40 



ANIMAL LOCOMOTION. 



and man. In the horse, as in all quadrupeds endowed with 

 great speed, the bones of the extremities are inclined obliquely 

 towards each other to form angles ; the angles diminishing as 

 the speed increases. Thus the angles formed by the bones of 

 the extremities with each other and with the scapulje and 

 iliac bones, are less in the horse than in the elephant. For 

 the same reason they are less in the deer than in the horse. 

 Ill the elephant, where no great speed is required, the limbs 

 are nearly straight, this being the best arrangement for sup- 

 porting superincumbent weight. The angles formed by the 

 different bones of the wing of the bird are less than in the 

 fleetest quadruped, the movements of wings being more rapid 

 than those of the extremities of quadrupeds and bipeds. 

 These are so many mechanical adaptations to neutralize shock, 

 to increase elasticity, and secure velocity. The paces of the 

 horse are conveniently divided into the walk, the trot, the 

 amble, and the gallop. If the horse begins his walk by rais- 

 ing his near fore foot, the order in which the feet are lifted is 

 as follows : — first the left fore foot, then the right or diagonal 

 hind foot, then the right fore foot, and lastly the left or 

 diagonal hind foot. There is therefore a twisting of the 

 body and spiral overlapping of the extremities of the horse 

 in the act of walking, in all respects analogous to what 

 occurs in other quadrupeds ^ and in bipeds (figs. 1 8 and 1 9, pp. 

 37 and 39). In the slowest walk Mr. Gamgee observes "that 

 three feet are in constant action on the ground, whereas in 

 the free walk in which the hind foot passes the position from 

 which the parallel fore foot moves, there is a fraction of time 

 when only two feet are upon the ground, but the interval is 

 too short for the eye to measure it. The proportion of time, 

 therefore, during wKich the feet act upon the ground, to that 

 occupied in their removal to new positions, is as three to one 

 in the slow, and a fraction less in the fast walk. In the fast 

 gallop these i^roportions are as five to three. In all the paces 

 the power of the horse is being exerted mainly upon a fore 



1 If a cat when walking is seen from above, a continnons wave of move- 

 ment is observed travelling along its spine from before backwards. This 

 movement closely resembles the crawling of the serpent and the swimming of 

 tlie eel. 



