Health Dictionary
Reliable, easy-to-read patient information on common medical conditions — written in plain language, free of jargon, and grounded in current evidence. Browse the most frequent diagnoses, understand what they mean for everyday life, and learn which steps and questions help you have a focused conversation with your doctor.
External os
Introduction
The external orifice of the uterus (or ostium of uterus, or external os) is a small, depressed, somewhat circular aperture on the rounded extremity of the vaginal portion of the cervix. Through this aperture, the cervical cavity communicates with that of the vagina.
The external orifice is bounded by two lips, an anterior and a posterior. The anterior is shorter and thicker, though it projects lower than the posterior because of the slope of the cervix. Normally, both lips are in contact with the posterior vaginal wall.
Prior to pregnancy, the external orifice has a rounded shape when viewed through the vaginal canal (as through a speculum). Following parturition, the orifice takes on an appearance more like a transverse slit or is “H-shaped”.
Additional images
Additional images
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Vessels of the uterus and its appendages, rear view. -
Median sagittal section of female pelvis.
External links
External links
- Template:SUNYAnatomyFigs – “The uterus, uterine tubes and ovary with associated structures.”
Editor-In-Chief: Template:Infobox Anatomy C. Michael Gibson, M.S., M.D. [1]