4. _The fleshy sole_ or _velvety tissue of the sole_ (Fig. 29, _b_) is that part of the pododerm which covers all the under surface of the foot except the plantar cushion, the bar laminæ, and the bar portion of the coronary band. It is sometimes slate-colored or studded with black spots, but is usually dark-red. It is thickly set with villi, which are especially long and strong[1] near its periphery. =The fleshy sole= covers the solar plexus, or net-work of veins, and =secretes the horny sole=. [1] In order to see the length, thickness, and abundance of the villi of the pododerm, place the foot deprived of its hoof in a clear glass jar and cover it with water, renewing the latter until it is no longer tinged with blood. 5. _The velvety tissue of the frog_ (Fig. 29, _c_) covers the lower surface of the plantar cushion, and in the region of the bulbs (_e_) passes insensibly into the perioplic band. In comparison with the fleshy sole, it has much finer and shorter villi and contains fewer blood-vessels. =It secretes the soft, horny frog.= [Illustration: FIG. 30. Side view of hoof recently removed: _a_, the perioplic horn-band; it is swollen from prolonged maceration in water; the upper border shows adhering hairs; the inner surface (perioplic groove) presents many minute openings; _a′_, the perioplic horn-band broadens in passing over the bulb or glome of the heel, and is finally lost in the horny frog; _a″_, section of wall removed. That part of hoof on the right of _b_ is called the toe; between _b_ and _c_ is the side wall or “mamma,” and between _c_ and _d_ the “quarter;” _e_, projecting horny frog; _f_, coronary groove with numerous minute openings; _g_, keraphyllous layer of the wall (horny leaves).] (_c_) =The horn capsule= or =hoof= (Fig. 30) is the entire mass made up of the horn-cells secreted from the whole surface of the pododerm, and next to the shoe is the organ with which the horseshoer has most to do. The horn capsule or hoof is nothing more than a very thick epidermis that protects the horse’s foot, just as a well-fitting shoe protects the human foot. The hoof of a sound foot is so firmly united with the underlying pododerm that only an extraordinary force can separate them. In its normal condition the hoof exactly fits the soft structures within it; hence it is evident that local or general contraction of the hoof must produce pressure on the blood-vessels and nerve-endings of the pododerm, disturb the circulation of the blood and the nutrition of the foot, and cause pain. [Illustration: FIG. 31.