Plagiavlacidm also persisted 
into the lower part of the Eocene division of the Tertiary period ; 
Neoplagiavlax being a Tertiary form common to Europe and the 
United States, while Liotomus and Ptilodvs are at present known 
only from the latter country. 

The present group is also represented in the upper Cretaceous 
of the United States by Sdemcodon (Mcnisco'essiis in part), Cimoliomys, 
etc. Polymastodon, of the Lowest or Puerco Eocene of New Mexico 
is the largest known form, and is characterised by the presence 
of only one premolar and the elongated molars. The angle of 
the mandible is inflected after the Marsupial fashion. 

Polyprotodmt Types. — The second type of mammalian dentition 
found in the Mesozoic period resembles that occurring among 
recent Polyprotodont Marsupials — that is to say there are at 
least three lower incisors, the canines are well developed, and the 
premolars and molars are cuspidate, the number of the latter reach- 
ing in some cases to seven or eight. There has been much dis- 
cussion as to the taxonomic position of these forms, and while the 
majority of writers admit the Marsupial affinities of at least a 
moiety, it has been contended that others indicate distinct ordinal 
groups more or less closely allied to the Insectivora. At present, 
however, there is no decisive evidence to support such a view. 
Important proof of the Marsupial affinity of one of these forms is 
afforded by the replacement of the teeth, which appears to be of the 
same nature as in the existing Marsupials, that is to say, the last 
premolar alone is preceded by a milk-tooth. 

The most generalised forms appear to be Dromatherium and 
Microconodon, from Lower Mesozoic beds in the United States, of 
which enlarged views of the teeth are given in Fig. 4 (1, 2), p. 
3 1 . Professor Osborn points out the extremely simple character of 
these teeth, and it is quite possible that these forms may prove 
to be Prototheria. There are three premolars and seven molars in 
the lower jaw of Dromatherium. 

A common form in the Purbeck of Dorsetshire is Triconodon 
(TriacantJwdoit), in which the formula of the lower teeth is i 3, c 1, 
p 4, m 3-4. A lower jaw is shown in 
Fig. 28, and an enlarged view of a molar 
tooth in Fig. 4 (5). The molar teeth con- 
sist of three flattened cones placed in the 
same antero- posterior line, those of the 

_ li i • Ti t> ■ Fig. 28. — Reversed view of the 

upper and lower jaw being alike. Pria- left ramus of the mandible of 

COdan, of the Jurassic Of the United States, Triconodon mordax ; from the 

is probably inseparable from Triconodon. Pmbeck of Swanage. Natural 

T ,, m i n ■ mil nr\\ r size - (After Owen.) 

In the genus Phascolotlienurii (rig. 29) of 

the Lower Jurassic Stonesfield Slate, the lower teeth may be 

classified as i 4, c 1, p 3, in 4, the premolars and molars being 

8 




ii4 



GEOLOGICAL DISTRIBUTION 



much alike. The molars approximate to the type of those of 
Triconodon, but the anterior and posterior cones are relatively 
smaller. Like that of the last-named genus, the mandible of 




1 




- 



Fig. 29. — Inner view of the right ramus of the mandible of Phascolotherium bucklandi ; 
from the Stonesfiekl Slate. The outline shows the natural size, i, Incisors (one missing) ; c, 
canine ; p, premolars ; m, molars. The mylohyoid groove is seen near the lower border. (After 
Owen.) 

Phascolotherium is remarkable for the extremely low position of 
its articular condyle. In Amphilestes (Fig. 30) of the Stonesfiekl 
Slate the molars appear to be of the same general type as those 
of Phascolotherium, but are more numerous, although their exact 
number cannot be determined. A somewhat different type 
of lower molar is displayed by the genus Amblotherium, of the 
Dorsetshire Purbeck, to which Amphitherium of the Stonesfield Slate 
was probably allied. This type of tooth is shown in Fig. 4 (8, 9, 
12) p. 31, and, as there stated, represents that modification of the 
tritubercular type known as the tubercular sectorial. The three 
primitive tritubercular cusps form what is known as the blade of 

the tooth, behind which 
there is the talon or 
hypocone. A similar 
form of molar occurs 
in the existing Opos- 
sums and Bandicoots. 
The number of lower 
teeth in Amfohtherium 
is i 4, c 1, p 4, m 
7-8. Numerous allied 
types, such as Achyro- 
don and Dryolestes occur in the Upper Jurassic of Europe or the 
United States, while from only one side of the jaw being exposed 
in each case so-called genera like Stylodon and Sly! a radon have been 
formed upon specimens showing the opposite side to that which 
is exposed in the types of Amblothenuin and Amphitherium. The 




Fig. 30.— Reversed inner view of the left ramus of the 
mandible of Amphilestes broderipi ; from the Stoneslield 
Slate. Twice natural size. The restoration of the anterior 
teeth is conjectural, and the condyle is placed too high. 
(After Owen.) 




TERTIARY MAMMALS 115 

only parallel among existing forms to the excessive number of 
molar teeth found in these Mesozoic genera occurs in the Mar- 
supial genus Myrmecobius, of which a description is given in a 
succeeding chapter. Jaws more or less closely resembling those 
described under the names mentioned above are also found in 
the uppermost Cretaceous of the United States. A feature com- 
mon to these Mesozoic mammals and Myrmecobius and some other 
existing forms is the presence of a narrow channel on the inner 
side of the mandibular ramus known as the mylohyoid groove 
(Fig. 29). 

The last type of molar dentition occurring among the Mesozoic 
Mammalia is that found in the 
lower jaws (Fig. 31), upon which 
the genus Spctiacotherium was 
established, the upper jaws, 
described as Peralestes, being; 

, f ,, i ° Fig. 31.— Part of the left ramus of the man 

apparently referable to the Same clible, viewed from the outer side, of Spcda- 
ailimal. Upper and lower teeth cotherium tricuspidens ; from the Purbeek of 

of this form are represented in Swanage " Twice natural size - (After Owen.) 
Fig. 4 (6, 7), p. 31, where they are described as typical examples 
of the tritubercular type of molars, the upper teeth having one 
inner and two outer cusps, and the reverse condition obtaining in 
the lower ones. This type of molar presents a marked resemblance 
to that found in the existing Insectivorous genus Chrysochloris ; the 
number of lower teeth in Spalacotherium is, however, i 3, c 1, 
p + m 1 0, by which it is widely distinguished from all the Insect- 
ivora. Menacodon, of the Upper Jurassic of the United States, 
appears to be allied to Spalacotherium. 

Tertiary Mammals. — The more important types of Tertiary 
mammals will, as already mentioned, be noticed under the heads 
of the groups to which they are severally allied ; but a few general 
remarks on this subject may be advantageously recorded in this chap- 
ter. In the first place, it may be observed that the comparatively 
scanty evidence of mammalian life hitherto yielded by the Cretaceous, 
coupled with the number and variety of forms approximating to 
the existing groups found even in the lowest Tertiary, indicates a 
great imperfection of the geological record. At present, indeed, 
we have no decisive evidence of the existence of any members of 
the Eutherian subclass previously to the Tertiary; but it can hardly 
be doubted that in some part of the world they had made their 
appearance before that epoch. The Eutherian mammals of the 
lowest Eocene, both in Europe and the United States, are of an 
extremely generalised type ; and although many of them approximate 
to existing groups, they show such a combination of characters, now 
restricted to individual groups, as to indicate that several of the 
various orders into which the subclass is now divided were at that 



n6 GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION 



period very intimately connected. A marked feature of these 
early Eutherians is the prevalency of trituberculism in the dentition, 
not less noteworthy being the frequent occurrence of pentaclactylism 
in the feet, while many of the individual bones were devoid of the 
grooves and ridges found in those of later types. By the time 
that we reach the upper division of the Eocene period, such as the 
horizon of the well-known gypsum of the Paris basin, nearly all the 
chief groups of mammals had become clearly differentiated from 
one another, although their representatives were usually more 
o-eneralised than their existing allies. From this date to the later 
geological periods there is a gradual approximation to the types of 
mammalian life existing at the present day. 

In addition to the features of trituberculism and pentadactyl- 
ism so characteristic of the oldest known Eutherians, we may notice 
some other points in connection with the earlier types. Thus the 
older Tertiary mammals, as we have already stated, had relatively 
smaller and simpler brains than the later types, so that a gradual 
evolution in this respect may be traced from the Eocene to the 
Pleistocene. Again, there is a great tendency among the Eocene 
forms to a retention of the typical Eutherian dental formula noticed 
on page 25, and also to the absence of an interval, or diastema, in 
the dental series. Concomitantly with this feature we may notice 
the short crowns and simpler structure of the molar teeth of the 
earlier Ungulates as compared with those of to-day, of which details 
will be given in a later chapter. Another instance of the more 
generalised characters of the earlier mammals is afforded by the 
absence or slight development of horns, antlers, and tusks among 
the Ungulata. Thus the earlier Khinoceroses were hornless, and 
the Deer either without antlers or with antlers of a very simple 
kind, while the male Swine were not furnished with the formidable 
tusks of the existing Wild Boars. Finally, all, or nearly all of the 
mammals, from the lowest Eocene of Rheims present the pecu- 
liarity of having a vertical perforation in the astragalus. 

The intimate connection existing during the Middle Tertiary 
between many families of mammals now widely distinguished from 
one another may be more conveniently noted when we come to the 
consideration of the families in question. 



CHAPTEE V 

THE SUBCLASS PROTOTHERIA OR ORNITHODELPHIA 

General Characters. — The characters of the Prototheria can at 
present only be deduced from the two existing families, since 
hitherto no extinct animals which can he referred with certainty 
to other divisions of this remarkable and well-characterised group 
have been discovered. These two isolated forms, in many respects 
widely dissimilar, yet having numerous common characters which 
unite them together and distinguish them from the rest of the 
Mammalia, are the Ornithorhynchidce and the Echidnidce, both re- 
stricted in their geographical range to the Australian region of the 
globe. Taken altogether they represent the lowest type of evolution 
of the mammalian class, and most of the characters in which they 
differ from the other two subclasses tend to connect them with the 
inferior, vertebrates, the Sauropsida and Amphibia ; for, though 
the name Ornithodelphia owes its origin to the resemblance of the 
structure of the female reproductive organs to those of birds, there 
is nothing especially bird-like about them. 

Their principal distinctive characters are these. The brain has 
a very large anterior commissure, and a very small corpus callosum, 
agreeing exactly in this respect with the Marsupials. The cerebral 
hemispheres, in Echidna at least, are well developed and convoluted 
on the surface. The auditory ossicles present a low grade of de- 
velopment, the malleus being very large, the incus small, and the 
stapes columelliform. The coracoid bone is complete, and articu- 
lates with the sternum, and there is a precoracoid (epicoracoid) in 
advance of the coracoid, while there is also a large " interclavicle " 
or episternum in front of the sternum, and connecting it with the 
clavicles. There are also " epipubic " bones. The oviducts (not 
differentiated into uterine and Fallopian portions) are completely 
distinct, and open, as in oviparous vertebrates, separately into a 
cloacal chamber, and there is no distinct vagina. The testes of 
the male are abdominal in position throughout life, and the vasa 



1 1 8 MONO TREMA TA 



deferentia open into the cloaca, not into a distinct urethral passage. 
The penis, attached to the ventral Avail of the cloaca, is perforated 
by a canal in the greater part of its length, and not merely grooved, 
as in reptiles and those birds which have such an organ. The 
canal is open at the base and brought only temporarily in contact 
with the termination of the vasa deferentia, so as to form a seminal 
urethra when required ; but it never transmits the urinary secretion. 
This condition is a distinct advance on that of the Sauropsida in 
the direction of the more complex development of these parts in 
most of the other Mammalia. The ureters do not open into the 
bladder, but behind it into the dorsal wall of the genito-urinary 
passage. The mammary glands have no distinct nipple, but pour 
out their secretion through numerous apertures situated in a cup- 
shaped depression of the abdominal skin, forming a mammary 
marsupium, especially developed in the females during lactation. 
It should be mentioned that, according to the observations of Pro- 
fessor Gegenbaur, the mammary glands of the Monotremes are the 
simplest found in the entire class. The region of the glands is, 
indeed, distinguished from the rest of the abdomen merely by its 
thicker layers of muscles. The glands themselves are closely con- 
nected with the hair-follicles, and belong to the sudoriparous type, 
whereas the glands of all other mammals are of sebaceous origin. 

The young are produced from eggs laid by the female parent, 
which are meroblastic, like those of birds; that is to say only a 
portion of the yolk segments and forms the embryo, the remainder 
serving for the nourishment of the latter. 

The above are the principal distinguishing characters of the 
group, and apply not only to the subclass, but of course equally to 
the one order Monotremata, in which the two existing genera are 
included. In addition to these more important characters, the 
following minor features may also be mentioned. 

The scapula differs from that of all other mammals in that the 
ridge corresponding to the spine of other forms is situated on the 
anterior border instead of in the middle of the outer or dorsal surface. 
The humerus is much expanded at its two extremities, and has a very 
prominent deltoid crest, and a well-marked entepicondylar foramen. 

The dorso-thoracic vertebras are nineteen in number, and have 
no terminal epiphyses to their bodies. The tranverse processes of 
the cervical vertebrae are of autogenous formation, and remain 
suturally connected with the remainder of the vertebra until the 
animal is full-grown. Though in this respect they present an 
approximation to the Sauropsida (Reptiles and Birds), they differ 
from these classes, inasmuch as there is not a gradual transition from 
these autogenous transverse processes of the neck (or cervical ribs, 
as they may be considered) into the thoracic ribs, for in the seventh 
vertebra the costal element is much smaller than in the others, 



( )RNITHORH YNCHID. E 1 1 9 

indicative of a very marked separation of neck from thorax, not 
seen in the existing Sauropsida. The upper ends of the ribs 
are attached to the sides of the bodies of the dorsal vertebras 
only, and not to the transverse processes. The sternal ribs are 
well ossified, and there are distinct partly ossified intermediate ribs. 
The cerebral cavity, unlike that of the lower Marsupials or the 
Reptiles, is large and hemispherical, flattened below and arched 
above, and about as broad as long. The cribriform plate of the 
ethmoid is nearly horizontal. The cranial Avails are very thin, and 
smoothly rounded externally, and the sutures become completely 
obliterated in adult skulls, as in Birds. The broad occipital region 
slopes upwards and forwards, and the face is produced into a long 
and depressed rostrum. The bony palate is prolonged backwards, 
so that the posterior nares are nearly on a level with the glenoid 
fossa;. The mandible is without distinct ascending ramus ; the 
coronoid process and angle are rudimentary, and the two halves are 
loosely connected at the symphysis. The fibula has a broad, 
flattened process, projecting upwards from its upper extremity 
above the articulation, like an olecranon. In the male there is an 
additional, flat, curved ossicle on the hinder and tibial side of the 
plantar aspect of the tarsus, articulating chiefly to the tibia, which 
supports in the adult a sharp-pointed perforated horny spur, with which 
is connected the duct of a gland situated beneath the skin of the back 
of the thigh, the function of which is not yet clearly understood. (A 
rudimentary spur is found in the young female Oriiithorhynchus, but 
this disappears when the animal becomes adult.) The stomach is 
sub-globular and simple ; the alimentary canal has no ileo-caecal valve, 
or marked distinction between large and small intestine, but has a 
small, slender vermiform c?ecum with glandular walls. The liver 
is divided into the usual number of lobes characteristic of the 
Mammalia, and is provided with a gall-bladder. 

In the presence of three distinct bones developed from cartilage 
in the shoulder-girdle (viz. scapula, coracoid, and pre- or epi-coracoid) 
the Monotremes agree with the Anomodont reptiles (see p. 83), 
and with no other representatives of that class. The precoracoid 
of the Anomodonts is, however, distinguished by extending upwards 
to articulate with the acromial process of the scapula. The 
Monotreme humerus is, moreover, strikingly like the corresponding- 
bone of many of the Anomodonts and of some of the allied 
Labyrinthodont Amphibians. 

Family ORXITHORHYNCHIDiE. 

Ornithorh/nchus. 1 — Cerebral hemispheres smooth. Premaxillfe 
and mandible expanded anteriorly and supporting a horny beak 

1 Blumenbach, Voigts Magazin, vol. ii. p. 205 (1800). 



1 20 MONO TREMA TA 



something like that of a duck, bordered by a naked and very sensitive 
membranous expansion. The place of teeth in the adult is supplied 
functionally by horny structures, elongated, narrow, and sharp- 
edged, along the anterior part of the sides of the mouth, and broad, 
flat-topped or molariform behind. Functional molar teeth present 
in the young and adolescent condition. Legs short, fitted for 
swimming ; feet webbed, each with five well-developed toes armed 
with large claws, beyond which in the fore feet the interdigital 
membrane is extended. Vertebrae: C 7, D 17, L 2, S 2, Ca 21. 
Acetabulum not perforated. Tongue not extensile. Mucous mem- 
brane of small intestine covered with delicate, close-set transverse 
folds or ridges. Tail rather short, broad, and depressed. Eyes 
very small. Fur close and soft. 

The Duck-billed Platypus (Platypus anatinus) was the name 
assigned to one of the most remarkable of known animals by 
Shaw, who had the good fortune to introduce it to the notice 
of the scientific world in the Naturalists Miscellany (vol. x., 1799). 
In the following year it was independently described by Blumenbach 
(Voigts Magazin, ii. p. 205) under the name of Ornitliorhynchus 
paradoxus. Shaw's generic name, although having priority to that 
of Blumenbach, could not be retained, as it had been used at 
a still earlier time (1793) by Herbst for a genus of Coleoptera. 
Omithorhynchus is therefore now universally adopted as the scien- 
tific designation, although Duck-billed Platypus or Duck-bill may 
be conveniently retained as a vernacular appellation. By the 
colonists it is called " Water-Mole," but it need scarcely be said, 
its affinities with the true moles are of the slightest and most 
superficial description. Until the last few years the early stages 
of the development of the young were not fully known. It had, 
indeed, been repeatedly affirmed, in some cases by persons who 
have had actual opportunities of observation, that the Platypus lays 
eggs ; but these statements were generally received with scepticism 
and even denial. This much-vexed question was, however, settled 
by the researches of Mr. W. H. Caldwell in 1884, who found that 
these animals, although undoubtedly mammals throughout the 
greater part of their structure, are oviparous, laying eggs, which in 
the manner of their development bear a close resemblance to the 
development of those of the Eeptilia. Two eggs are produced at 
a time, each measuring about three-fourths of an inch in its long, 
and half an inch in its short, axis, and enclosed in a strong, flexible, 
white shell. 

The Platypus is pretty generally distributed in situations 
suitable to its aquatic habits throughout the island of Tasmania 
and the southern and eastern portions of Australia. Slight variations 
in the colouring and size of different individuals have given rise to 
the idea that more than one species may exist ; but all naturalists 



ORNITHORHYNCHin.K 



121 



who have had the opportunity of investigating this question by the 
aid of a good series of specimens have come to the conclusion that 
there is but one, and no traces of any extinct allied forms have yet 
been discovered. 

The length of the animal when full grown is from eighteen to 
twenty inches from the extremity of the beak to the end of the tail, 
the male being slightly larger than the female. The fur is short, 
dense, and rather soft to the touch, and composed of an extremely 
fine and close under-fur, and of longer hairs projecting beyond 
this, each of which is very slender at the base, and expanded, 




Fig. 32. — Platypus or Duck-bill (Omithorhynchus anatinus). From Gould's Mammals of 

Australia. 

flattened, and glossy towards the free end. The general colour is 
deep brown, but paler on the under parts. The tail is short, broad, 
and depressed, and covered with coarse hairs, which in old animals 
generally become worn off from the under surface. The eyes are 
small and brown. There is no projecting pinna or ear-conch. The 
mouth, as is well known, bears a striking resemblance to the bill of 
a Duck. It is covered with a naked skin, a strong fold of which 
projects outwards around its base. The nostrils are situated near 
the extremity of the upper surface. There are no true teeth in the 
adult, but their purposes are served by horny prominences, or 
cornules, two on either side of each jaw — those in the front narrow, 
longitudinal, sharp-edged ridges, and those behind broad, flattened, 



122 MONO TREMA TA 



and molariform. The upper surface of the lateral edges of the 
mandible has also a number of parallel fine transverse ridges, like 
those on the bill of a Duck. Until 1888 it was thought that true 
teeth were totally wanting throughout the life of this animal ; but in 
the spring of that year Mr. E. B. Poulton 1 announced the discovery 
in an embryo of teeth which were regarded as quite functionless. In 
the following year, however, Mr. 0. Thomas 2 was fortunate enough 
to find some young skulls with functional teeth in situ, and was thus 
enabled to give a detailed account of their structure and of their 
relations to the cornules. From these specimens it appears that 
the teeth are functional for a considerable part of the life of the 
animal, cutting the gum in the usual manner, and, after being worn 
down by friction with food and sand, are shed from the mouth 
in the same manner as are the milk-teeth of other mammals. The 
cornules are developed from the epithelium of the mouth under and 
around the teeth, and the hollows found in the middle of them are 
the vestiges of the alveoli from which the teeth have been shed. 
One of the skulls showed on either side, both above and below, two 
completely calcified teeth ; but in another example there were three 
teeth on either side of the lower jaw. According to Mr. Thomas's 
account, " the teeth themselves are broad, flat, and low-crowned. 
The upper ones have each two high, conical, internal cusps, from 
which minute ridges run downwards and outwards to the outer 
borders of the crowns, where the edge is peculiarly crenulate rather 
than cuspidate, in the ordinary sense of the word. On the whole, 
the anterior and posterior upper teeth are essentially similar to one 
another, except that the former are narrower, and their outer edges 
are less markedly crenulated. In the lower jaw there is a greater 
difference between the two. The anterior is triangular in outline, 
its longest side is placed antero-externally, and its anterior and 
postero-external angles have each a high pointed cusp, ridged on 
its internal aspect, while the posterior and internal borders are 
indistinctly crenulated. The posterior tooth is broadly quadrangular 
in outline, with a projecting antero-internal angle. As in the cor- 
responding tooth above, there are two cusps on one side, and a series 
of crenulations on the other, but they are of course reversed, the 
cusps being external and the crenulations internal. The cusps are 
high, and connected with transverse ridges running across towards 
the internal border." 

