Plantar surface of right fore-hoof: a, a, bearing-surface of the toe; a, b, bearing-surface of the side walls or mammæ; b, c, bearing-surface of the quarters; d, buttress, or angle formed by wall and bar; e, bar; f, sole; f′, branches of the sole; g, white line; it passes between the sole and bars and ends at g′; h, horny frog; i, branches of the frog; k, heels, bulbs, or glomes of the hoof; l, median lacuna of horny frog. Between the bars and the horny frog lie the lateral lacunæ of the frog.
The hoof is divided into three principal parts, which are solidly united in the healthy foot,—namely, the wall, the sole, and the frog. That part of the hoof which is almost wholly visible when the foot is on the ground ([Fig. 30, b, c]), and which protects the foot in front and upon the sides, is known as the wall. In position, course, direction, and arrangement of its parts it simulates the different parts of the pododerm from which it is developed. It extends from the edge of the hair just above the coronary band to the ground; backward it gradually decreases in height (length), passes around the bulbs of the heels, and turns forward and inward ([Fig. 32, d, e], and [34, a, b]) to form the bars, which are finally lost in the edge of the sole near the summit of the frog. It thus forms at each heel an angle ([Fig. 31, d], and [32, d]) known as a buttress, which encloses a branch of the horny sole. Externally the wall is smooth, covered with the varnish-like periople, and presents indistinct ring-like markings ([Fig. 30]). Its inner surface, on the contrary, presents a great number of horn-leaves which are spoken of collectively as the keraphyllous tissue ([Figs. 32, g], and [35, f]). The upper or coronary border of the wall is thin and flexible, and on its inner aspect is the coronary groove, into which fits the coronary band ([Fig. 30, f]). The lower border of the wall, called the “bearing-edge” or plantar border ([Fig. 31, a]), is the one to which the horseshoe is fastened. By dividing a hoof from before to behind along its median line, outer and inner halves or walls are produced, and by dividing the entire lower circumference of the wall into five equal parts or sections, a toe, two side walls or mammæ, and two quarters will be exhibited ([Figs. 32] and [33]). In order to designate these regions of the hoof still more accurately, they are spoken of as outer and inner toes, quarters, and heels.
Fig. 32.
Wall and bars seen from below: a, toe; b, side wall, or mamma; c, quarter; d, buttress; e, bar; g, horn-leaves; h, space occupied by the frog.
The direction (slant) and length of the wall vary in one and the same hoof, as well as between fore and hind hoofs. The portion of the wall of fore-hoofs is the most slanting,—that is, forms the most acute angle with the surface of the ground,—and is also the longest. Towards the quarters the wall gradually becomes very nearly vertical; in almost all hoofs the posterior part of the quarters slants downward and inward towards the median vertical antero-posterior plane of the foot. At the same time the wall, in passing back from the toe to the heel, becomes gradually shorter in such a manner that the heights of the toe, side walls, and quarters are related to one another about as 3: 2: 1 in front hoofs and as 4: 3: 2 in hind hoofs. The outer wall is, as a rule, somewhat more slanting than the inner. Viewing a foot in profile, the toe and heel should be parallel; that is, the line from the hair to the ground at the toe should be parallel to the line from the hair to the ground at the buttress. All deviations of the wall from a straight line (outward or inward bendings) are to be regarded as faults or defects.
Fig. 33.
A hoof in profile; a, toe (one half); b, side wall; c, quarter.
Fig. 34.