THE ORGANS OF RESPIRATION 243 



The apex (apex pulmonis) is rounded, and extends 

 about 1 inch to 2 inches above the anterior end of 

 the first rib. It is grooved by the subclavian artery 

 on the left side, but on the right side the impression of 

 the innominate vein is the most prominent groove seen. 



Fissures and Lobes. The left lung is divided into 

 two lobes, an upper and a lower, by an oblique fissure, 

 which extends from the outer to the inner surface of 

 the lung both above and below the hilum. The right 

 lung is divided into three lobes, an upper, middle, 

 and lower, by an oblique fissure, separating the lower 

 and middle lobes, a horizontal fissure separating the 

 upper and middle lobes. 



The Root of the Lung (Radix Pulmonis). This lies 

 a little above the centre of the mediastinal surface, 

 and approaches nearer to the posterior than to the 

 anterior border. It transmits the bronchus, the 

 pulmonary artery, the two pulmonary veins, usually 

 the bronchial arteries and veins the former supply 

 the bronchi and lungs with blood the pulmonary 

 plexus of .nerves, lymphatics, the bronchial lymph 

 nodes, and areolar tissue, surrounded by a reflection 

 of the pleura which fuses with the pericardium at 

 this point. 



Structure of the Lungs. The color of the lungs at 

 birth is a pinkish white; in adult life, a dark slate 

 color, mottled in patches; and as age advances this 

 assumes a black color. 



The lungs are composed of an external serous coat, 

 subserous areolar tissue, and parenchyma, consisting 

 of numbers of lobules (f to 1-i- inches in size). The 

 structures enclosed within the lungs consist of bronchi, 

 their subdivisions which end in the air cells, blood- 

 vessels, lymphatics and nerves, all embedded in a sup- 

 porting net-work of fibrous and elastic tissue. These 

 structures can only be seen under the microscope. 



The bronchi, on passing to the periphery of the 

 lung, become smaller and smaller as they divide and 



