Sternum (redirected from Sterna)

sternum: see rib.

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sternum

1. (in man) a long flat vertical bone, situated in front of the thorax, to which are attached the collarbone and the first seven pairs of ribs

2. the corresponding part in many other vertebrates

3. a cuticular plate covering the ventral surface of a body segment of an arthropod

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sternum [′stər·nəm]

(anatomy)

The bone, cartilage, or series of bony or cartilaginous segments in the median line of the anteroventral part of the body of vertebrates above fishes, connecting with the ribs or pectoral girdle.

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Sternum 

the complex of skeletal elements in terrestrial vertebrates and man that unite, along the midline of the body, the ventral ends of the true ribs and parts of the pectoral girdle and to which the sternal muscles are attached.

The sternum is a derivative of the ribs and first appeared in terrestrial vertebrates when a strengthening of support for the pectoral girdle was required in connection with the progressive evolution of the forelimbs. In amphibians and reptiles the sternum is usually cartilaginous; in the latter, only a few ribs are attached, forming the thorax. In birds the sternum is osseous; in flying birds there is a median process, the keel, to which the powerful pectoral muscles are attached. In mammals the sternum consists of three sections: the manubrium, the corpus sterni, and the xiphoid process. In man the sternum, or breastbone, is an unpaired flat bone that forms the middle part of the anterior wall of the thorax.