126 THE LUNGS AND RESPIRATION. 



flammation of the pleurae or pleurisy, they become thick- 

 ened and roughened and friction results, as is shown 

 by the sounds heard through the stethoscope. Fric- 

 tion causes effusion and fluid collects. This generally 

 absorbs again, but occasionally the serous fluid becomes 

 pustular and empyema results. 



In front, between the two pleurae, which are wholly 

 separate, is the mediastinal space or mediastinum, which 

 extends from the sternum to the spinal column and con- 

 tains all the thoracic viscera except the lungs and heart, 

 that is, the trachea, esophagus, thoracic duct, and many 

 large vessels and nerves. 



FIG. 50. Diagrammatic representation of the termination of a bronchial 

 tube in a group of infundibular B, Bronchial tube; LB, bronchiole; A, atrium; 

 /, 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 gradu- 

 ally 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. 



