THE BRONCHI. 



265 



In the thorax, the trachea is covered, above, by the first itiecc of the 

 sternum, together with the sterno-thyroid and sterno-hyoid muscles ; 

 lower down, by the left innomi- 

 nate vein, then by the com- Fig- ISI. 

 raencement of the innominate 

 artery and left carotid, which 

 pass round to its sides ; next by 

 the arch of the aorta and the 

 deep cardiac plexus of nerves, 

 and, quite at its bifurcation, by 

 the extremity of the pulmonary 

 artery, where this divides into its 

 right and left branches. Placed 

 between the two pleura, the 

 trachea is contained in the pos- 

 terior mediastinum, and has on 

 its right side the pleura and 

 pneumo-gastric nerve, and on 

 the left, the left carotid artery, 

 the pneumo-gastric and its re- 

 current branch, together with 

 some cardiac nerves. 



The right and left bronchi 

 (fig. 180, b, h') proceed each to 

 the root of its corresponding 

 lung. They differ from each 

 other in length, width, direc- 

 tion, and relation to surround- 

 ing parts. The right bron- 

 chus (&), wider but shorter 

 than the left, measuring a])out 

 an inch in length, passes out- 

 wards almost horizontalh^ into 

 the root of the right lung on 

 a level with the fourth dorsal 

 vertebra : it is embraced above 

 by the vena azygos, which 

 hooks forwards over it, to end 

 in the vena cava superior; the 

 right pulmonary artery lies at 

 first below it and then in front 

 of it. On looking down the 

 windpipe towards the bifurca- 

 tion, the right bronchus appears 

 to be a more direct continua- 

 tion of the trachea than the left. 

 The left bronchus (&'), smaller 

 in diameter, but longer than the 

 right, being nearly two inches in 

 length, inclines downwards and 

 outwards beneath the arch of the aorta to reach the root of the left 

 lung, which it enters on a level with the fifth dorsal vertebra, that is, 

 about an inch lower than the right bronchus. The left bronchus crosses 



Fig. 181. — Outline showing the General 

 Form of the Larynx, Trachea, and 

 Bronchi as seen from behind (Allen 

 Thomson). 



h, great cornu of tlie hyoid bone ; t, superior, 

 and t' , inferior cornu of the thyroid cartilage ; 

 e, the epiglottis ; «, points to the back of both 

 the arytenoid cartilages, which are surmounted 

 by the cornicula ; c, the middle ridge on the 

 back of the cricoid cartilage ; t r, the posterior 

 membranous pai't of the trachea ; b, U, right 

 and left bronchi. 



