ANATOMY OF VERTEBRATES. 



135 



mastoids. The premaxillary is either wanting,, or it is very small, 

 and represented by its alveolar border only ; the maxillaries 

 meeting above it. The alveolar borders of both upper and lower 

 jaws show a regular series of vascular pits or foramina, indica- 

 tive of the primitive separate matrices, like those of teeth, winch 

 laid the foundation in the young animal of the continuous horny 

 coverings of the jaws. 



Temminck's Snapper (Chelonura Temminckii) is remarkable for 

 the upper convexity and enormous expanse of the cranium, chiefly 

 due to the temporal fossae, contrasted with the short and narrow 

 face. In a fossil chelonian from the Portland stone ( Ch. planiceps) 

 and in another from the Chalk ( Ch. pulcliriceps) the nasals were 

 distinct from the prefrontals, which is a rare exception in existing 

 species. 



93 



Nnr 



Side view of cranial vertebra and sense-capsules, Crocodile 



32. Skull of Crocodilia. Passing next to the skull of the 

 Crocodile, we find the first difference in the less complex condition 

 of the epencephalic arch, fig. 93, N i, which consists of four, instead 

 of, as in the Fish and Turtle, six bones. The basioccipital, figs. 93 

 and 94, i, presents, like the centrums of the trunk, a convexity at 

 its posterior articular surface ; but its anterior one, like the hind- 

 most centrum of the sacrum, unites with the next centrum in ad- 

 vance, ib. 5, by a flat rough sutural surface. Like most of the cen- 

 trums in the neck and beginning of the back, that of the occiput 

 developes a hypapophysis, but this descending process is longer and 

 larger. The exoccipitals, ib. 2, articulate suturally, like the neur- 

 apophyses of the trunk, with the upper and lateral parts of their 



