XIII. 



SNAKES. 



197 



scales form large scraper-like plates the edge projecting 

 backwards. Thus we have an admirable set of rib-levers 

 with the scraper-like plates at one end and the 

 vertebra? of the spine at the other. The scraper readily 

 slides over the ground forwards, but catches on being 

 drawn backwards. It bites on the roughened surface of 

 the ground, and by the movement of the rib-levers the 

 body is drawn forwards. Such is the mode of progression 



CORAL SNAKE OF BRAZIL. 



on a plain surface. Through the grass the snake 

 progresses by swimming, with a sinuous motion of the body 

 from side to side. Even on a plain surface the snake will 

 adopt this sinuous motion if frightened, and though it does 

 not much aid progression, it makes the creature difficult 

 to catch. 



It is largely with the aid of its ribs, as I once had an 

 opportunity of observing, that the snake is enabled to 

 walk out of his skin when he wishes to change his coat. 



