PINE-LIZARD AND ITS ALLIES: REPTILIA 355 



oesophagus is facilitated by an abundant secretion from sali- 

 vary glands, and escape of the prey is prevented by the sharp, 

 backward-pointing teeth in both jaws. The union of the two 

 sides of the lower jaw in front is so loosely made by a carti- 

 laginous connection that each side of the jaw can be pushed 

 forward independently, thus getting a fresh hold on the food- 

 mass. Some of the larger snakes, as the pythons and boas, 

 kill their prey by constriction ; the non-poisonous kinds may 

 swallow theirs alive ; the poisonous species generally kill the 

 animal, unless it be a small one. Snakes progress by means 

 of muscles attached to the ribs and scales of the under side. 

 These scales have a free posterior edge, which can be inserted 

 into rough places in the surface of the ground. 



The poisonous snakes of the United States are the prettily 

 colored beadsnake (E'laps ful'vius) and the water-moccasin 

 (Agkis'trodon 

 pisciv'orus) of 

 the southern 

 states ; the 

 copperhead 

 (Agkistrodon 

 contor'trix], 

 found from 

 New England 

 to Wisconsin 

 and southward; 

 and more than 

 a dozen species 

 of rattlesnakes 



FIG. 181. Photograph of .Rattlesnake 



(Fig. 181), found mostly in the arid regions of the West 

 and Southwest. The use of the peculiar horny appendage 

 at the end of the tail of the rattlesnake has occasioned 

 much discussion. By some it has been thought to be a 

 means of terrifying its prey, so that escape may be rendered 



