Costal margin
Encyclopedia
The costal margin, sometimes referred to as the costal arch, is the medial margin formed by the false ribs
and one true rib -- specifically, from the seventh rib to the tenth rib.
False ribs
The false ribs, are the five sets of ribs below the top seven true ribs. A rib is considered to be "false" if it has no direct attachment to the sternum, also known as the breast bone...
and one true rib -- specifically, from the seventh rib to the tenth rib.