They are more or less oval in form, and can be easily recog-
nized under the microscope by their dark contours and by the
oblique lines produced by the transversely running connective-
tissue fibres of the outer surface of the corpuscle. There may
THE SKIN.
281
be two or more corpuscles within a single papilla (Thin), but
each corpuscle invariably has a special nerve passing into it.
Frequently, however, an appearance as if two corpuscles were
present is produced by a single corpuscle having the shape
of a figure 8. The medullated nerve-fibre, in passing to the
corpuscle, pursues a more or less curved course, and usually
enters it at or near its lower extremity. It may, however, en-
ter at any part of the corpuscle, and sometimes winds around
it for a considerable distance before entering. After entering
the corpuscle the medullary sheath is lost, and its course now
becomes difficult to pursue, except in the case of very small
or young corpuscles. The intimate structure of these bodies
and the arrangement of their formative elements are still mat-
ters of discussion and uncertainty. The external portion of a
corpuscle appears to be composed, in great part, of larger or
smaller bundles of white, fibrous connective tissue anastomos-
ing with each other and running transversely, or in a spiral
direction, to the long diameter of the corpuscle. This part
of the corpuscle differs, as regards
irregularity of surface, with the size
and the manner in which the fibrous
fascicles divide and anastomose. The
coarser the bundles and the anastomo-
ses the more irregular will be its sur-
face. Between the fibres are found
oval or round bodies which color deep-
ly in gold, and have been regarded as
elastic elements (Thin). Other obser-
vers consider them as connective tis-
sue, or nerve-fibres. Some of these
bodies undoubtedly represent the
nerve-fibre in transverse or oblique
section ; for the nerve pursues a more
or less zigzag course within the corpuscle, and, consequently,
a section of the body will probably show the nerve cut across
in one or more places (Pig. 120, b). The arrangement of the
elements forming the central part of the corpuscle is not yet
thoroughly understood. These bodies have hitherto been
usually regarded as end-organs that is, it has been believed
that the medullated nerve-fibre terminates within the corpuscle,
hence the name, tactile corpuscle. Observers, however, have
Fio. 120. Tactile corpuscle, show-
ing termination of nerve : a, corpuscle;
6, nerve, cut obliquely; c, apparent
division of nerve-fibre ; e, similar ap-
pearance as at c ; /, blood-vessel ; g,
rete cells; A, nerve-fibre cut trans-
versely.
282 MANUAL OF HISTOLOGY.
not agreed as to the mode of termination of the nerve, and
some have maintained that it has not been clearly proven that
they really do terminate in the corpuscle. From specimens
which I have recently obtained I am led to believe that the
nerve does not terminate within the corpuscle, but passes on
into the rete Malpighii.
The best corpuscles for studying this point are small ones,
as in these a section is more likely to include the entire upper
extremity of the corpuscle at the same time that it is not too
thick for examination with the microscope. Even in a small
corpuscle, however, unless the nerve passes onward in a direct
level with the corpuscle after leaving it, the nerve, in a vertical
section, will be cut across, and it will, therefore, be impossible
to follow it from the corpuscle into the rete. I believe the
nerve frequently, perhaps generally, changes the direction of
its course after leaving the corpuscle, and hence we often see
a transverse section of the nerve at the upper extremity of the
corpuscle. In Fig. 120 is seen the location of the termination
of the nerve-fibre as observed in one of my specimens. In
one place its course between the rete cells was very indistinct,
though recognizable. The nerve passed obliquely upward be-
tween the cells of the rete to the space between the second
and third rows of cells, where it assumed a longitudinal di-
rection. At the commencement of the curve the nerve ap-
peared to have undergone division (c). After passing a short
distance horizontally it ran almost perpendicularly downward,
and near g was lost to view. At e it appeared to have again
undergone division. According to the appearances here fig-
ured the corpuscles are not the structures in which the nerve
terminates, the latter passing from the corpuscle (as -a non-
medullated fibre) into the epidermis, where it divides and
probably terminates in the same manner as the other nerves.
This mode of termination cannot be regarded as strange, as we
have already seen that some medullated nerve-fibres lose their
medulla deeper in the corium, and afterward continue their
course as non-medullated fibres.
