TRUE REPTILES. 



207 



poison -fangs are 



extremely large, 



and the snake is 



much dreaded. 



They are confined 



to the Old World. 



Rattlesnakes 



(Crotalidce). In 



this family are the 



rattlesnakes (Fig. 



248), moccasins, 



and copperheads, 



forty species in 



all, and extremely 



poisonous. The 



upper jaws con- 

 tain few teeth, but 



have needle-like, 



recurved, grooved 



fangs, that are 



raised at the 



slightest alarm. The poison-glands (Fig. 249) are at their 



base, and when the mouth closes upon an enemy the 



muscles that ef- 

 fect it press the 

 gland, forcing the 

 poison into the 

 wound. They 

 have a pit or de- 

 pression between 

 the nostrils. The 

 true rattlesnakes 

 rarely exceed 

 four feet in 

 length, and have 

 the tail terminat* 



FIG. 248. Rattlesnake (Crotalus). 



FIG. 249. Jaw of a rattlesnake. /_/; 

 poison-fangs ; , gland secreting poison ; 

 c, canal leading from gland to base of fang ; 

 t, harmless tongue ; s, saliva-glands. 



