Having thus paved the way, we are now in a better position to discuss our original question (Are the horny laminæ secreted by the sensitive?), and better able to appreciate the work that has been done towards the elucidation of the problem. A most valuable contribution to this study is an article published in 1896 by Professor Mettam.[A] Here the question is dealt with in a manner that must effectually silence all other views save such as are based upon similar methods of investigation--namely, histological examination of sections of equine hoofs in various stages of foetal development. [Footnote A: The _Veterinarian_, vol. lxix., p.1.] Professor Mettam commences by drawing attention to the error that has been made in this connection by studying the soft structures of the foot separated by ordinary putrefactive changes from the horny covering. "In this way," the writer points out, "a wholly erroneous idea has crept in as to the relation of the one to the other, and the two parts have been treated as two anatomical items, when, indeed, they are portions of one and the same thing. As an illustration, and one very much to the point at issue, the soft structures of the foot are to the horny covering what the corium of the skin and the rete Malpighii are to the superficial portions of the epidermis. Indeed, the point where solution of continuity occurs in macerating is along the line of the soft protoplasmic cells of the rete." In the foregoing description of the skin we have seen that the corium is not a _plane_ surface, but that it is studded by numerous papillary projections, and that these projections, with the depressions between them, are covered by the cells of the epidermis. The corium of the horse's foot, however, although possessed of papillæ in certain positions (as, for example, the papillæ of the coronary cushion, and those of the sensitive frog and sole), has also most pronounced ridges (laminæ) which run down the whole depth of the os pedis. Each lamina again carries ridges (laminellæ) on its lateral aspects, giving a section of a lamina the appearance of being studded with papillæ. We have already pointed out the ridge-like formation of the human nail-bed, and noted that, with the exception that the secondary ridges are not so pronounced, it is an exact prototype of the laminal formation of the corium of the horse's foot.