t slackens the
tendon that attaches to the under surface of the coffin bone (perforans
tendon), and therefore allows the fetlock joint to sink downward and
backward and the long pastern to assume a more nearly horizontal
position. The foot-axis, viewed from one side, is now broken forward;
that is, the long pastern is less steep than the toe, and the heels are
either too long or the toe is too short. On the other hand, raising the
toe or lowering the heels of a foot with a straight foot-axis not only
tilts the coffin bone backward and renders the toe more nearly
horizontal, but tenses the perforans tendon, which then forces the
fetlock joint forward, causing the long pastern to stand steeper. The
foot-axis, seen from one side, is now broken backward--an indication
that the toe is relatively too long or that the heels are relatively too
low.

The elastic tissues of the foot are preeminently the lateral cartilages
and the plantar cushion. The lateral cartilages are two irregularly
four-sided plates of gristle, one on either side of the foot, extending
from the wings of the coffin bone backward to the heels and upward to a
distance of an inch or more above the edge of the hair, where they may
be felt by the fingers. When sound, these plates are elastic and yield
readily to moderate finger pressure, but from various causes may undergo
ossification, in which condition they are hard and unyielding. The
plantar cushion is a wedge-shaped mass of tough, elastic, fibro-fatty
tissue filling all the space between the lateral cartilages, forming the
fleshy heels and the fleshy frog, and serving as a buffer to disperse
shock when the foot is set to the ground. It extends forward underneath
the navicular bone and perforans tendon, and protects these structures
from injurious pressure from below. Instantaneous photographs show that
at speed the horse sets the heels to the ground before other parts of
the foot--conclusive proof that the function of this tough, elastic
structure is to dissipate and render harmless violent impact of the foot
with the ground.

The horn-producing membrane, or "quick," as it is commonly termed, is
merely a downward prolongation of the "derm," or true skin, and may be
conveniently called the pododerm (foot skin). The pododerm closely
invests the coffin bone, lateral cartilages, and plantar cushion, much
as a sock covers the human foot, and is itself covered by the horny
capsule, or hoof. It differs from the