In trying to find any teeth like those of the Duck-bill among 
other known mammals Mr. Thomas considers, as was first suggested 
by Professor Cope, that those of the Mesozoic Multituberculata (p. 109) 
make the nearest approximation. He adds, however, that " it must 
be insisted that the resemblance between the Multituberculate 

1 Proceedings of the Royal Society of London, vol. xliii. p. 353 (1888). 
- Ibid. vol. xlvi. p. 126 (1SS9). 



ORNITHORHYNCHIDM 123 

and the Ornithorhynchus teeth is of the most general character, 
and that the two are certainly widely separated generically, even if 
we do admit that they appear to possess a relationship nearer to 
each other than to any other known groups of mammals." 

Reverting to the description of the Duck-bill, Ave find that in 
the cheeks are tolerably capacious pouches, which appear to be used 
as receptacles for food. The limbs are strong and very short, each 
with live well-developed toes provided with strong claws. In the 
fore feet the web not only fills the interspaces between the toes, but 
extends considerably beyond the ends of the long/ broad, and some- 
what flattened nails, giving great expanse to the foot when used for 
swimming, though capable of being folded back on the palm when 
the animal is burrowing or walking on the land. On the hind foot 
the nails are long, curved, and pointed, and the web extends only 
to their base. On the heel of the male is a strong, curved, sharply 
pointed, movable horny spur, directed upwards and backwards, 
attached by its expanded base to the accessory bone of the tarsus. 
This spur, which attains the length of nearly an inch, is traversed 
by a minute canal, terminating in a fine longitudinal slit near 
the point, and connected at its base with the duct of a large gland 
situated at the back part of the thigh. The whole apparatus is so 
exactly similar in structure to the poison-gland and tooth of a 
venomous snake as to suggest a similar function, but evidence that 
the Platypus ever employs its spur as an offensive weapon has, at 
all events until lately, been wanting. A case is, however, related 
by Mr. Spicer in the Proceedings of the Royal Society of Tasmania 
for 1876 (p. 162), of a captured Platypus inflicting a severe wound by 
a powerful lateral and inward movement of the hind legs, which wound 
was followed by symptoms of active local poisoning. It is not improb- 
able that both the inclination to use the weapon and the activity of the 
secretion of the gland may be limited to the breeding season, and 
that their purpose may be, like that of the antlers of deer and 
many similar organs, for combat among the males. In the young 
female the spur is present in a rudimentary condition, but it dis- 
appears in the adult of that sex. 

The Platypus is aquatic in its habits, passing most of its time in 
the water or close to the margin of lakes and streams, swimming 
and diving with the greatest ease, and forming for the purpose of 
sleeping and breeding deep burrows in the banks, which generally 
have two orifices — one just above the water level, concealed among 
long grasses and leaves, and the other below the surface. The 
passage at first runs obliquely upwards in the bank, sometimes to 
a distance of as much as fifty feet, and expands at its termination 
into a cavity, the floor of which is lined with dried grass and 
leaves, and in which the eggs are laid and the young brought up. 
The food consists of aquatic insects, small crustaceans, and worms, 



1 24 MONO TREMA TA 



which are caught under water, the sand and small stones at the 
bottom being turned over with the bill. The creatures appear 
at first to deposit what they have thus collected in their cheek 
pouches, and when these are filled they rise to the surface and 
quietly triturate their meal with the horny plates before swal- 
lowing it. Swimming is effected chiefly by the action of the 
broad forepaws, the hind feet and tail taking little share in 
locomotion in the water. When asleep they roll themselves into 
a ball, as shown in the figure. In their native haunts they are 
extremely timid and wary, and very difficult to approach, being 
rarely seen out of their burrows in the daytime. Mr. A. B. 
Crowther, who has supplemented the often quoted observations 
of Dr. Bennett upon the habits of these animals in confinement, 
says, " They soon become very tame in captivity ; in a few days 
the young ones appeared to recognise a call, swimming rapidly 
to the hand paddling the water ; and it is curious to see their 
attempts to procure a worm enclosed in the hand, which they 
greedily take when offered to them. I have noticed that they 
appear to be able to smell whether or not a worm is contained in 
the closed hand to which they swim ; for they desisted from their 
efforts if an empty fist was offered." When irritated they utter a 
soft low growl, resembling that of a puppy. 



Family Echidnid.e. 

Cerebral hemispheres larger and well convoluted. Facial portion 
of skull produced into a long, tapering, tubular rostrum, at the 
end of which the anterior nares are situated. Rami of mandible 
slender, styliform. Opening of mouth small, and placed beloAv the 
extremity of the rostrum. No teeth or laterally placed hoimy plates, 
though the palate and tongue are furnished with spines. Tongue 
very long, vermiform, slender, and protractile. Lining membrane 
of small intestine villous, but without transverse folds. Feet not 
webbed, but with long strong claws fitted for scratching and 
burrowing. The hinder feet with the ends of the toes turned 
outwards and backwards in the ordinary position of the animal 
when on the ground. Tail very short. Acetabulum with a large 
perforation, as in Birds. Calcaneal spur and gland of the male 
much smaller than in Ornitliorhynchus. Fur intermixed with strong, 
sharp-pointed spines. Terrestrial and fossorial in habits, feeding 
exclusively on ants, and recalling in the structure of the mouth and 
various other parts relating to their peculiar mode of life the true 
Anteaters of the order Edentata. 

The Echidnas or Spiny Anteaters constitute a family which 
appears in some respects to be less specialised than the Ornitho- 
rln/uchidce. According to Mr. 0. Thomas, all the living forms may 



ECHIDNID. E 



be included in two species, which, with some hesitation, are referred 
to two genera — Echidna and Proechidna (Acanthoglossus). 

Echidna} — In Echidna there are five toes, all of which are 
provided with claws, those of the fore feet being broad, slightly 
curved, and directed forwards, while the posterior ones are slender, 
more curved, and inclined outwardly. The beak is about as long 
as the rest of the head, and either nearly straight, or slightly curved 
upwards, while the palate is comparatively wide, and but slightly 
vaulted. The number of the vertebrae is C 7, D 16, L 3, S 3, Ca 12. 
The one existing representative of the genus (E. aculeata) occurs in 
Xew Guinea, Tasmania, and Australia. 

So much variation is displayed by this animal, that it has been 
divided into several species, but the latest researches tend to show 
that these variations cannot be regarded as indicating more than 
races, of which there are three well-marked types. 

The first race, or variety, has been termed the Port Moresby 
Echidna, and is only known from that Papuan locality. It is 
distinguished from the typical form by its smaller size, by the 
shorter spines on the back, which admit of the fur being seen, and 
by the more spinous covering of the head, belly, and limbs, as well 
as by the lighter skull and relatively larger beak. 

The typical variety is confined to the Australian mainland, and 
is of medium size. The spines of the back are very long and stout, 
often reaching a length of two inches, and almost completely con- 
cealing the hair. The colour of these spines varies from yelloAV at 
the roots to black at the tips, but some may be altogether yellow. 
The hair of the back is black or dark brown in colour, but it may 
be occasionally absent, or in the region of the loins may exceed the 
spines in length. The limbs and under surface of the body are 
covered with dark brown hair, thinly interspersed with short spines ; 
and the hair of the face is of the same general hue as that of the 
body. The skidl has a slender rostrum and a flat and narrow 
brain-case. 

In the third or Tasmanian race, which is confined to Tasmania, 
the average size is somewhat larger than in the typical form. The 
most characteristic feature is, however, the shortness of the spines 
of the back, which in the greater part of that region are almost or 
quite concealed by the hairs. The hairs of the back are dark 
brown, those of the under surface and sides of the head being 
generally rather paler. There is often a white spot on the chest. 
Very frequently there is a difference in the proportionate lengths 
of the hinder claws from those of the typical race. In the skull 
the beak is comparatively short and stout, and the brain-case large 
and wide. 

Echidnas are usually found in rocky districts, and more especially 

1 Cuvier, Tableau EUmentairc d'Hist. Nat. p. 143 (1798). 



126 



MONOTREMATA 



in the mountains. In a wild state they live mainly on ants. Speci- 
mens have been brought to this country and kept in the Zoological 
Society's Gardens ; and in captivity they will readily eat eggs, and 
bread-and-milk. They are able, however, to endure long fasts, an 
individual having been known to go without food for upwards of a 
month. 

These animals seem to be mainly of nocturnal habits, and if 
brought out during the day-time appear to be sluggish and stupid, 
crouching to the ground with the head between the legs, and thus 
presenting a mass of spines to an enemy. They burrow rapidly in 
soft ground, sinking directly downwards, and not going head for- 
wards. A specimen placed on a large chest of earth containing 
plants reached the bottom in less than two minutes ; and it is said 
that the muzzle assists in the work of burrowing. 

Proechidna. 1 — The one known representative of the genus 
Proechidna (Fig. 33) attains dimensions about equal to those of 




Fio. 33. — The Three-toed Echidna (Procchihia Iruijnii). From Gervais. 

the largest race of Echidna aculeata. The skull is less depressed 
than in the latter, with the anterior portion of the palate very 
concave, and the deflected beak nearly twice the length of the 
remainder of the skull. As a rule, there are only three claws to 
each foot ; but the first and fifth digits are represented by several 
phalanges, and one instance is known where there are five complete 
claws on the anterior and four on the posterior feet. There are 
two more vertebra? in the dorsal and lumbar region than in 
Echidna. 

The head and body are covered with a thick coat of hair, 
among which there are a number of short spines in the region of 
the back, which are much less numerous than in the typical race of 
the last species. The colour of the fur is generally dark brown or 
black, but the head may be almost white ; and the spines are 
usually entirely white, although in certain cases they may be brown 
at the root. 

1 Gervais, Osteogmphie des Monotremes, p. 43 (1877). 



ECHIDNIDsE 127 



This species is known only from New Guinea, the recorded 
specimens being from the north-western regions of that country. It 
inhabits rocky ground, and dwells chiefly in the mountains, the 
specimens which were first described having been obtained at an 
elevation of about 3500 feet above the sea level. The Papuans capture 
it by digging trenches in the ground to a depth of about a yard, by 
which means they generally come upon its runs. 

Fossil Species. — Remains of a species of Echidna of very much 
larger size than the existing forms have been obtained from the 
cave-deposits of New South Wales, which appear to be of Pleisto- 
cene age. This species was named Echidna oweni by the late Mr. 
Krefl't, but was subsequently called E. ramsayi by Sir R. Owen. 
In referring this species to the genus Echidna, that term must be 
regarded as including Proechidna. 



CHAPTEE VI 

THE SUBCLASS METATHERIA OR DIDELPHIA 

General Characters. — The Metatheria or Didelphia are represented at 
present by numerous species, presenting great diversities of general 
appearance, structure, and habits, although all united by many 
essential anatomical and physiological characters, which, taken 
altogether, give them an intermediate position between the Proto- 
theria and the Eutheria. 

Although the striking differences in external form, in many 
anatomical characters, and in mode of life of various animals of this 
section might lead to their division into groups equivalent to the 
orders of the Eutheria, it is more convenient on the whole to adhere 
to the usual custom of treating them all as forming one order called 
Marsupialia, 1 the limits of which are therefore equivalent to that 
of the subclass. The more essentially distinctive characters are as 
follows. 

In the structure of the brain and the presence of epipubic bones 
they agree with the Prototheria, while in the structure of the ear- 
bones and the shoulder- girdle and the presence of teats on the 
mammary glands they resemble the Eutheria, the reproductive 
organs belonging to neither one nor the other type, but having a 
special character representing an intermediate grade of develop- 
ment. The ureters open into the base of the bladder. The 
oviducts are differentiated into uterine and Fallopian portions, and 
open into a long and distinct vagina, quite separate from the cystic 
urethra. The penis is large, but its crura are not directly attached 
to the ischia. The spongy body has a large bifurcated bulb. The 
young are born in an exceedingly rudimentary condition, and are 
never nourished by means of an allantoic placenta, but are trans- 
ferred to the nipple of the mother, to which they remain firmly 

1 For the detailed characters of all the genera and species of Marsupials the 
reader should consult the British Museum Catalogue of Marsupialia and Afono- 
tremata, by Old field Thomas, 1888. 



GENERAL CHARACTERS 129 

attached for a considerable time, nourished by the milk injected 
into the month by compression of the muscle covering the 
mammary gland. They arc therefore the most typically mam- 
malian of the whole class. The nipples are nearly always concealed 
in a fold of the abdominal integument or " pouch " (marsupinm) 
which serves to support and protect the young in their early 
helpless condition. 

Entering more fully into the characters of the subclass, which 
are also those of the order Marsupialia, it may be observed that the 
brain is generally small in proportion to the size of the animal, and 
the surface-folding of the cerebral hemispheres, though well marked 
in the larger species, is never very complex in character, and is 
absent in the medium-sized and smaller species. The arrangement 
of the folding of the inner wall of the cerebrum differs essentially 
from that of all known Eutheria, the hippocampal fissure being 
continued forward above the corpus callosum, which is of very 
small size. The anterior commissure is, on the other hand, greatly 
developed. 

The teeth are always divisible, according to their position and 
form, into incisors, canines, premolars, and molars ; but they vary 
much in number and character in the different families. Except in 
the genus Phascolomys, the number of incisors in the upper and 
lower jaws is never equal. The true molars are very generally four 
in number on either side of each jaw. The chief peculiarity in the 
dentition lies, however, in the mode of succession. Thus there is no 
vertical displacement and succession of the teeth, except in the case 
of a single tooth on either side of each jaw, which is always the 
hindermost of the premolar series, and is preceded by a tooth 
having more or less of the characters of a true molar (see Fig. 34); 
this deciduous tooth 
being the only one 
comparable to the 
" milk-teeth " of the 
diphyodont Eu- 
theria. In some 
cases (as in Poto- 
rous) this tooth re- 
tains its place and 

•fi-mfti'nn until thp FlG- 3i '~~ Teeth of Upper Jaw of °P 0Ssum (Didelphys mar- 

iuntLiou Liiiuii Liie mvia ^ all of which are uncn anged, except the last premolar, 

animal has nearly, the place of which is occupied in the young animal by a molari- 

if not Ollite attained form tooth, represented in the figure below the line of the other 

its full stature, and 

is not shed and replaced by its successor until after all the other 
teeth of the permanent series, including the posterior molars, are 
fully in place and use. In others, as the Thylacine, it is very 
rudimentary in form and size, being shed or absorbed before any 

9 




i *> ME TA THERIA 



of the other teeth have cut the gum, and therefore quite function- 
less. It must further be noted that there are some Marsupials, 
as the Wombat, Myrmecobius, and the Dasyures, in which no such 
milk-tooth, even in a rudimentary state, has yet been discovered, 
possibly in some cases from want of materials for observation at 
the right stage of development. 

Epipubic or marsupial bones are present in both sexes of nearly 
all species. In one genus alone, Thylacinus, they are not ossified. 
The number of dorso-lumbar vetebra? is always nineteen, although 
there are some apparent exceptions caused by the last lumbar being 
modified into a sacral vertebra. The number of pairs of ribs is 
nearly always thirteen. The tympanic bone remains permanently 
distinct. The carotid canal perforates the basisphenoid. The 
lachrymal foramen is situated upon or external to the anterior margin 
of the orbit, and there are generally large vacuities in the bony 
palate. The angle of the mandible is (except in Tarsipes) more or 
less inflected. The hyoid bones have always a peculiar form, 
consisting of a small, more or less lozenge -shaped basi-hyal, broad 
cerato-hyals, with the remainder of the anterior arch usually 
unossified, and stout, somewhat compressed thyro-hyals. There are 
two anterior venae cava?, 1 into each of which a "vena azygos " 
enters. In the male the testes are always contained in a scrotum, 
which is suspended by a narrow pedicle to the abdomen in front of 
the penis. The vasa deferentia open into a complete and continuous 
urethra, which is also the passage by which the urine escapes from 
the bladder, and is perfectly distinct from the passage for the feeces, 
although the anus and the termination of the urethro-sexual canal 
are embraced by the same sphincter muscle. The glans is often 
bifurcated anteriorly. In the female the oviducts never unite to 
form a common cavity or uterus, but open separately into the 
vagina, which at least for part of its course is double. The 
mammae vary much in number, but are always abdominal in 
position, having long teats, and in most of the species are more 
or less enclosed in a fold of the integument forming a pouch 
or marsupium, though in some this is entirely wanting, and the 
newly -born, blind, naked, and helpless young, attached by their 
mouths to the teat, are merely concealed and protected by the 
hairy covering of the mother's abdomen. In this stage of their 
existence they are fed by milk injected into their stomach by the 
contraction of the muscles covering the mammary gland, the 
respiratory organs being modified temporarily, much as they are 
permanently in the Cetacea — the elongated upper part of the 
larynx projecting into the posterior nares, and so maintaining a free 
communication between the lungs and the external surface 

1 Except in Petaurus (Belidcus) brcviceps (Forbes, Proc. Zool. Soc. 1881, 
p. 188). 



DISTRIBUTION 



131 



independently of the mouth and gullet, thus averting the danger of 
suffocation while the milk is passing down the latter passage. 

Distribution. — The existing species of Marsupials are, with the 




region, 



forming 



->v 



the chief 



Fig. 35. — Front view of skull of Sarcophilus ursinas, showing polyprotodont and carnivorous 
dentition (Quart. Journ. Geol. Soc. vol. xxiv. p. 313). 

exception of one family (the Didelphyidce), limited in geographical 
distribution to the Australasian 
mammalian fauna of Australia, 
New Guinea, and some of the 
adjacent islands. The Didel- 
phyides are almost purely Neo- 
tropical, one or two species 
ranging northwards into the 
Nearctic region. Fossil re- 
mains of members of this 
family have also been found in 
Europe and America in strata 
of the Eocene and early Mio- 
cene periods ; and it is probable 
that at least many of the poly- 
protodont Mesozoic mammals 
noticed in Chapter IV. are 
referable to the Marsupialia. 

Classification. — In dividing 
the Marsupials into minor 
groups, it may be observed 
that one of the most obvious 
distinctive characters among 
them is derived from the form 




Fig. 36. — Front view of skull of Koala (Phas- 
colarctics cinereus), showing diprotodont and 
herbivorous dentition (Quart. Journ. Geol. Soc. 
vol. xxiv. p. 313). 



and arrangement of the teeth. 
1 Including the transitional Austro-Malayan region. 



1 32 MARSUPIALIA 



In certain species, as the Opossums, Dasyures, and Thylacine, 
the incisors are numerous, small, and subequal in size, and the 
canines large, as in the typical placental Carnivores (Fig. 35). 
To these the term " polyprotodont " is applied, and they are all 
more or less carnivorous in their habits. In others the central 
incisors are very prominent, and the lateral incisors and canines 
absent or subordinate in function (Fig. 36). These are called 
" diprotodont," and they are all wholly or in great part vegetable 
feeders. In one group of these, the Wombats, there are but two 
incisors above and the same number below ; but all the others, in- 
cluding the Kangaroos, Koalas, and Phalangers, have two functional 
incisors below and as many as six above, three on each side, but 
of these the first or central pair is the most fully developed. 

Some hesitation has frequently been expressed as to whether the 
Polyprotodont and Diprotodont types are entitled to constitute 
distinct primary groups, owing to the presence of syndactylism 
among the Peramelidte in the former, as well as in the latter ; but if 
Mr. 0. Thomas is right in regarding this feature as acquired 
independently in the two groups we may safely adopt such a 
division. Taking various combinations into consideration, the 
existing Marsupials readily group themselves into six very natural 
families, the leading characters of which may be summarised as 
follows : — 

Order Marstjpialia. 

