THE CRUST OR WALL OF THE HOOF. 373 



and a half in depth (see cut, p. 374), shallower at the sides, which are denomi- 

 nated the quarters, and of least extent behind, where it is seldom more than an 

 inch and a half in height, and is termed the heel. The crust in the healthy 

 foot presents a flat and narrow surface to the ground, ascending obliquely back- 

 wards, and possessing different degrees of obliquity in different horses. In a 

 sound hoof the proper degree of obliquity is calculated at forty-five degrees, or 

 the fourth part of a semicircle, at the front of the foot. When the obliquity is 

 greater than this, it indicates undue flatness of the sole, and the crust is said 

 to have " fallen in." If the obliquity is very much increased the sole projects, 

 and is said to be pumiced or convex. 



If the foot is more upright, or forms a greater angle than forty-five degrees, 

 it indicates much contraction, and a sole too concave ; and this difference of obli- 

 quity is often so great, that the convexity or concavity of the sole may be 

 affirmed without the trouble of raising the foot for the purpose of examination. 



It is of some importance to observe whether the depth of the crust appears 

 rapidly or slowly to decrease from the front to the heel. If the decrease is little, 

 and even at the heel the crust is high and deep, this indicates a foot liable to 

 contraction, sandcrack, thrush, and inflammation. The pasterns are upright, 

 the paces of that horse are not pleasant. On the other hand, if the crust 

 rapidly diminishes in depth, and the heels are low, this is accompanied by too 

 great slanting of the pastern, and disposition to sprain in the back sinew. The 

 foot, generally, is liable to be weak and flat, and bruised, and there is more 

 tendency to the frequent, but obscure lameness, of which there will presently 

 be occasion to treat — the navicular-joint disease. 



The crust is composed of numerous horny fibres, connected together by an 

 elastic membranous substance, and extending from the coronet to the base of 

 the hoof. It differs materially in its texture, its elasticity, its growth, and its 

 occasional fragility, according to the state in which it is kept, and the circum- 

 stances that are acting upon it. 



The exterior wall of the hoof should be smooth and level. Protuberances or 

 rings round the crust indicate that the horse has had inflammation in the feet, 

 and that to such a degree, as to produce an unequal growth of horn, and pro- 

 bably to leave some injurious consequences in the internal part of the foot. If 

 there is a depression or hollow in the front of the foot, it betrays a sinking of 

 the coffin- bone, and a flat or pumiced sole. If there is a hollow at the quar- 

 ters, it is the worst symptom of bad contraction. 



The thickness of the crust, in the front of the foot, is rather more than half an 

 inch ; it becomes gradually thinner towards the quarters and heels, but this 

 often varies to a considerable extent. In some hoofs, it is not more than half 

 the above thickness. If however there is not, in the majority of horses, more 

 than half an inch for nail-hold at the toe, and not so much at the quarters, it will 

 not appear surprising that these horses are occasionally wounded in shoeing, and 

 especially as some of them are very unmanageable while undergoing this process. 



While the crust becomes thinner towards both quarters, it is more so at the 

 inner quarter than at the outer, because more weight is thrown upon it than 

 upon the outer. It is more under the horse. It is under the inner splint-bone, 

 on which so much more of the weight rests than on the outer ; and, being thin- 

 ner, it is able to expand more. Its elasticity is called more into play, and con- 

 cussion and injury are avoided. When the expansion of the quarters is pre- 

 vented by their being nailed to an unbending shoe, the inner quarter suffers 

 most. Corns are oftenest found there ; contraction begins there ; sand-crack is 

 seated there. Nature meant that this should be the most yielding part, in order 

 to obviate concussion, because on it the weight is principally thrown, and 

 therefore when its power of yielding is taken away it must be the first to suffer. 



A careful observer will likewise perceive that the inner quarter is higher 