The tactile corpuscles are found in greatest number in
the ends of the fingers. They are also present on other parts
of the hand and on the foot, and sometimes in the lips and
nipple.
The sweat-glands. The sweat-glands glandulce sudorif-
THE
283
erce are found in the skin of all parts of the body except that
of the glans penis and margin of the lips. They are most nu-
merous in the palms of the hands and the soles of the feet,
where they number, according to Krause, 2,685 to 2,736 to the
square inch.
A sweat-gland is composed of two parts, viz.: the gland
proper, or secreting part, and an excretory duct. The gland
proper lies in the subcutaneous tissue,
and consists of the lower part of the sweat-
gland rolled and coiled upon itself into a
more or less globular form, the tube ter-
minating in a cul-de-sac, the blind extrem-
ity generally lying in the centre of the coil.
The diameter of the secreting tube is
greater than that of the excretory duct.
The former is composed of secreting cells,
unstriped muscular fibres, and a basement-
membrane. The cells (glandular or secret-
ing epithelial cells) are polygonal in shape
and form only a single layer. They are
strongly granular in appearance and have
a very distinct nucleus. Their basal end
is sometimes notched where they are in-
serted into the basement-membrane. In
normal conditions these bodies are never
found in the sweat-fluid, but in inflamma-
tion of the surrounding connective tissue
they frequently become separated from
the basement-membrane. Oil-globules are frequently seen in
the cell- body, and are to be regarded as a normal constituent
of the corpuscles.
The basement-membrane is a thin, transparent structure,
lying beneath the epithelial cells and composed of flat endo-
thelial elements, as shown by the action of silver nitrate on
the fresh tissue.
In certain glands, especially those of the axilla, a layer of
unstriped muscular fibres is found external to the basement-
membrane. These fibres are present in only a small number
of sweat-glands ; by their contraction they assist in the expul-
sion of the secreted sweat. They are the smallest unstriped
muscular fibres met with in the human body.
FIG. 121. Lower part of a
sweat-gland : a, excretory duct ;
6, coil of secreting-tube ; c, sc-
creting-tube cut transversely;
d blood-vessels cut across.
284 MANUAL OF HISTOLOGY.
The sweat-glands are surrounded by a somewhat loose
fibrous connective tissue, from, which fibres pass inward and
form a closer network between the coils of the gland. Some
of the fibres run parallel, and others transversely or obliquely,
to the long diameter of the convoluted tube. A large number
of lymphoid cells are always present in this interglandular
connective tissue. The sweat-glands are richly supplied with
blood-vessels.
The excretory duct passes upward from the gland proper
in a more or less vertical direction through the different layers
of the skin to its free surface, where it opens with a funnel-
shaped orifice. In passing through the corium it pursues a
straight or slightly wavy course, and enters the lowest part
of the inter-papillary rete. The structure of this part of
the excretory duct differs from that of the gland proper, in
the shape of the cells, the absence of muscle-fibres, and the
presence of a cuticula. This cuticula lines the inner surface
of the epithelial coating and limits the lumen of the duct.
As the rete Malpighii is entered there are generally two or
more layers of cells lining the duct, the number increasing
as the rete is approached. The transition from secreting cells
to lining cells is gradual, so that the presence of a cuticula
decides the nature of the tube. The basement -membrane
corresponds in structure with that of the gland proper. The
fibres of surrounding connective tissue run parallel with the
duct.
As the duct approaches the rete Malpighii its epithelial
cells increase in number and form two or more layers, which
are really only a continuation downward of the cells of the
rete. When the duct enters the rete it loses its basement-
membrane and is formed only of the cells of the mucous layer,
which have become more or less flattened and spindle-shaped.
The direction of the duct through the rete is sometimes straight
and sometimes spiral.
In passing through the stratum corneum the duct pursues
a spiral direction on account of the horizontally flattened cells
of this layer (see Fig. 114, /), and the number of spirals pres-
ent depends upon its thickness. The largest number is found
in the palms of the hands and soles of the feet, where it may
amount to twenty or more, whilst on some parts of the body
there is not even a single complete spiral. The wall of the
THE SKIN. 285
duct is formed of the cells of tlie corneous layer, and the duct
opens on the free surface at the summit of the ridges.
