and there among the Marsupials, which are sometimes held to point to a
primitive ancestry. It has been remarked that in Marsupials it is the
fourth toe which is dominant in size, whereas in Ungulates it is the third.
An attempt has been made to explain this on the view (reasonable enough in
itself) of a tree-living ancestry for the group. A greater development of
the fourth toe is, however, by no means a necessary character of arboreal
creatures; the Primates themselves are an exception. Nor is this prevalence
universal among the Marsupials; {119} in _Myrmecobius_ (alone) is the third
toe the longest; and no great difference can be detected between the third
and fourth toes in the case of the genera _Phascologale_, _Didelphys_, and
some others. Professor Leche compares the predominance of the fourth toe
with the hyperphalangeal condition in the fourth toe of the embryo
Crocodile, and considers it an archaic feature, not surpassed by the
ancient characteristics of the Monotremata. Again it has been pointed out
that in _Phascologale_ and _Perameles_, the epistropheus (axis vertebra)
has a separate rib as in _Ornithorhynchus_. In the third place, the
likeness of the teeth of _Myrmecobius_ to those of _Ornithorhynchus_ is an
argument in the same direction, which is furthermore supported by the great
age (Mesozoic) of the Metatherian group, if we are right in regarding those
extinct creatures as Marsupials.
We may now mention certain facts which are not so generally used. The
partly primitive structure of the right auriculo-ventricular valve in the
Monotremata has no counterpart in any Marsupial which has been dissected;
but there are traces in the latter of the characteristic "ventral
mesentery" of _Ornithorhynchus_ and _Echidna_.[67] Mr. Caldwell's
interesting observation upon the segmenting egg of the Marsupial, the
incompleteness of the first segmentation furrow (reminding us of the
meroblastic ovum of the Monotreme), may possibly not turn out to be so
exclusively Marsupial a feature as has been thought.
The balance of evidence thus points to the nearer relationship of the
Marsupials to the Eutherian mammals; and their great specialisation
combined with certain evidences of degeneration (disappearance in part of
the milk dentition), and their age, point to the fact that they are, at any
rate, the descendants of an early form of Eutherian. But they must have
separated from the Eutherian stock after it had acquired a definite
diphyodonty and the allantoic placenta, the two principal features of the
Eutherian as opposed to the Prototherian mammals.
Nevertheless it seems probable that the Marsupial tribe is derived from
some of the earliest Eutherians. And on this view may be explained the
retention of Prototherian characters.
The remaining Eutheria are obviously all to be referred to one great
division with the possible exception of the Whales, whose affinities form
one of the principal difficulties to the student {120} of this group. A
short resume of what is at present thought of the systematic position of
this anomalous order is appropriate here. Albrecht went so far as to regard
the Cetacea as the nearest group of animals to the hypothetical
Promammalia.[68] But discounting his arguments by the removal of such of
them as relate to structure plainly altered by the singular mode of life of
these creatures, there is really a great deal to be said in favour of his
view.
The chief facts which argue a primitive position among mammals for the
Cetacea are perhaps: (1) the slight union of the rami of the lower jaw; (2)
the occasionally rather marked traces of the double constitution of the
sternum; (3) the long and simple lungs; (4) the retention of the testes
within the body-cavity; (5) the occasional presence (in _Balaenoptera_) of
a separate supra-angular bone. These points, however, are but few, and are
not of such great weight as those which ought to be present to establish a
claim to separate treatment for the Cetacea as opposed to the Eutheria. If
this group of mammals can be tacked on anywhere, it appears to us that the
nearest relatives are not, as is sometimes put forward, the Ungulata or the
Carnivora, but the Edentata. There are quite a number of rather striking
features in which a likeness is shown between these apparently diverse
orders of mammals. The chief ones are these: (1) the existence of traces of
a hard exoskeleton, of which vestiges remain in the Porpoise; (2) the
double articulation of the rib of the Balaenopterids to the sternum, with
which compare the conditions obtaining in the Great Anteater; (3) the
concrescence of some of the cervical vertebrae; (4) the share which the
pterygoids may take in the formation of the hard palate; (5) the fact that
in the Porpoise, at any rate, as in many Edentates, the vena cava, instead
of increasing in size as it approaches the liver, diminishes.
Another group which is perfectly isolated is that of the Sirenia. The
alliance advocated by some with the Cetacea, and quite recently renewed by
Professor Haeckel, is contradicted by so many important features that it
seems necessary to abandon it. The recent discovery of a fossil Sirenian
jaw by Dr. Lydekker with teeth highly suggestive of those of Artiodactyla,
may prove a clue. A third group which is so isolated as to have been placed
in a {121} primary division, proposed to be called Paratheria, is that of
the Edentates. Probably the group so called should really be divided into
the Edentata and the Effodientia, the latter containing the Old World
forms. Whether or not it be ultimately shown that the Ganodonta are
ancestral Edentates (_sensu strictiori_), the connexion of the group with
others is not at present plain. The same is the case with the extensive
order of Rodents. It is true that the extinct order of the Tillodontia
shows certain Rodent-like characters on the one hand, and likenesses to
Ungulates on the other. Certain likenesses shown by such apparently diverse
animals as the Rabbit and the Elephant used to be insisted upon by
Professor Huxley. For the present, however, the Rodents must remain as an
isolated group with only very dubious affinities to others. The remaining
groups of existing mammals are easier to connect. At first the differences
between a Cat and a Horse seem to be quite as wide as those which separate
any two of the higher Eutherian orders. But it seems to become clearer and
clearer, as palaeontological investigation proceeds, that the bulk of the
Ungulate and the Carnivorous, Insectivorous, and perhaps Lemuroid stocks
converge into the early Eocene Creodonta. From the Lemuroid branch the
higher Primates can be derived. The only "Ungulates" which cannot be fitted
in with some reasonable probability is the group of the Proboscidea. But of
the early forms of this division we have at present no knowledge.
* * * * *
{122}
CHAPTER VII
EUTHERIA--MARSUPIALIA
ORDER I. MARSUPIALIA[69]
The Marsupials may be thus defined:--Terrestrial, arboreal, or burrowing
(rarely aquatic) mammals, with furry integuments; palate generally somewhat
imperfectly ossified; jugal bone reaching as far as the glenoid cavity;
angle of lower jaw nearly always inflected. The clavicle is developed.
Arising from the pubes are well developed and ossified epipubic bones.
Fourth toe usually the most pronounced. Teeth often exceed the typical
Eutherian number of forty-four; molars generally four on each side of each
jaw. As a rule but one tooth of the milk set is functional, which is
(according to many) the fourth premolar. Teats lying within a pouch, in
which the young are placed. Young born in an imperfect condition, and
showing certain larval characters. There is a shallow cloaca. The testes
are extra-abdominal, but hang in front of the penis. In the brain the
cerebellum is completely exposed; the hemispheres are furrowed, but the
corpus callosum is rudimentary. An allantoic placenta is rarely present.
Structurally the Marsupials are somewhat intermediate between the
Prototheria and the more typical Eutheria, with a greater resemblance to
the latter.
[Illustration]
FIG. 59.--Rock Wallaby (_Petrogale xanthopus_), with young in pouch. x 1/7.
(After Vogt and Specht.)
The name Marsupial indicates what is perhaps the most salient character of
this order. The pouch in which the young are carried is almost universally
present. It is less developed {123} on the whole in the Polyprotodont
forms, such as the Thylacine, Dasyures, etc., but is found in so many of
them that the two divisions of the Marsupials, the Diprotodonts and the
Polyprotodonts, cannot be raised to distinct orders on this and other
grounds. The marsupial pouch of the Marsupials must not, as has been
already pointed out, be confounded with the pouch of the Monotreme mammals.
Distinct teats are found in the marsupium of the Marsupials, while there
are none in the mammary pouch of the Monotreme, the pouch itself indeed
representing an undifferentiated teat, of which the walls have not closed
up. The pouch opens forward in the Kangaroos, and backwards in the
Phalangers and in the Polyprotodonts. Its walls are supported by a pair of
bones diverging from each other in a [70]-shaped manner; these are
cartilaginous and vestigial in the Thylacine. They {124} are the precise
equivalents of similar bones in the Monotremata. It has been held, but
apparently erroneously, that these bones are mere ossifications in the
tendons of the external oblique muscle of the abdomen, or of the
pyramidalis of the same region; and vestiges have been asserted to exist in
the Dog. Such bonelets are undoubtedly present in the Dog; but it seems
clear from their development in Marsupials, as structures actually
continuous with the median unossified portion of the symphysis pubis, that
the "marsupial bones" belong to that part of the skeleton, and that they
correspond with the epipubis of certain amphibians and reptiles. The pouch,
it may be remarked, exists in a rudimentary form in the males of many
Marsupials.
[Illustration]
FIG. 60.--Ventral surface of innominate bone of Kangaroo (_Macropus
major_). x 1/3. _a_, Acetabulum; _ab_, acetabular border of ilium; _is_,
iliac surface; _m_, "marsupial" bone; _pb_, pubic border; _pt_, pectineal
tubercle; _s_, symphysis; _si_, supra-iliac border; _ss_, sacral surface;
_thf_, thyroid foramen; _ti_, tuberosity of ischium. (From Flower's
_Osteology_.)
[Illustration]
FIG. 61.--Mammary foetus of Kangaroo attached to the teat. (Nat. size.)
(From Parker and Haswell's _Zoology_.)
The most salient feature in the life-history of the Marsupials is the
imperfect condition in which the young are born. The egg is no longer laid,
as in the Monotremes; but curiously enough the ovum, which has the small
size of that of the Eutheria, divides incompletely at the first division
(as Mr. Caldwell has shown), and this developmental feature may perhaps be
looked upon as a reminiscence of a former large-yolked condition. The young
when born are small and nude; the newly born young of a large Kangaroo is
perhaps as large as the little finger. The young are transferred by the
lips of the mother to the pouch, where they are placed upon a teat. It is
an interesting fact that they are not merely imperfect foetuses, but that
they are actual larvae. They possess in fact at any rate one larval organ
in the shape of {125} a special sucking mouth. This sucking mouth is an
extra-uterine production, and is of course an adaptation to the particular
needs of the young, just as are other larval organs, such as the
chin-suckers of the tadpole, or the regular ciliated bands of the larvae of
various marine invertebrate organisms.
There are a number of other features which distinguish the Marsupials from
other mammals.
The cloaca of the Marsupials is somewhat reduced, but is still
recognisable. Its margins in _Tarsipes_ are even raised into a wall, which
projects from the body.
The tooth series of the Marsupials was once held to consist of one
dentition only, with the exception of the last premolar, which has a
forerunner. The interpretation of the teeth of Marsupials are various.
Perhaps most authorities regard the teeth as being of the milk dentition,
with the exception of course of the single tooth that has an obvious
forerunner. But there are some who hold that the teeth are of the permanent
dentition. In any case it is proved that a set of rudimentary teeth are
developed before those which persist. Those who believe in the persisting
milk dentition describe these as prelacteal. Another matter of importance
about the teeth of this order of mammals is that their numbers are
sometimes in excess of the typical Eutherian 44. This, however, holds good
of the Polyprotodonts only.
It was for a long time held that the Marsupials differed from all other
mammals in having no allantoic placenta. But quite recently this supposed
difference has been proved to be not universal by the discovery in
_Perameles_ of a true allantoic placenta. The Marsupials have been
sometimes called the Didelphia. This is on account of the fact that the
uterus and the vagina are double. Very frequently the two uteri fuse above,
and from the point of junction an unpaired descending passage is formed
(see Fig. 48 on p. 74).
A character of the brain of Marsupials has been the subject of some
controversy. Sir Richard Owen stated many years ago that they were to be
distinguished from the higher mammals by the absence of the corpus
callosum. Later still it was urged that a true corpus callosum, though a
small one, was present; while, finally, Professor Symington[71] seems to
have shown that {126} the original statement of Owen was correct, at least
in part. It is at most feebly developed (see Fig. 58, p. 118).
As to skeletal characters, the Marsupial skull has on the whole a tendency
towards a permanent separation of bones usually firmly ankylosed. Thus the
orbitosphenoids remain distinct from the presphenoid. The palate is largely
fenestrated, a return as it were--says Professor Parker--to the
Schizognathous palate of the bird. The mandible is inflected; this familiar
character of the Marsupials goes back to the earliest representatives of
the order in Mesozoic times (see p. 96); but it is not absolutely
universal, being absent from the much weakened skull of _Tarsipes_. On the
other hand, the inflection is nearly as great in certain Insectivores, in
_Otocyon_, etc. The malar always extends back to form part of the glenoid
cavity. The shoulder girdle has lost the large coracoid of Monotremes; this
bone has the vestigial character that it possesses in other Eutheria. The
clavicle is present except in the Peramelidae. A third trochanter upon the
femur seems to be never present.
[Illustration]
FIG. 62.--Skull of Rock Wallaby (_Petrogale penicillata_). (Ventral view.)
_ali_, Alisphenoid; _bas.oc_, basi-occipital; _bas.sph_, basi-sphenoid;
_ex.oc_, ex-occipital; _ju_, jugal; _max_, maxilla; _pal_, palatine;
_par.oc_, paroccipital; _p.max_, premaxilla; _pr.sph_, presphenoid; _pt_,
pterygoid; _sq_, squamosal; _ty_, tympanic. (From Parker and Haswell's
_Zoology_.)
