Hip bones. Artwork of a frontal (anterior) view of the left hip, showing the bones that articulate to form this joint. At lower right is the femur (thigh bone). The head of the femur (ball-shaped) is covered in cartilage (grey) that cushions it as it moves in the acetabulum, the hip socket in the pelvis. The pelvis bones that form part of the hip joint are the ischium and pubis (centre left) and the ilium (upper centre). At top left are the lower bones of the spine, the tailbone (coccyx), sacrum, and several lumbar vertebrae.