32 HORSE-BACK RIDING. 



stroy, we see also that it is the muscular contraction 

 which brings it, and that it also determines the fixed- 

 ness of the points of support, and that the muscles 

 are the agents of the movements. 



But we should strangely deceive ourselves if we im- 

 agined that those muscles only act which have been 

 named in studying the movements of the equestrian. 

 There is not, perhaps, a single muscle which does not 

 come into play in horse-back riding, either for pre- 

 venting a displacement or restoring a disturbed equi- 

 librium. It is not necessary for them all, however, to 

 contract with the same energy, and while some, as the 

 adductor muscles of the thigh, the sacro-lumbar and 

 long dorsal muscles, may be termed essentials, others 

 intervene only accidentally, as it were, or to meet 

 certain exigencies, or produce special movements, as 

 in the high school exercises, parades, etc. 



Others are assistants merely of the muscles which 

 we call essentials, and may be termed auxiliaries, 

 and, lastly, we know that when a muscle causes a 

 movement in a certain direction, there is always one 

 or more the action of which is opposed to it, and 

 which are therefore called antagonistic. 



