586 THE LIVING ANIMALS OF THE WORLD 



disfavour with which these reptiles are commonly regarded. Among the uneducated even at 

 the present day it is not unusual to hear the tongue, with reference to its peculiar shape 

 and vibrating action, pronounced to be the seat and instrument of the animal's poisonous . 

 properties. The swift, silent, stealthy, gliding motions with which, apart from any visible 

 organs of locoqidtion, a snake slides, as it were, along the ground and over all obstacles fill 

 to the brink the measure for its condemnation in the estimation of all but the snake-devotee 

 or the naturalist. 



The locomotion of the snake is, as a matter of fact, one of the most remarkable 

 and beautifully contrived phenomena in animal mechanics. The peculiarly jointed and 

 abnormally mobile ribs constitute the mystic deus ex viachind by which the reptile accom- 

 plishes its migration. These ribs articulate in pairs by a single mobile head with their 

 respective segment of the vertebral column. At their opposite extremity they impinge 

 on and are in muscular connection with the broad, slightly overlapping, shield-like scales 

 which clothe the under surface of the body. The rib-muscles, contracting in rh3'thmical 

 succession, raise the free overlapping edges of the shield-like scales, which, striking against the 

 ground in the same regular order, push the body forward. Adopting an easily comprehensible 



simile, the snake's body is 

 j ■ ■ . ■ carried along the ground on 



, . '; ' the same principle as a pad- 



dle-wheel steamer is pushed 

 along the surface of the water, 

 the paddle-boards in the case 

 of the snake being affixed to 

 a long, narrow plane instead 

 of a circular wheel. 



The poison-fangs of 

 snakes are highly specialised 

 structures, and their presence 

 or otherwise was formerly 

 considered sufficiently dis- 

 tinctive for the separation 

 of these reptiles into two- 

 sharpl)' dcfinednatural series. 

 More recent investigations 

 have, however, shown tlwt 

 such a system of classification is entirely artificial, both venomous and harmless species 

 occurring among groups which are related to one another by essential structural characters. 

 The teeth in the ordinary or harmless snakes are usually represented by two rows of slender, 

 recurved, sharply pointed teeth in the upper jaw, and a single row of a similar character in 

 the lower one. This recurved character of the dentition effectively assists the snake in gorging 

 its quarry whole, nothing once seized by the hook-like teeth having a chance of retreating, 

 the snake itself being unable to eject the prey upon which the teeth have fastened. In the 

 most poisonous series, such as a rattle-snake, there is but a single row of recurved teeth in 

 the upper jaw, and these are the equivalents of the inner set of the harmless species. Among 

 the most venomous snakes the poison-fangs are tubular in character, the poison being received 

 from the venom-glands at their open base, and discharged at the apex. In other forms the fangs 

 have grooved channels only for the passage of the virus, while in the other species there may be 

 an intermediate condition. In all cases the poison-secreting glands are modifications of the 

 ordinary salivary glands of other vertebrate animals. They are situated, one on each side,, 

 immediately below and behind the eyes, and are in some instances so abnormally developed 

 as to extend backwards along the sides of the body. Special muscles envelop these glands, 

 and force the poison into the hollow base of the fangs when the mouth is opened to strike. 



S^^ 



?h,toh H. G. F. SpiirrM, £•}.] \_Eailbwrne 



DARK GREEN SNAKE 



Closely allied to the rat-snake of India j and preys in a similar manner on rats^ micc^ and birds 



