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Stages in the Development of the External Sexual Organs in the Male and Female

  • Drawn from the Ecker-Ziegler models.
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The External Organs of Generation

  • cloacal membrane, composed of ectoderm and endoderm (entoderm), originally reaches from the umbilicus to the tail
  • mesoderm extends to the mid-ventral line for some distance behind the umbilicus
    • forms the lower part of the abdominal wall
    • ends below in a prominent swelling, the cloacal tubercle
  • Behind the tubercle the urogenital part of the cloacal membrane separates the ingrowing sheets of mesoderm
  • The first rudiment of the penis (or clitoris) is a structure termed the phallus
    • derived from the phallic portion of the cloaca which has extended on to the end and sides of the under surface of the cloacal tubercle
  • The terminal part of the phallus representing the future glans becomes solid
  • the remainder, which is hollow, is converted into a longitudinal groove by the absorption of the urogenital membrane

Female

  • a deep groove forms around the phallus and separates it from the rest of the cloacal tubercle, which is now termed the genital tubercle.
  • sides of the genital tubercle grow backward as the genital swellings, which ultimately form the labia majora
  • tubercle itself becomes the mons pubis
  • labia minora arise by the continued growth of the lips of the groove on the under surface of the phallus
  • remainder of the phallus forms the clitoris

Male

  • early changes are similar
  • pelvic portion of the cloaca undergoes much greater development, pushing before it the phallic portion
  • genital swellings extend around between the pelvic portion and the anus, and form a scrotal area
  • during the changes associated with the descent of the testes this area is drawn out to form the scrotal sac
  • penis is developed from the phallus
  • urogenital membrane undergoes absorption, forming a channel on the under surface of the phallus; this channel extends only as far forward as the corona glandis

(Text modified from Gray's Anatomy)

entoderm - is a historic term for endoderm.



Gray's Images: Development | Lymphatic | Neural | Vision | Hearing | Somatosensory | Integumentary | Respiratory | Gastrointestinal | Urogenital | Endocrine | Surface Anatomy | iBook | Historic Disclaimer
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Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)
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Reference

Gray H. Anatomy of the human body. (1918) Philadelphia: Lea & Febiger.


Cite this page: Hill, M.A. (2024, June 16) Embryology Gray1119.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Gray1119.jpg

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current08:06, 28 May 2011Thumbnail for version as of 08:06, 28 May 2011700 × 807 (115 KB)S8600021 (talk | contribs)==Stages in the development of the external sexual organs in the male and female== * Drawn from the Ecker-Ziegler models. {{Historic Disclaimer}} ===The External Organs of Generation === * The cloacal membrane, composed of ectoderm and endoderm (entoder