ormed of angular cells, and known as
the _Medulla_. The walls of the tube, or the main substance of the hair, is
made up of a pigmented, _horny, fibrous material_. This fibrous structure
is covered by a delicate layer of finely imbricated scales, and is termed
the _Hair Cuticle_.

The root of the hair, that portion within the follicle, has exactly the
same formation save at its extreme end. Here it becomes enlarged into
a knob-like formation composed of soft, growing cells, which knob-like
formation fits over a vascular papilla projecting up in the bottom of the
follicle.

We have already stated that the hairs are down-growths of the epidermis.
It follows, therefore, that the hair follicles, really depressions
or cul-de-sacs of the skin itself, are lined by epithelial cells and
connective tissue. So closely does the epidermal portion of the follicle
invest the hair root that it is often dragged out with it, and is known
as the _Root Sheath_. This is made up of an outer layer of columnar cells
(_the outer root sheath_) corresponding to the Malpighian layer of the
epidermis, and of an inner horny layer, next to the hair, corresponding to
the more superficial layer of the epidermis, and known as the _inner root
sheath_.

The hair grows from the bottom of the follicle by a multiplication of the
cells covering the papilla upon which its root is moulded. When a hair is
cast off a new one is produced from the cells covering the papilla, or, in
case of the death or degeneration of the original papilla, the new hair is
produced from a second papilla formed in place of the first at the bottom
of the follicle.

[Illustration: FIG. 24.--SECTION OF SKIN WITH HAIR FOLLICLE AND HAIR. _a_,
The hair follicle; _b_, the hair root; _c_, the medulla; _d_, the hair
cuticle; _e_, the outer root sheath; _f_, the inner root sheath; _g_, the
papilla from which the hair is growing; _h_, a sebaceous gland; _i_, a
sudoriferous gland.]

THE SEBACEOUS GLANDS are small saccular glands with their ducts opening
into the mouths of the hair follicles. They furnish a natural lubricant to
the hairs and the skin.

THE SUDORIFEROUS OR SWEAT GLANDS are composed of coiled tubes which lie in
the deeper portion of the skin, and send up a corkscrew-like duct to open
on the surface of the epidermis. They are numerous over the whole of the
body.

[Illustration: FIG. 25.--LONGITUDINAL SECTION THROUGH NAIL AND NAIL-BED OF
A HUMAN FOETAL FINGER.[A] _a_, The na