THE TRACHEA AND BROXCHI. 



In the thorax, the trachea is covered by the first piece of the sternum, 

 together with the sterno- thyroid and sterno-hyoid muscles ; lower down, by 

 the left innominate vein, then by the commencement 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 it divides into its right and 

 left branches. Placed between the two pleurae, the trachea is contained in 

 the posterior 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 recurrent branch, together with some cardiac nerves. 



Fig. 623. 



Fig. 623. OUTLINE SHOWING THE GENE- 

 RAL FORM OF THE LARYNX, TRACHEA, 

 AND BRONCHI, AS SEEN FROM BEFORE, i 



7i, the great cornu of the hyoid bone ; e, 

 epiglottis ; t, superior, and t', inferior 

 cornu of the thyroid cartilage ; c, middle 

 of the cricoid cartilage ; t r, the trachea, 

 showing sixteen cartilaginous rings ; 6, the 

 right, and &', the left bronchus. 



The right and left bronchi com- 

 mence at the bifurcation of the 

 trachea and diverge to reach the cor- 

 responding lungs. They differ from 

 each other in length, width, direc- 

 tion, and connection with other 

 parts. The right bronchus, wider 

 but shorter than the left, measuring 

 about an inch in length, passes out- 

 wards almost horizontally 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. The left 

 bronchus, smaller in diameter, but 

 longer than the right, being nearly 

 two inches in length, inclines ob- 

 liquely 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 bron- 

 chus. The left bronchus crosses in 

 front of the oesophagus and descend- 

 ing aorta : the arch of the aorta turns backwards and to the left over 

 it, and the left pulmonary artery lies first above it and then on its 

 anterior surface. The remaining connections of each bronchus, as it lies 

 within the root of the corresponding lung, and the mode in which it sub- 

 divides there into bronchia, will be hereafter described. 



