CHEST (palatalization of AS. cist, test, from Lat. vista, Gk. 00771, kiste, chest, box). or THORAX. In anatomy, the part of the body which lies beneath the neck and above the ab domen (q.v.), constituting the uppermost of the two divisions of the trunk, or that which con tains the heart and lungs and is bounded exter nally by the ribs. The chest is somewhat conical in form, the broad ,,r lower end of the cone being shut in by the diaphragm. a large muscu lar partition which projects upward from the lower ribs, being convex toward the chest and concave toward the abdomen. In respiration (q.v.), the diaphragm descends by its own cular contraction, while at the same time the ribs are drawn upward and outward by the ac cessory muscles of inspiration. The cavity of the chest is thus enlarged. the lungs are expand ed, and air is drawn into them through the trachea, or windpipe, and the bronchial tithes. The combination of bone, cartilage, muscle, and tendon entering into the composition of the chest are such as to permit of expansile move ment to the extent required. and yet to guard against overexpansion. which would he fatal to the delicate structures within. The bones of the chest are at the same time a powerful pro tection against external injury.
'The structures forming the walls of the chest are: (1) The backbone or spinal column, divided into twenty-four true vertebra?, twelve of which, called the dorsal vertebra?, form the thoraeie por tion. (2) 'twelve ribs on either side. attached behind the dorsal and ending in front in the costal cartilages. (3) The sternum, or breast-bone. which occupies the middle line in front, and to which the costal cartilages are at tached on either side. (4) The diaphragm (q.v.). See also SKELETON.
The contents of the chest are the heart, the great arteries and veins, the lungs, the trachea or windpipe, the bronchi or branches of the trachea, leading to the lungs, the (esophagus or gullet, certain important nerve-trunks, and the thoracic duet (q.v.) or general terminus of the
lymphatic system of vessels, by which the chyle and lymph are discharged into the blood. The very great importance of these parts to life, and their great liability to deranged action, renders the chest the seat of a large proportion of the diseases which afflict humanity, and especially of those which end in death. Indeed, of the three organs which the great physiologist Biehat called the 'tripod of life'—viz. the brain, heart, and lungs—the chest contains two: hence its condition in almost all diseases, and especially in fatal diseases, is an object of the utmost solicitude to the physician.
The diseases of the chest depend in some cases -c.n alterations in its form. as by rickets (q.v.) and other conditions affecting the bones in early childhood or in youth, or by too tight lacing in girls. The lungs and air-tubes are subject to a great variety of diseases, among which the prin cipal are consumption, or pulmonary tubercu losis (q.v.), pneumonia (q.v.), pleurisy (q.v.), and bronchitis q.v.). The heart is subject to pericarditis, endoearditis, enlargement (hyper trophy), dilatation, and degeneration of its muscular texture. The aorta, or great artery, is often affected with degeneration of its walls, and occasionally with aneurism. The great veins are liable to over-distension, and to ob struction by tumors or by coagulation of the contained blood. The thoracic duet is also sometimes obstructed by external pressure. and the oesophagus has a number of diseases usually described in connection with the alimentary canal. Most of the diseases here referred to are described either in special articles, or under HEART, DISEASES Or. See also the articles Aus CITT.TATIoN, and PERCUSSION.