8o THE FOOD OF ANIMALS 



the Cobra de Capello (Naia tripudians) and Giant Cobra 

 bungarus] of South Asia, the African Asp (N. haie), and the 

 Death- Adders of the Australian region. Here also are included 

 the poisonous Sea-Snakes (Hydropkida) of the Indian and Pacific 

 Oceans. 



The poison arrangements, however, are by far the most 

 specialized in the great group of Vipers (Viperidcz\ represented 

 in this country by the Adder (Pelias berus\ and which includes 

 such notorious forms as the Puff Adder ( Vip^ra arietans) of Africa 

 and the Rattlesnake (Crotalus durissus) (see vol. i, p. 235) of 

 North America. It is serpents of this kind in which the flattened 

 head, broad at the back, presents the oft-cited resemblance to the 



ace of spades. The breadth is mainly due 

 to the presence of very large poison- 

 glands, one behind each eye (fig. 363). 

 These are modified salivary glands, and 

 therefore furnish an instance of the prin- 

 Fi g . 3 6 3 .-skuii of Rattlesnake ciple f " change of function" which has 



a, Brain-case; b, maxilla; c, poison-fang; elsewhere been noted. Each of them is 



a, lower jaw. 



covered by a layer of muscle, which by its 



contraction forces out poison into the fang-canals at the moment 

 when the snake opens its mouth to " strike" its prey. It is, 

 however, in the structure of the upper jaw that the viperine 

 snakes are most remarkable. The external bones (maxilla) of 

 this region are attached by a hinge -joint to the skull, so that they 

 can be moved forwards or backwards. They are extremely short,, 

 and instead of carrying a number of teeth, as in the front-fanged 

 and hind-fanged species, each of them bears but a single tooth in 

 the form of a long sharp poison-fang, traversed by a canal which 

 is open both above and below. Through the upper opening 

 poison is passed into it, flowing out again by the lower aperture 

 placed near but not actually at the tip of the fang. Were the 

 opening in the latter position it would be liable to blockage, but 

 as it is a wound can be inflicted without danger of this. The 

 piercing tube (cannula), attached to a hypodermic syringe, such 

 as doctors employ for injecting various solutions (morphia, &c.) 

 under the skin, is constructed on the same principle. As often 

 remarked, many of the products of human ingenuity are copied 

 from or anticipated by structures possessed by the bodies of 

 animals. 



