Artwork of a section through the human rectum and anus, the opening at the lower end of the alimentary canal, through which faeces are passed. The rectum, the terminal portion of the large intestine, is about 12cm in length and runs from the sigmoid colon to the anal canal. Faeces are stored in the rectum prior to defaecation. The anus, the opening of the anal canal, is guarded by two ring-like muscular sphincters, which are contracted and closed except during defaecation.