• 4 weeks:
  • Germ cells arise from yolk sac
  
  
• 5-6 weeks:
  • Germ cell migrate to urogenital ridge, mesothelium of urogenital ridge proliferates to form epithelium and stroma of gonad, incorporating germ cells, resulting in elevation of overlying ectoderm
  • Anteriorly, this results in the formation of the genital tubercle, which becomes the clitoris
  • Laterally, two parallel ridges, each composed of a medial and lateral fold, develop into the labia minora
  • They are joined anteriorly to form the clitoral frenulum and posteriorly to form the fourchette or posterior frenulum of the labia
  • The epithelium of the labia minora and of the clitoral hood are of ectodermal origin
  
  
• By the end of 6 weeks:
  • The urorectal septum divides the cloaca anteriorly in the urogenital sinus, posteriorly in the anal canal; both of these structures are covered respectively by the urogenital and the anal membrane
  • The degeneration of the central portion of the urogenital membrane results in the hymen opening
  • Lateral mullerian ducts (paramesonephric ducts) form from fusion of coelomic lining epithelium, proximal portion forms fallopian tubes, caudal portion fuses to form uterus, upper vagina
  • Urogenital sinus forms lower vagina and vestibule, fuses with mullerian ducts
  
  
• By 16th week:
  • The junction of the distal vagina with the urogenital sinus results in the development of the vaginal vestibule, which is identifiable by the 16th week
  • The vaginal vestibule is of endodermal origin except for a small area immediately anterior to the urethra, which is of ectodermal origin - this area represents the site of insertion of the urethral septum, dividing the urethra from the genital tubercle
  • The junction of the epithelium derived from endoderm and that derived from ectoderm is seen in the adult on the inner aspects of the labia minora, marked by the junction of keratinized with nonkeratinized epithelium
  • This line of demarkation is referred to as the vestibular line of Hart
  
  
• In men:
  • Mullerian inhibitory substance from testes causes regression of mullerian ducts and paired wolffian (mesonephric) ducts form epididymis and vas deferens
  • If no functional testes, mullerian ducts persist and mesonephric duct regresses; mesonephric duct vestiges may persist as Gartner duct cysts in cervix or vagina

• Solapav-Course of vulvar pathology from 2006 (pdf)

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