ANATOMY AND PHYSIOLOGY OF THE HORSE’S FOOT. 639 
lodged within the inner face of this covering, one of whose chief 
functions is the maintenance of its integrity. These tissues, 
in fact, are incessantly engaged in the formation of the new 
horn needed to counterbalance the effects of external agen- 
cies, and in keeping the whole covering in a condition to meet 
the requirements exacted from it, just as the skin and other 
parts are being regularly supplied with new material to com- 
pensate for that removed by wear. 
But even before the birth of the animal, and at a some- 
what early period of foetal existence, nature has begun to 
make provision for this contact with the ground, and conse- 
quent wear, by surrounding the extremity of the limb with 
horny matter, which, though comparatively immature and 
pulpy at the period immediately preceding birth — because if 
hard it would prove dangerous to the mother — is quickly 
transformed into a denser and more resisting protection 
shortly after that event, when it is necessary that it should be so. 
This special function of the living parts may be aptly and 
properly designated the “ keratogenous” or horn producing; 
and that it belongs to the tegumentary membrane within 
the hoof is made evident from daily experience, and the 
results of surgical operations on the foot. For instance, a 
piece of horn is removed either from the sole, frog, or wall, 
and the living textures beneath it are exposed, but otherwise 
not materially injured. In the course of one or two days 
the reparative or restorative process has made some progress ; 
the surface of the denuded textures has exuded a kind of 
semi-fluid, yellow, or greyish-looking substance, that entirely 
covers it ; if carefully observed, it will be seen that this case- 
ous sort of matter becomes hourly increased in volume, and 
in doing so acquires solidity, from exposure to the air, the 
dessication of its outer surface, and its gradual removal from 
the living membrane that generated it, and on which, of 
course, it is exactly moulded. 
When the regenerated horn has attained a proper degree 
of thickness, it commences, in certain regions of the foot, to 
exfoliate. This new concressible matter, if examined by 
means of the microscope, is found to possess the same cellular 
elements as the horn which has been removed. 
After the application of a blister to the skin, we witness 
the same results as those that follow the removal of a portion 
of hoof from the foot of the horse ; the regeneration of the 
epiderm from the denuded surface of the derm, and the for- 
mation of a new skin possessing the identical histological 
characters of that destroyed by the vesicant. So that it may 
be unhesitatingly asserted that, after the operation, the solu- 
