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Other Terms: Costa prima (I), Costa prima [I]
Ribs are long, slender flat bones. They fall under the classification of flat bone rather than long bone because they do not have an epiphysis with a medullary cavity. The bone consists of an outer shell of compact bone with a trabecular center. The rib has a bow-like shape. The first rib is the shortest of the ribs. It is distinguishable from the other ribs in being flat in the horizontal plane. The proximal aspect of the rib has more character than the distal aspect of the rib. The proximal end forms a ridged head with a single articular surface for the vertebral body. Just distal to the head is a long, tapered neck region that has a prominent tubercle projecting dorsally from its base. Just beyond the neck the rib angles sharply acquiring a flatter profile. This long, flat, gently arching portion of the rib is the costal body. The dorsal surface is rough and has two groove-like impressions for the subclavian vessels. The ventral surface is smooth. The body ends simply, forming a flattened end with a rough, oval surface for the attachment of the costal cartilage. This rib is one of the true ribs or vertebrosternal ribs. It receives this name because the costal cartilage unites the rib directly to the sternum.
The word comes from the Old English word ribbe and this derives from the Anglo-Saxon word ribb. The words had the original meaning of a beam or strip of something. They are closely related to the term ribbon meaning, a narrow band. These are the beams of the chest wall, similar in appearance to the ribs or beams of a boat's walls. The Latin equivalent of rib is costa. Costa is an ancient term that Celsus first used to describe these bones around 30 A.D.
The rib articulates with two bones: the correspondingly numbered thoracic vertebra and the sternum. The rib forms two articular surfaces with the vertebra of the same segment. One where the head joins the posterolateral aspect of the superior border of the vertebral body, the other where the tubercle joins the anterior apex of the transverse process. Distally, the rib forms a rough, oval surface that articulates with the sternum via the costal cartilage.
Ossification of the rib begins in a primary center during the last portion of the second embryonic month. This center arises near the angle of the rib spreading both proximally and distally. Between the fifteenth and twentieth year three secondary centers arise. These are small epiphyses corresponding to the head, the articular portion of the tubercle, and the nonarticular aspect of the tubercle. They ossify with the rib proper between the twentieth to twenty-fourth year.
Costa prima [I]