568 DISEASES OF THE HORSE. 



of the foot, excepting the fleshy frog and bars. The horny sole is 

 produced by the fleshy sole. (5) The fleshy frog, which covers the 

 under surface of the plantar cushion and produces the horny frog. 



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. 



The bars (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 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, un- 

 even, 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, 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 de- 

 pression 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 



