THE HORSE IN MOTION. 79 



half of the stride, when it is in the power of the animal to give an 

 impulse to the movement, that settles effectually the question of the 

 power of the anterior extremity as a propeller. The proof will be 

 given hereafter, but the modus operandi is as follows: As the foot 

 is about to leave the ground, the angles of the limb being extended to 

 their utmost, the great pectoral, the great dorsal, and the great serratus, 

 by a vigorous and simultaneous effort, in conjunction with the spring 

 of the suspensor}' ligament and its reinforcing tendons, are capable of 

 deflecting the centre of gravity of the whole body of the horse, going 

 with a velocity of twenty miles an hour, four inches in a distance 

 of ten feet 1 



At the completion of the stride, the last impulse given by the 

 reaction of the suspensory ligament is like the spring of a bow, and 

 the flexor muscles regain control of their tendons, which had just been 

 serving as reinforcements to the suspensory ligament. 



At this moment, the foot being off the ground, the knee bends 

 under the contraction of the perforatus and perforans muscles. The 

 superspinatus and all the muscles of the triceps are relaxed ; the 

 flexors of the shoulder and of the arm contract; at the same time the 

 mastoido humeralis and superficial pectoral, acting on the shoulder, 

 carry the whole limb forward on its centre, the great pectoral and 

 great dorsal consenting. In this order they pass the perpendicular, 

 when the order is quickly reversed ; in twice the speed used in the 

 retrograde movement, the foot is again in position to take the ground. 

 The extensors of the feet, after a rest of three fourths of a stride, again 

 straighten the knee, raise the toe, and the triceps is ready with all its 

 heads to take the shock. The sterno prescapularis pulls the slack out 

 of all the tissues connecting the shoulder with the trunk, that nothing 

 may be lost to effect the last line in extension. 



The action of the anterior extremity in the three characters whose 

 parts it performs at the same time, we have endeavored to represent. In 

 these three characters it is a complicated machine. The object in its 

 construction was to enable the limb to support the body for the 

 greatest length of time, and to graduate that support so that it should 

 be uniform and constant, and that there should be no loss of momen- 



