EXTERNAL CHARACTERS 9 



Viperidse, may be remarkable for the flattening of 

 the body, which they may further increase when 

 basking in the sun or in order to assume a more 

 formidable appearance on the approach of an 

 enemy. This power of flattening out the whole or 

 the anterior part of the body is possessed by many 

 snakes, poisonous as well as harmless, and reaches 

 its highest degree in the Cobras of India and Africa, 

 the expanded anterior part being known as the 

 " hood," from the Portuguese name " Cobra di 

 capello." 



Thoroughly aquatic snakes are often short and 

 heavy, but some of the marine forms, or Hydrophids, 

 may be extremely slender, with the posterior part of 

 the body compressed. In some of these Sea-snakes 

 the gracility of the anterior part, or "neck," as it 

 has been called, contrasts very strikingly with the 

 great girth of the body towards the tail, and sug- 

 gests a limbless Plesiosaur. 



The tail, the part of the body behind the trans- 

 versely cleft vent, is most frequently about one- 

 fourth or one-fifth of the total length ; but it may be 

 much shorter, even reduced to a mere stump, as in 

 the Typhlops, or, at the opposite extreme, enter for 

 one half in the length of the snake, as in the 

 African Xenurophis. This organ may taper gradually 

 to a fine point ; or end abruptly, as if mutilated ; or 

 terminate in a horny spine, such as we see in some 

 of the Typhlops or in the Australian Death-adder, 



