62 MECHANISM OF EQUINE LOCOMOTION. 



gravity falls 4 inches, and that the animal has to go a distance of 1000 yards 

 on a horizontal plane. It is evident that, in this case, the muscles of the 

 horse's limbs would not alone have to carry the weight of the body 1000 

 yards, but would also have to raise it ZZZ\ feet (1000 X ^^, which would be 

 approximately equivalent to going over a hill that was m^ feet high and 

 whose base was 1000 yards broad. I need hardly say that the less the fall 

 and rise at each step, the lower this supposititious hill would be, and, 

 consequently, the easier it would be to walk over. 



Although the duty of forward propulsion is chiefly performed by the hind 

 limbs ; the greater part of the work of adjusting the position of the centre of 

 o-ravity during ordinary locomotion, falls on the fore limbs. When a horse, 

 for instance, performs the high -school feat of cantering to the rear, the 

 respective roles would obviously be reversed. The question of the adjustment 

 of the centre of gravity of the body, so that the muscles of locomotion may 

 act to the best possible advantage, will be considered further on. 



Comparative Speed in the Action of the Limbs.— The 



speed with which the body is projected forward, is directly proportionate to 

 the speed with which the limb or limbs are straightened out, and has 

 nothino" to do with the strength of the muscles that move the parts. Hence, 

 any excess of muscular development beyond that required for the due 

 workino- of the limbs, will tend to diminish the speed by unnecessarily adding 

 to the weight to be carried. For this reason, we never see great race- 

 horses of the weight-carrying hunter build. Some of the best (St. Simon and 

 Tim Whiffler, for instance) have been slight horses. In fact, the son of 

 Galopinand St. Angela {see Pis. 7 and 18) had singularly light hind quarters. 

 Even Ormonde, who was very muscular for a race-horse, was anything but 

 broad when viewed from behind {see Frontispiece). 



The question of the speed of muscular contraction is an abstruse one 

 which still remains unsettled. We know that if a muscle be stimulated by a 

 shock of electricity, it will contract throughout its entire length at (practically) 

 the same moment. Hence, under this condition, a long muscle would 

 contract very nearly in the same time as a short one. When, however, a 

 muscle is stimulated by the nerves which act in obedience to the will, the 

 contraction of its various parts does not take place simultaneously, though 

 at such a brief interval that we may regard the delay as unappreciable. 

 Hence, in two limbs which resemble each other in every particular, except 

 that one is short and the other long, the respective extension of both will be 

 accomplished in very nearly the same time, and consequently, the speed of 



