588 DISEASES OF THE HORSE. 
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. Ofcourse, when 
the lateral cartilages are ossified, not only is no expansion of the 
quarters possible, but frog pressure often leads to painful compres- 
sion of the plantar cushion and to increase of lameness. Frog pres- 
sure is therefore contraindicated in lameness due to sidebones (ossi- 
fied 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 some- 
times 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 contrac- 
tion 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 reason- 
able work and his hoofs proper care. 
GROWTH OF THE HOOF. 
All parts of the hoof grow downward and forward with equal 
rapidity, the rate of growth being largely dependent upon the 
amount of blood supplied to the pododerm, or “ quick.” Abundant 
and regular exercise, good grooming, moistness and suppleness of the 
hoof, going barefoot, plenty of good feed, and at proper intervals 
removing the overgrowth of hoof and regulating the bearing surface, 
by increasing the volume and improving the quality of the blood 
