THE INTEGUMENTARY APPENDAGES. 805 



influence of any inflammatory cause (laminitis, ablation of the wall), these 

 denticulae become largely developed, and transformed into veritable papillae. 

 Their sides are traversed by folds, about sixty in number, which pass 

 uninteruptedly from top to bottom. These secondary leaves, or lamellae, 

 are fixed obliquely on the sides of the laminae, as the barbules of a feather 

 are attached to the barbs. 



The podophyllous tissue is not in immediate contact with that of the 

 keraphyllous tissue, or horny laminae ; between the two there is a mass of 

 soft, elliptical cells, always destitute of pigment, easily stained with carmine, 

 and appearing to stud the ramifications of the vascular laminae. A trans- 

 verse section of the union of the hoof with these laminae, when treated with 

 carmine, presents a very fine aspect, appearing as so many fern or acacia-of- 

 Judea leaves placed between the keraphyllous laminae : the principal nerve, 

 and the secondary nervnles of the leaves, being represented by the lamina 

 and its lateral ridges, the limb of the leaves by the young cells spread 

 around the latter. 



The structure of the podophyllous membrane resembles that of the other 

 parts of the keratogenous apparatus. Its corium is, like that of the peri- 

 pheral portion of the velvety tissue, separated from the os pedis by a fibrous 

 reticulum, which supports the veins, and forms, to some extent, the periosteum 

 of the third phalanx. 



The leaves of the podophyllous membrane are immense lamellar papillae, 

 which should be included among the principal instruments concerned in the 

 tactile sensibility of the Horse's foot, and which play a really mechanical 

 part, in concurring, by their dovetailing with the keraphyllous (or horny) 

 laminae, to assure the solidity of the union of the hoof with the living parts. 

 The cells which multiply on their surface have usually but little share iu 

 the formation of the horn. This will, however, be alluded to hereafter. 



b. Description of tlie Hoof. 



The hoof of the Horse, considered as a whole, represents a kind of box 

 that envelops the inferior extremity of the digit, by fitting closely on the 

 keratogenous membrane, to which it is united in the most intimate manner 

 by a reciprocal penetration of the prolongations into the cavities that exist 

 on the surfaces in contact. 



Its general shape is, as was demonstrated by Bracy Clark, that of the 

 moiety of a cylinder cut obliquely across its middle, and resting on the 

 surface of this section. In nearly all feet, however, it is slightly conical. 



Prolonged maceration separates it into three portions : the wall, sole, 

 and frog. 



WALL. The wall, also named the crust, is that part of the hoof which is 

 apparent when the foot rests on the ground. This thick plate of horn 

 covers the anterior face of the foot, and, gradually narrowing in width and 

 diminishing in thickness, passes round each side until it reaches the bulbs 

 of the plantar cushion, when its extremities are sharply inflected inwards, 

 between the frog and internal border of the sole, becoming confounded with 

 the latter about its middle or anterior third, after being greatly reduced in 

 breadth and substance. 



The middle, or anterior part, of this horny envelope is popularly known 

 as the toe, the two sides of which are designated as outside and inside toe ; 

 the lateral regions constitute the quarters ; the heels are formed by the angles 

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