SKIN MARKINGS AND CALLOSITIES OF THE HORSE 501 



Sir William Flower combats the view wliicli has been very generally 

 accepted, that the callosities are the remains of the first digits, and his 

 argument is well worth attention. After a concise description of the skin, 

 with its inner layer of interlacing fibres, blood-vessels and nerves, and 

 glands and follicles, constituting the true skin, and the layer of flattened 

 cells which form a protecting layer of insensitive structure — the epidermis 

 or cuticle, — the author refers to the hairy coat of the horse, with its varieties 

 of fine and coarse hairs; the "chestnuts" are described as "mallenders" and 

 " sallenders", with the remark that they are treated as a disease by the 

 older veterinary writers. It is true that these words are used by ancient and 

 modern veterinary writers to indicate an eruptive aftection in the bend of 

 the knee-joints and hock-joints respectively, but the terms have never been 

 applied by them to the horny excrescences called chestnuts or callosities. 



Sir W. Flower's chief objection to the view that the chestnuts are rudi- 

 mentary digits is based on the fact that in the case of the excrescences 

 which are most constant — those on the fore-limbs — the position which they 

 occupy on the forearm, at some distance above the knee, is quite inconsistent 

 with the theory that they represent the thumbs. 



Sir W. Flower concludes "that the callosities belong to a numerous 

 class of special modifications of particular parts of the skin surface which 

 occur in many animals, the use of which is in most cases remarkably 

 obscure. Bare spots, thickened patches or callosities, and tufts of elongated 

 or modified hair, often associated with groups of peculiar glands, are very 

 common in various parts of the body, but especially in the limbs of many 

 ungulates, and to this category the chestnuts of the horse undoubtedly 

 belong." 



A somewhat similar horny excrescence has already been mentioned as 

 existing at the back of the fetlock of the horse, hidden by the tuft of long 

 hairs which give the name feetlock or fetlock to the joint. To this excres- 

 cence, owing to its growth occasionally in the form of a sjjur, the term ergot 

 is applied, and with regard to its significance Sir W. Flower suggests that it 

 corresponds to the foot- pads of animals which walk more or less on the palm 

 and the sole. As no one has previously offered any explanation of the uses 

 of the horny growths at the back of the fetlocks, it will be interesting to 

 give Sir W. Flower's description verbatim. "If we look at the palms of our 

 own hands (which, as shown before, correspond with the hinder surface of the 

 fore-limb of the horse below the so-called knee) we see slight prominences 

 just behind the root of each finger and opposite the knuckles at the back of 

 the hand, which mark the position of the joint between the metacarpal bones 

 and the first phalanges of the digits. Over these, especially when the 

 palm is subject to pressure and friction from hard manual labour, the 



