148 ANIMAL LIFE OF THE BRITISH ISLES. 



definite name, but for the purposes of this book it is not 

 necessary to enter upon a tedious recital of these terms, beyond 

 giving them for reference under the diagram of a Snake's head. 

 The eyes of a Snake are always wide open, for there are no 

 movable eyelids to close them. The eyeball has slight power 

 of movement under its transparent cover, which protects it 

 much as the watch-glass protects the delicate hands of the 

 watch. As in the Slow-worm, there is no external indication of 

 ears, though these are present under the scales. The very long 



Skeleton of Snake. 



and slender tongue divides forwards into two branches, and 

 when not in use is drawn into a sheath at its base. It is 

 constantly used to ascertain the nature of things by contact, 

 and for this purpose is protruded through a little gap in the 

 front of the upper jaw. The gape of the mouth extends far 

 beyond the eye. The forward extremity (glottis] of the wind- 

 pipe can be thrust outside the mouth when, owing to the passage 

 of a bulky victim, there is danger of obstruction by compression. 

 The British Snakes represent the two families Colubridas and 

 Viperidce. 



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