ich is visible when the foot is on the
ground (see fig. 8). As already stated, it consists of three layers--the
periople, the middle layer, and the leafy layer.

The bars (see fig. 1c) are forward prolongations of the wall, and are
gradually lost near the point of the frog. The angle between the wall
and a bar is called the "buttress." Each bar lies against the horny frog
on one side and incloses a wing of the sole on the other, so that the
least expansion or contraction of the horny frog separates or
approximates the bars, and through them the lateral cartilages and the
walls of the quarters. The lower border of the wall is called the
"bearing edge," and is the surface against which the shoe bears. By
dividing the entire lower circumference of the wall into five equal
parts, a toe, two side walls, and two quarters will be exhibited. The
"heels," strictly speaking, are the two rounded soft prominences of the
plantar cushion, lying one above each quarter. The outer wall is usually
more slanting than the inner, and _the more slanting half of a hoof is
always the thicker_. In front hoofs the wall is thickest at the toe and
gradually thins out toward the quarters, where in some horses it may not
exceed one-fourth of an inch. In hind hoofs there is much less
difference in thickness between the toe, side walls, and quarters. The
horny sole, from which the flakes of old horn have been removed, is
concave and about as thick as the wall at the toe. It is rough, uneven
and often covered by flakes of dead horn in process of being loosened
and cast off. Behind the sole presents an opening into which are
received the bars and horny frog. This opening divides the sole into a
body and two wings.

The periphery of the sole unites with the lower border of the wall and
bars through the medium of the white line, which is the cross section of
the leafy horn layer of the wall and of short plugs of horn which grow
down from the lower ends of the fleshy leaves. This white line is of
much importance to the shoer, since its distance from the outer border
of the hoof is the thickness of the wall, and in the white line all
nails should be driven.

The frog, secreted by the pododerm covering the plantar cushion or fatty
frog, and presenting almost the same form as the latter, lies as a soft
and very elastic wedge between the bars and between the edges of the
sole just in front of the bars. A broad and shallow depression in its
center divides it