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 were 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 Palæarctic and

Ethiopian forms, with 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 _Antilope_ (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 Palæarctic Red Deer belongs. True Chevrotains

(_Tragulus_) 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 only

by a single species in the desert area of the Indian sub-region, while

the two species of _Rhinoceros_ differ 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

Palæarctic. Civets are abundant, comprising some peculiar genera, of

which it will suffice to mention the well known _Paradoxurus_. Wolves

closely allied to the Palæarctic 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 Palæarctic region.

The striped Hyæna 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 _Muridæ_

and _Sciuridæ_. In the former family we have numbers of true Mice

(_Mus_), and also the peculiar genus _Nesocia_ (Bandicoot-Rat), while in

the latter both the true Squirrels (_Sciurus_) and the Flying-Squirrels

(_Pteromys_) attain great development. The genus (_Pteromys_) is, indeed,

mainly characteristic of this region, although in Kashmir and Japan it

enters the Palæarctic. The Bats are very numerous, being represented

by all the families, with the exception of the _Phyllostomatidæ_, or

Vampyres, of South America. Among the Insectivora the genera _Tupaia_ and

_Galeopithecus_ (Flying Lemur) are peculiar to this region, although not

found in India. Finally, in the Primates we have the genera _Macacus_

and _Semnopithecus_ very abundantly represented, although both also

enter the Palæarctic region; but the Anthropoid types are confined to

the south-eastern half of the region, and include the Orangs (_Simia_)

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.

_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 we 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 (_Muridæ_), 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 Opossums (_Didelphyidæ_), 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_.

_Nearctic 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 Palæarctic 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 we have, in addition to

the forms already mentioned, one species of the Palæarctic genus _Ovis_,

namely the Bighorn, and the Prong-buck (_Antilocapra_), which is quite

peculiar. There are, however, no Perissodactyla. The Raccoons and Coatis

(_Procyonidæ_) constitute a family represented out of the New World

only by the aberrant Cat-Bear (_Ælurus_) of Nipal. The characteristic

American feline known 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 extremely numerous, and comprise several

characteristic types, which alone would tell us what part of the globe we

were visiting. The most distinctive are the Pouched Rats (_Geomyidæ_),

and the Beaver-like rodents known as the _Haplodontidæ_. 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 _Cricetus_, although often

separated as _Hesperomys_. This feature alone would seem to justify the

distinction of the Nearctic from the Palæarctic 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 (_Taxidea_). 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 Perissodactyles except Tapirs. Deer are, however,

represented, although by peculiar forms (_Cariacus_) unknown beyond

the New World. The Peccaries (_Dicotyles_), which 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

Palæarctic Camels. The Carnivora include several Cats (_Felis_), among

which the Puma and the Jaguar are the most noticeable; and there are

also Raccoons, Coatis, Foxes, and one species of Bear. Insectivora are

totally wanting; but the Bats are characterised by the presence of

the Vampyres (_Phyllostomatidæ_), which are almost restricted to this

region. The Rodents likewise include three families unknown elsewhere,

namely the Chinchillas and Viscacha (_Chinchillidæ_), the Agouties

(_Dasyproctidæ_), and the Cavies (_Caviidæ_); while a large number of the

_Octodontidæ_ 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 _Cebidæ_ or Prehensile-tailed

Monkeys, and the _Hapalidæ_, or Marmosets, 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 _Bradypodidæ_ or Sloths, which solely inhabit the

forest region; the _Myrmecophagidæ_ or Anteaters; and the _Dasypodidæ_

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 _Didelphys_. 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 obtaining 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 characters upon which specific determination

can be based that the opposite view is gaining ground; and, since some

species are undoubtedly 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 (_Physeter macrocephalus_)

is known to be almost cosmopolitan, inhabiting or passing through all

the tropical and temperate seas, although not found near either pole.

At least three of the well-known species of Rorqual (_Balænoptera_) 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 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 delphis_) and the so-called _D. bairdi_

of the North Pacific and _D. forsteri_ of the Australian seas. The

Pilot Whale (_Globicephalus melas_) and the _Pseudorca_ 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 (_Balæna_)

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. japonica_), 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 distribution,

others are certainly restricted; thus the Arctic Right Whale (_Balæna

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

Hyperoödon 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 (_Neobalæna

marginata_) has only been met with hitherto in the seas round Australia

and New Zealand; and a large Ziphioid (_Berardius arnouxi_) only near the

last-named islands.