The formation of the sweat-glands commences in the fifth
month of foetal life by the pushing of epithelial cells from the
rete mucosum into the cutis. In the seventh month the epi-
thelial cells form a canal, and the lower end of the tube be-
comes dilated and somewhat twisted. In the ninth month the
tube is coiled upon itself to form the gland proper. According
to Ranvier, who believes that the muscular fibres lie between
the epithelial cells and the basement-membrane, the muscle-
cells arise from the external cells of the gland proper by a
process of simple differentiation. The lumen of the tube is
formed not by a softening down of the central cells, but by the
formation of the cuticula, which occurs first at the lowest part
of the excretory duct (Ranvier).
The sebaceous glands. The sebaceous glands are seated in
the corium and are in close connection with the hair-follicles.
When the hairs are large the sebaceous glands appear as ap-
pendages to the hair-follicles into which their ducts enter, and
by which their contents are carried to the free surface. As
regards the small downy, or lanugo hairs, they may be said to
open into the ducts of the sebaceous glands, the ducts of the
latter having in this case a much greater diameter than in the
previous instance. They also open directly on the free surface.
The sebaceous glands are almost without exception acinous
glands, the number of lobules forming a single gland, ranging
from two to twenty, or more. The largest glands are seated in
the nose, cheeks, scrotum, about the anus, and in the labia.
Occasionally the secreting portion of a sebaceous gland con-
sists of a single tubule, or sac, whose duct opens into a hair-
follicle.
Every sebaceous gland is composed of two parts, viz.: the
secreting portion, or gland proper, and the duct. The gland
proper is formed of a basement-membrane, or sac, externally,
and secreting cells, or their products, internally. The basement-
membrane is continuous with the transparent membrane de-
scribed as lying directly beneath the rete Malpighii and above
the corium, and has a similar structure. This basement-mem-
brane passes from the sebaceous gland to the hair-follicle, where
it forms the inner layer of the hair-sac. The membrane of the
sebaceous gland is surrounded externally by bands of dense
286 MANUAL OF HISTOLOGY.
connective tissue containing blood-vessels, nerves, and lym-
phatics.
The secreting part of the gland (Fig. 122, t) is composed of
layers of cells very similar to the cells present in the epidermis,
those of the outer part corresponding to the cells of the rete
Malpighii. The first layer of cells, viz., those seated upon the
basement-membrane, is composed of cylindrical, or cubical,
cells, like those of the rete. They have a very distinct nucleus.
Further inward the cells become larger, more or less polyhe-
dral in form, and contain fat, which obscures or conceals the
nucleus. If the fat is extracted the nucleus can be seen lying
in the centre of the space previously occupied by the fat. The
nearer the centre of the gland the greater the quantity of fat
in the cells. The most external layer of cells contains but a
small quantity. In the centre of the gland, free fat, fat-crys-
tals, and remnants of epithelial cells are found.
The duct of the sebaceous gland is similar in structure to
that of the gland proper. Externally is the basement-mem-
brane, lined inside by epidermis-like cells, containing more or
less fat, and enclosing a central cavity through which the seba-
ceous matter passes to reach the hair-follicle or the free surface.
The contents of this canal are fat, fat-crystals, and remnants
of epithelial cells. Internal to the polyhedral cells of the duct
are the cells of the corneous layer of the epidermis, which di-
minish in number in proportion to the distance from the free
surface.
In large hairs the duct of the sebaceous gland opens at an
acute angle into the hair-follicle near its upper third, and the
gland proper lies about on a level with the middle third of the
hair-follicle.
At the place of union of the hair-follicle with the sebaceous
gland the cells of the latter become continuous with the cells
of the external root-sheath of the hair. This latter root-sheath
becomes continuous above with the cells of the rete Malpighii.
The development of the sebaceous glands commences at the
third month of foetal life, as a projection downward and out-
ward of a part of the external root-sheath of the hair, at the
place where the future opening of the duct will be situated.
It consists, at first, entirely of epithelial cells, which by sub-
sequent multiplication and further projection downward, form
the sebaceous gland.
THE SKIN. 287
Muscles. Striated and non-striated muscles are present in
the skin. The former are found both in the smooth and in the
bearded parts of the face, and also in the nose. They arise from
the deeply seated muscles, and passing vertically, or more or
less obliquely, upward between the hair-follicles and the glands
of the skin, terminate in the corium.
