320 SNAKES, 



if it take the form of a groove or depression. In the 

 Tropidonoti the keel is so developed as to distinguish 

 the group ; yet many with keels have comparatively 

 smooth skins. The carinated scales of vipers (from carina, 

 a keel) are sharply defined, like the keel at the prow of a 

 ship, or like the breast - bone of the swift-flying birds 

 which Mr. Sclater, in one of his zoological lectures, 

 described as the carinate birds. It is these sharply-defined, 

 stiff, and dull scales belonging to the vipers which produce 

 the rustling noise when the snake is agitated, as described in 

 the little Indian Echis carinata in the chapter on hissing. 

 In the Cerastes I have witnessed the same agitated con- 

 volutions accompanied by the audible rustling produced by 

 the rough scales. See illus. p. 317. 



What are called ' horns ' in some of the African vipers are 

 curiously-modified scales, which, under close examination, 

 present the appearance of half-curled leaves, sometimes of 

 ears, like those of a rabbit or a mouse. Being only cuticle, 

 and liable to injury, these ' horns ' vary in size and colour 

 as well as form. 



The accompanying figure is from 

 the slough of the Vipera nasicornis 

 of the coloured illustration. They 

 were not reversed in desquamation, 

 but came off with a portion of the 

 fine spiny head scales. They were so The sloughed horns of V:>... 



■, 11'iiijjI ^' 1^1 J nasuorm's (exact size). 



dry and shrivelled at the time, that 



it is hard to conceive how they could possibly be reversed, 

 the rest of the bristly head-scales peeling off in pieces. Yet 

 we cannot conclude from this that the horns are never 