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 supposed _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 existing 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 Dugong (_Halicore_) is distributed

in different colonies, at present isolated, throughout the Indian Ocean

from Arabia to North Australia. The _Rhytina_ 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 quite distinct. In fact, the only

known exception is the case of a colony of the Sea-Elephant (_Macrorhinus

leoninus_), 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. PALÆOZOIC 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. Archæan—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 satisfactory conclusion as to the

absolute length of time indicated by 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 Palæozoic.

_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 Polecat 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

complete limb.[29] 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 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.[30]

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 show that the owners of this form of

dentition cannot be included in that group.

[Illustration: FIG. 24.—Frontal and oral aspects of the cranium of

_Tritylodon longævus_; from the Karoo system of Basuto-land, South

Africa. ⅔ natural size. (After Owen.)]

_Multituberculata._—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 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 premolars (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 which these teeth are known, while

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 _Macropodidæ_ 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,

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 Multituberculata 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 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.

[Illustration: FIG. 25.—The right ramus of the mandible of _Plagiaulax

beklesi_; from the Purbeck of Swanage. Twice natural size. _i_, Incisor;

_m_, molar; _b_, coronoid process; _c_, condyle. (After Owen.)]

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

_Bolodon_, closely allied to which is _Allodon_ of the Upper Jurassic of

the United States.

[Illustration: FIG. 26.—The imperfect right ramus of the mandible

of _Plagiaulax minor_; from Swanage. Four times natural size. _p_,

Premolars; _m_, molars. (After Lyall.)]

The first discovery of the remains of Mesozoic mammals was made in the

Keuper or Upper Trias of the Rhætian 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 unrecognisable 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_. Subsequently Mr. C. Moore discovered in a bone bed of Rhætic

(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 _Hypsiprymnopsis rhæticus_, Professor Boyd Dawkins described a single

tooth with two roots discovered in the Rhætic 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.

[Illustration: FIG. 27.—_Stereognathus oölithicus_. Fragment of jaw with

three teeth (_a_, _b_, _c_), in matrix; from the Stonesfield Slate.

Natural size. (After Owen.)]

_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 _Macropodidæ_, although

readily 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 organisation 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.[31]

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

Jurassic of North America; and the _Plagiaulacidæ_ also persisted

into the lower part of the Eocene division of the Tertiary period;

_Neoplagiaulax_ being a Tertiary form common to Europe and the United

States, while _Liotomus_ and _Ptilodus_ are at present known only from

the latter country.

The present group is also represented in the upper Cretaceous of the

United States by _Selenacodon_ (_Meniscoëssus_ 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.

_Polyprotodont 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 reaching in some cases to seven or eight. There

has been much discussion 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. 31. 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_.

[Illustration: FIG. 28.—Reversed view of the left ramus of the mandible

of _Triconodon mordax_; from the Purbeck of Swanage. Natural size. (After

Owen.)]

A common form in the Purbeck of Dorsetshire is _Triconodon_

(_Triacanthodon_), 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 consist of three

flattened cones placed in the same antero-posterior line, those of

the upper and lower jaw being alike. _Priacodon_, of the Jurassic of

the United States, is probably inseparable from _Triconodon_. In the

genus _Phascolotherium_ (Fig. 29) of the Lower Jurassic Stonesfield

Slate, the lower teeth may be classified as _i_ 4, _c_ 1, _p_ 3, _m_

4, the premolars and molars being 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 _Phascolotherium_ is remarkable for the extremely low

position of its articular condyle. In _Amphilestes_ (Fig. 30) of the

Stonesfield 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

Opossums and Bandicoots. The number of lower teeth in _Amblotherium_ is

_i_ 4, _c_ 1, _p_ 4, _m_ 7-8. Numerous allied types, such as _Achyrodon_

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 _Stylacodon_ have been formed upon

specimens showing the opposite side to that which is exposed in the

types of _Amblotherium_ and _Amphitherium_. The only parallel among

existing forms to the excessive number of molar teeth found in these

Mesozoic genera occurs in the Marsupial 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 common 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).

[Illustration: FIG. 29.—Inner view of the right ramus of the mandible

of _Phascolotherium bucklandi_; from the Stonesfield 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.)]

