586 DISEASES OF THE HORSE. 
parallel to one another, running downward and forward from the 
lower edge of the coronary band to the margin of the fleshy sole. 
They produce the soft, light-colored horny leaves which form the 
deepest layer of the wall, and serve as a strong bond of union between 
the middle layer of the wall and the fleshy leaves with which they 
dovetail. (+) The fleshy sole, which covers the entire under surface 
of the foot, excepting the fleshy frog and bars. The horny sole is 
produced by the fleshy sole. (5) The fleshy frog, which covers the 
under surface of the plantar cushion and produces the horny frog. 
The-horny box or hoof consists of wall and bars, sole and frog. 
The wall is all that part of the hoof which is visible when the foot is 
on the ground (see fig. 8). As already stated, it consists of three lay- 
ers-——the periople, the middle layer, and the leafy layer. 
The bars (see fig. le) 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 les 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 
part, 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, un- 
even 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 
