lded onto_ the dermis, filling up the
depressions between the papillae and having corresponding irregularities
(Fig. 121). No blood vessels are found in the epidermis, its nourishment
being derived from the lymph which reaches it from the dermis. Only the
part next to the dermis is made up of _living_ cells. These are active,
however, in the formation of new cells, which take the place of those that
are worn off at the surface. Some of the cells belonging to the inner
layer of epidermis contain _pigment granules_, which give the skin its
color (Fig. 121). The epidermis contains no nerves and is therefore
non-sensitive. The hair and the nails are important modifications of the
epidermis.

*A Hair* is a slender cylinder, formed by the union of epidermal cells,
which grows from a kind of pit in the dermis, called the _hair follicle_.
The oval and somewhat enlarged part of the hair within the follicle is
called the _root_, or _bulb_, and the uniform cylinder beyond the follicle
is called the _shaft_. Connected with the sides of the follicles are the
_oil_, or _sebaceous, glands_ (Figs. 121 and 122). These secrete an oily
liquid which keeps the hair and cuticle soft and pliable. Attached to the
inner ends of the follicles are small, involuntary muscles whose
contractions cause the roughened condition of the skin that occurs on
exposure to cold.

*A Nail* is a tough and rather horny plate of epidermal tissue which grows
from a depression in the dermis, called the _matrix_. The back part of the
nail is known as the _root_, the middle convex portion as the _body_, and
the front margin as _the free edge_ (Fig. 123). Material for the growth of
the nail is derived from the matrix, which is lined with active epidermal
cells and is richly supplied with blood vessels. Cells added to the root
cause the nail to grow in length (forward) and cells added to the under
surface cause it to grow in thickness. The cuticle adheres to the nail
around its entire circumference so that the covering over the dermis is
complete.

[Fig. 123]

Fig. 123--*Section of end of finger* showing nail in position.

*Functions of the Skin.*--The chief function of the skin is that of
protection. It is able to protect the body on account of the tough
connective tissue in the dermis, the non-sensitive cells of the epidermis,
and also by the touch corpuscles and their connecting nerve fibers. This
protection is of at le