The Vagina (Plates II and III) is simply the external outlet or passage from the uterus. It is longer in back than in front, being from three to four inches in front and from five to six inches in the posterior portion. It is a cylindrical tube of firm elastic tissue, capable of great distension. The neck of the uterus dips into the upper part of the vagina about three-fourths of an inch. The communication between these organs is the cervical canal, which in health is found closed, admitting a probe with difficulty. The uterus and vagina are not one and the same as many suppose, yet communicate with each other. The vagina serves as a passage for the menstrual fluid, for the fetus at birth, and for the reception of the male organ in copulation, and in a state of health assists the perineal muscles in sustaining the uterus.
The mammary glands or breasts (Plate XI) are accessory to the generative system. They secrete milk which supplies the child with nourishment after birth. They are rounded and prominent, keeping their form and position through life, if the surrounding muscles and tissues have not been weakened by pressure of clothing.
Conception or impregnation takes place by the union of the male sperm and female germ. Whether this is accomplished in the ovaries, the oviducts or the uterus, is still a question of discussion and investigation by physiologists.
The ovum, or egg, matures and is taken up by the fimbriated extremities of the oviducts at the time of menstruation. To reach the outer world it must pass the length of the oviducts, the cavity and canal of the uterus and vagina. The fructifying principle of the semen consists of zoosperms, which under strong magnifying powers are seen to be filaments endowed with power of propulsion.
Once entering the uterine cavity there is no reason why they should not be able to pass into the oviducts or even to reach the ovaries. The probabilities are impregnation can take place at any point in the generative tract, providing the ovum and sperms come in contact while they still live. It is pretty well proven that the ovum after maturing and being dislodged from the ovaries may retain its life from six to eight days, and also be that length of time in making its exit from the uterus. That the sperms are viable, also, for some days, if retained in their own element at a certain temperature, has been established quite definitely.
With many women the ovum passes off within twenty-four or forty-eight hours after menstruation begins. Some, by careful observation, are able to know with certainty when this takes place. It is often accompanied with malaise, nervousness, headache, or actual uterine pain. A minute substance like the white of an egg, with a fleck of blood in it, can frequently be seen upon the clothing. Ladies who have noticed this phenomenon testify to its recurring very regularly upon the same day after menstruation. Some delicate women have observed it as late as the fourteenth day.
Nourishment and development of the embryo.—There are three distinct periods of nutrition in the uterine development of the human being:
First—Yolk nutrition.
Second—Tuft nutrition.
Third—Placental nutrition.