6 VENOMS 



The palate and lower jaw are furnished with small hooked teeth, 

 which are solid and non-venomous. 



With the exception of the species of Atractaspis, these snakes 

 are all ovoviviparous. The majority are terrestrial ; a few lead a 

 semi-aquatic existence, while others are arboreal. 



Their distribution includes Europe, Asia, Africa (with the excep- 

 tion of Madagascar), and North and South America. They do not 

 exist in Australia. 



They are divided into two Sub-families: — 



A. The ViperincB, in which the head, which is very broad and 

 covered with little plates and scales, has no pit between the nose 

 and the eyes ; 



B. The GrotalincB {KporaXop, a rattle), in which the head is 

 incompletely covered with scales, and exhibits a deep pit on each 

 side, between the eye and the nostril. 



Among snakes, the characters that serve as a basis for the 

 determination of genera and species are the general shape of the 

 body, especially that of the head, the arrangement of the cephalic 

 scales, the cranial skeleton, and the dentition. 



Cranial Skeleton. — The cranium is composed of a certain number 

 of bones, the homologues of which are found in the mammalian 

 skeleton ; but the bones are complex, and subject to modifications 

 according to the structure and habitat of each species. 



The special arrangement of the bones of the face is above all 

 characteristic of the poisonous snakes. Those forming the upper 

 jaw, the palate and the mandibles or " inter-maxillaries " are mov- 

 able upon each other and on the cranium. The upper and lower 

 maxillaries are united by an extensile ligament and articulated 

 with the tympanic bone, which permits the mouth to be opened 

 very widely when the animal swallows its prey. 



De7itition. — The non-poisonous snakes have two rows of teeth in 

 the upper jaw — one external, the maxillary , usually composed of 



