elations with its surroundings. It is
because of this function that we take up the study of the skin at this
time.

*The Skin* is one of the most complex structures of the body, and serves
several distinct purposes. It is estimated to have an area of from 14 to
16 square feet, and to have a thickness which varies from less than one
eighth to more than one fourth of an inch. It is thickest on the palms of
the hands and the soles of the feet, the places where it is most subject
to wear. It is made up of two distinct layers--an outer layer called the
_epidermis_, or cuticle, and an inner layer called the _dermis_, or cutis
vera (Fig. 121).

*The Dermis.*--This is the thicker and heavier of the two layers, and is
made up chiefly of connective tissue. The network of tough fibers which
this tissue supplies, forms the essential body of the dermis and gives to
it its power of resistance. It is on account of the connective tissue that
the skins of animals can be converted into leather by tanning. A variety
of structures, including blood and lymph vessels, oil and perspiratory
glands, hair follicles, and nerves, are found embedded in the connective
tissue (Fig. 122). These aid in different ways in the work of the skin.

[Fig. 121]

Fig. 121--*Section of skin* magnified, _a, b._ Epidermis, _b._ Pigment
layer. _c._ Papillae, _d._ Dermis. _e._ Fatty tissue. _f, g, h._ Sweat
gland and duct. _i, k._ Hair and follicle. _l._ Oil gland.

On the outer surface of the dermis are numerous elevations, called
_papillae_. These average about one one-hundredth of an inch in height, and
one two hundred and fiftieth of an inch in diameter. They are most
numerous on the palms of the hands, the soles of the feet, and the under
surfaces of the fingers and toes. At these places they are larger than in
other parts of the body, and are closely grouped, forming the parallel
curved ridges which cover the surfaces. Each papilla contains a loop of
capillaries and a small nerve, and many of them are crowned with touch
corpuscles (page 342).

[Fig. 122]

Fig. 122--*Diagram* of section of skin showing its different structures.

*The Epidermis* is much thinner than the dermis. It is made up of several
layers of cells which are flat and scale-like at the surface, but are
rounded in form where the epidermis joins the dermis. The epidermis has
the appearance of being _mou