CLASS REPTILIA 



417 



Nostril 



Venom (poison) gland 



Opening of fong 



Constrictor muscle 



Reserve 

 fang 



Muscles 



Mucous membran 

 Fang 



Tongue 



Figure 288. Rattlesnake drawing, showing the hollow teeth (fangs), venom gland, venom 

 duct, and muscles used in forcing poison into the victim's flesh, as is done with a hypodermic 

 needle. Note the pit between the nostril and eye, which is characteristic of pit vipers. (After 

 drawing, courtesy of American Museum of Natural History.) 



scutes forward in alternate sections of the 

 body. The body is drawn forward in the 

 latter method by pressing the rough pos- 

 terior edges of the abdominal scutes against 

 the substratum. Most snakes cannot move 

 fonvard efficiently on a smooth surface. All 

 species are able to swim, and this, of course, 

 is the normal method of locomotion of the 

 aquatic forms. 



The majority of snakes are oviparous, but 

 some are ovoviviparous, like the garter snake 

 which brings forth its young alive. The idea 

 that they swallow their young in order to 

 protect them and then spew them out again 

 when danger has passed is one of the com- 

 mon snake fallacies. 



The tropics, perhaps, are more plentifully 

 supplied with snakes than the temperate 

 zones; and snakes are found in many places 

 not inhabited by lizards. Madagascar seems 

 to be the only large country in warm and 

 temperate latitudes not inhabited by dan- 

 gerous snakes. As in the other groups of 

 vertebrates, the snakes are found in almost 

 every kind of habitat; some species live in 

 salt water, others in fresh water, some are 

 arboreal, and many live underground. 



Only 5 of the 10 families of Serpentes oc- 

 cur in North America. With a few excep- 



tions those described below are found in the 

 United States. 



Blind snakes 



Two species of these small burrowing 

 reptiles (genus Leptotyphlops) occur in the 

 United States. They burrow long tunnels in 

 the earth and feed on worms and insect 

 larvae. 



Other snakes 



Pythons (Fig. 291) and boas (Fig. 290) 

 live almost exclusively upon birds and mam- 

 mals which they squeeze to death in their 

 coils. None of them is venomous and only 

 a few are large enough to be dangerous to 

 man. There is only one boa constrictor. It 

 is a native of the tropical parts of the Amer- 

 icas and reaches a length of 18 feet. Boa 

 constrictors are readily tamed in captivity 

 and therefore preferred by snake "charmers." 



The common garter snake (Fig. 292) of 

 eastern North America is the most abundant 

 of our harmless snakes. It feeds largely on 

 frogs, toads, fishes, and earthworms. The 

 young are born alive, usually in August. The 

 common water snake Natrix is semiaquatic 



