Ilium (bone)

Overview
The ilium of the pelvis is divisible into two parts, the body and the ala; the separation is indicated on the internal surface by a curved line, the arcuate line, and on the external surface by the margin of the acetabulum. The name comes from the Latin, meaning "groin" or "flank."

Body (corpus oss. ilii)
The body enters into the formation of the acetabulum, of which it forms rather less than two-fifths.

Its external surface is partly articular, partly non-articular; the articular segment forms part of the lunate surface of the acetabulum, the non-articular portion contributes to the acetabular fossa.

The internal surface of the body is part of the wall of the lesser pelvis and gives origin to some fibers of the Obturator internus.

Below, it is continuous with the pelvic surfaces of the ischium and pubis, only a faint line indicating the place of union.