ANATOMY. 43 



The sensitive frog covers the lower face of the plantar cushion, and 

 from its villi the horny frog is secreted. 



The coronary frog band or perioplic ring is a narrow band of flesh 

 running around just above the coronary band and separated from it 

 by a faint groove. From the fine villi on the surface of this ring the 

 delicate fibers grow which form the periople. 



The hoof. 



The box or case of horn, called the hoof, which incloses and protects 

 the other structures of the foot, is divided into three parts — wall, 

 sole, And frog. In a healthy foot these parts are solidly united. 



The wall is the part seen when the foot is on the ground ; it extends 

 from the edge of the hair to the ground and is divided into the toe, 

 quarters, heels, and hars; it has an internal surface, an external surface, 

 and an upper and a lower border. 



The toe is the front part of the wall. It is steeper in the hind foot 

 than in the fore. The quarters extend backward from the toe to the 

 heels. The hed or buttress is that part of the wall where it bends 

 inward and forward, and the har is the division of the wall running 

 from the heel to within about 1 inch of the point or apex of the frog. 

 It lies between the homy sole and the frog. 



The external surface of the wall is covered by a thin varnish-like 

 coat of fine horn, called the periople. 



The internal surface of the wall is covered by from 500 to 600 thin 

 plates or leaves of horn, called the homy laminae. Between the 

 homy laminae, which run parallel to each other and in a direction 

 downward and forward, there are fissures into which dovetail the 

 sensitive laminse, and this union, as previously stated, binds the wall 

 of the hoof to the os pedis and lateral cartilages. 



The upper border of the wall shows a deep groove (coronary groove) 

 into which fits the coronary band. 



The lower border is called the "bearing edge" (or "spread" in the 

 unshod foot) and is the part to which the shoe is fitted. 



The homy sole is a thick plate of horn, somewhat half-moon-shaped, 

 and has two surfaces and two borders. 



The upper surface is convex (round or bulging upward) and is in 

 union with the sensitive sole from which the homy sole grows. The 

 lower surface is concave or hollowed out and is covered with scales or 

 crusts of dead horn, which gradually loosen and fall off. 



The outer border of the sole joins the inner part of the lower border 

 of the wall by means of a ring of soft horn, called the white line. This 

 mark or line is sometimes called the guide line, as it shows where the 

 nail shoyld be started in shoeing. 



The inner border is a V-shaped notch and is in union with the bars, 

 except at its narrow part where it joins the frog. 