A. Polyprotodontia. — Incisors numerous, small, subequal. Canines 

larger than the incisors. Molars with sharp cusps. 

a. Incisors f-. Hind feet with the four outer toes subequal, 
distinct, and a well-developed opposable hallux. Didel- 
phyid(B. 

ft. Incisors |. Hind feet with four outer toes distinct, Hallux 
small or rudimentary, rarely opposable. Dasyuridce. 

y. Incisors ^ ~ . Hind feet long and narrow. Fourth toe 

larger than the others. Hallux rudimentary or absent. 
Second and third toes very slender, and united in a 
common integument (syndactylous). Peramelidc. 

B. Diprotodontia. — Incisors not exceeding § , usually f, but occasion- 

ally \. Central (first) upper and lower incisors large and 
cutting. Upper canines generally, and lower invariably, absent 
or small. Molars with bluntly tuberculated or transversely 
ridged crowns. 

a. Teeth with persistent pulps. Incisors \, large, scalpriform, 

with enamel on the outer surface only. No canines. 

Hind feet with four subequal outer toes, partially 

syndactylous, and with rudimentary hallux. Phascolo- 

myidce. 



DIDELPHYID.-E 



'33 



B. Teeth rooted. Three upper incisors and a canine. Hind 
limbs not disproportionately large. Feet syndactylous, 
broad, with tour subequal outer toes, and a huge 
opposable hallux. l'lt«l<uitjerid<r. 

y. Teetli rooted. Three upper incisors, and frequently a 
canine. Hind limbs disproportionately large, with 
syndactylous feet as in Peramelidcc. Macropodidce. 



Suhorder Polyprotodontia. 

The loading characters of this group are given in the foregoing 
schedule. This group is the only one represented at the present 
day, and so far as we know also in past epochs, beyond the confines 
of the Australasian region and adjacent islands. 



Family Didelphyid^. 



Dentition : i -f , c ^, p 



35 



m ^ • total 50. Incisors very small 
and pointed. Canines large. Premolars Avith compressed pointed 
crowns. Molars with numerous sharp cusps. The last premolar 
preceded by a deciduous multicuspidate milk-molar, which remains in 
place until the animal is nearly adult (Fig. 34). Limbs of moderate 
development, each with five complete and distinct toes, all of which 
are provided with short, compressed, 
curved, sharp claws of nearly equal 
size, except the first toe of the hind 
foot or hallux (Fig. 37), which is large, 
widely separable from the others, to 
which it is opposed in climbing, and 
terminates in a dilated rounded ex- 
tremity, without a nail. Tail gener- 
ally long, partially naked and prehen- 
sile. Stomach simple. Caecum of 
small or moderate size. Pouch gener- 
ally absent, sometimes represented by 
two lateral folds of the abdominal 
integument, partially covering the 
teats, rarely complete. Vertebrae : 
C 7, D 13, L 6, S 2, C 19-35. 

The Didelphyidce, or true Opos- 
sums, differ from all other existing 
Marsupials in their habitat, being- 
peculiar to the American continent. 
They are mostly carnivorous or insectivorous in their diet, and 
arboreal in habits. 

Opossums occur throughout the greater part of the American 




Fig. 37.— Skeleton of th e right hind 
foot of the Virginian Opossum (Didelphys 
inarsupialis). 



134 MARSUPIALIA 



continent, ranging from the United States to Patagonia, the greater 
number of species being found in the warmer regions. In South 
America the opossums take the place of the Eutherian Insectivora, 
and the sharp cusps on their teeth are admirably adapted for crushing 
the insects on which they mainly subsist. 

Chironectes. 1 — The family comprises two genera only, namely 
Diddphys, containing all the species, with the exception of the curious 
Yapock, which forms by itself the genus Chironectes, and is distin- 
guished from all other Opossums by its webbed feet, non-tuberculated 
soles, and peculiar coloration. Its ground colour is light gray, with 
four or five sharply-contrasted brown bands passing across its head 
and back, and thus giving it a very peculiar mottled appearance. 
It is almost wholly aquatic in its habits, living on small fish, 
crustaceans, and water insects. Its range extends from Guatemala 
to southern Brazil. 

Didelphys. 2 — The type genus Didelphys is a very large one, con- 
taining, according to Mr. 0. Thomas, twenty-three existing species. 
It may be divided into five groups, or sub-genera, all of which have 
received distinct names. The typical group is represented only by 
the common or Virginian Opossum {p. marsupial is), of which the 
numerous varieties have received separate specific names. This 
species is of large size, with a long, scaly, prehensile tail, and long 
bristle-like hairs mingled with the fur. The pouch is complete. 
It ranges over all temperate North America, and is also found in 
central and tropical South America, where it is commonly known 
as the Crab-eating Opossum. This animal is extremely common, 
being even found living in the towns, where it acts as a scavenger 
by night, retiring for shelter by day upon the roofs of the houses or 
into the sewers. The female produces in the spring from six to 
sixteen young ones, which are placed in her pouch immediately 
after birth, and remain there until able to take care of them- 
selves. 

The second or Metachirine group includes three species found 
all over the tropical parts of the New World. They are of medium 
size, with short close fur, very long, scaly, and naked tails, and 
less developed ridges on their skulls than in the type species. As 
a rule there is no pouch adapted to carry the young, which 
commonly ride on their mother's back, holding on by winding 
their prehensile tails round hers. The Philanderine group is 
closely allied to the preceding, but is readily distinguished by the 
woolly hair, and the brown streak down the middle of the face. 
The Woolly Opossum (D. lanigera), which is represented in the 
accompanying woodcut (Fig. 38) carrying its young in the fashion 
mentioned above, is one of the two species of this group. In the 

1 Illiger, Prod. Syst. Mamm. ct Avcs, p. 76 (1811). 
- Linn. Syst. Nat. Ed. 12, vol. i. p. 71 (1766). 



DIDELPHYID.E 



135 



fourth or Micouri ine group the numerous species are all smaller 
than in the preceding groups, and have short and close hair, and 
no dark streak down the face. The best known species is the 
Murine Opossum (D. murina), little larger than a House-Mouse, 
and of a blight i*ed colour, which is found as far north as central 
Mexico, and extends thence right down to the south of Brazil. The 
last or Peramyne group contains several extremely shrew-like 
species, of very small size, with short, hairy, and usually non-pre- 
hensile tails, not half the length of the trunk, and with wholly 
unridged skulls. The most striking member of the group is the 
Three-striped Opossum (D. americana), from Brazil, which is of a 
reddish-gray colour, with three clearly-defined deep-black bands 




■0P ! ,,'• ^ - 

Fio. 3S. — The Woolly Opossum (Diddphys lanigera). 



down its back, very much as in some of the striped mice of 
Africa. 

The numerous fossil species of Opossum found in the Upper 
Eocene and Lower Miocene of Europe are of especial interest from a 
distributional point of view, since they indicate how the Opossums of 
America may have been connected with the Australian Marsupials. 
These forms were originally referred to Diddphys, but have been 
subsequently described as Peratherium and Amphiperatherium. The 
characters of the molar teeth on which these genera are based do 
not appear to be sufficiently important to justify their separation 
from Diddphys. Allied forms occur in the Tertiaries of North 
America, which were originally described under the name of Her- 
petotherium, but have been subsequently referred to Peratherium. 
Kemains of many of the existing species of Opossum are found in 
a fossil condition in the Pleistocene cave-deposits of Brazil. 



!j6 



MARSUPIALIA 



Family DasyuridtE 

Dentition : i j^, c \,p and m numerous, variable. Incisors small ; 
canines well developed ; molars with pointed cusps. Limbs equal. 
Fore feet with five subequal toes terminating in claws. Hind feet 
with the four outer toes well developed, and distinct from each 
other and bearing claws ; the first (or hallux) clawless, generally 
rudimentary, sometimes entirely wanting. Stomach simple. No 
csecum. Predatory carnivorous or insectivorous animals, inhabit- 
ants of Australia, Tasmania, and the southern parts of New Guinea 
and some of the adjacent islands. The aberrant genus Myrmecobius, 
though clearly a member of this family, is so sharply distinguished 




Fig. 39.— The Thylacine (Thylacinw cynoceplmlus). 

from all the others as to render a division into two subfamilies 
necessary. 

Subfamily Dasyurinse. — This comprises the more typical Dasy- 
nridce, in which the premolars and molars never exceed the normal 
number of seven on either side of each jaw, and in which the tongue 
is not specially extensile. 

Thylacinus. 1 — Dentition : i f, c \-,p%, m| = 46. Incisors small, 
vertical, the outer one in the upper jaw larger than the others. 
Summits of the lower incisors, before they are worn, with a deep 
transverse groove dividing them into an anterior and a posterior cusp. 
Canines long, strong, and conical. Premolars separated from one 
another by intervals, with compressed crowns, increasing in size 
from before backwards. True molars in general characters re- 

1 Temminck, Monographies de MammaJogic, vol. i. p. 60 (1827). 



DASYURWsE 



137 



sembling those of Dasywus, but of more simple form, the cusps 
being not so distinct nor sharply pointed. Milk-molar very small, 
and shed before the animal leaves the mother's pouch. Humerus 
with an entepicondylar foramen. General form very Dog-like. 
Head elongated. Muzzle pointed. Ears moderate, erect, triangular. 
Fur short and closely applied to the skin. Tail of moderate length, 
thick at the base and tapering towards the apex, clothed with short 
hail-. Hallux (including the metacarpal bone) wanting. Vertebrae : 
C 7, D13, L 6, S 2, C 23. Marsupial bones represented only by 
small unossified fibro-cartilages. 

The only known existing species of this genus, T. cynocephalus 
(Fig. 39), though smaller than a common Wolf, is the largest preda- 
ceous Marsupial at present living. It is now entirely confined to the 
island of Tasmania, although fragments of bones and teeth found in 
caves afford evidence that a closely allied species once inhabited the 
Australian mainland. The general colour of the Thylacine is 




Fig. 40.— Right lateral aspect of the skull of the Thylacine. 

grayish brown, but it has a series of transverse black bands on the 
hinder part of the back and loins, whence the name of "Tiger" 
frequently applied to it by the colonists. It is also called " Wolf," 
and sometimes, though less appropriately, " Hyama." Owing to 
the havoc it commits among the sheepfolds, it has been nearly 
exterminated in all the more settled parts of Tasmania, but still 
finds shelter in the almost impenetrable rocky glens of the more 
mountainous regions of the island. The female produces four 
young at a time. The pouch opens backwardly, and there are four 
mammae. The figure of the skull exhibits the peculiar Dog-like 
form so characteristic of the genus. 

Sarcophilus} — Dentition : i -*-, c \, p f , m |-. Upper incisors nearly 
equal, and placed vertically, the first not differentiated from the 
rest. Premolars rounded and closely crowded between the canine 
and molars, with broad crowns ; molars broad and heavy, the last 
one without a distinct hind talon. Form thick and powerful ; 

1 F. Cuvier, Hist. Nat. des Mammiferes, iv. (1837). 



133 MARSUPIAL1A 



head disproportionately large for the body ; muzzle sbort and 
broad ; ears broad and rounded ; tail of moderate length, and 
evenly hairy. Hallux wanting ; soles of feet naked, without defined 
pads. Humerus with entepicondylar foramen. 

This genus is now represented only by a single species 
(S. ursinus) found in Tasmania, where, from its ferocious and des- 
tructive habits, it is commonly known under the name of the " Devil." 
A front view of the skull is shown in Fig. 35. 

The prevailing colour of this animal is black, and the size about 
equal to that of an English Badger ; its habits are fossorial, and it 
is very destructive to sheep. On account of the similarity in the 
number of its teeth this genus has been generally included in the 
next one, but in the structure of the teeth it is much nearer to 
Thylacinus. An extinct species is found in the Pleistocene deposits 
of the mainland of Australia. 

It may be observed that the two premolars missing from ' the 
typical series of four in this and the next genus are the second and 
the fourth ; the fourth milk-molar being likewise absent. In 
Thylacinus and other Polyprotodonts with three premolars it is the 
second that is missing. 

Dasyurus. 1 — Dentition : i -J, c \, p f , m -f- ; total 42. Upper 
incisors nearly ecpial, and placed vertically ; first slightly longer, 
narrower, and separated from the rest. Lower incisors sloping 
forwards and upwards. Canines large and sharply pointed. Pre- 
molars with compressed and sharp-pointed crowns, and slightly 
developed anterior and posterior accessory basal cusps. True 
molars with numerous sharp-pointed cusps. In the upper jaw the 
first three with crowns having a triangular oral surface, the fourth 
small, simple, narrow, and placed transversely. In the lower jaw 
the molars more compressed, with longer cusps ; the fourth not 
notably smaller than the others. Form viverrine. Ears long and 
narrow, prominent, and obtusely pointed. Hallux rudimentary, or 
absent ; its metatarsal bone always present. Tail long and well 
clothed with hair. Humerus without an entepicondylar foramen. 
Vertebra? : C 7, D 13, L 6, S 2, C 18-20. 

The Dasyures are small Civet-like animals with a gray or brown 
pellage profusely spotted with white ; they are mostly inhabitants 
of the Australian continent and Tasmania, where in the economy of 
nature they take the place of the smaller predaceous Carnivora, the 
Cats, Civets, and Weasels of other parts of the world. They hide 
themselves in the daytime in holes among rocks or in hollow trees, 
but prowl about at night in search of the small living mammals 
and birds which constitute their prey. The species are not numer- 
ous, and include D. maculatus, about the size of a common Cat, 
inhabiting Tasmania and the southern part of Australia ; D. viver- 
1 Geoffroy, Bull. Soc. Philom. vol. i. p. 106 (1796). 






DASYURIDAZ 139 



rinus, Tasmania and Victoria; P. geoffroyi, nearly all Australia; 
D. hallucatus, North Australia ; D. albopunctatus, New Guinea. 

Remains referred to 1). vivernnus occur in the Australian Pleis- 
tocene deposits. 

Phascologale} — This genus comprises a considerable number of 
small Marsupials, none of them exceeding a common Rat in size, 
differing from the Dasyures in possessing an additional pre- 
molar — the dentition being i |, c \,p f, m £ ; total 46, — and having 
the teeth generally developed upon an insectivorous rather than a 
carnivorous pattern, the upper middle incisors being larger and 
inclined forwards, the canines relatively smaller, and the molars 
with broad crowns, armed with prickly tubercles. The muzzle is 
pointed. Ears moderately rounded and nearly naked. Feet broad 
and short, Fore feet with five subequal toes, having compressed, 
slightly curved, pointed claws. Hind feet with the four outer toes 
subequal, having claws similar to those in the fore feet ; the hallux 
always distinct and partially opposable, though small and nailless. 
Tail long, very variable in its covering, being either bushy, crested, 
or nearly naked. Pouch represented merely by a few folds of skin. 
Mamma? varying from four to ten in number. The food of these 
animals is almost entirely insects ; some species pursuing their prey 
among the branches of trees, while others are purely terrestrial. 
They are found throughout Australia, and also in New Guinea and 
the Aru and some of the adjacent islands. 

P. cristicaudata, a species with a thick compressed tail orna- 
mented upon its apical half with a crest of black hair, differs from the 
others by the very reduced size of the fourth premolar in the upper, 
and its complete absence in the lower jaw, thus forming an interest- 
ing transition in dentition towards Dasyurus. It constitutes the 
genus Chcetocercus of Krefft, but is included by Mr. 0. Thomas in 
Phascologale, the frequent absence of the fourth lower premolar in 
P. thorbeckiana indicating that the total absence of this tooth in the 
known specimens of this species cannot be regarded as of generic 
importance. All the members of this and the two following genera 
can be at once distinguished from Dasyurus by the absence of white 
spots on the fur. 

Sminthopsis. 2 — The genus Sminthojms includes several small 
species allied to Phascologale but characterised by the narrowness 
of the hind foot, and by the soles of the feet being either granulated 
or hairy, instead of naked. 

Antechinomys. 3 — The last genus of the Dasyurince is Antechinomys, 
represented only by A. laniger of Queensland and New South Wales. 
This elegant little mouse-like creature, which has large oval ears and 

1 Temminck, Monographies de Mammalogie, vol. i. p. 56 (1827). 

2 Thomas, Ann. Mus. Genov. ser. 2, vol. iv. p. 503 (1887). 

3 Krefft, Proe. Zool. Soe. 1866, p. 434. 



MO 



MARSUPIALIA 



a long tail with the terminal part bushy, is distinguished from 
Sminthopsis by the absence of the hallux and the great elongation 
of the limbs. The tympanic bullae of the skull are also unusually 
large, with the mastoid portion much swollen. A full account of 
the habits and anatomy of this animal, which appears to be of very 
rare occurrence, is given in the Proc. Zool. Soc. 1880, p. 454. 

Subfamily Myrmecobiinse. — Molars and premolars exceeding 
the normal number of seven on each side. Tongue, long cylindrical, 
and extensile. 



MyrmecoMus. 1 — Dentition 



h c hP f > m t or f '} total 52 or 56, 




► '■'.-■"'■ '■.;''''-'' ' 1- 



Fig. 41. — Myrmecobius fasciatus. From Gould. 

being the largest number of teeth in any existing Marsupial. The 
distinction between the molars and premolars is founded not on 
a knowledge of the succession of the teeth, but on their form. The 
teeth are all small and (except the four posterior inferior molars) 
separated from each other by an interval. Head elongated, but 
broad behind. Muzzle long and pointed. Ears of moderate size, 
ovate, and rather pointed. Fore feet with five toes, all having 
strong, pointed, compressed claws, the second, third, and fourth 
nearly equal, the fifth somewhat, and the first considerably, shorter. 
Hind feet with no trace of hallux externally, but the metatarsal bone 
1 Waterhouse, Proc. Zool. Soc: 1836, p. 69. 






PERAMELIDjE 141 



present. Tail long, clothed with long hairs. Fur rather harsh and 
bristly. Female without any pouch, the young when attached to 
the nipples being concealed only by the long hair of the abdomen. 
Vertebrae : C 7, D 13, L 6, S 3, C 23. A gland on the under 
surface of the body just in advance of the sternum. 

Of this singular genus but one species is known, M. fasciatus 
(Fig. 41), found in western and southern Australia. It is about the 
size of an Fnglish squirrel, to which animal its long bushy tail 
gives it some resemblance ; but it lives entirely on the ground, 
especially in sterile, sandy districts, feeding on ants. Its pre- 
vailing colour is chestnut-red, but the hinder part of the back 
is elegantly marked with broad, white, transverse bands on a dark 
ground. 

The special interest of this form lies in its apparent relationship 
to those Mesozoic mammals which possess a large number of true 
molars (seep. 114); and it is suggested by Thomas that it may 
eventually be found advisable to include some of the latter in the 
present subfamily. 

Family Peramelid.e. 

Dentition : i —^- , c - p g, m - • total 46 or 48. Upper incisors 

small, with short broad crowns. Lower incisors moderate, nar- 
row, proclivous. Canines well developed. Premolars compressed, 
pointed. Molars with quadrate tuberculated crowns. Fourth pre- 
molar preceded by a small molariform tooth, which remains in place 
until the animal is nearly full grown. Fore feet with two or 
three of the middle toes of nearly equal size, and provided 
with strong, sharp, slightly curved claws ; the other toes rudi- 
mentary. Hind feet long and narrow ; the hallux rudimentary 
or absent ; the second and third toes very slender, and united in a 
common integument ; the fourth very large, with a stout elongated 
conical claw ; the fifth smaller than the fourth (see Fig. 43). The 
ungual phalanges of the large toes of both feet cleft at their ex- 
tremities (as in Maids among the Edentata, but in no other 
Marsupials). Head elongated. Muzzle long, narrow, and pointed. 
Stomach simple. Caecum of moderate size. Pouch complete, 
opening backwards. Alone among Marsupials they have no clavicles. 

The PeramelidcB form a very distinct family, in some respects 
intermediate between the sarcophagous Dasytiridce and the 
phytophagous Macropodidce. In dentition they resemble the former, 
but they agree with the latter in the peculiar structure of the hind 
feet. In the construction of the fore feet they differ from all other 
Marsupials. 

The Bandicoots, as these Marsupials are popularly termed, are 



14: 



MARSUPIAL/A 



of fossorial habits, and subsist either on an insectivorous or omni- 
vorous diet. It has been generally considered that their syndac- 
tylous feet indicate direct affinity with the Diprotodonts, but owing 
to the essentially Polyprotodont character of the organisation — 
which extends even to their carpal and tarsal bones — Thomas 
dissents from this view, and concludes that their syndactylism is an 
independently acquired character, and that they are really a direct 
offshoot from the Dasyuridce. Some individuals are remarkable for 
the presence of a longitudinal groove in the root of the canines, by 
which feature they approximate to some of the Mesozoic Polypro- 
todont forms. They may be divided into three genera. 

