62 THORAX 



none of the bars or plates of cartilage extend completely 

 round the walls of the tubes. 



In the left lung the arrangement of the bronchi differs 

 from the arrangement in the right lung because in the left 

 lung there is no eparterial branch. The first ventral hyparterial 

 branch is distributed to the upper lobe, and is accompanied 

 by a branch of the left pulmonary artery and by the upper 

 left pulmonary vein. All the remaining branches are distributed 

 to the lower lobe, and are accompanied by corresponding 

 branches of the pulmonary artery and by tributaries of the 

 lower left pulmonary vein. 



Arterise Bronchioles. As a rule, two bronchial arteries are 

 distributed to the left lung and one to the right lung. The 

 two left bronchial arteries spring from the descending aorta. 

 The right bronchial artery is a branch either of the first right 

 aortic intercostal artery or of the upper left bronchial artery. 

 The bronchial arteries and their branches run along the 

 posterior surfaces of the bronchi and their branches, and 

 are the proper nutrient vessels of the lungs. Part of the 

 blood which they convey to the lungs is returned by the pul- 

 monary veins to the left atrium of the heart, but the remainder 

 is returned by bronchial veins, which open on the right side 

 into the vena azygos, and on the left side into the vena 

 hemiazygos accessoria, or into the left superior intercostal 

 vein. 



Arteriae Pulmonales. One pulmonary artery is distributed 

 to each lung. As it passes through the root of the lung it 

 crosses anterior to the stem bronchus, and it descends in the 

 interior of the lung, postero-lateral to the stem bronchus, and 

 between its ventral and dorsal hyparterial branches. It gives 

 off branches which correspond with and are distributed with 

 the branches of the bronchus. When the bronchi terminate 

 in the alveolar passages the final ramifications of the arteries 

 terminate in capillaries which form a vascular network between 

 the walls of the alveoli. The pulmonary arteries carry venous 

 (de-oxygenated and carbonic acid laden) blood from the right 

 ventricle of the heart to the lungs, where, as the blood runs 

 through the capillaries between the walls of the alveoli, it 

 gives off its excess of carbonic acid to and receives oxygen 

 from the air in the alveoli. 



Venae Pulmonales. As a rule there are four pulmonary 

 veins upper and lower, on each side. Variations are, 



