86 THE OSTEOLOGY OF THE REPTILES 



from the palatal surface, except rarely just back of the premaxillae 

 in the caimans, or in front of the pterygoids in the tomistomids. 

 The palatines also meet in the middle line in all, sending up proc- 

 esses for articulation with the postorbital, and forming the floor of 

 the respiratory canals. The prevomers form a pair of tubes above 

 the maxillae and palatines, articulating posteriorly with a supra- 

 palatal prolongation of the pterygoids; they are separate as usual, 

 and do not often appear on the palatal surface. The pterygoids also 

 meet in the middle line, in all procoelian forms completely surround- 

 ing the internal nares, which may or may not be divided by a median 

 partition, meeting below the nasal tubes in front of them. In the 

 early teleosaurs these openings were at the posterior border of the 

 palatines. In the goniophilids the openings are surrounded by both 

 palatines and pterygoids. 



The pterygoids articulate posteriorly and externally with the post- 

 optics by a narrow pillar, possibly representing the epipterygoids. 

 There are large posterior palatine vacuities at the sides of the pala- 

 tines, and, in Hylaeochampsa, an additional opening in the palate 

 between the ectopterygoid and maxilla. 



In the mandible (Fig. 69 d) the splenials meet in a median sym- 

 physis in slender jaws. The prearticular is apparently wholly absent, 

 or fused with the angular. There is a large mandibular foramen be- 

 tween the angular, surangular, and dentary on the outer side, absent 

 in the Thalattosuchia. 



