



of the two, is situated below and behind the fissure, and comprises almost the 

 whole of the base, a large portion of the costal surface, and the greater part of 

 the posterior border. 



The right lung is divided into three lobes, superior, middle, and inferior, by 

 two interlobular fissures. One of these separates the inferior from the middle 

 and superior lobes, and corresponds closely w T ith the fissure in the left lung. Its 

 direction is, however, more vertical, and it cuts the lower border about 7.5 cm. 

 behind its anterior extremity. The other fissure separates the superior from the 

 middle lobe. It begins in the previous fissure near the posterior border of the lung, 

 and, running horizontally forward, cuts the anterior border on a level with the 

 sternal end of the fourth costal cartilage; on the mediastinal surface it may be 

 traced backward to the hilus. The middle lobe, the smallest lobe of the right 

 lung, is wedge-shaped, and includes the lower part of the anterior border and the 

 anterior part of the base of the lung. 



The right lung, although shorter by 2.5 cm. than the left, in consequence of the 

 diaphragm rising higher on the right side to accommodate the liver, is broader, 

 owing to the inclination of the heart to the left side; its total capacity is greater 

 and it weighs more than the left lung. 



The Root of the Lung (radix pulmonis). A little above the middle of the medias- 

 tinal surface of each lung, and nearer its posterior than its anterior border, is its 

 root, by which the lung is connected to the heart and the trachea. The root is 

 formed by the bronchus, the pulmonary artery, the pulmonary veins, the bronchial 

 arteries and veins, the pulmonary plexuses of nerves, lymphatic vessels, bronchial 

 lymph glands, and areolar tissue, all of which are enclosed by a reflection of the 

 pleura. The root of the right lung lies behind the superior vena cava and part 

 of the right atrium, and below the azygos vein. That of the left lung passes 

 beneath the aortic arch and in front of the descending aorta; the phrenic nerve, 

 the pericardiacophrenic artery and vein, and the anterior pulmonary plexus, lie 

 in front of each, and the vagus and posterior pulmonary plexus behind each; 

 below each is the pulmonary ligament. 



The chief structures composing the root of each lung are arranged in a similar 

 manner from before backward on both sides, viz., the upper of the two pulmonary 

 veins in front; the pulmonary artery in the middle; and the bronchus, together 

 with the bronchial vessels, behind. From above downward, on the two sides, 

 their arrangement differs, thus: 



On the right side their position is eparterial bronchus, pulmonary artery, 

 hyparterial bronchus, pulmonary veins, but on the left side their position is 

 pulmonary artery, bronchus, pulmonary veins. The lower of the two pulmonary 

 veins, is situated below the bronchus, at the apex or lowest part of the hilus 

 (Figs. 972, 973). 



Divisions of the Bronchi. Just as the lungs differ from each other in the number 

 of their lobes, so the bronchi differ in their mode of subdivision. 



The right bronchus gives off, about 2.5 cm. from the bifurcation of the trachea, 

 a branch for the superior lobe. This branch arises above the level of the pulmonary 

 artery, and is therefore named the eparterial bronchus. All the other divisions 

 of the main stem come off below the pulmonary artery, and consequently are 

 termed hyparterial bronchi. The first of these is distributed to the middle lobe, 

 and the main tube then passes downward and backward into the inferior lobe, 

 giving off in its course a series of large ventral and small dorsal branches. The 

 ventral and dorsal branches arise alternately, and are usually eight in number 

 four of each kind. The branch to the middle lobe is regarded as the first of the 

 ventral series. 



The left bronchus passes below the level of the pulmonary artery before it divides, 

 and hence all its branches are hyparterial; it may therefore be looked upon as 



