234 TROPICAL MEDICINE AND HYGIENE 



(ii) Elapince. In this subfamily the tail is of the 

 ordinary tapering, cylindrical kind : the head is covered 

 with large shields, and the ventral shields are enlarged 

 transversely. There are about 140 species, of which 

 nearly half belong to the Australian region, and the 

 other half are divided pretty equally between Africa, 

 Southern Asia and its islands, and the tropical and 

 subtropical parts of the American continent and islands. 

 The exact geographical distribution of the more im- 

 portant forms will be considered subsequently, together 

 with that of the more notorious Viperidce. 



(2) Viperidce. All the snakes about no species 

 of this family are more or less poisonous, possessing 

 not only a poison-gland, but also large tubular poison- 

 fangs for injecting the venom. It is popularly supposed 

 to be easy to distinguish a Viperine from any Colubrine 

 snake by the narrow neck, by the very broad head 



trans. pal. 



FIG. 100. 



covered with small scales, by the elliptical pupil, and 

 by the stumpy tail. But there are Colubrines in which 

 these features are present, singly, or even in some 

 combination ; and, on the other hand, there are not a 

 few vipers that are without one or more of these sup- 

 posed characteristic features. The distinctive mark of 

 the Viperidce is the maxilla (fig. 100), which is a very 

 short bone hanging obliquely to the palate, and capable 

 of being " erected" into .a perpendicular position. 



