Ilium - Os ilium; Ilium
The ilium, so-called because it supports the flank, is the superior broad and expanded portion of coxal bone which extends upward from the acetabulum.
The ilium 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.
This definition incorporates text from a public domain edition of Gray's Anatomy (20th U.S. edition of Gray's Anatomy of the Human Body, published in 1918 – from http://www.bartleby.com/107/).
General Anatomy > Bones; Skeletal system > Appendicular skeleton > Bones of lower limb > Pelvic girdle > Hip bone; Coxal bone; Pelvic bone > Ilium