Many of the important nerves in the gluteal region are in the plane between the superficial and deep groups of muscles.
The piriformis muscle is the most superior of the deep group of muscles (Fig. 6.45) and is a muscle of the pelvic wall and of the gluteal region (see Chapter 5, p. 443). It originates from between the anterior sacral foramina on the anterolateral surface of the sacrum and passes laterally and inferiorly through the greater sciatic foramen.