‘Anus’ is a general term for the outlet of the bowel and includes both the anal canal and the peri-anal skin. The canal is 3 to 4 cm long, the superior limit being the palpable upper border of the anal sphincters and puborectalis muscles of the anorectal ring and the distal limit, or anal verge, being the level at which the walls of the canal come into contact in their normal resting state. The peri-anal area, sometimes called the anal margin, is the skin within a 5-cm radius of the anal verge.