54 



MECHANISM OF EQUINE LOCOMOTION 



amble than it is in the trot. In the gallop there is a strong tendency to lateral 

 displacement ; for at this pace each leg gives its own separate stroke (pp. 95 

 and 96). When either of the near ones act, the centre of gravity is canted to 

 the right; when the off ones make their respective effort, it is thrown to the 

 left The retention of the centre of gravity ni a more or less straight line, 

 entails a certain expenditure of muscular work, and consequent fatigue. 



It is evident that the nearer (Fig. 37) ^x is to by and d to e, the less 

 will be the lateral displacement of the centre of gravity, and the smaller 

 the loss of speed from this cause. Hence we fmd that in animals of great 

 speed, like the cheetah, antelope, greyhound, and race-horse, both the fore 

 and hind legs are respectively placed much closer together than in animals of 

 comparatively greater strength, but of slower movement. The faster the 



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Fig. 37.— Lateral Displacemeni of Body. 



pace (p. 103), the moxe do the footprints of the horse tend to come into 

 the line of the direction in which movement is taking place. This principle 

 is well exemplified in man; for all fast walkers, lunners and skaters try to 

 place the feet, at each step, as nearly as possible, in one straight line. 



As I have already said, the tendency to lateral displacement of weight 

 is corrected to a certain extent, in his various paces, by the horse, who has, 

 however, to do it by a muscular effort, which is a lost force as regards 

 propulsion. 



Effect of Instability of Equilibrium on Speed-^The more un^ 

 stable the equilibrium is, during each step of the horse at any paiticular 

 pace, the greater will be the speed which can be developed at that pace, 

 whatever it may be. This follows from the fact that the more insecure is the 

 equilibrium, the quicker, when it is disturbed, will the new base of support 

 have to be formed. Thus, in the walk of the horse (p. 87) there are never 

 less than two feet on the ground ; three as often as two ; and sometimes 

 even four. In the canter (p. 90), we have respectively m three steps, a 

 support of one foot, of two (or of three) feet, and of one foot. In the trot 



