92 OUTLINES OF NATURAL HISTORY. 



this mixture. As one result of this, the temperature of 

 the body is low, and the animal is " cold-blooded." The 

 nervous system, lastly, consists of a brain and spinal cord, 

 with the nerves which these give oflF. 



It stiU remains to say a few words about the skeleton 

 of the snake, and especially as to the peculiarities which 

 are connected with its mode of locomotion. The brain is 

 protected within a bony skull, and the spinal cord is pro- 

 tected by a very long and extremely flexible backbone, 

 with which the skull unites by a single joint. There are 

 no traces of Umbs, and the snake progresses by gliding 

 upon its belly, walking in reality upon the ends of its 

 ribs. In accordance with this, the ribs are exceedingly 

 numerous, and instead of a number of them being united 

 to a breast-bone in front, this latter bone is absent, and 

 the ribs are simply connected with the horny shields 

 which cover the belly. The snakes creeps along the 

 ground, therefore, by the movements of the numerous ribs, 

 which it employs in progression somewhat in the same 

 way that a centipede uses its legs. 



The common Rattlesnake of North America is usually 

 about three or four feet in length, sometimes more. Its 

 general colour is brownish-yeUow, with two rows of par- 

 tially united brown blotches of an irregularly lozenge- 

 shaped figure, but the tail is black. The " rattle " is 

 light brown in colour, and increases in length with the 

 years of the animal, though not receiving an additional 

 joint per annum, as is often stated. Full-grown speci- 

 mens ordinarily possess a rattle of from sixteen to twenty- 

 four joints. The snake shakes the rattle when alarmed 

 or about to strike, but what the function of this singular 

 organ may be, must, in spite of recent speculations, be 

 regarded as still unknown. The Rattlesnake lives upon 

 small animals, such as hares or squirrels, and birds, which 

 it kills by its poisonous bite, and then swallows whole, 

 the teeth permitting neither division of the food nor masti- 

 cation. It is a sluggish animal, which remains torpid 

 during the winter, and is most active and most poisonous 

 in the hottest weather. 



