THE SPINAL COLUMN OF REPTILES. 161 



the ribs assist in locomotion ; they take the 

 place of limbs, and their action is very like 

 that of the limbs of the millepede, as may be 

 ascertained by any person who will allow a snake 

 to crawl quietly over his hand, when their action 

 wUl be plainly felt. It is, in fact, on the ends 

 of the arched ribs, that the snake rests, and 

 each pair is connected by means of a slender 

 cartilage, and a set of short muscles, with 

 one of the scuta or broad abdominal scales, 

 with which the under surface is invested. 

 As the ribs are put into action, each pair, 

 on being advanced, carries forward with it 

 the scale to which their extremities are at- 

 tached ; then the next scale in succession, 

 and again the next, are brought forward in 

 progressive order, the anterior ribs retaining 

 the advantage gained, by the energy of the 

 muscles which govern them. These scales 

 may therefore be regarded each as a common 

 foot to a pair of ribs, and their posterior 

 edges, which overlap each other, aiding the 

 ribs in their progressive advancement, by 

 catching hold of the ground or other objects, 

 "become in turn so many fixed points, whence 

 the forward movement is dated. 



It is well known, that the terrible boa 



