J
%r
.
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 
