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placed one at each side on the front of the thorax. A little below the centre of
each breast, on a level with the fourth rib, or slightly lower, projects a small
cylindrical or conical body named the nipple (mamilla}, which points somewhat
upwards and outwards. Each gland is situated in the superficial fascia, and extends,
in a vertical line passing through its nipple, from the second to the sixth or seventh
rib, and in a horizontal line, through the same structure, from a little internal to


(from Luschka).

a, a, a, undissected part of the mamma ; 1, the mamilla ; 2, areola ; 3, subcutaneous masses of
fat ; 4, loculi in the connective tissue which supports the glandular substance ; 5, three lactiferous
ducts passing towards the mamilla where they open ; 6, one of the sinuses or ampulla? ; 7, some of
the glandular lobules which have been unravelled ; 7', others massed together.

the lateral border of the sternum opposite the fourth costal cartilage to the fifth
intercostal space opposite the mid-axillary line, 1 and measures some 4^ inches
(112 mm.) from above down; about 5 inches (128mm.) across ; and about 2 inches
(54 mm.) thick. The average weight of each gland in the virgin is from 150 to
200 grammes ; in the nursing woman from 400 to 500 grammes (Testut).

Structure of the nipple. The surface of the nipple is dark, and around it
there is a coloured circle or areola,, within which the skin is also of a darker tinge
than elsewhere. In the virgin, these parts are of a rosy pink colour, differing some-
what according to the complexion of the individual, but they are always darker in
women who have borne children. Even in the second month of the first pregnancy,
the areola begins to enlarge and acquire a darker tinge ; these changes go on

1 The lateral extension of the mammary gland given above is based upon the observations of
Stiles, Edin. Med. Journal, 1892.



increasing as gestation advances, and are regarded as signs to be relied on in
judging of suspected pregnancy. After lactation is over, the dark colour subsides,
but never entirely disappears. The skin of the nipple is marked with many
wrinkles, and is covered with papillae ; besides this, it is perforated at the tip by

Fig. 295. TRANSVERSE SECTION OF THE NIPPLK. (Testut, after de Sinety.)

a, sections of galactophorous ducts, with, e, columnar epithelium : b, connective tissue ; m, m! , plain
muscular fibres cut longitudually and transversely respectively ; v, bloodvessels.

numerous foramina, which are the openings of the lactiferous ducts ; and near its
base, as well as upon the surface of the areola, there are scattered rounded elevations,
which are caused by the presence of well-marked sebaceous glands with branched
ducts four or five of which open on each elevation. The sudoriparous glands of
the areola are also large and much convoluted, but there are no sudoriparous glands
in the nipple proper nor are there any hair follicles here. The tissue of the nipple
contains a large number of vessels together with much plain muscular tissue, and its
papillae are highly sensitive ; it becomes firmer and more projecting from mechanical
excitement, a change caused by contraction of the muscular fibres, which form
concentric circles round the base of the nipple and radiating bands running from
base to apex.

Structure of the mamma. The mamma is composed of glandular tissue,
supported by a connective tissue stroma in which the blood-vessels, lymphatics and
nerves ramify. It also comprises a greater or less amount of adipose tissue. The
relative amount and distribution of these constituents varies considerably according
to the age of the individual, and whether the gland is, has been, or has not been,
functionally active. In the adult nullipara the gland is usually a firm conical mass
with its apex at the nipple. This part is called the corpus mammce ; from it peri-
pheral processes extend in various directions. Under the nipple and areola the
stroma is entirely devoid of fat, but towards the circumference a few fat lobules may
be embedded in it. The anterior surface of the gland is convex, but uneven, owing
to the presence of numerous irregular processes passing towards the skin, with which



some of them are united by bands of connective tissue, the so-called ligaments of
Cooper. Lobules of fat occupy the intervals between these processes. The posterior



The specimen was kept for 2 days in a 5 p. c.
solution of nitric acid, then washed in water and
preserved in methylated spirit.

