ANATOMY OF VERTEBRATES. 



135 



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

 and represented by its alveolar border only; the mamillaries 

 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, which 

 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. pulchriceps) the nasals were 

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

 species. 



93 



Side view of cranial vertebra; anil 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, l, 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 