Perameles. 1 — Anterior and posterior extremities not differing 
greatly in development. Fore feet with the three middle toes well 




- — : jg= - 

Fig. 42. — Perameles gunni. From Gould. 

developed, the third slightly larger than the second, the fourth 
somewhat shorter, provided with long, strong, slightly curved, 
pointed claws. First and fifth toes very short and without claws. 
Hind feet with hallux of one or two phalanges, forming a distinct 
tubercle visible externally ; the second and third toes very slender, 
of equal length, joined as far as the ungual phalanges, but with 
distinct claws ; the fifth intermediate in length between these and 
the largely developed fourth toe. Ears of moderate or small size, 
ovate, pointed. Tail rather short, clothed with short adpressed 
hairs. Fur short and harsh. Vertebrae ; C 7, D 13, L 6, S 1, C 17. 
Skull long and narrow, with the bulla single, and its mastoid portion 
not inflated. 

The animals of this genus are all small, and live entirely on the 
ground, making nests composed of dried leaves, grass, and sticks in 
1 Geoffrey, Bull. Soc. Philom. vol. iii. p. 249 (1803). 



PERAMELIDjE 143 



hollow places. They arc rather mixed feeders; but insects, worms, 
roots, and bulbs constitute their ordinary diet. The various species 
are widely distributed over Australia, Tasmania, New Guinea, and 
several of the adjacent islands, as Am, Kei, and New Ireland. The 
best known are — P. gunni (Fig. 42), bougamvilki, nasuta, obesida, and 
macrura from Australia, and /'. doreyana, raffirayam, and longicaadata 
from New Guinea. 

Remains apparently referable to existing species are found in 
the cave-deposits of New South Wales. 

Peragah. 1 — Molar teeth curved, typically with longer crowns 
and shorter roots than in the last. Hinder extremities proportionally 
longer, and hallux without claw. Muzzle much elongated and 
narrow. Fur soft and silky. Ears very large, long, and pointed. 
Tail long, its apical half clothed on the dorsal surface with long 
hairs which form a crest. Vertebrae : C 7, D 13, L 6, S 2, C 23. 
Skull distinguished from that of Perameles by the large size and 
double structure of the auditory bulla, of which the mastoid portion 
is inflated. There is also an abrupt contraction of the muzzle at 
the third premolar. 

The type species of Rabbit - Bandicoot (P. lagotis), as these 
animals are called, is found in Western Australia, and also occurs 
fossil in the cave-deposits of New South Wales. It is the largest 
member of the family, being about the size of the common Rabbit, 
to which animal it bears sufficient superficial resemblance to have 
acquired the name of " Native Rabbit " from the colonists. It 
burrows in the ground, but in other respects resembles the true 
Bandicoots in its habits. 

The smaller P. leucura has short-crowned molars, with distinct 
cusps, which are almost obsolete in the type species. 

Chceropus.- — Dentition generally resembling that of Perameles, 
but the canines are less developed, and in the upper jaw two-rooted. 
Limbs very slender ; posterior nearly twice the length of the anterior. 
Fore feet with the functional toes reduced to two, the second and 
third, of equal length, with closely united metacarpals and short, 
sharp, slightly curved, compressed claws. First toe represented by 
a minute rudiment of a metacarpal bone ; the fourth by a metacarpal 
and two small phalanges without a claw, and not reaching the 
middle of the metacarpal of the third ; fifth entirely absent. Hind 
foot (Fig. 43) long and narrow, mainly composed of the strongly 
developed fourth toe, terminating in a conical pointed nail, with a 
strong pad behind it ; the hallux absent or represented by a rudi- 
mentary metatarsal ; the remaining toes completely developed, and 
with claws, but exceedingly slender ; the united second and third 
reaching a little way beyond the metatarso-phalangeal articulation of 

1 Gray, in Grey's Australia, vol. ii. p. 401 (1841). 
2 Ogilby, Froc. Zool. Soc. 1838, p. 25. 



144 



MARSUPIALIA 



the fourth ; the fifth somewhat shorter. Tail not quite so long as 
the body, and covered with short hairs forming a slight crest. Ears 
large and pointed, and folded down when the animal 
is at rest. Fur soft and loose. Vertebrae : C 7, D 
13, L 6, S 1, C 20. Skull short and wide, with a 
small and single bulla, and a contraction of the 
muzzle at the third premolar. 

The only known species of this genus (Fig. 44), 
chiefly remarkable for the singular construction of 
its limbs, is an animal about the size of a small 
Eat, found in the interior of the Australian continent. 
Its general habits and food appear to resemble those 
of the other Peramelidce. It was first described as 
C. ecaudatus by Ogilby from a mutilated specimen, 
but the specific name was afterwards changed, as being 
inappropriate, by Gray to castanotis. 



Suborder Diprotodontia. 

For the leading characters of this group, see 
page 132. 

Family Ehascolomyid^e 

Dentition : c f, i $, p ^, m £ = 24. All the teeth 
with persistent pulps. The incisors large, scalpriform, 
with enamel only on the front surface, as in the 
Eodentia. The molars strongly curved, forming from 
the base to the summit about a quarter of a circle, 




Fig. 43.— Skele- 
ton of right hind 
foot of Chmropus 
castanotis. c, Cal- 
caneum ; a, astra- 
galus ; cb, cuboid ; 
ii, navicular ; c3, 
ectocuneiform ; II 
and III, the con- 



third digits ; IV, 
the large and only 
functional digit ; 
V, the rudiment- 
ary fifth digit. 

equal, stout, 



joined second and ^ e CO ncavity being directed outwards in the upper 
and inwards in the lower teeth. The first of the 
series, or premolar, appears to have no milk-prede- 
cessor, and is single-lobed ; the other four composed 
of two lobes, each subtriangular in section. Limbs 
and short. Fore feet with five distinct toes, each 
furnished with a long, strong, and slightly curved nail, the first and 
fifth considerably shorter than the other three. Hind feet with a very 
short nailless hallux, the second, third, and fourth toes partially 
united by integument, of nearly equal length, the fifth distinct 
and rather shorter ; all four provided Avith long and curved nails. 
In the skeleton of the foot, the second and third toes are distinctly 
more slender than the fourth, showing a slight tendency towards 
the peculiar character so marked in the next two families. Tail 
rudimentary. Stomach simple, provided with a special gland 
situated near the cardiac orifice. Caecum very short, wide, and with 
a peculiar vermiform appendage. Eouch present. The auditory 
bullae of the skull are imperfect, open behind, with their anterior 



PHASC0L0MY11KE 



M5 



wall formed by a descending process of the squamosal, instead of the 




WF^Wimm 



Fig. 4-1. — Clmropus castanotts. From Gould. 

alisphenoid. Masseteric fossa of mandible with a perforation and 
a deep pit. 




Fig. 45. — Common Wombat (Phascolornys itrsinus). 

Phascolomys. 1 — The existing Wombats (Fig. 45) comprise three 
1 GeoiTrov, Ann. du Museum, vol. ii. \>. 365 (1803). 

10 



146 MARSUPIALIA 



species, all of which are included in the one genus Phascolomys, 
and all of which date from the Pleistocene. 

In the typical group we find the following characters. Fur 
rough and coarse. Ears short and rounded. Muffle naked. Post- 
orbital process of the frontal bone obsolete. Ribs fifteen pairs. 
Vertebras: C 7, D 15, L 4, S 4, C 10-12. The Wombat of Tas- 
mania and the islands of Bass's Straits (P. ursinus) and the closely 
similar but larger animal of the southern portion of the mainland of 
Australia (P. mitchelli) belong to this group. 

In the second group the characters are as follows. Fur smooth 
and silky. Ears large and more pointed. Muffle hairy. Frontal 
region of skull broader than in the other group, with well- 
marked postorbital processes. Ribs thirteen. Vertebras : C 7, D 
13, L 6, S 4, C 15-16. One species, P. latifrons, the Hairy-nosed 
"Wombat of Southern Australia. 

In their general form and actions the Wombats resemble small 
bears, having a somewhat similar shuffling manner of walking, but 
they are still shorter in the legs, and have broader, flatter backs than 
bears. They live entirely on the ground, or in burrows or holes 
among rocks, never climbing trees, and feed entirely on grass, 
roots, and other vegetable substances. They sleep during the day, 
and wander forth at night in search of food, and are shy and 
gentle in their habits generally, though they can bite strongly when 
provoked. The only noise the common Wombat makes is a low 
kind of hissing, but the Hairy-nosed Wombat is said to emit a short 
quick grunt when annoyed. The prevailing colour of the last- 
named species, as well as of P. ursinus of Tasmania, is a brownish 
gray. The large wombat of the mainland is very variable in colour, 
some individuals being found of a pale yellowish brown, others 
dark gray, and some quite black. The length of head and body is 
about three feet. 

It is noteworthy that P. mitchelli was first described from the 
evidence of fossil remains, the living form subsequently described as 
P. platyrhinus being found to be indistinguishable. Other extinct 
species occur in the Pleistocene of Australia. 

Phascolonus. 1 — Remains of a large extinct Wombat, which must 
have nearly equalled the dimensions of a Tapir, occur in the 
Pleistocene of Queensland, and have been described as Phascolonus. 
It is probable that the expanded and flattened upper incisors from 
the same deposits iq>on the evidence of which the presumed genus 
Scf'jHiriwdon was founded, are likewise referable to the same form. 
The characters of both the upper and lower incisors distinguish 
Phascolonus from Phascolomys. 



1 Owen, Phil Trans. 1872, p. 257. 



PHALANGERin.K 147 



Family Phalaxgkkid.k. 

Dentition extremely vaxiable, owing to the presence of minute 
rudimental teeth not constant in the same species, or even in the 
two sides of the jaws of the same individnal ; exclusive, however, of 

m .■. j- ,.31 ('2—3) (3—4) , . , .. 

Tarsipes, the formula 1 r, c ^, p , __.n> w> (B—V t re P resen ' ; s fairly the 

general condition of the functional teeth. First incisors long and 
stout ; the lower pair very large and pointed, but without the scissoi'- 
like action found in the existing Macropodidce ; second and third 
lower incisors minute and probably functionless. Fourth premolar 
generally secant ; milk-molar generally minute and deciduous at an 
early period. Molars either with sharp cutting-crests or bluntly 
tuberculate; fourth sometimes absent. Mandible without pit, and 
at most a very minute perforation in the masseteric fossa. Limbs 
subequal. Fore feet with five distinct, subequal toes, furnished with 
claws. Hind feet short and broad, with five well-developed toes ; the 
hallux large, nailless and opposable ; the second and third slender, 
and united by a common integument as far as the claws. Tail 
generally long, and frequently more or less prehensile. Stomach 
simple. Caecum present (except in Tarsipes), and usually large. 
Pouch complete. Animals of small or moderate size and arboreal 
habits, usually feeding on a vegetable or mixed diet, inhabiting 
Australia and the Papuan Islands. 

The homologies of the lower functionless teeth between the first 
incisor and fourth premolar are very difficult to determine, but 
it is probable that one represents a canine only when the largest 
known number is present ; this tooth, according to Mr. Thomas, 
being the first to disappear. 

Phalangers are small woolly-coated animals, with long, power- 
ful, and often prehensile tails, large claws, and, as in the American 
opossums, Avith opposable nailless great toes. Their expression 
seems in the day to be dull and sleepy, but by night they 
appear to decidedly greater advantage. They live mostly upon 
fruit, leaves, and blossoms, although some few feed habitually upon 
insects, and all relish, when in confinement, an occasional bird 
or other small animal. Several of the Phalangers possess flying 
membranes stretched between their fore and hind limbs (Fig. 48), 
by the help of which they can make long and sustained leaps 
through the air, like the Flying Squirrels, but it is interesting to 
notice that the possession of these flying membranes does not seem 
to be any indication of special affinity, the characters of the skull 
and teeth sharply dividing the flying forms, and uniting them with 
other species of the non-flying groups. Their skulls (Fig. 47) 
are as a rule broad and flattened, with the posterior part swollen 



148 



MARSUPIALIA 



out laterally, owing to the numerous air-cells situated in the 
substance of the squamosal. 

The Phalangers are interesting from an historical point of 
view, since the Gray Cuscus (Phalanger orientalis) was the first of 
the Marsupials of the eastern hemisphere brought to the notice of 
Europeans, having been described in a work published at Leyden 
in 1611, from an account of a specimen seen at Amboyna during 
the third expedition of Admiral Van der Hagen. 

The present family corresponds to the Dasyuridce among the 




Fig. 46. — Tarsipes rostratus. From GouM. 

Polyprotodonts as presenting, on the whole, the most generalised 
types of the suborder. The existing forms may be divided into 
three subfamilies. 

Subfamily Tarsipedinse. — Cheek-teeth almost rudimentary and 
variable in number. Tongue long, slender, pointed, and very ex- 
tensile. Tail long. Caecum absent. 

Tarsipes. 1 — So named from some supposed resemblance of its 
foot to that of the Lemurine genus Tarsivs; but it must be remarked 
that it has none of the peculiar elongation of the calcaneum and 



navicular so characteristic of that genus. 



Head with elongated 



1 Gervais and Verraux, Proc. Zool. Soc. 1842, p. 1. 



PHALAXGERIlhE 149 



and slender muzzle. Mouth - opening small. The two lower 
incisors are long, very slender, sharp- pointed, and horizontally 

placed. All tin' other teeth are simple, conical, minute, and placed 
at considerable and irregular intervals apart in the jaws, the number 
appearing to vary in different individuals and even on different 

sides of the same individual. The formula in a specimen in the 
.Museum of the Royal College of Surgeons is i f, c ±, p and m § on 
one side, and i on the other; total 20. Kami of the mandible 
extremely slender, nearly straight, and without coronoid process or 
inflected angle. Fore feet with five well-developed toes, furnished 
with small, Hat, scale-like nails, not reaching to the extremity of 
the digits. Hind feet rather long and slender compared with those 
of the Phalangerince, Inning a well-developed opposable and nailless 
hallux ; second and third digits syndactylous, with sharp compressed 
curved claws ; the fourth and fifth free, and with small flat nails. 
Ears of moderate size and rounded. Tail longer than the body and 
head, scantily clothed with short hairs, prehensile. Vertebrae : C 7, 
D 13, L 5, S 3, C 24. 

Of this singular genus but one species, T. rostratus (Fig. 46), is 
known, about the size of a common Mouse. It inhabits Western 
Australia, lives in trees and bushes, uses its tail in climbing, and 
feeds on honey, which it procures by inserting its long tongue into 
the blossoms of Melaleucas, etc. One kept in confinement by Mr. 
Gould Avas also observed to eat flies. 

Subfamily Phalangerinse. — Teeth normal. One or more 
rudimentary teeth between the upper canine and fourth premolar, 
and between the first lower incisor and fourth premolar. Tongue 
of ordinary structure. No cheek-pouches. Stomach and ascending 
colon simple. Caecum long, simple. Tail well -developed, generally 
prehensile. 

A numerous group of animals, varying from the size of a mouse 
to that of a large cat, arboreal in their habits, and abundantly 
distributed throughout the Australian region. The members of 
this group are the typical representatives of the family, and are 
commonly known to the colonists as Opossums. 

Phalanger. 1 — The typical genus Phalanger (Cuscus) presents the 
following characters. No flying membrane ; size large or medium, 
and build stout and clumsy ; fur thick and woolly. Ears short 
or medium, hairy externally, and in some cases also internally. 
Toes of fore feet subecpial, their relative lengths in the order 4, 3, 
5, 2, 1. Claws long, stout, and curved. Soles of feet naked and 
striated, with large ill-defined pads. Tail stout and markedly 
prehensile, with the proximal half furred like the body, and the 
terminal portion entirely naked. Four mamma?. Skull (Fig. 47) 

1 Storr, Prodrome Meth. Mamm. \k 33 (1780). Syn. Phalangista, Geoffroy, 
Pull. Soc. Philom. vol. i. p. 106 (1796). 



HO 



MARS UP I A LI A 




Fig 47. — Left lateral view of skull of Gray Cuscus (Plw.l- 
anger orientalis). After Peters. 



stout and strong, with large vacuities in the hinder half of the 
palate, and the auditory bullae thick and inflated. Dentition usually 
i §, c -i, p fj '»< {■ First upper incisor with nearly circular section, 

or only slightly flat- 
tened in front ; can- 
ine more or less 
closely approximated 
to third incisor 
(which is very small), 
and situated partly 
in front of the suture 
between the pre- 
maxilla and maxilla. 
Fourth premolar 
large, secant, and 
placed obliquely to 
line of molars. 
Molars four-cusped, 
with the inner cusps 
of the upper ones 
crescentoid, and imperfect transverse ridges connecting each pair 
of cusps. 

The discuses are curious sleepydooking animals, inhabiting the 
various islands of the East Indian Archipelago as far west as Celebes, 
and being the only Marsupials found west of New Guinea. As 
already noted, it was a member of this genus, the Gray Cuscus 
(P. orientalis), a native of Amboyna, Timor, and the neighbouring 
islands, which was the first Australasian Marsupial known to European 
naturalists. There are altogether five species known, all of about 
the size of a large cat ; their habits resemble those of other Phalan- 
gers, except that they are said to be somewhat more carnivorous. 

Trichomrus} — The members of the genus Trichosurus are of 
relatively large size, and are distinguished from Phalanger by the 
following characters. Ears more or less hairy behind. Relative 
lengths of toes of fore feet in the order 4, 3, 2, 5, 1. Hair on the 
soles of the hind feet beneath the heel, but not elsewhere. Tail 
thick, not tapering, covered with bushy hair up to the extreme tip, 
which is naked, but with a naked strip on the inferior surface in 
the distal third or half. A gland on the chest. Dentition usually 
* ir > c -o> P h m f- Upper incisors of nearly uniform length, the 
first much flattened in front. Canine situated some distance behind 
the third upper incisor, which it scarcely exceeds in size. Last 
premolar and molars very similar to those of Phalanger. 

The true Phalangers comprise two species, of which the best 
known is the Vulpine Phalanger (T. vulpecula), so common in 
1 Lesson, Did. Class. d'Eist. Nat. vol. xiii. p. 333 (1828). 



/ "HALANGERW. K 1 5 1 



zoological gardens, where, however, it is seldom seen, owing to 
its nocturnal habits. It is of about the size and general build of 
a small fox, whence its name. In the typical variety the colour 
is gray, with a yellowish white belly, white ears, and a black tail. 
This variety is a native of the greater part of the continent of 
Australia, but is replaced in Tasmania by the closely allied Brown 
Phalanger (var. fuliginosa). Its habits are very similar to those of 
the Yellow-bellied Flying-Phalanger (Petaurus australis) described 
below, except that it is unable to take the flying leaps of that animal. 
Like all the other phalaugers, its flesh is freely eaten both by the 
natives and the lower class of settlers. 

Psetudochirus} — The genus Psmdochirus agrees with the pre- 
ceding in the absence of a flying membrane, and presents the 
following leading characters. Size large or medium. Fur com- 
paratively short and woolly. Ears medium or short, hairy 
behind, although seldom closely furred over all this aspect. 
Claws medium. Fore toes subequal, the first two distinctly 
opposable to the other three. Soles of feet naked, with large, 
striated, round pads, and hair beneath the heels. Tail tapering, 
markedly prehensile, with its distal third and the whole of the 
under surface short-haired ; tip naked underneath for a short 
distance. Four marnmse. No gland on chest, Skull with larger 
nasals than in the preceding genera; the posterior part of the 
palate in most cases fully ossified, and the auditory bulla? generally 

somewhat inflated. Dentition (at most) i 2 , c — ^— , p ~, m -. 

Upper teeth nearly uniform in length, but the first incisor distinctly 
longer than second. Upper premolars variable. Molars with both 
inner and outer cusps distinctly crescentoid, and recalling those 
of the Selenodont Artiodactyle Ungulates. 

Range. — Tasmania, Australia, and New Guinea. 

There are about ten species of this genus known, of which the 
commonest is Cook's Ring-tailed Phalanger {Psmdochirus peregrinus), 
an animal discovered by Captain Cook during his first voyage, at 
Endeavour river, North Queensland. 

The complex and sub-selenodont character of the molars of this 
and the folloAving genus readily distinguish them from the more 
typical Phalaugers, and show an approximation to the type of 
dentition prevailing in Phascolarctus ; according, however, to Mr. 
0. Thomas, a tendency towards the same structure is observable 
in unworn molars of young discuses. The genus may be divided 
into three groups, of which the first, as typified by the common P. 
peregrinus, is restricted to Australia and Tasmania, while the third, 
as represented by P. canescens, is only found in New Guinea. P. 
albertisi may be taken as the type of the second group, which is 

1 Ogilby, Proc. Zovl. Soc. 1836, p. 26. 



152 MARSUPIALIA 



represented by that species in New Guinea, and by P. archeri in 
Queensland. With the exception of P. peregrinus, the species have 
a more or less restricted range. Remains of Pseud < whims, probably 
referable to existing species, are found in the cave-deposits of New 
South Wales. 

