MONOTREMATA. 
cava by a single large vein. The lower jaw 
articulates with the base of the zygomatic, and 
not with the tympanic element of the temporal 
bone, and the cranium articulates by two dis- 
tinct condyles with the atlas. 
The quadrupeds which combine these essen- 
tial mammalian characters with the oviparous 
modifications above-mentioned are peculiar to 
Australia and Van Dieman’s Land; they form 
three well-marked species, referable to two 
distinct genera. One of these genera, called 
Echidna by Cuvier, is characterized by an 
elongated slender muzzle, terminated. by a 
small mouth, and containing a long and exten- 
sible tongue like that of the Ant-eaters. The 
jaws are edentulous, but the palate is provided 
with many rows of small, sharp, hard, epidermal 
spines, which are directed backwards, and the 
base of the tongue is similarly armed. The 
feet are short, but remarkably broad and strong, 
and are each provided with five very long and 
strong claws. The upper part and sides of the 
body are defended by spines similar to but 
larger than those of the hedge-hog. The tail 
is very short. The genus Echidna contains two 
species, one ( Ech. hystrix) characterized by a 
more complete armour of spines, with a scantier 
admixture of darker coloured hair; the other 
( Ech. setosa), by being clothed with a greater 
proportion of lighter coloured hair, which half 
conceals the spines. These characters are 
constant in both sexes, and as well marked in 
the mature as in the young individuals. 
Both species of Echidna are terrestrial and 
fossorial ; they feed almost exclusively on ants, 
and abound in certain districts of both Australia 
and Tasmania, playing there the same part in 
the economy of Nature which is assigned to 
the Pangolins ( Manis ) in Asia and Africa, and 
to the Ant-eaters ( Myrmecophaga) in South 
America. 
The Ornithorhynchus—the second genus of 
the Monotrematous order—is an aquatic Insec- 
tivore,* but combines water-snails, worms, and 
other small Invertebrata with the insects that 
constitute the staple article of its food. These 
it obtains, not by its tongue, which is short 
and inextensible, but by its lips, which are 
largely developed, and supported by singularly 
modified intermaxillary and lower maxillary 
bones; the whole mouth presenting a close 
resemblance to the broad and flattened beak of 
a duck. The similarity is increased by the 
lateral lamelle of the lower jaw; but both 
jaws are provided with four horny teeth; the 
anterior one on each side, both above and 
below, is long, narrow, and trenchant; the 
posterior one is broad, flat, and shaped like a 
molar tooth. The feet are short, broad, armed 
each with five claws, but less robust than in 
the Echidna. The fore feet have a web, which 
* See No. 541, B. Physiological Series, Museum 
Royal College of Surgeons, London. ‘‘ Debris of 
Insects belonging to a genus of the Nawceride, 
which were found in the cheek-pouches of the 
Ornithorhynchus age Mr. Bennett (Zool. 
Trans. 1834, p. 239) found in the cheek-pouches 
of the Ornithorhynchns mud and gravel, with frag- 
ments of insects and shell-fish. 
367 
not only unites and fills the interspaces of the 
toes, but extends beyond the extremities of the 
claws; the web of the hind foot terminates at 
the base of the claws. With these swimming- 
feet is associated a strong, broad, horizontally 
flattened tail, which completes the organic 
locomotive machinery for the aquatic existence 
of an air-breathing and warm-blooded quadru- 
ped. The body is clothed with a dense coat 
of hair, which consists of a fine fur, intermixed 
with long, stiff, flattened, and sharp-pointed 
hairs, that seem to represent the spines of the 
Echidna. Only one species of Ornithorhynchus 
is as yet satisfactorily defined ; it occurs in the 
fresh-water rivers, ponds, and lakes of Australia 
and Van Dieman’s Land. 
As external ears and large eyes would be ill 
suited to the habits either of a burrowing or a 
swimming animal, both genera of Monotremes 
are characterized by the absence of the auricle 
and the small size of the visual organs. The 
male in both genera bears a horny pointed spur 
upon the heel, which is perforated, and trans- 
mits into the wound it inflicts the secretion of 
a peculiar gland. This singular repetition of 
an offensive mechanism, which, prior to the 
discovery of the monotrematous mammals, was 
known only in certain insects and serpents, 
completes the anomalous combinations in the 
external characters of the present order. 
Echidna hystrix and Ornithorhynchus para- 
dorus were first described and figured by Dr. 
Shaw ; the former as early as the year 1792 in 
the third volume of the Naturalists’ Miscellany, 
under the denomination of Myrmecophaga acu- 
leata ; the latter in the tenth volume of the 
same work in the year 1799, by the name of 
Platypus anatinus. 
In the following year this more extraordinary 
animal received a further description, together 
with its present zoological denomination from 
Professor Blumenbach, in “ Voigt’s Magazin 
fiir den neuesten Zustand der Naturkunde, 
Bd. ii, 1800;” and soon after Sir Everard 
Home gave an account of some of its ana- 
tomical peculiarities, which appeared in the 
Philosophical Transactions for the year 1800. 
As these observations, however, were limited 
to the head and beak, they rather tended to 
perplex than guide the naturalist in assigning 
the position of the animal in the natural 
system. 
Professor Blumenbach, in his Elements of 
Natural History, placed the Ornithorhynchus 
paradoxus among the Palmata of his mamma- 
logical system, between the otter and the 
walruss; while Dr. Shaw more naturally re- 
ferred it to the Bruta of Linneus; but being 
limited to such points of comparison as the exter- 
nal form alone presented, he merely discerned 
the affinities of the Platypus and the Echidna 
to the Myrmecophage. The real value and 
extent of these affinities could only be deter- 
mined by a deeper insight into their respective 
organizations. The important memoirs on the 
anatomical structure of both these animals read 
before the Royal Society by Sir Everard Home, 
and published in the Philosophical Transactions 
for 1802, drew the attention of the scientific 
