635 
ON THE FUNCTION OF THE FROG. 
Bi/ Mr. J. Stewart, Veterinary Professor at the Andersonian 
University at Glasgow. 
Professor Coleman and B. Clark, as every body knows, are 
our most, if not our only, valuable authors on the structure and 
functions of the horse’s foot. Between these two gentlemen, it 
is said, that the frog prevents the horse from slipping; prevents 
the hoof from contracting; acts as a spring, by admitting of the 
descent of the sole; and preserves the tendon and navicu a 
joint from external violence. I do not mean to deny tha 
frog performs these different offices. There can be no dou 
that it does ; and if I were to add, that it also fills up a certain 
space which would otherwise be vacant, no one could contradict 
it. But there is a difference between what a thing does, and 
what it was expressly designed to do. . , , 
The purpose for which I conceive the frog to have been intend¬ 
ed has never, as far as I know, been described. Tne view 1 
have taken of its functions has been derived, not so much from 
dissections of the part, as from observation of what takes p ace in 
the foot of the living animal. Horses of large size, wit 1 ong 
pasterns, and rather fiat feet, may be plainly perceived throwing 
a considerable portion of their weight from the small/j^es 
bone on to the upper and posterior part of the frog. AH horses 
under certain circumstances do so; but it is most evident in those 
particularly alluded to, and especially when they are coming down 
hill heavily laden. If a large draught horse is shod with ig - 
heeled shoes, the frog, in process of time, becomes icmaikably 
prominent, the heels weak, and the coronet at the heels and 
quarters bulges over. The frog is fairly thrust downwards be¬ 
tween the heels of the shoe, not by the descent of the navicular 
bone, but by that of the small pastern bone. ® 0 , ^ 
shod without calkins, the frog is then compressed between the 
ground below and the small pastern bone above ; and the heels 
and quarters of the crust recede outwards. This, then, is the 
use of the frog. It is formed merely to act as a firm yet yielding 
point of support to the small pastern bone. This oone, it may 
be observed, has a considerable prominence at its upper and 
posterior part, by which it, m a manner, meets the fro o . 
way. By such an arrangement, extent and freedom of motion 
and elasticity are conferred. The expansion of the hee s an 
quarters of the crust is a necessary consequence of the circum¬ 
stances under which the frog is placed. The sole no doubt, has 
some influence; but, compared with that which the flog cxei s. 