Petauroides. 1 — With the genus Petauroides, containing only the 
single species P. volans, we come to the first of the Flying-Phalangers, 
characterised by the possession of a flying membrane along the flanks. 
The characters of this genus are as follows. Size large. Fur very 
long and silky. Ears large and oval, thickly furred on the back, 
but naked internally. Flying-membrane reaching from wrist to 
ankle, but very narrow along the sides of the fore-arm and lower 
leg. Fore toes subequal, their relative lengths in the order 4, 3, 5, 
2, 1. Claws long, curved, and sharp. Tail long, cylindrical, and 
bushy, except near its tip, where it is naked and prehensile. Skull 
short and broad, with the nasals short, and not extending nearly as 
far forwards as the premaxillae. Large vacuities in hinder part of 
palate. Auditory bullae inflated and smooth. Dentition usually 
* I) c i)i P t> m i> General characters of teeth very similar to those 
of Pseudochirus, but the first upper incisor scarcely longer than the 
second. 

The single species is found in Australia, from Queensland to 
Victoria, and is commonly known as the Taguan Flying-Phalanger. 
The structure of the skull and teeth indicates close affinity with 
Pseudochirus, although the external form is widely different in the 
two genera. This Phalanger seems, indeed, to be, so to speak, a 
very specialised Pseudochirus, in which the teeth have become 
somewhat further diminished and the flying membrane has been 
developed. 

Dactylopsila." — The genus Dactylopsila is one of the forms with- 
out any trace of a flying membrane, its characters being as follows. 
Size medium. Body striped black and white. Ears oval, nearly 
naked at the ends. Fore toes of very unequal length, the fourth 
being enormously elongated ; fourth and fifth toes of pes also 
markedly elongated. Claws long, moderately curved. Tail long, 
cylindrical, and evenly bushy, with the extremity more or less 
naked below. Skull narrow, but with the zygomatic arches greatly 
expanded ; palate fully ossified. Dentition : i -if-, c ^, p f , m j . 
Upper incisors very large, the third being directed horizontally 
forwards; canine small and approximated to the third incisor, which 
it resembles. The fourth premolar of moderate size, with its longer 
axis placed obliquely. First lower incisor longer than in any other 
genus. Molars oblong, with four cusps. 

The typical D. trivirgata, or Striped Phalanger, inhabits the 

1 Thomas, Cat. Marsupials Brit. Mm. p. 163 (1888). 
- Cray, Proc. Zool. Soc. 1858, p. 109. 



PHALANGERIDAZ 153 



Papuan and North Australian sub-region ; a second species (D. 
palpator), characterised by the still greater elongation of the fourth 

tinker, occurring in South New Guinea. These animals are said 
to he of insectivorous habits, the elongated fourth finger, as in the 
analogous instance of the Lemuroid genus Chironiys, being appar- 
ently specially adapted for extracting insects and larva' from their 
hiding places. 

Petaurus. 1 — Size medium or small. Fur very soft and silky. 
A broad Hying membrane extending from the outer side of the fifth 
digit of the maims to the ankle. Fore toes usually increasing 
regularly in length from the first to the fifth, but in some of the 
smaller species the fourth is the longest. Claws strong, sharp, and 
much curved. Tail long, evenly bushy to the extremity. Glands 
on the chest and between the ears. Skull short and wide, with 
the nasals expanded posteriorly, and usually two small palatal 
vacuities near the second molars. Auditory bullae inflated, and 
variable in size. Dentition : i f , c £, p -if, m f . First upper incisors 
very large, and taller than canine. Molars with square crowns 
rounded at the angles, and four cusps, except in the last, which is 
triangular. 

This genus, which ranges from New Ireland to South Australia, 
but is not found in Tasmania, contains three species, the largest of 
which is the Yellow-bellied Flying-Phalanger (P. amtralis), whose 
habits are recorded by Mr. Gould as follows. "This animal is 
common in all the brushes of New South Wales, particularly those 
which stretch along the coast from Port Philip to Moreton Bay. 
In these vast forests trees of one kind or another are perpetually 
flowering, and thus offer a never-failing supply of the blossoms 
upon which it feeds ; the flowers of the various kinds of gums, 
some of which are of great magnitude, are the principal favourites. 
Like the rest of the genus, it is nocturnal in its habits, dwelling in 
holes and in the spouts of the larger branches during the day, and 
displaying the greatest activity at night while running over the 
small leafy branches, frequently even to their very extremities, in 
search of insects and the honey of the newly-opened blossoms. Its 
structure being ill adapted for terrestrial habits, it seldom descends 
to the ground except for the purpose of passing to a tree too dis- 
tant to be reached by flight. "When chased or forced to flight it 
ascends to the highest branch and performs the most enormous 
leaps, sweeping from tree to tree with -wonderful address ; a slight 
elevation gives its body an impetus which, with the expansion of 
its membrane, enables it to pass to a considerable distance, always 
ascending a little at the extremity of the leap; by this ascent the 
animal is prevented from receiving the shock which it would other- 
wise sustain." 

1 Shaw, Naturalist's Miscellany, vol. ii. pi. lx. (1791). 



154 



MARSUPIALIA 



A second species, P. scmreus, in some ways one of the most 
beautiful of all mammals, has been chosen for the accompanying 
woodcut. 

Gymnobelideus. 1 — Like Petaurus in every respect, but without 
any trace of a flying membrane, and with the fifth digit of the 
manus slightly shorter than the third. This genus is represented 
only by G. leadbeateri of Victoria, and according to Mr. Thomas, 
may be regarded as the primitive form from which the specialised 
Petaurus has been developed. 







Fig. 4S. — Squirrel Flying-Phalanger (Petaurus sciureus). 



Dromicia. 2 — Size small, and general appearance dormouse- 
like. Ears large and thin, almost naked, and without internal 
or basal tufts. No flying membrane. Digits of normal propor- 
tions, the relative lengths of those of the manus in the order 
3, 4, 2, 5, 1 ; fore claws rudimentary, hind ones long and sharp. 
Tail mouse -like, cylindrical, furry at base, the remainder scaly, 
with fine hairs, except at the tip, which is naked and prehensile. 

1 M'Coy, Ann. Mag. A r . H. (3) xx. p. 2S7 (1S67). 
" Gray, in Grey's Australia, appendix, vol. ii. p. 407 (1841). 



PHALANGERIDAZ 155 



Skull short and broad, with the hinder part of the palate in- 
complete, and the auditory bullae large, much inflated, and trans- 
parent. Dentition : i 5, c -. p z, n -'. First upper incisor spat- 

ulate. and much longer than either of the others. Canine large, 
placed at some distance behind the third incisor. Molars (except the 
last) with evenly rounded crowns, carrying four small smooth cusps. 

This genus, which occurs in New Guinea, Western Australia, and 
Tasmania, is represented by four species. It seems to be inter- 
mediate between Petaurus and Acrobates, and it has apparently had 
to yield place to those more highly organised types in regions where 
they have come in contact with one another. 

Distccchurus} — Size small. Ears rather short, thinly covered 
with hair, but with small tufts at the base. No flying membrane. 
Digits of normal proportions, without expanded terminal pads. 
Claws curved and sharp. Tail, skull, and dentition as in Acrobates, 
with the exception that the fourth premolar is small in the upper, 
and absent in the lower jaw. 

The one species of Feather-tailed Phalanger (I), pennatus) is 
found in New Guinea. 

Acrobates.' 2 — Size very small. Ears moderate, thinly covered 
with hair, but with small tufts round the base and on the internal 
prominences. A narrow flying membrane, fringed with long hairs, 
running from the elbow to the flank, and from the latter to the 
knee. Four mammae. Digits furnished with expanded and striated 
terminal pads, the relative length of those of the manus being in the 
order 4, 3, 5, 2, 1. Claws sharp, although somewhat concealed by 
the terminal pads. Tail short-haired above and below, with a broad 
fringe on either side. Skull short, wide, and depressed. Posterior 
portion of palate very imperfectly ossified ; anterior palatal vacuities 
almost confined to the maxillae. Auditory bullae low, rounded, and 
but slightly prominent. Dentition : i f , c J-, p f, m f . Teeth sharp, 
and of an insectivorous type. Upper canine long, and approximated 
to third incisor. The three upper premolars large, functional, and 
taller than the molars. Molars small and rounded, with smooth 
unridged cusps. 

There is only one species in this genus, the beautiful little 
Pigmy Flying-Phalanger (A. pygmceus), not so big as a Mouse, which 
is found in Queensland, New South Wales, and Victoria, and feeds 
on the honey it abstracts from flowers, and on insects. Its agility 
and powers of leaping are exceedingly great, and it is said by 
Mr. Gould to make a most charming little pet. 

Subfamily Phaseolaretinae. — Teeth large, normal; no rudi- 
mentary premolars before the last upper premolar, or any teeth 

1 Peters, Ann. Mus. Gcnov. vol. vi. p. 303 (1874). 
2 Desmarest, Nouv. Did. d'Hist. Nat. ser. 2, vol. xxv. p. 405 (1817). 



i 5 6 



MARSUPIAL! A 



between the first lower incisor and fourth premolar. Tongue 
of ordinary structure. Distinct cheek -pouches. Stomach with a 
special gland near the cardiac orifice. Caecum very long, and (with 
the upper portion of the colon) dilated and provided with numerous 
longitudinal folds of mucous membrane. In many anatomical 
characters, especially the possession of a special gastric gland, this 
group resembles the Pkascolomyidce. 1 

Phascolarctus. 2 — Dentition: i%, c^,%> \, m±; total 30. Upper 
incisors crowded together, cylindroidal, the first much larger than 
the others, with a bevelled cutting edge (Fig. 36). Canine very 
small ; a considerable interval between it and the premolar, which 
is as long from before backwards but not so broad as the true 
molars, and has a cutting edge, with a smaller parallel inner ridge. 
The molars slightly diminishing in size from the first to the fourth, 
with square crowns, each bearing four pyramidal cusps, with curved 
ridges radiating from them, and having a structure very similar to 
these of Pseudochiriis. The loAver incisors are semiproclivous, com- 



pressed and tapering, bevelled at the ends. Premolars and molars 
in continuous series, as in the upper jaw. Milk-tooth very minute, 
and almost functionless. Fore feet Avith the two inner toes slightly 
separated from and opposable to the remaining three, all with strong, 

curved, and much compressed 
claws. Hind foot (Fig. 49) with 
the hallux placed very far back, 
large and broad, the second and 
third (united) toes considerably 
smaller than the other two ; the 
fourth the largest. Xo external 
tail. Fur dense and woolly. 
Ears of moderate size, thickly 
clothed with long hairs. Verte- 
bras : C 7, D 11, L8, S2, C8. 
Ribs eleven pairs, a rare excep- 
tion to the usual number (13) 
in the Marsupialia. 

There is but one species, 
the Koala or Native Bear of 
the Australian colonists (P. cin- 
' r< us), an animal of compar- 
atively large size and heavy 
build (Fig. 50), found in the 
south-eastern parts of the Aus- 
tralian continent. It is about two feet in length, and of an ash- 
gray colour, an excellent climber, and residing generally in lofty 

1 Cf. W. A. Forbes, "Anatomy of the Koala," Proc. Zool. Soc. 1881, p. 180. 
- Blainville, Bull. Soe. Philom. 1816, p. 116. 




f Fig. 4 1 .'.— Skeleton of right hind foot of Koala 
(I'hascolarctus cinereus), showing the stout op- 
posable hallux, followed by two slender toes, 
which in the living animal are enclosed as far 
as the nails in a common integument. 



l^HALAXGERin.E 



157 



Eucalyptus trees, on the buds and tender shoots of which it feeds, 
though occasionally descending to the ground in the night. 



Extinct Phalangeroids. 

Numerous imperfect remains recently described by De Vis are 
regarded as indicating large extinct types of Phalangeridce, but 
further evidence is required before all these determinations can he 
definitely accepted. Thus part of an upper jaw is provisionally 
referred to a large species of Pseudochirus, while part of a scapula 
is made the type of a genus Archizonums which appears to be 




Fig. 50. — The Koala (Phascolarctus cinereus). From Sclater, Proc. Zool. Soc. 18S0, p. 355. 

allied to the former. Another fragmentary scapula is considered to 
indicate a large Phalanger. Finally, part of a fibula described under 
the name of Koalemus is regarded as affording evidence of the 
former existence of a large ancestral form allied to the Koala, and 
it is suggested that an upper jaw with teeth may belong to the 
same or an allied type. 

Thylacoleo. 1 — Dentition of adult: i -J, c ^, p -|, I m\ m > total 28. 
First upper incisor much larger than the others ; canine and first 
two premolars rudimentary. In the lower jaw the two small 
anterior premolars are functionless, and often deciduous ; posterior 
premolars of both jaws formed on the same type as those of Potorous, 
but relatively much larger ; true molars rudimentary, tubercular. 
One species, T. carnifex. This animal presents a most anomalous 

1 Owen, in Gervais's Zool. et Pal. frangaises, 1st ed. pt. i. p. 192 (1849-52). 



i 5 8 



MARS UP I A LI A 



condition of dentition, the functional teeth being reduced to one 
pair of large cutting incisors situated close to the median line, and 
one great, trenchant, compressed premolar, on each side above and 

below. It was first 
described as a car- 
nivorous Marsupial, 
and named, in ac- 
cordance with its 
presumed habits, 
" as one of the fel- 
lest and most de- 
structive of preda- 
tory beasts " ; but, 
as its affinities are 
certainly with the 
Phalangerida' and 
Macropodidce, and 
its dentition com- 
pletely unlike that 
of any known pre- 
daceous animal, this 
view has been called 
in question. 

The dentition is 
nearer to that of the 
existing Phalangerida than to that of the Macropodidce, and the 
genus may be provisionally regarded as the type of a distinct 
subfamily of the former. 




Pig. 51. — Front view of skull of Thylacoleo carnifex, restored. 
J natural size. From Quart. Journ. Gcol. Soc. vol. xxiv. p. 312. 



Family Macropodid.e. 



Dentition i 



(0-1) 



1' 



P 



2' m i 



Incisors sharp and cutting, 



&> 



those of the lower jaw frequently having a scissor -like action 
against one another ; upper canine, if present, small. Penultimate 
premolar shed with the fourth milk-molar, which is molariform and 
long persistent. Molars wide, and either transversely ridged or 
bluntly tuberculate. Premolars and molars moving forwards in the 
skull as the age of the animal increases, this being most marked in 
the larger species. Masseteric fossa of mandible hollowed out 
below into a deep cavity walled in externally by a plate of bone, 
and communicating with the inferior dental canal by a large 
foramen. Hind limbs usually larger than the anterior ones, and 
progression generally saltatorial. Fore feet with five digits ; hind 
feet syndactylous, the fourth digit being very large and strongly 
clawed ; hallux usually absent. Tail generally long and hairy, 



MACROPODIDjE 



•59 



large 



and 



by peculiarities 

teeth, and other 
that of a sheep 
head, especially 



occasionally prehensile; stomach sacculated. Pouch 
opening forwards. 

The Macrqpodidce or Kangaroos, taken as a whole, form a very 
well-marked family, easily distinguished from the other members of 
the suborder by their general conformation, and 
in the structure of their limbs, 
organs. They vary in size from 
down to a small rabbit. The 
in the larger species, is small, 
compared with the rest of the body, and tapers 
forward to the muzzle. The shoulders and fore 
limbs are feebly developed, and the. hind limbs 
usually of dispi'oportionate strength and magnitude, 
which gives them a peculiarly awkward appearance 
when moving about on all fours, as they occasion- 
ally do when feeding. Rapid progression is, how- 
ever, performed only by the powerful hind limits, 
the animal covering the ground by a series of 
immense bounds, during which the fore part of the 
body is inclined forwards, and balanced by the 
long, strong, and tapering tail, which is carried 
horizontally backwards. When not moving they 
often assume a perfectly upright position, the tail 
aiding the two hind legs to form a sort of support- 
ing tripod, and the front limbs dangling by the 
side of the chest. This position gives full scope 
for the senses of sight, hearing, and smell to warn 
of the approach of enemies, from which these 
animals save themselves by their bounding flight. 
The fore paws have five distinct digits, each armed 



with a strong curved claw. 



Fig. 52. — Skeleton 
of right hind foot of 
Kangaroo. 



The hind foot (Fig. 52), as being a typical 
example of the syndactylous modification, may be 
noticed in some detail. It is extremely long and 
narrow, and (with only one exception) without any 
hallux or great toe. It consists mainly of one very large and strong 
toe, corresponding to the fourth of the human or other typically 
developed foot, ending in a strong, curved, and pointed claw. 
Close to the outer side of this lies a smaller fifth digit, and to the 
inner side two excessively slender toes (the second and third), 
bound together almost to the extremity in a common integument. 
The two little claws of these toes, projecting together from the 
skin, may be of use in scratching and cleaning the fur of the 
animal, but the toes themselves must have cpiite lost all connexion 
with the functions of support or progression. 

The dentition of the Kangaroos, functionally considered, 



i6o 



MARSUPIAL! A 



consists of sharp -edged incisors, most fully developed near the 
median line of the mouth, for the purpose of cropping the various 
kinds of herbage on which they feed, and ridged and tuberculated 
molars for crushing it, there being no tusks or canines for offensive 
or defensive purposes. 

The number of vertebras is — in the cervical region 7, dorsal 13, 
lumbar 6, sacral 2, caudal varying according to the length of the 
tail, but generally from 21 to 25. In the fore limb the clavicle 
and the radius and ulna are well developed, allowing of considerable 
freedom of motion of the hand. The pelvis has large epipubic or 
" marsupial " bones. The femur is short, and the tibia and fibula 




Fig. 53.— The Great Gray Kangaroo (Macropus giganteus). 

are of great length, as is the foot, the whole of which is applied to 
the ground Avhen the animal is at rest in the upright position. 

The stomach is of large size, and very complex, its walls being 
puckered up by longitudinal muscular bands into a great number of 
sacculi, like those of the human colon. The alimentary canal is 
long, and the caecum well developed. All the species have a 
marsupium or pouch formed by a fold of the skin of the abdomen, 
covering the mammary glands with their four nipples. In this 
pouch the young are placed as soon as they are born ; there their 
growth and development proceeds ; and to it they resort tempor- 
arily for the purpose of shelter, concealment, or transport, for some 
time after they are able to run and jump about the ground and 
feed upon the same herbage which forms the nourishment of the 
parent. During the early period of their sojourn in the pouch, 



MACROPOniD.K 161 



i lie blind, naked, helpless young creatures (which in the Gic.it 

Kangaroo (Fig. 53) scarcely exceed an inch in length) are attached 
by their mouths to the nipples of the mother, and are fed by 
milk injected into their stomach by the contraction of the muscle 
covering the mammary gland. 

The Kangaroos are all vegetable feeders, browsing on grass and 
various kinds of herbage, the smaller species also eating roots. 
They are naturally timid, inoffensive creatures; but the larger ones 
when hard pressed will turn and defend themselves, sometimes 
killing a dog by grasping it in their fore paws, and inflicting 
terrible wounds with the sharp claws of their powerful hind legs, 
sustaining themselves meanwhile upon the tail. A few aberrant 
forms are arboreal. The great majority are inhabitants of Australia 
and Tasmania, forming one of the most prominent and characteristic 
features of the fauna of these lands, and in the scenery of the 
country, as well as the economy of nature, performing the part of 
the deer and antelopes of other parts of the world, which are 
entirely wanting in Australia. Kangaroos were very important 
sources of food-supply to the natives, and are hunted by the colon- 
ists, both for sport and with a view to their destruction, on account 
of the damage they naturally do in consuming the grass, now 
required for feeding cattle and sheep. Notwithstanding this, they 
have in some districts increased in numbers, owing to the sup- 
pression of their former enemies, the aborigines and the Dingo or 
native dog. A few species are found in New Guinea and the 
adjacent islands, Avhich belong, in the zoological sense, to the 
Australian region. 

Before noticing the various generic types of the Macropodidce, a 
few words are necessary in respect of the tooth-change, and we may 
here quote the observations of Mr. 0. Thomas on this subject. 
" The full dentition of the members of this family consists, in the 
upper jaw, first of three incisors, then of a small canine (often, 
however, suppressed, as in Fig. 55), and then of six cheek-teeth, 
of which the second in the series is the only one which has a milk 
or deciduous predecessor, and is therefore the one to be regarded 
as the last premolar of the typical mammalian dentition. The 
special characteristics that render the development and succession of 
the teeth in the Macropodidce, and especially in the genus Macropux, 
so puzzling to systematic zoologists, are : firstly, a general pro- 
gression forwards in the jaw of the whole tooth-row, comparable to 
that found elsewhere only in the Elephants and some Sirenians ; 
and, secondly, the fact that before the tooth-change the first tooth 
of the series (p 3) and the single milk-tooth (dm 4) placed next to 
it, both of which fall out at the change, are respectively so very 
similar in shape and size to the first and second teeth of the 
permanent series, viz. the permanent premolar (p 4) and the first 

11 



1 62 MARSUPIALIA 



molar (m 1), as to be most naturally mistaken for, or compared with, 
them in specific descriptions. . . . The necessary knowledge as to 
the stage of dentition in which any skull may be, can often be 
gained only by cutting open the bone either above and behind the 
first tooth of the series to see if the true permanent p 4 be still 
buried there (in which case, of course, that first tooth is only p 3), 
or behind the last visible molar to see if there be yet another tooth 
behind it, showing it to be m 3 and not m 4. The first plan is, 
as a rule, the better, since p 4 is generally by far the most 
important tooth for diagnostic purposes, and its characters have, 
therefore, in any case to be taken into account." 

