502 THE HOKSE'S POSITION IN THE ANIMAL WORLD 



epidermis is thickened. The sole of the foot presents exactly the same 

 arrangement. 



" In such an animal as a dog or a cat, in which this part of the foot 

 comes to the ground in walking, there is a large, trilobed, prominent, bare 

 pad, composed of a thick, fetty cushion covered with hardened epidermis, 

 generally of a black colour. There are also smaller pads in front of this on 

 the under surface of each of the toes, but the large one corresponds with the 

 coalesced three middle prominences of the human palm or sole just noticed. 



" In the horse's nearest relatives, the tapir and rhinoceros, the same 

 arrangement holds good. There is a large pad under the fore part of the 

 middle of the foot, which in these animals rests on the ground, and there 

 is also a hard sole under each toe. Now the ergot of the horse clearly, 

 both by structure and jiosition, corresponds to the palmar or the plantar 

 pads of those animals which walk more or less on the palm and the sole. 



" Owing to the modified position of the horse's foot, standing only on 

 the end of the last joint of the one toe, this part of the foot no longer 

 comes to the ground, and yet the pad, with its bare and thickened epidermic 

 covering, greatly shrunken in dimensions, and concealed among the long 

 hair around, and now apparently useless in the economy of the animal, 

 remains as art eloquent testimony to the unity of the horse's structure with 

 that of other mammals, and its probable descent from a more generalized 

 form for the well-being of whose life this structure was necessary." 



In the illustration (fig. 664) the position of the parts described is shown. 



In the description quoted, the reference to the ergot of the horse's 

 fetlock — representing the palmar or plantar pad — as being characterized 

 by " its bare and thickened epidermic covering greatly shrunken " does- 

 not convey an idea of its true structure. The excrescence, both in the 

 horse and in the ass, is a decided prominence, and is identical in its^ 

 minute structure with the hoof of the horse, as will shortly ajjpear, while 

 the palmar and the plantar pads of man and the dog are correctly described 

 as " thickened epidermic covering " quite distinct from hoof horn. 



A careful examination of specimens which have been obtained for the 

 particular purpose of ascertaining what are the structural relations between 

 the callosities and the ergots of the horse tribe and the plantar and the 

 palmar pads in man and the dog has led to some very interesting results. 



The several parts referred to may, for convenience, be considered in the 

 fii'st place as they appear to the unaided eye of the ol)server. After which 

 their minute structure will be more easily explained. 



Man has no distinct pads beyond those which have been described as 

 hardened cuticle, the result of pressure and of friction affecting certain 

 prominent parts of the soles of the feet and the palms of the hands. These 



