This mingled mass of epithelial cells, blood and mucus leaves the body in form of menstrual discharges. Menstruation, therefore, is a retrograde process, in consequence of the failure of the impregnation of the ovum. The monthly flow is like the shedding of the leaves by the tree, the getting rid of some material the function of which has been frustrated and for which the economy has no more use.
Menstruation is thus the manifest phenomenon of the retrograde metamorphosis which ensues at the failure of the ovum to become fertilized. Where there is fertilization there is no menstruation. Hence, those women who marry immediately after menstruation sets in, at puberty,[H] and are impregnated and those women who are impregnated immediately after they finished nursing their babies, will seldom show the phenomenon of menstruation. This is the reason why menstruation is so rarely observed among animals.[I]
The concubitalis function of the uterus.—Another highly important function of the uterus is to serve as an organ of copulation. During the orgasm, at the moment of the highest excitement, the uterus descends deeper into the small pelvis.[J] It is assisted in the descent by the pressure of the abdominal muscles. The uterus, usually flattened in the sagittal direction, assumes a round, pear-shaped form during the orgasm and for some time afterwards. In this way a real cavum uteri is produced, and through the vacuum thus produced, the uterus is able to suck in the semen by means of aspiration. Furthermore, through the excitation, the circular fibres of the cervix contract at the same time as the longitudinal fibres. The result is a dilatation of the cervical orifice. The formerly flat opening becomes round. At the same time the uterine orifices of the tubes, which are generally closed, open widely and challenge the entrance of the spermatozoa.
Female ejaculation.—The contraction of the cervical fibres also causes the erection of the vaginal portion and of the neck of the uterus. This erection, at the moment of the highest orgasm, serves to expel Kristeller’s slimy plug from the cervix. This expulsion represents female ejaculation. After the expulsion the cervix becomes soft and flabby. The erection and sudden relaxation of the cervix cause the external os to open, sometimes to the extent of fully three centimeters, and to make several successive gasps. Each time the gasp draws powerfully the external os into the cervix and causes the aspiration of the semen.
Function of the vagina.—The function of the vagina is to serve as a receptacle of penis and semen. The erectile tissue which runs along the entire length between the different membranes, forming the vaginal wall, helps the vagina to adjust itself to the volume of the penis and to augment its turgescence. The muscular fibres, situated within the tunica media of the vaginal mucous membrane, contract during the ejaculation of the semen. The contraction is of a peristaltic nature, starting from the vaginal aperture. In this way the semen is stowed toward the uterine orifice under a certain pressure and is prevented from flowing off.
Previous to this contraction the sphincter cunni, the analogous muscle to the musculus bulbo-cavernosus in the male, also contracts and clinches the penis, pressing, at the same time, upon the two bulbs of the vestibule. In this way the vaginal orifice is more firmly compressed.
Function of the Bartholinian glands.—Through the activity of the constrictor cunni, the Bartholinian glands are also compressed. Normally these glands are inactive. They only secrete on irritation.[K] At the first voluptuary thrills, the lubricating fluid gushes forth from the Bartholinian glands, moistens the sexual organs, prepares the way for the painless entrance of the male organ and furnishes the ante-orgastic libido which is second only to the orgasm itself, and is the only libido experienced by many women throughout their lives.
The alkaline lubricating fluid from the Bartholinian glands serves the further purpose of neutralizing the vaginal contents which are of an acid reaction. But for the alkaline secretions, before the male ejaculation, the spermatozoa would be killed by the acids, or, at least, checked in their movements. The secretion of the Bartholinian glands has, therefore, a threefold purpose: it facilitates the frictions, neutralizes somewhat the vaginal contents, and increases or furnishes the ant-orgastic libido.
Function of the clitoris.—The most sensitive organ of the female genital apparatus is the clitoris. In the female child the clitoris, analogous to the penis in the male, represents the main erogenous zone, and its activity manifests itself by frequent twitchings and erections. After puberty the main function of the clitoris is, according to Freud, to transmit the stimuli to the other genital organs.
The erection of the clitoris is produced in the same way as the erection of the penis, by the relaxation of the arteries of the corpora cavernosa of the clitoris, which are thus filled with blood. The erection is further helped by the contraction of the muscles ischio-cavernosus and constrictor cunni. The clitoris has a direction, inverse to that of the erected penis, namely, downward. By virtue of its direction and its angle, the erected clitoris is able to yield and descend to meet the dorsal face of the glans and body of the penis, without being in a position to rise again during its action. The contraction of the two last named muscles will, therefore, help to press the right-angled clitoris on the dorsal side of the penis. The erection and the bending of the clitoris are further helped by the action of the bulbs of the vestibule which, through the pressure of the penis, send their fluid to the corpora cavernosa and the glans of the clitoris and thus increase the sensitiveness.