48 THE HORSE AND ITS RELATIVES 



Having now stated some of the objections 

 against identifying the horse's chestnuts with the 

 foot-pads of polydactyle mammals, it remains to 

 consider whether they can be identified with any 

 other structures. Now a certain numtfer of repre- 

 sentatives of the deer family notably the reindeer, 

 the white-tailed deer, the mule-deer, and, in a 

 rudimentary condition, the elk are furnished on 

 the inner side of the hock with a glandular tuft 

 corresponding very closely in situation with the 

 hind -chestnut of the horse. In fact, the only 

 difference in the position of the two structures is 

 that the tarsal tuft of the deer is placed rather 

 lower on the hock. From the fact of its occurrence 

 in deer so widely separated from one another as 

 are the species mentioned, it seems evident that 

 the tarsal gland (which is doubtless a scent-organ) 

 is a very ancient structure, which was present in 

 all the ancestors of the group, but has been lost, 

 probably from disuse, in the great majority of Old 

 World deer. 



Judging from their position, there would seem 

 to be a certain probability that the hind-chestnuts 

 of the horse and the tarsal glands of the deer are 

 corresponding structures. 



With regard to the correspondence of the fore- 

 chestnut of the horse, it may be mentioned that 

 many gazelles have tufts of hair (" knee-brushes") 

 at the knee (carpus), which are certainly glandular 



