268 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



drawn back again the body of the snake is thrust forward. 

 It is the movement of these scutes, accompanied by the 

 undulations of the body, that enables the snake to crawl so 

 rapidly. They cannot move forward on smooth surfaces 

 because the scutes have nothing to catch against. The scales 

 on the head are quite regular in their arrangement, forming 

 definite patterns. The bones of the jaws are so arranged 

 that the mouth is very distensible. This allows the snakes 

 to swallow objects which are greater in size than the normal 

 diameter of the body and it is not an unusual sight to see a 



FIG. 122. A garter-snake, Thamnophis parietalis. (After Snyder.) 



snake with a part of its body very greatly distended by 

 some small animal that it has swallowed whole. The tongue 

 is slender, protrusible and deeply notched. It is commonly 

 supposed that the tongue can inflict injury, but this is not 

 true. It doubtless serves as a special organ of touch. The 

 teeth are sharp and recurrent. In the poisonous snakes cer- 

 tain of the teeth develop into long sharp fangs which are 

 grooved or tubular and serve to conduct the poison from the 

 poison gland in the head into the wound. The food of snakes 

 consists very largely of other animals which are usually caught 

 alive. Many species feed on the eggs of other animals. Many 

 persons erroneously regard all snakes as dangerous, and try to 

 kill all that they see. But most of our common kinds are not 

 only harmless but very serviceable because they destroy mice, 



