CHEST, or Tuo'nnx, in anatomy, is the part of the body which lies beneath the neck and above the abdomen (q.v.), constituting the uppermost of the two divisions of the trunk, or that which contains the heart and lungs, and is bounded externally by the ribs. The C. is somewhat conical in form, the broad or lower end of the cone being shut in by the diaphragm, a large muscular partition which projects upwards from the lower ribs, being convex towards the C., and concave towards the abdomen. In respiration (q.v.), the diaphragm descends by its own muscular contraction, while at the same time the ribs are drawn upwards and outwards by the intercostal muscles. The cavity of the C. is thus enlarged, the Dings are expanded, and air is drawn into them through the trachea or windpipe and bronchi. See LUNGS. The combination of bone, cartilage, muscle, and tendon entering into the composition of the C. is such as to per mit of expansion-movement to the extent required, and yet to guard against overexpan sion, which would be fatal to the delicate textures within. The bones of the C. are at the same time a powerful protection against external injury.
The structures forming the walls of the C. are: 1. The backbone or spinal column, divided into 24 vertebra;, 12 of which, called the dorsal vertebra;, form the thoracic portion. 2. Twelve ribs, attached to the transverse processes or projecting portions of the dorsal vertebrze, and ending in front in the costal cartilages, by which the ribs are connected with. 3. The sternum or breast-bone, which occupies the middle line. 4. The diaphragm (q.v.). See also SKELETON.
The contents of the C. 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 oesophagus or gullet, and the thoracic duct (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 C. 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, Bichat, called the " tripod of life"—viz., the brain, heart, and lungs—the C. 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 C. depend in some cases on alterations in its form, as by rickets (q v.) and other diseases affecting the bones in early childhood or in youth, as by too tight lacing in girls. The lungs and air-tubes are subject to a great variety of diseases, among which the principal are consumption or plithisis puhnoual is, pneumonia, pleurisy, bronchitis or pulmonary catarrh. The heart is subject to pericarditis, endocarditis, and chronic organic disease of the valves, as well as to enlargement (hypertrophy), dilatation, and degenerations 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 obstruction by tumors or by coagulation of the contained blood. The thoracic duct 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 under special articles, or under LUNGS and HEART.
The examination of the C. by physicians is now conducted not only by an investiga tion of the symptoms or obvious characters of the disease, but by a minute and elaborate examination into the physical condition of the contained organs by means of auscultation (q.v.), percussion (q.v.), measurement, etc. The application of these methods is too complicated and technical for explanation in detail, but their results will be shortly alluded to incidentally in the articles above referred to on the diseases of the chest. The name of Laennec (q.v.) will be long remembered in medicine as that of a great original observer, who has contributed more than any other to the progress of knowl edge in this department.