The study of obstetrics is an investigation of the passage, the passenger, and the driving powers of labor, as well as of the various complications and anomalies that may attend the process of reproduction.

The passage is composed of a bony canal, called the pelvis, and the soft tissues which line and almost close its outlet.

The pelvis is made up of four bones; the sacrum, the coccyx, and two other large structures of irregular shape, called the hip, or innominate bones. Joined by cartilage and held in place by ligaments, they form a cavity or basin which, in the male is deep, narrow, small and funnel-shaped, while in the female, slighter bones, expanded openings and wider arches make a broad, shallow channel, through which the child is born.

The bony pelvis is divided for description into two parts, the upper or false pelvis, and the lower or true pelvis. The upper pelvis is formed by the wings of the innominate bones and has but two functions of importance to child-bearing. It acts as a guide to direct the child into the true passage, and when measured by the pelvimeter, it gives information as to the shape and size of the inlet to the true pelvis. The true pelvis is of most concern to the obstetrician, because anomalies in its size or shape may impede the progress of labor or render it impossible. The pelvis is divided conveniently into three parts: the brim, the outlet, and the cavity.

The brim, inlet, or upper pelvic strait, is the boundary line between the false and true pelvis. It is traced from the upper border of the symphysis along the iliopectineal line on both sides to the promontory of the sacrum. The shape and size of this opening varies much in different races and individuals, both normally and through disease; and when pathologically altered, both shape and size may exercise a marked influence on the course of labor. In American women, the outline of the brim is roughly heart-shaped, like an ovoid with an indentation where the promontory of the sacrum impinges upon the opening.

The brim or inlet has four important diameters to be remembered; important because the hard, round head of the child must pass through them by accommodating its diameters as favorably as possible to those of this opening. These diameters are named respectively the anteroposterior or conjugate diameter, the transverse, and the right and left oblique diameters. The two oblique diameters attain their greatest importance when the pelvis is irregularly distorted, but the others are essential in every case where labor impends. It is to secure an estimate of these latter diameters that the bony prominences are measured. This upper opening lies not horizontally, but in oblique relation to the body in standing position, and the weight of the abdominal viscera rests largely upon the bones and in consequence does not crowd into the inlet unless forced in by corsets or faulty habits.

Passing through the brim, a cavity is found below it, midway between the inlet and outlet, which is nearly round in shape. This is the “excavation,” or the true pelvis. Then comes the outlet, bounded in front by the pubic arch and soft parts, and behind by the coccyx pushed back as far as it can go. It is ovoid in shape, but the long axis of this ovoid lies at right angles with the axis of the ovoid inlet.

We find, therefore, a succession of three geometric figures or planes through which the head must pass by means of a spiral motion called rotation. These figures are inclined to one another so markedly in front that a line drawn through the center of each will curve forward at both ends, one end passing out near the umbilicus, the other through the vulva. This is known as the axis of the pelvis or the curve of Carus.

THE SOFT PARTS

Inside the pelvis are the organs of generation with their accessory structures and supporting tissues.

Of first importance are the ovaries, tubes and uterus, together with the vagina. These special structures are the true genital organs. They are bounded in front by the bladder, behind by the rectum, above by the abdominal viscera, and surrounded everywhere by muscular, mucous and fatty tissues, which support them and aid their function.

The Vagina.—The vagina is a hollow organ, about four inches long, attached to the cervix above and the vulva below. It is an elastic sheath bounded in front by the bladder and behind by the rectum. Under normal conditions, this tube easily admits one or two fingers, but during labor it dilates enormously to allow the head to pass. The vagina is lined with a thick mucous membrane, ridged and roughened by folds, which are called rugÆ. Thus a continuous channel connects the ovary with the outside and through it pass, at appropriate times, the ovule, the menstrual blood, the uterine secretions, the child, the placenta, and the lochia.

The Uterus.—The uterus (womb) is a pear-shaped organ, flattened from before backward, and composed of unstriped or involuntary muscle cells and connective tissue. Normally the virgin uterus measures from two and one-half to three inches in length, and weighs about two ounces. It is suspended in the middle of the pelvis by strong ligaments, so that the fundus inclines gently forward against the bladder. When the bladder fills, the uterus is pushed backward. Most of the organ is internal, but a small part of the lower pole is grasped by the vagina, in which the lower end with its invaluable aperture, the os, dips and swings. The part above the vagina is called the body or fundus, and is covered with the serous membrane (peritoneum) that lines the abdominal cavity. Below the fundus is the cervix or neck, which lies partly above and partly within the vagina. The cavity of the uterus is usually closed by the apposition of the walls. The inner surface is covered with a peculiar kind of membrane called the endometrium, which is highly vascular. The uterine cavity opens into the vagina through the os, which is small and round in the nulliparous woman, and slit-shaped or gaping in the woman who has borne a child.

Fallopian Tubes.—On either side of the upper end of the uterus are the orifices of the Fallopian tubes, through which the egg, escaping from the ovary, finds access to the uterine cavity. These tubes extend outward from the uterus about four inches, and terminate in a bell-shaped opening with long, ragged fingers which hang loosely down toward the ovary. The tubes are lined by epithelial cells having hair-like projections, (ciliÆ) which wave automatically toward the uterus. Thus impelled by a gentle current, the egg moves definitely along the tube toward the uterus and against this current the spermatozoa force their way to meet and fertilize the egg.

