• Is formed by the fusion of the ilium, ischium , and pubis of the pelvis.
• Articulates with the sacrum at the sacroiliac joint to form the pelvic girdle.

Ilium

• Forms the lateral part of the hip bone and consists of the body, which joins the pubis and ischium to form the acetabulum, and the ala or wing, which forms the iliac crest.
• Also comprises the anterior-superior iliac spine, anterior-inferior iliac spine, posterior iliac spine, greater sciatic notch, iliac fossa, and gluteal lines.

Pubis

• Forms the anterior part of the acetabulum and the anteromedial part of the hip bone.
• Comprises the body , which articulates at the symphysis pubis; the superior ramus, which enters the formation of the acetabulum; and the inferior ramus , which joins the ramus of the ischium, a part of the obturator foramen (formed by fusion of the ischium and pubis).

Ischium

• Forms the posteroinferior part of the acetabulum and the lower posterior part of the hip bone.
• Consists of the body , which joins the ilium and superior ramus of the pubis to form the acetabulum, and the ramus , which joins the inferior pubic ramus to form the ischiopubic ramus.
• Has the ischial spine, ischial tuberosity, and lesser sciatic notch.

Acetabulum

• Is an incomplete cup-shaped cavity on the lateral side of the hip bone in which the head of the femur fits.
• Includes the acetabular notch, which is bridged by the transverse acetabular ligament.
• Is formed by the ilium superiorly, the ischium posteroinferiorly, and the pubis anteromedially.