The Marsupials cannot be regarded as an intermediate stage in the origin of
the Eutheria for a number of reasons. In the first place, the nature of
their teeth shows them to be degenerate animals; one set, whether we regard
it as the milk or permanent dentition, has become vestigial. The recent
discovery of a true allantoic placenta in _Perameles_ removes one reason
for regarding {127} the Marsupials as primitive creatures. It implies on
the whole that the Marsupials have sprung from a stock with an allantoic
placenta. The alternative is to assume the independent development of an
allantoic placenta in both groups of the Mammalia; unless indeed the genus
_Perameles_ is to be held to be the most primitive race of Marsupials
living, a hypothesis which does not appear on the face of it likely. So
long as it was believed that the mammary pouch of the Monotremes was the
equivalent of the marsupium of the Marsupials, the persistence of this
structure seemed to be a bond of union between the groups. But it is now
known that the marsupium is a special organ confined to the Marsupials, an
argument which is rather in favour of their being a lateral development of
the mammalian stem. It is to be remarked also that the marsupium is
feeblest in the Polyprotodonts, which may perhaps be looked upon as the
most primitive of the Marsupials, owing to their more numerous teeth and
other points to be referred to immediately.
Not only are the Marsupials interesting from the point of view of their
structure; their present and past distribution is of equal interest. During
the Mesozoic epoch they occurred in Europe and North America; but not, so
far as negative evidence means anything, in Australia, which is now their
headquarters. In Europe Marsupials lingered on into the Tertiary period,
when they finally became extinct. In America, of course, the group has
persisted to the present day. Now it is important to notice that the two
main subdivisions of the Marsupials, the Polyprotodontia and the
Diprotodontia, exist to-day in both Australia and South America. These two
divisions, it should be explained, differ principally in that one has
numerous, the other rarely more than two,[72] incisors in the lower jaw. It
is perhaps the more widely distributed opinion that the Polyprotodontia are
the more archaic group; this opinion rests upon one or two facts in
addition to the absence of specialisation in the incisor teeth. Among the
Polyprotodontia the total number of teeth is greater--a clearly primitive
character; secondly, the general form of the body of these animals, with
four subequal limbs and carnivorous or omnivorous diet, contrasts with the
purely vegetarian and much specialised Kangaroos at any rate. Finally--and
sufficient stress {128} has perhaps not been laid upon this matter--the
brain among the Polyprotodonts is less convoluted than among the genera of
the other division. This statement is of course made with due regard to
parallelism in size (see p. 77). It is well known that the complexity of a
brain bears a distinct relation to the size of its possessor within the
group. Now the most ancient Marsupials are decidedly more
Polyprotodont-like. No European form from the earlier periods is distinctly
to be referred to the Diprotodonts. But both divisions now exist in America
and Australia.
We must assume, therefore, one of three hypotheses. Either the
differentiation into the two great divisions occurred in Jurassic or
Cretaceous times before the migration of the order southwards; or the
Diprotodont type is only a type, and not a natural group, _i.e._ it has
been separately evolved in America and Australia; or, finally, there was
formerly a land-connexion in the Antarctic hemisphere, along which the
Diprotodonts of Australia wandered into South America. The middle
hypothesis has this to commend it, that syndactylism occurs in both
divisions, and that in some Diprotodonts the pouch opens backwards as it
does in the Polyprotodonts. So great are the resemblances that but little
difference is really left--of great importance that is to say. Hence it is
not difficult to imagine the reduction of the incisors having taken place
twice. In favour of the first hypothesis there are no positive facts.
Finally, in favour of the last, which is so strongly supported by the facts
of distribution derived from the study of other groups of animals,[73]
there is at least this striking fact or rather series of facts: that some
of the South American fossil Polyprotodonts have a "strictly Dasyurine
relationship."[74] If there has not been a direct migration, then the
Dasyurine type has been twice evolved, an improbability that few will
attempt to explain away. In any case we shall adopt here the usual division
of the Marsupials into Diprotodontia and Polyprotodontia.
SUB-ORDER 1. DIPROTODONTIA.
This group includes the herbivorous Marsupials. The incisors are as a rule
three above, but one only in the Wombats. Below {129} is one strong pair,
with occasionally one or two rudimentary incisors. The upper canines, if
present, are not large. The molars are tuberculate or ridged. All
Marsupials (except the Wombats) to some extent, and the Macropods
especially, are characterised by the prolongation of the tubes of the
dentine into the clear enamel. The significance of this fact is, however,
lessened by the fact that the same penetration of the enamel by dentinal
tubes occurs in the Jerboa, the Hyrax, and some Shrews. The feet have two
syndactylous toes,[75] less marked in the Wombats than in the Kangaroos and
Phalangers.
[Illustration]
FIG. 63.--Skull of Wombat (_Phascolomys wombat_). (Lateral view.) _ang_,
Angular process; _cond_, condyle of mandible; _ext.aud_, opening of bony
auditory meatus; _ex.oc_, exoccipital; _ju_, jugal; _lcr_, lachrymal;
_max_, maxilla; _nas_, nasal; _p.max_, premaxilla; _sq_, squamosal; _ty_,
tympanic. (From Parker and Haswell's _Zoology_.)
This order is mainly Australian at the present day, using the term of
course in the "regional" sense (see p. 84); the only exception indeed to
this statement is the occurrence of the genus _Caenolestes_ in South
America. But it is now known that Diprotodont Marsupials formerly existed
in the same part of the world.
[Illustration]
FIG. 64.--Bones of right foot of Kangaroo (_Macropus bennetti_). _a_,
Astragalus; _c_, calcaneum; _cb_, cuboid; _e_^3, ento-cuneiform; _n_,
navicular; _II-V_, second to fifth toes. (From Flower's _Osteology_.)
{130}
[Illustration]
FIG. 65.--Skeleton of Wallaby (_Macropus ualabatus_). The scapula is raised
somewhat higher than in nature. The end of the tail is omitted. The head of
the femur has been separated from the acetabulum. _acet_, Acetabulum;
_acr_, acromion process; _ast_, astragalus; _cal_, calcaneum; _cbd_,
cuboid; _chev_, chevron-bones; _cl_, clavicle; _cun_, cuneiform of carpus;
_epi_, epipubis; _fb_, fibula; _fem_, femur; _hd_, head of femur; _hu_,
humerus; _il_, ilium; _isch_, ischium; _obt_, obturator-foramen; _orb_,
orbit; _pis_, pisiform; _pub_, pubis; _rad_, radius; _rb_^1, first rib;
_rb_^{13}, last rib; _sc_, scapula; _st_, sternum; _tb_, tibia; _troch_,
great trochanter of femur; _uln_, ulna; _unc_, unciform; _IV_, fourth toe.
(From Parker and Haswell's _Zoology_.)
FAM. 1. MACROPODIDAE.--This family contains the Kangaroos, Wallabies,
Rat-Kangaroos, and Tree-Kangaroos. With the exception of _Dendrolagus_ the
family is terrestrial, and its numerous species progress by leaps effected
by the long hind-limbs, which are decidedly, often greatly, longer than the
fore-limbs. In the hind-limb the fourth toe is very long and strong; the
fifth moderately so; the second and third are slender and united by skin.
The tail is always long, but differs in its characters from {131} genus to
genus. The stomach is much sacculated. The dental formula is I 3/1 C (1 or
0)/0 P 2/2 M 4/4. The atlas is often open below, forming thus an incomplete
ring.
Though the number of the incisor teeth in the adult Diprotodonts is never
more than three on each side in each jaw, more numerous rudiments are
present. Mr. M. Woodward[76] has lately investigated the subject with
interesting results. He finds that many species present decided traces of
two additional incisors, raising the total to that which characterises the
Polyprotodontia; but in two cases, viz. _Macropus giganteus_ and _Petrogale
penicillata_, a sixth is present, the total number being thus in excess of
that found in any other Marsupial. This, as the author himself admits,
proves too much. No mammal is known which in the adult condition has so
many incisors; nor do the fossil Mammalia help us to get over the
difficulty; even among reptiles it is not usual for so many teeth to occur
upon the premaxillaries.
It is a curious fact that the two long lower incisors can be used after the
fashion of a pair of scissors, or rather a pair of shears. Their inner
edges are sharpened, and they are capable of some motion towards and away
from each other; by their means grass is cropped.
The stomach of _Macropus_ (and of other allied genera) is peculiar by
reason of its long and sacculated character; the oesophagus enters it very
near the cardiac end, which is bifid. Messrs. Schaefer and Williams[77]
have shown that the squamous, non-glandular epithelium of the oesophagus
extends over the greater part of the stomach, only the pyloric extremity
and one of the two cardiac caeca being lined with columnar epithelium.
The Macropodidae are clearly divisible into three sub-families, which are
distinguished by marked anatomical characters.
In the sub-family MACROPODINAE (including the genera _Macropus_,
_Petrogale_, _Lagorchestes_, _Dorcopsis_, _Dendrolagus_, _Onychogale_, and
_Lagostrophus_) there is no hallux, and the tail is hairy. The oesophagus
enters the stomach near the cardiac end. The caecum when short has no
longitudinal bands; the liver has a Spigelian lobe.
The second sub-family, POTOROINAE or HYPSIPRYMNINAE (including the genera
_Potorous_, _Aepyprymnus_, _Bettongia_, and {132} _Caloprymnus_), consists
of smaller animals than the Macropodinae, which, however, resemble them in
having no hallux, but a hairy tail. The oesophagus enters the stomach near
the pyloric end of that organ. The caecum, though short, has lateral
longitudinal bands. The liver has no special Spigelian lobe. The canines
are always present, being rarely so in Macropodinae, and are usually well
developed.
The third sub-family, that of the HYPSIPRYMNODONTIDAE, is doubtfully
referable to the family; it consists of but one genus _Hypsiprymnodon_,
which is in many points more like a Phalanger than a Kangaroo. It has an
opposable hallux and a non-hairy, but scaly, tail. It has canines in the
upper jaw.
[Illustration]
FIG. 66.--Red Kangaroo. _Macropus rufus._ x 1/18.
SUB-FAM. 1. MACROPODINAE.--The genus _Macropus_ includes not only the
Kangaroos but also the Wallabies, which are really indistinguishable,
though they have sometimes been placed in a separate genus _Halmaturus_.
The genus thus enlarged contains twenty-three species. It may be thus
characterised: the ears are long, the rhinarium is usually naked, but in
_M. giganteus_ and others a band of hairs descends to the upper lip; a
naked band extends from the ankle to the pads on the digits, which is
interrupted in _M. rufus_ by a band of hairs just in front of the digits.
The mammae are four. The tail is not bushy, {133} but is crested in _M.
irma_. They are for the most part found on the Australian continent, but
some species are found in the islands to the north which belong to the
Australian region. Thus _M. brunii_, which is of interest as the first
Kangaroo seen by a European, is a native of the Aru islands. A specimen of
this animal, which was then living in the garden of the Dutch governor of
Batavia, was described by Bruyn in the year 1711. _M. rufus_, the largest
member of the group, is remarkable for the red secretion which adorns the
neck of the male. It is caused by particles which have the appearance and
colour of carmine. _M. giganteus_ is not, as its specific name might imply,
the "giant" of the race; its dimensions are given as 5 feet, while _M.
rufus_ is said to attain a length of 5 feet 5 inches, exclusive (in both
cases) of the tail.
The account which Sir Joseph Banks gives[78] in his diary of the Kangaroo
is interesting, since he was one of the first naturalists to see that
creature. In July 1770 it was reported to him that an "animal as large as a
greyhound, of a mouse colour, and very swift" had been seen by his people.
A little later he was surprised to observe that the animal "went only upon
two legs, making vast bounds just as the jerboa does." The second
lieutenant killed one of these Kangaroos, of which Sir Joseph Banks wrote
that "to compare it to any European animal would be impossible, as it has
not the least resemblance to any one I have seen. Its fore-limbs are
extremely short and of no use to it in walking; its hind, again, as
disproportionately long; with these it hops seven or eight feet at a time,
in the same manner as the jerboa, to which animal indeed it bears much
resemblance, except in size, this being in weight 38 lbs., and the jerboa
no larger than a common rat." The beast was killed and eaten, and proved
excellent meat. Sir Joseph Banks' observations upon the leaping of the
Kangaroo are of interest, because it is often asserted that the tail is
largely made use of as a third foot or as a support. Mr. Aflalo declares in
the most positive way that after repeatedly examining the tracks upon soft
sand immediately after the animal had passed, not the very faintest trace
of the impression of the tail could be discovered. The leaps of a big
Kangaroo seem to be somewhat greater than is recorded {134} by Banks. It is
said that 15 or even 20 feet are covered at a bound, and in bound after
bound. But in walking slowly it can be readily seen from an inspection of
Kangaroos at the Zoological Society's Gardens that the animal does rest
upon its tail, which with the hind-legs forms a tripod.
_Petrogale_ with six species comes next to _Macropus_, and is indeed only
to be differentiated from it by the thickly-haired and more slender tail,
which is not used, as it is sometimes in the Kangaroos, as an extra
hind-limb. The Rock-Kangaroos live among rocks, which they climb, and from
which they leap; and the tail acts rather as a balancing pole. The most
elaborate account of the anatomy of _Petrogale_ known to me is by Mr.
Parsons.[79] The dentition as given by Mr. Thomas is I 3/1 C 0/0 Pm 2/2
M 4/4--that of _Macropus_ without the occasionally occurring canine of the
upper jaw. The osteological characters which separate it from _Macropus_
are quite insignificant. Mr. Parsons mentions a wormian bone, "os
epilepticum," at the junction of the coronal and sagittal sutures. It was
found to occur in two out of five skulls examined, and appears not to occur
in other Kangaroos. The palatine foramina of _Petrogale_ are so large that
the posterior part of the bone is only a narrow thickened ridge. The small
intestine of _P. xanthopus_ is 102 inches long, the large intestine 44
inches. The caecum has a length of 6 inches, and is not sacculated,
differing in this from the caecum of _Macropus major_. The best known
species are _P. xanthopus_ and _P. penicillata_. The genus is confined to
Australia itself, and does not enter Tasmania.
