THE LUNGS. 



1853 



FIG. 1576. 



Capillary net- 

 work over 

 alveolus 



Alveolu 



Branch of 



Portion of injected and inflated lung. X 80. 



olar walls, it is highly probable that such cells are important agents in transporting 

 the particles of inspired carbon through the walls of the air-cells. Additional par- 

 ticles, however, usually occupy the cement-substance between the alveolar epithelial 



cells, sometimes lying appar- 

 ently within the cytoplasm of 

 the latter. 



Blood-Vessels of the 

 Lung. The pulmonary artery, 

 serving not for the nutrition of 

 the lung but for the aeration of 

 the blood, is very large, at 

 first larger than the bronchus, 

 which it follows very closely 

 throughout its ramifications to 

 the terminal bronchi. Situated 

 at first anterior to the bronchus, 

 it passes onto its superior and 

 then onto its outer side, and in 

 most cases twists around the 

 bronchus, so as finally, when 

 deep in the lung, to reach its 

 dorsal aspect. This is very dif- 

 ferent from Aeby's alleged cross- 

 ing of the main bronchus. The 

 arterial branches accompanying 

 the apical bronchus are in the 

 main anterior to the tubes in the 

 right lung and behind them in the left. According to Narath, the general course 

 of the artery along the main bronchus is between the ventral and dorsal branches ; 

 but, as he states, this 



is not constant. We FIG. 1577. 



have found certain 

 ventral bronchi in 

 the lower part of the 

 lung with the artery 

 before them. An in- 

 tralobular branch en- 

 ters each lobule near 

 the apex with the 

 bronchus, and follows 

 its ramifications until 

 the ultimate bronchi 

 have ended in the air- 

 chambers of the lung- 

 unit. The terminal 

 arterioles are in its 

 interior until they 

 break up into capil- 

 laries in the walls of 

 the alveoli. Side 

 branches, interlobu- 

 lar arteries, run in 

 the connective tissue 

 between the lobules. 

 It is from these, ac- 

 cording to Miller, that the subpleural net-work is filled ; formerly the latter was 

 held to be supplied by the bronchial arteries. 



The pulmonary veins, which return the aerated blood to the left auricle, are also 

 large when they leave the hilum, two on each side, one near the top and the other 



Smaller cells 

 Larger cells 



Section of lung, showing collections of particles of carbon in perivascular connective 

 tissue. X 14. 