The Macropodidce are divided into three well-marked sections : 
(1) the true Kangaroos (Macropodince) ; (2) a group consisting of 
smaller animals, commonly called Rat Kangaroos, or (improperly) 
" Kangaroo Rats," or sometimes Potoroos ; and (3) the Hypsipryrrir 
nodontince, now represented only by a single species. 

Subfamily Hypsiprymnodontinse. — Size very small. Claws 
small, feeble, and subequal. Hind feet with an opposable hallux. 
Tail naked and scaly. The fourth premolar twisted obliquely out- 
wards, as in Phalanger. Other teeth as in the Potoroince. 

This subfamily is now represented only by the genus Hypsi- 
prymnodon, 1 which is a form of great interest, as showing a structure 
of foot connecting that of the Kangaroos Avith that of the Phalan- 
gers. The single known species, H. moschatus, was described by 
Ramsay from specimens discovered in north-east Australia. It 
was described almost simultaneously by Owen under the name of 
Pleopus nudicaudatus. From the resemblance in the structure of the 
foot and the obliquity of the premolars to the Phalangers Mr. 
Thomas has some hesitation as to which family should receive this 
genus, but the macropine characters of the mandible preponderate 
in favour of the Maoropodiace. 

Triclis.' 2 — A lower jaw of a much larger form from the Pleisto- 
cene deposits of Australia apparently indicates another member of 
this subfamily, having the outwardly directed and grooved pre- 
molar characteristic of Hypsiprymnodon. It differs, however, from 
that genus, and also from all other known Macropodidce, in having 
a small tooth between the incisor and fourth premolar, which 
apparently represents a canine, or perhaps an anterior premolar. 
This form indicates, therefore, a closer connexion between the 
Phalangeridce and Macropodidce than any other. 

Subfamily Potopoinse. — The second section or subfamily, the 
Potoroinm, have the first upper incisor narrow, curved, and much 
exceeding the others in length (Fig. 54). Upper canines always 
persistent, flattened, blunt, and slightly curved. Premolars of both 

1 Ramsay, Proc. Linn. Soc. K. S. Wales, vol. i. p. 33 (1876). 
2 De Vis, Proc. Roy. Soc. Queensland, ser. 2, vol. iii. p. 8 (1888). 



MACROPODin.E 163 



jaws always having large, simple, compressed crowns, with a nearly 
straight or slightly concave free cutting edge, both outer and inner 
surfaces usually marked by a series of parallel, vertical grooves and 
ridges, these teeth heinir either set in the same line with the 
molars, or slightly bent outwards. Molars with quadrate crowns, 
having a blunt, conical cusp at each corner, the fourth notably 
smaller than the third, sometimes rudimentary, and appearing early. 
Fore feet narrow ; three middle toes considerably exceeding the 
first and fifth in length ; their claws long, compressed, and but 
slightly curved. Hind feet as in Macropus. Tail long and hairy, 
sometimes partially prehensile, being used for carrying bundles of 
grass with which these animals build their nests. 

The Potoroos or Rat Kangaroos are all small animals, none of 
them exceeding a common rabbit in size. They inhabit Australia 
and Tasmania, are nocturnal, and feed on the leaves of various 




m m 1:1 m 

Fig. 54.— Skull and Teeth of Rat Kangaroo (Bettongia lesueuiri). c, Upper canine. 
The other letters as in Fig. 51. 

kinds of grasses and other plants, as well as roots and bulbs, which 
they dig up with their fore paws. Nine species are known, present- 
ing a considerable range of diversity in minor characters, and 
admitting of being grouped in four principal sections, which may 
be allowed the rank of genera. These are : 

Potorous. 1 — Head long and slender. Auditory bullae some- 
what inflated. Eidges on premolars few and perpendicular. 
Large palatine foramina. Tarsus short. Muffle naked. Three 
species, viz. P. tridaetylus, P. gilberti, and P. platyops ; the last two 
being confined to West Australia. 

Bettongia. 7, — Head comparatively short and broad. Ears short 
and rounded. Auditory bullae generally much inflated. Large 
palatine foramina. Tarsus long. Eidges on premolars numerous 

1 Desmarest, Nbuv. Diet. d'Hist. Nat. ser. 1, vol. xxiv. Table Meth. p. 20 
(1804). Syn. Hypsiprymnus, Illiger, Prodromus Syst. Mamm. p. 79 (1811). 
- Gray, Charlesworth's Mag. Nat. Hist. vol. i. i>. 584 (1837). 



1 64 



MARSUP1ALIA 



and oblique. Tail more or less prehensile, thickly haired, and 
the hairs on the upper surface longer than those on the lower, and 
forming a crest. Muffle naked. Four species, viz. B. pcnicillato, 

B. cunicidus, B. gaimardi, B. lesiieuiri. 

Caloprymnus. 1 — Muffle naked, as in Bettongia, but the edge of the 
hairy part less emarginate backwards in the middle line. Ears 
short, rounded, and hairy. Auditory bullae much inflated, and of 
large size. Nasals larger and wider behind than in the other 
genera. Very long anterior palatine foramina. Limbs as in 
Bettongia. Tail thin, cylindrical, evenly coated with short hair, 
without trace of a crest. Skull broad and flat, with a remarkably 
short and conical muzzle. The sole representative of this genus is 

C. campestris of South Australia, originally referred to Bettongia. 




jj m i 



Fig. 55. — Skull and Teeth of the Red-necked Wallaby (Macropus ruficoUis). i 1 , i-, i 3 , First, 
second, and third upper incisors ; pm, fourth or posterior premolar (the penultimate or third 
having been already shed); ml, m 2 , 7)13, m t t the four true molars. The last, not fully de- 
veloped, is nearly concealed by the ascending ramus of the jaw. 

JEpyprymnus.- — Head short and broad. Auditory bullae not 
inflated. No palatine foramina. Tarsus long. Muffle partially 
hairy. Tail evenly hairy, not crested above. Molars oblong, less 
distinctly quadritubercular, and not decreasing so much in size pos- 
teriorly as in the other genera. Represented only by JE. rufescens. 

Remains of JE. rufescens occur in the Pleistocene cave-deposits 
of New South Wales. 

Subfamily Maeropodinae. — This subfamily includes the largest 
forms. The cutting edges of the upper incisors are nearly level, or 
the first pair but slightly longer than the others (Fig. 55). The 
canines are rudimentary and often wanting. The premolars are 
usually not longer (from before backwards) than the true molars 

1 Thomas, Cat. Marsup. Brit. Mas. p. 114 (1888). 
" Garrod, Proc. Zool. Soc. 1875, i». 59. 



MACROPODID.i: 165 



and less compressed than in the last subfamily; they are placed 
in precisely the same line with the molars. The crowns of the 
molars always have two prominent transverse ridges; and these 
teeth increase in size from before backwards, the fourth molar 
appearing very late. The fore limbs are small, with sul)equal toes 
armed with strong, moderately long, curved claws. Hind limbs 
very long and strongly made. Head small, with more or less 
elongated muzzle. Ears generally rather long and ovate. 

Upwards of forty-four existing species of this group have been 
described, and many attempts have been made to subdivide them into 
smaller groups or genera for the convenience of arrangement and 
description, but these have generally been based upon such trivial 
characters that it is preferable to speak of many of them as sections 
of the genus Macropus, reserving generic rank only to forms some- 
what aberrant in structure. According to this arrangement the 
genera Anil be as follows : 

Lagostrophus. 1 — Eepresented only by the Banded Wallaby 
(L. faseiatus) of Western Australia, which presents the following 
distinctive features. Size small. Muffle naked. Hind feet covered 
with long bristly hairs, concealing the claws. Lower part of back 
marked by dark cross-bands. Skull with a narrow pointed muzzle 
and inflated auditory bullae ; symphysis of mandible firmly united. 
No canine. Upper incisive series meeting at a sharp angle, and 
diverging but slightly behind. First incisor smaller in section than 
either of the others and scarcely longer, bluntly pointed ; second 
with a flattened oral surface ; third smaller, similarly flattened, but 
with a groove on oral surface forming a notch at its postero- 
external angle. Fourth premolar short, with a distinct inner ledge. 
Molars as in Macropus. 

Dendrolagus. 2 — General proportions of limbs and body normal 
and unlike those of other members of the family. Muffle broad and 
only partly naked. Fur on nape, and sometimes on back, directed 
forwards. Fore limbs nearly as large as the hind ; hind feet with 
the syndactylous second and third digits relatively large ; claws of 
fourth and fifth hind digits curved like those of the manus. Tail 
very long, and thickly furred. Skull stout, with a short and wide 
muzzle ; the posterior part of the palate fully ossified, and the 
auditory bullae not inflated. A small canine. Fourth premolar 
large, but much shorter antero-posteriorly than in the next genus ; 
molars as in the latter. 

This genus includes four species of Tree-Kangaroos, three of 
which occur in New Guinea, while D. lumholtzi is found in North 
Queensland. They differ greatly from all the other forms in being 
chiefly arboreal in their habits, climbing with facility among the 

1 Thomas, Proc. Zool. Soc. 1886, p. 544. 
2 Schlegel and Miiller, Verh. Nat. Ges. Nederland, p. 138 (1839-44). 



1 66 MARSUPIALIA 



branches of large trees, and feeding on the bark, leaves, and fruit. 
They are confined to the tropical forests of the regions mentioned ; 
and it would appear that we must regard their resemblance in the 
proportions of the limbs and habits to the Phalangers as having 
been independently acquired. 

Dorcopsiz. 1 — Hind limbs relatively less large than in Macropu*. 
Muffle large, broad, and naked. Ears small. Fur on nape directed 
wholly or partially forwards. Hind claws not concealed by hair. 
Tail with a nearly naked tip. Skull long and narrow, with the 
auditory bullae not inflated. A well-developed canine. First upper 
incisor somewhat short ; second and third nearly equal, notched 
externally. Fourth premolar greatly elongated antero-posteriorly, 
its length generally exceeding the united lengths of the first and 
second molars ; a distinct inner ledge, and vertical grooves on both 
sides. Molars low and rounded, with the median longitudinal 
bridge between the ridges almost or quite aborted, and the talon in 
front of the first transverse ridge very narrow, and not extending 
to the inner side. The two series of cheek-teeth parallel, or nearly 
so, instead of converging at the extremities. 

Three species of this genus are known, all of Avhich are from 
New Guinea ; the type being D. muclleri. In the characters of the 
dentition, the forward inclination of the fur on the nape, and other 
points, this genus is allied to Dendrolagus ; but Dorcopsis macleayi 
connects the other species with Mavropus. 

Lagorchestes.' 2 — Muffle entirely or partially covered with hair. 
Fourth hind digit with a long claw, not concealed by hair. Tail 
rather short, evenly furred, without a spur. Skull with short 
muzzle and diastema, and inflated auditory bulla. Canine present, 
sometimes very small. Fourth premolar large, not constricted in 
the middle, with a continuous inner ledge. 

This genus includes the Hare - Kangaroos, a group of small 
hare-like animals, great leapers and swift runners, which mostly 
affect the open grassy ridges, particularly those of a stony character, 
sleeping in forms or seats like the common hare. Their limbs are 
comparatively small, their claws sharp and slender, and their muffle 
is clothed with velvet-like hairs. Three species — M. leporoides, M. 
/nrsutiis, M. conspicillatux. 

The range extends over the whole of Australia, but does not 
embrace Tasmania. 

Onychogale. 3 — Muffle hairy. Fourth hind claw long, narrow, 
compressed, and sharp. Tail long and tapering, covered with short 
hair, and furnished at the tip with a horny spur. Skull nearly as in 
Macropus, with the auditory bullae more or less inflated. Canine 

1 Schlegel and MLiller, Vcrh. Nat. Gcs. Ncderland, p. 130 (1839-44). 

- Gould, Monograph of Macropodid(c,\>\. xiii. (1S41). 

3 Gray, in Greys Australia, vol. ii. appendix, p. 402 (1841). 



MACROPODW.E 167 



small or wanting. Upper incisors small, decreasing in size from first 
to third. Fourth premolar small, hour-glass shaped, and without, 
inner ledge. Molars as in Macropus. 

This genus contains three species, having the same distribution 
as Lagorehesft s. Mr. 0. Thomas observes : " The spur-tailed Wallabies 
form a natural little group, distinguished both by the shape of the 
incisors and the peculiar horny excrescence at the tip of the tail. 
The latter character is altogether unique among Marsupials, and is 
only found among other mammals in the Lion, which occasionally 
has a somewhat similar horny spur at the end of its tail. In the 
case of the Wallabies it is difficult to conceive what can be the 
use of this spur ; and observations on the living animal are much 
needed with regard to this interesting point." 

Petrogale? — Muffle naked. Fur of nape directed backwards. 
Claw of fourth hind digit very short. Tail long, cylindrical, thinner 
than in Macropus, and thickly haired and pencilled at the extremity. 
Sktdl as in the smaller sj)ecies of Macropus, with large posterior 
palatal vacuities, and the bulla? sometimes inflated. No canine. 
Upper incisors small, the third resembling that of Macropus. Fourth 
premolar large and stout, as in some of the Wallabies, with a con- 
tinuous inner ledge, and two or three indistinct vertical ridges 
externally. Molars as in the Wallabies. 

This genus is represented by six species, of which P. penicillata 
is a well-known example, ranging over the whole of the mainland of 
Australia. The Rock- Wallabies, as its members may be called, are 
very closely allied to some of the true Wallabies ; and some hesitation 
may be expressed as to the advisability of accepting their generic 
separation from Macropus. They inhabit rocky regions, making 
their retreats in caverns and crevices, leaping with surprising agility 
from one narrow ledge to another, and browsing upon the scanty 
herbage that the neighbourhood of such situations affords. The 
species are P. mnthopus, P. penicillata, P. lateralis, P. concinna, P. 
brachyotis, P. inornata. 

Remains of P. penicillata are found in a fossil state in the 
Pleistocene cave-deposits of New South Wales. 

Macropus. 2 — Muffle generally completely naked. Ears large. 
Fur on nape (with an occasional exception in two species) directed 
backwards. Claw of fourth hind digit very long. Tail thick, 
tapering, and evenly furred. Four mamma?. Skull (Fig. 55) long, 
smooth, and rounded ; the nasals expanded behind ; generally large 
palatal vacuities ; and the auditory bullae not inflated. Canine 
minute, and shed at an early period. Incisor series forming an 
open curve ; the first the tallest, and the third nearly always the 
longest antero-posteriorly, and generally with an infolding of enamel 

1 Gray, Oharlesworth's Mag. Nat. Hist. vol. i. p. 583 (1837). 
2 Shaw, Naturalist's Miscellany, vol. i. pi. xxxiii. (1790). 



1 68 MARSUPIALIA 



e> 



near its posteroexternal angle. Fourth upper premolar with a 
secant edge, and an inner basal ledge or tubercle ; correspondin 
lower tooth secant ; both may be longer or shorter than first molar 
Molars (except very occasionally) with a distinct longitudinal bridge 
connecting transverse ridges. Lower incisors long and scalpriform, 
with inner secant edges opposable, owing to the loose articulation of 
the mandibular symphysis. 

This genus includes the true Kangaroos and Wallabies, the size 
of the individual existing species varying from that of a Rabbit 
to that of a Man. There are no less than twenty-three existing 
species, which may be divided into three groups, as well as many 
extinct ones. The genus is found in Australia and New Guinea, 
as well as in the eastern half of the Austro-Malayan transitional 
region. 

The first group, or true Kangaroos, comprises the largest 
existing forms, which are generally of a uniform and sombre colour. 

The skull is of a large and massive type, with the palate more 
or less well ossified posteriorly, while the molars frecpiently have 
a median longitudinal bridge connecting the first transverse ridge 
with the anterior talon, and no antero-external bridge between the 
same ridge and talon. The history of the discovery of the typical 
representative of this group, as being of considerable interest, may 
be given at some length. When Captain Cook, during his first 
memorable voyage of discovery, was detained for the purpose of 
refitting his ship at Endeavour river on the north-east coast of 
Australia, a strange-looking animal, entirely unknown to them, was 
frecpiently seen by the ship's company; and it is recorded in the 
annals of the voyage that, on the 14th of July 1770, "Mr. Gore, 
who went out this day with his gun, had the good fortune to kill 
one of the animals which had been so much the subject of our 
speculation, . . . and which is called by the natives kanguroo," a 
name which, though it does not appear to be now known to any of 
the aboriginal tribes of the country, has been adopted for this 
animal in all European languages, with only slight modifications of 
spelling. With the exception of a passing glimpse in the beginning 
of the same century by the Dutch traveller Bruyn of some living 
examples of an allied species, this was the first introduction to the 
civilised world of any member of a group of animals now so 
familiar. The affinities of the species, skins of which were brought 
home by Captain Cook and subsequent voyagers, were recognised 
by Schreber as nearer to the American opossums (then the only 
known Marsupials) than to any other mammals Avith which zoologists 
were acquainted, and consequently it Avas placed by him, in his 
great work on the Mammalia, then in the course of publication, in the 
genus Didel/phys, with gigantea for a specific designation, — the latter 
having been bestowed upon it by Zimmermann under the impression 



MACROPODID.K 169 



that it was a huge species of jerboa. Soon afterwards (1791) Dr. 
Shaw very properly formed a new genus for its reception, which 
he named Macropus, in allusion to the peculiar length of its hind 
foot. By the name thus formed, Macropus giganteus, this kind of 
Kangaroo has ever since been known in zoological literature. It is 
the common Gray Kangaroo, called " boomer," " forrester," or " old 
man" by the colonists, and frequents the open grassy plains of the 
greater part of eastern Australia and Tasmania; a figure being 
given in the woodcut on p. 1G0. The muffle is partly covered 
with hair, and the fourth premolar very short. Several varieties 
are known. 

A sub-group, distinguished from the above by the naked 
muffle, includes some very large and handsome species, which prin- 
cipally dwell in rocky mountain ranges, as 31. rufus, the great Red 
Kangaroo, M. antilopinus, and 31. robustus. The fourth premolar is 
of large or medium size in these forms. Remains of 31. giganteus 
occur fossil in the Pleistocene of Australia, where we also find the 



allied extinct M. titan, which attains somewhat larger dimensions. 
M. robustus also dates from the same geological epoch, where it was 
accompanied by two allied types known as M. alius and 31. cooperi. 

The second group includes the larger Wallabies, which are 
smaller than the true Kangaroos, with a brighter and more 
variegated coloration. The palate is generally more incomplete 
than in the typical group ; and in the molars the anterior talon is 
connected with the first transverse ridge by an external instead of 
a median longitudinal bridge. The members of this group are 
frequenters of forests and dense impenetrable brushes and scrubs, 
and hence are often called Brush Kangaroos, though a native name, 
" Wallaby," is now generally apjilied to them. There are several 
species, of which 31. rvficollis, 31. ualabatus, M. parryi, and 31. agilis 
are the best known. 

.1/. ualabatus and 31. parryi are found fossil in the Pleistocene 
deposits of Australia. In those beds we also meet with remains of 
several very large extinct species, which appear to be allied to those 
Wallabies in which the fourth premolar is large and elongated, all 
of them agreeing with the Wallabies in the absence of the median 
bridge between the first ridge and talon of the molars. These fossil 
forms comprise 31. brehus, in which the skull Avas probably about 
one foot in length, and 31. roxhus, and 31. anak, which were of some- 
what inferior dimensions. In the last-named species the length of 
the fourth upper premolar is equal to that of the first and half of 
the second molar. 1 

The third and last group of the genus includes the small 

1 For the characters of these species and the undermentioned distinct genera, 
see Owen's Extinct Mammals of Australia (1877), and Lydekker's Catalogue of 
Fossil Mammalia in the British Musacn, pt. v. (1887). 



i7o MARSUPIALIA 



Wallabies, which are small and lightly-built animals, in some 
instances not larger than a Rabbit. Their muffles are always naked, 
and in the skull the anterior palatine foramina are small and the 
posterior vacuities very large, while the posterior expansion of the 
nasals is very marked. The third upper incisor is smaller than in 
the last group. This group extends farther into the tropics than 
either of the others, being found in the New Britain and Aru 
islands, as well as in New Guinea. M. brachyurus is remarkable for 
its comparatively short and slender tail and small ears. The earliest 
known species of Kangaroo, referred to before, M. bruni, belongs to 
this section. Several examples Avere seen by Bruyn in 1711 living 
in captivity in the garden of the Dutch governor of Batavia, and 
described and figured in the account of his travels (Eeizen over 
Moskovie, etc.) under the name of "Filander." It was quite lost 
sight of, and its name even transferred by S. Muller to another 
species (Dorcopsis muelleri), until rediscovered in 1865 by Rosenberg, 
who sent a series of specimens to the Leyden Museum from the 
islands of Aru and Great Key, thus determining its true habitat. 
M. thetidis is a well-known Australian representative of this 
group. 

