=The Sternum.=--The sternum or breast-bone is a long narrow bone and has three parts, the _manubrium_ or handle above, the _gladiolus_ or sword, and the _ensiform cartilage_ at the lower end. On either side are notches for the costal cartilages; for the first seven ribs as well as the clavicle articulate with it. Except for some muscles along the edges it lies directly under the skin and the ridge between the manubrium and the gladiolus can be felt in the living, a fact which assists in determining the position of the different ribs in cases of fracture, as the second rib articulates at this point. [Illustration: FIG. 37.--A and B, typical ribs; C, first rib; D, twelfth rib. 1, head; 2, neck; 3, tuberosity; 4, grooved edge; 5, shaft; 6, oval depression for costa cartilage.] =The Ribs.=--The ribs are twenty-four in number, twelve on each side, of which the upper seven, which articulate with the sternum by individual cartilages, are called _true ribs_, the other five _false ribs_. Of the false ribs the upper three articulate indirectly with the sternum through the seventh cartilage, with which their cartilages unite, while the other two have their anterior extremities free and are called _floating ribs_. All the ribs slope down toward the front and are by nature more freely movable in women than in men. Most of the ribs have a head divided by a little ridge into two facets for articulation with the dorsal vertebræ, a flattened neck, a tuberosity at the base of the neck with a facet for articulation with the transverse process of the vertebra below, an angle, and a shaft, which is externally convex and is grooved on its lower edge for the intercostal vessels and nerve. The first and second, eleventh and twelfth ribs, however, are somewhat peculiar, the first two being shorter, flatter and rather broader than the rest and the first having only one facet on the head, while the last two have only one facet on the head and no neck or tuberosity. The _costal cartilages_ serve to prolong the ribs and greatly increase the elasticity of the chest wall. They grow longer down to the seventh and then decrease again in length. The ribs, except the first and second, which are protected by the clavicle, are frequently _broken_. Such a break causes pain in breathing and sometimes the end of a rib pierces the lung tissue and swelling all over the body results, due to the presence of air. _Caries_ or death of the rib is also frequent. _Fracture of the sternum_ occurs occasionally, generally from direct force, as from a blow with the knee in foot-ball, and there may be dislocation between the manubrium and gladiolus.