It is called the utero-rectal fossa, also known as the Douglas sink, because of the fossa-shaped junction of the uterus and the rectum. The utero-rectal fossa is the lowest part of the abdominal cavity, where blood, fluid and pus accumulation in the abdominal cavity tend to accumulate. Since only a layer of peritoneum and the mucosa of the vaginal wall separates the rectal fossa from the posterior vaginal fornix, posterior vaginal fornix aspiration can be performed to obtain fluid here for laboratory examination, which is a common clinical aid for diagnosis. It is suitable for abdominal bleeding and pelvic effusion caused by ectopic pregnancy, ovarian corpus luteum rupture, etc. The puncture can also be used for drainage, drug injection treatment and tissue biopsy. The presence of lesions can be determined by triage examination and ultrasound examination of the rectal fossa of the uterus, which can sometimes reveal fluid in the rectal fossa of the uterus. a small amount of fluid is usually not a problem and can be seen during menstruation and ovulation, while a larger amount of fluid needs to be investigated for pelvic inflammatory disease and pelvic tumors. The most common lesion in the rectal fossa is an endometriotic nodule. If a palpable nodule can be felt in the rectal fossa, it is usually a specific sign of pelvic endometriosis. If there are no obvious clinical symptoms, it can be followed up and observed. If there are clinical symptoms but the lesion is not large, medication can be taken, such as oral short-acting contraceptive pills and the Manned IUD. If the lesion is large and cannot be excluded from malignant possibility, it needs to be removed surgically. Ovarian cancer can also manifest as implantation nodules in the rectal fossa of the uterus. In addition to pelvic and ovarian masses, a triple examination or ultrasound examination can reveal nodules in the rectal fossa of the uterus, which are usually not painful to touch and can be diagnosed clearly by tissue biopsy.