318 THE KESPIRATOEY SYSTEM 



of the larger bronchial tubes are supplied with bronchial blood, and, 

 according to Schaffer, a few branches at the root of the lung are also 

 distributed to the adjacent pleura. Many of the bronchioles, the res- 

 piratory bronchioles, and also the alveolar ducts, pulmonary alveoli, and 

 the pleura all receive their nutrition from the pulmonary arteries. 

 Finally it may be said that there are no anastomoses between the pul- 

 monary arteries and veins except among the capillaries of the alveolar 

 walls. 



LYMPHATICS 



The pulmonary lymphatics form a plexus in the walls of the bronchi 

 and bronchioles, penetrating to the mucous membrane. Branches from 

 this plexus frequently anastomose with perivascular lymphatic vessels 

 about the branches of the pulmonary artery and veins. A close network 

 of lymphatic vessels is also found in the pleura, its efferent vessels passing 

 into the interlobular tissue to join those vessels which accompany the 

 veins. The pulmonary lymphatics are supplied with frequent valves and 

 numerous anastomoses. At the atria the lymphatics pass to the inter- 

 lobular septa, so that the alveolar walls lack lymph vessels. 



The lymphatic vessels of the bronchi are connected with larger lym- 

 phatic vessels of the outer fibrous coat and with the lymph nodules in 

 the walls of the larger tubes. Many of the larger vessels in the outer 

 fibrous coat of the bronchi, and also those which accompany the pul- 

 monary artery, enter those lymph nodes which are in relation with the 

 bronchial walls at the root of the lungs. The pleural lymphatic plexus 

 arid the vessels accompanying the pulmonary veins, after pursuing much 

 of their course through the interlobular connective tissue in company 

 with the pulmonary veins, also open into the bronchial lymph nodes. 

 Much pigment is conveyed through these vessels and is deposited in (a) 

 the interlobular connective tissue, (&) the fibrous tissue about the pul- 

 monary arteries, and most abundantly in (c) the bronchial lymph 

 nodules and nodes. 



Lymphoid tissue forms an important constituent of the lungs, serv- 

 ing as filters in the lymph circulation and as centers to which the 

 phagocytes carry their collected material. It occurs as nodes, nodules, 

 or as smaller masses of more diffuse lymphoid tissue; it may be peri- 

 bronchial, periarterial, perivenous or subpleural in position. Lymph 

 nodes are associated with the larger divisions of the bronchi and located 

 at the points of branching. The smaller masses are found in greatest 



