xiii.] EDENTATA. 211 



ankylosed with the maxillae. The pterygoids are much 

 smaller, but sometimes are bullate. 



The upper margin of the mandible is produced anteriorly 

 into a spout-like process. The condyle is scarcely above 

 the level of the molar teeth, and is wide from side to side. 

 The angular projection is smaller and thicker. 



The hyoid (in an old specimen) has a strongly ossified 

 anterior arch, consisting of two bones of nearly equal length, 

 the proximal one with a stout rounded process projecting 

 backwards and outwards from near its upper end.- The 

 second is bent at a right angle near its lower end, and may 

 result from the ossification of two elements. The basi- and 

 thyro-hyals are ankylosed to form a wide U-shaped bone. 

 . Order Marsupialia. — The skull of the large carnivorous 

 Marsupial, the Thylacine {Thylacinns cynocephalus), resembles 

 so closely that of a Dog in its general aspect, that it will be 

 well to commence an account of the peculiarities of the 

 crania of Marsupials generally by comparing these two 

 skulls. 



It will be seen by the section (Fig. 66) that the brain cavity 

 of the Thylacine is very much smaller than that of the Dog 

 (Fig. 45) in relation to the size of the rest of the cranium, 

 or to that of the whole animal, a sign of great inferiority 

 of organization. This diminution affects chiefly the cere- 

 bral fossa ; the cerebellar fossa is nearly equal in size, 

 but it is placed more directly behind the cerebral, and is 

 not in the least overlapped by it, as in the Dog. The 

 occipital plane is vertical, or even inclining forwards above. 

 The tentorial plane is nearly horizontal. The olfactory 

 fossa, though smaller in vertical extent than that of the Dog, 

 is more produced anteriorly. Thus in form, as well as in 

 relative size, the cerebral cavity is far more reptilian than 

 that of the Dog. The basicranial axis is very straight, and 



p 2 



