Dictionary > External os

External os

A small, somewhat circular aperture on the extremity of the extocervix
At the lower part of the uterus, there is a part resembling a neck and is called the cervix uteri. It appears like a neck because it forms a narrow canal in between the uterine cavity and the lumen of the vagina. The cervix uteri is essential during reproduction since it allows the passage of semen. It is also the birth canal wherein the fetus would pass through during parturition. The cervix has two openings: (1) internal os and (2) external os. The internal os is one that is located internally and opens into the uterus. The external os is the opening found on the extremity of the extocervix. The extocervix is the vaginal portion of the cervix projecting free into the anterior wall of the vagina. The external os has anterior and posterior lips. The anterior lip of the external os is shorter and thicker. It projects lower than the posterior lip due to the slope of the cervix.1

  • ostium of uterus
  • external orifice of the uterus


  • internal os
  • See also:

    • cervix
    • vagina


    1 External orifice of the uterus. Retrieved from ://en.wikipedia.org/wiki/External-orifice-of-the-uterus

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