THE POISONOUS SNAKES OF INDIA. 



55 



last costafo 



dual 



Fig. 4.— -Xenopeltis unicolor. 



Z astrewofcostats 



TOt%TTOl 



L U^L^LLJJ^LL 



ffentrafa. 



Fig. 5. — Belly of Russell's viper. 



A glance at this simple key will enable the enquirer to isolate two 

 large groups of harmless snakes, by an inspection of the belly shields 

 abova, and a third group of poisonous snakes by the conformation of 

 the tail (sea snakes). 



It is a somewhat difficult matter to decide where to draw the line 

 between the so-called non-poisonous and the poisonous varieties. To 

 begin with, all the viperine snakes are poisonous, and from investigations 

 conducted by Alcock and Kogers* in Calcutta in 1902 it appears 

 probable that all colubrine snakes contain in their saliva a toxic element 

 identical with that to which the poisons of the cobras, kraits, and other 

 deadly colubrines owe their lethal properties. If this is so, strictly 

 speaking, all colubrines are poisonous, and their various salivas merely 

 differ in degrees of toxicity. 



The Colubridai are divided into three groups : (1) Aglypha, 

 characterised by the absence of a poison fang, (2) Opntlioglypha, snakes 

 furnished with a specialised tooth in the form of a grooved fang situated 

 at the back of the maxilla (upper jaw bone), and (3) Proteroglypha, 



* Proceedings of tbe Royal Society, 1902, p. 446. 



