Ovulation.—Ovulation is the process whereby the eggs are discharged from the Graafian follicle which matures and protects them in the ovary. The egg is a true cell with one, and sometimes more than one, nucleus.

The ripening of the eggs, as well as their discharge, is attended with much general disturbance and great physical changes. This phenomenon begins from the twelfth to the fifteenth year, depending on race, climate, occupation and temperament, and marks the transition of the individual from childhood into maturity.

This period is called puberty. At this time the breasts enlarge, the hips round out, the vagina, uterus and external genitals increase in size. Hair appears upon the vulva, the emotions become more evident, and modesty develops through a consciousness of sexual difference and attraction.

Simultaneously a new function appears—

Menstruation.—Menstruation may be defined as a process wherein a bloody fluid is discharged from the uterus at regularly recurring periods between puberty and the menopause, except during pregnancy and lactation. It is a hÆmorrhage which in some way is closely associated with ovulation, but it is not known positively which is the precedent of the other, or whether one causes the other.

Menstruation is not essential to pregnancy, for pregnancy may occur when the flow is normally absent, as before puberty, after the menopause, or during lactation. Nevertheless, regularity of menstruation is the rule in fertile women and clinicians agree that while conception may occur at any part of the menstrual cycle, it is most likely to happen just before or just after the menstrual flow.

The best authorities at present support the theory that ovulation usually occurs soon after the close of the menstrual period. This is confirmed by the similarity of the physical changes that take place in the endometrium during menstruation and after conception.

As the period of the flow approaches, the lining membrane of the uterus becomes hyperÆmic and swollen with blood, serum, and glandular secretions. The blood vessels are engorged, the glands become longer and more tortuous, little hÆmorrhages appear, and the superficial epithelium is thrown off. A large amount of mucus is produced by the increased activity of the glands, and all is discharged into the vagina as a bloody, incoagulable flow with an odor of marigolds. The process continues usually from three to seven days, when the discharge ceases and the endometrium slowly resumes its uncongested state.

Meanwhile, the psychic and bodily conditions have not remained unaffected. The nervous system is disturbed, the disposition is irritable and capricious and the head may ache. The woman takes cold easily. She is indisposed to exertion from a sense of languor and malaise. Pain may develop in the back, or cramps in the pelvis, so severe as to keep the woman in bed. Frequently the approach of the period is signalized by skin changes, such as a marked odor or an eruption of acne pustules.

The flow usually returns every twenty-eight days, but it may vary within normal limits from twenty-one to thirty days. The flow continues at such intervals regularly from puberty to the menopause (change of life), which occurs between the ages of forty-five and fifty.

Conception, or Fertilization.—This is the process wherein the male element (spermatozoon) meets and unites with the female egg. From what is known from investigations of lower animals, this meeting usually takes place in the Fallopian tube.

The egg expelled from the ovary is carried into the open end of the tube by peritoneal currents and passed on toward the uterus by the waving action of the hair-like outgrowths of the cells (ciliÆ) that line the tube, aided, possibly, by the tubal muscle.

The spermatozoon makes its way upward from the vagina by means of its tail. This activity, like the tail of a fish, or snake, or as a boat is sculled, drives the cell forward through the thin layer of fluid that covers the mucous membranes.

The arrow-shaped spermatozoon travels at a rate that completes the passage to the ovary in twenty-four hours, but spermatozoa may lie in wait for the egg a considerable time, as is shown by the fact that they have been found alive in Fallopian tubes removed three and a half weeks after copulation. As soon as the male and female elements approach each other, they exercise a powerful magnetic attraction, which draws them together, and as soon as they touch, the two cells unite and the spermatozoon almost immediately disappears.

Only one spermatozoon is required for the fertilization of an egg, and hence enormous numbers must perish without achieving their destiny.

