486 



Comparative Morphology of Chordates 



Fig. 375. {Left and Center) Skull of a lizard (Gerrhontus imbricatus). (After 

 Siebenrock.) (Right) Skull of snake, Tropidonotus. (After Parker.) (av) articular; 

 (bo) basioccipital; (bs) basisphenoid; (d) dentale; (eo) exoccipital; (epo) epiotic; 

 (/) frontal; (j) jugal; (mi) maxilla; (n) nasal; (oo) opistbotic; (p) parietal; (pf) 

 postfrontal; (pi) palatine; (pm, pmx) premaxilla; (prf) prefrontal; (pro) prootic; 

 (pt) pterygoid; (a) quadrate; (qj) quadratojugal; (sa) supra-angular; (sbo) subocular; 

 (so) supraoccipital ; (spt) supratemporal ; (sq) squamosal; (tr) transversum; (v) 

 vomer. (Courtesy, Kingsley: "Comparative Anatomy of Vertebrates," Phila- 

 delphia, The Blakiston Company.) 



tympanic auditory apparatus and the parietal eye (Fig. 377) 

 usually well developed. Urinary bladder present in most groups. 

 Some lizards are viviparous. 



Some lizards are exceptional in that, in varying degree, the body 

 is elongated and the legs are reduced (Fig. 378) — a condition culmi- 

 nating in the "legless lizards," Amphisbaenia. These burrowing 

 animals appear snakelike, having no external legs, although vestiges 

 of girdles may persist. The sternum is reduced or absent. The tympanic 

 structures of the ear are less well developed than in typical lizards. The 

 urinary bladder is lacking, as in snakes. 



Order Serpentes (Ophidia) 



Snakes (Fig. 379). Body much elongated and cylindric. No legs, 

 although occasional vestiges of the pelvic (but never the pectoral) 

 girdle occur and in pythons there are vestiges of hindlegs appearing 

 externally as a pair of clawlike projections (Fig. 380). Bones of upper 

 jaw (maxillary, palatine, pterygoid) movably joined by elastic 

 ligaments. Bight and left halves (rami) of lower jaw joined in front by 