The non-striated muscles are very numerous, and run either
in a parallel or in an oblique direction to the general surface
of the skin. Those lying parallel with the general surface run
either in a straight or circular direction. When they run in a
straight direction and anastomose with each other they form
a network, as in the scrotum, prepuce, and perineum. The
straight running muscles are found, especially in the scalp and
in the axilla, both above and below the sweat-glands. Where
the muscles have a circular course, as in the areola of the nip-
ple, a continuous ring muscle is formed.
The majority of the muscles running in an oblique direc-
tion have a special relation to the hair-follicles. The muscle
arises from the internal sheath of the hair-follicle and passing
obliquely upward, skirting the lower surface of the sebaceous
gland, terminates in the upper part of the corium (Fig. 122, ri).
Occasionally two muscles, situated on opposite sides, arise
from a single hair-follicle sheath. A muscle in its course up-
ward frequently divides into two or more bundles, these sec-
ondary bundles afterward pursuing different directions from
each other, and sometimes uniting with fibres from other mus-
cles, form a network in the corium. Sometimes an entire
muscle, or a secondary bundle, passes upward into a papilla
of the cutis and is inserted into the dense fibrous connective tis-
sue directly beneath the rete Malpighii. Occasionally several
secondary bundles run nearly parallel with each other and ter-
minate either separately in the corium, or conjointly, after
uniting.
The skin is provided with other muscles which have no spe-
cial relation to the hair- follicles, but pass more or less verti-
cally upward from the subcutaneous tissue to be inserted in
the corium.
The number of muscles present in the skin varies in differ-
ent regions of the body. They are most numerous in the scro-
tum. The order of frequency in the different parts of the body
is as follows : Scrotum, penis, anterior part of perinseum, scalp,
288
MANUAL OF HISTOLOGY.
forearm, thigh, arm, shoulder, forehead, abdominal wall, ax-
illa, fore-leg, face, volar and dorsal surfaces of the hands and
feet (Neumann). They are less
developed on the flexor than on
the extensor surfaces.
The size of the individual mus-
cles varies according to the person
and the region of the body. It is
impossible, therefore, to recognize
with certainty a slight hypertro-
phy or atrophy of these structures.
For information as to their
blood, lymph, and nerve supply
see the article on unstriped muscle.
TJie Jiair. The parts to be
studied in connection with the hair
proper are the hair-follicle and
the hair-papilla. Tb e hair proper
is a cylindrical structure seated
within the hair-follicle and upon
the hair-papilla. Its base lies
embedded either in the subcuta-
neous connective tissue or in the
corium. The portion of the hair
proper within the follicle is called
the root of the hair, and the re-
mainder the shaft of the hair.
The true hair-follicle includes all
that part of the hair-sac below
the place where the sebaceous
duct enters the hair- follicle. It
is of very variable size and con-
sists of a blind extremity and a
funnel - shaped orifice (a). The
follicle is narrowed just below
this funnel-shaped orifice and
forms the so-called neck of the
hair-follicle (5). This is the nar-
rowest part of the follicle, and
is the place where the duct of the sebaceous gland enters.
From the neck downward the hair-follicle increases in size, be-
Fio. 122. Hair from beard : a, canal of
exit ; ft, neck of hair-follicle ; c, lower part of
hair-follicle : d, external sheath of hair-folli-
cle ; e, internal sheath of hair-follicle : /, ex-
ternal root-sheath of hair; gr, internal root-
Bheath of hair ; h, cortical substance ; k, me-
dulla of hair; /, root of hair ; m, fat-cells ; n,
arector pili ; o, papillae of skin ; p, papilla of
hair ; , rete mucosum ; t, sebaceous gland ;
ep, stratum corneum, which is continued into
the follicle. Biesiadecki.
THE SKIN. 289
ing largest at its lower end, where it rests upon the papilla.
Below the neck we have the follicle and the root of the hair.
The follicle consists, anatomically, of three layers : the ex-
ternal, middle, and internal hair-follicle sheaths.
The external sheath of the follicle (d) consists of connective-
tissue fibres, which extend from the upper corium and running
parallel to the long axis of the hair-follicle surround the base
of the latter and send some fibres into the papilla. The fibres
forming the inner portion of this sheath are arranged much
more closely than the fibres forming the external part. In this
latter situation there is no sharp dividing line between the
sheath and the surrounding loose connective tissue, the one
merging gradually into the other. Within this sheath run the
special blood-vessels and nerves of the hair-follicle.
