REPTILES. 



347 



ORDER II. OPHIDIA (Snakes). 



These are like the lizards in the movable quadrate, but 

 they differ in the absence of limbs and of sternum, the 

 presence of broad scales (scutelto) on the belly, and in the 

 fact that the lower jaw is connected with the cranium by 

 elastic ligaments, so that it can be displaced in swallowing 

 food. Many snakes are poisonous, the poison being con- 



FIG. 145. Dissection of head of Rattlesnake. /, poison-fangs; p, poison-sac. 



veyed into the wound by specialized teeth, the so-called 

 poison-fangs, which are either grooved or are tubular, the 

 grooved teeth being capable of being folded back when not 

 in use, the others being permanently erect. The rattle- 

 snakes (fig. 145) and moccasins belong to the former 

 group. The largest snakes, the pythons of India and 

 Africa and the boas and anacondas of South America, 

 kill their prey by crushing, as do most of the smaller 

 snakes our black-snakes, for example. 



Some snakes are protected against their enemies by 

 their colors, which render them inconspicuous in their 

 usual haunts; others by the nauseous smell which is pro- 



