Bone · Pelvis

Ischium

Os ischii

The ischium is the lower, posterior part of the hip bone — the part you actually sit on. Its thick tuberosity is the origin of all three hamstrings and part of the adductor magnus, and the sacrotuberous ligament ties it back to the sacrum. It also forms the back of the hip socket and the rear rim of the obturator foramen, the large opening the obturator muscles and nerve pass across.