are ribs that are attached directly to the sternum
Ribs: There are 12 pairs of ribs, all of which are attached posteriorly to the respective thoracic vertebrae. The upper 7 pairs are attached to the sternum directly through their costal cartilages. Ribs 8 through 10 are attached indirectly to the sternum through the seventh costal cartilage. Their costal cartilages are also attached with each other at different points.