68 ELEMENTS OF COMPARATIVE ZOOLOGY. 



ence of broad scales (scutellae) 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- 

 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 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 they produce 

 by certain glands in the skin; still others by their poison- 



Fio. 25. Dissection of head of Rattlesnake. /, poison-fangs ; p, 

 poison-sac. 



glands. Most of the snakes are terrestrial, but some, 

 like our water-snakes, take to the water, while in the Indian 

 Ocean are found truly aquatic snakes, which never go on 



