irregularly crescentic, its posterior portion, that between the horns of
the crescent, being deeply indented in a V-shaped manner to receive the
frog. Its upper surface is convex, its lower concave. It may be recognised
as possessing two faces and two borders.

_The Superior or Internal Face_ is adapted to the sole of the os pedis. Its
highest point, therefore, is at the point of its V-shaped indentation. From
this point it slopes in every direction downwards and outwards until near
the circumference. Here it curves up to form a kind of a groove in which
is lodged the inferior edge of the os pedis. In the centre of its anterior
portion--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 papillæ 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 laminæ of the wall. At its circumference the sole, if unpared, is
ordinarily as thick as the wall. This thickness is maintained for a short