Which muscle along with levator ani is responsible for formation of the pelvic diaphragm ?

The Coccygeus is a muscle of the pelvic floor, located posterior to levator ani and anterior to 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 inseed by its base into the margin of the coccyx and into the side of the lowest piece of the sacrum. In combination with the levator ani, it forms the pelvic diaphragm. Ref - sciencedirect.com