_Onychogale_ includes the so-called "Nail-tailed Wallabies," which have a
thorn at the end of the tail, reminding one of the Lion and the Leopard,
whose tails have a similar armature. The muffle is hairy. Three species are
allowed by Mr. Thomas.
_Lagorchestes_ has, like the last genus, the rhinarium, _i.e._ that part of
the nose immediately surrounding the nostrils, hairy instead of smooth as
in the Kangaroos proper. It is distinguished from _Onychogale_ by the
absence of the terminal callosity to the tail, which is rather short. The
name Hare-Kangaroo is given to the members of this genus (three species) on
account of their exceeding fleetness. This genus is limited to Australia
itself. _L. conspicillatus_ is said to present "a remarkable {135}
resemblance to the English hare," and _L. leporoides_ was so called by
Gould on account of general appearance as well as face.
_Dorcopsis_ has shorter hind-legs than _Macropus_, and a naked muffle. The
ears are small. The structure of _D. luctuosa_ has been studied by
Garrod,[80] who pointed out the existence of four enlarged hair follicles
on the neck near the mandibular symphysis. These are, however, represented
in the next genus _Dendrolagus_, and occur also in _Petrogale_. The limbs
are not so disproportionate as in _Macropus_, and the tail is naked at the
tip.
_Dorcopsis_ and the next genus to be described, _Dendrolagus_, differ from
_Macropus_ and its immediate allies, _Petrogale_ and _Lagorchestes_, in a
number of anatomical points. In the first place, the premolars are twice
the size of those of _Macropus_, and they have a characteristic pattern not
observable in the Kangaroos. This consists of a median ridge (the whole
tooth being rather prismatic in shape), with lateral ridges at right angles
to it. The upper canines are developed, but are minute.
The stomach is not quite like that of _Macropus_, though built upon a
similar plan. The blind cardiac extremity is a single, not a double
cul-de-sac; in this it is like that of _Petrogale_. The distribution of the
squamous, white, oesophageal epithelium is very much like that of
_Dendrolagus_. In both genera the orifice of the oesophagus into the
stomach is guarded by two strong longitudinal folds, which run for some
distance towards the pylorus. In _Dendrolagus_, at any rate, this tract is
bordered on each side by glandular patches. In _Dendrolagus_, moreover, the
squamous epithelium does not extend into the cardiac cul-de-sac. This
latter is separated from the rest of the stomach by two slightly diverging
folds, which are faintly represented in _Petrogale_ and in _Halmaturus_. In
the last two genera the folds surrounding the oesophageal orifice are but
slightly represented; better in _Halmaturus_ than in _Petrogale_. But there
are not the patches of glands already referred to. The small intestine of
_Dorcopsis_ is 97 inches in length, the large being 32, _i.e._
proportionately long, as in Marsupials generally. The small caecum (2-1/2
inches) is not sacculated.
The spleen is Macropodine, being [81]-shaped or [82]-shaped. The
differences between _Dorcopsis_ and the evidently closely allied
_Dendrolagus_ will be further considered under the description of {136} the
latter. _Dorcopsis_ is confined to New Guinea, and contains three species,
viz. _D. muelleri_, _D. luctuosa_, and _D. macleani_. _D. muelleri_ has a
striking resemblance to _Macropus brunii_, with which it has been
confounded. Though intermediate between _Macropus_ and _Dendrolagus_, these
Kangaroos are not arboreal.
The genus _Dendrolagus_ is remarkable for its un-kangaroo-like habit of
living in trees. In accordance with this change of habit is a relative
shortening of the hind-limbs, a feature which begins to be observable in
_Dorcopsis_. "The general build," writes Mr. Thomas, "is of the ordinary
mammalian proportions, not macropodiform at all." The muffle is not naked
for the greater part, though the shortness of the hairs gives that effect.
As in _Dorcopsis_, but not as in _Macropus_, the bulla tympani is not
swollen. There are altogether five species, the fifth, _D. bennetti_,
having been lately described from specimens living in the Zoological
Society's Gardens.
[Illustration]
FIG. 67.--Tree-Kangaroo. _Dendrolagus bennetti._ x 1/12.
The anatomy of this genus has been described by Owen for _D. inustus_,[83]
and by myself for _D. bennetti_. The stomach, which {137} has a single, not
bifid, cul-de-sac, is sacculated by two principal bands and other
subsidiary ones. Its internal structure has already been to some extent
described. The spleen of _D. bennetti_ is remarkable for the fact that it
is not [84]-shaped, whereas _D. inustus_ agrees with other Macropodines in
the form of this organ. The small intestine of _D. bennetti_ is 95 inches
long, the large 38. The caecum appears to differ in the two species; it is
smaller in _D. bennetti_, where it is only 2 inches in length. The most
remarkable feature of the liver is the large size of the left lateral lobe
and the bilobed condition of the Spigelian lobe; this at least was the case
with _D. bennetti_. A recently-described species[85] has been attentively
studied in its native haunts by Dr. Lumholtz.[86] It lives in the highest
parts of the mountainous scrubs of Queensland, where it moves quickly on
the ground as well as among the trees. It is hunted with Dingos by the
"blacks," and is eaten by them.[87]
_Lagostrophus_ is a generic name that has been proposed by Mr. Thomas for a
small Wallaby 18 inches in length, which is distinguished by the fact that
the long claws of the hind-limbs are entirely hidden by long and bristly
hairs; the muffle is naked; there is no canine. The bullae are swollen.
There is but one species of the genus, _L. fasciatus_, a native of West
Australia.
SUB-FAM. 2. POTOROINAE.--_Aepyprymnus_ and the other genera placed in this
sub-family are known by the vernacular name of Rat-Kangaroos, or sometimes
Kangaroo-Rats. The latter term has been called "incorrect," though it is
just as good as the former, both of them in fact being inaccurate as
implying some likeness to or relation with a Rat. The present genus has a
partially hairy rhinarium; the auditory bullae are not swollen. It contains
but one species, _Ae. rufescens_, a native of Eastern Australia, which is
distinguished by its very long hind-feet.
_Bettongia_ has long hind-feet as in _Aepyprymnus_, but the rhinarium is
entirely naked instead of being partially hairy, while the ears are much
shorter. The genus, which contains four species, is remarkable as being the
only ground-living mammal with a prehensile tail, which it uses to carry
grass, etc. {138} _B. lesueuri_ burrows in the ground, often to so great a
depth as 10 feet. The genus occurs in Tasmania as well as in Australia.
_Caloprymnus_, with one species, is a genus instituted by Mr. Thomas in his
Catalogue of Marsupials for a form (_C. campestris_) which combines in a
remarkable way the characters of _Aepyprymnus_, _Bettongia_, and
_Potorous_. The external characters and the general shape of the skull are
as in _Bettongia_, while the molars have the structure of those of
_Aepyprymnus_. The last premolar is as in _Potorous_.
Of the genus _Potorous_ there are three species, which are Tasmanian as
well as Australian. Unlike the other Rat-Kangaroos, the hind-feet are
comparatively short, and the animal is therefore less addicted to jumping
than its relatives. The rhinarium is naked, and the ears are of fair
length.
SUB-FAM. 3. HYPSIPRYMNODONTINAE.--The Musk-Kangaroo, _Hypsiprymnodon_, is
the last genus of the present family, and the only genus of this
sub-family. It is intermediate between the Macropodidae and the
Phalangeridae, the annectant character being mainly the hind-feet, which
though they have the same long fourth digit as the Kangaroos, have it more
feebly developed, and possess also an opposable hallux, which is one of the
salient features in the structure of the Phalangeridae. The tail is naked
and scaly; the rhinarium is entirely naked. The ears are large and not
furry. The single species, _H. moschatus_, appears to feed upon insects as
well as vegetables.
"Its habits are chiefly diurnal, and its actions when not disturbed by no
means ungraceful. It progresses in much the same manner as the
Kangaroo-Rats (_Potorous_), to which it is closely allied, but procures its
food by turning over the debris in the scrubs in search of insects, worms,
and tuberous roots, frequently eating the palm berries, which it holds in
its fore-paws after the manner of the Phalangers, sitting up on its
haunches, or sometimes digging like the bandicoots." This is Mr. Ramsay's
description of the animal, which he was the first to discover.[88]
FAM. 2. PHALANGERIDAE.--The genus _Hypsiprymnodon_ bridges over the not
very wide gap which separates the Kangaroos from the Phalangers. The
Phalangers are Marsupials with five fingers and toes; the second and third
toes are bound together by a {139} common integument as in the
Macropodidae. The hallux is opposable and nailless. The tail is nearly
always long and prehensile. The pouch is well developed; the stomach not
sacculated; a caecum is present (except in _Tarsipes_). These are really
the principal distinctions between the two families. In addition, it may be
mentioned that the lower incisors have not a scissor-like action as in the
Kangaroos.
The Phalangers may be divided into four sub-families.
The first of these, that of the PHALANGERINAE, contains the genera
_Phalanger_ (including _Cuscus_), _Acrobates_, _Distaechurus_, _Dromicia_,
_Gymnobelideus_, _Petaurus_, _Petauroides_, _Dactylopsila_, _Pseudochirus_,
and _Trichosurus_.
These genera agree in the following generalities:--Tail well developed,
often very long; three incisors above, and at least two premolars both
above and below; caecum long and simple; stomach without a cardiac gland;
liver not very complicated by secondary furrows, with a distinct caudate
lobe; the vaginal median culs-de-sac often coalesced; lungs with an azygos
lobe.
[Illustration]
FIG. 68.--Bones of leg and foot of Phalanger. _ast_, Astragalus; _calc_,
calcaneum; _cub_, cuboid; _ect.cun_, ecto-cuneiform; _ent.cun_,
ento-cuneiform; _fb_, fibula; _mes.cun_, meso-cuneiform; _nav_, navicular;
_tib_, tibia; _I-V_, first to fifth toes. (After Owen.)
The second sub-family, PHASCOLARCTINAE (with the Koala only), is thus
characterised:--Tail rudimentary; cheek-pouches present; superior incisors
three, but only one premolar above and below; {140} caecum extraordinarily
long; stomach with a cardiac gland; liver complicated by additional
furrows, without a free caudate lobe; no azygos lobe to lungs; vaginal
culs-de-sac free.
The third sub-family, PHASCOLOMYINAE, contrasts with the others as
follows:--Tail rudimentary; cheek-pouches present, but rudimentary; one
incisor on each side above, but no additional premolars; all the teeth
rootless; caecum not peculiar in shape; stomach with a cardiac gland; liver
complicated by secondary furrows, without a free caudate lobe; lung with an
azygos lobe; vaginal culs-de-sac free.
The last sub-family, TARSIPEDINAE, is thus defined:--Tail long; tongue
extensile; only one premolar; molars reduced; caecum absent.
[Illustration]
FIG. 69.--Vulpine Phalanger. _Trichosurus vulpecula._ x 1/6.
SUB-FAM. 1. PHALANGERINAE.--The genus _Phalanger_ embraces five species,
sometimes called by the generic name of _Cuscus_. They are largish animals
with short ears; only the end of the tail is naked. Of these animals only
one species is found in Australia itself, the rest inhabiting the islands
lying to the north. The Spotted Cuscus, _Ph. maculatus_, is in spite of its
vegetarian diet, and perhaps on account of its spots, spoken of as the
"Tiger Cat." Mr. Aflalo remarks of it that though provided with a
prehensile tail, it is little better as a climber than the tailless Koala.
_Trichosurus_, including the "True Phalangers," includes largish species,
which can be distinguished from the last genus by a chest-gland similar to
that which occurs in _Myrmecobius_ and some other Marsupials of the present
group. There are but two species, which are purely Australian. The
"Brush-tailed Opossum," _T. vulpecula_ (perhaps better known as
_Phalangista_ {141} _vulpina_), like its American pseudo-namesake (a true
Opossum, genus _Didelphys_), "plays 'possum" on occasions. The dental
formula is I 3/2 C 1/0 Pm 2/3 M 4/4. The ears are shortish.
The Ring-tailed Phalangers, _Pseudochirus_, are more widely distributed
than the last two genera; they range from Tasmania in the south to New
Guinea in the north. They are not, however, ring-tailed, though the tip of
the tail is generally white. As in the last genera, which have prehensile
tails, the end of this appendage is naked. The mammae are four. The tooth
formula is I 3/2 C 1/0 Pm 3/3 M 4/4. There are some ten species of the
genus.
The Striped Phalanger, _Dactylopsila trivirgata_, is an animal about a foot
long, whose identity can be ascertained by its striped, black and white
skin. It is an arboreal creature that lives apparently both on leaves and
grubs like so many arboreal creatures of quite different groups--Squirrels,
for instance, and New-World Monkeys. The tooth formula is I 3/3 C 1/6
Pm 3/2 M 4/4.
_Gymnobelideus leadbeateri_ is a small creature with a body 6 inches in
length. It is restricted to the colony of Victoria. The general look is
that of _Petaurus_; the ears are naked.
_Dromicia_ is a genus of Phalangers which although devoid of a parachute,
such as is possessed by certain genera that will be considered immediately,
is able to leap with great agility from branch to branch. The ears are
large and thin and almost naked; the tooth formula is I 3/2 C 1/0 Pm 3/3
M 4/4. They are minute creatures, the longest measuring, with the tail, but
10 inches. Dormouse-Phalanger is a name sometimes given to them. There are
four species, ranging from Tasmania to New Guinea. The name Dormouse as
applied to the genus seems to be owing to the way in which they hold a nut
in the paws when feeding. _D. nana_ is 4 inches long, with a tail of nearly
the same length. It is thick at the base.
