PHYSIOLOGY OF MOVEMENT. 749 



striking the ground considerably in front of the track of the fore feet and 

 the velocity of motion rising to from eight to twelve meters per second. 

 The walk turns into the trot when, the body being supported on two 

 diagonal feet, the opposite hind foot rapidly leaves the ground and 

 swings forward so that it strikes the ground simultaneously with the 

 diagonal fore foot, or by one hind foot, as soon as it strikes the ground, 

 rapidly passing into extension simultaneously with the diagonal fore 

 foot. 



(d) The Gallop. — The more the long axis of the body coincides 

 with the axis of the propelling hind legs, the greater is the propulsive 

 power of the legs. The angle between the hind legs and the body may 

 be increased by elevation by means of the fore legs, and in the act of 

 galloping the fore legs are raised up, while the main propulsive power 

 conies from the hind legs, so that the gallop is a series of jumps. Accord- 

 ing to the rapidity of the gallop or run of quadrupeds, four strokes of 

 the feet on the ground are heard in a slow gait or canter, three in the 

 ordinary run, and two in running at full speed. Ordinarily, the legs of 

 the two sides of the body do not act simultaneously, and, according 

 as the right or the left hind leg is extended farthest behind, one speaks 

 of a right- or a left-handed gallop. Thus, in the right-handed run, the 

 left hind leg, stretched far under the body, first in its extension gives the 

 impulse to the body, the right hind leg at this moment swinging forward 

 to add the impulse of its extension a moment later, while both fore feet are 

 off the ground, swinging forward, the left being the farthest advanced in 

 commencing extension, while the right fore leg is still flexed. Then, while 

 the left hind leg is still on the ground, though extended far behind the 

 body, the right hind leg strikes the ground and adds its impulse in 

 extension, while the extended left fore foot approaches the ground and 

 the swinging right fore foot passes into extension. Then the left fore 

 foot, reaching the ground, acts as a support on which the weight of the 

 body is sustained, both hind legs being extended behind the body, the left 

 being farthest extended, while the extended right fore foot is just about 

 to touch the ground. Finally, the right fore leg reaches the ground and 

 receives the weight of the body, while flexion commences in the left fore 

 leg, both hind legs being now flexed under the body, the left hind foot 

 being somewhat the farthest advanced. ■ 



At this moment the left fore foot is raised and the right fore leg, 

 which alone sustains the weight of the body, leaves the ground after 

 having passed the vertical, the body being then entirely free from all 

 support, the fore legs flexed, and the hind legs drawn under the body, 

 the left first reaching the ground. 



Thus, there is a moment in which, alternately, each limb alone sus- 

 tains the weight of the body, and a moment in which both hind legs are 



