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The posterior fornix of the vagina is the most prominent. It is located between the posterior wall of the vagina and the cervix. The posterior fornix is clinically important because it is closely associated with the pouch of Douglas [finger is in the Douglas pouch, and tip of probe is in the posterior fornix]. Thus, only the posterior wall of the vagina, which is covered by peritoneum, separates the lumen of the vagina from the pouch of Douglas. The pouch of Douglas is the lowest point of the peritoneal cavity in the female. Clinicians, diagnostically, can access the peritoneal cavity by culdocentesis (placing the needle through the wall of the posterior fornix into the pouch of Douglas).
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