NAVICULARTHRITIS. 145 



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 Hable to become a hard 

 fixed body the same as in the navicularthritic foot. For let it be 

 here observed, that exposure of the frog alone, 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 1 



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, 



VOL. IV. u 



