SKIN 137 



In snakes the eyeballs can not be moved beneath 

 this outer skin. In rattlesnakes every time this skin 

 is shed there is left a ridge or rim of it at the 

 tail, which forms a rattle. The first remnant is 

 called a " button." The skin may be shed more than 

 once a summer so that the number of rattles may 

 not tell the age in years, but they form a means of 

 rough comparison. As already noted, the folds of 

 the thick skin proper become horny and form the 

 scales ; and thus the skin has built all the outer 

 coverings for the reptiles, and many bones that are 

 beneath it besides. 



