OF THE MARSUPIALIA. 391 
but the latter are small. The condyles are perforated anteriorly by two foramina. The 
composition and form of the foramen magnum we have already spoken of. It is of great 
size, in relation to the capacity of the cranium ; the aspect of its plane is backwards, and 
slightly downwards. 
In the Kangaroo and Phalanger a thin ridge of bone extends for the distance of one 
or two lines into the periphery of the tentorial process of the dura mater, and two sharp 
spines are sent down into it from the upper part of the cranium in the Phalangista Vul- 
pina. The tentorium is supported by a thick ridge of bone in the Thylacine; but it is 
not completely ossified in any of the Marsupiata ; indeed, the Dasyures, the Koala, and 
the Wombut, have not the bony crista above described. ‘There is no ossification of the 
, falciform ligament, as in the Ornithorhynchus. The anterior depression, or olfactory 
division of the cavity of the cranium, as it may be termed, from its large size, is sepa- 
rated in a well-marked manner from the proper cerebral division of the cavity. It is 
relatively smallest in the Koala. In all the Marsupials it is bounded anteriorly by the 
cribriform plate of the zthmoid 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 anterior aperture; the anterior margin of the septum is 
slightly concave in the Koala, describes a slightly convex line in the Wombat, Kangaroo 
and Phalanger, and a sigmoid flexure in the Dasyure. A longitudinal ridge 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 convoluted bone are arranged obliquely from below, upwards and forwards. 
They are extremely delicate and numerous in the Dasyures and Phalangers ; they consist 
of thin lamin of bone, beautifully arranged on the convex surface of the os turbinatum, 
and placed vertically to that surface in the Potoroo; 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 dry skull the nasal cavity communicates with the mouth, as before 
mentioned, by means of the various large vacuities in the palatal processes. 
The lower jaw of the Marsupiata is a part of their osseous structure which claims 
more than ordinary attention, in consequence of the discussions to which the fossil speci- 
mens 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 Didelphys. This opinion of the great founder of 
VOL, II.—PART V. 3F 
