THE LUNGS AND RESPIRATION. 



125 



The Bronchi. The two bronchi, of which the right is 

 the larger and shorter, resemble the trachea in struc- 

 ture. As they enter the root of the lung they divide, 

 the right into three and the left into two branches, one 

 for each lobe, after which they divide and subdivide, 

 the bronchioles becoming smaller and smaller and finally 

 ending in the infundibula, pouch-like places lined with 

 air cells, in which cilia keep the air in motion. As they 

 grow smaller the bronchioles gradually become wholly 

 membranous. 



The Lungs. The lungs themselves, two in number, 

 lie each in a serous sac or pleura, similar in structure 



Right common 



carotid artery. 



Subclavian 



arteries . 



Innominate 

 artery. 



Arch of aorta 

 Right lung. 



Superior vena 



cava. 

 Right auricle. 



Larynx. 



Trachea. 

 Subclavian 

 arteries. 



Pulmonary 

 artery. 



FIG. 49. Relation of lungs to other thoracic organs. (Ingals.) 



to the pericardium and serving a like purpose. The 

 outer layer of the pleura is reflected back over the tho- 

 racic wall and 'diaphragm. There is no pleural cavity 

 in health between the two layers of the pleura, the two 

 surfaces being in close contact, though moistened with 

 lymph to prevent friction during respiration. In in- 



