246 
NAVICULARTHRITIS. 
one, the subject of disease in the navicular joint. If pressure to 
the frog be — as I think I shall be able to demonstrate that it is — 
fruitfully productive of navicularthritis, how comes it that flat feet, 
in which such pressure is remarkable, should be exempt from or in- 
susceptible of it I The answer to this question is, that such is the 
normal thinness or weakness of the horn of such feet, and such 
their consequent properties of yielding and elasticity, that pressure 
and contusion from the ground upon the frog is thereby, in any in- 
jurious effect it might have, counteracted, the frog not being under 
such circumstances rendered inexpansible or liable to become a hard 
fixed body the same as in the navicularthritic foot. For let it be 
here observed, that exposure of the frog alon e, frog-pressure as it is 
called, is not, of itself, sufficient for the production of navicularthritis; 
there must be present rigidity of the hoof as well, soft and elastic 
horn, as I said before, defeating the mischief pressure to the frog 
would otherwise be likely to entail. 
The foot predisposed to take navicularthritis — the one indeed we 
might, a priori , imagine would become the subject of the disease — 
is the strong, round, short-toed or clubby foot, open at the heels, 
with a sound frog jutting prominently out between them. Here is 
a frog exposed to all the pressure Lafosse or Coleman would have 
desired for it, bounded at its sides by heels thick and strong, and 
indisposed to yield, and itself liable from its very exposure to be- 
come, in the warm stable, hard and dry, and incompressible. 
Pressure from the ground upon such a frog must render it in effect 
a fixture ; it cannot, will not expand ; and at the very moment 
pressure from below would force it upwards, weight from above 
is with more or less violence descending upon it. Under 
such circumstances, can we wonder that the delicate synovial 
lining of the navicular joint should become crushed and broken 1 
Rather, is this not the very way in which, when we come to reflect 
upon the matter, we should suppose such a lesion would be most 
likely to happen? 
But, if exposure of frog and rigidity of hoof prepare the foot 
for taking the disease, how happens it that navicularthritis does 
not occur in the hind feet 1 — which, we believe, it never does. It 
is very well known that the fore feet are liable to many diseases to 
which the hind are hardly if at all obnoxious, and navicularthritis 
constitutes a most important ailment in this catalogue. The weight 
of the head and neck, in addition to that of half the body, upon the 
fore feet has been adduced by way of accounting for this ; also con- 
cussion, &c. has likewise been mentioned ; but, the real fact of the 
case is, that the disease — or one precisely analogous to it — does 
occur in the hind as well as the fore limb, though not in the foot, 
but in the hock joint. Articular spavin to all intents and purposes 