_Distaechurus_ is the last genus of non-flying Phalangers. Its name refers
to the arrangement of the hairs on the tail, which are disposed on either
side in a row like the vane of a feather. The tooth formula is I 3/2 C 1/0
Pm 3/2 M 3/3, very nearly as in _Acrobates_. The ears are as in that genus.
_Petaurus_ is the first genus of the Flying Phalangers, all of which are
provided with a parachute-like expansion of the skin between the fore- and
hind-limbs; the ears are large and naked; and the tooth formula is I 3/2
C 1/0 Pm 3/3 M 4/4. There are three {142} species of the genus, which
extend through pretty well the entire Australian region. The term "flying"
as applied to these and the other "flying" genera is of course an
exaggeration. The animals cannot fly upwards; they can only descend in a
skimming fashion, the folds of skin breaking their fall. _P. breviceps_ is
perhaps the best-known species. The body is 8, the tail 9 inches long.
_Petauroides_ seems to be chiefly distinguished from _Petaurus_ by the fact
that, as in its ally _Dactylopsila_, the tail is partly naked terminally.
In _Petaurus_ and _Gymnobelideus_ the tail is bushy to the very end,
including its extreme tip below.
A third genus of Flying Phalangers is the minute _Acrobates_, which has a
distichous tail like that of _Distaechurus_. It is not more than 6 inches
in length including the tail. As to these Flying Phalangers it is
exceedingly instructive to observe that the same method of "flight" has
been apparently evolved three times; for the three genera are each of them
specially related to a separate type of non-flying Phalanger. The same
observation can be made about the Flying Squirrels, _Anomalurus_ and
_Sciuropterus_. The dental formula is I 3/2 C 1/0 Pm 3/3 M 3/3. The ears
are thinly clad with hair. There are four teats.
SUB-FAM. 2. PHASCOLARCTINAE.--The Koala, or Native Bear, _Phascolarctos
cinereus_, is the only representative of its sub-family. It is, like the
Wombat, aberrant in the lack of an obvious tail. The absence of this
appendage is curious in an arboreal creature whose near allies have a long
and prehensile one. The structure of the Koala was investigated by the late
Mr. W. A. Forbes.[89] There are some unexpected points of likeness to the
Wombat: thus they agree in the absence of the tail, in the structure of the
stomach, and in the great subdivision of the lobes of the liver. The brain,
however, is smooth, and the caecum is exceedingly large and complicated in
structure, that of the Wombat being short. That both animals have
cheek-pouches is perhaps due to similar habits of temporarily storing
masses of food. This animal has only eleven pairs of ribs. The tail has
only seven or eight vertebra, and these have no chevron-bones.
A peculiarity of the skull is seen in the great size of the alisphenoid
bulla, which is comparable in size and appearance with that of the Pig. As
in the Kangaroos, the atlas is incomplete below. {143}
The tooth formula of the genus is I 3/1 C 1/0 Pm 1/1 M 4/(4 or 5). The
additional lower molar seems to be exceptional, and has been found in one
specimen only.
In the alimentary tract the most remarkable structure is the large
intestine, which is very capacious for the first 28 inches or so of its
course. This section of the colon is lined with rugae precisely like those
which are found in the caecum. These folds, which at first are some twelve
in number, fuse lower down, and by the time that the colon approaches the
external orifice are reduced to five. Similar folds, as already stated,
occur in the caecum, but do not extend as far as its blind end. The caecum
is proportionately and actually larger than in any other Marsupial. The
gall-bladder is unusually elongated.
[Illustration]
FIG. 70.--Koala. _Phascolarctos cinereus._ x 1/9.
The Koala is mainly crepuscular or nocturnal in its habits. It feeds so
exclusively upon the leaves of the gum-tree (_Eucalyptus_) that it is
impossible to keep the creature long in captivity in lands where that
particular kind of food is not available.
The female, though she seems to bear but a single young one, which is
carried on the back after the fashion of some Opossums, has two nipples.
The animal's slow habits seem to require a nocturnal and retired life. It
is about as lethargic as the Sloth, and it is said to further resemble that
animal in clinging firmly to a branch even after it is shot. {144}
[Illustration]
FIG. 71.--Wombat. _Phascolomys wombat._ x 1/12.
SUB-FAM. 3. PHASCOLOMYINAE.--_Phascolomys_, the Wombat, is the only genus
of this sub-family. This animal has the appearance of a heavily-built
Marmot, like which it has a mere stump for a tail, and a pair of strong
chisel-shaped and Rodent-like incisors, which, however, differ from those
of Rodents in having a complete coating of cement. All the teeth of the
animal are rootless, and there are no canines. The incisors have enamel on
the front and lateral faces only. The dental formula is I 1/1 C 0/0 Pm 1/1
M 4/4. The affinities with other Diprotodont Marsupials are shown by the
commencing syndactyly of the second and third toes. The rhinarium is naked
or hairy. There is a rudimentary cheek-pouch, as in _Phascolarctos_. The
Wombat has, like the Koala, and also the Beaver--which does away with some
of the value of the comparison--a peculiar gland-patch in the stomach, a
raised area of collected glands. In no other Marsupial is such a structure
found, "whilst in the two forms under consideration its identity is almost
precise. That such a unique structure should have been independently
developed in two forms unrelated to each other, appears to me to be in the
highest degree improbable." This is Mr. Forbes' opinion. It might be
strengthened by adding the observation that, as there are other points of
likeness between the Wombat and the Koala, it seems more unlikely that a
structure so nearly identical should have been twice {145} developed in two
not very distant forms. As in the Kangaroos, the atlas is open below. _Ph.
ursinus_ has 15 ribs; the other species the normal (for Marsupials) 13.
Other points of likeness will be mentioned under the description of the
Koala. These animals mainly feed upon roots; they live in companies in
burrows. There are three species--_Ph. ursinus_, _Ph. latifrons_, and _Ph.
mitchelli_. _Ph. ursinus_ is Tasmanian in range, the other two species
South Australian.
[Illustration]
FIG. 72.--Skull of Wombat. _Phascolomys wombat._ (Lateral view.) _ang_,
Angular process; _cond_, condyle of mandible; _ex.oc_, exoccipital;
_ext.aud_, opening of bony auditory meatus; _ju_, jugal; _lcr_, lachrymal;
_max_, maxilla; _nas_, nasal; _p.max_, premaxilla; _sq_, squamosal; _ty_,
tympanic. (From Parker and Haswell's _Zoology_.)
SUB-FAM. 4. TARSIPEDINAE.--The genus _Tarsipes_ ought perhaps to be removed
from the present family. There is but a single species, which is a small
creature of 7 inches in total length, of which the tail measures 4 inches.
The teeth are much dwindled, the formula being I 2/1 C 1/0 Pm 1/0 M 3/3 =
22. The lower incisors are procumbent. The lower jaw, moreover, has not the
characteristic Marsupial inflection. The intestinal canal is without the
caecum present in the remaining Phalangeridae. It is a curious fact that
this aberrant little Phalanger should come from Western Australia, like the
even more aberrant _Myrmecobius_. Like the latter also, _Tarsipes_ has a
long exsertile tongue, with which, however, it extracts honey from flowers.
Probably it also catches minute insects in the corollas of the flowers. It
has been proved, in fact, that in captivity at any rate the animal is
insectivorous; for it has been known to eat moths.
FAM. 3. EPANORTHIDAE.--The extinct Epanorthidae of {146} Patagonia are
represented to-day by a small Marsupial which has been rediscovered within
the last two or three years. This little animal, formerly called
_Hyracodon_ (a pre-occupied name), is now termed _Caenolestes_, and is a
native of Colombia and Ecuador. There are two species, and of these _C.
obscurus_ is called by the inhabitants "Raton runcho," which means
opossum-rat. It lives apparently upon bird's eggs and small birds, though
it belongs to the Diprotodont division of the Marsupials. _Caenolestes_,
however, although diprotodont, has not the syndactylous character of the
digits of the feet already referred to in the Kangaroos and their allies.
The pouch is small and rudimentary. The dentition is I 4/3 C 1/1 Pm 3/3
M 4/4 = 46, and the teeth are said by Mr. Thomas to be much like those of
the Australian _Dromicia_.[90]
In the skull a peculiarity which does not bear upon its affinities to other
Marsupials, but is still interesting, is mentioned by Mr. Thomas. The
nasals are not sufficiently prolonged to meet the upper edge of the
maxillae, and so a vacuity is left, as in the skulls of many Ruminants
(_e.g._ the Sable Antelope). The palate is very imperfect; the foramina,
which render it so, reach as far forward as the last premolar. The lower
jaw has quite the appearance of that of a _Macropus_ or _Phalanger_, with
long and forwardly projecting incisors.
EXTINCT DIPROTODONTS.--The great _Diprotodon_ is a creature with a skull a
yard long, which must have been of the size of a large Rhinoceros. Though
closely allied to _Macropus_, it seems that this great beast did not hop
after the fashion of a Kangaroo, its limbs being of a more equal size than
in the Kangaroo. Recently some further remains of _Diprotodon_ have been
discovered in a lake known as Lake Mulligan, where they had apparently been
bogged. Professor Stirling has contributed an account of these remains,
which fills up a considerable gap in our knowledge. He has been able to
state the structure of the fore- and hind-limbs. Both limbs are
pentadactyle, the fingers of the fore-limb being approximately equal in
length and general development. In the hind-limb the hallux is small, and
consists of the metatarsal only. This bone is fixed in the position of
"extreme abduction," and is suggestive of an arboreal limb. Digits two and
three may have {147} been syndactylous, and the authors of the account[91]
of these bones think that the fourth toe may have shared in this
syndactyly. The metatarsal of the fifth digit is enormously expanded at its
edge, and seems to have furnished a strong support to the creature; this is
also seen in the metacarpal of the fore-limb. Probably, therefore,
_Diprotodon_ was quadrupedal in its mode of progression, with the emphasis
laid upon the little finger and the little toe instead of, as in ourselves,
the first toe. The hind-foot of the _Diprotodon_ could not be more unlike
that of a Kangaroo than it actually is.
[Illustration]
[Illustration]
FIG. 73.--_Diprotodon australis._ (After Owen.)
FIG. 74.--_Thylacoleo carnifex._ Side view of skull. (After Flower.)
Another giant among these Marsupials was the genus _Thylacoleo_, whose name
was given to it by Sir Richard Owen on the view that it was a Marsupial
Tiger. Sir W. Flower has, however, controverted this opinion, and the genus
is in fact, in spite of its large size, closely allied to the Phalangers
and {148} Cuscuses.[92] The dental formula is I 3/1 C 1/0 Pm 3/1 M 1/2; the
last premolar is a great blade-shaped tooth like that of _Potorous_.
_Nototherium_ was a creature smaller than _Diprotodon_, but still of large
size; it is believed to have been a burrowing creature, and to connect the
Wombats with _Diprotodon_. More certainly allied to the existing Wombat was
_Phascolonus_, a Wombat as big as a Tapir.
[Illustration]
FIG. 75.--_Nototherium mitchelli._ Side view of skull. x 1/6. (After Owen.)
Of extinct American Diprotodonts the Epanorthidae, already referred to in
connexion with the living _Caenolestes_, were the most prominent forms. The
genus _Epanorthus_ occurs in the Santa Cruz formation of Patagonia, which
is believed to be Miocene. The incisors are three in the upper jaw; and the
single incisor of each ramus of the lower jaw is a great chisel-shaped,
cutting instrument.
_Abderites_ is also typically Diprotodont by reason of the large projecting
incisors of the lower jaw. It has a large cutting tooth in the lower jaw,
which appears to be the last premolar, and is thus comparable to the great
cutting tooth of the lower jaw and of the upper jaw of the extinct
Phalanger, _Thylacoleo_. {149} It may also be comparable to the great
premolar of such Multituberculata as _Ptilodus_ and _Plagiaulax_. It is,
moreover, marked with vertical grooves.
An interesting form, which is unfortunately but little known, is the
Australian and Pleistocene genus _Triclis_, with one species, _T.
oscillans_. In having a minute canine tooth in the lower jaw it agrees with
some Phalangeridae, and being otherwise closely allied to _Hypsiprymnodon_,
it unites the Macropodidae with the Phalangeridae.
SUB-ORDER 2. POLYPROTODONTIA.
In this mainly carnivorous or insectivorous division of the Marsupials the
incisors are four or five on each side of the upper jaw, and one or two
fewer in the lower jaw. Figs. 76 and 77 illustrate the Polyprotodont and
Diprotodont dentitions. The canines are those of flesh-eaters and so are
the molars, being as a rule sharply cuspidate. As a rule, which has an
exception in the Peramelidae, there is no syndactylism of toes in the
hind-foot. This sub-order is at the present day Australian and American in
its range.
[Illustration]
FIG. 76.--Front view of the skull of Tasmanian Devil (_Sarcophilus
ursinus_), showing Polyprotodont and carnivorous dentition. (After Flower.)
FAM. 1. DASYURIDAE.--This family consists of Marsupials which are generally
pentadactylous, but with occasionally the hallux missing. The tail is long
but not prehensile. The pouch is present or absent. The teeth vary in the
different genera, but {150} the upper incisors are never less than three,
and may be as many as five in the upper jaw and six in the lower. The
canines are trenchant. There is no caecum.
[Illustration]
FIG. 77.--Front view of skull of Koala (_Phascolarctos cinereus_),
illustrating Diprotodont and herbivorous dentition. (From Flower.)
