500 THE HORSE'S POSITION IN THE ANIMAL WORLD 



one of any other colour, instead of the expected black one, or a foal with 

 a large white blaze when only a small spot was desii-ed, is not a freak of 

 nature, but the consequence of a sternly enforced law of heredity which 

 never dies, although it may seem to slumber now and again. 



Callosities (Chestnuts and Ergots). — Of all the peculiar markings 



which have been referred to, the most remarkable and least ex2)licable 

 are the horny growths or callosities on the inner sides of the legs and the 

 backs of the fetlock-joints of horses and their allies. It has been remarked 

 by an American naturalist " that whoever discovers the meaning of the 

 horse's callosities will become famous amono; naturalists all the world over". 

 Why so much thought and speculation has been devoted to these bodies 

 is not at all easy to understand. They are so placed inside the forearm 

 and at the lowBr and back part of the hind-leg, just below the hock and 

 behind the fetlocks, that they are quite out of the way. They are never 

 affected by or connected with any disease, and when they grow long enough 

 to be unsightly, as they sometimes do, the shoeing-smith pares them down 

 with his knife, just as he pares the sole of the foot. In size the horny 

 structures vary from that of a hazel-nut to that of an oval mass nearly 

 3 inches long and 1^ inch broad in the centre in coarse-bred horses. Their 

 shape is most commonly an elongated oval, those in the fore-legs being 

 larger and more distinctly pear-shaped than those in the liiml-legs. Some 

 of the earlier veterinary writers — Snape (1687), Bracken (1739), Gibson 

 (1751), Blaine, and also James White (1802) — do not mention the 

 chestnuts, although Gibson figures them in his plates of the limbs of the 

 horse in the fore-arm, but not in the hind-legs. 



In a later edition (1832) Blaine ascribes to the chestnuts a fanciful value 

 as adjuncts to the generative organs of the stallion, apparently disregarding 

 the fact that they are quite as well developed in the mare. Chauveau, in 

 his Comjiarative Anatomy (1873), refers to the chestnuts as little horny 

 oval or round plates found in the horse in the inner face of the forearm, 

 and at the upper extremity of the inner surface of the metatarsal bone. 

 They are composed of a mass of epithelial cells, arranged in tubes like the 

 horn of the hoof. " In solipeds," it is said, " the chestnut is the representa- 

 tive of the thumb. 



" In fine-bred horses this horny production is much less developed than 

 in coarser breeds. It is always smaller in the hind-limbs. 



" In the hind-legs and the fore-legs we also find a similar but smaller 

 horny mass growing from the skin in the tuft of hair behind the fetlock, 

 and named the ergot. Like the chestnut, it bears the same relative 

 development in fine-bred and in coarse-bred horses." This is all that 

 Chauveau has to say on the subject. 



