190 



Comparative Morphology of Chordates 



(Fig. 381). The snake's ability to swallow relatively enormous objects 

 of prey is due to the extreme elasticity of the whole complex of jaw- 

 bones, and to the freedom of the ribs in the absence of a sternum. 



The superficial resemblance of legless lizards and snakes affords a 

 good example of "convergence." In most respects the amphis- 



baenians are definitely lizard-like. 

 The skull is not like that of snakes and 

 even has some features which seem 

 more amphibian than lacertilian. 

 There is doubt as to the proper classi- 

 fication of amphisbaenians. Although 

 usually placed in a suborder of Lacer- 

 tilia, it is possible that they should be 

 ranked as a third order of Squamata. 



The Squamata, both lizards and 

 snakes, are the most widely distrib- 

 uted and numerous of living reptiles. 

 They range over the whole earth where 

 temperature permits. The majority are 

 terrestrial, many are arboreal, some 

 are burrowing, a few are aquatic, and 

 the "flying lizards " {Draco volans: Fig. 

 605) of southern Asia and the Malayan 

 region make long gliding flights by use 

 of their flying membranes, which con- 

 sist of a broad, thin fold of skin pro- 

 jecting from each side of the body and 

 stiffened by greatly elongated ribs. 

 Among ancient reptiles were some real 

 fliers, the pterosaurs (pterodactyls: Fig. 389), which were the rep- 

 tilian equivalent of mammalian bats. The burrowing amphisbaenians 

 are mostly American, but some occur in Africa and the Mediterranean 

 region. 



Most snakes and lizards are relatively small animals, but they 

 range in size up to that of the python and boa constrictor and, among 

 lizards, the American iguana, which may exceed 5 feet in length, and 

 the "monitors" (Varanus) of southern China and the Malayan region, 

 for which lengths up to 9 or 10 feet have been reported. 



Order Crocodilia 



Crocodiles and Alligators. Large horny scales strongly devel- 

 oped, especially on the back, where they are reinforced by thick 



Fig. 381. Diagrams of skull 

 of a venomous snake with open 

 and closed jaws, (m) Maxilla 

 (md) mandible; (p) poison-tooth 

 (pf) prefrontal; (pt) pterygoid 

 (q) quadrate; (s) squamosal; (t) 

 transversum. (After Biitschli. 

 Courtesy,' Kingsley: "The Verte- 

 brate Skeleton," Philadelphia. The 

 Blakiston Company.) 



