THE HORSE IN MOTION. 99 



There is another class of quadrupeds, whose posterior extremities 

 are developed to a much greater degree than the anterior ones, and 

 their mode of progression varies more or less from the theory of motion 

 as given in the preceding pages. The only one of this class of whose 

 stride we are able to present an analysis is the deer. In this animal 

 the same order of succession of the feet may be observed ; but, at the 

 moment when it might be expected that he would, as in the horse, rise 

 from one of the fore legs, owing to its feebleness he fails to do so, but 

 the hind legs are thrust forward to the ground, one of them in advance 

 of the fore foot and the centre of gravity, and, while one of the fore 

 legs still supports the weight of the anterior part of the body, by the 

 combined action of the posterior extremities he projects himself by 

 a bound, and alights, not upon one of the hind feet, but upon one of 

 the anterior extremities; but the action of the limbs in pairs is not 

 sj'nchronous, one of them being a pace in advance of the other, to dis- 

 tribute the shock. This mode of progression the deer is able to per- 

 form by reason of the length and angles of the bones of his limbs 

 and the lightness of his body, and it is adapted to the nature of the 

 ground among the hills where he finds his only safety, and where 

 the horse would be at as great a disadvantage as the deer is upon the 

 plain. For reasons already stated, it is not possible to sustain this 

 gait for a long time from the exhaustion which it produces. The 

 action of the horse in leaping will be reserved for another chapter. 



From the knowledge we have gained, by the use of instantaneous 

 photography, as to the action of the feet in running, the answer to the 

 questions propounded by William Percivall thirty years ago is obvious: 

 " What is the reason why the flexor tendons fail so much more fre- 

 quently than others ? Another, Why those of the fore limb should 

 fail rather than the flexor tendons of the hind leg." * 



In the following quotation he gives the answer to his own question, 

 in accordance with the heretofore accepted theory of the run. " I 

 have more than once had occasion to direct attention to the important 

 functions performed by the hind limbs in the acts of progression, and 

 to contrast these with the comparatively light duties of the fore limbs. 



* Hippopatliology, Vol. IV. p. 346 



