--that is to say, at the toe--will be seen a small inverted V-shaped
ridge, which is a direct continuation of the same shaped prominence before
mentioned on the internal face of the wall. This Fleming has termed the
toe-stay, from a notion that it serves to maintain the position of the os
pedis. The whole of the superior face of the sole is covered with numerous
fine punctures which receive the papillae of the sensitive sole.

_The Inferior Face_ is more or less concave according to circumstances, its
deepest part being at the point of the frog. Sloping from this point to its
circumference, it becomes suddenly flat just before joining the wall. Its
horn in appearance is flaky.

[Illustration: FIG. 21.--INFERIOR ASPECT OF HOOF. _a_ The inferior face of
horny sole; _b_, inferior border of the wall; _c_, body or cushion of the
frog; _d_, median lacuna of the frog; _e_, lateral lacuna of the frog; _f_,
the bar; _g_, the quarter; _h_, the point of the frog; _i_ the heel.]

_The External Border_ or Circumference is intimately dovetailed with the
horny laminae of the wall. At its circumference the sole, if unpared, is
ordinarily as thick as the wall. This thickness is maintained for a short
distance towards its centre, after which it becomes gradually more thin.

_The Internal Border_ has the shape of an elongated V with the apex
pointing forwards. It is much thinner than the external border, and,
like it, is dovetailed into the horny laminae of the inflections of the
wall--namely, the bars. In front of the termination of the bars it is
dovetailed into the sides and point of the frog. Where unworn by contact
with the ground, the horn of the sole is shed by a process of exfoliation.

3. THE FROG.--Triangular or pyramidal in shape, the frog bears a close
resemblance to the form of the plantar cushion, upon the lower surface of
which body it is moulded. It offers for consideration two faces, two sides,
a base, and a point or summit.

[Illustration: FIG. 22.--HOOF WITH THE SENSITIVE STRUCTURES REMOVED. 1,
Superior face of horny frog; 2, the frog-stay; 3, the lateral ridges of
the frog's superior surface; 4, the horny laminae at the inflections of the
wall.]

_The Superior Face_ is an exact cast of the lower surface of the plantar
cushion. It shows in the centre, therefore, a triangular depression, with
the base of the triangle directed backwards. Posteriorly, the depression
is continued as two lateral channels divided by a me