[Illustration]
FIG. 78.--Longitudinal section of the skull of the Thylacine (_Thylacinus
cynocephalus_). x 1/2. _a_, Angular process of mandible; _AS_, alisphenoid;
_BO_, basioccipital; _BS_, basisphenoid; _cd_, condyle of mandible; _ET_,
ethmoturbinal; _Ex.O_, exoccipital; _Fr_, frontal; _ME_, ossified portion
of mesethmoid; _MT_, maxilloturbinal; _Mx_, maxilla; _Na_, nasal; _OS_,
orbitosphenoid; _Pa_, parietal; _Per_, periotic; _Pl_, palatine; _PMx_,
premaxilla; _PS_, presphenoid; _Pt_, pterygoid; _SO_, supraoccipital; _Sq_,
squamosal; _Vo_, vomer. (From Flower's _Osteology_.)
The genus _Thylacinus_ contains but a single species, which is now limited
to Tasmania, and is generally known as the Tasmanian Wolf. It has the build
of an ordinary Wolf, and is of about the same size. The hinder part of the
body is marked with a series of black transverse bands. The hallux is
entirely wanting; the pouch opens backwards. The marsupial bones are minute
and unossified. The dental formula is I 4/3 C 1/1 Pm 3/3 M 4/4 = 46. There
are four mammae. This animal, now confined to Tasmania, {151} is getting
rarer on account of its sheep-killing propensities, and the consequent war
of extermination declared upon it by the colonists. It will, however, feed
upon other animals; and it is related that the first specimen ever captured
had in its stomach the remains of an Echidna! Mr. Thomas thinks that the
persistence of this and of some of the other larger carnivorous Marsupials
in Tasmania after their extinction in Australia is not unconnected with the
advent of the Dingo. But it is stated that the Thylacine is quite capable
of keeping even a pack of dogs at bay.
[Illustration]
FIG. 79.--Tasmanian Devil. _Sarcophilus ursinus._ x 1/10.
The genus _Sarcophilus_ has been frequently confounded with the next, but
it is kept apart by Mr. Thomas, who follows Cuvier in this. An alternative
generic name is _Diabolus_, which, like the first name, refers to the
habits and character of the single species which this genus contains. The
genus is more like _Thylacinus_ than is _Dasyurus_. The hallux is wanting,
and the teeth, though fewer in number (42), resemble those of the Thylacine
more closely than do those of the Dasyure. The species is called _S.
ursinus_, the popular name being Tasmanian Devil. It is black with a
variable number of white patches on the body. It is of about the size of a
Badger, and is, like the Thylacine, a nocturnal animal. The Tasmanian Devil
is said to be one of the most ferocious of animals, and to express its
ferocity by a "yelling growl."
{152} [Illustration]
FIG. 80.--Skull of _Dasyurus_. (Lateral view.) _al.sph_, Alisphenoid;
_ang_, angular process of mandible; _fr_, frontal; _ju_, jugal; _lcr_,
lachrymal; _max_, maxilla; _nas_, nasal; _oc.cond_, occipital condyle;
_par_, parietal; _par.oc_, paroccipital process; _p.max_, premaxilla;
_s.oc_, supraoccipital; _sq_, squamosal; _sq_', zygomatic process of
squamosal. (From Parker and Haswell's _Zoology_.)
[Illustration]
FIG. 81.--Dasyure. _Dasyurus viverrinus_. x 1/5. (After Vogt and Specht.)
The next genus of this family, _Dasyurus_, comprises five species, which
range over the whole of the Papuan and Australian sub-regions. The general
form is Viverrine, and the hallux is sometimes present though small. The
dental formula is as in the last genus, but the teeth "are more
insectivorous in their character." There are six or eight mammae. The
members of this genus are grey or brown, and spotted with white; they are
all arboreal, and feed largely upon birds and their eggs. Mr. Thomas has
pointed out that in two species, _D. viverrinus_ and _D. geoffroyi_, the
striae upon the foot-pads are absent, and that therefore these at least are
probably not so purely arboreal as the rest. The animals are not diurnal,
and during the day hide themselves in the hollow trunks of trees. They are
spoken of as "Native Cats," but have the general habits of Martens. _D.
maculatus_ is common in Tasmania, but is rare in Australia, thus
"approaching the condition now exhibited by the Thylacine and {153}
Tasmanian Devil, namely, complete extermination in Australia, where both
once lived." _D. hallucatus_ shows an approach to _Phascologale_ in its
five-toed hind-feet and slender build.
_Phascologale_ is a genus which, like the last, is usually arboreal
(although not _P. virginiae_ of North Queensland), but is of much smaller
size, the species not exceeding the dimensions of a rat. They have no
spots, but there is sometimes a stripe down the back. There are thirteen
species, which have the same range as the last genus. The hallux is present
though small, but the pouch is "practically obsolete," though there is a
small fold of skin behind the teats. The rhinarium is naked; the tail is
long, "bushy, crested, or nearly naked." The mammae are four to ten in
number. The dental formula is as in _Dasyurus_, and the teeth are not very
different in form; sometimes the last premolar is wanting. "The members of
this genus," remarks Mr. Thomas, "evidently take the place in the
Australian region filled in the Oriental by the Tupaiae, and in the
Neotropical by the smaller Opossums."
The genus _Sminthopsis_ comprises not more than four species, even smaller
than the last. The largest species, _S. virginiae_, is only 125 mm. in
length. The hallux is present, and there is a well-developed pouch. There
are forty-six teeth, as in the Dasyures. The feet are narrow with
granulated or hairy soles, whereas in _Phascologale_ they are broad with
smooth soles. The mammae are eight or ten. The genus ranges through
Australia and Tasmania.
The genus _Antechinomys_ has but a single species, which is a native of
Queensland and New South Wales. The build is Jerboa-like, and the animal
is, as might be inferred, terrestrial. The ears are very long, and the
limbs elongated; the hallux is absent; the teeth are exactly as in
_Sminthopsis_.
_Antechinomys_ has thirteen dorsal and seven lumbar vertebrae; three
sacrals and twenty-five caudals, the latter number being in excess of that
of its allies. The stomach is nearly globular, with approximated orifices;
the intestine measured 6.8 inches, a little more than twice the length of
the animal itself. _A. lanigera_ is a native of East Central Australia, and
appears to be entirely terrestrial in habit, and to progress by a series of
leaps--at any rate when going at full speed.
Professor Spencer, who found examples of this rare species, gives {154} an
interesting description of its habits. _Antechinomys_ has much the look of
the Australian Rat, _Hapalotis mitchelli_; and as the two animals lead a
similar kind of life, the resemblance is not unexpected. Professor Spencer
wonders why these creatures are saltatory in habit. The country which they
inhabit is arid, but with patches of grass and shrubs. For a big kangaroo
the advantage of the power of leaping over such obstacles may be obvious,
but not for the small and slender _Antechinomys_. The chief foes of this
rare Marsupial appear to be predatory birds; and Professor Spencer thinks
that the saltatory mode of progression may be more baffling to such
pursuers than even a rapid run.
The genus _Dasyuroides_ has been lately instituted by Professor Spencer for
a Marsupial from Central Australia somewhat intermediate between
_Sminthopsis_ and _Phascologale_. As there is but one species, the generic
will be considered with the specific characters. _D. byrnei_ is an animal
of about the size of the Common Rat. The hallux is absent. The tail is
fairly thick, but not "incrassated." There are six mammae, and the pouch is
but slightly developed, with two low lateral folds. The dentition is I 4/3
C 1/1 Pm 3/2 M 4/4. This Marsupial is nocturnal, and burrowing in habit.
Its food consists of insects.[93]
_Myrmecobius_ is so different from the last-described genera (DASYURINAE)
that it is usually separated from them as a sub-family MYRMECOBIINAE. The
animal is of a bright rufous colour, banded posteriorly with white. There
is no hallux, though the metatarsal belonging to that digit is present.
There are four mammae.[94] On the chest is a naked patch of some extent,
upon which open the ducts of a complex gland, which has been described and
figured by myself.[95] There is no pouch, but a tract of skin shows
indications of a pouch-like structure. The teeth are extraordinarily
numerous, fifty to fifty-four; the formula being I 4/3(4) C 1/1 Pm 3/3
M 5/6. Their resemblance to those of certain Jurassic Marsupials is dealt
with on p. 100.[96] In this matter lies of {155} course the chief interest
of the genus, which may be "an unmodified survivor from Mesozoic times, and
therefore from a time long before the Didelphyidae, Peramelidae, and
Dasyuridae were differentiated one from the other." Another ancient feature
(found in Jurassic mammals) is a mylo-hyoid groove upon the lower jaw,
which, however, is not always present, and its existence has therefore been
denied. The single species, _M. fasciatus_, is partly arboreal and partly
terrestrial in habit, and feeds upon ants. It is a Western and Southern
Australian form.
[Illustration]
FIG. 82.--Banded Australian Anteater. _Myrmecobius fasciatus._ x 1/5.
FAM. 2. DIDELPHYIDAE.--All the members of this family are pentadactylous.
The teeth are fifty in number, arranged thus: I 5/4 C 1/1 Pm 3/3 M 4/4. The
caecum is small; the pouch is generally absent; the tail generally long and
prehensile.
[Illustration]
FIG. 83.--Virginian Opossum. _Didelphys virginiana._ x 1/5. (After Vogt and
Specht.)
The genus _Didelphys_ contains most of the forms belonging to this family,
including as it does some twenty-three species. The Opossums are mainly
arboreal animals, insectivorous in their food; but the larger species eat
reptiles, birds, and their eggs. Several of the small species carry their
young, when able to leave the teats, on {156} their back, the tails of the
young being wrapped round that of the mother. It is not only the pouched
species which carry their young in something of this fashion. Azara's
Opossum, an animal as big as a cat, is said to carry its eleven young ones
(themselves as large as rats) on the back, though their foothold does not
appear to be strengthened by intertwining the tails. Even with this huge
family on her back, the mother can climb trees with considerable alacrity.
The mammae are seven to twenty-five in number. The genus has been lately
split up into a number of genera, _Marmosa_, _Dromiciops_, _Peramys_, etc.
[Illustration]
FIG. 84.--Thick tailed Opossum. _Didelphys crassicaudata._ x 1/5.
_Chironectes_ is hardly different from _Didelphys_. It has webbed
hind-feet, and is aquatic in habit. The one species of the genus is known
as the Yapock, and is a Central and South American form. It is of about the
size of a large rat, and appears to be an expert diver after the fish upon
which it lives.
FAM. 3. PERAMELIDAE.--The Bandicoots, although clearly belonging to the
Polyprotodont Marsupials, yet agree with the Diprotodonts in the fact that
the second and third toes of the feet are bound up in a common integument,
which is not the case with the Diprotodont _Caenolestes_. The hind-feet are
longer than the front; of the former limb, two or three of the fingers
alone are long and functional; the others are rudimentary or absent. Tail
long, hairy, and non-prehensile. Dentition I 5/3 C 1/1 Pm 3/3 M 4/4 = 48,
or sometimes, owing to the absence of a pair of upper incisors, 46. There
is a caecum.
{157} [Illustration]
FIG. 85.--Bones of manus. A, of _Choeropus castanotis_. x 2. B, of
Bandicoot (_Perameles_). x 1-1/2. _c_, Cuneiform; _l_, lunar; _m_, magnum;
_R_, radius; _s_, scaphoid; _td_, trapezoid; _tm_, trapezium; _u_,
unciform; _U_, ulna; _I-V_, digits. (From Flower's _Osteology_.)
[Illustration]
FIG. 86.--Rabbit Bandicoot. _Peragale lagotis._ x 1/5.
The genus _Peragale_, the Rabbit-Bandicoots, consists of two species
entirely Australian in range. The enormous ears (whence "Rabbit" Bandicoot)
distinguish this genus from _Perameles_. The pouch opens backwards, and
there are eight mammae. _P. lagotis_, the only species about whose ways of
life anything is {158} known, burrows in the soil, whence it extracts
grubs; it is also a grass-feeder, and it is said that its likeness to a
Rabbit in appearance is strengthened by its similarity in flavour!
_Perameles_ is a genus consisting of twelve species, which are found in
Tasmania, Australia, and New Guinea. Like the last genus, from which it
does not widely differ in other points, _Perameles_ consists of species
which combine insectivorous and vegetarian habits. One species is said to
become in captivity an expert in catching mice. The pouch opens backwards,
and there are six or eight mammae.
[Illustration]
FIG. 87.--Pig-footed Bandicoot. _Choeropus castanotis._ x 1/3.
The last genus of this family is _Choeropus_, containing but one species,
_Ch. castanotis_. It is confined to the Australian continent. It is to be
distinguished from the last two by the fact that there are only two
functional digits, the second and third, in the fore-limb; the fourth is
rudimentary; the other two are absent. It burrows, and is omnivorous like
its allies. The two metacarpals that are developed are very long and
closely apposed; they have hence a remarkably pig-like aspect, and justify
its name. The pouch opens backwards, and there are eight mammae.
FAM. 4. NOTORYCTIDAE.--This family contains but a single genus and species,
the recently-discovered _Notoryctes typhlops_.[97]
{159} We may regard as family-characters the pentadactyle limbs, the
existence of three pairs of incisors in the lower and four in the upper
jaw; and the tritubercular nature of the upper molars. _Notoryctes
typhlops_, the "Marsupial Mole" as it has been termed, was originally
discovered by Professor Stirling in Central South Australia. It is a
burrowing creature, clothed in a silky fur of a pale golden red, without
external ears. It has been compared in appearance with _Chrysochloris_, the
Cape Golden Mole, and the eminent palaeontologist, Professor Cope, has even
insisted upon a real genetic affinity. Edentate affinities have also been
suggested. But _Notoryctes_ has a small pouch opening backwards as in other
Polyprotodonts,[98] and as it also possesses marsupial bones it must
undoubtedly be referred to the Marsupialia. The animal shows many curious
adaptations to its underground mode of life. Certain of the vertebrae in
the neck and in the lumbar region are firmly welded together, giving of
course a strength of push, and suggesting the Armadillos; the claws of the
third and fourth front-toes are greatly enlarged, and must be efficient
digging organs. The track of the animal is like that of a railway in
mountainous country; it burrows for a short distance, emerges, and then
descending beneath the surface re-emerges. The red colour of the fur is
said to be in harmony with the arid soil in which it lives. The native name
of the creature is "Urquamata." It feeds upon ants and other insects.
