A plate of cartilage, or a series of bony or cartilaginous plates or segments, in the median line of the pectoral skeleton of most vertebrates above fishes; the breastbone. [1913 Webster
" The sternum is connected with the ribs or the pectorial girdle, or with both. In man it is a flat bone, broad anteriorly, narrowed behind, and connected with the clavicles and the cartilages of the seven anterior pairs of ribs. In most birds it has a high median keel for the attachment of the muscles of the wings."