The anus, which structurally begins at the dentate line and ends at the anal verge, is the very end of the digestive tract and the interface between the body and the outside world, and is the anal canal in the anatomical sense. The anus begins at the bottom of the rectum and is the last part of the colon. The dentate line is the boundary between the rectum and the anus, and the organs adjacent to it are the prostate and urethra in the anterior position, the uterus and vagina in women, and the coccyx in the posterior position. The surrounding structure is surrounded by fascial-like tough tissue, and the anal canal is surrounded above by the internal sphincter and below by the anal canal formed by the external sphincter. The main function is to close and open the anal canal by contraction and relaxation, helping to control feces and to avoid leakage or expulsion of feces from the body. Due to the special structure and environment of the anus, the chance of infection and contamination is much higher than that of other body organs, so care should be taken to maintain cleanliness and hygiene.