One of the two halves of the sternum, or chest. These bones are usually imbedded in cartilage and are sometimes poorly ossified. In dinosaurs, they generally do not articulate directly with the shoulder girdle (at the coracoids) but "float free" in the chest cartilage. They serve to anchor the tips of the thoracic ribs and the front of the abdominal ribcage, and they act as braces and spacers for the lower shoulder bones (coracoids). In flying birds, the sternal plates are fused solidly together into a relatively huge, keeled breastbone that serves to anchor the pectoral muscles that work the wings.