SKULL 



117 



by an elastic ligament. Teeth are usually present on the relatively 

 short maxilla, the palatine, pterygoid, and dentary. The hyo- 

 branchial apparatus is much reduced, and consists merely of 

 a pair of cartilaginous rods situated beneath the trachea. 



In Viperine Snakes the maxillopalatine apparatus is par- 

 ticularly mobile, and the very short maxilla is articulated with 

 the pre frontal and can swing forward in order to erect the 

 fang. In the burrowing TyphlopidaB, on the other hand, amongst 



Fov 



Fi<;. 8.3. SKULL OF COLUBRINE SNAKE (Tropidonotus natrix), dorsal and 



ventral views. 



Ay, angular; Art, articular; Bp, basioccipital ; Bs, basisphenoid ; Ch, internal 

 nostrils ; Cocc, occipital condyle ; Dt, dentary ; Eth, ethmoid ; F, frontal ; 

 F 1 , postorbital ; For, fenestra ovalis ; //, optic foramen ; M, maxilla ; JV, 

 nasal ; 01, exoccipital ; Osp, supraoccipital ; P, parietal ; Pe, periotic ; Pf, 

 pref rental ; Pf, palatine ; P/nx, premaxilla ; Pt, pterygoid ; Qu, quadrate ; 

 SA, supra-angular ; Squ, squamosal ; Ts, trauspalatine ; Vo, vomer. 



other characters in which they differ from the majority of 

 Snakes, the facial bones are immovably connected with the 

 cranium, and there is no transpalatine. 



Chelonia (Fig. 84). The chondrocranium essentially re- 

 sembles that of Lizards and Crocodiles, and much of the 

 naso-ethmoidal cartilage persists. There is a large supraoccipital 

 crest and usually a lower temporal arcade or jugal arch, except 

 in certain cases where the paraquadrate ("quadrato-jugal") is 

 wanting. The nearly vertical quadrate, which is grooved pos- 

 teriorly for the columella auris, is very firmly united with the 

 neighbouring bones, and above it is a squamosal. There are no 

 separate nasals or lacrymals, their position being taken by a " pre- 

 frontal." The parietals do not unite. The orbit is completely 



