The axial skeleton

Anatomists divide the skeleton into two major groups. The axial skeleton forms the body’s central axis — the skull, the vertebral column (spine), and the rib cage together with the breastbone (sternum). Its main job is protecting the brain, spinal cord, and the organs of the chest, while also supporting the head and torso.

The skull is itself made of many separate bones fused together into one rigid case around the brain, with additional bones forming the face. The spine develops from about 33 vertebral segments: adults usually have 24 separate vertebrae plus fused segments forming the sacrum and coccyx, running from the base of the skull to the pelvis, that both supports the body’s posture and encloses the spinal cord. The rib cage — twelve pairs of curved ribs, most of them attached at the front to the sternum — expands and contracts with every breath while shielding the heart and lungs.