Ilium bone

Ilium of pelvis
Overview of Ilium as largest region of the pelvis.
Capsule of hip-joint (distended). Posterior aspect. (Ilium labeled at top.)
Details
Identifiers
Latin	Os ilium
MeSH	A02.835.232.611.434
TA	A02.5.01.101
FMA	16589
Anatomical terms of bone []

The ilium (/ˈɪlɪəm/) is the uppermost and largest region of the coxal bone, 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 (, 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.

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, with only a faint line indicating the place of union.

The body of ilium together with the wing forms the ilium.

The wing of ilium (or ala) is the large expanded portion which bounds the greater pelvis laterally. It presents for examination two surfaces—an external and an internal—a crest, and two borders—an anterior and a posterior.