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THE SKIN. 149
also spaces between these cells containing air -svhich are called hair-
lacunae ; these are more abundant in white hair than in colored. Ex-
amined by transmitted light, these spaces are dark, but with reflected
light they are a brilliant white.
The Medulla or Pith is usually absent in the fine hairs coverino- the
surface of the body, and is not commonly met with in those coverino- the
scalp. It is also lacking in the hair of children under five years of aoe.
It is met M'ith, however, in the short thick hairs. When present, it is
found in the centre of the shaft and is lost before reaching the point.
It is composed of soft cells, oblong or rectangular in shape, containing
minute particles, some of which appear like fat-granules. There are
also air-spaces between the cells.
Under the microscope, with transmitted light, the medulla appears to
be darker than the fibrous substance of the hair. When reflected light
is used, however, it ajjpears white. This change in appearance is due to
the lacunae found within its substance.
The Hair-follides contain the hair, and are generally found in groups
of three or four, more rarely two ; very rarely are they single. With
few excepted places they are found all over the entire integument. This
follicle is an elongated pear-shaped sac passing obliquely down through
the dilFerent strata of the skin into the subcutaneous tissue, in which tat
is found. The follicles of small hairs do not pass so deeply as those
of larger ones, and those which accommodate Moolly hairs are curved
at the bottom, the ends often curving so far as to extend upward.
The mouth of the follicle is slightly funnel-shaped, the lower
portion being enlarged to accommodate the bulb or root of the hair.
The follicle is also invaginated over a pear-shaped papilla. It is
formed by the skin dipping down into the tissue below.
The coats of the follicle are separated into two divisions, dermic and
epidermic. These are again subdivided, the dermic into three layers
external, middle, and internal ; and the epidermic into an outer and an
inner root-sheath.
The External Layer is formed in a manner precisely similar to the
lower layer of the corium, with which it is continuous above. It, in a
measure, determines the form of the follicle, and in composition is highly
vascular and supplied with nerve-filaments. No elastic tissue enters
into its structure. The bundles composing this layer are laid longitu-
dinally with the axis of the follicle.
The 3Iiddle Layer is very similar in its structure and arrangement
of blood-vessels to the external layer of the corium. It is thinner, and
composed of transverse connective-tissue fibres with elongated nuclei.
Nerves have not been found in this layer.
The Internal Layer, or " glass membrane," corresponds in structure to
the basement-membrane of Todd and Bowman. It is a transparent,
homogeneous stratum, the inner surface of which is raised, the outer
surface being smooth.
The Epidermic or Cuticidar Coat is that portion of the follicle derived
exclusively from the epidermis, and is continuous with it. It adheres
closely to the root of the hair, and is generally removed with the root
in extractina; the hair. For this reason it is called the root-sheath,
THE SKIN. 149
also spaces between these cells containing air -svhich are called hair-
lacunae ; these are more abundant in white hair than in colored. Ex-
amined by transmitted light, these spaces are dark, but with reflected
light they are a brilliant white.
The Medulla or Pith is usually absent in the fine hairs coverino- the
surface of the body, and is not commonly met with in those coverino- the
scalp. It is also lacking in the hair of children under five years of aoe.
It is met M'ith, however, in the short thick hairs. When present, it is
found in the centre of the shaft and is lost before reaching the point.
It is composed of soft cells, oblong or rectangular in shape, containing
minute particles, some of which appear like fat-granules. There are
also air-spaces between the cells.
Under the microscope, with transmitted light, the medulla appears to
be darker than the fibrous substance of the hair. When reflected light
is used, however, it ajjpears white. This change in appearance is due to
the lacunae found within its substance.
The Hair-follides contain the hair, and are generally found in groups
of three or four, more rarely two ; very rarely are they single. With
few excepted places they are found all over the entire integument. This
follicle is an elongated pear-shaped sac passing obliquely down through
the dilFerent strata of the skin into the subcutaneous tissue, in which tat
is found. The follicles of small hairs do not pass so deeply as those
of larger ones, and those which accommodate Moolly hairs are curved
at the bottom, the ends often curving so far as to extend upward.
The mouth of the follicle is slightly funnel-shaped, the lower
portion being enlarged to accommodate the bulb or root of the hair.
The follicle is also invaginated over a pear-shaped papilla. It is
formed by the skin dipping down into the tissue below.
The coats of the follicle are separated into two divisions, dermic and
epidermic. These are again subdivided, the dermic into three layers
external, middle, and internal ; and the epidermic into an outer and an
inner root-sheath.
The External Layer is formed in a manner precisely similar to the
lower layer of the corium, with which it is continuous above. It, in a
measure, determines the form of the follicle, and in composition is highly
vascular and supplied with nerve-filaments. No elastic tissue enters
into its structure. The bundles composing this layer are laid longitu-
dinally with the axis of the follicle.
The 3Iiddle Layer is very similar in its structure and arrangement
of blood-vessels to the external layer of the corium. It is thinner, and
composed of transverse connective-tissue fibres with elongated nuclei.
Nerves have not been found in this layer.
The Internal Layer, or " glass membrane," corresponds in structure to
the basement-membrane of Todd and Bowman. It is a transparent,
homogeneous stratum, the inner surface of which is raised, the outer
surface being smooth.
The Epidermic or Cuticidar Coat is that portion of the follicle derived
exclusively from the epidermis, and is continuous with it. It adheres
closely to the root of the hair, and is generally removed with the root
in extractina; the hair. For this reason it is called the root-sheath,
