=The Genital Organs of Woman.=--The organs described in Chapter II (Figs. 18 and 19), constitute the internal and more important part of the female sexual apparatus. In women, the urethra opens externally on its own account. It is much shorter and wider than in men. At its external extremity is a small cavernous body called the _clitoris_, which corresponds embryologically to the penis in man, and chiefly to the glans. Like the latter it is specialized for sexual irritation and possesses very sensitive nerves. The opening of the female urethra is situated in front of the vulva directly under the pubic bone, at the same place as the root of the male penis. From this point, on each side of the middle line, extend two longitudinal folds, one external covered with skin and called the larger lip of the vulva (Fig. 18, _labia majora_), the other internal, hidden under the first, called the lesser lip of the vulva (_labia minora_), and covered with thin mucous membrane. Between the two lesser lips is the sexual aperture, which, with the labia majora and minora is called the _vulva_. This opening is distinct from that of the urethra, and leads to the internal cavity or _vagina_ (Fig. 18). The vagina is about ten to twelve centimeters long (2 to 2-½ inches) and terminates in a _cul-de-sac_ which surrounds the vaginal portion of the womb, of which we have spoken above. In virgins the entrance to the vagina is more or less closed by a delicate transverse membrane called the _hymen_, which is only perforated by a narrow opening. At the first coitus the hymen is torn, causing a certain amount of pain and bleeding. The walls of the vagina are thrown into transverse folds, which render them somewhat rough. The remains of the hymen torn by the first coitus afterward form behind the vulva small excrescences named _carunculæ myrtiformes_. In the first chapter we have spoken of the changes undergone by the fecundated ovule till it becomes the embryo and then the infant. It remains to speak of the mechanism of expulsion of the ovule and of its fecundation, as well as the changes in the womb which result from these phenomena.