POISONOUS SNAKES OF NORTH AMERICA. 



381 



It may seem sapertinons to (Inscribe 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 difficult to explain the develop 

 ment and u:-e of this orijan, 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 tapering to a pi>int covered by a cone-shaped more or less 



Fig. -.1. 



PERFECT RATTLE OF A LARGE BANDED RATTLKSNAKK. 



Side view. Tliree-fourths natural size. 



A tie 



iin.) 



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 figures, and appears externally to consist of a series of 

 strongly comi^ressed horny rings joined rather loosely together, the 

 termiiuil one, the so-called ''button," ending in a compressed, somewhat 

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

 constriction. 





Fig. 2J. 



LONGITUDINAL SECTION OF RATTLE. 



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

 straight but curved lines, the tenden(;y of the joints to sag downward 

 by their own weight being counteracted by the fact that the widtli 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 ])rotect the rattle 



.-SEPARATE SEGMENTS OF DISJOLNTED PERFECT RATTLE OF CRUTAH>. 



Side view. 

 !( button ; /i basal joint. 



{After Czerrnnk.l 



against injury and moistuie wiu'n 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 judl 

 them apart separately (fig. 25) or make a longitudinal section through 



