‘STRUCTURE AND DISEASES OF THE HORSE’S FOOT. 363 
and backward, parallel to those of the toe. The quarters slope down- 
ward and backward, and become thinner as they approach the heels. 
The heels (Fig. 12 7, 2) are the two protuberant portions of the wall - 
by which it is terminated posteriorly. The wall here is shortest and 
thinnest, the fibers being ouly about an inch in length, and not exceed- 
ing the fourth of an inch in thickness. While, i in its natural state, there 
is some degree of elasticity in the entire wall, there is much more in the 
portion that covers the heels. 
The bars (Fig. 13, f, f) are reflections of the wall in toward the center 
of the foot, on its ground surface. They gradually approach each other, 
and come together a little in front of the center of the foot. The bars are 
usually regar rded as parts of the sole, but maceration shows them to be 
separable from the sole, but inseparable from the wall. In the natural, 
healthy foot, that has never been shod, the bars appear as sharpened 
prominences, like braces, between the center of the foot and the heels. 
The best writers agree that they are well adapted to keep the heels open, 
and prevent contr action of the hoof. Inthe unshod foot, the bars have a 
bearing upon the ground, second only to that of the edge of the wall. 
The sole (Fig. 13, d, d, d) fills the space between the wail and the bars. 
It is in the form of an irregular arched plate, the concavity being 
toward the ground. It is firmly attached, by its outer convex edge, to 
the inner surface of the solar border of the wall, while its inner straight 
edges are attached io the bars. It has been described as joining the 
frog, but throughout its whole extent the bars intervene between the 
sole and the frog. The center of the sole is the thinnest portion of it, 
and it also constitutes the summit of the arch. The lower cireumfer. 
ence of the arch, which is also the thickest and strongest, everywhere 
abuts against the sides of the wall. The result of this mechanism is, 
that atevery step, as the weight is thrown upon the foot, the coffin-bone 
descends, elongating the elastic fibrous tissue connected with the sensi- 
tive lamin, and, pressing upon the highly elastic tissue of the sensitive 
sole, which rests. upon the arch of the horny sole, causes the latter to 
yield and descend. The wall being elastic, especially toward the heels, 
is readily pressed outward, so that the ¢ eround surface of the foot is 
larger while bearing the weight than it is when the pressure is removed. 
Whenever the weight i is taken off, the wall springs back, and the sole 
recovers its arched form. By this means the step is rendered elastic, 
jarring is obviated, and injury to the sensitive sole and sensitive frog i is 
prevented. 
The frog (Fig. 13, h, k, 1) is a wedge-like mass filling the angular 
space between the bars, and consists not of solid horn, as might at first 
seem, but of a series of elastic arches. It has been not inaptly com- 
pared to an elastic keystone received into an elastic arch, communicating 
in some eases, and admitting in all, the springing movements of which 
such an arch is capable. "The base of the frog lies between and con- 
nects the posterior curved portions of the hoof, limiting to some ex- 
tent their action. The sides are connected with the bars by their upper 
edges, leaving upon the ground surface two deep channels between the 
lower border of the bars ‘and frog, which have been termed the commis- 
sures of the frog. (Fig. 13,9.) ‘The horny material arching over these 
channels ic called the arch of the commissures. In the center of the frog, 
as we look upon its ground surface, is a deep, narrow depression, the 
cleft of the frog, (Fig. 13 k,) which extends farther into the soft tissues 
of the foot than the commissures. This cleft is arched over in a similar 
manner; and the cone-like mass, as viewed on se inner upper surface, 
has received the name of frog stay or‘bolt. 
