The anus is the end of the large intestine, below the rectum, through which stool (solid waste) leaves the body. The anus is formed partly from the outer skin layers of the body and partly from the intestine. Two ring-like muscles, called sphincter muscles, open and close the anal opening and let stool pass out of the body. The anal canal, the part of the anus between the rectum and the anal opening, is about 1-1½ inches long.
The skin around the outside of the anus is called the perianal area. Tumors of the perianal skin that do not involve the anal sphincter are usually treated the same as anal cancers, although local therapy may be used for some.Read more