131 



gasseriana, at the commencement of the forameti ovale ; the šame 

 groove is indicated in a slighter degree in the Dasyuri and Phalan- 

 gers, but is almost obsolete in the Wombat and Koala. The carotid 

 canals pierce the body of the sphenoid, as in the bird, and terminale 

 in the skull, very olose together, behind the sella turcica, which is 

 not bounded by a posterior clinoid process. The petrous bone in 

 the Kangaroo, Koala, and Phalanger, is impressed above the meatus 

 auditorius, by a deep, smooth, round pit which lodges the lateral 

 appendage of the cerebellum. The corresponding pit is shallower 

 in the Dasyuri, and almost obsolete in the Wombat. The middle, 

 and posterior fissurce lacerce have the usual relative position, but the 

 latter are small. The condyles are each perforated anteriorly by 

 two f oramina. 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 do\\Tiwards. 



" In the Kangaroo and Phalanger a thin ridge of bone extends for 

 the distance of one or two lines into the peripherj' of the tentoricd 

 process of the dura mater, and two sharp spines are sent down into 

 it from the upper part of the cranium in the Pkalangista Vulpina, 

 The tentorium is supported by a thick ridge of bone in tlie Thyla- 

 cine, but it is not completely ossified in any of the Mars-upiata ; in 

 some species indeed, as the Dasyures, the Koala, and the Wombat, 

 the bony ridge above described does not exist. There is no ossifi- 

 cation of the falciform ligament, as in the Ornithorhj'nchus. 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 weU-marked 

 manner from the proper cerebral division of the cavity. It is rela- 

 tively smallest in the Koala. In all the Marsupials it is bounded 

 anteriorly by the cribriform plate of the ethmoid bone, which is con- 

 verted 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 ■CT'ith- 

 in 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 down\vards 

 from the inside of each of the nasal bones, and is continued poste- 

 riorly into the superior turbinated bone ; this bone extends into the 

 dilated space anterior to the cranial caA'ity, which corresponds "n-ith 

 the frontai 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 obliąuely from below, upwards 

 and forvvards. Tliey are extremely delicate and numerous in the 

 Dasyures and Phalanger ; they consist of thin lamina of bone beau- 

 tifully arranged on the convex surface of the os turbinatum, and 

 placed vertically to that surface in the Potoroo ; but the bone be- 

 comes very simple in the Kangaroo, Koala, and Wombat. The 

 nasal cavity communicates freely with large maxillary sinuses, and, 



