ANATOMY AND PHYSIOLOGY OF THE HORSE*S FOOT. 151 
length and thickness. Its consistence, as a rale, increases in 
proportion as its fibres are distant from the living tissues con- 
tained in its cavity. Therefore it is that the thin upper 
border, being in close proximity to the coronary cushion, is 
soft and flexible ; while the lower border, being far removed 
from the vital textures, is very hard and resisting ; and that 
while the external surface is close and rigid in substance, 
the internal, including the horny laminae, is spongy and easily 
cut. 
From this it will be readily understood that the thicker 
and the further removed from the vascular structures the wall 
is, the more firm and tenacious we may expect it to be. And 
this is in reality the case, as we may prove by sections made 
at the lower margin of the toe, points of the heels, and even 
on the whole lower border of the wall and bars in an over- 
grown foot. 
The colour of the wall is intimately allied to the tint of the 
skin above it, being white, grey, or black, when the cuticle 
has either of these colours ; even if the black skin be flecked 
with white, or the white with black, the outer fibres of the 
wall are the same to an exactly corresponding extent. This 
colour does not permeate the whole thickness of the wall, for 
the laminae are, as a rule, apparently always white, and the 
layers of fibres adjoining them are also white, or more or less 
grey, or streaked with white, when the outer layers are alto- 
gether black ; these variations depend, it would appear, upon 
the colour of the coronary cushion and the zone. 
We sometimes see horses with entirely white legs, having 
the hoofs, nevertheless, streaked with grey or black patches. 
I have noticed this more particularly in roan-coloured 
horses. 
We will consider the minute structure of the wall when we 
have examined the anatomy of the sole and frog, and con- 
sidered the hoof as a whole. 
The sole . — The “ sole” ( hornsohle of the Germans), in 
concert with the bars and the frog, completes the plantar 
surface of the hoof, or, in other words, forms its floor. It is 
contained within the lower circumference of the wall, which 
fixes its contour. It is irregularly crescentic, its posterior 
portion being deeply indented by a somewhat triangular- 
space, in which is lodged the frog ; it appears as a thick 
plate of horn, unevenly convex on it upper, and concave on 
its lower surface. 
Its upper face is exactly adapted to the sole of the os pedis, 
being convex towards its middle and depressed at its circum- 
ference. Its highest point is at the bottom or apex of the 
