10 



the fleshy sole. (5) The fleshy frog, which covers the under surface 

 of the plantar cushion and produces the horny frog. 



Horny box, or hoof. — The horny box, 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 already 

 stated, it consists of three layers — the periople, the middle layer, and 

 the leafy layer. 



Bars. — The bars (see fig. 1) 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 horny 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 horny 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 white 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. — The frog, secreted by the pododerm covering the plantar 

 cushion or fatty frog, and presenting almost the same form as the lat- 

 ter, 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 

 they pass backward into the horny 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 



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