The fertilized egg has become the ovum, and originally 1/125 of an inch in diameter, it now begins to grow, and filled with a new energy, it passes down the tube and enters the uterus. Here it comes into contact with the soft mucosa and digs a hole for itself—a nest, very much as a warm bullet might sink into ice or snow—and is soon completely surrounded by a proliferating tissue called the decidua. The woman is now pregnant. The menstrual flow does not appear, and local and systematic changes are inaugurated.

The egg enlarges rapidly. Little glove-finger-like projections (the villi) appear on its surface and dip down into the maternal tissues. Through these villi the egg gets nourishment until about the twelfth week, when the placenta forms. Externally the ovum resembles a chestnut burr. As the egg grows, the villi on the surface find it more and more difficult to secure nutriment, and except at one place, all gradually shrink and disappear. At this significant point, they increase greatly in size, number, and complexity to form the thick, cake-like placenta.

The egg or ovum is simply a growing cyst, filled with a fluid, normally sterile, in which the developing embryo lives and swims. This fluid is the liquor amnii and it is retained by a cystic wall made up of two layers—the chorion, which represents the original cell membrane, and the amnion, which develops out of the foetus. At maturity, the ovum will contain from one to two pints of liquor amnii.

The Liquor Amnii.—The liquor amnii is of vast importance to the child. It allows free movement for the growing limbs and body, protects the child from sudden changes of temperature, prevents injury both from without and within, saves the child from birthmarks and deformities by keeping it from contact with the surrounding walls, and in labor lubricates the passages for the advancing part. In a measure, too, it probably serves as a food. In labor it forms a pouch called the bag of waters, which aids in dilating the os.

Gradually, as nutrition becomes more abundant at the site of the growing placenta, a stalk-like structure thrusts out from the foetal abdomen and forms an attachment with the formative placenta. This is called the ventral stalk and as soon as the communication with the placenta is established, it is combined with other parallel structures and becomes vascularized, to form the umbilical cord.

The Umbilical Cord.—The umbilical cord at maturity measures from five to fifty inches in length and from one-half to one inch in thickness. The cord is composed of a gelatinous connective tissue, called Wharton’s jelly, in the midst of which lie the twisted vessels (two arteries and a vein) that supply the embryo with air and food and carry off the waste.

The Placenta.—The placenta or “after-birth” is an oval or circular somewhat flattened disc, six to ten inches in diameter, and three-quarters to one and one-half inches thick. It weighs about a pound and a half. It is the organ of respiration and nutrition for the foetus.

It is formed about the third month outside the membranes covering the child and is more or less loosely attached to the uterine wall. The umbilical cord is attached to its foetal surface, inside the ovum. Like a flat sponge it takes oxygen, blood, and the nourishing fluids from the blood vessels in the uterine wall, carries them to the child by means of the umbilical vein, and carries back the carbonized blood and waste products by the umbilical arteries to the placenta, and there returns them to the maternal blood for disposal. The blood of the veins is bright red, and of the arteries, dark and turbid.

There is no direct communication between the maternal tissues and the placenta, hence all the changes occur by osmosis, and by the activity of the cells which form the walls of the villi.

The liver of the child is large and active. The stomach and intestines functionate mildly. The kidneys act, and urine is discharged into the liquor amnii, which the child occasionally swallows.

During development, the movements of the child become more and more pronounced. Arms, legs, and entire body participate in turn. Periods of rest are also observed. Gradually the child assumes a definite attitude in the uterus. It becomes more and more folded and flexed to accommodate its size to the limitations of space. The head bends on the chest, the arms are folded, the thighs flex against the abdomen, the legs on the thighs, and even the back ultimately becomes convex. It attains a complete flexion, the normal attitude of the child. As maturity approaches, the head becomes more and more palpable and seeks its usual location in the lower pole of the uterus, resting on the pelvic brim.

The foetal skull at maturity (at term) is still incompletely ossified. The bones are thin and pliable and separated at their edges by intervals of unossified membrane which form the sutures and fontanelles. Thus the skull is compressible to a slight degree and capable of much change in shape. It can be measurably moulded by the uterine contractions to suit the pelvis.

