Lower back. Coloured X-ray of a normal lower back (lumbosacral region) seen from the side; the front of the body is at left. At upper centre are the bones of the spine (vertebrae, red/blue). They are separated by intervertebral discs of soft cartilage, which are not shown clearly on the X- ray. At lower right is the upper part of the sacrum (green), composed of five fused vertebrae, which forms the rear of the pelvis.