[Illustration]
FIG. 88.--Australian Marsupial Mole. _Notoryctes typhlops._ x 1/4.
EXTINCT POLYPROTODONTS.--Of extinct Polyprotodonts (apart from those
Mesozoic forms which are considered on p. 100) extinct species of
_Thylacinus_ and _Dasyurus_ are known from {160} Australia. The most
interesting fact in connexion with the Tertiary Polyprotodonts is the
existence in South America of such genera as _Prothylacinus_ and
_Amphiproviverra_, which are not merely Polyprotodonts but definitely
Dasyures, and not referable to the Didelphyidae.
These forms have been included in an order, SPARASSODONTA. But it is not by
any means certain whether these forms are rightly placed in the
neighbourhood of the carnivorous Marsupials; it is possible that they ought
to be relegated to the Creodonta or to their allies. Their structure is in
fact somewhat intermediate between those two groups. The teeth seem to be
carnivorous and Marsupial-like in form; but as already mentioned, in
connexion with the general structure of teeth, more than a single premolar
is replaced. These animals in fact, in so far as regards their teeth, are
midway between the Marsupials and the typical Eutheria. The angle of the
lower jaw is inflected, but the palate is not marked by deficient
ossification. At least this is not the case with all the members of the
group. Whether the small _Microbiotherium_, which is made the type of a
family, is rightly referred here is not certain. This animal had palatine
vacuities as well as an inflected angle to the lower jaw.
* * * * *
{161}
CHAPTER VIII
EDENTATA--GANODONTA
ORDER II. EDENTATA
Terrestrial, partly subterranean, or arboreal creatures of quite small to
gigantic size (some extinct genera), with frequently a covering of scales
or bony scutes. Limbs clawed. Teeth either totally absent or, if present,
imperfect in structure, being without enamel, and not forming a complete
series; incisors and canines being as a rule absent. Teats axillary,
pectoral, or inguinal.[99] Retia mirabilia very common in the extremities.
To this group the name of Bruta was given by Linnaeus, but then it included
not only the families which we now place in the modern order Edentata, but
also the Elephant and the genus _Trichechus_. Mr. Thomas has proposed to
change the name into Paratheria, which name is suggestive of what he and
some others think concerning the systematic position of the group, _i.e._
that it is not to be placed in the Eutherian group of mammals at all, but
represents a separate twig which has arisen with the Eutheria from a low
mammalian stock. This view can hardly be accepted if the Ganodonta--which
will be treated of presently--be really ancestral Edentates, for they are
not in any way a Prototherian mammalian group, so far as their remains
enable us to judge.
The Edentata contain the Sloths, Ant-bears, Armadillos, _Manis_ and
_Orycteropus_, among living forms. The great Ground-Sloths, _Megatherium_,
etc., and Armadillos, _Glyptodon_, etc., represent the extinct forms.
The name that has been applied to this group is inappropriate {162}
inasmuch as many Edentates have teeth. It is, however, by a number of small
tooth-characters that the order can be defined. Thus if teeth are present
they are simple in structure, without enamel in the adult condition, though
a rudimentary enamel-organ has been discovered in an Armadillo. The teeth,
moreover, are not found in the anterior part of the mouth, and they grow
from persistent pulps; neither is there much differentiation among them. It
is not possible, however, to speak of the Edentates as quite homodont,
since in _Orycteropus_ there are large cheek-teeth; but there is at any
rate not a marked heterodonty in that or in any other Edentate. It used to
be said that the Edentates were monophyodont. But the Armadillo _Tatusia_
was subsequently found to possess a second suppressed dentition, and after
this discovery Mr. Thomas proved that _Orycteropus_ is also diphyodont.
Since then other Armadillos have been shown to be diphyodont; and the whole
group therefore, so far as concerns those members that have teeth, may in
all probability be regarded as typically mammalian in this respect.
These characters are slender enough, but there seem to be no others by
means of which the members of this order can be satisfactorily linked
together. The fact is, that we have here a polymorphic order which contains
in all probability representatives of at least two separate orders. We have
at present a very few, and these perhaps highly modified, descendants of a
large and diverse group of mammals. For convenience' sake they will be all
treated of under the head of Edentata.
Although for the probable reasons already stated it is a hard matter to
frame such a definition as will include all existing Edentates, it is easy
enough to define two groups in this heterogeneous order; to define one
group we should say, rather, and then to regard the leavings as forming
another not so easily definable a group.
The perfectly-definable group is that which includes the American
Anteaters, the Armadillos, and the Sloths. In all these creatures, which
may certainly be regarded as representing on their own account as many
family types, there are a number of important and highly-characteristic
anatomical features which they share in common. So exceedingly different
are these three types in general appearance and (correlated with that) in
way of life that these common characters acquire increased importance.
{163}
[Illustration]
FIG. 89.--Great Anteater (_Myrmecophaga jubata_). A, Side view of twelfth
and thirteenth thoracic vertebrae. B, Posterior surface of second lumbar
vertebra. C, Anterior surface of third lumbar vertebra, x 2/3. _az_,
Anterior zygapophysis; _az_^1, _az_^2, _az_^3, additional anterior,
articular facets; _cc_, facet for capitulum of rib; _m_, metapophysis;
_pz_, posterior zygapophysis; _pz_^1, _pz_^2, _pz_^3, additional posterior
articular facets; _t_, transverse process; _tc_, facet for articulation of
tubercle of rib. (From Flower's _Osteology_.)
The first of these characters is the series of additional zygapophyses on
the posterior dorsal and lumbar vertebrae; these are very clear in the
Anteaters and Armadillos; less clear, but still obviously represented, in
the Sloths. In the second place, they all possess a clavicle, rudimentary,
it is true, in the Great Ant-bear, but still present. Thirdly, the testes
are abdominal throughout life, a character which they share with such
lowly-organised animals as the Monotremata and the Whales. Finally, and
this is by no means a matter to be overlooked, not only are all the
existing members of this group American in range, but there is no evidence
to prove that they have ever existed elsewhere. No European or Old-World
{164} representatives have as yet been discovered which can be referred to
the Anteater, Armadillo, or Sloth type with certainty.[100]
Of these American forms, which will be treated of first, the Armadillos are
further apart from either Sloths or Anteaters than the last two are from
each other. The name XENARTHRA has been suggested for the American
Edentates with "abnormal" vertebral articulations; the corresponding
NOMARTHRA includes the Old-World forms.
[Illustration]
FIG. 90.--Right scapula and clavicle of Two-toed Sloth (_Choloepus
hoffmanni_). x 1-2/3. _a_, Acromion; _af_, prescapular fossa; _c_,
coracoid; _cl_, clavicle; _csf_, coraco-scapular foramen; _gc_, glenoid
cavity; _pf_, postscapular fossa. (From Flower's _Osteology_.)
Between the Sloths and Anteaters the extinct _Megatherium_ and some of its
allies are to a certain extent intermediate. But it may be pointed out in
the first place that there are certain important resemblances between the
living forms. In both, retia mirabilia are developed in the tail (in spite
of its reduction in the Sloths) and in the limbs. But, as is well known,
retia are also found in other mammals far removed in the series from these
under consideration. The reproductive organs generally are very similar,
and they have both a dome-shaped and deciduate placenta. The latter
character they share with the Armadillos and with the Aard Vark; _Manis_
having a non-deciduate placenta which is, like that of the Carnivora,
zonary in form. The Edentates, at any rate the American forms, have a
double vena cava posterior and no azygos vein. This condition is also met
with among Whales.
Osteologically the Sloths and Anteaters are united by the fact that the
coracoid becomes fused with the coracoid border of the scapula, thus
forming a foramen; the importance of this character is, however, discounted
by its occurrence in three genera of Cebidae.
The above facts embody the views of Sir William Flower.[101]
{165} A subsequent study of the brain and of the muscles of these animals
has led to results not entirely in harmony with these views.
Dr. Elliot Smith is of opinion,[102] after an exhaustive study of the
Edentate brain, that in this region of the body the present group shows
very decided points of likeness to the Carnivora; that is, so far as
concerns the Anteaters. On the other hand, _Orycteropus_ is as distinctly
comparable with a primitive Ungulate type, such as is exemplified by
_Moschus_. "If the brain of _Orycteropus_," he remarks, "were given to an
anatomist acquainted with all the other variations of the mammalian type of
brain, there is probably only one feature which would lead him to hesitate
in describing it as an exceedingly simple Ungulate brain. That one feature
is the high degree of macrosmatism.[103] _Manis_, on the other hand, does
not come especially near to _Orycteropus_. The brain of _Manis_ conforms to
a simple type of architecture, which agrees in many points with both those
of _Orycteropus_ and the American Edentates; there is not sufficient
evidence to show which type it really favours." Elliot Smith would, in
fact, agree with Max Weber that it is better, if a division is to be made,
to divide the group into three orders:--the Xenarthra (Sloths, Anteaters,
and Armadillos), Tubulidentata (_Orycteropus_), and Squamata (_Manis_),
instead of into Xenarthra and Nomarthra.
Messrs. Windle and Parsons[104] are disposed to see in muscular
similarities reasons for uniting _Manis_ with the American Edentates,
though they confess to being unable to place _Orycteropus_; in this animal,
they say, "we are more struck by the generalised mammalian arrangement of
its muscles than by any special Edentate characters. There are, however,
two muscles in _Orycteropus_ which show peculiarities not found elsewhere
than in the Edentates";--the triceps, which has more than one scapular
head, and the tibialis posticus, which is double. They conclude that
_Orycteropus_ "presents some feeble claims to be taken into the order."
We shall here adopt the following divisions. {166}
SUB-ORDER 1. XENARTHRA.
FAM. 1. MYRMECOPHAGIDAE.--The family Myrmecophagidae contains three genera,
all South American in range. These genera, _Myrmecophaga_, _Tamandua_, and
_Cycloturus_, agree greatly in their outward form. They are all without
teeth, and have long snouts and long protrusible tongues. The fur is thick,
and they have powerful claws wherewith to break down the strong ant-hills
upon whose inhabitants they feed. _Tamandua_ and _Cycloturus_ are arboreal,
_Myrmecophaga_ is terrestrial in habit. The claws of the arboreal forms are
useful to destroy the bark, and thus bring to light insects which lurk in
such situations.
[Illustration]
FIG. 91.--Great Anteater. _Myrmecophaga jubata._ x 1/10.
The genus _Myrmecophaga_ contains but one species, the Great Anteater,
_Myrmecophaga jubata_. It is a large and handsome animal, with long,
shaggy, greyish-black hair and a broad white stripe across the shoulder.
The coloration is similar in the two sexes. Including the long and bushy
tail it reaches a length of over 7 feet. It is on account of its long
tongue and greatly developed salivary glands that this and the allied
genera were originally placed with _Manis_. It is the submaxillary glands
which are so enormous; they extend back over the chest, and open by three
distinct ducts, of which two unite just before the external orifice. {167}
Along their course these ducts are provided with a sphincter muscle, which
squeezes the secretion towards the external orifice into the mouth-cavity.
The stomach is somewhat gizzard-like. The intestine has no caecum.[105]
The Anteater's great claws are not only serviceable in tearing up the
ground to get at its food; armed with them he does not fear, as Mr.
Waterton remarked, "the fatal pressure of the serpent's fold or the teeth
of the famished jaguar." An Anteater, too, is more than a match for a big
dog, and will rip open its belly with the claws while the dog is vainly
trying to make an impression with its teeth upon the shaggy hair.
_Tamandua_ is a smaller animal than _Myrmecophaga_, and, as has been
stated, is arboreal; associated with this habit is a prehensile tail. Like
the last genus, _Tamandua_ has a rudimentary clavicle, this bone being well
developed in the little _Cycloturus_.
[Illustration]
FIG. 92.--Skull of Anteater (_Myrmecophaga_). Lateral view, _al.sph_,
Alisphenoid; _cond_, condyle of mandible; _cor_, coronoid process of
mandible; _ex.oc_, exoccipital; _ext.aud_, external auditory meatus; _fr_,
frontal; _ju_, jugal; _lcr_, lachrymal; _max_, maxilla; _nas_, nasal;
_occ.cond_, occipital condyle; _pal_, palatine; _par_, parietal; _p.max_,
premaxilla; _s.oc_, supraoccipital; _sq_, squamosal; _ty_, tympanic. (From
Parker and Haswell's _Zoology_).
The skull of the Anteater[106] is very long and low; the fore-part is
tubular, and there appear to be no traces of teeth. The premaxilla is very
small; the zygomatic arch is imperfect, and does not reach the squamosal
behind. A curious feature of this genus, which it shares with some Dolphins
and other Whales, is that the pterygoid bones develop palatine plates which
meet each other in the middle line, and thus shift the opening of the {168}
posterior nares backwards. This is also, of course, a character of various
lower vertebrates. Another Whale-like character in the skull is the weak
character of the mandible, which does not give off a marked coronoid
process. But then in neither group is there much mastication. The tympanic,
periotic and squamosal are ankylosed together. A peculiarity of the
cervical vertebrae is that (as in the Camels) the vertebrarterial canal of
several of the vertebrae perforates the pedicle obliquely. There are
fifteen or sixteen dorsal and three or two lumbar vertebrae. The additional
zygapophyses upon the former have been already referred to. The mode of
articulation of the ribs is highly singular.
