HORSESHOFING. 585 
yield readily to moderate finger pressure, but from various causes 
may undergo ossification, in which condition they are hard and un- 
yielding. The plantar cushion is a wedge-shaped mass of tough, 
elastic, fibro-fatty tissue filling all the space between the lateral car- 
tilages, 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 ex- 
tends 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 fcot, and is itself 
-eovered by the horny capsule, or hoof. It differs from the external 
skin, or hair skin, in having no sweat or oil glands, but, like it, is 
richly supplied with blood vessels and sensitive nerves. And, just 
as the derm of the hair skin produces upon its outer surface layer 
upon layer of horny cells (epiderm), which protect the sensitive and 
vascular derm, so, likewise, in the foot the pododerm produces over 
its entire surface soft cells, which, pushed away by more recent cells 
forming beneath, lose moisture by evaporation and are rapidly trans- 
formed into the corneous material which we call the hoof. It is 
proper to regard the hoof as a greatly thickened epiderm having 
many of the qualities possessed by such epidermal structures as hair, 
feathers, nails, claws, etc. 
The functions of the pododerm are to produce the hoof and to unite 
it firmly to the foot. 
There are five parts of the pododern, easily distinguishable when 
the hoof has been removed, namely: (1) The perioplic band, a nar- 
row ridge from one-sixteenth to one-eighth of an inch wide, running 
along the edge of the hair from one heel around the toe to the other. 
This band produces the perioplic horn, the thin varnishlike layer of 
glistening horn, which forms the surface of the wall or “crust,” and 
“whose purpose seems to be to retard evaporation of moisture from 
the wall. (2) The coronary band, a prominent fleshy cornice encir- 
cling the foot just below and parallel to the perioplic band. At the 
heels it is reflected forward along the sides of the fleshy frog, to be- 
come lost near the apex of this latter structure. The coronet pro- 
duces the middle layer of the wall, and the reflexed portions produce 
the “bars,” which are, therefore, to be regarded merely as a turning 
forward of the wall. (3) The fleshy leaves, 500 to 600 in number, 
