750 PHYSIOLOGY OP THE DOMESTIC ANIMALS. 



propelling the body, and one in which both fore legs are supporting it. 

 In the analysis of the movements of the limbs in the run the greatest 

 confusion has existed as to the functions of the fore limbs ; this has now, 

 thanks to instantaneous photography, been cleared up. In the first 

 place, it is seen that at one time the body is entirely clear from the 

 ground, and that the weight of the body is not received on one or both 

 of the fore legs, but on one hind leg, advanced under the body so that 

 the foot is nearly under the centre of gravity. In the second place, the 

 fore legs do not serve merely as " props or stilts " for the support of the 

 body in motion, but are themselves also propelling organs. At first 

 sight this might seem impossible, for the insertion of the fore limbs, 

 acting on the body at rest, and being inserted in front of the centre of 

 gravity, could not advance, but only elevate it, as in rearing. In the 

 running animal, however, the propulsion from the hind legs advances the 

 centre of gravity, but at the same time tends to lower it, and if the fore 

 feet were immovable, the animal would tend to fall forward on its head. 

 This is prevented by the shifting of the fore feet, while at the same 

 time a distinct upward impulse is communicated to the centre of gravity. 

 This may be seen in Mr. Muybridge's photographs, where there is a 

 distinct elevation of the body at each time the fore legs leave the ground. 

 The centre of gravity of the body is thus acted on by two forces, one 

 from the hind legs tending to advance and lower it, the other from the fore 

 legs tending to elevate it ; the resultant of these two forces will evidently 

 be a diagonal between the two ; and the upward lift from the fore feet 

 will more than compensate the downward tendency, and the body will 

 be lifted and advanced. 



In this gait but two strokes of the feet are heard, the first pro- 

 duced by the contact of the left hind leg, lengthened by the fall of the 

 right hind foot, the second by the contact of the left fore foot with the 

 ground, lengthened by the fall of the right fore foot. The interval 

 between the first and second sounds is very short, that between the 

 second and first, while the hind legs are swinging through the air, some- 

 what longer. The length of the strides in the full run may amount to 

 six or seven meters, and a velocity of nearly fifteen meters per second 

 be attained. 



In a slower run or gallop three strokes of the feet are heard, the 

 body, as in the trot, being supported on the diagonal limbs. The differ- 

 ence of this gait from the trot consists in the fact that in the latter the 

 support on the diagonal limbs is equally prolonged, while in the gallop 

 the support on one pair is longer than on the other. A conception of 

 this gait is obtained if it is imagined that one pair of feet are acting as 

 in the trot, the other as in the movement of jumping. 



1. In this gait, when right-handed, the left hind leg is extended on 



