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Costae or ribs
Other Terms: Ribs, Rib cage, Ribcage, Ribs [I-XII], Set of ribs [I-XII], Ribs set, Costae [I-XII]
Together they unite the thoracic vertebrae to the sternum via costal cartilages to form the thoracic skeleton, a flexible, bony wall that protects thoracic viscera and facilitates respiratory function. Although we only describe the twelve thoracic ribs, there are in reality ribs for every vertebra. The cervical, lumbar, and sacral ribs fuse to their corresponding vertebra becoming the major contributor to what is described as the transverse process. The ribs can be divided into two groups - true ribs and false ribs. The last two false ribs are called floating ribs. True ribs, ribs one through seven, are those that have their costal cartilages attached directly to the sternum. False ribs, ribs eight through twelve, have costal cartilages that do not attach directly to the sternum. The costal cartilage of the first three false ribs attach to the cartilage of the superior rib. The last two false ribs do not attach to other ribs and are therefore called floating ribs.
Costae is a Latin word meaning ribs. The word rib means the beams of the chest. It arises from the Middle English word ribbe that came from the Anglo-Saxon word ribb meaning beam or strip.
The ribs form synovial articulations with the vertebrae and the sternum. The joints are simple synovial joints called plane joints.
Ossification of the rib skeleton is via endochondral bone formation. The sternal end of the cartilaginous anlagen remain unossified and connect the bone to the sternum as the costal cartilages. In later life these cartilages may calcify, but they never become true bone.