Organisms in the dinosauria clade are defined by a perforate acetabulum, which can be thought of as a 'hip-socket'. In reptiles and birds, the acetabula are deep sockets. Reptiles and birds An example of a perforated acetabulum on an ornithischian dinosaur Deep branches of the superior gluteal artery supply the superior region and the inferior gluteal artery supplies the postero-inferior region. The pubic branches supply the pelvic surface of the acetabulum. The acetabular branch of the obturator artery supplies the acetabulum through the acetabular notch. Friction inside a normal hip is less than one-tenth that of ice gliding on ice. The well-fitting surfaces of the femoral head and acetabulum, which face each other, are lined with a layer of slippery tissue called articular cartilage, which is lubricated by a thin film of synovial fluid. This is what holds the head of the femur securely in the acetabulum. The notch is converted into a foramen by the transverse acetabular ligament through the foramen nutrient vessels and nerves enter the joint. The acetabulum is also home to the acetabular fossa, an attachment site for the ligamentum teres, a triangular, somewhat flattened band implanted by its apex into the antero-superior part of the fovea capitis femoris. Its counterpart in the pectoral girdle is the glenoid fossa. The rest of the acetabulum is formed by a curved, crescent-moon shaped surface, the lunate surface, where the joint is made with the head of the femur. At the lower part of the acetabulum is the acetabular notch, which is continuous with a circular depression, the acetabular fossa, at the bottom of the cavity of the acetabulum. It is bounded by a prominent uneven rim, which is thick and strong above, and serves for the attachment of the acetabular labrum, which reduces its opening, and deepens the surface for formation of the hip joint. The rest is formed by the pubis, near the midline. The ilium forms the upper boundary, providing a little less than two-fifths of the structure of the acetabulum. Contributing a little more than two-fifths of the structure is the ischium, which provides lower and side boundaries to the acetabulum. There are three bones of the os coxae (hip bone) that come together to form the acetabulum. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint. The acetabulum ( / ˌ æ s ɪ ˈ t æ b j ə l ə m/), also called the cotyloid cavity, is a concave surface of the pelvis.

Acetabulum of pelvis