N, nipple ; s, skin ; L.C, ligament of Coopei
connecting a process of the gland with the skin :
P.P, peripheral processes ; F.L., fat lobules ; P.M,
pectoralis major muscle.

surface of the gland is flat or slightly con-
cave, and much more even than the anterior,
as the corpus mammae is bounded here by a
smooth compact layer of gland tissue.
Delicate glandular processes do, however,
extend from this aspect into the retro-
mammary tissue, reaching close to the
subjacent muscles and even, according to
Heidenhain, passing into the pectoralis
major. The upper and inner portion of
this surface, comprising about two-thirds
of its whole extent, lies upon the pectoralis
major; external to this muscle the posterior
surface rests on the axillary fascia which
separates it from the serratus magnus, and
lower down it is in relation with the digi-
tations of the serratus magnus and external
oblique which arise from the fifth and
sixth ribs (Stiles). The edges of the
mamma are not sharply defined as, at its
periphery, the corpus mammas breaks up
into numerous irregular processes which
branch and unite to form a reticular
formation enclosing lobules of fat. The
stroma of the peripheral processes, where
the gland tissue ceases, becomes directly
continuous with the connective tissue
framework of the adjacent fat lobules.
At puberty the gland appears on external
examination to be well developed, but it
really consists mainly of stroma and excre-
tory ducts, the true secreting acini being
few in number. During lactation the
gland tissue proper undergoes a marked
development, and the stroma is relatively
reduced in amount, so that on section the
gland presents to the naked eye a close
resemblance to a salivary gland. After the period of functional activity is ended
the gland returns by a process oi involution to its resting stage, but it does not
regain the appearances it exhibited before pregnancy. Thus the corpus mammae
is less distinct, and its stroma is looser and contains numerous fat lobules, while





the peripheral processes are larger and have a more extensive distribution. A layer
of fat of greater or less thickness is now found between the gland and the deep fascia.


SHOWN IN KIG. 296. (Stiles.) {

M.S, sinus or ampulla of milk duct ; R.M.F,
retromammary fat ; other letters as in tig. 296.'

After the menopause the appearance
of the gland varies according to the
general condition of the subject. Thus
in thin women it forms a somewhat
flattened disc which comes into close
relation both with the skin and the
subjacent muscles, while in obese
women the mamma is composed mainly
of fat, the stroma investing the paren-
chyma forming a wide open meshwork,
except in the immediate vicinity of the

The glandular substance of the
mamma consists of numerous distinct
lobes, twelve to twenty in number, held
together by firm intervening fibrous or
areolar tissue, and having adipose tissue
penetrating between them. Each of
these lobes is provided with an excre-
tory duct, and is subdivided into smaller
lobes, and these again into the lobules
which are beset with the alveoli. Each
lobe is practically a distinct gland,
although the lobes come into close
contact with one another. Sometimes,
besides the principal lobes, small acces-
sory lobes or glands are met with near
the base of the nipple. The lobules are
separated from one another in the human
subject by a large quantity of areolar
tissue (fig. 298). The interlobular tissue
contains numerous plasma-cells. The
substance of the lobules is of a pale
reddish cream-colour, contrasting with
the adjacent fat, and is rather firm.
The excretory ducts, named the galacto-
phorous ducts, are, like the lobes, about
twenty in number ; they converge
towards the areola, beneath which they
become considerably dilated, especially
during lactation, so as to form ampulla
-or sinuses about 12 mm. long and mm. wide (fig. 294, G), which serve as small
temporary reservoirs for the milk. At the base of the nipple all these ducts, again
reduced in size, are assembled together, those in the centre being the largest, and



then proceed, side by side, surrounded by areolar tissue and vessels, and without
communicating with each other, to the summit of the mamilJa, where they open
by separate orifices ; these orifices are seated in little depressions, and: are smaller
than the ducts. The walls of the ducts are composed of areolar tissue, with longi-

a, lobule of gland ; I, acini lined by cubical epithelium ; c, duct ; t, connective tissue stroma.

tudinal and circular elastic fibres but without muscular tissue. The membrana
propria of the alveoli is described as consisting of a homogeneous membrane having
stellate and anastomosing cells upon its inner surface next to the epithelium.



a, b, section through the middle of two alveoli at the commencement of lactation, the epithelium
cells being seen in profile ; c, part of the wall of an alveolus in a similar condition with the epithelium
cells seen flat ; d, an alveolus in full secretory activity.

Both the alveoli and the ducts are lined with a simple layer of epithelium, which
is flattened in the alveoli and in the lobular ducts ; cubical in the larger ducts and
columnar in the excretory ducts and ampullae. Near the external openings on the
nipple it becomes scaly stratified.

