POISONOUS SNAKES OF NORTH AMERICA. 



381 



It may seem superfluous to describe this well-known instrument in 

 detail, but as the internal structure may not be clear to everybody, and 

 as without such a knowledge it will be diiificult to explain the develop- 

 ment and use of this organ, we are obliged to investigate it more closely. 



It will be seen (tigs. 23, 24) that the tail end of the Rattlesnake instead 

 of gradually ta})ering to a point covered by a cone-shaped more or less 



Fig. 2:i. 



PEEFKCT RATTLE OF A LARGE BANDED RATTLESNAKE. 



Side view. Three-fourths natural size. 



(After Garm:in.) 



acute scale, as in most other snakes, continues rather thick to where 

 the rattle is appended. The rattle itself in its perfection is shown in 

 the above ligures, and appears externally to consist of a series of 

 strongly compressed horny rings joined rather loosely together, the 

 terminal one, the so-called "button," ending iu a compressed, somewhat 

 cone-shaped cap, which is set off from the basal swelling by a slight 

 constriction. 



Fig. 24. 



LONGITUDINAL SECTION OF BATTLE. 



The upper and lower outlines of the rattle will be seen not to be 

 straight but curved lines, the tendency of the joints to sag downward 

 by their own weight being counteracted by the fact that the width of 

 each ring is greater at the lower edge of the rattle than at the upper. 

 Mr. Quelch, the director of the museum in Georgetown, Demerara, has 

 shown that the object of this arrangement is to protect the rattle 



SEPARATE SEGMENTS OF DISJOINTED PERFECT RATTLE OF CROTALUS. 



Side view. 

 a button; /ibaaal joint. 



(After Czermak.i 



against injury and moisture when the snake is moving over the ground 

 by keeping the somewhat delicate instrument automatically raised. 



In order to study the internal structure of the rattle so as to learn 

 how the various joints are linked together we will have to either i)ull 

 them apart sei^arately (fig. 25) or make a longitudinal section through 



