56 THE HORSE IN MOTION. 



oblique, so that when flexion takes place at that joint, the lower ray 

 is carried obliquely outward, and when the other leg is passed, and the 

 extension takes place again, its action is reversed, and the foot is 

 returned to the position required to support the centre of gravity. 

 By this simple contrivance the danger of this accident is placed beyond 

 the will of the animal, and in well-formed horses beyond the possibility 

 of accident. Some horses circumduct the hind feet more than others, 

 and in others the stifle action is most marked ; but it is not common 

 to see both excessive in the same horse. 



There is often considerable difference in different horses in the 

 length of the hock. The long hock gives the greatest power, for the 

 reason that the leverage is greater; but what is gained in power is 

 lost in speed. 



Sometimes there is a looseness in the articulations of the tarsal 

 bones immediately below the hock joint, which, by their freedom of 

 motion upon each other, enables the joint to become more extended, 

 and the last effort of the gastrocnemii muscles is given with great 

 advantage of mechanical power from the practical shortening of the 

 arm of the lever on which they act, and from the ability the limb 

 acquires of retaining its position upon the ground for a longer time. 

 It is a point in some fast animals, but would be considered a defect in 

 a draught horse. 



Having given a detailed description of the parts concerned in the 

 motion of the posterior limb, and their action, I will now endeavor to 

 show how the machine acts as a whole. If the reader has familiarized 

 himself with the parts by reference to the plates, while he has followed 

 the description, he will experience no difficulty ; but if he has not, it 

 would be as well for him to pass over the rest of this chapter. The 

 analysis has no reference to any particular gait or co-ordination of the 

 limbs with each other, but it is confined to the action of one posterior 

 limb alone, and it will be found to be the same in all the paces, differ- 

 ing only in the degree of action according to speed. 



We will take for our guide the posterior extremity as it has just left 

 the ground, after the act of propulsion is complete, and in the medium 

 pace, the trot. 



