BRANCH CHORD AT A: CLASS REPTILIA 319 



Usually they have the body regularly cylindrical, and 

 without distinct division into body regions. Legs are 

 wanting, locomotion being effected by the help of the 

 scales and the ribs. No snake can move forward on a 

 perfectly smooth surface and no snake can leap. In some 

 forms, such as the pythons, external rudiments of the hind 

 limbs are present, but do not aid in locomotion. The 

 mouth is large and distensible so that prey of considerably 

 greater size than the normal diameter of the snake's body 

 is frequently swallowed whole. The sense of taste is very 

 little if at all developed, as the food is swallowed without 

 mastication. The tongue, which is protrusible and usually 

 red or blue-black, serves as a special organ of touch. 

 Hearing is poor, the ears being very little developed. 

 The sense of sight is also probably not at all keen. 

 Snakes rely chiefly on the sense of smell for finding their 

 prey and their mates. The colors of snakes are often 

 brilliant, and in many cases serve to produce an effective 

 protective resemblance by harmonizing with the usual 

 surroundings of the animal. The food of snakes consists 

 almost exclusively of other animals, which are caught 

 alive. Some of the poisonous snakes kill their prey before 

 swallowing it, as do some of the constrictors. While most 

 snakes live on the ground, some are semi-arboreal and 

 others spend part or all of their time in water. Cold- 

 region snakes spend the winter in a state of suspended 

 animation ; in the tropics, on the contrary, the hottest part 

 of the year is spent by some species in a similar * ' sleep. ' ' 

 There are so many common snakes in the United States 

 that only a few of the more familiar forms can be men- 

 tioned. The non-poisonous species of America belong 

 to the family Colubridae, while all but one of the poisonous 

 species belong to the family Crotalidre, characterized by 

 the presence of a pair of erectile poison-fangs on the upper 

 jaw. Among the commonest of the Colubridae are the 



