sacrotuberous ligament

noun

sa·​cro·​tu·​ber·​ous ligament ˌsā-krō-ˌt(y)ü-b(ə-)rəs-, ˌsak-rō- 

: a thin fan-shaped ligament on each side of the body that is attached above to the posterior superior and posterior inferior iliac spines and to the sacrum and coccyx, that passes obliquely downward to insert into the inner margin of the ischial tuberosity, and that with the sacrospinous ligament closes off the lesser sciatic notch to form the lesser sciatic foramen