CHEST

is bounded above by the root of the neck, below by the diaphragm, in front by the sternum or breast bone, behind by the backbone, and on each side by the ribs. The chest contains the heart with its great ve els enclosed in a bag—the pericardium—which is attached below to the diaphragm; the lower end of the wind-pipe dividing into the two bronchi, to each of which a lung is attached. Each lung is covered by a membrane—tho pleura—which sor from the root of the lung over the pericardium to the bone, and thence over the inncr surfuce of the chest wall to the backbone, and from there back to the root of the lung. The space between the lung and the chest wall is thus lined with pleura, and is known as the pleural cavity, which is normally very small, because the lung remains in contact with the chest wall The pleura! cavity contains a little fluid, and when the pleara is inflamed this fluid is often much increased, the lung is compre ed, and the pleural cavity enlarged. Lastly, pa ing down in front of the backbone behind the heart are the gullet, the descending aorta, the two sympathetic and vagus nerves and the thoracic duct. [s. 342]