glands; while on the vestibule, around the meatus urinarius and around the entrance of the vagina, there is an abundance of racemose mucous glands, opening on the surface of the membrane by shorter and longer ducts. The glands of Bartholine are common racemose mucous glands, nearly half an inch in diameter, and made up of pyriform glandular vesicles, lined by squamous epithelium, and surrounded by a dense nucleated areolar tissue. Their excretory ducts, more than half an inch in length, are invested by columnar epithelium, and surrounded by a thin layer of smooth-muscle cells, disposed longitudinally. The secretion of these glands is a clear, yellowish, viscous mucus.

Vessels and Nerves. The external organs of generation are abundantly supplied with arteries, chiefly by the internal pudic; they terminate in a deep and superficial capillary plexus, as in other mucous membranes. Valentin has described helicine arteries in the clitoris. The veins returning the blood from the capillaries form a rich plexus, which is especially abundant in the bulbi vestibuli of Kobelt. The lymphatics are numerous, and communicate partly with the inguinal and partly with the pelvic glands. The nerves are derived partly from the hypogastric plexus and partly from the sacral plexus.

MAMMARY GLANDS.

The Mamma are situated in the pectoral region, and are separated from the pectoralis major muscle by a thin layer of superficial fascia. Their base is somewhat elliptical, the long diameter corresponding with the direction of the fibres of the pectoralis major muscle; and the left mamma is generally a little larger than the right. They exist in the male, but in a rudimentary state, unless excited into growth by some peculiar or morbid action, such as the loss or atrophy of the testes.

Near the centre of the convexity of each mamma is a small prominence of the integument, called the nipple (mamilla), which is surrounded by an areola

[FIG. 391.

having a colored tint. In females of fair complexion before impregnation, the color of the areola is a delicate pink; after impregnation, it enlarges and assumes a brownish hue, which deepens in color as pregnancy advances; and after the birth of a child, the brownish tint continues through life.

The areola is furnished with a number of sebiparous glands, which secrete a peculiar fatty substance for the protection of the delicate integument around the nipple. During suckling these glands increase in size, and have the appearance of small pimples, projecting from the skin. At this period they serve by their secretion to defend the nipple and areola from the excoriating action of the mouth of the infant.

In structure, the mamma is a compound racemose or conglomerate gland, consisting of lobes, lobules, and gland-vesicles. The lobes, from 15 to 25 in number, have each a separate system of lobules and gland-vesicles, and a distinct excretory duct; hence, the mamma may be regarded as being composed of a number of separate glands, their ex 1, 1. Galactophorous ducts. 2, 2. cretory ducts converging to the mamilla, and termiLc buli.] nating at its extremity by distinct apertures. The lobes are irregular in size and form, flattened, and bounded by rounded angles; they are made up of smaller lobes or lobules,

and the lobules of other lobules still more diminutive, the smallest lobules consisting of round or pyriform gland-vesicles.

The gland-vesicles, about of an inch in diameter, are composed of a structureless membrane, or membrana propria, lined with an epithelium of spheroidal nucleated cells. The gland-vesicles communicate with an excretory duct, and the excretory ducts of all the lobules unite to form a common excretory duct or canal for each lobe, ductus lactiferus, ductus galactophorus. The ductus lactiferus taking its course beneath the areola, dilates into an elongated sac or ampulla, sacculus vel sinus lactiferus, and reaching the base of the mamilla, . contracts in size and bends outwards into that process to terminate at its extremity by a small aperture. At the point of escape from the lobe, the lacteal duct measures from one to two lines in diameter; the lacteal sac is double that size: within the mamilla the duct measures between half a line and a line, and the excretory aperture about one quarter of a line. There are from 15 to 25 ducts in the nipple, a number corresponding with the number of lobes composing the gland.

The gland-vesicles are held together by a dense white areolar tissue, which unites the lobules into lobes, and connects the different lobes with each other, forming a covering for the whole, and being itself surrounded with adipose tissue. The lactiferous ducts are composed of areolar tissue, which is homogeneous internally, and fibrillated and nucleated and mingled with elastic fibres. externally. Moreover, according to Henlé, there is an indication of longitudinal smooth muscular fibre. The fibrous coat of the lactiferous tubes is plaited, and their interior lined by a columnar epithelium.

The mamilla or nipple is covered by a thin epidermis, presenting more or less pigment in its rete mucosum; it possesses at the extremity a number of papillæ, between which are the lactiferous openings, and it is composed internally of the lactiferous ducts, united together and surrounded by areolar and smooth muscular tissue, the latter giving the nipple the faculty of erection and retraction. The integument of the areola, besides possessing a colored epidermis with numerous large sudoriparous and sebiparous glands, the latter associated with fine hairs, is also provided with a layer of smooth muscular fibre, which gives it a power of contraction.

