xiir.] MARSUPIALIA. 215 



large, more vaulted cerebral fossa, and the Opossums and 

 Dasyures the other. 



2. There is no distinct pituitary fossa, orclinoid processes. 



3. The ossification of the mesethmoid is extensive, and 

 has an abrupt, nearly vertical, anterior termination. 



4. The nasal bones are large, and the anterior nares more 

 or less terminal. 



5. The zygoma is complete, but the orbit has not a 

 perfect posterior boundary. 



6. The malar is large, reaches the lachrymal anteriorly, 

 and extends posteriorly beneath the zygomatic process of 

 the squamosal, to form part of the outer wall of the glenoid 

 fossa. 



7. The perforation in the lachrymal is usually upon, and 

 frequently external to, the anterior boundary of the orbit. 



8. The ascending processes of the premaxillse never 

 quite reach the frontals. 



Pq. The palate has often, but not always, large vacuities 

 ar its posterior margin. 

 10. The pterygoids are always small and lamelliform. 



11. The alisphenoids are more or less dilated, and form 

 the anterior wall of the tympanic cavity, which is often quite 

 open below in the dried skull. It may be noted as a special 

 peculiarity in the Kangaroos, that the alisphenoid extends 

 backwards beneath the tympanic cavity to join the long 

 paroccipital process of the exoccipital. In the larger mem- 

 bers of the group it can scarcely be said to form a distinct 

 bulla, but in some of the Hypsiprynmi (Rat Kangaroos) it is 

 immensely , expanded. In the Koala (Phascolarctos), the 

 alisphenoid bulla is very large, elongated vertically and 

 compressed, having a very similar appearance in fact to the 

 tympanic bulla of the Pig. 



12. The tympanic is small, simple, and annular in 



s 



