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.