5. The Crooked Hoof.
A crooked hoof ([Fig. 212]) is one whose walls (viewed from in front or behind) do not pass in a straight, natural direction from the coronet to the ground, but are bent in such a manner that the bearing-surface of the wall in relation to the foot-axis lies either too far out or in.
It may occur on any foot, but is seldom strongly marked.
Causes.—The causes are either long-continued leaving of one-half of the wall too high, or the use of shoes shaped for normal feet upon hoofs of the base-wide position.
Fig. 212.
A crooked right fore-hoof of the base-wide position: a, convex wall, too high; b, concave wall, too low; c d shows how much of the outer wall must be removed with the hoof-knife; f, superfluous horn to be removed gradually with the rasp; c e and g h indicate the position of the shoe with relation to the hoof.
The principal part of the treatment is the proper dressing of the hoof. The wall which is bent out at the middle and drawn in at the plantar border is, as a rule, too high and too near the centre of the foot (too narrow); the opposite wall, on the contrary, is too low and too far from the centre of the foot (too wide). This explains the manner in which the hoof should be cut down and rasped. The shoe must be laid out as far as possible towards the side which is too high and narrow. A straight edge placed against the high wall touches it only at its middle. The distance of this line from the lower edge of the wall shows us how far the surface of support—namely, the shoe—should be set out beyond the horn. If the straight edge be placed against the opposite wall, it will touch only at the coronet and at the plantar border, showing that the wall is concave. The distance of the middle of this wall from the straight edge shows us how much too wide this half of the wall is at its plantar border, and how much of the outer surface of the wall at its plantar border should be removed with the rasp. The restoration of a crooked hoof to its normal form requires several shoeings.
6. Ossification of the Lateral Cartilage
(Side-Bone).
The ossification of a lateral cartilage ([Fig. 213]) consists in a change of the cartilage into bone. Heavy horses are more frequently affected than lighter ones. It most often involves the outer cartilages of the forefeet, seldom both cartilages. Side-bones always interfere with the physiological movements of the foot, and may, indeed, entirely suppress them.