252 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



ternal to the smooth circular muscle layer of the 

 bronchi. Lymph nodes are interpolated every- 

 where in these plexuses. Just beneath the pleura, 

 all over the surface of the lung, lymphatics ramify 

 and drain toward the root of the lung, where they 

 join the lymphatics located in the bronchial walls. 



The alveolar set accompany the pulmonary vessels. 

 These lymphatics have their origin in a plexus that 

 surrounds the respiratory or alveolar portions of the 

 lungs, and then accompanies the pulmonary arteries 

 and veins along the external surfaces of the bronchial 

 tubes to the root of the lungs, where they ultimately 

 unite with the bronchial lymphatics. While lym- 

 phatic nodes are present everywhere, they are par- 

 ticularly abundant at the root of the lung. As 

 tuberculosis spreads along the lymphatics, the dif- 

 ferent clinical aspects of this disease depend to a 

 considerable extent on which of these systems be- 

 comes involved. 



Nerves. The nerves of the lung come from the 

 pneumogastric and the sympathetic, and are made 

 up of medullated and non-medullated fibers. They 

 enter at the root of the lung and accompany the 

 blood-vessels to the terminal air passages, where 

 they arborize about the lung alveoli just external to 

 the epithelial lining. Many nerve ganglia are located 

 along their course and many fine fibers are given off 

 that innervate the musculature and epithelial lining 

 of the bronchial tubes and the walls of the blood- 

 vessels. 



