The acetabulum (Cotyloid cavity) is a deep socket on the outer surface of the hip bone into which the head of the femur (thigh bone) fits forming the hip joint. The acetabulum is the point where the three components of the hip bone (ilium, ischium and pubis) meet. The upper part and sides of the acetabulum forms the horse-shoe shaped lunate surface.
This is where the head of the femur chiefly articulates and where the weight of the trunk is transferred to the lower limb; it is covered in life by articular cartilage. The inferior parts of the acetabulum is non-articular and is usually filled with fat covered by synovial membrane.
The acetabulum is an excellent socket but is made deeper still by a fibrocartilaginous labrum (= lip) which surrounds it. The ligament of the head of the femur arises from this labrum.
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