The anal canal is the lowermost portion of the gastrointestinal tract, a short tube connecting the rectum to the external skin, through which stool leaves the body. It is usually around 3 to 4 cm in length and is an area of transition from the mucosa of the rectum to the anus and skin of the perianal area. It has an important function in defaecation and maintaining faecal continence. It is richly supplied by blood vessels and nerves and is usually in the collapsed position due to the contraction of the internal and external anal sphincters (muscles). Any malignancy arising in the anal canal is called an anal canal cancer.