SNAKES. 



23 



It is a common notion that Vipers, Rattle- Snakes, and their like 

 (family Viper idee) are the only poisonous Snakes. This is a mistake, 

 the Cobra, which is one of the most deadly Snakes, not being a 

 member of the Viper family. It is, however, a fact that all the 

 representatives of that group are deadly. The Vipers and their 

 kindred may be distinguished by the following features. In the 

 fore part of the mouth is a pair of poison-fangs, supported by the 

 short and otherwise toothless maxillary bones, which are capable of 

 being vertically erected ; the scales on the under surface of the body 



Fig. 21. 



The Puff-Adder (Bitis arietans) ; \ nat. size. (No. 315) 



are transversely elongated ; and the eyes are weU developed. The 

 poison-fangs are tubular, having a broad hole at the front of the 

 base in connection with the poison-gland. Successional teeth are 

 developed behind the fangs in use, and take the place of the latter 

 when they are broken off or worn out. All the species are viviparous 

 as well as poisonous. The family is divided into two groups — True 

 Vipers and Pit-Vipers. 



The True Vipers {Viper idee) are confined to the Old World and 

 have no pit between the eye and the nose. Among familiar forms 

 may be mentioned the Common Viper, or Adder (Vipera berus, 318, 