[Illustration: FIG. 30.—Reversed inner view of the left ramus of the

mandible of _Amphilestes broderipi_; from the Stonesfield Slate. Twice

natural size. The restoration of the anterior teeth is conjectural, and

the condyle is placed too high. (After Owen.)]

The last type of molar dentition occurring among the Mesozoic

Mammalia is that found in the lower jaws (Fig. 31), upon which the

genus _Spalacotherium_ was established, the upper jaws, described as

_Peralestes_, being apparently referable to the same animal. Upper

and lower teeth of this form are represented in 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_ 10, by which it is widely distinguished

from all the Insectivora. _Menacodon_, of the Upper Jurassic of the

United States, appears to be allied to _Spalacotherium_.

[Illustration: FIG. 31.—Part of the left ramus of the mandible, viewed

from the outer side, of _Spalacotherium tricuspidens_; from the Purbeck

of Swanage. Twice natural size. (After Owen.)]

_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 chapter. 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 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

pentadactylism 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 generalised 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 pentadactylism 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 Rhinoceroses 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 peculiarity 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.

CHAPTER 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 be 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 _Ornithorhynchidæ_ and the _Echidnidæ_,

both restricted 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 development, the malleus

being very large, the incus small, and the stapes columelliform. The

coracoid bone is complete, and articulates with the sternum, and there

is a pre-coracoid (epi-coracoid) 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

deferentia open into the cloaca, not into a distinct urethral passage.

The penis, attached to the ventral wall 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 Professor 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 connected 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 vertebræ are nineteen in number, and have no terminal

epiphyses to their bodies. The transverse processes of the cervical

vertebræ 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, 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 vertebræ 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 walls

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 fossæ. 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 _Ornithorhynchus_, but this disappears when the animal becomes

adult.) The stomach is subglobular and simple; the alimentary canal

has no ileo-cæcal valve, or marked distinction between large and small

intestine, but has a small, slender vermiform cæcum 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 pre-coracoid 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_ ORNITHORHYNCHIDÆ.

_Ornithorhynchus._[32]—Cerebral hemispheres smooth. Premaxillæ and

mandible expanded anteriorly and supporting a horny beak 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. Vertebræ: C 7, D 17, L 2, S 2,

Ca 21. Acetabulum not perforated. Tongue not extensile. Mucous membrane

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

_Naturalist’s Miscellany_ (vol. x., 1799). In the following year it was

independently described by Blumenbach (_Voigts Magazin_, ii. p. 205)

under the name of _Ornithorhynchus 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. _Ornithorhynchus_ is therefore now universally adopted as the

scientific 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 Reptilia. 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 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.

[Illustration: FIG. 32.—Platypus or Duck-bill (_Ornithorhynchus

anatinus_). From Gould’s _Mammals of Australia_.]

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, 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, 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[33] announced the discovery in an embryo of teeth which were

regarded as quite functionless. In the following year, however, Mr. O.

Thomas[34] 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 those 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 corresponding 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 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, we 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

five 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 somewhat 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 improbable 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 disappears 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, 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 swallowing 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_ ECHIDNIDÆ.

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 below the extremity of the rostrum.

No teeth or laterally placed horny 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

_Ornithorhynchus_. 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 _Ornithorhynchidæ_. According

to Mr. O. Thomas, all the living forms may be included in two species,

which, with some hesitation, are referred to two genera—_Echidna_ and

_Proechidna_ (_Acanthoglossus_).

_Echidna._[35]—In _Echidna_ there are five toes, all of which are

provided with claws, those of the fore foot 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

vertebræ is C 7, D 16, L 3, S 3, Ca 12. The one existing representative

of the genus (_E. aculeata_) occurs in New 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 concealing the

hair. The colour of these spines varies from yellow 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 skull 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

in the mountains. In a wild state they live mainly on ants. Specimens

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 daytime 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 forwards. 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.

[Illustration: FIG. 33.—The Three-toed Echidna (_Proechidna bruijnii_).

From Gervais.]

_Proechidna._[36]—The one known representative of the genus _Proechidna_

(Fig. 33) attains dimensions about equal to those of 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 vertebræ 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.

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 Pleistocene age. This species was

named _Echidna oweni_ by the late Mr. Krefft, 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_.

