Ilium (bone)

The ilium (/ˈɪlɪəm/) is the uppermost and largest bone of the pelvis, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.

The name comes from the Latin (ile, ilis), meaning "groin" or "flank."

The ilium of the human is divisible into two parts, the body and the ala; the separation is indicated on the top surface by a curved line, the arcuate line, and on the external surface by the margin of the acetabulum.

Structure

Body (corpus ossis ilium)

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.