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 Viperine, 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 Crotaline (xporadov, 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. 
Dentition.—The non-poisonous snakes have two rows of teeth in 
the upper jaw—one external, the mazillary, usually composed of 
