278 THE VERTEBRATE SKELETON. 



most Lacertilia. The posterior part of the skull is curiously 

 modified in some Chamaeleons, the parietal s and supra- occipitals 

 being drawn out into a backwardly-projecting sagittal crest 

 which unites with the two prolongations from the squamosals. 

 In other Chamaeleons (C. bifidus) prolongations of the pre- 

 frontals and maxillae form large forwardly-projecting bony 

 processes. 



The roof of the skull is characterised by the development 

 of prefrontals and postfrontals, which lie respectively near the 

 anterior and posterior extremity of the orbit. In Theromorpha, 

 Squamata, Crocodilia, arid some Dinosauria lachrymals are 

 developed. There is a ring of bones in the sclerotic in the 

 Ichthyosauria (fig. 32, 15), the Metriorhynchidae among Croco- 

 diles and some Rhynchocephalia, Dinosauria, and Pterosauria. 



The pro-otic lies in front of the exoccipital and together 

 with the opisthotic forms the hind border of the fenestra 

 ovalis. In Chelonia the opisthotic remains separate, in all other 

 living reptiles it fuses with the exoccipital. The epi-otic fuses 

 with the supra-occipital. 



The parasphenoid, so important in Ichthyopsids, has very 

 often disappeared completely; it is present, however, in the* 

 Ichthyosauria, the Plesiosauridae, and a number of Squamata, 

 in many Ophidia its anterior part forming the base of the 

 interorbital septum. 



In the Plesiosauridae and most Lacertilia, but not in the 

 Amphisbaenidae, a slender bone, the epipterygoid, occurs unit- 

 ing the parietal or the anterior end of the pro-otic with the 

 pterygoid. A homologous arrangement occurs in the Ichthyo- 

 sauria and some Chelonia. 



In most reptiles a transpalatine occurs, connecting the 

 maxilla with the pterygoid, but this is absent in the Chelonia, 

 and some Dinosauria, and in the Typhlopidae among snakes. 



The quadrate is always well developed, and except in the 

 Squamata is firmly fixed to the surrounding bones. The 

 Chamaeleons also, among the Squamata, have a fixed quadrate, 



