In the male the peritoneum encircles the sigmoid colon, from which it is reflected to the posterior wall of the pelvis as a fold, the sigmoid mesocolon. It then leaves the sides and, finally, the front of the rectum, and is continued on to the upper ends of the seminal vesicles and the bladder; on either side of the rectum it forms a fossa, the pararectal fossa, which varies in size with the distension of the rectum. In front of the rectum the peritoneum forms the rectovesical excavation, which is limited laterally by peritoneal folds extending from the sides of the bladder to the rectum and sacrum. These folds are known from their position as the rectovesical or sacrogenital folds.
In the female, pararectal fossæ similar to those in the male are present: the lateral limit of the paravesical fossa is the peritoneum investing the round ligament of the uterus.