INSTABILITY OF EQUILIBRIUM. 17 



In quadrupeds as well as in bipeds, instability of equi- 

 librium is an essential element of speed ; for the more insecure 

 the equilibrium, the quicker can the new base of support 

 be formed. Hence the faster the pace, the more unstable 

 will be the equilibrium. For instance, the centre of gravity is 

 carried farther beyond the base of support in the gallop 

 (Fig. 12), than in the canter (Fig. 24). By Figs, i to 16 we 

 see that the gallop may be divided into the following suc- 

 cessive though not very clearly separated periods, namely : 

 (i) support by the hind legs ; (2) propulsion by the hind 

 legs ; (3) support by the fore legs ; (4) elevation of the fore- 

 hand and to a slight extent propulsion by the fore legs ; (5) 

 suspension. Not only doss increased instability of equili- 

 brium add to the quickness of the stride, but it also augments 

 its length, as has been proved by experiment with race-horses 

 ridden at the gallop by lads who, on different occasions, em- 

 ployed respectively the ordinary seat and the " crouching " 

 seat. It is evident that the more a rider leans forward, the 

 more unstable will be the equilibrium and the greater will 

 be the strain thrown on the ligaments of the fore legs during 

 their period of support, and on the back tendons while the 

 fore-hand is being raised. The attainment of increased speed 

 by the rider bringing his weight forward, is accompanied not 

 only by greater danger to soundness, but also by loss of stay- 

 ing power, on account of an unduly large amount of labour 

 being thrown on the muscles which extend (straighten) the 

 fore legs and thus serve to raise the fore-hand. It is evi- 

 dent that the shorter the distance of a race, the more will 

 a jockey have to consider speed ; and the longer the jour- 

 ney, the more attention will he have to devote to staying 

 power. In almost all cases when a horse gets tired in a race, 

 he shows by his up-and-down motion (inability to raise the 

 fore-hand to a sufficient height) that the muscles of the fore- 

 hand are at that time more fatigued than those of the hind 



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