I02 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



each other. The hyoid apparatus bears two cornua which either end freely in 

 the neck or may reach the parotic process (fig. 203). 



In the fossil Pythonomorphs the striking features are the large supratem- 

 poral fossae, the quadrate recalling that of chelonians; and the joint in the lower 

 jaw, between dentary and angular regions, allowing the jaw to bend on itself. 



The Ophidia (snakes) lack parotic process, parietal foramen, temporal 

 arcades and epipterygoid, and have the squamosal excluded from the cranial 

 wall. The attachment of the visceral skeleton to the cranium is loose, the 

 pterygoid being connected to the other parts by a long bar, consisting of squa- 

 mosal and quadrate behind, and by transversum and palatine in front, features 



as 



Fig. 106. — Skull of snake, Tropidonolus, after W. K. Parker, an, angular; av, 

 articular; bo, basioccipital; bs, basisphenoid; d, dentary; eo, exoccipital; epo, epiotic; 

 /, frontal; mx, maxillary; «, nasal; 00, opisthotic; p, parietal; pi, palatine; pm, premaxil- 

 lary; pro, prootic; ps, parasphenoid; pt, pterygoid; q, quadrate; sa, surangulare; so, 

 supraoccipital; sq, squamosal; tr, transversum. 



related to the great distensibility of the jaws. In the poisonous serpents the 

 poison fangs are either permanently erect, or they fold back when the mouth 

 is closed. In the latter the fangs are supported on the maxillaries, which are 

 moved by a rod formed of quadrate, pterygoid and ectopterygoid. In the lower 

 jaw distensibility is provided for by the elastic ligament connecting the two 

 halves in front. Some species have remnants of the hyoid apparatus, but 

 occasionally all are lost in the adult. 



When the whole series of Crocodilia, recent and extinct, is considered; the 

 range of variation in the skull is considerable. In all, supra- and infratemporal 

 fossae are present, the quadrate is immovable, there is more or less of a secondar>- 



