Ischium

Situated below the ilium and behind the pubis, it is one of these three bones whose fusion creates the coxa. The superior portion of this bone forms approximately one third of the acetabulum.

It is divisible into three portions:

• Body of ischium - Contains a prominent spine which serves as the origin for gemellus superior. The indentation inferior to the spine is the lesser sciatic notch. Continuing down the posterior side, the ischial tuberosity is a thick, rough surfaced prominence below the lesser sciatic notch. This is the portion that supports weight while sitting (especially noticeable on a hard surface). It can be felt simply by sitting on one’s fingers. Additionally, it serves as the origin for gemellus inferior and adductor magnus.

• Superior ramus of the ischium - Serves as a partial origin for obturator internus and obturator externus.

• Inferior ramus of the ischium - Serves as a partial origin for gracillis and adductor magnus.

The ischial ramus joins the inferior ramus of the pubis anteriorly. It is the strongest of the coxal bones.