_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=. [Illustration: FIG. 33. A hoof in profile; _a_, toe (one half); _b_, side wall; _c_, quarter.] [Illustration: FIG. 34. Vertical section through the middle of a hoof, with horny frog removed, to show the position of the bar: _a_, _b_, marks the line at which the wall bends forward and inward towards the median line of the foot to become the bar. Bar runs forward and passes imperceptibly into the sole _c_; _a_, _a′_, the light shading shows the part of the bar that was in contact with the horny frog.] The _thickness of the wall_ is also variable. In front hoofs the wall is thickest at the toe, and becomes gradually thinner towards the quarters, while in hind hoofs, there is very little difference in the thickness of the wall of the toe, sides, and quarters. _The more slanting half of the hoof is always the thicker_; thus, for example, the outer wall of a base-wide foot is always longer and more oblique than the inner wall, and is also thicker. According to Mayer, the thickness of the wall at the toe varies from three- to five-eighths of an inch, and at the quarters from two to three-eighths of an inch. These measurements are dependent upon the size and breeding of the horse. [Illustration: FIG. 35.