xiii.] MARSUPIAL1A. 239 



general appearance from that of the Thylacine, agree with it 

 in the following important particulars : 



1. The brain cavity is small, with the cerebella fossa 

 entirely behind, and the olfactory fossa entirely in front of 

 the cerebral fossa. There are, however, degrees in this res- 

 pect, the Kangaroos representing one extreme, with large, 

 more vaulted cerebral fossa, and the Opossums and Dasyures 

 the other. 



2. There is no distinct pituitary fossa, and the clinoid 

 processes are obsolete. 



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 lacrymal 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 lacrymal is usually upon, and 

 frequently external to, the anterior boundary of the orbit. 



8. The ascending processes of the premaxillae never quite 

 reach the frontals. 



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

 near 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- 



