GLUTEAL LIGAMENTS The parts of the bony pelvis—hip bones, sacrum, and coccyx—are bound together by dense ligaments (Fig. 5.33). The posterior sacro-iliac ligament is continuous inferiorly with the sacrotuberous ligament. The sacrotuberous ligament extends across the sciatic notch of the hip bone, converting the notch into a foramen that is further subdivided by the sacrospinous ligament and ischial spine, creating the greater and lesser sciatic foramina. The greater sciatic foramen is the passageway for structures entering or leaving the pelvis (e.g., sciatic nerve), whereas the lesser sciatic foramen is the passageway for structures entering or leaving the perineum (e.g., pudendal nerve). It is helpful to think of the greater sciatic foramen as the “door” through which all lower limb arteries and nerves leave the pelvis and enter the gluteal region. The piriformis muscle (Fig. 5.34D–G; Table 5.6) also enters the gluteal region through the greater sciatic foramen and fi lls most of it.