348 ANATOMY OF VERTEBRATES. 



gista vulpina. The tentorium is supported by a thick ridge of 

 bone in the Thylacine ; but it is not completely ossified in any of 

 the Marsupials : in some species, indeed, as the Dasyures, the 

 Koala, and the Wombat, the bony crista above described does not 

 exist. There is no ossification of the falciform ligament as in the 

 Ornithorhynchus. 



The rhinencephalic division of the cranial cavity is well defined 

 from the prosencephalic one. It is relatively smallest in the Koala. 

 In all Marsupials it is bounded anteriorly by the cribriform plate, 

 wliich 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 turbinal 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 slight convex line in the Wombat, Kangaroo, and 

 Phalanger, and a sigmoid flexure in the Dasyure. A longitudinal 

 ridge projects doAvnward from the inside of each of the nasal 

 bones, and is continued posteriorly into the superior turbinal; 

 this bone extends into the dilated space anterior to the cranial 

 cavity, which corresponds with the frontal sinnses. The convo- 

 lutions of the middle turbinal are extended chiefly in the axis of 

 tlie skull ; the processes of the anterior turbinal are arranged 

 obliquely from below npward and forward. 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 various large vacuities in the palatal 

 processes. 



In the carnivorous Marsupials, as the Thylacine, the lower 

 maxillary bone resembles in general form that of the correspond- 

 ing species in the placental series, as the Dog : a similar transverse 

 condyle is placed low down near the angle of the jaw, on a level 

 mth the series of molar teeth ; a broad and strong coronoid pro- 

 cess rises high above the condyle, and is slightly curved back- 

 ward ; there is the same well-marked depression on the exterior 

 of the ascending ramus for the firm implantation of the temporal 

 muscle, and the loAver boundary of this depression is formed by a 

 strong ridge extended downward and forward from the outside of 

 the condyle. But in the Dog and other placental Carnivora (some 

 Seals excepted), a process, representing the angle of the jaw, 

 extends directly backward from the middle of the above ridge, 

 which process gives precision and force to the articulation of the 



