HOESESHOEING. 585 



yield readily to moderate finger pressure, but from various causes 

 may undergo ossifica-tion, in which condition they are hard and un- 

 yielding. The plantar cushion is a wedge-shaped mass of tough, 

 clastic, 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 fimction 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 pododerni (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 homy 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 pododem, 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 vamishlike 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, 



