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.

The distribution of the laminæ over the foot we have discussed in the