Development of the External Genitalia in Rat Fetuses

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  • INOMATA Tomoo
    <I>Department of Laboratory Animal Science, Azabu University School of Veterinary Medicine</I>
  • EGUCHI Yasunobu
    <I>Department of Anatomy II, Azabu University School of Veterinary Medicine</I>
  • NAKAMURA Tsunenori
    <I>Department of Laboratory Animal Science, Azabu University School of Veterinary Medicine</I>

Bibliographic Information

Other Title
  • ラット外生殖器の発達について
  • ラットガイ セイショクキ ノ ハッタツ ニ ツイテ

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Description

Development of the external genitalia in rat fetuses was studied with special reference to the formation of the labia pudenda and the determination of the stage at which the sex difference could be recognized from changes in the external structures. The urogenital fold located on either side of the urogenital groove gradually enlarges and begins to enclose the genital tubercle with its counter fold on day 20 of gestation. Thus, the urogenital folds, which are known to become the labia minora and the prepuce of clitoris in the human, are differentiated only into the prepuce of clitoris in the rat. The genital swellings situated caudally to the urogenital folds are not well developed and come to be inconspicuously flat in situ at the end of gestation. However, the labia majora are formed by the time of puberty when the vagina opens. Therefore, it seems that the genital swellings contribute to the formation of the labia majora after birth. Sex difference in development of the external genitalia is recognized on day 17 of gestation ; a small oval urogenital orifice is larger in male than in female and the genital swellings are better developed in male than in female.

Journal

  • Experimental Animals

    Experimental Animals 34 (4), 439-444, 1985

    Japanese Association for Laboratory Animal Science

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