The genital tract in the female arises from two embryonic sources, the Mullerian ducts (mesodermal in origin) and the urogenital sinus (endodermal in origin). Abnormal Mullerian differentiation is frequently associated with urologic malformations.

EMBRYOLOGY

The Mullerian (paramesonephric) ducts appear in the 10-mm crown-rump length embryo (about five weeks) by an invagination of the coelomic epithelium into the underlying mesenchyme lateral to the cranial extremity of the Wolffian ducts (Figure 35.1).

In the female, the site of invagination becomes the future abdominal opening of the Fallopian tube. At the caudal tip of this invagination, a solid bud is formed, which burrows in the mesenchyme lateral to and parallel with the Wolffian ducts. At the caudal extremity of the mesonephros, the Mullerian duct crosses ventrally and medially and grows mediocaudally to meet and fuse with the duct of the opposite side (Figure 35.2). Fusion of the Mullerian ducts is at first incomplete, so that for a short while a septum separates their two cavities. In embryos about 56 mm long (about twelve weeks), the septum degenerates and gives a single cavity, the uterovaginal (genital) canal. The caudal tip of this canal comes in contact with the dorsal wall of the urogenital sinus, producing an elevation, the Mullerian tubercle (Figure 35.3). Proliferation of the tip of the uterovaginal canal results in the formation of a solid vaginal cord.