[Illustration]
FIG. 93.--Skull of Anteater (_Myrmecophaga_). Ventral view. Letters as in
Fig. 92. In addition, _b.oc_, basioccipital; _glen_, glenoid surface for
mandible; _pter_, pterygoid. (From Parker and Haswell's _Zoology_.)
[Illustration]
FIG. 94.--Side view of three mesosternal segments of a young Anteater
(_Tamandua_), showing the mode of articulation of the sternal rib (_sr_).
_mst_, The upper or inner surface of the mesosternal segment; _sy_, the
synovial articulation between the segments. (From Flower's _Osteology_,
after Parker.)
Each segment of the sternum (of which there are eight) is separated from
the next by a synovial membrane: and it has on either side two facets for
articulation with the ribs. The way in {169} which these latter bones are
connected with the sternum is curiously like their mode of connexion with
the spinal column at their other end. With this may be possibly compared
the double articulation of the single rib (which articulates with the
sternum) in the Rorquals. In _Cycloturus_ this mode of articulation does
not occur.
The manus of _Myrmecophaga_ is five-fingered. Of these the third digit (as
in Perissodactyles) is the most prominent; it is at least double the width
of the second or third finger; the pollex is very slender. In the little
_Cycloturus_ this is carried to a greater extent: the third digit is
relatively enormous; the first and the fourth have become quite
rudimentary; while the fifth is only just recognisable as a minute
ossification.
[Illustration]
FIG. 95.--A, Manus of Great Anteater (_Myrmecophaga jubata_). x 1/3. B,
Manus of Little Anteater (_Cycloturus didactylus_). x 2. _c_, Cuneiform;
_l_, lunar; _m_, magnum; _p_, pisiform; _s_, scaphoid; _td_, trapezoid;
_tm_, trapezium; _u_, unciform; _I-V_, digits. (From Flower's _Osteology_.)
The chevron-bones in the tail surround a well-developed rete mirabile, a
rete being found in precisely the same position in the Eastern _Manis_.
_Tamandua_ has also retia, which are also found in the Spider-monkeys.
_Cycloturus_ is by far the smallest of the Anteaters. It has {170} only two
toes on the fore-feet. It is to be distinguished, anatomically, from its
larger relatives by the complete clavicle, and by the fact that the
pterygoids do not meet in the middle line of the skull. The ribs, too, are
unusually wide, as in the Whale _Neobalaena_, and form a bony encasement
for the body. It has two small caeca. Of fossil Anteaters but little is
known. The most interesting form is _Scotaeops_, interesting because it has
two small back teeth, which are totally lost in its living allies. The huge
Patagonian extinct bird _Phororhacos_, first known by a lower jaw, was at
one time regarded as a member of this group on account of the form and
edentulous character of the jaw.
[Illustration]
FIG. 96.--Unau, or Two-toed Sloth. _Choloepus didactylus._ x 1/5. (After
Vogt and Specht.)
{171} [Illustration]
FIG. 97.--Skull of Three-toed Sloth. _Bradypus tridactylus._ Lateral view.
_fr_, Frontal; _ju_, jugal; _lcr_, lachrymal; _max_, maxilla; _nas_, nasal;
_par_, parietal; _s.oc_, supra-occipital; _ty_, tympanic. (From Parker and
Haswell's _Zoology_.)
FAM. 2. BRADYPODIDAE.--The Sloths, genera _Bradypus_ and _Choloepus_, come,
as already stated, very near to the Anteaters, in spite of their striking
difference in appearance. The Sloths are purely arboreal creatures, with
strong recurved claws, which serve as hooks to keep them suspended from the
lower side of a branch. The three-toed sloth, _Bradypus_ (or "Ai"), has the
exceptional number of nine cervical vertebrae; the two-toed sloth,
_Choloepus hoffmanni_ (or "Unau"), has the equally exceptional number of
six. The hair is long and shaggy, and gets an adventitious green colour
from the presence of minute algae.[107] This gives to the animal the
appearance of a lichen-covered bough, a resemblance which is increased in
one species by an oval mark upon the back, which suggests forcibly a broken
end of such a branch. The likeness of a Sloth to its surroundings is
pointed out by Dr. Siemann,[108] who observed that a species occurring in
Nicaragua "has almost exactly the same greyish-green colour as _Tillandsia
usneoides_, the so-called 'Vegetable Horsehair' common in the district....
If it could be shown that it frequented trees covered with that plant ...
there would be a curious case of mimicry between the sloth's hair and the
_Tillandsia_, and a good reason why so few of these Sloths are seen." The
stomach in the Sloths is complicated in structure, with several chambers;
one of these gives off a long crescent-shaped caecum. The skull of the
Sloths agrees in a number of particulars with that of the Anteaters. {172}
[Illustration]
FIG. 98.--Skeleton of Three-toed Sloth. _Bradypus tridactylus._ (After de
Blainville.)
The zygoma is incomplete, though the part connected with the frontal has a
strong downward process like that found in _Diprotodon_ and some other
mammals. There is, moreover, a process from the squamosal, though it does
not reach the anterior part and thus {173} complete the arcade. The
premaxillaries are very small, and are usually lost in dried skulls.
Coupled with these points of likeness are some differences. The lower jaw,
for instance, has a well-marked coronoid process. The pterygoids do not
meet in the middle line. The teeth are five or four in each half of each
jaw. There is no trace of a second set.
A peculiarity of the Sloths is the enormous number of dorsal vertebrae.
There are twenty-three of these in _Choloepus hoffmanni_, but only fifteen
to seventeen in the Three-toed Sloth, _Bradypus_. As in other American
Edentates, the acromion joins the coracoid. This connexion occurs in both
the Two-toed and the Three-toed species. The limbs of these creatures are
very long, a concomitant of an arboreal life. The femur has no third
trochanter. The genus _Bradypus_, which by reason of the fact that it has
not lost the third toe on the manus seems to be more primitive than
_Choloepus_, shows another structural feature which does not bear out this
conclusion. The trapezoid and the os magnum of the carpus are united, while
in _Choloepus_ they are perfectly distinct bones.
The intestine has no caecum.
There are several species of Sloths. Eminently perfect though the
organisation of the Sloth in relation to its particular surroundings
appears to us, Buffon selected the animal as the very type of imperfection
in nature. "One more defect," he wrote, "they could not have existed."
FAM. 3. DASYPODIDAE.--The family Dasypodidae or Armadillos contains a
considerable number of genera. _Tatusia_, _Tolypeutes_, _Dasypus_,
_Xenurus_, _Priodon_,[109] and _Chlamydophorus_. They have all a more or
less rigid covering of bony plates imbedded in the skin, which are not in
the least comparable with the scales of the Manis. Save the Whales, in one
or two genera of which traces of a dermal armature exist, the Armadillos
are unique among existing mammals in this particular. The term "Edentate"
is especially inapplicable to the Armadillos; the genus _Priodon_ may have
more than forty teeth in each jaw; a total of ninety was found in one
specimen examined by Professor Kuekenthal. In the tendency of the teeth to
multiply, we have another example of a state of affairs which characterises
so many Whales. Generally, however, seven to nine is the number of teeth in
each {174} half jaw, of which one is often implanted in the premaxilla. The
Armadillos show their alliance with the other American Edentates in the
points enumerated above. Their teeth specially ally them to the Sloths,
while the salivary and digestive organs generally are on the Anteater plan,
but present a less extreme development. There are, however, caeca, paired
as in birds, in the genera _Dasypus_ and _Chlamydophorus_. The others have
none. But there is a dilatation at the commencement of the large intestine,
which is not very different from the slightly-developed caeca of _Dasypus_.
There are certain peculiarities in the skeleton, which distinguish this
family.
[Illustration]
FIG. 99.--Skull of Armadillo. _Dasypus sexcinctus._ x 2/3. _ex.oc_,
Exoccipital; _fr_, frontal; _max_, maxilla; _nas_, nasal; _par_, parietal;
_peri_, periotic; _p.max_, premaxilla; _s.oc_, supraoccipital; _sq_,
squamosal; _ty_, tympanic. (From Parker and Haswell's _Zoology_.)
{175}
[Illustration]
[Illustration]
FIG. 100.--Bones of the right manus of the Hairy Armadillo. _Dasypus
villosus._ x 2/3. _c_, Cuneiform; _l_, lunar; _m_, magnum; _p_, pisiform;
_R_, radius; _s_, scaphoid; _td_, trapezoid; _tm_, trapezium; _u_,
unciform; _U_, ulna; _I-V_, digits. (From Flower's _Osteology_.)
FIG. 101.--Bones of the manus of the Great Armadillo. _Priodon giganteus._
x 1/3. _a_, An accessory carpal ossicle in front of the pisiform, which is
not seen in the figure. Other letters as in Fig. 100. (From Flower's
_Osteology_.)
The skull in the Armadillos presents a number of likenesses to the other
American Edentates.[110] The premaxillaries are small, but are larger in
_Dasypus_ than in _Tatusia_. On the other hand the lachrymals are larger in
the latter. The zygomatic arch is complete, but there is no downward
process as in the Sloths. In _Tatusia_ (but not in _Dasypus_) the "short
thick pterygoids add somewhat to the hard palate." This is clearly a
beginning or a remnant of the quite crocodilian character of the palate of
_Myrmecophaga_. In the cervical vertebrae we see the Whale-like character
of fusion between individual vertebrae; and also, as in the Whales, the
degree to which this fusion is carried out varies; two to four may be thus
united. The additional articular facets upon the dorsal vertebrae have been
already commented upon as a point of important likeness to other American
Edentates. The dorsal vertebrae are commonly eleven in number, the lumbar
being three. But in _Priodon_ the numbers are twelve and two respectively.
There are traces to be observed of the double-headed attachment of the ribs
to the sternum. The shoulder girdle of the Armadillos is somewhat diverse
in form in different genera; the acromion is always large, and is
remarkable in _Priodon_ for the fact that the humerus also articulates with
it, its extremity being recurved, and forming a socket for this purpose. As
in some other Edentates there is a second spine on the scapula behind the
first. The clavicle is strong. There is some variation in the form of the
manus. It is five-fingered in _Dasypus_; in _Tolypeutes_ the first digit
has vanished; on the other hand, in _Priodon_, the fifth has become
rudimentary {176} and the third enormously enlarged. This latter fact
recalls the arrangement characteristic of _Myrmecophaga_. The pelvis is
greatly attached by the ischium to the vertebral column. The femur has a
third trochanter.
The various forms of Armadillos are largely distinguished by the number of
movable thin bands of scutes lying between the large anterior and posterior
shields. Thus we have _Dasypus sexcinctus_, _Tolypeutes tricinctus_, etc.
[Illustration]
FIG. 102.--Pelvis and sacrum of Armadillo. _Dasypus sexcinctus._ _ac_,
Acetabulum; _il_, ilium; _isch_, ischium; _obt.for_, obturator-foramen;
_pect.tub_, pectineal tubercle; _pub_, pubis. (From Parker and Haswell's
_Zoology_.)
The little Pichi-chago (or, more correctly, Pichy-ciego), _Chlamydophorus_,
which only grows to about 5 inches in length, has no movable bands at all.
It is covered with a uniform series of plates, which, moreover, are not
discontinuous at the neck. It differs, too, from the prevailing
Armadillo-type by the absence of conspicuous external ears. In the anterior
part of the body the armature consists of little more than the horny
plates, which in other Armadillos overlie the bony dermal plates. In the
hinder region the bony plates are strong. In this animal, therefore, we
have the dermal armature reduced to a minimum; but it must be noticed that,
like the extinct Glyptodons, the armature is continuous and nowhere ringed.
The genus _Tolypeutes_, of which the best-known species is _T. tricinctus_,
the Apar (there are two other species in the genus), can roll itself up
into a ball like the Pill-Millipede (_Glomeris_), and, protected by its
armour, roll away from its enemies like the Arthropod under similar
circumstances. This mode of protection, be it observed, is also adopted by
the Pangolin and by the {177} Hedgehog. The genus has only three movable
bands. The tail is short, and is covered with large tubercles. This genus
is very markedly digitigrade when running.
[Illustration]
FIG. 103.--Three-banded Armadillo or Apar. _Tolypeutes tricinctus._ x 1/4.
[Illustration]
FIG. 104.--Peludo Armadillo. _Dasypus sexcinctus._ x 1/4. (After Vogt and
Specht.)
The Peludo, _Dasypus sexcinctus_, is, like other Armadillos, an omnivorous
creature, and appears to be particularly fond of carrion. It will burrow up
to a decaying carcase like the ground-beetles. {178} Mr. W. H. Hudson has
described the way in which this Armadillo will kill a snake by holding it
down and literally sawing the reptile in half by help of the sharp and
serrated edges of the carapace. _Dasypus_ has a very short tail, which is
shielded by distinct rings near the base.
_Tatusia novemcincta_ is a species with nine movable bands. The genus has
four teats; the ears are near together. There are no caeca and no azygos
lobe to the lung. A species apparently belonging to this genus, but
described under the generic names of _Cryptophractus_ and _Praopus_, is
remarkable for the thick covering of hair, not entirely wanting but usually
thin in other Armadillos. In this particular species the coat of hair is so
thick as to conceal the underlying plates of the carapace. The individual
hairs are stiff, and one inch and a half in length.[111]
The genus _Xenurus_ contains several species, the best known of which is
inaptly named _X. unicinctus_. As a matter of fact the characteristic
feature of the genus is the existence of twelve or thirteen movable plates
between the two ends of the body. _X. unicinctus_ has twelve dorsal and
three lumbar vertebrae. This Armadillo, known by the vernacular name of the
Cabassou, has one of the most modified hands that are found in the family.
