196 



NORMAL HISTOLOGY. 



Capillary net- 

 work over 

 alveolus 



Alveolus 



arise the radicles of \\\& pulmonary veins which carry away the oxygen-renewed 

 blood. These vessels, however, do not immediately join the arteries, but, 

 running first on the outside of the lung-units, unite with others and then 

 emerge at the periphery of the lobules and run in the interlobular connective 

 tissue, later meeting the interlobular parts of the arteries and bronchi which 

 they thence accompany to the hilum of the lung. At the surface, where 

 the pulmonary tissue is in contact with the overlying serous membrane, 

 twigs from the pulmonary artery communicate with the pleural capillaries. 

 The bronchial arteries, the nutrient vessels of the lungs, supply the walls of 

 the air-tubes as far as the terminal bronchioles, as well as the walls of the 

 branches of the pulmonary artery and veins, the bronchial lymph-nodes and 

 the visceral pleura. Within the walls of the bronchial tubes they form a 

 deeper capillary network for the muscle and glands and a superficial one for 



the tunica propria. The 

 bronchial veins are trib- 

 utary for the most part 

 to the pulmonary veins; 

 to a small extent, how- 

 ever, blood passes from 

 them into the azygos 

 system. Both the bron- 

 chial arteries and veins 

 communicate with the 

 pulmonary vessels at 

 many points. 



The lymphatics 

 include a superficial net- 

 work, well developed 

 and beneath the pleura, 

 and a deep interlobu- 

 lar plexus surrounding 

 the bronchi. The deep 

 ones probably begin as 

 lymph-spaces distal to 

 the terminal bronchi- 

 oles, around which tu- 

 bules definite lymphatics first appear. The superficial vessels are con- 

 nected with small uncertain subserous lymph-nodes, subsequently joining 

 the interlobular trunks, which ultimately are efferent to the larger nodes 

 situated in the hilum and roots of the lungs. The pulmonary lymph- 

 nodes are deeply pigmented owing to the accumulation of inspired colored 

 particles. Where cartilage exists, the plates are enclosed by double net- 

 works of lymphatics, the inner one lying within the submucosa. 



The nerves of the lungs, from the vagi and sympathetics, are numerous 

 and include both medullated and nonmedullated fibres. The latter are 

 associated with minute groups of ganglion-cells along their course and are 

 destined chiefly for the walls of the blood-vessels and of the air-tubes, some 

 fibres finding their way into the interalveolar septa. Free terminal filaments 

 within the tunica propria and between the epithelial cells are described as 

 sensory endings in the mucous membrane of the air-tubes. 



The Pleurae. The pleurae, the serous membranes lining the cavities 

 containing the lungs and covering the latter except at the roots, where enter 

 the bronchi and the blood-vessels, in structure closely resemble other serous 



Branch of pulmonary vein 



FIG. 244. Section of injected and inflated lung. X 80. 



