Tl 



ROOT OF THE LUNG, 



1097 



Trachea 



Eparterial bronchus* 



Dorsal branches 



of bronchus j^^L. 



e pulmonary artery occupies a different position on the two sides, in relation to the 

 main or undivided part of the bronchus. On the right side it is placed below 

 it, whilst on the left side it crosses the bronchus and occupies a higher level in 

 the pulmonary root. The two pulmonary veins, on both sides, lie at a lower level in 

 the root of the lung than the pulmonary artery and bronchus, whilst the superior of 

 the two veins occupies a plane ventral to the pulmonary artery (Figs. 870 and 871). 

 Distribution of the Bronchial Tubes within the Lungs. The two lungs are 

 not symmetrical ; the right lung is subdivided into three lobes, and the left lung is 

 cleft into two lobes. The bronchi exhibit a corresponding want of symmetry. The 

 right bronchus, as it approaches the pulmonary hilum, gives off two branches for 

 the superior and middle lobes of the right lung respectively, and then the main 

 stem of the tube enters the inferior lobe. The left bronchus sends off a large branch 

 to the superior lobe of the left lung, and then sinks into the inferior lobe. The 

 first branch of the right bronchus, for the superior lobe, leaves the main stem about 

 one inch from the trachea. The first branch of the left bronchus, on the other 

 hand, takes origin about twice that distance from the trachea. 



The relation of the pulmonary artery to the bronchial subdivisions is different 

 on the two sides. On the right side it turns dorsally, to reach the dorsal aspect 

 of the bronchus, inferior to the first, and superior to the second, bronchial branch. 

 On the left side the pul- 

 monary artery turns dorsally 

 above the level of the first 

 bronchial branch. On the 

 right side, therefore, the 

 first bronchial branch is 

 placed above the pulmonary 

 artery, and in consequence 

 it is termed the eparterial 

 bronchial ramus ; all the 

 others lie below the artery, 

 and are termed hyparterial 

 bronchial rami. On the left 

 side there is no eparterial 

 branch ; they are all hyp- 

 arterial. 



When the main stem of 

 the bronchus is followed 

 into the inferior lobe of each 

 lung, it is seen to travel 

 downwards and dorsally in 

 the pulmonary substance 

 until it reaches the thin 



iprsal part of the diaphragmatic surface of the lung which lies between the 

 laphragm and the thoracic wall, and there it ends. As it proceeds through 



5 inferior lobe it gives off a series of large ventral and a series of smaller dorsal 



inches. As a rule these are three in number in each case, and the dorsal and 



bral branches do not arise opposite to each other, but alternately, one from 



dorsum, and then another, after a slight interval, from the ventral surface of 



i tube. The first hyparterial division on each side (i.e. the branch to the middle 



e of the right lung and the branch to the superior lobe of the left side) is 



aerally regarded as the first member of the ventral group. 



t was Aeby who first recognised the existence in each lung of a main or stem bronchus 



a ventral and dorsal series of branches, and who drew the distinction between the 



1 hyparterial bronchial rami. A consideration of these relations led this author to 



the eparterial bronchus and the superior lobe of the right lung have no morpho- 



eqiuvalents on the left side of the body. In other words, he was led to believe that the 



the right lung is the homologue of the superior lobe of the left lung. Hasse, who 



stigated the subject, endorsed this view, with certain modifications and additions 



sis, either in its original state as presented by Aeby, or as subsequently modified 



sse, has been, until lately, very generally accepted by anatomists. More recent research, 



^ Left pulmonary artery 

 Hyparterial 

 bronchus 



_ Dorsal branch 

 of bronchus 



FIG. 872. DIAGRAM OF THE RELATIONS OP THE PULMONARY 

 ARTERY TO THE BRONCHI. 



