Pelvic x-ray. Composite image of a computer model of the pelvic bones (green) on a coloured X-ray of the pelvis of a 6-month-old baby girl, showing flesh (pink). The lowest lumbar vertebra of the spinal column (top centre) forms a joint with the sacrum. The sacrum forms the back of the pelvis (centre) and is connected to the large ear-shaped hip bones (centre left and right). Each hip bone is formed from three fused bones and accommodates the ball of the head of each femur (thigh bone, lower left and right), forming the hip joints. In the adult female, the pelvis is wider and shallower.