EXTERNAL CHARACTERS n 



Although never actually compressed, except in the 

 rostral region, it may be very narrow and elongate, 

 whilst in the opposite extreme it may be strongly 

 depressed, and so broad behind as to be abruptly 

 defined from the anterior part of the body, or 

 " neck." This feature is very marked in some of 

 the Viperidae, and this has given rise to the incorrect 

 generalization that poisonous snakes are distin- 

 guished from the harmless by a broad and flat 

 head, notwithstanding the fact that some of the 

 most dangerous, such as the Mambas, Cobras, and 

 Kraits, have a comparatively narrow or small head, 

 not or but slightly defined behind, whilst, on the 

 other hand, the very opposite condition obtains in 

 not a few of the harmless Colubrids. 



Leaving the Typhlopidae and Glauconiidse aside 

 for the present, snakes have a wide gape, cleft far 

 beyond the vertical of the eyes, with, when closed, 

 one or two notches in front for the passage of the 

 protrusible, bifid tongue. In most snakes this chink 

 is in the lower border of the rostral shield, capping 

 the tip of the snout, and allows free passage to the 

 whole tongue; in the Hydrophids, or Sea-snakes, 

 there are two notches in the lower border of the 

 rostral shield, through which only the bifid end 

 of the tongue can be protruded. The eyes, varying 

 from minute to enormous, are usually free from the 

 surrounding shields, and may move under a trans- 

 parent cap like a watch-glass, which appears to 



