DISEASES OF THE HOESE. 555 



excepting the flesh}^ frog and bars. The horny sole is produced by 

 the fleshy sole. (5) Th&feshyfi^og, which covers the under surface of 

 the plantar cushion and produces the horny frog. 



The horny hox^ or hoof^ consists of wall and bars, sole and frog. The 

 wall is all that part of the hoof which is visible when the foot is on 

 the ground (see fig. 8). As alread}^ stated, it consists of three layers — 

 the perioplo, the middle layer, and the leaf}^ la3'er. 



The hars (see fig\ Ic) are forward prolongations of the wall, and are 

 gradually lost near the point of the frog. The angle between the wall 

 and a bar is called the ."buttress." Each bar lies against the horny 

 frog on one side and incloses a wing of the sole on the other, so that 

 the least expansion or contraction of the horn}^ frog separates or 

 approximates the bars, and through them the lateral cartilages and the 

 walls of the quarters. The lower border of the wall is called the 

 "bearing edge," and is the surface against which the shoe bears. By 

 dividing the entire lower circumference of the wall into five equal 

 parts, a toe, two side walls, and two quarters will be exhibited. The 

 "heels," strictly speaking, are the two rounded soft prominences of 

 the plantar cushion, lying one above each quarter. The outer wall is 

 usually more slanting than the inner, and the more slanting half of a 

 hoof is always the thicker. In front hoofs the wall is thickest at the 

 toe and gradually thins out toward the quarters, where in some horses 

 it may not exceed one-fourth of an inch. In hind hoofs there is much 

 less difference in thickness between the toe, side walls, and quarters. 

 The horny sole, from which the flakes of old horn have been removed, 

 is concave and about as thick as the wall at the toe. It is rough, 

 uneven, and often covered by flakes of dead horn in process of being 

 loosened and cast off. Behind, the sole presents an opening into which 

 are received the bars and horn}' frog. This opening divides the sole 

 into a body and two wings. 



The periphery of the sole unites with the lower border of the wall 

 and bars through the medium of the vjhite line, which is the cross- 

 section of the leafy horn layer of the wall, and of short plugs of horn 

 which grow down from the lower ends of the fleshy leaves. This 

 white line is of much importance to the shoer, since its distance from 

 the outer border of the hoof is the thickness of the wall, and in the 

 white line all nails should be driven. 



The frog, secreted by the pododerm covering the plantar cushion or 

 fatty frog, and presenting almost the same form as the latter, lies as a 

 soft and very elastic wedge between the bars and between the edges of 

 the sole just in front of the bars. A broad and shallow depression in 

 its center divides it into two branches, which diverge as the}^ pass 

 backward into the horn}' bulbs of the heel. In front of the middle 

 cleft the two branches unite to form the body of the frog, which ends 

 in the point of the frog. The bar of a bar shoe should rest on the 



