SNAKES. 



31 



A pair of ribs extend downward from each vertebra 

 of the spinal column, and to the lower ends of these 

 ribs a ventral plate is 

 attached by muscles. 

 The snake then moves 

 its ribs much as a mil- 

 lipede or " thousand- 

 legged worm " moves 

 its legs. The edges of 

 a few of the ventral 

 plates catch against 

 any roughness on the 

 surface over which the 

 snake is crawling, and 

 hold that part of the 

 body while another 

 part advances. Put a 

 snake onto a smooth 

 surface as ice or a pol- 

 ished floor and it will 

 move with much diffi- 

 culty, if at all. Hence, 

 we see, that a snake in 

 reality walks with its 

 ribs. 



The skin of a snake, 

 scales, plates and every- 

 thing, is shed several 

 times a year. *The first 

 moult of the season usu- 

 ally takes place in the Fig.5 Skeleton of a Snake. 



early spring, soon after the snake regains activity ; 



