The buttress (angle formed by the union of wall and bar) requires special attention. In healthy unshod hoofs the bars run backward and outward in a straight line from the anterior third of the frog. In shod hoofs, however, it happens that the buttresses gradually lengthen, curl inward, and press upon the branches of the frog, causing the latter to shrink. In such cases the indication is to remove these prolongations of horn from the buttresses so as to restore to the bars their normal direction.
The sharp edge of the plantar border of the wall should be broken away with a rasp until the relative thickness of the wall equals its absolute thickness. ([Fig. 97]). However, in healthy hoofs, that is, in those whose walls are straight from the coronet to the ground, the outer surface of the wall should never be rasped. The only exceptions to this rule are those cases in which there is an outward bending of the lower edge of the wall, most frequent on the inner side wall and quarter.
Fig. 97.
Longitudinal (vertical) section of the wall at the toe: a c is the absolute, and a b the relative thickness of the wall. With a as the centre, and the line a c as a radius, a circle is drawn; the corner of horn in front of this circle and indicated by dotted lines is to be removed with the rasp.
With respect to the inclination of the ground-surface of the hoof to the direction of the foot-axis, as viewed from in front, the following facts are established:
In the regular standing position of the limbs (seen from in front) the plantar surface of a hoof is at right angles to the foot axis, and the outer and inner walls are of equal heights.
In the base-wide position of the limbs the plantar hoof-surface is more or less inclined to the foot-axis, usually to a very small degree, and the outer wall is somewhat higher (longer) and more slanting than the inner.
In the base-narrow position of the limbs the plantar hoof-surface is more or less inclined to the direction of the foot axis, usually quite considerably, and the inner wall is somewhat higher than the outer.
The foot is observed from the side in order to determine the proper relation of the length of the toe to the height of the quarters.