SERPENTS. 305 



treme extensibility of the jaws, which are readily dis- 

 located, allows serpents to swallow animals much larger 

 than themselves. Many of these reptiles inject into the 

 wounds made by their teeth an exceedingly poisonous 

 liquid ; the venom is secreted by glands located behind the 

 eye, and communicating by a duct with the fangs. These 

 teeth are rooted in the upper jaw, and have either a 

 tubular canal or a simple groove by which the venom 

 descends when the poison-bag is compressed by muscu- 

 lar contraction as the serpent strikes ; serpents do not 

 bite. It has been recently found that venomous serpents 

 suifer no ill effects from self-inflicted wounds, and that 

 the poison is not dangerous to other individuals of the 

 same species, nor to other ophidia generally. 



We may classify serpents as venomous and non-ven- 

 omous. 



The largest of the non-venomous serpents are the 

 pythons of Asia and Africa, and the anacondas and boas 

 of South America. The first two may attain a length 

 of twenty or thirty feet, and they have great crushing 

 power, being able to seize even large animals, and strangle 

 and crush them in their folds. The largest animals that 

 they can swallow do not, however, exceed the size of a 

 small dog. 



Among the non-venomous snakes of the United States, 

 the more common are the black snake, the pine-snake, 

 which is mottled white and black or brown, and is some- 

 times more than six feet long, the scarlet snake of the 

 South, the garter-snakes, the small green snakes, the 

 common water-snakes of a dark greenish color, and the 

 banded and striped water-snakes. These snakes are 

 more useful than noxious to man, for they destroy for 

 their food large numbers of snails and insects, field rats 

 u 26* 



