d, too, with the foot lifted, that the wall projects beyond
the level of the other structures of the plantar surface, taking upon
itself the bearing of the greatest part of the animal's weight.

The horn of the wall, viewed immediately from the front, is known as the
_Toe_, which again is distinguished as _Outside Toe_ or _Inside Toe_,
according as the horn to its inner or outer aspect is indicated. The
remainder of the external face of the wall, that running back to the heels,
is designated the _Quarters_.

In the middle region of the toe, the wall following the angle of the bones
is greatly oblique. This obliquity decreases as the quarters are reached,
until on reaching the heels the wall is nearly upright.

[Illustration: FIG. 19.--THE WALL OF THE HOOF. 1, The toe; 2, inner toe; 3,
outside toe; 4, the quarter; 5, entigeral groove; 6, horny laminae.]

For observation the wall offers two faces, two borders, and two
extremities.

_The External Face_ is convex from side to side, but straight from the
upper to the lower border. Examined closely, it is seen to be made up of
closely-arranged parallel fibres running in a straight line from the upper
to the lower border, and giving the surface of the foot a finely striated
appearance. In addition to these lines, which are really the horn tubules,
the external face is marked by a series of rings which run horizontally
from heel to heel. These are due to varying influences of food, climate,
and slight or severe disease. This will be noted again in a later page. In
a young and healthy horse the whole of the external face of the wall
is smooth and shining. This appearance is due to a thin layer of horn,
secreted independently of the wall proper, termed the periople.

[Illustration: FIG. 20.--INTERNAL FEATURES OF THE WALL, FROG, AND SOLE
(MESIAN SECTION OF HOOF). 1, Horny laminae covering internal face of wall;
2, superior border of wall; 3, junction of wall with horny sole; 4, the
cutigeral groove; 5, the horny sole; 6, the horny frog (that portion of
it known as the 'frog-stay'); 7, inverted V-shaped ridge on wall and sole
(known as the 'toe-stay'); 8, anterior face of wall; 9, inferior border of
wall.]

_The Internal Face_ of the wall, that adapted to the sensitive laminae,
is closely covered over its entire surface with white parallel leaves
_(Keraphyllae_, or horn leaves, to distinguish them from the _Podophyllae_,
or sensitive leaves). These keraphyllae dovetail intima