22 

 PAET I. 



THE snake's motion CONSIDERED AS IN A SIMPLE' 

 ELASTIC EOD. 



§ 12. The snake seems to afford the best oppor- 

 tunity for observing the play of the spine. Its 

 locomotion is obviously produced, simply by the 

 action of its back-bone upon its ribs, the remote 

 end of the ribs being thrust against the ground,, 

 so as to propel the animal in the direction of the 

 general resultant of all the forces developed. 



§ 13. On studying the mode of locomotion in 

 the snake, it is, we think, evident that this animal 

 propels its body with a succession of undulatory 

 curves, the flexures of which alternately replace 

 each other in such a manner that those portions 

 of the body which, during one act of propulsion, 

 are either convex or concave, become, respectively, 

 concave or convex for the next act. 



§ 14. If we take a piece of twine, or, stiU better,, 

 of whip-lash (which, for description's sake, we will 

 suppose held perpendicularly before the face), and,, 

 holding an end in either hand, turn these ends in 

 contrary directions, so as to twist the intermediate 

 portion, we shall find that this central part wilL 

 xeadily form itself into flexures similar to those 



