432 MANUAL OF ZOOLOGY. 



The sub-order Viperina comprises the comrrton Vipers 

 {ViperidcR), and the Rattlesnakes {Crofalida), the former being 

 mostly confined to the Old World, whilst the latter are wholly 

 American. The common Viper (Pelias berus), occurs abun- 

 dantly in England and Scotland, and is capable of inflicting 



Fig. 167. — The Naja Haje, a venomous Colubrine Snake. 



a severe and even dangerous bite, though it is doubtful if 

 fatal effects ever follow except in the case of children or sub- 

 jects previously debilitated. The Rattlesnakes are exclusively 

 natives of America, and they are highly poisonous. The ex- 

 tremity of the tail in the true Rattlesnake ( Crotalus horridus) 

 is furnished with a series of horny epidermic cells of an undu- 

 lated pyramidal shape, articulated one within the other, consti- 

 tuting an appendage which is known as the "rattle." Before 

 striking its prey, the Rattlesnake .throws itself into a coil, and 

 shakes its rattle, as it does also when alarmed. The head of 

 the Viperine Snakes (figs. 166, 168) is broad, somewhat tri- 

 angular in shape, broadest at its middle, and showing a very 

 distinct line of demarcation between the head and neck. The 

 head, also, is usually covered with small scales, rarely inter- 

 spersed with larger plates or "scuta" (fig. 168). Other well- 

 known members of this group are the Death Adder {Acanthophis 

 tortor) of Australia, the Horned Viper {Cerastes) of Africa, and 



