Page:Structure and functions of the body; a hand-book of anatomy and physiology for nurses and others desiring a practical knowledge of the subject (IA structurefunctio00fiskrich).pdf/132

 *flammation of the pleuræ or pleurisy, they become thickened and roughened and friction results, as is shown by the sounds heard through the stethoscope. Friction causes effusion and fluid collects. This generally absorbs again, but occasionally the serous fluid becomes pustular and empyema results.

In front, between the two pleuræ, which are wholly separate, is the mediastinal space or mediastinum, which extends from the sternum to the spinal column and contains all the thoracic viscera except the lungs and heart, that is, the trachea, esophagus, thoracic duct, and many large vessels and nerves.

—Diagrammatic representation of the termination of a bronchial tube in a group of infundibula: B, Bronchial tube; LB, bronchiole; A, atrium; I, infundibulum; C, alveoli. (de Nancrede.)

Roughly speaking, the lungs begin at the sterno-*clavicular articulation above, the apex coming up above the level of the first rib, and extend downward together to the fourth cartilage, where the lower margins gradually separate, the lowest lung limit being the eleventh rib in the vertebral region. Each lung is conical. The apices extend upward and the bases, which are broad and concave, rest upon the diaphragm. The right lung is divided by a fissure into three lobes, the left into two. The root consists of a bronchus and pulmonary arteries, veins, lymphatics, and nerves. The tissue itself is composed of an aggregation of lobules, each consisting of a terminal bronchiole with its alveoli or air cells, blood-vessels, and nerves, a lung in miniature.