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maxillary bones, and in two rows on the premaxillary. The crowns are simple, 

 and offer various modifications of the cone. Their dentinal substance is 

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

 which occupies the alveolus of the jaw, and projects above 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 by true dentinal 

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

 not possess true roots. The crowns are covered with enamel, and their 

 forms indicate the carnivorous habits of these reptiles. 



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

 anteriorly, and much attenuated posteriorly, separating the maxillaries above 

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

 the latter. The anterior extremity bears two teeth on each side in the 

 known species. 



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

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

 nate in a narrow process behind, whose extremity is broken in the specimens 

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

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

 septum composed of coossified nasal and frontal bones. The nares extend 

 to a point in advance of the anterior margin of the orbit. The prefrontals 

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

 species, their posterior exterior margin projects strongly in the 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 ate medially. The post-frontals are large. Hat, and prominent, and project 

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

 they embrace between them a broad, rectangular process of the parietal, 

 which, in Clidastes, contains, near its front suture, the parietal fontanelle. In 

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



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

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

 parietal crests arc separated by a plane which is narrowed, or they unite into 



