The Art of Horse-Shoeing: A Manual for Farriers

by William Hunting

Dissection of the Foot.

So far we have only described the outer covering of the foot and the structure from which it grows and by which it is connected to the parts within. A little deeper examination is necessary to understand the mechanism of the whole organ.

Fig. 11.—Section of Foot.

If we divide into two lateral halves a foot cut off at the fetlock joint, we have a section which should show the whole of the deeper structures. In the centre we see the three lower bones of the limb—the pastern, coronet, and pedal. ([Fig. 11]). On the front surface of these bones we notice a tendon or sinew which comes from above the knee and is fixed to the upper part of the pedal bone. At the back of the bones two very large tendons run down and are fixed on the last two bones. These tendons are the structures through which the movements of the foot are made. They have in themselves no power of contraction but they are connected above the knee, and in the hind leg above the hock, to powerful muscles which possess the power of contraction. When these muscles contract the tendons are drawn up towards knee or hock, and so move the foot backwards or forwards.

To permit movement of one bone upon another the ends of the bones are suitably shaped, and covered with a layer of gristle or cartilage. To limit the movement and to hold the bones together the ends of each bone are surrounded by ligaments, and thus we have joints formed.

Fig. 12.—Side view of Pedal Bone.

The pastern bone is altogether above the level of the foot, the coronet bone is partially within the hoof, and the joint between it and the pedal bone is quite within. The pedal, often called the coffin bone, ([Fig. 12]) is entirely within the hoof and fills the front part of the horny envelope completely. It is a peculiarly shaped bone, being continued backwards by two projections which follow the course of the wall to a little beyond the quarters of the foot. ([Fig. 13]). From this point to the extremity of the heels the wall is not supported by bone but by strong plates of gristle, which are called the lateral cartilages.

Fig. 13.—Under surface of Pedal Bone.

Fig. 14.—The Lateral Cartilage.

The Lateral Cartilages are situated one on either side of the foot partly within and partly without the hoof. They form the basis upon which the back part of the wall is moulded, and being elastic permit a certain amount of movement in the posterior parts of the foot. ([Fig. 14]). If the coffin bone filled the whole hoof, the foot would be too rigid. With bone at the front portion we have a firm surface for attachment, and with cartilage at the back we have an equally firm attachment, but one that will yield to blows or pressure and thus better protect the internal parts. These cartilages extend above the level of the hoof, and may be easily felt in the living horse at the back part of the coronet. ([Fig. 15]). Between them, and behind the body of the coffin bone is a large space which is filled up by a mass of soft tissue to which various names have been given, such as plantar-cushion, frog-pad, etc.

Fig. 15.—Coffin Bone and Lateral Cartilages seen from above.

The Frog-Pad is the name under which we shall notice it. It forms the bulbs of the heels and is the soft basis upon which is spread the sensitive frog. It extends from side to side of the foot between the two lateral cartilages, and fills up all the space within the hoof behind the body of the coffin bone. The structure of this pad may be described roughly as consisting of a network of fibrous bands, having the interstices filled up with elastic tissue. ([Fig. 16]). Down the centre of the pad runs a vertical partition of inelastic fibres; from this strong fibrous bands pass to each cartilage, and so the whole of the back part of the foot is tied together. The heels and quarters may be pressed together to some extent, but they are prevented from being forced asunder by the fibrous connections of the frog-pad. During progression the downward movement of the coronet bone is provided for by this soft pad, and so is an upward movement of the frog when excessive bearing is placed upon it.

Fig. 16.—Section of foot showing the frog-pad and at each side the cut edge of the lateral cartilage.

The frog-pad serves other purposes besides those we have just referred to. It is essentially a cushion or pad to prevent jar or concussion, but it also plays an important part in the action of the foot, as we shall see later on.

The Coronary Cushion or Pad is another mass of tissue of a similar nature to the frog-pad. It is situated just above the upper border of the hoof, and gives to the coronet its prominence and elasticity. At this part of the foot there is an enormous number of small blood-vessels and nerves, and the coronary pad forms not only a base for these to rest on but a necessary protection for them. If instead of this elastic bed they were placed merely between the skin and the hard bones and tendons of the part, they would be injured by every slight bruise. Even with this cushion, we have in practice very many serious conditions following bruise of the coronet.

Blood-vessels of the Foot. It is not necessary to describe the course of these vessels. All we need remember is that every part of the tissues within the hoof is very plentifully supplied with blood, and that the flow of blood is most rapid when the foot is in action. In a dead foot from which the blood has escaped a certain amount of movement of the bones within the hoof is easily effected. In the living foot when every vessel is filled with blood no such movement takes place. The blood in the vessels forms a sort of waterbed which assists in preventing concussion and which distributes evenly over the whole organ the pressure applied when weight is thrown on the foot. In studying the dead foot with a view to understand its mechanism we must not lose sight of the difference which results from having in one case the blood-vessels empty, and in the other—the living animal—the blood-vessels full.