256 THE ANATOMY OF VEETEBEATED ANIMALS. 



branch, whicli traverses the basisphenoid, and a posterior, 

 which passes up in the basi-occipital. The posterior branch 

 receives the narrow lateral canal of its side (which runs 

 vertically up to it), and then opens into the posterior part 

 of the floor of the tympanum. The anterior l^ranch opens 

 into its anterior wall. 



The tympanic cavities of embryonic Crocodiles communi- 

 cate with the mouth by wide and simple apeiiiures, and the 

 complicated an-angement of canals just described results 

 from the great downward development of the basisphenoid 

 and basi-occipital, and their encroachment iipon these aper- 

 tures on the inner side, while the quadi-ate bone narrows 

 them on the outer. 



In adult Crocodilia, air-passages extend from each tym- 

 panum to that of the opposite side, through the bones 

 which form the roof of the posterior region of the skull. 

 On the other hand, they excavate the quadrate bone, from 

 whence the air passes through a membranous tube into the 

 hollow articular piece of the mandil^le. The hyoidean 

 apparatus is greatly simplified, consisting only of a broad 

 plate of cartilage, which may become partially ossified, 

 and of two ossified comua which are not dii-ectly connected 

 with the skull. A minute styliform cartilage, which lies in 

 close proximity with the i^ortio dura, on the uj^per part of 

 the posterior face of the quadrate bone, represents the stylo- 

 hyal, or proximal end of the hyoidean arch. 



The pectoral arch has no clavicle, and the coracoid has no 

 distinct epicoracoidal element, nor any fontaneUe. The 

 carpus consists proximally of two elongated and somewhat 

 houi-glass-shaped bones, articulated respectively with the 

 radius and the ulna. The radial is the larger, and is par- 

 tially articulated with the ulna. Behind these, and directed 

 transversely, lies another c'ai-ved ossification, the upper 

 concave face of which articulates with the ulna. It is united 

 with the latter bono on the one hand, and with the fifth 

 metacai-pal, on the other, by strong ligaments, and represents 

 a pisiform bone. Distally, there lies on the ulnar side the 

 so-called lenticular bone, an oval ossicle interposed between 



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