ANATOMY AND PHYSIOLOGY OF THE HOUSERS FOOT. 155 
the upper margin of the bars, when it terminates abruptly 
behind. This part fits into what we may call the cleft” of 
the plantar cushion, and has been named the “ frog-stay,” 
from an idea, perhaps, that it prevented the displacement of the 
frog laterally. In this sense, the designation is, I think, per- 
fectly correct. As this thin tapering ridge, inserted in the deep 
fissure that almost makes two complete divisions of the plantar 
cushion, retains each portion in its proper situation during 
the time the horny frog is in contact with the ground, and 
thus, by preventing the elastic mass from being pushed too 
much to one side or the other at a most momentous crisis in 
locomotion, it maintains it in a position most favorable for 
the discharge of its function. By solidly fixing this part of 
the foot it immensely aids the laminae — vascular and horny — 
and what we have named the “ toe-stay,” in keeping the foot 
from rotating with the hoof, especially during rapid or violent 
movements. For this reason, doubtless, we find the frog-stay 
most largely developed in horses adapted for speed, or wdiat 
is called (e well-bred” horses. Another feature to be noticed, 
and which affords further evidence that this is the chief, if not 
the sole function of the frog- stay, is that it is directly in a line 
with the small projection in the centre of the sole and wall, 
the “ toe-stay.” In this manner is the foot fixed securely in 
the hoof, before as well as behind, and the horny case insured 
against lateral displacement. 
The whole inner or upper face of the frog is perforated by 
little openings, like the corresponding surface of the sole, for 
the passage of the papillee which we have described as cover- 
ing the surface of the cushion which rests on it. They are 
consequently widest and deepest in the cavity of the frog, 
and smallest on its sides and on the frog-stay. Their direc- 
tion in the bottom of this cavity is forwards ; on the sides, 
towards the circumference of the hoof ; and on the stay, 
backwards. 
There is much that is interesting to be noted on the lower 
or ground face of the frog. We see in it the reverse of its 
upper surface ; the triangular cavity being here represented 
by a somewhat conical projection that stands well out from 
the concavity of the side, and the frog-stay being replaced 
by a longitudinal fissure or cleft that divides the salient horny 
mass into two branches. The somewhat bulging portion 
immediately in front of the cleft is the “ body” or <f cushion 
of the frog,” and corresponds to the deepest part of the 
cavity, and to the faint transverse depression on the upper 
face of the sole. The branches correspond to the two diverging 
channels that limit the base of the frog-stay, and passing to 
