The rib-cage is a bony framework that protects the heart, lungs, and other underlying organs. The rib-cage is made up of three groups of bones – the sternum (breastbone), 12 pairs of ribs, and 12 thoracic vertebrae.
All of the ribs are attached to the spinal column, but only the top seven pairs connect to the sternum. These are called true ribs and are joined to the sternum by strips of cartilage known as costal cartilage. The next three pairs of ribs are known as false ribs. Instead of attaching directly to the sternum, they all attach to the lowest true rib. The last two pairs of ribs are called floating ribs and attach only to the spine.
Upon inhalation, muscles between the ribs, called intercostal muscles, lift the rib-cage helping the lungs to expand. Upon exhalation, the rib-cage moves down, squeezing air out of the lungs.