The inferior border of the wall ([Fig. 100]) is, in the case of unshod horses, always in wear when in contact with the ground. It is intimately united to the circumference of the sole (see [further on]).
Fig. 100.—Inferior Surface of a Fore-hoof of the Horse: Left Side.
1, Internal border of the wall (toe); 2, wall; 3, quarter; 4, heel; 5, bar; 6, sole; 7, frog; 8, median cavity; 9, prominence of the frog; 10, lateral cavity.
The superior border is hollowed on its internal surface by a groove, the cutigerous cavity or basil, which lodges the cushion (see [Fig. 95]). We have described this latter [above], in connection with the flesh of the foot.
The substance of the wall presents a fibrous appearance which is pretty strongly pronounced. The constituent fibres from which this appearance results are directed from the superior border towards the inferior in parallel and regular lines.
The sole is a horny plate which occupies the inferior surface of the hoof ([Fig. 100]). It is situated between the inferior border of the wall and the bars; and, on account of the oblique direction of these latter, it presents a strongly-marked groove of a V-form, with the opening directed backwards. In this depression is lodged the frog.
The inferior surface is concave, and thus forms a sort of vault, more or less deep, according to the individual. The sole has a scaly, laminated aspect.
We have seen ([Fig. 93], and [p. 249]) that on the inferior surface of the claws of carnivora is found a small interval which is filled by a plate of a more friable horny substance, to which has been given the name of the plantar nail. It seems to us that there is an interesting relationship between the said plantar nail and the sole which we have just been studying.