CHAPTER 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 Prototheria 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,[37]

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 development. 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 transferred

to the nipple of the mother, to which they remain firmly attached for

a considerable time, nourished by the milk injected into the mouth by

compression of the muscle covering the mammary gland. They are therefore

the most typically mammalian of the whole class. The nipples are nearly

always concealed in a fold of the abdominal integument or “pouch”

(marsupium) 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.

[Illustration: FIG. 34.—Teeth of upper jaw of Opossum (_Didelphys

marsupialis_), all of which are unchanged, except the last premolar, the

place of which is occupied in the young animal by a molariform tooth,

represented in the figure below the line of the other teeth.]

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 Eutheria. In some cases

(as in _Potorous_) this tooth retains its place and function until the

animal has nearly, if not quite, attained 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 of the other teeth have

cut the gum, and therefore quite functionless. 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 vertebræ 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

basihyal, broad ceratohyals, with the remainder of the anterior arch

usually unossified, and stout, somewhat compressed thyrohyals. There

are two anterior venæ cavæ,[38] 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 fæces, 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 mammæ 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 independently

of the mouth and gullet, thus averting the danger of suffocation while

the milk is passing down the latter passage.

[Illustration: FIG. 35.—Front view of skull of _Sarcophilus ursinus_,

showing polyprotodont and carnivorous dentition (_Quart. Journ. Geol.

Soc._ vol xxiv. p. 313).]

_Distribution._—The existing species of Marsupials are, with the

exception of one family (the _Didelphyidæ_), limited in geographical

distribution to the Australasian region,[39] forming the chief mammalian

fauna of Australia, New Guinea, and some of the adjacent islands. The

_Didelphyidæ_ are almost purely Neotropical, one or two species ranging

northwards into the Nearctic region. Fossil remains of members of this

family have also been found in Europe and America in strata of the Eocene

and early Miocene periods; and it is probable that at least many of the

polyprotodont Mesozoic mammals noticed in Chapter IV. are referable to

the Marsupialia.

[Illustration: FIG. 36.—Front view of skull of Koala (_Phascolarctus

cinereus_), showing diprotodont and herbivorous dentition (_Quart. Journ.

Geol. Soc._ vol. xxiv. p. 313).]

_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 and arrangement of the teeth. 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, including

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

_Peramelidæ_ in the former, as well as in the latter; but if Mr. O.

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_ MARSUPIALIA.

_A._ POLYPROTODONTIA.—Incisors numerous, small, subequal. Canines larger

than the incisors. Molars with sharp cusps.

α. Incisors ⁵⁄₄. Hind feet with the four outer toes subequal,

distinct, and a well-developed opposable hallux. _Didelphyidæ._

β. Incisors ⁴⁄₃. Hind feet with four outer toes distinct.

Hallux small or rudimentary, rarely opposable. _Dasyuridæ._

γ. Incisors ⁴⁻⁵⁄₃. 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). _Peramelidæ._

_B._ DIPROTODONTIA.—Incisors not exceeding ³⁄₃, usually ³⁄₁ but

occasionally ¹⁄₁. 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.

α. Teeth with persistent pulps. Incisors ¹⁄₁, large,

scalpriform, with enamel on the outer surface only. No

canines. Hind feet with four subequal outer toes, partially

syndactylous, and with rudimentary hallux. _Phascolomyidæ._

β. Teeth rooted. Three upper incisors and a canine. Hind

limbs not disproportionately large. Feet syndactylous, broad,

with four subequal outer toes, and a large opposable hallux.

_Phalangeridæ._

γ. Teeth rooted. Three upper incisors, and frequently a canine.

Hind limbs disproportionately large, with syndactylous feet as

in _Peramelidæ_. _Macropodidæ._

_Suborder_ POLYPROTODONTIA.

The leading 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_ DIDELPHYIDÆ.

Dentition: _i_ ⁵⁄₄, _c_ ¹⁄₁, _p_ ³⁄₃, _m_ ⁴⁄₄; total 50. Incisors very

small and pointed. Canines large. Premolars with 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 extremity, without a nail. Tail generally

long, partially naked and prehensile. Stomach simple. Cæcum of small

or moderate size. Pouch generally absent, sometimes represented by two

lateral folds of the abdominal integument, partially covering the teats,

rarely complete. Vertebræ: C 7, D 13, L 6, S 2, C 19-35.

[Illustration: FIG. 37.—Skeleton of the right hind foot of the Virginian

Opossum (_Didelphys marsupialis_).]