The epithelium differs in its appearance according to the state of activity of the
gland. When entirely inactive the alveoli are very small, and the epithelium cells

VOL. III., PT. 4. U


small and granular. At the commencement of lactation the alveoli enlarge and
become distended with clear secretion (fig. 299, a, Z>) ; the cells are flattened out
against the membrana propria and contain fat globules of varying size and in the
fluid contents of the alveoli besides similar fat globules, some of which have a
partial surrounding of protoplasm, a few uni- or multi-nucleated granular cells are
seen. During full activity the cells become cubical or even columnar, but are
irregular in size and exhibit indications of division and of budding off into the
interior of the alveoli (fig. 299, d). By the breaking down of parts of the cells
which have thus become free in the alveoli the constituents of the milk appear to be
formed, the fat globules which were present within the cells becoming suspended in
the fluid of the alveoli as milk globules, and the albuminous constituents of the cells
becoming dissolved and forming the casein and other proteid substances of the milk.

There is a rich network of blood-capillaries investing the alveoli, and the alveoli
are surrounded by sinus-like lymphatics, as in other racemose glands.

In the adult male the mammary gland and all its parts exist, but quite in a
rudimentary state, the gland itself measuring only from half to three-quarters of an
inch across, and one-sixth of an inch thick. Occasionally the male mamma,
especially in young subjects, enlarges and gives out a thin watery fluid ; and, in
rare cases, it has secreted milk.

Blood-vessels, Lymphatics, and Nerves. The arteries which supply the
mammary glands are the long thoracic and some other branches of the axillary artery,
the internal mammary, and the subjacent intercostals. The veins have the same
denomination. Haller described a sort of anastomotic venous circle surrounding
th.3 base of the nipple as the circulus venosus. The lymphatics within tbe
mammary gland form plexuses in the connective tissue around the alveoli and ducts.
There are also lymphatics which accompany the blood-vessels in the gland, and, as
elsewhere, the smaller blood-vessels have usually a single accompanying lymphatic
vessel of much larger calibre than the artery itself, while the sheaths of the larger
vessels contain two or three lymphatics (Stiles). These perivascular lymphatics
communicate freely with those around the lobules and ducts of the gland. In addition
to the iniramammary lymphatics there are four other sets of vessels connected with
the mammary lymphatic system, viz., cutaneous, subareolar of Sappey, circummam-
mary, and retromammary . The lymphatics from the inner part of the gland pass with
the perforating branches of the internal mammary artery to join the small sternal
glands situated along the course of this vessel. On the outer side of the gland the
vessels are much larger and unite to form two or three principal trunks which pass to
lymphatic glands in the axilla. The nerves proceed from the anterior and lateral
intercostal cutaneous branches. They pass partly to the glandular substance and blood-
vessels, partly to the skin. In the nipple many of them end in tactile corpuscles
within the papillae, and some of those in or near the areola enter Pacinian corpuscles.

Varieties. Entire absence of both glands and nipples is very rare ; a few such instances,
however, are recorded in otherwise normally developed individuals. Thus "Wylie met with a
case in a woman, aged twenty-one years. A small mole existed where the right nipple is
normally situated. Batchelor describes a similar condition in an adult female, but in this
instance the usual position of each nipple was occupied by a small area of pigmented skin.
In a boy three-and-a-half years old J. Hutchinson found complete absence of both mammary
glands, associated with absence of hair and an atrophic condition of the other integumentary
appendages. Absence of one mammary gland is almost as uncommon as that of both, and is
usually associated with an imperfect development of the thoracic wall on the same side. The
glands themselves may be well formed, but the nipples absent. Such cases are of interest in
connection with the fact that in the ornithorhynchus there are no nipples, the mammary
secretion being discharged on to a plane surface ; further in the development of the
mammary gland the papillary elevation of the skin giving rise to the nipple is secondary to
the epithelial downgrowth from which the gland itself is formed.

