(Fig. 18). Their number is enormous: it has been computed that the two ovaries together contain 72,000 ova.

THE MÜLLERIAN DUCTS.

The Müllerian ducts appear shortly after the Wolffian body as a funnel-shaped invagination from the endothelium of the peritoneum

Graafian Follicle from a Girl seven months old (enlarged 220 times; natural size, 0.351 mm. longest diameter): a, epithelium (membrana granulosa) detached from fibrous membrane; b, discus proligerus, situated far away from the surface. It contains the ovum, on which the zona pellucida and the germinal vesicle are visible. The surrounding fibrous membrane is not yet separated into two layers, and there is no distinct line of demarkation between it and the surrounding stroma (Kölliker).

at the inner side of the upper end of the Wolffian body (Fig. 19). Thence it extends behind this body and comes to lie outside of the Wolffian duct, but turns in a spiral line round the latter, so as to

Primordia: Ova undergoing division, from a Human Embryo of six months (enlarged 400 times): 1, two primordial ova surrounded by a common layer of epithelium, one of which has a prolongation by means of which it probably was attached to another ovum, as in 2, where two primordial ova are linked together by a band of protoplasm, the whole surrounded by one epithelial layer; 3 primordial ovum with two nuclei (germinal vesicles) (Kölliker).

pass in front of it, and finally lie behind it. The lower part is at first formed by a solid column of cells which later is tunnelled so as to form a tube.

The Müllerian duct has a mesentery, by which it is fastened to the Wolffian body. After the disappearance of that body it springs from the posterior abdominal wall; still later from the mesoarium (Fig. 9), until, finally, in the fully-developed body we find it as part of the broad ligament of the uterus.

In the male the Müllerian ducts soon disappear, leaving as remnants the hydatid of Morgagni on the epididymis and the vesicula

Transverse Section through the upper end of the Wolffian Body of the Embryo of a Rabbit of fourteen days (enlarged 114 times): wg, Wolffian duct; m, connection between a tubule of the Wolffian body with a Malpighian body; t, entrance to the Müllerian duct (later the abdominal ostium of the Fallopian tube); gg', mesentery of the Wolffian body, containing a glandular tubule; W, surface of the liver; hb, posterior abdominal wall; mg, lateral part of the Müllerian duct (Kölliker).

prostatica (sinus copularis, or male uterus). In the female they form the Fallopian tubes, the uterus, and the vagina.

The Fallopian Tubes.-The Fallopian tubes are formed of that part of the Müllerian ducts which lies above the round ligament of the uterus (the inguinal ligament of the Wolffian body, Fig. 4). The cells of the wall form the fibrous, muscular, and mucous coat of the fully-developed tube, and fringes grow out around the abdominal opening, forming the fimbria. The duct follows the ovary in its descent, and comes to lie above and in front of that organ, running from the upper corner of the uterus to the wall of the pelvis.

The Uterus and the Vagina.-The part of the Müllerian ducts below the round ligament forms, together with the lower ends of the

Transverse Section of the Genital Cord of the Embryo of a Cow, 21⁄2 inches long (enlarged 14 times): 1, from the upper end of the cord (the ducts have been cut somewhat obliquely): 2, somewhat lower down; 3 and 4, from the middle of the cord, showing incomplete and complete fusion of Müller's ducts; 5, from the lower end, showing the two Müllerian ducts separated; a, anterior side of genital cord; p, posterior side; m, Müller's ducts; wg, Wolffian duct (Kölliker).

FIG. 21.

Wolffian ducts, a quadrangular cord with rounded edges, the genital cord (Fig. 20). The tissue that separates the two Müllerian ducts is gradually absorbed until there is one canal instead of two at the end of the second month. The genital cord is developed so as to form the uterus above and the vagina below. While the fusion of the Müllerian ducts is incomplete, they are yet separated above, forming the two horns of the uterus (Fig. 21). About the middle of pregnancy the uterus forms one sac without horns (Fig. 22).

The Müllerian ducts open into the lower part of the urachus, that part of the allantois which is included in the body, and later forms the bladder (Fig. 23). This lower part, situate below the openings of the Müllerian and Wolffian ducts, is called the urogenital sinus (Fig. 2). Originally this sinus opens into the cloaca (Fig. 24). Later

2

Uterus of Human Embryo from the tenth week, 26 mm. long: 1, natural size; 2, enlarged 4 times; a, round ligament; b, rectum (H. Meyer).

a septum is formed, dividing the cloaca and thereby Ovaries, Tubes, and separating the sinus urogenitalis from the rectum, and the urogenital opening from the anus, and forming the perineum (Fig. 25). The urogenital sinus grows much less than the other parts. The urethra is differentiated as a special organ from the bladder, with which it heretofore formed one sac called the urachus, and the vagina is undergoing a great development. Thus the change

is brought about that the urogenital sinus, which seemed to be a continuation of the bladder, now appears as the continuation of the vagina, and forms the vestibule (Fig. 26).

Abdominal and Pelvic Viscera of Female Fetus of five months (length from vertex to sole, 19 cm.): t, tube; r, round ligament; v, bladder; u, umbilical artery; ur, urachus; c, cæcum; pv, vermiform appendix (Kölliker).

In the fifth and sixth months the vagina is separated from the uterus by the formation of a ring (Fig. 26, 3), which finally becomes the vaginal portion.

FIG. 23.-all, allantois, which becomes the bladder; r, rectum; m, Müller's duct, which later is transformed into the vagina; a, indentation of the skin, which forms the anus (Schroeder).

FIG. 24.-cl, cloaca; all, allantois; m, Müller's duct; r. rectum (Schroeder). FIG. 25.-su. urogenital sinus: r. rectum, separated from the former by the perineum; v. vagina (lower part of Müller's duct); b, bladder; u, urethra (Schroeder).

About the same time the cervix is being distinguished from the

body of the uterus by the formation of transverse folds on its mucous membrane.

In the new-born child the cervix is nearly twice as long as the body of the uterus, and its walls are much thicker. The anterior and posterior surfaces of the body have longitudinal folds, and in either edge is found another longitudinal ridge from which start to both sides fine transverse folds, ending at the longitudinal folds of the surfaces. They are a continuation of the transverse folds of the cervix. Later in life all these folds disappear from the cavity of the body of the uterus, while those in the cervix remain.

During the first ten or twelve years of the child's life the uterus changes very little, even in size, but at the approach of menstruation the organ undergoes a great development; and this increase in size

Urogenital Sinus and its Appendages, from Human Embryos (life-size): 1, from a threemonths' fetus; 2, from a four-months'; 3, from a six-months'; b, bladder; h, urethra; ug, urogenital sinus; g, genital canal (common rudiment of vagina and uterus); s, vagina; u, uterus (Kölliker).

continues until the rest of the body has attained the limit of its growth.

After the differentiation between the uterus and the vagina, about the middle of pregnancy, the vagina becomes much wider, and its columns and rug make their appearance.

The Hymen. The hymen is formed in the fifth month by a development of the posterior wall of the vagina.

THE VULVA.

We have seen that originally the urogenital and the digestive tract open into one common cavity called the cloaca. Toward the end of the first month the cloaca opens on the surface of the body by a slit called the cloacal opening. In front of this opening there appears in the sixth week a protuberance called the genital tubercle, which soon thereafter is surrounded by two lateral folds called the genital folds. The genital tubercle grows, and toward the end of the second month