504 THE HORSE'S POSITION IN THE ANIMAL WORLD 



are to be accepted as the rudiments of the plantar pads in the primeval 

 horse, it must not be forgotten that they differ in structure from the pads 

 of animals in which pads are essential organs of progression, as the ergots 

 are distinctly horny structures and not merely hardened cuticle. 



Ergots are constantly present in horses and in asses; in the latter 

 indeed they are relatively broader than in the horse, although they do not 

 often protrude quite as far above the skin. After maceration the horny 

 growths are easily pulled off, and even a naked-eye inspection suffices to 

 prove their identity with horn of the sole or coronary surface of the foot. 



Chestnuts or callosities are met with in different forms and in varied 

 positions in the several members of the equine family. In the horse, 

 breeding exercises some considerable influence on their development, and 

 in their earliest condition in the foetus they are not at all like the horny 

 excrescences which they afterwards become, but, on the contrary, corre- 

 spond strictly to the description given of them in the other ec[uidpe, i.e. 

 bare patches of skin with a thickened epidermic covering. It is interesting 

 to note, however, that their true nature is at once ascertained by micro- 

 scopic examination. 



Among asses, chestnuts are usually found in the distinctly modified 

 form descrilied — i.e. bare patches of skin, often rather larger and more 

 circular in form than the chestnuts of the horse, — and to the naked eye 

 are covered with thickened epidermis. It may be added, however, that 

 in some specimens of chestnuts recently obtained from asses the horny 

 substances projected something like ^ of an inch above the surface of the 

 skin, in fact they were larger than some which have been lately obtained 

 from the legs of well-bred horses. 



In the following illustrations (fig. 665) are represented a chestnut from 

 the fore-leg of a cart mare and one of the ergots from the fetlock joint; 

 •also specinrens of a chestnut or bare patch from the fore-leg of an ass and 

 one from the fore-leg of a foetus of a mare at about the eighth month of 

 gestation. 



To the naked eye the chestnuts of the ass and those of the foetus of 

 the mare are identical in appearance, differing altogether from the chestnuts 

 of the adult horse; but under the microscope the three forms are seen to be 

 essentially the same in their minute structure (Plate LXIX). 



That all the cuticular appendages, hair, nail, and horn, are composed 

 of epidermic cells arranged in various ways is c[uite well known. To 

 assert, therefore, in respect to any of the structures, that they are 

 hardened, condensed, or modified cuticle is correct; at the same time the 

 statement is not sufficiently definite from the point of view of the scientific 

 enquirer. 



