A ring of muscles that together comprise a variety of muscles, including the internal anal canal sphincter, the lower part of the rectal wall longitudinal muscle, the deep and superficial parts of the external anal canal sphincter and some of the adjacent anal raphe (puborectalis) fibres.
It wraps around the division between the anal canal and the rectum and can be palpated during rectal fingering. This ring is an important structure of the anal canal, which is surrounded by the internal and external anal sphincter, and is generally contracted in a circular fashion to close the anal canal. If it is inadvertently cut completely during surgery, it can cause fecal incontinence.