il; _b_, the rete mucosum; _c_, the
longitudinal ridges of the corium.]

[Footnote A: Seeing that the section is a longitudinal one, it would appear
from the way the ridges cut that they are running transversely beneath the
nail. Their extreme delicacy, however, prevents a single one showing itself
along the length of the section, and their constant accidental cutting
makes them _appear_ to run transversely (H.C.R.).]

THE HUMAN NAILS are thickenings of the lowermost layer of the horny portion
of the epidermis, the stratum lucidum. They are developed over a modified
portion of the corium known as the nail-bed. The horny substance of the
nail is composed of clear horny cells, and rests immediately upon a
Malpighian layer similar to that found in the epidermis generally. Instead
of the papillae present elsewhere in the skin, the corium of the nail-bed is
marked by longitudinal ridges, a similar, though less distinct, arrangement
to that found in the laminae of the horse's foot.

Having thus paved the way, we are now in a better position to discuss our
original question (Are the horny laminae 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 forego