[FIG. 392.

The secretion of milk is effected by the formation of oil-globules in the epithelial cells of the gland-vesicles; the epithelial cells being perfected, are pushed outwards and displaced by a new layer of similar cells which form beneath them; they are thus carried forwards into the lacteal ducts, where the cell bursts and gives exit to its oilglobules, now become milk-globules; and the cell-membrane and nucleus are lost. These milk-globules suspended in a fluid, the milk-plasma, constitute the milk. Previously to conception, the mammæ only secrete a yellowish viscid mucus, and at the commencement of lactation the milk is imperfect and termed colostrum, having entering into its composition a number of cells filled with yellow fat-globules, named colostrum-corpuscles.

MILK. Milk-globules and colostrum-cor puscles, the latter being the largest.]

The mammary gland of the male is rudimentary; it varies in size from a quarter of an inch to two inches in breadth, by one to three lines in thickness.

It is firm in texture, presents no division into lobes, and its ducts are small without dilatations, and terminate in gland-vesicles larger than those of the female.

The development of the mammary gland commences at the fourth or fifth month of embryonic life, at first by a papilla of the rete mucosum, which subsequently gives off primary and secondary branches; the papilla and its branches are for a time solid, but as development advances they become hollow and invested externally by a fibrous membrane. At birth the gland measures between two and four lines in breadth, and presents from twelve to fifteen lobular divisions, and then goes on gradually, but very slowly, increasing in bulk. True gland-vesicles do not make their appearance until the period of menstruation, and are not fully developed throughout the entire gland until the first pregnancy. After the period of child-bearing, the gland gradually degenerates, the gland-vesicles disappear, and in old age the organ passes into a state of atrophy, the ducts, with their epithelium in a state of fatty degeneration alone remaining, surrounded by a cushion of fat which takes the place of the glandular tissue.

Vessels and Nerves. The mammæ are supplied with Arteries from the thoracic branches of the axillary, the intercostals, and internal mammary; having entered the substance of the gland they divide into capillaries, which constitute a close network around the gland-vesicles. The Veins form an incomplete circle around the base of the nipple, circulus venosus Halleri, from which larger veins conduct the blood to the circumference of the gland, and by these communications form a plexus on its surface. They terminate in the axillary vein, internal mammary, intercostals, and jugular veins.

The Lymphatics are abundant in the integument covering the mamma, but have not yet been observed in the structure of the gland; they take the course of the veins, inwards, to the anterior mediastinal glands; and outwards along the border of the pectoralis major to the axillary glands.

The Nerves of the mammary gland are derived from the anterior cutaneous branches of the second, third, and fourth intercostal nerves; and from the lateral cutaneous branches of the same nerves.

CHAPTER XII.

ANATOMY OF THE FETUS.

THE medium weight of a child of the full period, at birth, is seven pounds, and its length seventeen inches; the extremes of weight are four pounds and three-quarters, and ten pounds; and the extremes of measurement fifteen and twenty inches. The head is of large size, and lengthened from before backwards; the face small. The upper extremities are greatly developed, and the thorax expanded and full. The upper part of the abdomen is large, from the great size of the liver; the lower part is conical and small. And the lower extremities are diminutive in proportion to the rest of the body. The external genital organs are large, and fully developed, and the attachment of the umbilicus is one inch further from the vertex of the head than from the soles of the feet; and one inch further from the ensiform cartilage than from the symphysis pubis.

OSSEOUS SYSTEM. of in the first chapter.

-The development of the osseous system has been treated

The LIGAMENTOUS SYSTEM presents no peculiarity deserving of remark.

MUSCULAR SYSTEM. - The muscles of the foetus at birth are large and fully formed. They are of a lighter color than those of the adult, and of softer texThe transverse striæ on the fibres of animal life are not distinguishable until the sixth month of foetal life.

ture.

VASCULAR SYSTEM. The circulating system presents several peculiarities: 1stly, in the heart; there is a communication between the two auricles by means of the foramen ovale. 2ndly, in the arterial system; there is a communication between the pulmonary artery and arch of the aorta, by means of a large trunk. the ductus arteriosus. 3rdly, also in the arterial system; the internal iliac arteries, under the name of hypogastric and umbilical, are continued from the foetus to the placenta, to which they return the blood which has circulated in the system of the foetus. 4thly, in the venous system; there is a communication between the umbilical vein and inferior vena cava, called the ductus venosus.

FETAL CIRCULATION.

