Sacrotuberous ligament

The sacrotuberous ligament is situated at the lower and back part of the pelvis. It is flat, and triangular in form; narrower in the middle than at the ends; attached by its broad base to the posterior inferior spine of the ilium, to the fourth and fifth transverse tubercles of the sacrum, and to the lower part of the lateral margin of that bone and the coccyx. Passing obliquely downward, forward, and lateralward, it becomes narrow and thick, but at its insertion into the inner margin of the tuberosity of the ischium, it increases in breadth, and is prolonged forward along the inner margin of the ramus, as the falciform process, the free concave edge of which gives attachment to the obturator fascia; one of its surfaces is turned toward the perineum, the other toward the Obturator internus. The lower border of the ligament is directly continuous with the tendon of origin of the long head of the Biceps femoris, and by many is believed to be the proximal end of this tendon, cut off by the projection of the tuberosity of the ischium.

Relations.—The posterior surface of this ligament gives origin, by its whole extent, to the Glutæus maximus. Its anterior surface is in part united to the sacrospinous ligament. Itsupper border forms, above, the posterior boundary of the greater sciatic foramen, and, below, the posterior boundary of the lesser sciatic foramen. Its lower border forms part of the boundary of the perineum. It is pierced by the coccygeal nerve and the coccygeal branch of the inferior gluteal artery.

These sacrotuberous and sacrospinous ligaments convert the sciatic notches into foramina.

• The greater sciatic foramen is bounded, in front and above, by the posterior border of the hip bone; behind,by the sacrotuberous ligament; and below, by the sacrospinous ligament. It is partially filled up, in the recent state, by the Piriformis which leaves the pelvis through it. Above this muscle, the superior gluteal vessels and nerve emerge from the pelvis; and below it, the inferior gluteal vessels and nerve, the internal pudendal vessels and nerve, the sciatic and posterior femoral cutaneous nerves, and the nerves to the Obturator internus and Quadratus femoris make their exit from the pelvis.
• The lesser sciatic foramen is bounded, in front, by the tuberosity of the ischium; above, by the spine of the ischium and sacrospinous ligament;behind, by the sacrotuberous ligament. It transmits the tendon of the Obturator internus, its nerve, and the internal pudendal vessels and nerve.