The Ovaries.—On either side of the pelvis, close to the fringed end of the Fallopian tube and attached to it, lies a small, hard, almond-shaped organ, called the ovary. This is the intrinsic sexual gland of the female. It contains the small cells which are to ripen and become eggs. Each ovary is said to contain about thirty-six thousand eggs, or ovules.

The Bladder.—The bladder lies between the pubic bone and the uterus. It is a reservoir for urine, filled by means of two little tubes called ureters, that run down from the kidneys. It drains through the urethra which opens just below the pubic bone in front of, and just above, the vaginal opening. The bladder should be emptied frequently during labor.

The Anus.—The large bowel (colon) terminates in an opening near the middle of the genital crease. This opening is called the anus. It is closed by a contracting muscle, the sphincter, which acts like a puckering string. Just inside of the opening is a group of large veins which may become enlarged, inflamed, and bleed during pregnancy. They are then called hÆmorrhoids.

The Rectum.—Upward from the anus and to the left of the uterus extends the rectum. This is the end of the intestinal canal and is supplied with an abundance of nerves. When the head presses upon it, it gives the sensation of a bowel movement, and warns the observer of the low position of the head. The anus pouts as the head comes down and the anterior walls become visible. In severe cases of labor, the sphincter is sometimes torn. The bowels should be emptied by an enema as early as possible in the first stage of labor.

The Peritoneum.—The peritoneum is a thin, glistening, serous membrane, which lines the abdominal cavity and drops down from above over the uprising tops of the bladder and uterus. Folding together at the sides and extending to the walls of the pelvis, it encloses the tubes and round ligaments in deep, flat masses, called the broad ligaments. This is the structure that becomes so perilously inflamed (peritonitis) when infected by germs that find entrance through the genital passage.

THE EXTERNAL GENITALS

The external genitals form the vulva. Under this name are included the mons veneris, the labia majora, the labia minora, the clitoris, the vestibule, the hymen and the glands of Bartholin.

The entire groove from the mons veneris to a point well up on the sacrum forms a deep fold or crevice, which is known as the genital crease. That part of the genital crease lying between the anus and vulva is technically known as the perineum (q.v.)

The Mons Veneris.—The mons veneris is a gently rounded pad of fat lying just above the junction of the pubic bones (the symphysis). The overlying integument is filled with sebaceous glands and covered with hair at puberty.

The Labia Majora.—The labia majora are the large lips of the vulva. They are loose, double folds of skin extending downward from the mons veneris to the anterior boundary of the perineum and covered externally with hair. Normally they lie in apposition and conceal the vaginal opening. They correspond to the male scrotum.

The Labia Minora.—The labia minora, or nymphÆ, are two small folds of skin and mucous membrane, that extend from the clitoris obliquely downward and outward for an inch and a half on each side of the entrance to the vagina. On the upper side, where they meet and invest the clitoris, the fold is called the prepuce, but on the under side they constitute the frÆnum.

The labia minora are sometimes enormously enlarged in the black races and are then called the Hottentot apron.

The Clitoris.—The clitoris is an erectile structure analogous to the erectile tissue of the penis. The free extremity is a small, rounded, extremely sensitive tubercle, called the glans of the clitoris. About the clitoris there forms a whitish substance called smegma. This is a good culture medium for germs and must be carefully sponged away when the vulva is prepared for delivery.

The Vestibule.—The vestibule is bounded by the clitoris above, the labia minora on the sides, and the vaginal orifice below. It contains the opening of the urethra, which is called the meatus urinarius.

The Hymen.—The hymen is a thin fold of membrane which closes the vaginal opening to a greater or lesser extent in virgins. It varies much in shape and consistency. It is sometimes absent, or it may persist after copulation, hence its presence or absence can not be considered a test of virginity. When torn, the edges shrink up and form little irregularities called carunculÆ myrtiformes.

Bartholin Glands.—Bartholin glands are located on each side of the commencement of the vagina. Each gland discharges by a small duct just external to the hymen. They are often the seat of a chronic gonorrhoeal inflammation and must be watched carefully, lest infection extend to the mother after labor, or to the eyes of the child in passing.

The Perineum.—The perineum is a body of muscle, fascia, connective tissue, and skin, situated between the vagina and the rectum. The vagina bends forward and the rectum backward, so a triangular area is left between them which is filled by the perineal body. It is about two inches long from before backward, and becomes progressively thinner the deeper it extends.

The perineal body is flattened out and compressed by the passage of the head and in many cases torn. (Thirty per cent of primiparas and ten to fifteen per cent of multiparas.) It should be repaired immediately.

The Mammary Glands.—The mammary glands are secondary but highly important parts of the genital system. They are formed by a dipping down of skin glands and they perform the special function of secreting milk.

The breast is made up of fifteen or twenty lobes, each of which, like a bunch of grapes, clusters about and discharges into a single tube which, in turn, leads to the nipple. The area between the lobes is filled with fat and connective tissue.

The nipple is pink or darkly pigmented. It is composed of erectile tissue and under stimulation, it rises from the surface of the gland so that it is easily taken into the mouth.

Surrounding the nipple is a darkly pigmented area from one inch to four inches in diameter that is called the areola. It contains hard, shot-like nodules, the glands, or tubercles, of Montgomery. These often secrete milk and sometimes become infected. It occasionally happens that more than two breasts may be found on the human female, and not infrequently pieces of mammary tissue may be discovered in the axilla or on the chest or back.

The mammary gland is undeveloped at birth, but, nevertheless it may fill with milk (witches’ milk). At puberty, after marriage, and during pregnancy, the gland reaches maturity. It is only after delivery, however, that the functional climax is attained.