ANATOMT OF THE FOOT. 567 



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 foot, and is itself covered 

 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 sup- 

 plied 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 transformed 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 pododerm, easily distinguishable when 

 the hoof has been removed, namely : (1) The perioplic hand, a narrow 

 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 perioplio horn, the thin varnishlike layer of glis- 

 tening horn, which forms the surface of the waU, or " crust," and 

 whose purpose seems to be to retard evaporation of moisture from 

 the wall. (2) The coronary hand, 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 refle'cted 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, 

 parallel to one another, running downward and forward from the 

 lower edge of the coronary band to the margin of the fleshy sole. 

 They produce the soft, light-colored homy leaves which form the 

 deepest layer of the wall, and serve as a strong bond of union between 

 the middle layer of the wall and the fleshy leaves with which they 

 dovetail. (4) The fleshy sole, which covers the entire under surface 



