rV. VERTEBRATA: REPTILIA, CROCODILIA 



531 



large poison gland, the duct of which opens at the base of the tooth; the poison 

 is led to the tip of the tooth either by a groove {protcroglyphic tooth, fig. 580, 

 A) or, when the groove is closed to a canal {solenoglyphic tooth, B), through 

 this canal which opens at base and tip of the tooth. 



The asymmetrical character of the lungs is interesting. In the Peropoda 

 the left lung is much smaller than the right; in the poison snakes and some others 

 it is rudimentary or even absent. In the Typhlojjhidte, on the other hand, the 

 right is degenerate. The urinary bladder is always absent. The excreta, 

 chiefly uric acid, accumulate as a solid mass and form the chief part of the 

 excrement; the fceces, on account of the extraordinary digestive powers, being 

 small in amount. 



Section I. Opoterodonta (Angiostoma). Burrowing blind tropical snakes. 

 Typhlops. Section II. Peropod.a.. Large snakes, viviparous or ovoviparous, 

 have paired lungs and rudiments of hind extremities; lack poison fangs, and kill 

 their prey by muscular power. Python, Asia and Africa; Boa and Euncctes 

 (anaconda). South America. Section III. 

 CoLUBRiFORMLi. Ordinary snakes (500 

 species) with numerous teeth in upper jaw, 

 appendages entirely absent. Some poison- 

 ous, some not, but no structural lines can be 

 drawn between them. Aglypha, no grooved 

 teeth. Tropidonolus* water snakes; Basca- 

 nion* black snakes; Eutainia* garter snakes. 

 The Proteroglypha, with grooved teeth, 

 permanently erect, poisonous. Most are 

 brightly colored. Elaps* the coral snake; 

 Naja tripiidians, the cobra of India; A^. haje, 

 Cleopatra's asp. Here belong the pelagic 

 sea snakes (Hydrophid^) of the Indo-Pacific, 

 viviparous. Section IV. Solenoglypha. 

 Maxilla reduced and serving as a socket for 

 the single large tubular tooth with one or 

 more reserve teeth (fig. 579). Viperid^, 

 Old World, no pit between nostril and eye. 

 Crotalid.e, New World and Asia, a pit be- 

 tween nose and eye. Crotalus* tail ending 

 in a rattle formed by remnants of cast skins; 

 Agkistrodon contortrix* copperhead, and A. 

 piscivorus, moccasin, lack the rattle. 



Order VIII. Crocodilia (Loricata). 



The crocodiles, alligators, etc., agree 

 with turtles in the oval cloacal opening 

 with single copulatory organ, immovable 

 quadrate, and the bony plates in the skin. 

 In shape they are lizard-like, but in 

 structure they differ from all other living 

 reptiles and approach most nearly to the 



Theromorphs. The maxillaries, palatines, and pterygoids are united 

 in the middle line, forming a hard palate and forcing the vomers up- 

 v/ards into the nasal region, and carrying the choana (fig. 581, Ch) to the 



Cocc 



Fig. 581. — Ventral surface of 

 skull of crocodile (from Wieder- 

 sheim). Cocc, occipital condyle; 

 Ch, choana; jg, jugal; il , maxil- 

 lary; Oh, basioccipital; Orb, orbit; 

 Qi, quadratojugal; Qu, quadrate; 

 PI, palatine; Pmx, premaxilla; Pt, 

 pterygoid; Ps, transversum. 



