Human skeleton. Computer illustration of the upper part of a male skeleton. The skeleton's 206 bones provide protection and support, while their joints allow locomotion. The skull (upper center) protects the brain. The ribs of the chest (center to lower center) enclose the heart and lungs. The upper ribs join onto the sternum (breastbone) at the front. The spine, running down the back of the body from the skull, surrounds the spinal cord. Long bones make up the arms. The humerus (upper-arm bone) articulates with the radius and ulna at the elbow. The two clavicles (collarbones) run from above the sternum across to the top of each humerus.