The Art of Horse-Shoeing: A Manual for Farriers

by William Hunting

The Secreting Structures.

If we macerate a dead foot in water for a week or two, the hoof may be removed entire without injuring the tissues within. In this way the sensitive foot or "quick" is exposed to view, and presents an exact counterpart of the inside of the hoof. The sensitive foot consists of a layer of fibrous tissue stretched over the bones and other structures which form the centre of the foot. It is plentifully supplied with blood-vessels and nerves necessary to its double function as the source of horn growth and as the tactile organ of the foot. Horn is, of course, not sensitive, although the slightest touch on a horse's hoof is recognised by the animal, and this feeling is due to the impression made upon the sensitive foot. In the living horse any injury to the "quick" causes the greatest pain, and although this sensitiveness is a serious disadvantage in disease it is a most valuable provision in health, enabling the horse, even through a thick layer of horn, to recognise the quality of the surface upon which he may be standing or moving. It is this sense of touch—this tactile function—which demands that the sensitive foot should be so bountifully supplied with nerves.

Every farrier knows how profusely blood flows from any wound of the "quick"—evidence that the part is well supplied with blood-vessels. This full supply of blood is not merely for the ordinary waste and repair which takes place in every tissue; it is to meet a special demand—to supply the material for the production of horn. The sensitive foot is the secreting structure of the hoof, and the source of the constant growth and reproduction of horn. It corresponds with great exactness to the inside of the hoof, and as we have described the hoof in sections it may be convenient to follow that course with this structure, and to describe the sensitive frog, the sensitive sole, and the sensitive laminæ. We shall begin with the last.

The Sensitive Laminæ. Corresponding to the horny leaves on the inside of the wall, the sensitive foot presents an arrangement of minute parallel folds which are called the sensitive laminæ. ([Fig. 11]). Between these the horny laminæ rest, so that there is a kind of interleaved attachment which affords the very firmest connection between the wall and the sensitive foot. If the laminæ be laid bare in a living horse by removal of the wall, it is found that they have the power to secrete a kind of horn, not a hard fibrous horn like that of the wall, but a softer variety. This function is not very active in health or we should find that the lower edge of the wall was thicker than the upper; but it exists, and is very evident in some cases of disease.

Fig. 11.—Foot with hoof removed showing at the upper part the Coronary band, and below the Sensitive Laminæ.

In laminitis the wall at the toe is often pushed forward out of position by a horny mass formed by the laminæ, and so we have the deformity of an excessive length of toe. In some cases of long continued sandcrack the irritation of the laminæ causes excessive secretion, and a horn tumour results. The sensitive laminæ, then, fulfil two functions; they offer a firm connecting medium for the wall, and they secrete horn. By the cruel experiment of removing the horny sole and frog of a living horse and then forcing him to stand on the maimed foot on a level surface, it has been shown that the laminæ are capable of alone supporting the weight of the animal. It has been argued from this that the laminæ always support the weight, and that the horse's foot may be described as being slung by the connecting laminæ. This is not true. The frog and sole help to support weight, and the hoof acts as one continuous whole, each part taking its direct and proportionate share of the weight placed upon the foot. The sensitive laminæ are not elastic, they are unyielding, and, therefore, allow no downward yielding which would impose excessive pressure on the sole.

The Coronary Band. (See [Fig. 11]). The sensitive laminæ do not cover the whole of the upright portions of the sensitive foot. There is between their upper extremity and the line which separates the skin from the sensitive foot, a convex band which runs round the upper border of the foot, and is turned downwards and inwards at the heels. This is called the coronary band, and corresponds to the groove which we noticed on the inner side of the upper border of the wall. On its surface are innumerable small projections or papillæ which, in the living animal, fit into the openings on the groove of the wall. From each of these papillæ grows a horn fibre, and from the surface between them is formed a softer horny matter—the two products forming together the substance of the wall. The coronary band is, then, an important structure, being the source from whence the wall is produced. Upon the healthy condition of this band depends the soundness of the wall, and any interference with its integrity must lead to defects or deformities in the wall.

The Sensitive Sole ([Fig. 12]) is that portion of the "quick" to which the sole is attached. Its surface is covered with papillæ, like those on the coronary band but much smaller, giving an appearance somewhat like the pile of velvet. From these the horn fibres of the sole are formed, and a firm means of connection is afforded for the floor of the hoof.

Fig. 12.—Under Surface of Foot showing Sensitive Frog and Sole.

The Sensitive Frog in structure resembles the sensitive sole, but its papillæ are very much smaller, and the surface therefore is smoother. The irregular prominent surface of the frog, with its cleft and the space at each side of it, is exactly reproduced on the sensitive frog, as might be expected, for the one is moulded on the other. There is one difference between the sensitive frog and the other portions of the sensitive foot which I may here mention. It is not attached to the bones of the foot except by its point, but is situated behind the bone, and has as a basis a mass of soft tissue which forms an important cushion or pad, to be referred to later.