The muscles within the pelvis may be divided into two groups:

  • the Obturator Internus and the Piriformis, which are muscles of the lower extremity, and will be described with these;
  • the Levator Ani and the Coccygeus or Ischiococcygeus, which together form the pelvic diaphragm which supports the pelvic viscera.

The Levator Ani is composed by three parts:

  • Iliococcygeus;
  • Pubococcygeus;
  • Puborectalis.

The classification of the two groups under a common heading is convenient in connection with the fasciae investing the muscles. These fasciae are closely related to one another and to the deep fascia of the perineum, and in addition have special connections with the fibrous coverings of the pelvic viscera; it is customary therefore to describe them together under the term pelvic fascia.