of the falciform ligament as in the Ornitho- 
rhynchus. 
___ The anterior depression or olfactory division 
_ of the cavity of the cranium, as it may be 
termed from its large size, is separated in a 
_ well-marked manner from the proper cerebral 
_ division of the cavity. It is relatively smallest 
_ in the Koala. In all Marsupials it is bounded 
_ anteriorly by the cribriform plate of the eth- 
moid bone, which is converted into an osseous 
reticulation by the number and size of the 
_ olfactory apertures. The cavity of the nose, 
from its great size and the complication of 
the turbinated bones, forms an important part 
of the skull. It is divided by a complete 
| bony septum to within one-fourth of the an- 
| terior aperture; the anterior margin of the 
| septum is slightly concave in the Koala; de- 
| scribes a slight convex line in the Wombat, 
| Kangaroo, and Phalanger, and a_ sigmoid 
| flexure in the Dasyure. A longitudinal ridge 
i projects downwards from the inside of each of 
; 
) 
_ the nasal bones, and is continued posteriorly 
_ into the superior turbinated bone; this bone 
| extends into the dilated space anterior to the 
cranial cavity, which corresponds with the 
frontal sinuses. The convolutions of the middle 
spongy bone are extended chiefly in the axis of 
the skull; the processes of the anterior con- 
voluted bone are arranged obliquely from 
below upwards and forwards. They are ex- 
tremely delicate and numerous in the Da- 
_syures and Phalangers; they consist of thin 
_lamine of bone beautifully arranged on the 
“convex surface of the os turbinatum, and 
placed vertically to that surface in the Po- 
 toroo; but the bone becomes very simple in 
the Kangaroo, Koala, and Wombat. The 
“nasal cavity communicates freely with large 
maxillary sinuses, and finally terminates by 
_ wide apertures behind the bony palate. In the 
‘skull the nasal cavity communicates with the 
‘mouth, as before mentioned, by means of the 
ious large vacuities in the palatal processes. 
Mazxilla inferior—The lower jaw of the 
arsupials is a part of their osseous structure 
vich claims more than ordinary attention in 
consequence of the discussions to which the 
| fossil specimens of this bone discovered in 
the oolitic strata of Stonesfield have given rise. 
‘These specimens, which are well known to the 
English reader by the figures of them published 
‘in the Bridgewater Treatise of Dr. Buckland, 
and in the Elements of Geology of Mr. Lyell, 
_were regarded by Cuvier as appertaining to 
the Marsupial series of Mammalia, and to be 
nearly allied to the genus Didelphis. 
_ This opinion of the great founder of Oryc- 
tological Science has been called in question 
by other naturalists, and has been more espe- 
cially opposed by Professor De Blainville, who 
oie it to be more probable that they be- 
ng to a genus of Saurian Reptiles than to 
the Didelphis or any genus of insectivorous 
Mammals. I have examined the two speci- 
Mens in the possession of Dr. Buckland, the 
— formerly in the collection of Mr. 
roderip and now in the British Museum, and 
‘that which is preserved in the Museum at York. 
MARSUPIALIA. 
273 
The composition of the lower jaw, each ramus 
of which consists of one piece of bone, the 
convex condyle, broad and high coronoid pro- 
cess, and the structure and mode of implan- 
tation of the molar teeth, sufficiently attest the 
mammiferous character of these remains: the 
size, elevation, and form of the coronoid pro- 
cess of the lower jaw, the process continued 
from the angle of the ramus, with the tubercular 
crowns of the molar teeth, indicate the carni- 
vorous and insectivorous character of the spe- 
cies in question. In the presence of canines 
and the number of the incisors and molars, 
one of these small Insectivora (Phascolotherium) 
approaches most nearly to the smaller species 
of the modern genus Didelphis; while in the 
structure of the molar teeth, and in the form 
of the coronoid process, it very closely re- 
sembles the Thylacinus. The number of the 
molars in the other genus ( Thylacotherium ) 
exceeds that of any known ferine Insectivore, 
placental or marsupial. We have seen, how- 
ever, that the marsupial Myrmecobius possesses 
nine molars on each side of both upper and 
lower jaws. Besides the osteological charac- 
ters above alluded to, there is a peculiarity in 
the lower jaw of the Marsupial animals, which 
was first indicated by Cuvier in the genus 
Didelphys, but which is not restricted to that 
genus. In the carnivorous Marsupials, as the 
Thylacine, the lower maxillary bone resembles 
in general form that of the corresponding spe- 
cies in the placental series, as the Dog: a 
similar transverse condyle is placed low down 
near the angle of the jaw, on a level with the 
series of molar teeth; a broad and strong 
coronoid process rises high above the condyle, 
and is slightly curved backwards; there is the 
same well-marked depression on the exterior 
of the ascending ramus for the firm implantation 
of the temporal muscle, and the lower boun- 
dary of this depression is formed by a strong 
ridge extended downwards and forwards from 
the outside of the condyle. But in the Dog 
and other placental Carnivora (the seals ex- 
cepted), a process, representing the angle of 
the jaw, extends directly backwards from the 
middle of the above ridge, which process gives 
precision and force to the articulation of the 
jaw, and increases the power by which the 
masseter acts upon the jaw. Now, although 
the same curved ridge of bone bounds the 
lower part of the external muscular depression 
of the ascending ramus in all the Marsupials, 
it does not in any of them send backwards, 
or in any other direction, a process correspond- 
ing to that just described in the Dog and other 
placental Carnivora. The angle of the jaw 
itself, in the Marsupials, is as if it were bent 
inwards in the form of a process encroaching 
in various shapes, and various degrees of deve- 
lopment in the different Marsupial genera upon 
the interspace of the rami of the lower jaw. 
In looking directly upon the lower margin of 
the jaw, we see, therefore, in place of the mar- 
gin of a vertical plate of bone, a more or less 
flattened triangular surface extended between 
the external ridge, and the internal process or 
inflected angle. This characteristic structure is 
T 2 
