44 THE HORSE AND ITS RELATIVES 



broad, deep, and spongy, like the ass and the 

 kiang, are better adapted for rocky ground. This 

 is confirmed by the fact that the kiang does inhabit 

 extremely stony and rocky country. 



By far the most remarkable and interesting 

 structures in the limbs of the horse are those com- 

 monly known as "chestnuts," although sometimes 

 called " castors," but in old French veterinary works 

 termed " sallenders " (from salendre) or " mal- 

 lenders," from an idea that they were due to dis- 

 ease. In the fore-limb of the horse the chestnut 

 (pi. vi. fig. 2) or callosity, takes the form of an 

 elongated patch of bare warty skin situated some 

 little distance above the knee, or carpus ; while 

 in the hind-limb there is a smaller patch — which 

 may be absent in some cases — a short distance below 

 the hock or tarsus, and likewise on the inner surface. 

 In all the other members of the family the chest- 

 nuts are wanting in the hind-limbs ; and in the 

 ass and the zebras the front chestnut is larger, 

 smoother, and softer than in the horse. 



The question as to what structures in other 

 mammals are represented by these chestnuts has 

 been much discussed. Practically all naturalists 

 are in accord in regarding them as vestigial struc- 

 tures ; Sir W. M. Flower,^ for instance, considering 

 them to be decadent skin-glands. A qualified 

 support to this theory is accorded by Mr. F. E. 



' The Horse, p. 165. 