The first two digits are slender and elongated; but are quite normal in the
number of their phalanges. In the remaining three digits the metacarpal is
short and broad, while the proximal phalanx is either suppressed altogether
or fused with the metacarpal, the middle phalanx is present but short,
while the third phalanx is very large indeed. As in _Dasypus_, but not as
in _Tatusia_, which is in so many other respects divergent from these
genera, the lungs have an azygos lobe. As a small point of difference,
tending to show an alliance between the genera _Xenurus_ and _Dasypus_ and
their difference from _Tatusia_, is the deeply-imbedded gall-bladder; this
sac is not nearly so deeply plunged into the hepatic tissue in _Tatusia_.
_Xenurus_ has no caecal dilatations. The brain "is intermediate in its form
and surface markings between _Dasypus_ and _Tolypeutes_." The small
intestine is nearly eighteen times the length of the large. But these
intestinal measurements are not of much avail in this group as marks of
affinity, since in three species of _Dasypus_ Garrod gives the following
widely-divergent lengths:--_D. villosus_, 11.5 feet and 1.25; _D. minutus_
{179} 5.1, with a large intestine of no less than 7 feet; _D. vellerosus_
4.3 and .66.
_Priodon_ is the giant of its race. This Armadillo may reach a length of 3
feet to the base of the tail. The tail is some 20 inches long. The large
number of teeth has been already noticed. There are twelve or thirteen
bands. Other points in the structure of this genus have already been
mentioned, and need not be recapitulated. This Armadillo feeds upon
termites and carrion.
_Scleropleura_ is unfortunately but imperfectly known. The single species,
named by Milne-Edwards[112] _S. bruneti_, is apparently a very rare
inhabitant of Brazil. It is known by a single skin, which was tanned by the
hunter who obtained it. Thus the hair, if any, has dropped out. The plates
in the skin are deficient along the back and even upon the top of the head,
and are barely represented upon the tail posteriorly. The ears are small
and distant from each other. The tail is longish, about one-third of the
length of the body. The total length of the creature including the tail is
rather more than a foot and a half. The hunter who obtained it regarded it
as a hybrid between an Armadillo and an Anteater.
EXTINCT XENARTHRA.--There are a good many extinct forms of Armadillo, apart
of course from the Glyptodons. _Peltephilus_ is referred to later (p. 186).
_Dasypus_ was represented by a large form, 6 feet long, with a skull of one
foot in length. The genus _Eutatus_ was also large. The carapace was formed
of thirty-three distinct bands, of which the last twelve are soldered
together, but not fused into a shield as in _Dasypus_, etc.
An extinct group of American Edentates, termed the GRAVIGRADA,[113] are
somewhat intermediate between the Sloths and the Anteaters. A number of the
genera are well known from complete skeletons.
One of the typical forms of this group is _Mylodon_, which, together with
its immediate allies, is often placed in a separate family, MYLODONTIDAE.
_Mylodon_ itself was a large creature, as big as a Rhinoceros. It was
covered externally by armour in the skin, which did not form a massive
armature as in the Glyptodonts, but was in the {180} form of scattered
plates, small and not fused together. The general aspect of the skull is
decidedly Sloth-like. As in that animal, the malar bone is bifid
posteriorly, and between the bifurcation is embraced the process of the
squamosal. This latter is thus more developed than in the Sloth, but there
is no actual union between it and the malar. The premaxilla is small. The
lower jaw has both coronoid and ascending processes, and is massive. There
are five teeth on each side above, and four on each side below, as in the
Sloths. There are the normal seven cervical vertebrae and sixteen dorsals.
The limbs are not long and slender,but short and strong, the animal having
been terrestrial. The fore-feet were five-toed, of which the three inner
toes had claws. The hind-feet were only four-toed, and the two inner only
were clawed.
[Illustration]
FIG. 105.--_Mylodon robustus._ (Restoration, after Owen.)
_Scelidotherium_ is a genus which is a trifle smaller than the last. It has
only four properly-developed toes in the fore-foot, the thumb being
rudimentary; of these, the first two bear claws. The hind-feet are also
four-toed. Like _Mylodon_, _Scelidotherium_ is a Pleistocene genus.
_Glossotherium_ has a skull very much like the last two genera; but it is
remarkable for the fact that the nostrils instead of being unprotected with
bone anteriorly are there closed by a plate of bone formed by the
well-developed premaxillae, the nostrils appearing at the sides, and giving
the skull a curious likeness to that of a Chelonian. From a series of
recent and most important observations it appears to be clear that this
genus has survived into quite modern times.[114]
{181}
The well-known naturalist of La Plata, Senor Moreno, engaged in studies
connected with the political boundary line between Chili and the Argentine,
had occasion to visit Consuelo Cove on Last Hope Inlet in Patagonia.
Hanging from a tree he noticed a piece of dried skin, which at once struck
him as looking more like the remains of a Mylodon than of any living
animal. The inhabitants regarded this piece of skin as a great curiosity,
but were of opinion that it was the hide of a cow encrusted with pebbles!
This fragment from a bygone age was originally described by Professor
Ameghino, who had apparently seen some of the bonelets imbedded in it, as
_Neomylodon listai_, "a living representative of the ancient Gravigrade
Edentates of Argentina." That this piece of skin is of quite recent date
seems to be proved by a number of considerations. In the first place it is
covered by long hair of a light yellowish-brown colour; it does not seem
likely that hair would preserve its character for geological epochs. The
nearest corresponding case is that of the remains of Moas in New Zealand,
whose feathers, dried skin, and tendons are known. Now the Moa was
unquestionably contemporaneous with man, as abundant surviving legends
prove, and indeed it cannot have been long extinct. Still, hair is a
resisting structure, and in a dry cave, with no possibility of irruptions
of floods, might retain its characters for long periods. The evidence,
however, of more recent date is stronger than this. The skin shows patches
of reddish colour, suggestive of course of blood-stains. A small piece of
the outside of the skin at the cut edge, which presented the appearance of
freshly or comparatively freshly dried fluid, was submitted to a chemical
examination and shown to be serum! Dr. Loennberg examined chemically a bit
of the skin itself and found in it, after boiling, glue, "which proves that
the collagen and gelatinous substances are perfectly preserved." After this
it seems impossible to suppose that the skin can be of any very great age;
for bacteria would have finished their work upon the serum and gelatine
long ago. Combined with the fresh appearance of the skin is the very fresh
appearance of the skull. In fact it is impossible to believe that the
animal was not alive quite a few years since, relatively speaking. It is
admitted that this animal was contemporaneous with man. There are actually
legends of a creature which may have been this _Glossotherium_. "Ancient
chroniclers inform us that the indigenous inhabitants recorded the
existence of a {182} strange, huge, ugly monster, which had its abode in
the Cordillera to the south of latitude 37. The Tehuelches and the
Gennakens have mentioned similar animals to me, of whose existence their
ancestors had transmitted the remembrance; and in the neighbourhood of Rio
Negro, the aged Cacique Sinchel, in 1875, pointed out to me a cave, the
supposed lair of one of these monsters, called 'Ellengassen'; but I must
add that none of the many Indians with whom I have conversed in Patagonia
have ever referred to the actual existence of animals to which we can
attribute the skin in question."
A rude painting in a cavern, in red ochre, seems to Dr. Moreno (whose words
we have just quoted) to be somewhat suggestive of a _Glyptodon_. There are
some reasons for believing that this quadruped was kept by man as a
domestic creature. In the cave are two walls of rough pieces of stone which
seem to have dropped down owing to the wearing away of the roof; they also
seem to have been loosely piled together to form two walls, within which
enclosure an imperfect skull of the animal was found. This skull shows
clearly that the so-called "_Neomylodon_" must be referred to
_Glossotherium_ or _Grypotherium_, as it is sometimes termed. This skull is
perforated on the roof in such a way as could only have been effected (in
the opinion of experts) by a weapon in the hand of a man. A hole in the
skin has been even compared to a bullet-wound. But this it is perhaps
unnecessary to discuss. The skin of _Glossotherium_ is, like that of other
extinct "Ground-sloths" (_e.g. Mylodon_), filled with small and irregular
ossicles. But in _Mylodon_, the sculptured appearance of the dermal
ossicles appears to indicate that they reached the surface of the body and
were covered by epidermis alone, which is not the case with the animal now
under consideration. The microscopic characters of the ossicles, too, show
differences in the two. _Glossotherium_ being "precisely intermediate
between _Mylodon_ and the existing Armadillo (_Dasypus_)." Now
_Glossotherium_ and _Mylodon_ are regarded as forms which lie between the
existing Anteaters and the Sloths of the same part of the world. We have
already pointed out the facts of structure which lead to this conclusion.
It might therefore be reasonably surmised that the hair of _Glossotherium_
would be also intermediate, or at least like that of one of the two genera
_Myrmecophaga_ and _Bradypus_. But microscopical investigation has {183}
negatived this supposition. It has shown that the Armadillos are in this
matter the nearest relatives of _Glossotherium_. This result is important
as tending further to confirm the close interrelationship of all the
American Edentates as contrasted with the Old-World forms--a matter which
has already been emphasised. It is suggested, however, that the absence of
under fur, which is so well developed in the Sloth, and the difference
shown in transverse sections from the hair of _Myrmecophaga_, may be
explained by difference in habitat. _Glossotherium_ lived under conditions
similar to those under which the Armadillos live to-day. Thus the outer
covering of the body became alike in the two cases, the same needs
supervening in both genera.
_Lestodon_ is another allied genus, which seems to possess canines. At any
rate, in front of the four molars, and separated from them by a diastema,
is a smallish, somewhat canine-like tooth, in both jaws.
_Megalonyx_ and its allies are sometimes placed in a distinct family,
MEGALONYCHIDAE. _Megalonyx_ itself had a skull very like that of
_Bradypus_, being shorter and not so elongated as in the Mylodontidae.
There is a strong tusk anteriorly, which is separated by a considerable
space from the three molars lying behind it. Both pairs of limbs seem to
have possessed five toes. This is a North American genus. It differs from
the bulk of the American Edentates in having a complete jugal arch.
_Megatherium_ is the type of yet a third family, MEGATHERIIDAE, of the
Gravigrade Edentates. This creature is familiar from the many restorations
which have been built up, and from its huge bulk, little short of that of
an elephant. The skull, which is small for the size of the creature, has a
complete jugal arch, from the middle of which depends a downward process as
in other allied forms. The teeth grow to an extraordinary depth, and there
are five of them in the upper and four in the lower jaw--on each side of
course. The fore-limbs of the _Megatherium_ are very much more slender than
the enormously bulky hind-limbs, upon which and the equally massive tail
the animal seems to have supported itself while tearing down branches of
trees, upon whose leaves it fed. In the scapula the acromion joins the
coracoid as in _Bradypus_; the clavicle is large. The fore-limb is
four-toed, and the hind-limb three-toed. The latter has but one clawed
digit (the third, _i.e._ the inner). {184} On the manus, the three inner
digits have powerful claws. This animal, too, was Pleistocene in time. The
Megatheriidae had, however, small as well as gigantic forms.
The genus _Zamicrus_ had a skull no bigger than that of a Sloth, while
_Nothrotherium_ was also a comparatively small creature; the teeth of the
latter genus are reduced to 4/3.
The extinct group of the GLYPTODONTIDAE comprises large creatures with a
dense covering of bony scutes which are arranged in a tesselated fashion,
and thus form an immobile armature of immense strength. In correspondence
with this massive carapace the dorsal vertebrae have fused together, and
the lumbar vertebrae form a series ankylosed to each other and to the
following sacrals. These creatures are all South American.
[Illustration]
FIG. 106.--_Glyptodon clavipes._ x 1/12. (After Owen.)
_Glyptodon_, the genus which gives its name to the family, is known from
numerous remains in South America, and also from so far north as Texas and
Mexico. It grew to be as long as 16 or 17 feet. In the skull there is an
exceedingly long downward process of the zygomatic arch, as in Sloths, the
arch itself being complete. The process extends so far down as to reach a
point about on a level with the middle of the lower jaw. The nasals are
short or rudimentary. As in _Myrmecophaga_, the pterygoids enter into the
formation of the bony palate. The lower jaw has a spout-shaped extremity,
and, behind, it rises into an enormous vertical branch as high as the front
part of the jaw is long. There are eight teeth in each half of each jaw. As
in {185} some Armadillos, the cervical vertebrae are at least partly fused.
The atlas is free, but the rest, or at any rate five of them, are united.
The last cervical is sometimes fused with the succeeding dorsals; the
latter are twelve in number, and are fused together so far as concerns
their centra and neural processes. The succeeding region of the vertebral
column includes seven to nine lumbars, which are fused with the eight
sacrals; in this region the neural processes are high, and there is thus
produced a strong and lofty ridge along the back, which forms a powerful
support for the carapace. The fore-limbs are shorter than the hind-limbs,
which latter are attached to an unusually massive pelvis. The claws of the
limbs are blunt and almost hoof-like.
The heavy carapace consists of sculptured, five or six-sided plates, which
have no particular arrangement in the middle, but towards the margins show
indications of an arrangement in transverse rows. The moderately long tail
is also encircled by bony skin-plates which are thorny above, or at least
provided each with a blunt upstanding process. It appears that outside this
bony system of scutes were horny epidermic scales, corresponding exactly
with the tesserae which they cover. There are apparently a good many
species of _Glyptodon_.
In the allied genus _Panochthus_ the tail is rather longer, and the bony
rings which surround it, instead of being all movable as in _Glyptodon_,
are at first so, but later, _i.e._ towards the end of the tail, become
welded into a single and massive piece. Both feet are here four-toed, while
in _Glyptodon_ the hind-feet are five-toed and the fore-feet four-toed.