This is a long bone, suspended from the dorsal spine by the ribs, the first eight of which articulate with it. In early life it is made up of six distinct pieces, united by intervening-cartilage or gristle. In front it is like the keel of a vessel, owing to the projection of a flattened piece of cartilage [cariniform cartilage) which curves upward and presents a sharpened border to the front, and below for about two-thirds of its length. The posterior extremity is continued backward by a flat piece of cartilage, called the xiphoid or ensiform cartilage, and along the superior part of each side of this bone are eight depressions, which receive the inferior ends of the cartilages of the true ribs to form so many synovial articulations or joints.

Fig. 292. - Sternum Cariniform Cartilage. 2 Ensiform Cartilage or Xiphoid Appendage. 3 Inferior Border. 4 4 4 Cavities for articulation with lower extremities of Costal Cartilages.

Fig. 293. - Sternum and Costal Cartilages. 1 Cariniform Cartilage. 2 Ensiform Cartilage. 3-10 Costal Cartilages.