The Ribs

Ribs are flat, curved bones that form the framework of the chest and make up a cage to protect the heart, lungs and other upper organs. There are twelve pairs of ribs, each joined at the back of the cage to a vertebra in the spine. Between the ribs, and attached to them, are thin sheets of muscle that help to expand and relax the chest during breathing. The spaces between the ribs contain nerves and blood vessels. There are seven true ribs attached to the sternum (breastbone) directly by their costal cartilages. The remaining five pairs are called "false ribs," because their cartilages do not reach the sternum directly. Instead, the cartilages of the upper three false ribs join the cartilages attached to the ribs above, while the last rib pairs have no cartilaginous attachments to the sternum at all. These last two pairs are sometimes called "floating" ribs." The front ends of the upper ribs are linked to the sternum by cartilage, which is tough, thick and elastic. It has no blood supply of its own, but obtains nutrients from tissue fluid. The ligaments which join the costal cartilages of the ribs to the clavicle (collarbone) are called the "costoclavicular ligaments."