RESPIRATION. 



339 



from the base of the cardiac organ. The bronchus on the right side, 

 about an inch in length, runs at a right angle to the root of the 

 lung on a level with the fourth dorsal vertebra and posterior to the 

 right pulmonary artery. The left bronchus, less in diameter than 

 the right, but about twice its length, passes downward and outward 

 beneath the arch of the aorta to the root of its corresponding lung. 

 The bronchi and the trachea are composed of a series of cartilaginous 

 rings lined with mucous membrane. The trachea and bronchi are 

 encircled by the cartilaginous rings, which are not closed posteriorly 



Fig. 112. Bronchia and Lungs, Posterior View. (SAPPEY.) (From 

 Mills's "Animal Physiology," copyright, 1889, by D. Appleton and 

 Company. ) 



1, 1, Summit of lungs. 2, 2, Base of lungs. 3, Trachea. 4, Right bron- 

 chus. 5, Division to upper lobe of lung. 6, Division to lower lobe. 7, Left 

 bronchus. 8, Division to upper lobe. 9, Division to lower lobe. 10, Left branch 

 of pulmonary artery. 11, Right branch. 12, Left auricle of heart. 13, Left 

 superior pulmonary vein. 14, Left inferior pulmonary vein. 15, Right superior 

 pulmonary vein. 16, Right inferior pulmonary vein. 17, Inferion vena cava. 

 18, Left ventricle of heart. 19, Right ventricle. 



except by a strong fibre-elastic membrane, and contain a layer of pale 

 unstriped muscular fibers running in a transverse and longitudinal 

 direction. The cartilaginous rings preserve the caliber of the trachea. 

 The bronchial mucous membrane is smooth and its color is reddish 



