Human Anatomy, Part 1 - K. A. Dyubenko, A. K. Kolomiytsev, Y. B. Chaykovsky 2002

Special Part
Reproductive Systems, systemata genitalia — Female Reproductive System, systema genitale femininum
External Female Genital Organs, organa genitalia feminina externa — Development of the External Genitalia

The Development of external genitalia, similarly to internal genitalia, comprises both an indifferent and a dimorphic stage. The indifferent stage begins in embryos 11-13 mm in length, when a prominence known as the genital tubercle, or tuberculum genitale, appears along the midline of the proctodeum (Fig. 340). Inferiorly in the caudal region, a groove-like depression forms and extends toward the proctodeum. This groove transforms into a deep cleft flanked on both sides by labioscrotal folds (genital folds). Peripherally to these folds, on each side, elevations known as genital swellings arise. Between the genital folds lies a deep cleft—the urogenital orifice, which communicates with the urogenital sinus. This orifice forms at the site of the urogenital septum and becomes separated from the anus as the cloaca is divided by the urorectal fold into the rectum and the urogenital sinus.

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Fig. 339. Diagram of female reproductive organ development (after Hertwig and B. Petten):

1 - diaphragmatic ligament of mesonephros; 2 - hydatid; 3 - opening of Uterine tube; 4 - epoophoron; 5 - Ovary; 6 - inguinal ligament; 7 - Urinary Bladder; 8 - ureteric orifices; 9 - Urethra; 10 - labium minus; 11 - labium majus; 12 - Vagina; 13 - ovary following descent; 14 - position of uterine tube; 15 - Ureter; 16 - mesonephric duct; 17 - uterine tube; 18 - Kidney

During the Development of the Perineum, the two openings move significantly apart, and the anus shifts outside the BOUNDARIES OF THE genital Swelling (Fig. 340B). Under male sex differentiation, the genital tubercle grows intensively and develops into the Penis (Fig. 340C). The urogenital groove is closed by the fusing genital folds, which form the proximal part of the urethra. Its distal part develops from a cord of ectodermal Cells within the phallus that grow from the glans penis toward the proximal urethra and subsequently canalize. The genital swellings enlarge to form the Scrotum. Along the line of fusion of the genital folds and swellings, the raphe of the penis and the scrotal raphe are formed.

Under female sex differentiation, the genital tubercle develops into the Clitoris, the genital folds become the Labia minora, and the genital swellings form the Labia Majora (see Fig. 340A). The entrance to the urogenital sinus, bounded laterally by the labia, forms the Vestibule of the vagina, or vestibulum vaginae (see Fig. 340B).