The hip bone, innominate bone is a large, flattened, irregularly shaped bone, constricted in the center and expanded above and below.
With opposite innominate bone and sacrum, the hip bone comprises the skeletal component of the pelvis.
It consists of three parts, the ilium, ischium, and pubis.
Each of these part is separate in childhood but fuse in adulthood by 25 years of age.
The ilium 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 medially and inferiorly from the acetabulum and articulates in the midsagittal plane at the pubic symphysis, with the bone of the opposite side: it forms the front of the pelvis and supports the external organs of reproduction.