THE TRACHEA AND BRONCHI 



1179 



to the median plane of about 25 degrees. The vena azygos major arches over it 

 from behind; and the right pulmonary artery lies below and then in front of it. 

 About three-quarters of an inch from its commencement it gives off a branch to 

 the upper lobe of the right lung. This is termed the eparterial branch bronchus 

 (ramus bronchialis eparterialis), because it is given off above the right pulmonarv 



artery. The bronchus now passes below the 

 artery, is known as the hyparterial branch bron- 

 chus (ramus bronchialis hyparterialis), and 

 divides into two branches for the middle and 

 lower lobes. 



The Left Bronchus (bronchus sinister) (Fig. 

 891) is smaller and longer than the right, being 

 nearly two inches in length. It forms an angle 

 to the median plane of about 46 degrees. It is 

 slightly curved and enters the root of the left 

 lung, opposite the sixth thoracic vertebra, about 

 an inch lower than the right bronchus. It 

 passes beneath the arch of the aorta, crosses in 

 front of the oesophagus, the thoracic duct, and 

 the descending aorta, and has the left pul- 



Lefl. 



Riflht. 



FIG. 892. Internal surface of the bronchi. 

 (Poirier and Charpy.) 



FIG. 893. Transverse section of the trachea, just above its 

 bifurcation, with a bird's-eye view of the interior. 



monary artery lying at first above, and then behind it. The left bronchus has 

 no branch corresponding to the eparterial branch of the right bronchus in the 

 sense that it is given off above the pulmonary artery. The first hyparterial branch 

 bronchus of the left side is the morphological equivalent of the right eparterial 

 branch bronchus, as shown by Huntington. 1 



The further subdivision of the bronchi will be considered with the anatomy 

 of the lung. 



If a transverse section of the trachea is made a short distance above its point 

 of bifurcation, and a bird's-eye view taken of its interior (Fig. 893), the septum 

 placed at the bottom of the trachea and separating the two bronchi will be seen 

 to occupy the left of the median line, and the right bronchus appears to be a 

 more direct continuation than the left, so that any solid body dropping into the 

 trachea would naturally be directed toward the right bronchus. This tendency is 

 aided by the larger size of the right tube as compared with its fellow. This fact 

 serves to explain why a foreign body in the trachea more frequently falls into the 

 right bronchus than into the left. 2 



Structure of the Trachea. The trachea is composed of imperfect cartilaginous rings, 

 fibrous membrane, muscular fibres, mucous membrane, and glands. 



The Cartilages vary from sixteen to twenty in number; each forms an incomplete ring, which 

 surrounds about two-thirds of the cylinder of the trachea, being imperfect behind, where the 



1 The Eparterial Bronchial System of the Mammalia, Annals N. Y. Acad. Sci.. 1898. 



2 Reigel asserts that the entrance of a foreign body into the left bronchus is by no means so infrequent as is 

 generally supposed. See also Med.-Chir. Transactions, vol. Ixxi, p. 121. 