The _Didelphyidæ_, or true Opossums, 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 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._[40]—The family comprises two genera only, namely

_Didelphys_, containing all the species, with the exception of

the curious Yapock, which forms by itself the genus _Chironectes_

and is distinguished 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._[41]—The type genus _Didelphys_ is a very large one,

containing, according to Mr. O. Thomas, twenty-three existing species.

It may be divided into five groups, or subgenera, all of which have

received distinct names. The typical group is represented only by the

common or Virginian Opossum (_D. marsupialis_), 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 themselves.

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 fourth

or _Micoureine_ 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 bright red 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-prehensile 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 down its

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

[Illustration: FIG. 38.—The Woolly Opossum (_Didelphys lanigera_).]

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 _Didelphys_, 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 _Didelphys_. Allied forms

occur in the Tertiaries of North America, which were originally described

under the name of _Herpetotherium_, but have been subsequently referred

to _Peratherium_. Remains of many of the existing species of Opossum are

found in a fossil condition in the Pleistocene cave-deposits of Brazil.

_Family_ DASYURIDÆ

Dentition: _i_ ⁴⁄₃, _c_ ¹⁄₁, _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 cæcum. Predatory

carnivorous or insectivorous animals, inhabitants 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 from all the others as to render a division

into two subfamilies necessary.

[Illustration: FIG. 39.—The Thylacine (_Thylacinus cynocephalus_).]

Subfamily =Dasyurinæ=.—This comprises the more typical _Dasyuridæ_, 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._[42]—Dentition: _i_ ⁴⁄₃, _c_ ¹⁄₁, _p_ ³⁄₃, _m_ ⁴⁄₄ = 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 resembling those of

_Dasyurus_, 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 hair. Hallux (including the metacarpal bone) wanting. Vertebræ:

C 7, D 13, 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 predaceous

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 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, “Hyæna.” 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

mammæ. The figure of the skull exhibits the peculiar Dog-like form so

characteristic of the genus.

[Illustration: FIG. 40.—Right lateral aspect of the skull of the

Thylacine.]

_Sarcophilus._[43]—Dentition: _i_ ⁴⁄₃, _c_ ¹⁄₁, _p_ ²⁄₂, _m_ ⁴⁄₄.

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;

head disproportionately large for the body; muzzle short 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 destructive 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._[44]—Dentition: _i_ ⁴⁄₃, _c_ ¹⁄₁, _p_ ²⁄₂, _m_ ⁴⁄₄; total

42. Upper incisors nearly equal, and placed vertically; first slightly

longer, narrower, and separated from the rest. Lower incisors sloping

forwards and upwards. Canines large and sharply pointed. Premolars 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. Vertebræ: 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 numerous, and include _D. maculatus_, about the size

of a common Cat, inhabiting Tasmania and the southern part of Australia;

_D. viverrinus_, Tasmania and Victoria; _D. geoffroyi_, nearly all

Australia; _D. hallucatus_, North Australia; _D. albopunctatus_, New

Guinea.

Remains referred to _D. viverrinus_ occur in the Australian Pleistocene

deposits.

_Phascologale._[45]—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 premolar—the dentition being _i_

⁴⁄₃, _c_ ¹⁄₁, _p_ ³⁄₃, _m_ ⁴⁄₄; 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. Mammæ

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 ornamented

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 interesting transition

in dentition towards _Dasyurus_. It constitutes the genus _Chætocercus_

of Krefft, but is included by Mr. O. 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._[46]—The genus _Sminthopsis_ 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._[47]—The last genus of the _Dasyurinæ_ 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 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 bullæ 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 =Myrmecobiinæ=.—Molars and premolars exceeding the normal

number of seven on each side. Tongue, long cylindrical, and extensile.

[Illustration: FIG. 41.—_Myrmecobius fasciatus._ From Gould.]

_Myrmecobius._[48]—Dentition: _i_ ⁴⁄₃, _c_ ¹⁄₁, _p_ ³⁄₃, _m_ ⁵⁄₅ or

⁶⁄₆; total 52 or 56, 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 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. Vertebræ: 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 English 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 prevailing 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 (see

p. 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_ PERAMELIDÆ.