Extinct genera. — In addition to the fossil forms already mentioned 
which can be referred to existing genera, there are others from the 
Australian Pleistocene indicating extinct generic types of Macropod- 
idcB, to which brief reference may now be made. The first of these 
is Sthmurus, 1 represented by a single large species (S. atlas), and 
characterised by the presence of a complete inner lobe to the fourth 
upper premolar, and of an outer one in the opposing lower tooth, 
so that these teeth present a flat and oval grinding surface when 
worn. The median longitudinal bridge connecting the transverse 
ridges of the molars is very imperfect ; and in the upper molars 
there is no bridge between the first ridge and talon. In Procoptodon 2 
the premolars resemble those of Sth&rwrus, but the molars are 
elongated, and usually have their enamel thrown into numerous 
vertical foldings. The most distinctive feature is, however, the 
complete ankylosis of the mandibular symphysis ; the mandibular 
rami being deep, and the diastema in the dental series short. The 
lower incisors are nearly cylindrical, and the palate has large 
vacuities. Three species are known. The largest representation of 
the whole family is the type of the genus Pabrchestes 3 (P. azael), in 
which the length of the skull is estimated at sixteen inches. It is 
distinguished from Procoptodon by the longer mandibular symphysis 
and diastema, and the spatulate lower incisors. The true molars 
have no distinct anterior talon, and are not grooved, while the 
palate was fully ossified. 

1 Owen, Phil. Trans. 1874, p. 264. 
2 Owen, op. cit. p. 788. 3 Owen, op. cit. p. 797. 



EX TIXC T FA Mil IKS 



171 



Extinct Families. 

Hero may be noticed two genera of extinct Marsupials, the remains 
of which have been found in the Pleistocene deposits of Australia, 
which agree with the MacropodidcB and the Phalange/idee in having 
I incisors, those of the lower jaw being very large and proclivous. 
As the whole of their structure, especially that of the hind feet, is 
not yet known, their precise affinities cannot he determined. 

DiprotodonJ 1 — Dentition : i f, c #, p \, m •£- ; total 28. The first 
upper incisor very large and sealpriform (Fig. 56). True molars 
with prominent transverse ridges, as in Macropus, but -wanting 
the longitudinal connecting bridge. Anterior and posterior limbs 
less disproportionate than in the Kangaroos. Humerus elongated, 
and differing from that of nearly all Marsupials in the absence of an 




Fig. 56. — Left lateral aspect of the skull of Diprotodon australis; from the Pleistocene of 
Australia. 7 V, natural size, i, Incisors ; p, premolar ; m, molars. (After Owen.) 

entepicondylar foramen. The palate is fully ossified, and there is 
no pit or perforation in the masseteric fossa of the mandible. I), 
australis is the largest known Marsupial, being fully equal in bulk 
to a Rhinoceros. It may be regarded as the type of a family — 
Diprotodontidce — having affinity on the one hand with the Phalangers 
and on the other with the Kangaroos. 

XutofJir r'ui in.' 1 — Represented by a species of somewhat smaller 
size than the type of Diprotodon, with a shorter skull, in which the 
zygomatic arches are very wide and the nasals curiously expanded 
at their extremities. The mandibular symphysis is ankylosed ; 

1 Owen, in MitchelVs Eastern Australia, 2d ed. vol. ii. p. 362 (1838). 
2 Owen, Cat. Mamm. a ml Arcs, Mas. /,'. Coll. Surgeons, p. 314 (1845). 



172 MARSUPIALIA 



and, as in Diprotodon, there appears to have been no tooth-change. 
The humerus probably referable to Nototheriwm is of a short and 
widely expanded type, with a large entepicondylar foramen, and 
coming nearer to that of the Wombat than to that of any other 
existing form. The Notothcriidre may apparently be regarded as a 
distinct family connecting the Diprotodontidce with the Phasco- 
lomyidce and Phalangeridce. 

Bibliography of Marsupialia. — G. R. "Waterhou.se, Ned. Hist, of the Mammalia, 
vol. i. " Marsupiata," 1846 ; J. Gould, Mammals of Australia, 1863 ; R. Owen, 
article "Marsupialia," in Cyclop, of Anatomy and Physiology, and various 
memoirs "On Extinct Mammals of Australia" in Philosophical Transactions; 
W. H. Flower, "On the Development and Succession of the Teeth in the Mar- 
supialia," Phil. Trans. 1867 ; 0. Thomas, "On the Homologies and Succession 
of the Teeth in the Dasyuridae," Phil. Trans. 1887 ; ami "Catalogue of Mar- 
supialia and Mouotremata in the British Museum," 1888. 



CHAPTEE VII 

THE SUBCLASS EUTHERIA AND THE ORDER EDENTATA 

The whole of the remaining groups of mammals are included in a 
single subclass, known by the names Eutheria, Monodelphia, or 
Placentalia. 1 The one distinctive feature they have in common 
(from which the last-mentioned name is derived) is the presence of 
an allantoic placenta by means of which the foetus is nourished within 
the uterus of the mother. Throughout the entire subclass, as a general 
rule, the urino-genital organs open quite independently of the rectum ; 
the corpus callosum of the brain is well developed ; the mandible does 
not show a marked inflection of its angle ; and distinct epipubic 
bones are not attached to the anterior margin of the pubic symphysis. 
In those cases where there is a heterodont and diphyoclont dentition 
the dental formula can be reduced to some modification of the one 
given on p. 25, there being only one known genus Avhere four 
true molars occur, and even that not invariably. As in the 
Metatheria, the coracoid is reduced to a mere appendage of the 
scapula, and the acetabular cavity of the pelvis is imperforate. 
While the survivors of the other subclasses have probably been 
for a long time in a stationary condition, these have, as there is 
already good evidence to show throughout all the Tertiary 
geological age, and by inference for some time before, been multi- 
plying in numbers and variations of form, and attaining higher 
stages of development and specialisation in various directions. 
They consequently exhibit far greater diversity of external or 
adaptive modification than is met with in either of the other sub- 
classes, — some being fitted to live as exclusively in the water as 
fishes, and others to emulate the aerial flight of birds. 

To facilitate the study of the different component members 
of this large group, it is usual to separate them into certain 

1 The characters of the chief groups of the Eutheria here given are, in some 
measure, a fuller recapitulation of those already detailed in Chapter III., pp. 
83-88. 



174 EUTHERIA 



divisions which are called " orders." In the main zoologists 
are now of accord as to the general number and limits of these 
divisions among the existing forms, but the affinities and relation- 
ships of the orders to one another are far from being understood, and 
there are very many extinct forms already discovered which do not 
fit at all satisfactorily into any of the orders as commonly defined. 

Commencing with the most easily distinguished, we may first 
separate a group called Edentata, composed of several very distinct 
forms, the Sloths, Anteaters, and Armadillos, which under great 
modifications of characters of limbs and digestive organs, as well as 
habits of life, have just enough in common to make it probable that 
they are the very specialised survivors of an ancient group, most 
of the members of which are extinct, although the researches of 
palaeontology have not yet revealed them to us. The characters of 
their cerebral, dental, and in many cases of their reproductive organs 
show an inferior grade of organisation to that of the generality of 
the subclass. The next order, about the limits of which there is no 
difficulty, is the Sirenia, — aquatic vegetable-eating animals, with 
complete absence of hind limbs, and low cerebral organisation, — 
represented in our present state of knowledge by but two existing 
genera, the Dugongs and Manatees, and by a few extinct forms, 
which, though approaching a more generalised mammalian type, 
show no special characters allying them to any of the other orders. 
Another equally well-marked and equally isolated, though far mure 
numerously represented and diversified order, is that of the Cetacea, 
composed of the various forms of Whales, Dolphins, and Porpoises. 
In aquatic habits, external fish-like form, and absence of hind limbs, 
they resemble the last, though in all other characters they are 
as widely removed as are any two orders among the Eutheria. 

All the remaining orders are more nearly allied together, the 
steps by which they have become modified from one general 
type being in most cases not difficult to realise. Their dentition 
especially, however diversified in detail, always responds to the 
formula already alluded to, and, although the existing forms are 
broken up into groups in most cases easy of definition, the discoveries 
already made in palaeontology have in great measure filled up the 
gaps between them. 

Very isolated among existing Eutheria are the two species of 
Elephant constituting the group called Proboscidea. These, however, 
are now known to be the survivors of a large series of similar animals, 
Mammoths, Mastodons, and Dinotheres, which as Ave pass backwards 
in time gradually assume a more ordinary or generalised type ; and 
the interval which was lately supposed to exist between even these 
and the rest of the class is partially bridged over by the discovery 
in American Eocene and early Miocene formations of the gigantic 
Dinocerata, evidently offshoots of the great group of hoofed animals, 



ORDERS 175 



or Ungulate, represented in the actual fauna by the Horses, 
Rhinoceroses, Tapirs, Swine, and Ruminants. Almost as isolated 
a> the Proboscidea anion,-; existing mammals are the few small 
species constituting the family Hyracidce, and in their case palaeon- 
tology affords no help at present, and therefore, pending further dis- 
coveries, it has been thought advisable in most recent systems to 
give them the honour of an order to themselves, under the name of 
Hyracoidea. But the number of extinct forms already known allied 
to the Ungulate, though not coming under the definition of either 
of the two groups (Artiodactyla and Perissodactyla) under which all 
existing species range themselves, is so great that either many new 
orders must be made for their reception or the definition of the old 
order Ungulate so far extended as to receive them all, in which 
case both Proboscidea and Hyracoidea may be included within it. 
Again, the Rodentia or gnawing animals — Rabbits, Rats, Squirrels, 
Porcupines, Beavers, etc. — are, if Ave look only at the present state 
of the class, most isolated. No one can doubt what is meant by a 
Rodent animal, or have any difficulty about defining it clearly, at 
least by its dental characters ; yet our definitions break down before 
the extinct South American Typotkerium, half Rodent and half 
Ungulate, which leads by an easy transition to the still more truly 
Ungulate Toxodon, for the reception of which a distinct order 
(Toxodontia) has been proposed. It has also been suggested that 
the Rodents are connected by some of the extinct Tillodontia (or 
Tseniodontia) with the Edentates. The Insectivora and the 
Carnivora again are at present quite distinct orders, but they merge 
into one another through fossil forms, and are especially connected 
by the large group of primitive Carnivora, so abundantly repre- 
sented in the Eocene deposits both of America and Europe, to which 
Cope has given the name of Creodonta. The Carnivora also appear 
to have been closely connected with the primitive Ungulates as repre- 
sented by the extinct group called Condylarthra. In another 
direction the step from the Insectivores to the Lemurs is not great, 
and in past times the transition was probably complete. The Bats 
or Chiroptera are allied to the Insectivora in all characters except the 
extraordinary modification of their anterior extremities into wings; 
but this, like the want of the hind limbs in the Cetacea and Sirenia, 
makes such a clear distinction between them and all other mammals 
that, in the absence of any knowledge of any completely inter- 
mediate or transitional forms, they can be perfectly separated, and 
constitute as well-defined an order as any in the class. We have, 
however, an inkling of the mode in Avhich the Insectivora were 
modified into Chiroptera shoAvn us by the so-called Flying Lemur 
(Goleopithecus). Finally, Ave have the important and Avell-character- 
ised group called Primates, including all the Monkeys and Man ; 
and the question is not yet solved as to hoAv and through what 



176 EDENTATA 



forms this is linked on to the other groups. It is commonly assumed 
that the Lemurs are nothing more than inferior Primates, but the 
interval between them in the actual fauna of the world is very great, 
and our knowledge of numerous extinct types recently discovered 
in America, said to be intermediate in characters, is not yet 
sufficient to enable us to form a definite opinion upon the subject. 

The Edentata may be taken first as standing in some respects 
apart from all the others ; and the Primates must be placed at the 
head of the series. The position of the others is quite arbitrary, as 
none of the hitherto proposed associations of the orders into larger 
groups stand the test of critical investigation, and palaeontological 
researches have already gone far to show that they are all modifica- 
tions of a common heterodont, diphyodont, pentadactylate form. 



Order Edextata. 

The name assigned to this group (Avhich some zoologists think 
ought rather to be ranked as a subclass 1 than an order) b}^ Cuvier 
is often objected to as inappropriate — for although some of the 
members are edentulous, others have very numerous teeth — and the 
Linnaean name Bruta is occasionally substituted. But that term is 
(piite as objectionable, especially since the group to which Linnaeus 
applied it is by no means equivalent to the order as now understood, 
as the names of the genera contained in it, viz. El&phas, Trickechus, 
Bradypus, Myrmecqphaga, Munis and Dasypus, indicate. It contained, 
in fact, all the animals then known which are comprised in the 
modern groups of Proboscidea, Sirenia and Edentata together with 
the Walrus, one of the Carnivora. If retained at all, it should 
rather belong to the Proboscidea, as Elcphas stands first in the 
list of genera in the Systema Natures. Cuvier's order included the 
Ornithorhynchus and Echidna, the structure of which was then im- 
perfectly known, and which are now by common consent removed 
to an altogether different section of the class ; but otherwise its 
limits are those now adopted. The name Edentata is so generally 
used, and its meaning so well understood, that it would be un- 
desirable to change it now ; in fact similar reasons might be assigned 
for ceasing to use nearly all the other current ordinal designations, 
for it might be equally well objected that all Carnivora are not 
flesheaters, many of the Marsupialia have not pouches, and so 
forth. 

If the teeth are not always absent, they invariably exhibit 
certain imperfections, which are indeed almost the only common 
characters binding together the various extinct and existing members 
of the order. These are — that they are homodont and, with the 

1 The name Paratheria has Wen suggested for this proposed subclass. 



uKXERA L CI I A RA CTERS 



177 



remarkable exceptions of Tatusia and Oryckropus, monophyodont ; 
they are never rooted, but have persistent pulps ; except in some 
fossil forms, they are always deficient in one of the constituents 
which enter into the formation of the complete mammalian 
tooth, the enamel : and, at least among living forms, are never 
present either in the upper or lower jaw in the fore part of 
the month, the situation occupied by the incisors of other 
mammals. 1 

The peculiar nature of the dentition in the aberrant Onjderopus 



will be noticed under the heading of that 



gem 



As a rule, the 




coracoid process of the scapula of the Edentates is more developed 
than in other Eutheria. 

The degree of development of the brain varies considerably in 
the different families, the 
hemispheres being in some 
cases almost or quite smooth 
(Fig. 57), with a small corpus 
callosum, and large anterior 
commissure ; while in other 
instances the hemispheres 
are convoluted, and the 
corpus callosum is larger. 

There is so great a differ- 
ence in structure and habits 
between some of the existing 
animals assigned to this order 
that, beyond the negative 
characters just mentioned, 
there seems little to connect 
them. The Sloths and Anteaters, for instance, in mode of life, 
general conformation of limbs, structure of digestive organs, etc., 
appear at first sight almost as widely separated as any mammals. 
Paleontology has, however, thrown great light upon their relations, 
and proved their real affinities. Perfectly intermediate forms have 
been discovered in the great Ground Sloths of America, which have 
the dentition and general form of the head of the Sloths, combined with 
the limbs and trunk of the Anteaters. It is, indeed, highly probable 
that the existing members of this order are very much differentiated 
representatives of a large group, the greater number of which are 
now extinct, and have become so without ever attaining a high 
grade of organisation. The great diversity of structure in the 
existing families, the high degree of specialisation to which many 
have attained, the paucity of species and even of individuals, their 

1 In some few Armadillos the suture between the premaxilla and maxilla 
passes behind the first upper tooth ; but iu all other known members of the order 
all the teeth are implanted in the maxilla. 

12 



Fig. 57. — Upper surface of the brain of the Broad- 
banded Armadillo (Xenurus nnicinctus). The large 
olfactory lobes are seen at the anterior extremity 
(left of figure) ; the hemispheres have only three 
sulci. (From Garrod, Proc. Zool. Soc. 1S7S, p. 230.) 



178 EDENTATA 



limited area of distribution, and their small size compared with 
known ancestral forms, all show that this is an ancient and a waning 
group, the members of which seem still to hold their own either by 
the remoteness and seclusion of their dwelling-places, by their 
remarkable adaptation of structure to special conditions of life, or 
by aid of the peculiar defensive armature with which they are 
invested. Their former history can, however, only be thus surmised, 
rather than read, at present ; for, though we have ample evidence 
of the abundance and superior magnitude of certain forms in the 
most recent or Pleistocene geological age, yet Ave have at present 
no definite evidence as to their origin, or relationship to other 
orders of mammals. 

The existing members of the order readily group themselves 
into five distinct families, the limits of which are perfectly clear. 
These are (1) Bradypodidce, or Sloths; (2) Myrmecophagidce, or Ant- 
eaters ; (3) Dasypodidce, or Armadillos ; (4) Manidce, Pangolins or 
Scaly Anteaters ; and (5) Orycteropodiclcc, Aard-varks or African 
Anteaters. The geographical distribution of these families coincides 
with their structural distinction, the first three being inhabitants of 
the New and the last two of the Old World. It has been usual to 
arrange these families into two large groups or suborders: (1) the 
Phyllophaga, leaf -eaters, also called Tardigrada, containing the 
Bradypodidoe alone; and (2) the Entomophaga, insect-eaters, or 
Vermilingua, containing all the other families, from which some- 
times the Orycteropodidce are separated as a third suborder under 
the name of Effbdientia, or Tubulidentata. Such an arrangement 
is, however, an artificial one, founded on superficial resemblance. 
The bonds which unite the Manidce to the Myrmecophagidce are 
mainly to be found in the structure of the mouth, especially the 
extensile character of the tongue, the great development of the sub- 
maxillary glands, and the absence of teeth. These characters are 
exactly analogous to those found in the Echidna among Monotremes, 
the Woodpeckers among Birds, and the Chamoeleon among Reptiles, 
— the fact probably being that in countries where Termites and 
similar insects flourish various distinct forms of vertebrates have 
become modified in special relation to this abundance of nutritious 
food, which could only be made available by a peculiar structure of 
the alimentary organs. A close study of the more essential 
portions of the anatomy of these animals l leads to the belief 
that all the American Edentates at present known, however di- 
versified in form and habits, belong to a common stock. Thus the 
Bradypodidce, Megatheriidce, and Myrmecophagidce are certainly allied, 
the modifications seen in the existing families relating only to food 
and manner of life. The ancestral forms may have been omni- 

1 See Flower, "On the Mutual Affinities of the Animals composing the 
Order Edentata," Proceedings of the Zoological Society, 1882, p. 358. 



BRADYPODIDjE 179 



\ Mums, and gradually separated into the purely vegetable and 
purely animal feeders; from the former are developed the modern 
Sloths, from the latter the Anteaters. The Armadillos (Dasypodida ) 
are another modification of the same type, retaining some 
generalised characters, as those of the alimentary organs, but in 
other respects, as in their defensive armature, remarkably special- 
ised. The two Old World families Manidce and Orycteropodidce are 
so essentially distinct, both from the American families and from 
each other, that it may even lie considered doubtful whether they 
are derived from the same primary branch of mammals, or whether 
they may not be offsets of some other branch, the remaining 
members of which have been lost to knowledge. Further remarks on 
this point are recorded under the description of the Orycteropodidce. 1 



Family Bradypodid.e. 

Externally clothed with long, coarse, crisp hair. Head short 
and rounded. External ears inconspicuous. Teeth f in each jaw, 
subcylindrical, of persistent growth, consisting of a central axis of 
vaso-dentine, with a thin investment of hard dentine, and a thick 
outer coating of cement ; without (so far as is yet known) any suc- 
cession. Clavicles present. Fore limbs greatly longer than the 
hind limbs. All the extremities terminating in narrow, curved 
feet ; the digits never exceeding three in number, encased for 
nearly their whole length in a common integument, and armed 
with long strong claws. Tail rudimentary. Stomach complex. No 
caecum. Uterus simple and globular. Placenta deciduate, dome-like, 
composed of an aggregation of numerous discoidal lobes. Strictly 

1 An attempt has been made to represent these views by the following 

classification : 

Order EDENTATA. 

Suborder Pilosa. 
Bradypodidce. 

Megatheriidce. 

My r mccophagidce. 
Suborder Loricata. 

Dasypodidce. 
Suborder Squamata. 

Manidce. 
Suborder Tubulidentata. 

Orycteropodidce. 

It may be objected to this arrangement that the present divergence between 
the Sloths and Anteaters is hardly sufficiently indicated by their association in 
one suborder. — Flower, "On the Arrangement of the Orders and Families of 
Mammals," Proc. Zool. Soc. 1883, p. 178. 



i8o 



EDENTA TA 



arboreal in habits, vegetable feeders, and limited geographically to 
the forest regions of South and Central America. 

