568 



COLLEGE ZOOLOGY 



are closed (Fig. 465, B), the fangs lie back against the roof of 

 the mouth. When the snake bites, the digastric muscle (Fig. 

 465, C, Di) opens the jaws; the sphenopterygoid muscle (Pe) 

 contracts, pulls the pterygoid bone (Pi) forward and pushes 

 the ectopterygoid bone (Tr) against the maxillary bone (M). 

 The maxillary bone is thus rotated, and the poison-fang (/) is 

 erected. The poison-glands are so situated that the opening 



of the jaws and erection of the 

 fangs squeezes the poison out 

 of them, through the fangs, 

 and into the object bitten. 

 There are several pairs of 

 small fangs lying just behind 

 the functional ones, which are 

 held in reserve to replace those 

 that are lost in struggles with 

 prey or are normally shed. 



Rattlesnakes are most abun- 

 dant both as regards the num- 

 ber of species and the number 

 of individuals in the deserts 

 of the southwestern United 

 States, but almost every part 

 of this country is inhabited 

 by one or more species. The 

 diamond-back rattlesnake, Cro- 

 talus adamanteus, is the most deadly and largest rattlesnake, 

 measuring sometimes over eight feet in length. It inhabits 

 the pine swamps and hummock lands of the southeastern United 

 States. A nearly allied species is the Texas rattlesnake, Crotalus 

 atrox (Fig. 466). This species inhabits the subarid and desert 

 regions of Texas and the Southwest. These snakes are nocturnal 

 in habit, and prefer the common rabbit as food. Their bite is 

 usually fatal to man within an hour. 



Other species that should be mentioned are the timber, or 



Fig. 466. — The Texas rattlesnake, 

 Crotalus atrox. (From Shipley and 

 MacBride, after Baird and Girard.) 