Dentition: _i_ ⁴⁻⁵⁄₃, _c_ ¹⁄₁, _p_ ³⁄₃, _m_ ⁴⁄₄; total 46 or 48. Upper

incisors small, with short broad crowns. Lower incisors moderate, narrow,

proclivous. Canines well developed. Premolars compressed, pointed. Molars

with quadrate tuberculated crowns. Fourth premolar 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 rudimentary. 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 extremities (as in _Manis_

among the Edentata, but in no other Marsupials). Head elongated. Muzzle

long, narrow, and pointed. Stomach simple. Cæcum of moderate size.

Pouch complete, opening backwards. Alone among Marsupials they have no

clavicles.

The _Peramelidæ_ form a very distinct family, in some respects

intermediate between the sarcophagous _Dasyuridæ_ and the phytophagous

_Macropodidæ_. 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 of

fossorial habits, and subsist either on an insectivorous or omnivorous

diet. It has been generally considered that their syndactylous 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 _Dasyuridæ_. 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 Polyprotodont forms. They may be divided into three genera.

[Illustration: FIG. 42.—_Perameles gunni._ From Gould.]

_Perameles._[49]—Anterior and posterior extremities not differing greatly

in development. Fore feet with the three middle toes well 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. Vertebræ; 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 hollow

places. They are 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 Aru, Kei, and New Ireland. The best known are—_P.

gunni_ (Fig. 42), _bougainvillei_, _nasuta_, _obesula_, and _macrura_

from Australia, and _P. doreyana_, _raffrayana_, and _longicaudata_ from

New Guinea.

Remains apparently referable to existing species are found in the

cave-deposits of New South Wales.

_Peragale._[50]—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.

Vertebræ: 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.

[Illustration: FIG. 43.—Skeleton of right hind foot of _Chœropus

castanotis_. _c_, Calcaneum; _a_, astragalus; _cb_, cuboid; _n_,

navicular; _c³_, ectocuneiform; II and III, the conjoined second and

third digits; IV, the large and only functional digit; V, the rudimentary

fifth digit.]

_Chœropus._[51]—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 rudimentary 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 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.

Vertebræ: 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 Rat, found in the interior of the Australian continent. Its general

habits and food appear to resemble those of the other _Peramelidæ_.

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_ PHASCOLOMYIDÆ.

Dentition: _c_ ¹⁄₁, _i_ ⁰⁄₀, _p_ ¹⁄₁, _m_ ⁴⁄₄ = 24. All the teeth with

persistent pulps. The incisors large, scalpriform, with enamel only

on the front surface, as in the Rodentia. The molars strongly curved,

forming from the base to the summit about a quarter of a circle, the

concavity being directed outwards in the upper and inwards in the

lower teeth. The first of the series, or premolar, appears to have no

milk-predecessor, and is single-lobed; the other four composed of two

lobes, each subtriangular in section. Limbs equal, stout, 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

with 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. Cæcum very short, wide, and with

a peculiar vermiform appendage. Pouch present. The auditory bullæ of

the skull are imperfect, open behind, with their anterior wall formed

by a descending process of the squamosal, instead of the alisphenoid.

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

[Illustration: FIG. 44.—_Chœropus castanotis._ From Gould.]

_Phascolomys._[52]—The existing Wombats (Fig. 45) comprise three

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. Postorbital process of the

frontal bone obsolete. Ribs fifteen pairs. Vertebræ: C 7, D 15, L 4, S

4, C 10-12. The Wombat of Tasmania 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.

[Illustration: FIG. 45.—Common Wombat (_Phascolomys ursinus_).]

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. Vertebræ: 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._[53]—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 upon

the evidence of which the presumed genus _Sceparnodon_ was founded, are

likewise referable to the same form. The characters of both the upper and

lower incisors distinguish _Phascolonus_ from _Phascolomys_.

_Family_ PHALANGERIDÆ.

Dentition extremely variable, 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 individual; exclusive, however, of _Tarsipes_,

the formula _i_ ³⁄₁, _c_ ¹⁄₀, _p_ ²⁻³⁄₀₋₂, _m_ ³⁻⁴⁄₃₋₄ represents

fairly the general condition of the functional teeth. First incisors

long and stout; the lower pair very large and pointed, but without the

scissor-like action found in the existing _Macropodidæ_; 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. Cæcum 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, powerful, and

often prehensile tails, large claws, and, as in the American opossums,

with 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 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 _Dasyuridæ_ among the

Polyprotodonts as presenting, on the whole, the most generalised types of

the suborder. The existing forms may be divided into three subfamilies.