The Sloths, as the animals of this family are called on account 
of the habitual sluggishness of their movements, are the most strictly 
arboreal of all mammals, living entirely among the branches of 
trees, usually hanging under them, with their backs downwards 
(Fig. 58), and clinging to them with the simple hookdike organs to 
which the terminations of all their limbs are reduced. When they 
are obliged from any cause to descend to the ground, which they 
rarely, if ever, do voluntarily, their limbs, owing to their unequal - 
length and the peculiar conformation of the feet — which allows 
the animals to rest only on the outer edge — are most inefficient 




Fig. 5S. — Two-toed Sloth (Ch.olce.pus hoffmanni). 

for terrestrial progression, and they crawl along a level surface 
with considerable difficulty. Though generally slow and inactive, 
even when in their natural haunts, Sloths can on occasions travel 
with considerable rapidity along the branches ; and, as they do not 
leap, like most other arboreal creatures, they avail themselves of 
the swaying of the boughs by the wind to pass from tree to tree. 
They feed entirely on leaves and young shoots and fruits, which 
they gather in their mouth, the fore limbs aiding in dragging 
boughs within reach, but not being used like hands, as they are by 
monkeys, squirrels, etc. When sleeping they roll themselves up in 
a ball, and, owing to the dry shaggy character of their hair, are 
very inconspicuous among the mosses and lichens with which the 



JiRADVPODIIh-K 181 



trees of their native forests abound; the concealment thus afforded 
being heightened in some species by the peculiar greenish tint 
of the outer covering — very uncommon in mammals. This is not 
due to the colour of the hair itself, but to the presence upon its 
surface of an alga, the lodgment of which is facilitated by the fluted 
or rough surface of the exterior of the hair, and the growth of which 
i> promoted by the dampness of the atmosphere in the gloomy 
tropical forests, as it soon disappears from the hair of animals kept 
in captivity in England. Sloths are nocturnal, silent, inoffensive, and 
solitary animals, and usually produce but one young at birth. They 
appear to show an almost reptilian tenacity of life, surviving the 
most severe injuries and large doses of poisons, and exhibiting 
longer persistence of irritability of muscular tissue after death than 
other mammals. 

In the Bradypodidce, as well as in the Myrmecophagidce, the 
testes are placed close to each other, tying on the rectum between 
it and the bladder ; the penis is epiite rudimentary, consisting 
of a pair of small corpora cavernosa, not directly attached by their 
crura to the rami of the ischia, and having a glans scarcely larger 
than that of the clitoris of most mammals, and, as in birds and 
reptiles, without any true corpus spongiosum. In the females of 
both families the uterus is simple and globular ; and the vagina, at 
least in the virgin state, is divided into two channels by a strong 
median partition. The deciduate placenta of Cholcepus is composed 
of a number of lobes aggregated into a dome-like mass : and it 
does not appear that the placenta of the Anteaters departs in any 
important characters from this type. According to the late Pro- 
fessor W. K. Parker, the embryos of the Sloths, Anteaters, and 
Pangolins have the stapes of the middle ear in the form of a rod, 
thus showing affinities with a very primitive type of mammalian 
organisation. 

The Sloths Avere all included in the Linnaean genus Bradypus, 
but Illiger very properly separated the species with but two claws 
on the fore feet, under the name of Choice-pus, leaving Bradypus 
for those with three. 

Bradypus. 1 — Three-toed Sloths. Teeth usually f on each side ; 
no tooth projecting greatly beyond the others ; the first in the 
upper jaw much smaller than any of the rest ; the first in the 
lower jaw broad and compressed ; the grinding surfaces of all much 
cupped. Vertebra? : C 9, D and L 20 (of which 15 to 17 bear ribs), 
S 6, Cll. All the known species present the remarkable pecu- 
liarity of possessing nine cervical vertebrae, i.e. nine vertebrae 
in front of the one which bears the first thoracic rib (or first 
rib connected with the sternum, and corresponding in its general 
relations with the first rib of other mammals) ; but the ninth. 
1 Linn. Hyst. Nat. 12tli ed. vol. i. p. 50 (1766). 



182 



EDENTA TA 



and sometimes the eighth, bears a pair of short movable ribs. 
The arms or fore limbs are considerably longer than the hind 
legs. The bones of the fore arm are complete, free, and capable of 
pronation and supination. The hand is long, very narrow, habit- 
ually curved, and terminates in three pointed curved claws, in 
close apposition with each other. The claws are, in fact, incapable of 
being divaricated, so that the hand is reduced to the condition of a 
triple hook, fit only for the function of suspension from the boughs 
of trees. The foot closely resembles the hand in its general struc- 
ture and mode of use ; the sole being habitually turned inwards, so 
that it cannot be applied to the ground in walking. The tongue is 
short and soft, and the stomach large and complex, bearing some 
resemblance to that of the ruminating Ungulates. The windpipe 
or trachea has the remarkable peculiarity among mammals — not 
unfrequent among birds and reptiles — of being folded on itself 
before it reaches "the lungs. The mammae are two, and pectoral in 
position. 

" Ai " is the common name given in books to the Three-toed 
Sloths. They were all comprised by Linnaeus under the species 
Bradypus tridadylus. More recently Dr. Gray described as many 
as eleven species, ranged in two genera, Bradypus and Arctopithecus ; 
but the distinctions which he assigned both to species and genera do 
not bear close examination. Some are covered uniformly with a 
gray or grayish-brown coat ; others have a dark collar of elongated 
hairs around the shoulders (B. torqmtus) ; some have the hair of 
the face very much shorter than that of the rest of the head and 
neck ; and others have a remarkable-looking patch of soft short hair 
on the back between the shoidders, consisting, when best marked, 
of a median stripe of glossy black, bordered on each side by bright 
orange, yellow, or white. There are also structural differences in 
the skulls, as in the amount of inflation of the pterygoid bones, 
which indicate real differences of species ; but the materials in our 
museums are not yet sufficient to correlate these with external 
characters and geographical distribution. The habits of all are 
apparently alike. They are natives of Guiana, Brazil, and Peru, 
and one if not two species (B. infuscatus and B. castanekeps) extend 
north of the Isthmus of Panama as far as Nicaragua. Of the 
former of these Dr. Seeman says that, though generally silent, 
a specimen in captivity uttered a shrill sound like a monkey 
when forcibly pulled away from the tree to which it was 
holding. 

Cholcepus. 1 — Teeth £ ; the most anterior in both jaws separated 

by an interval from the others, very large, caniniform, wearing 

to a sharp, bevelled edge against the opposing tooth, the upper 

shutting in front of the lower when the mouth is closed (Fig. 59), 

1 Illiger, I'rodromus Syst. Mamm. d Actum, p. 108 (1811). 



MEGATHER11P.E 



183 



unlike the true canines of heterodont mammals. Vertebrae: C6 
or 7, l> 23-24, L :?, S 7-8, C4-6. One species (C. didactylus) has 
the ordinary number of vertebrae in the neck; but an otherwise 
closely allied form (C. hoffmanni) has but six. The tail is very 
rudimentary. The hand generally resembles that of Bradypus; but 
there are only two functional digits with claws — those answering 
to the second and third of the typical pentadactylate manus. The 
structure of the hind limb generally resembles that of Bradypus, 
the appellation "two-toed" referring only to the anterior limb, 
for in the foot the 
three middle toes 
are functionally 
developed and of 
nearly equal size. 
C. didactylus, which 
has been longest 
known, is com- 
monly called by 
the native name 
of Unau. It in- 
habits the forests 
of Brazil. G. hoff- 
manni (Fig. 58) 
has a more north- 
ern geographical 
range, extending 
from Ecuador through Panama to Costa Rica. Its voice, which 
is seldom heard, is like the bleat of a sheep, and if the animal is 
seized it snorts violently. Both species are very variable in 
external coloration. 

Nothropus. 1 — The only fossil form which has been referred to 
this family is indicated by a lower jaw, described by Dr. Burmeister, 
from the Pleistocene of Argentina, which appears to have belonged 
to an animal of about double the dimensions of Choloepus didactylus. 
Professor Cope states, however, that this jaw really belongs to a 
Glyptodont ; while it is referred by Dr. Ameghino to the next 
family. 




Fig. 59.— Skull of Two-toed Sloth (ChoUxpus didactylus). 
Proc. Zool. Soc. 1871, p. 432. 



From 



Family Megatheriid^:. 

The members of this family are all extinct. Their characters, 
so far as is known from the well-preserved remains of many species 
found abundantly in deposits of Pleistocene age in both North and 
South America, were intermediate between those of the existing 
Bradypodidce and the Myrmecophagida, combining the head and 
1 Burmeister, Sitzb. Ak. Berlin, vol. xxviii. p. 613 (1882). 



1 84 



EDENTA TA 



dentition of the former with the structure of the vertebral column, 
limbs, and tail of the latter. Almost all the known species are of 
comparatively gigantic size, the smallest, Nothrotherium escrivanense, 
exceeding the largest existing Anteater, and the Megatherium 
being larger than a Rhinoceros. The femur has no third trochanter, 
and the odontoid process of the axis vertebra has a peculiar facet 
on the ventral surface. The dentition is usually £ on each side, as 
in the Sloths, but % in Nothrotherium. 1 This genus, and in a still 
more marked degree Megatherium, diner from all the others in the 
details of the structure of the teeth. They are very deeply 
implanted, of prismatic form (quadrate in transverse section), and 
the component tissues — hard dentine (Fig. 60, d), softer vaso-dentine 




Fig. 60. — Section of upper molar teeth of Megatherium americanum. xj. 
P, pulp-cavity ; the other letters explained in the text. (After Owen.) 

(v), and cement (c) — are so arranged that, as the tooth wears, the 
surface always presents a pair of transverse ridges, thus producing 
a triturating apparatus comparable to the " bilophodont " molar of 
Dinotherium, Tapirus, Manatus, Macrqpus, and others, though pro- 
duced in a different manner. In all the other genera the teeth are 
more or less cylindrical, though sometimes laterally compressed or 
even longitudinally grooved on the sides, and on the grinding 
surface the prominent ridge of hard dentine follows the external 
contour, and is surrounded only by a thin layer of cement, as 
in the existing Sloths. The Ground Sloths, as the members 

1 Lydekker, in Nicholson and Lydekker's Manual of Palaeontology, vol. ii. 
p. 1299 (1889). Originally described under the preoccupied name Ceelodon. 



MEGA THERlin.E 



185 



of this family may be conveniently designated, agree with the 
Sloths and Anteaters, and thereby ditler from all other mammals, 
in that the coracoid process of the scapula and the coracoidal 
border of the same unite over the coraco- scapular notch, 
which is thus converted into a foramen. Large clavicles are 
present. 

Megatherium} — The typical genus Megatherium, as being the 
longest known representative of the family, may be noticed in some 
detail. A nearly complete skeleton, found on the banks of the 
River Luxan, near Buenos Ayres, and sent in 1789 to the Royal 
Museum at [Madrid, long remained the principal if not the only 
source of information with regard to the species to which it belonged, 
and furnished the materials for many descriptions, notably that of 
Cuvier, who determined its affinities with the Sloths. 2 In 1832 an 
important collection of bones of the Megatherium was discovered 
near the Rio Salado, and secured for the Museum of the College 




Fio. 01. — Oral surface of mandible of Megatherium americcmum. 
a, Condyle ; b, masseteric process ; c, angle ; d, symphysis. (After Owen.) 

of Surgeons of England ; and these, with another collection found 
at Luxan in 1837, and now in the British Museum, supplied the 
materials for the complete description of the skeleton published 
by Sir R. Owen in 1861. Other skeletons have subsequently been 
received by several of the Continental museums, as Milan and Paris, 
and also by those in South America ; and consequently our know- 
ledge of the organisation of the Megatherium, so far as it can be 
deduced from the bones and teeth, is as complete as that of any 
other animal, recent or extinct. 

The remains hitherto spoken of are all referred to one species, 
Megatherium americanum of Blumenbach (71/. cuvieri of Desmarest), 
and are all from the newest or Pleistocene geological formations of 
the Argentine Republic and Paraguay, or the lands forming the 

1 Cuvier, Tableau EUm. d'Hist. Nat. des Animaux, p. 146 (1798). 

- An excellent figure of this skeleton, which unfortunately was incorrectly 
articulated, and wanted the greater part of the tail, was published by Pander 
and D' Alton in 1821, and has been frequently reproduced in subsequent 
works. 



i86 



E DENT A TA 



basin of the Eio de la Plata. Dr. Leidy has described, from similar 
formations in Georgia and South Carolina, bones of a closely allied 
species, about one-fourth smaller, which he has named M. mirabile. 
Three other South American species have been described ; but M. 
laurillardi, of Lund, founded upon remains found in Brazil, has 
been made the type of the genus Ocnopus. 

The following description will apply especially to the best-known 
South American form, Megatherium americanum. In size it exceeded 
any existing land animal except the elephant, to which it was 
inferior only in consequence of the comparative shortness of its 
limbs ; for in length and bulk of body it was its equal, if not 




Fig. G2. — Skeleton of Megatherium, from the specimen in the Museum of the Royal College 

of Surgeons. x",V 

superior. The full length of a mounted skeleton (Fig. 62), from 
the fore part of the head to the end of the tail, is 18 feet, of which 
the tail occupies 5 feet. The head, which is small for the size of 
the animal, presents a general resemblance to that of the Sloth ; 
the anterior part of the mouth is, however, more elongated, and the 
jugal bone, though branched posteriorly in the same way as that of 
the Sloth, meets the zygomatic process of the squamosal, thus 
completing the arch. The lower jaw has the middle part of its 
horizontal ramus curiously deepened, so as to admit of im- 
plantation of the very long-rooted teeth, the peculiar structure 
of which has been already described. A skull recently discovered 
shows that, instead of the wide gap between the extremity of 
the nasals and the premaxillse exhibited in Fig. 62, there was 
a prenasal bone, towards which a process extended upwards and 



MEGA THERIIDjE 187 



1 iack wan Is from the extremity of the upper surface of the pre- 
maxilhe. 

The vertebral column consists of seven cervical, sixteen dorsal, 
three lumbar, five sacral, and eighteen caudal vertebrae. The 

spinous processes are much better developed than in the Sloths, 
and are all directed backwards, there being no reversing of the 
inclination near the posterior end of the dorsal series, as in most 
active-bodied mammals. In the lumbar region, the accessory zyga- 
pophyses, rudimentary in Sloths, are fully developed, as in the 
Ant eaters. 

The tail is large, and its basal vertebra? have strong lateral and 
spinous processes and chevron bones, indicating great muscular 
development. The scapula resembles that of the Sloths in the 
union of the acromion with the coracoid, and in the bridging over 
of the supra-scapular notch. The clavicle is complete and very 
huge, much resembling that of man on a large scale. The fore 
limbs are longer than the hind limbs. The humerus has no ent- 
epicondylar foramen. The radius and ulna are both well developed, 
and have a considerable amount of freedom of movement. The 
hand is singularly modified. The pollex is represented only by a 
rudimentary metacarpal, but the next three digits are large, and 
terminate in phalanges adapted for the support of immense claws, 
the middle one being especially large. The outer or fifth digit has 
no claw, and it may be considered as certain that the weight of the 
foot was, in standing and walking, chiefly thrown upon this one, 
which was protected by a callous pad below, as in the existing 
great Anteater, while the other toes were curved inwards towards 
the palm, and only came in contact with the ground by their outer 
surfaces. The mechanical arrangements by which the weight of the 
body was thrown entirely upon the outer side of the foot are very 
curious, and are fully described in Owen's memoir. The pelvis is 
remarkably wide, even more so than that of the Elephant, but it is 
formed on the same principle as in the Sloths. The femur is 
extremely broad and flattened ; the tibia and fibula are short and 
strong, and united together at each end. The hind foot, contrary 
to the usual rule in the Edentata, is even more singularly modified 
than the hand. Thus the ankle-joint is formed upon a peculiar 
plan, quite unlike that of the Sloths, or of any other mammal, except 
the Megatherium's nearest allies ; and the calcaneum projects nearly 
as far backwards as the fore part of the foot does forwards. There 
is no trace of great toe or hallux, or of its corresponding cuneiform 
bone ; the second toe is rudimentary ; while the third has an enor- 
mous ungual phalanx, which, as in those of the hand, is remarkable 
for the immense development of the bony sheath reflected from 
its proximal end around the base of the claw. The two outer toes 
have large and very peculiarly-shaped metatarsals, but only small 



1 88 EDENTATA 



phalanges, and no claws. The creature probably walked upon the 
outer edge of the sole, so that the great falcate claw of the third 
toe did not come into contact with the ground, and so was kept in 
a state of sharpness ready for use. The foot was therefore formed 
upon quite a different principle from that of the Anteaters or 
Sloths, though somewhat like the latter in having two of the toes 
aborted. 

Taking all the various points of its structure together, they 
clearly indicate affinities both with the existing Sloths and with 
the Anteaters, the skull and teeth more resembling those of the 
former, and the vertebral column and limbs the latter. It is also 
not difficult to infer the food and habits of this enormous creature. 
That it was a leaf-eater there can be little doubt ; but the greater 
size and more complex structure of its teeth might have enabled it 
to crush the smaller branches as well as the leaves and succulent 
shoots which form the food of the existing Sloths. It is, however, 
very improbable that it climbed into the branches of the trees like 
its diminutive congeners, and it is far more likely that it obtained 
its subsistence by tearing them down with the great hook-like claws 
of its powerful prehensile fore limbs, being easily enabled to reach 
them by raising itself up upon the massive tripod formed by the 
two hind feet, firmly fixed to the ground by the one huge falcate 
claw, and the stout, muscular tail. The Avhole conformation of 
the hinder part of the animal is strongly suggestive of such an 
action. There can also be little doubt but that all its move- 
ments were as slow and deliberate as those of its modern repre- 
sentatives. 

An idea at one time prevailed that the Megatherium was 
covered externally with a coat of bony armour like that of the 
Armadillos ; but this originated in dermal plates belonging to the 
Glyptodon having been accidentally associated with bones of the 
Megatherium. Similar plates, on a smaller scale, have indeed been 
found in connection with the skeleton of the Mylodon, but never 
yet with the Megatherium, which Ave may therefore imagine with 
a covering of coarse hair like that of its nearest living allies, the 
Sloths and Anteaters. 

Scelidotheriv/m, Mylodon, etc. — Of the more important remaining 
genera of this family a briefer notice will suffice. Scdidotherium (in 
which Platyonyx may be included) comprises several species of 
considerably smaller dimensions than the Megatherium, and is in 
some respects intermediate between that genus and Mylodon. The 
teeth have an oval cross-section, like those of the Sloths, while the 
skull, in which the length of the nasals is subject to great variation 
in the different species, approximates more or less closely to that 
of the Myrmecophagidce. The humerus generally has an ent- 
epieniiilylar foramen ; and the form and relations of the bones of 









MEGA THERIIDAZ 



1S9 




Fig. 63.— Skeleton of Mylodon rolnistvs (Pleistocene, South 
America). From Owen. 



the feet differ considerably from those obtaining in the type genus. 
S. l&ptoc&plmhim, the type of the genus, occurs in Patagonia and 
Argentina but 

other species are 
found in Brazil 
and Chili. The 
genus Mylodon, in 
its widest sense, 
may he taken to 
include a number 
of comparatively 
large Edentates, 
some of which have 
been described 
under the names of 
Grypotherium, Lest- 
odon, and Pseudo- 
lestodon. The teeth 
of the upper jaw 
are generally of an 
oval or subtriangu- 
lar section ; and in 
the more typical forms the first and second teeth are separated 
by a short interval, the former being horizontally worn. In 
other species, however, like M. (Lestodon) armatus, there is a 
considerable space between the first and second teeth, and the 
first is worn obliquely. The skull is exceedingly like that of 
the Sloths in general contour ; and there is not the descending 
process at the angle of the mandible found in Megatherium. 
The humerus has no entepicondylar foramen. The species 
represented in Fig. 63 is from the Pleistocene of South America ; 
but the type of the genus is M. harlani, from beds of corre- 
sponding age in Kentucky. The Patagonian M. {Grypotherium) 
darwini is a remarkable form, characterised by the presence of a 
bony arch connecting the premaxillaB with the nasals, of which, as 
already mentioned, there is an incomplete development in 
Megatherivgn. Megalonyx, from the Pleistocene of Kentucky, differs 
from Mylodon by the long interval between the first and second 
teeth, and also by the presence of an entepicondylar foramen in 
the humerus. NothrotheHum is a smaller form, occurring in the 
deposits of the Brazilian caves, of which the dental features have 
been already mentioned. The osteological characters of these and 
other allied genera have been fully described in the works of 
Cuvier, Owen, Burmeister. Leidy, Ameghino, Gervais, Bernhardt, 
and others. 

Promegathenum. — Two genera from the infra-Pampean beds 



i go EDENTATA 



of Argentina, described as Promcgatlierium and Promylodon, are 
respectively distinguished from Megatherium and Myhdon by 
the presence of bands of enamel on the teeth, which points 
to the descent of the Edentates from mammals with enamelled 
teeth. 

The Tertiary North American forms described as Moropus and 
Morotherium, 1 and originally regarded as Edentates, would appear to 
be aberrant Ungulates. 



Family Myrmecophagid^:. 

Externally clothed with hair. No teeth. Head elongated. 
Mouth tubular, with a small terminal aperture, through which the 
long, vermiform tongue, covered with the viscid secretion of the 
en