sensitive and horny leaves to the wall. The coffin bone and navicular
bone sink a little and rotate backward. At the same time the short
pastern sinks backward and downward between the lateral cartilages and
presses the perforans tendon upon the plantar cushion. This cushion
being compressed from above and being unable to expand downward by
reason of the resistance of the ground acting against the horny frog,
acts like any other elastic mass and expands toward the sides, pushing
before it the yielding lateral cartilages and the wall of the quarters.
This expansion of the heels is assisted and increased by the
simultaneous flattening and lateral expansion of the resilient horny
frog, which crowds the bars apart. Of course, when the lateral
cartilages are ossified, not only is no expansion of the quarters
possible, but frog pressure often leads to painful compression of the
plantar cushion and to increase of lameness. Frog pressure is therefore
contraindicated in lameness due to sidebones (ossified cartilages).
Under the descent of the coffin bone the horny sole sinks a little; that
is, the arch of the sole around the point of the frog and the wings of
the sole become somewhat flattened. All these changes of form are most
marked in sound unshod hoofs, because in them ground pressure on the
frog and sole is pronounced; they are more marked in fore hoofs than in
hind hoofs.

The movement of the different structures within the foot and the changes
of form that occur at every step are indispensable to the health of the
hoof, so that these elastic tissues must be kept active by regular
exercise, with protection against drying out of the hoof. Long-continued
rest in the stable, drying out of the hoof, and shoeing decrease or
alter the physiological movements of the hoof and sometimes lead to foot
diseases. Since these movements are complete and spontaneous only in
unshod feet, shoeing must be regarded as an evil, albeit a necessary
one, and indispensable if we wish to keep horses continuously
serviceable on hard, artificial roads. However, if in shoeing we bear in
mind the structure and functions of the hoof and apply a shoe whose
branches have a wide and level bearing surface, so as to interfere as
little as may be with the expansion and contraction of the quarters, in
so far as this is not hindered by the nails, we need not be apprehensive
of trouble, provided the horse has reasonable work and his hoofs proper
care.

GROW