Beside the Thoracic vertebrae, the breast bone (Sternum), and the ribs (Costae) also belong to the thorax. The breastbone is a flat bone. From here, bone red marrow can be taken for diagnostic purposes; and this will be called sternal puncture.
From the twelve pairs of ribs, seven are directly connected to the breastbone. We call them "genuine ribs".

Between the first rib and the breastbone, a cartilage connection exists. Between the 2nd -5th Ribs (usually also 6th and 7th rib) and the breastbone, we find "genuine joint".

We call the remaining five pairs of ribs "wrong ribs", since they are only indirectly or not at all connected to the breastbone.

The 8th, 9th, and 10th ribs (the first three of the wrong ribs) are connected by cartigen among themselves and fastened also by cartigen to the lowest genuine pair of ribs.
The two lowest pairs of ribs end freely in the musculature.
We speak therefore of "free ribs".