Subfamily =Tarsipedinæ=.—Cheek-teeth almost rudimentary and variable in

number. Tongue long, slender, pointed, and very extensile. Tail long.

Cæcum absent.

[Illustration: FIG. 46.—_Tarsipes rostratus._ From Gould.]

_Tarsipes._[54]—So named from some supposed resemblance of its foot to

that of the Lemurine genus _Tarsius_; 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 and slender muzzle.

Mouth-opening small. The two lower incisors are long, very slender,

sharp-pointed, and horizontally placed. All the 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_ ²⁄₁,

_c_ ¹⁄₀, _p_ and _m_ ³⁄₂ on one side, and ⁴⁄₃ on the other; total 20.

Rami of the mandible extremely slender, nearly straight, and without

coronoid process or inflected angle. Fore feet with five well-developed

toes, furnished with small, flat, scale-like nails, not reaching to the

extremity of the digits. Hind feet rather long and slender compared

with those of the _Phalangerinæ_, having 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. Vertebræ: 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

_Melaleucæ_, etc. One kept in confinement by Mr. Gould was also observed

to eat flies.

Subfamily =Phalangerinæ=.—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. Cæcum 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._[55]—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

subequal, 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

mammæ. Skull (Fig. 47) stout and strong, with large vacuities in the

hinder half of the palate, and the auditory bullæ thick and inflated.

Dentition usually _i_ ³⁄₂, _c_ ¹⁄₀, _p_ ³⁄₃, _m_ ⁴⁄₄. First upper incisor

with nearly circular section, or only slightly flattened in front; canine

more or less closely approximated to third incisor (which is very small),

and situated partly in front of the suture between the premaxilla 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.

[Illustration: FIG. 47.—Left lateral view of skull of Gray Cuscus

(_Phalanger orientalis_). After Peters.]

The Cuscuses are curious sleepy-looking 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 Phalangers, except that they are

said to be somewhat more carnivorous.

_Trichosurus._[56]—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 _i_ ³⁄₂, _c_ ¹⁄₀, _p_ ²⁄₂, _m_ ⁴⁄₄. 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 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 phalangers, its flesh is freely

eaten both by the natives and the lower class of settlers.

_Pseudochirus._[57]—The genus _Pseudochirus_ agrees with the preceding

in the absence of a flying membrane, and presents the following leading

characters. Size large or medium. Fur comparatively 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 mammæ. 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 bullæ generally somewhat inflated. Dentition (at most) _i_

²⁻³⁄₂, _c_ ⁰⁻¹⁄₀, _p_ ³⁄₃, _m_ ⁴⁄₄. 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 (_Pseudochirus 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 following genus readily distinguish them from the more typical

Phalangers, and show an approximation to the type of dentition prevailing

in _Phascolarctus_; according, however, to Mr. O. Thomas, a tendency

towards the same structure is observable in unworn molars of young

Cuscuses. 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 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 _Pseudochirus_,

probably referable to existing species, are found in the cave-deposits of

New South Wales.

_Petauroides._[58]—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 living 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 forearm 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

premaxillæ. Large vacuities in hinder part of palate. Auditory bullæ

inflated and smooth. Dentition usually _i_ ³⁄₂, _c_ ¹⁄₀, _p_ ²⁄₂, _m_

⁴⁄₄. 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._[59]—The genus _Dactylopsila_ is one of the forms without

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_

³⁄₃, _c_ ¹⁄₀, _p_ ³⁄₂, _m_ ⁴⁄₄. 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 Papuan

and North Australian sub-region; a second species (_D. palpator_),

characterised by the still greater elongation of the fourth finger,

occurring in South New Guinea. These animals are said to be of

insectivorous habits, the elongated fourth finger, as in the analogous

instance of the Lemuroid genus _Chiromys_, being apparently specially

adapted for extracting insects and larvæ from their hiding places.

_Petaurus._[60]—Size medium or small. Fur very soft and silky. A broad

flying membrane extending from the outer side of the fifth digit of the

manus 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 bullæ inflated,

and variable in size. Dentition: _i_ ³⁄₂, _c_ ¹⁄₀, _p_ ³⁄₃, _m_ ⁴⁄₄.

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. australis_), 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 distant

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 otherwise sustain.”

A second species, _P. sciureus_, in some ways one of the most beautiful

of all mammals, has been chosen for the accompanying woodcut.