THE BRONCHIAL TUBES 



1231 



Branching of the bronchial tubes (fig. 995). — Each bronchus, from its origin at 

 the bifurcation of the trachea, takes an obUque course to the hilus, and then con- 

 tinues in the lung as a main tube, extending toward the posterior part of the base. 

 These stem-bronchi are curved, probably in adaptation to the heart, the right hke 

 the letter C and the left like an S. Throughout their course the stem-bronchi give 

 off in monopodic fashion collateral branches, the bronchial rami [rami bronchiales], 

 and these, branching in a similar way, reach all parts of the lung. 



The first bronchial ramus of the right stem-bronchus arises above the place where the latter 

 is crossed by the pulmonary artery and is named the eparterial bronchial ramus [ramus 

 bronchialis eparterialis]; it suppHes the superior lobe of the right lung, sending a special branch 

 to the apex. All other bronchial rami, whether in the right or left lung, take ongui from the 



Fig. 995. — Cast of the Air-tubes and Their Branches, viewed from in Front. 



(Spalteholz.) 



Trachea (also the position of the median plane) 

 I 



Eparterial bronchus to . 

 superior lobe 



Main bronchus 

 Hyparterial\ 



branch to 

 middle 



Bifurcation of trachea 

 /^ Left bronchus 



Hyparterial branch 

 to superior lobe 



■^■■■Z- 



j.-"^ 





Position of median plane 



stem-bronchi below the level of the crossing of the pulmonary artery and are called hyparterial 

 bronchial rami [rami bronchiales hyparteriales]. The second bronchial branch of the right Ivmg 

 goes to supply the middle lobe, while several bronchial branches enter the inferior lobe. On 

 the left side, the first bronchial branch arises below the crossmg of the pulmonary artery, and 

 goes to supply the superior lobe, providing it with an apical ramus. The other branches are 

 given to the inferior lobe. 



Structure of the bronchial rami. — The larger bronchial rami contain in their walls both 

 C-shaped and irregular plates of cartilage, the latter gradually replacing the former as the 

 branches become smaller. The membranous wall is lost and plates of cartilage are disposed 

 on all sides. The mucosa, with ciUated epithehum, is thrown into longitudinal folds covering 

 bundles of elastic fibres of the membrana propria. Next to the latter is a continuous layer of 

 smooth muscle-fibres circularly arranged. Mucous secreting bronchial glands [gl. bronchiales] 

 are present as far as tubes of 1 mm. diameter; here the cartilages also disappear. 



To W. S. Miller is due the credit of having greatly increased our knowledge of the finer 

 structure of the lung and for having presented the conception of the primary lung lobule now 

 generally accepted by anatomists. Some of the chief results of Miller's work are embodied in 



