2OO Descriptive Zoology. 



Locomotion of Snakes. The chief mode of locomotion in 

 a sinuous line is so well known that a double curve is desig- 

 nated as " serpentine. " It should first be noted that along 

 the whole length of the ventral surface is a series of broad, 

 overlapping plates, the scutes or ventral plates. By 

 means of these the snake "gets hold" of rough places, for 

 on a perfectly smooth surface it can make no progress. By 

 the winding, wavelike motion of its body it both pulls 

 and pushes itself along. The absence of limbs enables it 

 to glide through grass and weeds and into crevices and holes. 

 Snakes also glide along with the body straight. This is 

 accomplished by rhythmically drawing the ribs and scutes 

 forward and pushing them backward, or, as some express 

 it, by "walking on the ribs." 



Food of Snakes. Snakes are carnivorous and take only 

 living prey. This they swallow whole. The constrictors 

 wind the body around the victim and crush it. Our com- 

 mon black snake (blue racer) is a good example of a con- 

 strictor. Our commoner snakes feed on toads, frogs, birds, 

 etc. Garter snakes sometimes eat earthworms. Water 

 snakes catch fish, frogs, and other aquatic animals. 



Process of Swallowing. Birds are usually swallowed head 

 first. If the snake catches a frog by a hind leg, that part 

 leads the way in. The backward-pointing teeth prevent 

 escape. The two halves of the lower jaw are alternately 

 pushed forward and drawn backward, and the victim is 

 thus slowly drawn in. Meanwhile the salivary glands 

 lubricate the object. 



The Organs of Digestion. The gullet is as wide as the 

 mouth, and there is no constriction or line of demarcation 

 between it and the storm rh. The posterior end of the 

 stomach is glandular. About halfway back in the body 



