The Coccygeus is a muscle of the pelvic wall (i.e. peripheral to the pelvic floor), situated behind the levator ani and in front of the sacrospinous ligament. It is a triangular plane of muscular and tendinous fibers, arising by its apex from the spine of the ischium and sacrospinous ligament, and inserted by its base into the margin of the coccyx and into the side of the lowest piece of the sacrum. It assists the Levator ani and Piriformis in closing in the back part of the outlet of the pelvis. [WP,unvetted]. [ http://en.wikipedia.org/wiki/Coccygeus_muscle ]