|Henry Gray (18251861). Anatomy of the Human Body. 1918.|
|of the cells lining the celom (Fig. 1106). The orifice of the invagination remains patent, and undergoes enlargement and modification to form the abdominal ostium of the uterine tube. The ducts pass backward lateral to the Wolffian ducts, but toward the posterior end of the embryo they cross to the medial side of these ducts, and thus come to lie side by side between and behind the latterthe four ducts forming what is termed the genital cord (Fig. 1109). The Müllerian ducts end in an epithelial elevation, the Müllerian eminence, on the ventral part of the cloaca between the orifices of the Wolffian ducts; at a later date they open into the cloaca in this situation.|
| In the male the Müllerian ducts atrophy, but traces of their anterior ends are represented by the appendices testis (hydatids of Morgagni), while their terminal fused portions form the utriculus in the floor of the prostatic portion of the urethra (Fig. 1110, C).|
| In the female the Müllerian ducts persist and undergo further development. The portions which lie in the genital core fuse to form the uterus and vagina; the parts in front of this cord remain separate, and each forms the corresponding uterine tubethe abdominal ostium of which is developed from the anterior extremity of the original tubular invagination from the celom (Fig. 1110, B). The fusion of the Müllerian ducts begins in the third month, and the septum formed by their fused medial walls disappears from below upward, and thus the cavities of the vagina and uterus are produced. About the fifth month an annular constriction marks the position of the neck of the uterus, and after the sixth month the walls of the uterus begin to thicken. For a time the vagina is represented by a solid rod of epithelial cells. A ring-like outgrowth of this epithelium occurs at the lower end of the uterus and marks the future vaginal fornices; about the fifth or sixth month the lumen of the vagina is produced by the breaking down of the central cells of the epithelium. The hymen represents the remains of the Müllerian eminence.|
FIG. 1109 Urogenital sinus of female human embryo of eight and a half to nine weeks old. (From model by Keibel) (See enlarged image)
Genital Glands.The first appearance of the genital gland is essentially the same in the two sexes, and consists in a thickening of the epithelial layer which lines the peritoneal cavity on the medial side of the urogenital fold (Fig. 1106). The thick plate of epithelium extends deeply, pushing before it the mesoderm and forming a distinct projection. This is termed the genital ridge (Fig. 1106), and from it the testis in the male and the ovary in the female are developed. At first the mesonephros and genital ridge are suspended by a common mesentery, but as the embryo grows the genital ridge gradually becomes pinched off from the mesonephros, with which it is at first continuous, though it still remains connected to the remnant of this body by a fold of peritoneum, the mesorchium or mesovarium (Fig. 1111). About the seventh week the distinction of sex in the genital ridge begins to be perceptible.
The Ovary.The ovary, thus formed from the genital ridge, is at first a mass of cells derived from the celomic epithelium; later the mass is differentiated into a central part or medulla (Fig. 1112) covered by a surface layer, the germinal epithelium. Between the cells of the germinal epithelium a number of larger cells, the primitive ova, are found, and these are carried into the subjacent stroma by bud-like ingrowths (genital cords) of the germinal epithelium (Fig. 1113). The surface epithelium ultimately forms the permanent epithelial covering of this