The adult human skeleton normally has 12 pairs of ribs.
That gives most adults 24 ribs, arranged as curved bones on the left and right sides of the thorax. The ribs help protect the heart and lungs while forming part of the flexible chest wall needed for breathing. They articulate at the back with the thoracic vertebrae, and many connect toward the front through costal cartilage.
The first seven pairs are called true ribs because their cartilage connects directly to the sternum. Ribs eight through ten are false ribs because their cartilage joins the cartilage above rather than attaching directly to the sternum. Ribs eleven and twelve are floating ribs, with no front attachment. Anatomical variation occurs: some people have an additional cervical rib or other rib differences. Such variations do not change the standard anatomical count of 12 pairs.