REPTILES 



289 



Locomotion. — Locomotion is performed by pulling and push- 

 ing the body along the ground, a leverage being obtained by 

 means of the broad flat scales, or scutes, with which the ventral 

 side of the body is covered. Snakes can also move without twist- 

 ing the body. This is accomplished by a regular drawing forward 

 of the scutes (with the ribs under them) and then pushing them 

 backward rather more violently. 



Feeding Habits. — The bones of the jaw are very loosely joined 

 together. Thus the mouth of the snake is capable of wide disten- 

 tion. It holds its prey by means of incurved teeth, two of which 

 (in the poisonous snakes) are hollow, and serve as a duct for the 

 passage of poison. The 

 poison glands are found 

 at the base of the curved' 

 fangs in the upper jaw. 

 The tongue is very long 

 and cleft at the end. It 

 is an organ of touch and 

 taste, and is not, as many 

 people believe, used to 

 sting with. The food is 

 swallowed whole, after 

 having been caught by 

 the teeth, and pushed 

 down by rhythmic contractions of the muscles surrounding the 

 gullet. They refuse other than living prey. After a full meal, 

 one of which is sufficient for weeks, the snake remains in a torpid 

 condition. 



Adaptations. — The extreme length of the body in the snake 

 has resulted in the modification of the form of its internal organs. 

 One long, narrow lung is developed instead of two. The glands of 

 the body cavity are long and slender, while the kidneys are placed 

 so that one is anterior to the other. 



Snakes are usually colored to harmonize with their surround- 

 ings. Thus they may approach and seize their prey before it 

 escapes. They are not extremely prolific animals, but hold their 

 own with other forms of life, because of their numerous adaptations 



hunter's BIOL. — 19 



Skull of boa constrictor, two thirds natural size. 

 From photograph by Davison. 



