Rib cage coloured three-dimensional computed tomography (CT) scan. The thorax is made up of the breast bone (sternum, centre) at the front, the spine (vertebral column, upper centre) at the back and ribs (rib cage) around the sides (centre left & right). The thorax protects organs such as the heart & lungs (not seen). The arms bones (humeri) are seen at far left & right. The shoulder girdle (pectoral girdle) is made up of the collar bones (clavicles, upper right & left), and the shoulder bones (scapulae, connected at the top of each humerus). CT scans use X-rays to form slice images of the body. These are built into a three- dimensional image by computer.