In front, the two coronary sutures meet the frontal and sagittal sutures to produce a kite-shaped figure, called the large or anterior fontanelle, or the bregma. Behind, the lambdoidal suture meets the sagittal suture to form the small or posterior fontanelle.

The large fontanelle is made up of four bones and four angles; the small, of three bones and three angles, and are usually easy to differentiate. Furthermore, the difference between these fontanelles is of great importance in labor, since by it the observer is enabled to determine the position of the head. In America, the shape of the head is that of an ovoid with the long diameter anteroposterior (Dolico-cephalic). Thus it happens that when the head is completely flexed, the smallest diameters are presented for delivery.

The important diameters of the head, with their measurements and names, are as follows:

Nape of neck to center of bregma, 9.5 cm.—Suboccipito-bregmatic diameter. Occipital protuberance to root of nose, 11.25 cm.—Occipito-frontal diameter. Between the eminences of parietal bones, 9.25 cm.—Biparietal diameter. Between anterior ends of coronal sutures, 8 cm.—Bitemporal diameter.

The smallest circumference is that of the suboccipito-bregmatic plane, which comes into relation with the brim of the pelvis when the flexion of the head is complete. It measures 27.5 centimeters.

The foetus grows at a definite rate throughout gestation and so regularly that the increase is rarely simulated by any other condition.

To find the probable length of the foetus at any given time, square the month of the pregnancy (up to five) and the result is the foetal length in centimeters. After the fifth month, multiply the number of the month by five. Thus:

7th month ×5=35 cm., the approximate length of the foetus at the lunar month.—(Hasse’s rule.)

The Mature Foetus.—Although subject to considerable variation, the foetus at term will weigh about seven and one-fourth pounds, and measure 50 cm. in length. The weight is far more uncertain than the length, and therefore not so reliable as a sign of maturity.

To obtain an estimate of the weight of the child at any given month of the pregnancy, the number of lunar months minus 2, is squared and divided by 2, and the result is the average weight of the child at that time in hundreds of grams. Thus:

8th month -2=6. 6×6=36. 36÷2=18, or in hundreds of grams, 1800, the weight of the child.—(Tuttle’s rule.)

Differences between the mature and immature foetus:

The Foetal Circulation.—The placenta is an organ of nutrition as well as respiration, and through the umbilical vessels the food materials are brought to the foetus and the waste products removed.

Surrounded by the jelly of Wharton that fills out the cord, and running in and out between the two arteries, the umbilical vein passes into the foetal abdomen and divides into two branches, one, the larger, short-circuits directly into the inferior vena cava. This branch is called the ductus venosus. The other joins the portal vein and passes through the liver, after which it also enters the vena cava.

Thus the heart is fed with a mixed blood, part coming fresh from the placenta and part coming up from the lower half of the foetus. This blood is poured into the right auricle, where it becomes mixed again with the blood coming down from the upper pole of the foetus through the superior vena cava.

Now a small part goes down into the right ventricle and is forced into the pulmonary arteries to supply the lungs. But the lungs are not functionating, hence the greater part is again short-circuited through the ductus arteriosus into the arch of the aorta, where it meets with the great volume of blood which passed over into the left auricle through the hole in the septum between the right and left auricles, called the foramen ovale, thence down into the left ventricle and out through the aorta to supply the rest of the foetal body.

With the exception of the ductus venosus and the ductus arteriosus and the foramen ovale, the circulation is the same as in the adult.

The blood in the descending aorta again divides and part goes on to supply the lower extremities while the greater part leaves the internal iliac arteries by means of the hypogastric vessels and returns through the umbilical arteries to the placenta for oxygenation.

As soon as the child is born, the foetal structures are altered. The child breathes, the pulmonary circulation is established and the ductus arteriosus is closed. The placental circulation is abolished, and the ductus venosus and the hypogastric arteries are converted into solid fibrous cords. Owing to the immediate change of pressure in the auricles, the foramen ovale closes and the circulation assumes the adult type.