IIG 



itiaxillary hones, aiKi in two rows on llio prcmaxillary. The crowns are simple, 

 and offer various modifications of" the cone. Their dentinal sul)stance is 

 confined to the crown, and is attached, at the base, to a pedestal of ostein, 

 which occupies the alveolus of tlic jaw, and projects al)ovc it. This is 

 stated, by Cuvier, to be an ossification of the tissue surrounding the circu- 

 latory vessels and nerves which penetrate to the crown, and which remain 

 unossified in serpents and most fishes, but are surrounded l)y true dentinal 

 roots in most vertebrates of the land. Hence, the teeth, in this order, do 

 not possess tru(; roots. The crowns are covered witli enamel, and their 

 forms indicate the carnivorous habits of these reptiles. 



The premaxillari/ is a narrow, simple element, one-half of a cone 

 anteriorly, and much attenuated posteriorly, sejiarating the maxillaries above 

 by the widtli of its spine only. Its extremity projects considerably beyond 

 the latter. The antcM-ior extremity bears two teeth on each side in tiic 

 known species. 



The maxillary bones are widely separated on the palatal surface, in 

 front, by the vomers; behind, l)y the nares and palatine bones. They termi- 

 nate in a narrow j)rocess behind, whose extremity is broken in the specimens 

 at my disposal, Init which may have supported a malar arch, probably slender, 

 as in the dolphin.s. The nostrils are linear and superior, and separated by a 

 septmn composed of coossified na.sal and frontal bones. Tlie nares extend 

 to a point in advance of the anterior margin of' the orI)it. The prefronlals 

 are largely developed, and margin the posterior part of the nares. In many 

 species, their posterior exterior margin projects strongly in tlie plane of the 

 muzzle, and has caused the orbit to be horizontal, and the range of vision 

 vertical, as in some aquatic serpents; while, in others, it is decurved, as in 

 land-vertebrates. 



The frontal is a wedge-shaped, flat bone, and presents lateral descend- 

 ing alae medially. The post-frontals are large, flat, and prominent, and project 

 beyond the process they send, posteriorly, to join the squamosal. Posteriorly, 

 they embrace between them a broad, rectangular jn-ocess of the parietal, 

 which, in Clidastes, contains, near its front suture, the })arietal fontanelle. In 

 Platccarpus, the foramen is, usually, in or nearer to the suture. 



The parietal lias two broad lateral wings, which advance on the frontal, 

 and form posteriorly the broad anterior margin of the temporal fossa. The 

 |)ari('tal crests are separfited by a plane whicii is narrowed, or Ihey unite into 



