THE CRUST OF THE HOOF. 281 



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 thinner, it is able to expand more ; its elasticity is called more 

 into play, and concussion and injury are avoided. When the expansion of 

 the quarters is prevented 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 was 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 a little 

 higher than the outer. While it is thin to yield to the shock, its increased 

 surface gives it sufficient strength. 



On account of its thinness, and the additional weight which it bears, 

 the inner heel wears away quicker than the outer ; a circumstance that 

 should never be forgotten by the smith. His object is to give a plane and 

 level bearing to the whole of the crust. To accomplish this, it will be 

 often scarcely necessary to remove any thing from the inner heel, for it 

 is already removed by the wear of the foot. If he forgets this, as he too 

 often seems to do, and takes off with his knife or his buttress an equal 

 portion all round, he leaves the inner and weaker quarter lower than the 

 outer ; he throws an uneven bearing upon k ; and produces corns and 

 sand-cracks and splints, which a little care and common 

 sense might have avoided. The crust does not vary much 

 in thickness, (see a, page 249, and b in the accompanying 

 cut,) until near the top, at the coronet, or union of the 

 horn of the foot with the skin of the pasterns where («?, 

 page 249) it rapidly gets thin. It is in a manner scooped 

 and hollowed out. It likewise changes its colour and its 

 consistence, and seems almost like a continuation of 

 the skin, but easily separable from it by maceration, or 

 disease. This thin part is called the coronary ring, x, p. 249 ; and it 

 receives within it, or covers, a thickened and bulbous prolongation of the 

 skin, called the coronary ligament (see h in the accompanying cut). This 

 requires a better name, for it has not a portion of ligamentous structure 

 in it. This prolongation of the skin is thickly supplied with blood-vessels. 

 It is almost a mesh of blood-vessels connected together by fibrous texture, 

 and many of these vessels are employed in secreting or forming the crust 

 or wall of the foot. Nature has enabled the sensible laminse of the coffin- 

 bone, c, which will be described presently, to secrete some horn, in order 

 to afford an immediate defence for itself when the crust is wounded or 

 taken away. Of this we have proof, when in sand-crack, or quittor, we 

 are compelled to remove a portion of the crust. A pellicle of horn, or 

 of firm hard substance resembling it, soon covers the wound ; but the 

 crust is principally formed from this coronary ligament. Hence it is, that 

 in sand-crack, quittor, and other diseases, in which strips of the crust 

 are destroyed, it is so long in being renewed, or growing doion. It must 

 proceed from the coronary ligament, and so gradually creep down the 

 foot with the natural growth or lengthening of the horn, of which, as in 

 the human nail, a supply is slowly given to answer to the wear and tear 

 of the part. 



Below the coronary ligament is a thin strip of horny matter, which 



has been traced from the frog, and has been supposed by some to be 



connected with the support or action of the frog, but which is evidently 



intended to add to the security of the part on which it is found, and to 



T 



