120 LECTURE III. 



together with the disposition of the column 

 to maintain its u«ual form, and the^ ease 

 attendant on these nfrotions, cannot be 

 better exemplified than in the instance of 

 riding on horseback. A practised and 

 fearless rider will fold his saddle cloth 

 into a cushion, place it on the back of a 

 rough trotting herse, and sitting on it, keep 

 his seat, undisturbed by sufFeiing all the 

 succussations of the steed to be trans- 

 mitted to the body, above the pelvis, and 

 preserving that part fixed, ^ by constantly 

 keeping the line of gravity of the whole 

 perpendicular to the basis of support. 

 Thus do we enjoy the most springy ease of 

 motion, and perfect fixity of position, with 

 scarcely any muscular exertion, and with- 

 out any effort of mind, for volition cannot 

 regulate the action of muscles in this 

 manner, and those who, from apprehen- 

 sion, seek security in their own efforts, 

 lose it, in proportion as they strive to ob- 

 tain it. 



The vertebral column in the back affords 



