170 THE STKUCTUEE OF THE HOKSE 



covering, greatly shrunken in dimensions and concealed 

 among the long hair around, and now apparently useless 

 in the economy of the animal, remains as an eloquent 

 testimony to the unity of the horse's structure with that 

 of other mammals, and its probable descent from a more 

 generalised form, for the well-being of whose life this 

 structure was necessary. 



The ergot of the horse, placed in the middle line of 

 the foot, must not be confounded, as has sometimes been 

 done, with the parts bearing in French works the same 

 name in the ox, and which are placed one on each side in 

 a somewhat similar part of the foot. These are clearly 

 shown by the structure of their horny covering, by the 

 presence of bony elements within, and by comparison 

 with their more developed condition in other ruminants, 

 to be really the hoofs of the second and fifth digits, 

 reduced to a very rudimentary condition. 



Besides the ergot there are other patches, more 

 obvious to ordinary observation, in which the skin is 

 peculiarly modified from its usual structure. These are 

 the so-called c chestnuts,' or i mallenders ' and c sallen- 

 ders ' as they are designated in old books. They are 

 patches on which no hair grows, but in which the 

 papillae of the derm or true skin are much enlarged and 

 covered with an abundant and thickened epidermis, 

 which becomes dry and horny and sometimes accumu- 

 lates in considerable quantity on the surface, occa- 