In the majority of mammals more than two glands are normally present, indeed in some
of the Insectivora there are as many as eleven pairs. It has been shown by 0. Schultze that


in the embryo of various mammals, such as the cat, rabbit, and mole, a line of thickened
epithelium is formed on each side of the trunk extending from the axilla downwards and
inwards to the groin. It is in this situation that the mammary glands are usually developed
in polymastic mammals, and in the great majority of cases of additional glands in" the human
subject they are found in a corresponding position and may be designated axillary, pectoral,
abdominal, inguinal or vulval mammas. The supernumerary mammary structures are usually
represented by the nipple only, but in some cases the glandular tissue is well developed and
may be functionally active. Most of the cases of additional mammae appear, on one or both
sides, just below and internal to the normal pair. The largest number of additional glands
that has hitherto been recorded is eight. In this instance, which was described by Neugebauer
in a woman aged twenty-three, there were three pairs of nipples above the normal
ones, and one pair below. It is probable that in this case, as Roger Williams suggests,
the two nipples below the normal pair did not represent a pair of glands, but single
examples of two pairs, as the right one was some inches higher up than the left. If such
be the case there were representatives of six pairs of glands in this woman. Ammon
has described a case of three additional pairs of nipples in a man aged twenty-two
years. One pair was placed above the normal nipples on the anterior folds of the axilla?,
another near the lower margin of the chest wall, and the lowest on the anterior wall
of the abdomen above the level of the umbilicus. Bardeleben concludes from his most
recent investigations that the normal pair of glands represents a persistence of the sixth pair
counting from above downwards. Various cases of mammary glands appearing in the axilla
during pregnancy have been regarded as examples of excessive development of the cutaneous
glands of that region, or of a more or less complete separation of that process of the normal
gland which extends into the axilla. A few cases have been recorded of mammary glands
(inamm-ee erraticce) being found over the acromion process, on the upper part of the thigh, or
even on the back. Sometimes two or more nipples occur on one gland.

Milk. The milk is characterized by containing an immense number of fat-globules of
varying size but averaging from -,2600^ to sobo^h ^ an ^ ncn i n diameter. They appear to be
coated with an exceedingly thin investment of albuminous substance, probably casein, which
prevents them from running together into larger drops, but when this is dissolved by the
addition of an acid, they readily blend with one another. Rarely there is a more distinct


a, b, colostrum-corpuscles with fine and coarse fat globules respectively ;
c, d, e, pale cells devoid of fat globules.

envelope of granular substance, occasionally containing a nucleus,
and free nuclei have also been described as existing to a small extent
in the milk.

The mammary gland before and during the first two or three days after parturition yields
a small amount of a turbid fluid termed the colostrum. This contains besides milk-globules
single and in groups, amoeboid cells, containing small or large fat-globules, either closely
packed within the cell, or but few in number, and sometimes absent altogether : in the latter
case permitting the nucleus to be visible (fig. 300). These amoeboid cells are known as the
" colostrum-corpuscles " (" granular corpuscles " of Donne) : they occur either not at all or but
very rarely, when the gland is in full activity. It is uncertain whether they originate as
separated epithelium cells of the alveoli, or whether they are emigrated white corpuscles.

Development of the Mammary Gland. The first sign of the gland shows itself at
the end of the second month in the human embryo in the shape of a thickening and
downgrowth of the rete mucosum of the epidermis at the site of the future nipple. The
thickening spreads laterally so as to correspond with a small area (mammary area)
which soon becomes sunk below the general surface. From the thickened rete mucosum of
this area special outgrowths of the epithelium into the cutis vera occur, one for each of the
lobes of the future gland. These outgrowths, as with other racemose glands, become branched,
and their branches end in enlargements. The formation of these sprouts goes on until birth,
but the development of glandular alveoli from them does not occur until the approach of
puberty in the female, and in the male not at all. The projection of the nipple from the rest
of the mammary area does not begin until about the first year after birth ; within it a large
amount of plain muscular tissue becomes formed. The remainder of the mammary area
becomes the areola.

The subsequent growth of the gland is comparatively tardy. At the third or fourth year
of infancy, there is little or no difference in male and female children. The fuller develop-
ment of the gland in the female occurs only towards puberty. It is probable that during the
later period of pregnancy, not only do the alveoli increase in size, but new alveoli may bud
laterally from the pre-existing ones, and that after lactation some of the alveoli may become
atrophied and disappear.

u 2



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die Richtung der Korperhaare auf der Brust, Mitgetheilt in R. Weidersheim : Der Bau des Menschen
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Coen, Edmcmclo. Bcitrdyc zur normalcn und pathologischcn Histologic dcr MUchdriise,
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