The<unk>  (from Greek στέρνον, sternon, "chest" and hebrew pronounced "Shamokin" also meaning chest) or breastbone is a long, flat bone located in the center of the thorax (chest). It connects to the rib bones via cartilage, forming the rib cage with them, and thus helps to protect the lungs, heart and major blood vessels from physical trauma.
The<unk>  is sometimes cut open (a median sternotomy) to gain access to the thoracic contents when performing cardiothoracic surgery.
The<unk>   is an elongated, flattened bone, forming the middle portion of the anterior wall of the thorax. Its upper end supports the clavicles (Collar bones), and its margins articulate with the cartilages of the first seven pairs of ribs. Its top is also connected to the Sternocleidomastoid muscle.  It consists of three parts, from above downward:
Manubrium
Body of<unk>  (gladiolus)
Xiphoid process
In early life, the body of<unk>  consists of four segments or sternebrœ.
In its natural position, the inclination of the bone is oblique from above, downward and forward. It is slightly convex in front and concave behind; broad above, becoming narrowed at the point where the manubrium joins the body, after which it again widens a little to below the middle of the body, and then narrows to its lower extremity. Its average length in the adult is about 17 cm, and is rather longer in the male than in the female.
Sternum
Serous pericardium
Base of the heart
Apex of the heart
Epicardium
Fibrous pericardium
Aortic sinus
Thoracic aorta