70 MECHANISM OF EQUINE LOCOMOTION. 



touch the ground during each step. From this we may conclude that 

 the canter is a faster pace, naturally, than the trot or amble. I am 

 aware that this is not the case with many horses which have been 

 specially trained for match-trotting and match-pacing ; but that fact 

 does not bear on the subject in question. Of all paces, the gallop is 

 the one in which the equilibrium is most unstable : for during each 

 stride of it, the centre of gravity is carried farther beyond the base 

 of support (Fig. 167) than at any other pace. Besides, at each step 

 in it, there are fewer feet on the ground, at the same time, than at 

 any other pace. 



During continued movement, any addition to speed obtained by 

 increased instability of equilibrium, necessitates increased muscular 

 effort in maintaining the centre of gravity of the body at a suitable 



C B 



A E 



Fig. 44. — Resolution of forces in 

 canter and gallop. 



height. In this case, the work falls chiefly on the muscles which 

 straighten the fore legs (extensors of the shoulder and elbow joints, 

 and flexors of the fetlock and pastern joints) of the horse, and varies 

 according to the angles they make, at their respective moments of 

 action, with a vertical line drawn through their points of support on 

 the ground. Owing to the extreme complexity of the animal machine, 

 no exact calculation can be made on this subject ; although the 

 following rough statement will help to illustrate the principle under 

 consideration. For 'the sake of simplicity, only the action of the 

 leading fore leg, which is the chief factor in this question, will be 

 taken into account. 



Let BAG (Fig. 44) represent this angle at the canter in Fig. 153 ; 

 D A C, this angle at the gallop in Fig. 167 ; and let C B D be a line 

 drawn parallel to the ground (A E). According to the "resolution of 

 forces," the proportion between the work at the canter and the work at 

 the gallop, in these cases, will be equal to the proportion between the 

 respective lengths of the lines A B and A D ; the latter being longer 

 than the former. Also, the more the limb is straightened out, the 

 greater is the mechanical disadvantage at which its bony levers act. 

 And, as the extent to which the fore leg can be straightened out, is 



