TRUE REPTILES. 207 
poison-fangs are 
extremely large, 
and the snake is 
much dreaded. 
They are confined 
to the Old World. 
Rattlesnakes 
(Crotalide). — 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 Fic. 248,—Rattlesnake (Crotalus). 
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 
thenostrils. The 
true rattlesnakes 
rarely exceed 
four feet in 
Fic. 249.—Jaw of a rattlesnake. (7 
poison-fangs; g, gland secreting poison ; 
c, canal leading from gland to base of fang; length, and have 
¢, harmless tongue ;_ s, saliva-glands. the tail terminat- 
