There are three bones of the
os coxae (hip bone) that come together to form the
acetabulum. Contributing a little more than two-fifths of the structure is the
ischium, which provides lower and side boundaries to the acetabulum. The
ilium forms the upper boundary, providing a little less than two-fifths of the structure of the acetabulum. The rest is formed by the
pubis, near the midline. It is bounded by a prominent uneven rim, thick and strong on top, which serves as the point of attachment for the
acetabular labrum. The acetabular labrum reduces the size of the opening of the acetabulum and deepens the surface of the hip joint. 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. 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. Its counterpart in the pectoral girdle is the
glenoid fossa. 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. The notch is converted into a foramen by the transverse acetabular ligament; through the foramen nutrient vessels and nerves enter the joint. This is what holds the head of the femur securely in the acetabulum.
Blood supply The acetabular branch of the obturator artery supplies the
acetabulum through the acetabular notch. The pubic branches supply the pelvic surface of the
acetabulum. Deep branches of the superior gluteal artery supply the superior region and the inferior gluteal artery supplies the postero-inferior region.
Reptiles and birds In
reptiles and
birds, the
acetabula are deep sockets. Organisms in the
dinosauria clade are defined by a perforate
acetabulum, which can be thought of as a "hip-socket". The perforate
acetabulum is a cup-shaped opening on each side of the pelvic girdle formed where the
ischium,
ilium, and
pubis all meet, and into which the head of the femur inserts. The orientation and position of the
acetabulum is one of the main morphological traits that caused dinosaurs to walk in an upright posture with their legs directly underneath their bodies. In a relatively small number of dinosaurs, particularly
ankylosaurians (e.g.
Texasetes pleurohalio), an imperforate
acetabulum is present, which is not an opening, but instead resembles a shallow concave depression on each side of the pelvic girdle. ==Development==