SNAKES 



239 



(6) The upper and lower jaws are composed of movable bones, united by 

 fibrous ligaments, and in the act of swallowing these bones are widely 

 separated from each other. In swallowing the head of the snake 

 " appears pulled out of shape, and each single bone of the framework 

 of the jaws put out of joint." 



(c) How the Prey is swallowed. — After seizing a frog the snake inserts 

 its numerous teeth (on jaws and palate, and not lodged in sockets) into 

 its victim. All these teeth form so many hooks directed backwards, 

 from which escape is impossible. Next, the framework of the jaws is 

 elevated somewhat on one side, and moved some distance forwards. 

 Tne same movement is next performed 

 by the other side. In this manner the 

 prey is drawn slowly but surely down 

 the throat. In fact, the snake drags its 

 jaws by a sort of climbing motion over 

 its victim. 



(d) An abundant secretion of saliva u 

 renders the prey smooth and slippery 

 (importance of this). 



(e) The ribs are not united on the 

 ventral side (sternum absent) ; they 

 can thus be bent apart, thereby allow- 

 ing the gigantic morsel to pass down 

 the gullet, which is itself dilatable. 



(/) It might be supposed that 



during the process of deglutition the gKTOL 01 ,,,,,„ hNU! ,.„„„ i5 



snake would be suffocated. This is pre 

 vented by the extension of the trachea 

 along the floor of the mouth, almost 

 as far as the chin, so that the animal 

 is enabled to breathe while swallowing. 

 The lung, moreover (a single right lung only is present), consists of a 

 long membranous sac, which extends along the whole length of the 

 body, and contains in its posterior portion a sufficient store of respira- 

 tory air. 



5. Fleshy food being capable of digestion without previous mastication, 

 the snake is capable of taking its nutriment in huge morsels. (Compare, 

 on the other hand, the ox ; see Part L, p. 102, Section 2.) The food is 

 gradually dissolved by the strongly acid juices secreted in the stomach. 



6. From the manner in which the snake feeds, we can understand 

 why these animals only take food at comparatively long intervals, and are 

 able to endure long fasts. 



0., 



Maxilla ; U., mandible (the two rami of 

 the latter, which are drawn apart in 

 swallowing, are united by the tendinous 

 ligament B.) ; G., teeth of the palate ; 

 Qu., quadrate bone ; H., occipital con- 

 dyle. 



