104 THE GROWTH OF THE HOOF. 



the processes of renewal wliich are always going on in the 

 hoof-forming tissues. On page 62 it was shown that the 

 surface of the corium is continually secreting cells which 

 form the epidermis, that the older of these are compressed 

 by the younger and last-formed, in consequence of which 

 they become flatter and drier, take on a horny character, 

 and finally are thrust off*. The growth of the hoof is very 

 similar. Like the epidermis, the hoof consists of cells secreted 

 by the specialised corium, and gradually compressed and 

 dried into a solid adherent mass corresponding to the more 

 superficial epidermal layers. Nevertheless, the arrangement 

 and forward growth of the horn cells difl'er essentially 

 from those of the epidermis. As the hoof corium, which 

 produces horn cells, is not a level surface like that of the 

 skin, but presents numerous papilhe and laminae, the growth 

 and formation of horn naturally presents many peculiarities. 

 This folding of the horn-secreting surfaces ensures a very 

 intimate connection between the horny and sensitive parts, 

 a union characterised by firmness and resistance to dis- 

 placement, but presenting also a sufficiently yielding char- 

 acter to permit of the growing down of the wall. Leis- 

 ering suggested the following theory of the growth of the 

 hoof : — 



Every point in the corium, however small, is capable of 

 producing horn cells. The papillae, the little surfaces be- 

 tween them, the sensitive laminiii and their interspaces, are 

 all concerned in producing horn, but each in a particular 

 way. 



Let the reader imagine the papilke in function, ilrstly, they 

 produce a circular layer of horny cells ; below these another 

 layer, a second, a third, a fourth, and so on. As, however, the 

 older cells cannot continue to retain their original position as 

 the newer cells are formed, they are gradually thrust outwards 

 and onwards in proportion to the space required by the new 

 cells. As each papilla is more or less conical, the rows of 

 cells are first arranged in a funnel shape, and finally each 

 papilla becomes the growing base of a horn tube. As, 

 however, the individual (and concentric) layers of cells are 

 firmly united to one another, and as each layer is intimately 

 connected with the next, there are no marked intervals be- 



