Ilium (bone)

The ilium (/ˈɪliəm/) (pl.: ilia) 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, with the exception of some snake species which have a tiny bone considered to be an ilium.

The ilium of the human is divisible into two parts, the body and the wing; 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 name comes from the Latin (ile, ilis), meaning "groin" or "flank".

The ilium consists of the body and wing. Together with the ischium and pubis, to which the ilium is connected, these form the pelvic bone, with only a faint line indicating the place of union.

The body (Latin: corpus) forms less than two-fifths of the acetabulum; and also forms part of 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.

The wing (Latin: ala) is the large expanded portion which bounds the greater pelvis laterally. It has an external and an internal surface, a crest, and two borders—an anterior and a posterior.

In humans, biiliac width is an anatomical term referring to the widest measure of the pelvis between the outer edges of the upper iliac bones.

Biiliac width has the following common synonyms: pelvic bone width, biiliac breadth, intercristal breadth/width, bi-iliac breadth/width and biiliocristal breadth/width.