The hemispheric articular surface at the upper extremity of the thigh bone[Stedman, 26th ed]. The femur head is the highest part of the thigh bone. It is supported by the neck of the femur. The head is globular and forms rather more than a hemisphere, is directed upward, medialward, and a little forward, the greater part of its convexity being above and in front. Its surface is smooth, coated with cartilage in the fresh state, except over an ovoid depression, the fovea capitis femoris, which is situated a little below and behind the center of the head, and gives attachment to the ligament of head of femur. If there is a fracture of the neck of the femur, the blood supply through the ligament becomes crucial. In orthopedic surgery, the head of the femur is important because it can undergo avascular necrosis and consequent osteochondritis dissecans. The head is removed in total hip replacement surgery [WP]. [ http://en.wikipedia.org/wiki/Femur_head ]