Hip bone

The hip bone (or innominate bone) is a large, flattened, irregularly shaped bone, constricted in the center and expanded above and below. It is one of the few ball and socket synovial joints in the body.

It meets its fellow on the opposite side in the middle line in front, and together they form the sides and anterior wall of the pelvic cavity.

Together with the sacrum and coccyx, it comprises the pelvis.

Components
It consists of three parts, the ilium, ischium, and pubis, which are distinct from each other in the young subject, but are fused in the adult; the union of the three parts takes place in and around a large cup-shaped articular cavity, the acetabulum, which is situated near the middle of the outer surface of the bone.


 * The ilium, so-called because it supports the flank, is the superior broad and expanded portion which extends upward from the acetabulum.


 * The ischium is the lowest and strongest portion of the bone; it proceeds downward from the acetabulum, expands into a large tuberosity, and then, curving forward, forms, with the pubis, a large aperture, the obturator foramen.


 * The pubis extends medialward and downward from the acetabulum and articulates in the middle line with the bone of the opposite side: it forms the front of the pelvis and supports the external organs of generation.