The horn-tubes of the wall, sole, and frog always run downward and forward parallel to the direction of the wall at the toe,—that is, in a direction parallel with the inclination of the hoof as a whole. Although the wall, sole, and frog differ from one another considerably with respect to the size and number of the horn-tubes, the quality of the intertubular horn, and the thickness and strength of the horn-cells, these differences are only of subordinate interest or importance to the horseshoer; but he who desires to learn more of this matter is referred to the work of Leisering & Hartmann, “Der Fuss des Pferdes in Rücksicht auf Bau, Verrichtungen und Hufbeschlag,” eighth edition, Dresden, 1893. This book also treats of the variations in the quality of hoofs, which is very important for the practical horseshoer to know. It, furthermore, considers the solidity and strength of the horn of the different parts of the hoof.
With respect to solidity, two kinds of horn are distinguished,—namely, hard and soft horn. The periople, the white line, and the frog are soft horn structures; the middle layer of the wall and the sole are hard or solid horn. The wall, however, is somewhat harder and more tenacious than the sole, for the latter passes off in more or less large flakes (exfoliates) or crumbles away on its lower surface, at least in shod feet, while no such spontaneous shortening occurs in the wall.
Fig. 42.
Vertical section through middle of a forefoot, the skin and pododerm being in red. (In the figure the direction of both long and short pasterns, B and D, is too nearly vertical—too steep). A, metacarpal bone (cannon); B, os suffraginis (long pastern); C, inner sesamoid bone (to render it visible a portion of the intersesamoid ligament was removed); D, os coronæ (short pastern); E, os pedis (foot-bone); F, navicular bone; a, extensor tendon; b, suspensory ligament of the fetlock; b′, superficial inferior sesamoid ligament; c, perforatus tendon or flexor of the os coronæ; c′, ring passing forward from this tendon and encircling the perforans tendon; d, perforans tendon; e, capsular ligament of fetlock-joint; f, capsular ligament of coronary joint; g, g′, capsular ligament of pedal joint; h, synovial sheath of the perforans tendon; i, plantar cushion and fleshy frog; i′, bulbs or glomes of plantar cushion; i″, indicates the lowest point reached by the plantar cushion, which in the figure is hidden below by the frog-stay of the horny frog; k, coronary band (red); l, podophyllous tissue (red); m, velvety tissue of the sole (red); n, velvety tissue of fleshy frog (red); o, wall; p, sole; q, frog; q′, the inner half of the frog-stay which reposes in the median lacuna of the fleshy frog; s, hair-skin (red).
Soft horn differs from hard horn in that its horn-cells never become hard and horn-like. It is very elastic, absorbs water quickly, and as readily dries out and becomes very hard and brittle and easily fissured and chapped. With respect to quality, we distinguish good and bad horn; the former is fine and tenacious (tough), the latter coarse and either soft and crumbling or hard and brittle. If not dried out, all horn is elastic, though soft horn is more elastic than hard. All horn is a poor conductor of heat.
The relative positions of the various parts of the foot are shown in [Fig. 42].
[Fig. 43] represents the exterior of a well-formed foot.
Fig. 43.
