58 



THE OSTEOLOGY OF THE REPTILES 



or between them and the palatines, and, hke the external ones, are 

 small. There is always a remarkable posterior interpterygoidal 

 vacuity, divided in the middle throughout by the large parasphenoid, 

 the pterygoids meeting in front of and to a slight extent behind them. 



Fig. 48. Plesiosaur skulls: A, Elasmosaurus, from the s\Ae: pm, premaxilla; 

 w?, maxilla; po, postorbital; y, jugal. B, Plesiosaurus, from the side. One 

 sixth natural size. C, Trinacromerum, from the side: ang, angular; d, den- 

 tary; pm, premaxilla; po, postorbital; _/, jugal; sttr, surangular. 



An anterior interpterygoidal vacuity, as also posterior palatine and 

 other openings in the palate, may or may not be present. The in- 

 ternal nares are in front, sometimes very much in front, of the ex- 

 ternal nares. The coronoids are elongate bones, extending along 

 the sides of the teeth internally and meeting each other in some 

 forms in a median symphysis. As usual in long-faced forms, the 

 splenials meet in a median symphysis. 



