The Iliococcygeus arises from the ischial spine and from the posterior part of the tendinous arch of the obturator fascia, and is attached to the coccyx and anococcygeal raphC); it is usually thin, and may fail entirely, or be largely replaced by fibrous tissue. It is part of the levator ani group of muscles. An accessory slip at its posterior part is sometimes named the Iliosacralis. [ http://en.wikipedia.org/wiki/Iliococcygeus_muscle ]