CLASS REPTILIA 



567 



The rattlesnakes are easily distinguished by the rattle at the 

 end of the tail. This consists of a number of horny, bell-shaped 

 segments loosely held together. Each segment was once the 

 end of the tail; it was shed when the skin was shed, but was held 

 by the newly developed end of the tail. Rattles are therefore 

 added as often as the skin is shed, and, since this happens several 

 times per year, and also since rattles 

 are often detached and lost, it is 

 obvious that the number of rattles is 

 no indication of the age of the snake. 

 Usually before striking, the rattle- 



FIG. 465. Poison apparatus of the rattlesnake. A, A, eye; Gc, poison- 

 duct entering poison-fang at f I Km, muscles of mastication, cut at * ; 

 Me, Me', constrictor muscle; N, nasal opening; S, fibrous poison-sac; 

 2, tongue; za, opening of poison-duct; zf, pouch of mucous membrane 

 enclosing poison-fangs. B, position of apparatus when mouth is closed. 

 C, position when mouth is opened widely. Di, digastric muscle: G, groove 

 or pit characteristic of Crotaline snakes; /, poison-fang; M, maxillary; 

 P, palatine; Pe, sphenopterygoid muscle; Pm, premaxillary; Pt, pterygoid; 

 Q, quadrate; Sq, squamosal; Ta, insertion of anterior temporal muscle; 

 Tr, ectopterygoid. (A, from Parker and Haswell, after Wiedersheim; 

 B, C, from Gadow.) 



snake vibrates the end of the .tail rapidly, producing a sort 

 of buzzing noise, which, to the wise, serves as a warning. 



The poison apparatus of the rattlesnake is shown in Figure 

 465. The poison is secreted by a pair of glands (Fig. 465, A, S) 

 lying above the roof of the mouth. These glands open by poison 

 ducts (Gc) into the poison-fangs (f). The poison-fangs are 

 pierced by a canal, which opens near the end (za), and are en- 

 closed by a pouch of mucous membrane (zf). When the jaws 