The middle sheath of the follicle consists of a few transverse-
ly running connective-tissue fibres, between which lie oval nuclei
imbedded in a granular substance. Tliese latter, probably,
represent organic muscle-cells. This sheath begins at the neck
of the follicle and, surrounding its lower part, passes also within
the papilla. In this tissue is a close network of blood-capil-
laries. Nerves have not as yet been observed, though they
probably exist.
The internal sheath of the follicle is composed of a trans-
parent, homogeneous-looking structure the basement-mem-
brane, which is riot altered by the action of acids or alkalies.
It is merely a continuation of the transparent membrane found
between the rete mucosurn and the corium, which it resembles
in its structure. It contains neither blood-vessels nor nerves.
The external surface is smooth, but the internal surface has a
notched appearance, caused by prolongations inward between
the cells of the external root-sheath of the hair.
The hair -papilla is formed from the stroma of the hair-fol-
licle sheaths, especially from that of the middle sheath. It
consists of connective-tissue fibres, between which are found
numerous round cells. The internal follicle sheath separates
it from the root of the hair. Within the papilla are found
one or more arteries and veins besides non-medullated nerve-
fibres. The papilla has a narrow neck, a thicker body, and
a conical apex. It is, on an average, twice as long as it is
broad. The breadth is in direct proportion to the length of
the hair.
290 MANUAL OF HISTOLOGY.
The hair-follicles and hairs stand obliquely to the surface
of the skin. Their direction varies in different regions of the
body, and depends upon the structure of the connective tissue
of the corium and the degree of its tension. The contents of
the hair-follicles are the external and internal root-sheaths and
the hair proper.
The external root-sheath (/) adjoins the inner follicle sheath
and consists of rete cells continued into the hair-follicle from
the general rete mucosum layer of the skin. This sheath does
not extend as far as the lowest part of the follicle, generally
ending about on a level with the apex of the hair-papilla,
though it is sometimes continued as far as the base of the
latter. All the different kinds of cells present in the epi-
dermis are also found in this sheath as far down as the neck
of the follicle. Beyond this point the cells of the rete Mal-
pighii only enter into its formation. The number of rows of
cells forming it is subject to great variation. It diminishes
as the base of the follicle is approached, so that finally the
sheath is formed of a single row of cells. At the neck of
the follicle the sheath is usually narrower than directly above
or below this point, owing to the pressure to which the cells
are here subjected. Their form is very similar to that of
the corresponding cells of the rete mucosum. Those of the
deepest row are cylindrical, and those of the second row
polyhedral. In the other rows the cells are flatter, with the
exception of the most internal row, where all these bodies
are large and round. This last row is not subject to the same
changes as the others, and has been considered to be a distinct,
independent row of cells (Unna). The nuclei of all the cells
color strongly in carmine, haematoxylon, etc. Nerve-fibres have
been described as running between the cells of this sheath
(Langerhans).
The internal root-sheath (g) lies in direct contact with the
external root-sheath. It is usually described as consisting of
two layers, an external one, also called the sheatli of Henle,
and an internal one, or slieath of Huxley. Strictly speak-
ing, this division into two sheaths is incorrect, as it has been
shown (Unna) that the two sheaths supposed to be distinct
have a common origin from the cylindrical epithelial cells sur-
'rounding the neck of the hair-papilla at its lowest part. These
cells color very deeply in carmine. They surround the root of
THE SKIN. 291
the hair like a sheath. In the thick hairs of the beard the
sheath consists of three rows of cells the external row, after-
ward forming Henle's sheath, and the two inner rows of cells,
the sheath of Huxley. In finer hairs there are only two layers of
such cells. These corpuscles are originally similar in structure,
having a very granular appearance and an indistinct nucleus.
The sheath is thinnest where the hair-papilla is broadest.
The cells of the external layer (Henle's) become paler and lose
their nuclei earlier than those of the inner layer, so that on a
level with the upper part of the papilla there is a marked dif-
ference in the appearance of the two layers of cells. Formerly
it was supposed (Biesiadecki) that Henle's sheath commenced