The pure blood is brought from the placenta by the umbilical vein. The umbilical vein passes through the umbilicus, and enters the liver, where it

FOTAL CIRCULATION. 1. Umbilical cord, consisting of umbilical vein and two umbilical arteries; proceeding from the placenta (2). 3. Umbilical vein, dividing into branches; two (4, 4), to be distributed to the liver; and one (5), the ductus venosus, which enters the inferior vena cava (6). 7. Portal vein, returning the blood from the intestines, and communicating with the right hepatic branch. 8. Right auricle; the course of the blood is denoted by the arrow, proceeding from 8, to 9, the left auricle. 10. Left ventricle; the blood following the arrow to the arch of the aorta (11), to be distributed through the branches given off by the arch to the head and upper extremities. The arrows 12 and 13, represent the return of the blood from the head and upper extremities through the jugular and subclavian veins, to the superior vena cava (14), to the right auricle (8), and in the course of the arrow through the right ventricle (15), to the pulmonary artery (16). 17. Ductus arteriosus, which appears to be a proper continuation of the pulmonary artery; the offsets at each side are the right and left pulmonary artery; these are of extremely small size as compared with the ductus arteriosus. The ductus arteriosus joins the descending aorta (18, 18), which divides into the common iliacs, and these into the internal iliacs, or hypogastric arteries (19), and return the blood along the umbilical cord to the placenta; while the other divisions, the external iliacs (20), are continued into the lower extremities. The arrows at the terminations of these vessels mark the return of the venous blood by the veins to the inferior cava.

divides into several branches; two or three of these branches are distributed to the left lobe; one branch communicates with the portal vein in the transverse

fissure, and supplies the right lobe; and a large branch, the ductus venosus, passes directly backwards, and joins the inferior vena cava. In the inferior cava the pure blood becomes mixed with that which is returning from the lower extremities and abdominal viscera, and is carried through the right auricle (guided by the Eustachian valve) and through the foramen ovale, into the left auricle. From the left auricle it passes into the left ventricle, and from the left ventricle into the aorta, whence it is distributed by means of the carotid and subclavian arteries, principally to the head and upper extremities. From the head and upper extremities, the impure blood is returned by the superior vena cava to the right auricle; from the right auricle, it is propelled into the right ventricle; and from the right ventricle into the pulmonary artery. In the adult, the blood would now be circulated through the lungs, and oxygenated; but in the foetus the lungs are solid, and almost impervious. Only a small quantity of blood passes therefore into the lungs; the greater part courses through the ductus arteriosus, into the commencement of the descending aorta, where it becomes mingled with that portion of the pure blood which is not sent through the carotid and subclavian arteries.

Passing along the aorta, a small quantity of this mixed blood is distributed by the external iliac arteries to the lower extremities; the greater portion is conveyed by the internal iliac or hypogastric, and umbilical arteries to the placenta; the hypogastric arteries pass forwards by the side of the fundus of the bladder, and upwards along the anterior wall of the abdomen to the umbilicus, where they become the umbilical arteries.

From a careful consideration of this circulation, we perceive—

1st. That the pure blood from the placenta is distributed in considerable quantity to the liver, before entering the general circulation. Hence arises the abundant nutrition of that organ, and its enormous size in comparison with other viscera.

2dly. That the right auricle is the scene of meeting of a double current; the one coming from the inferior cava, the other from the superior, and that they must cross each other in their respective course. How this crossing is effected, a cursory examination of the foetal heart will show; for the direction of entrance of the two vessels is so opposite, that they may discharge their currents through the same cavity without admixture. The inferior cava opens almost directly into the left auricle; and, by the aid of the Eustachian valve, the current in the inferior cava is almost entirely excluded from the right auricle.

3dly. That the blood which circulates through the arch of the aorta comes directly from the placenta; and, although mixed with the impure blood of the inferior cava, yet is propelled in such abundance to the head and upper extremities, as to provide for the increased nutrition of those parts, and prepare them, by their greater size and development, for the functions which they are required to perform at the instant of birth.

4thly. That the blood circulating in the descending aorta is very impure, being obtained principally from the returning current in the superior cava; a small quantity only being derived from the left ventricle. Yet it is from this impure blood that the nutrition of the lower extremities is provided. Hence we are not surprised at their insignificant development at birth; while we perceive the providence of nature, which directs the nutrient current, in abundance, to the organs of sense, prehension, and deglutition, organs so necessary, even at the instant of birth, to the safety and welfare of the creature.

After birth, the foramen ovale becomes gradually closed by a membranous layer, which is developed from the margin of the opening from below upwards, and completely separates the two auricles. The situation of the foramen is seen in the adult heart, on the septum auricularum, and is called the fossa ovalis; the prominent margin of this opening is the annulus ovalis.

As soon as the lungs have become inflated by the first act of inspiration, the