THE SKULL OF REPTILES 



71 



pit on the upper side of the pterygoids and extending to or toward 

 the parietals. 



The frontals usually and the parietals always are fused in the mid- 

 line (Fig. 55 a).^ The parietal foramen, usually present, is absent in 

 many terrestrial lizards and in the Rhiptoglossa. The frontals and 

 parietals may be either paired or unpaired. The frontals in the 

 Varanidae, Helodermatidae, and some others have descending proc- 

 esses of the frontals which 

 meet in the middle below, en- 

 closing a rhinencephalic cham- 

 ber, very much like the prim- 

 itive one of the early reptiles. 



The brain-case of lizards, 

 as of other reptiles, is formed 

 by the supraoccipital, exocci- 

 pitals, paroccipitals, basiocci- 

 pital, basisphenoid, prootics, 

 and postoptics, but is more or 



less membranous in front on the sides. The postoptics (Fig. 55 d, al) 

 are small ossifications in the wall membrane, usually lost in macer- 



FiG. 57. Piatecarpus, occ\p\ta\ view. i'0,has\- 

 occipital; eo, exoccipital; p/, postfrontal; st, 

 stapes; pt, pterygoid; q, quadrate. 



AMAi-i-#^^ 





Fig. 58. Mosasaur mandible: Clidastes, inner side of right mandible, ang, angular; art, 

 articular; cor, coronoid; pa, prearticular; sur, surangular. 



ation. In the Amphisbaenia (Fig. 56 c) and Mosasauria the sides 

 of the parietals are partially decurved, forming incomplete cerebral 

 walls, but they do not reach, as in the snakes (Fig. 59 b), to the 

 basisphenoid. 



The mandibles (Figs. 55 b, 58) are composed of the dentary coro- 

 noid, surangular, articular, angular, and splenial, with a long fused 

 prearticular, which in the mosasaurs is more or less ensheathed by 

 the union of the coronoid and angular, strengthening the peculiar 



1 [Some geckos have them separate. — G. K. N.] 



