External orifice of the uterus
|External orifice of the uterus|
|Posterior half of uterus and upper part of vagina. (External orifice labeled at bottom.)|
|Uterus and right broad ligament, seen from behind. (External uterine orifice labeled at bottom.)|
|Latin||ostium uteri, orificium externum uteri|
|Gray's||subject #268 1260|
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".
This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant.