TERMINAL DIVISIONS OF BRONCHI AND ULTIMATE AIR-SPACES. 317 



to the structure they supply finer and more closely arranged in the 

 mucous membrane, and coarser in the connective-tissue walls. In 

 the neighborhood of the terminal bronchial tubes the capillary nets 

 anastomose freely with those of the' respiratory capillary system. 

 From the capillaries of the bronchial arteries, veins are formed which 

 empty either into the bronchial veins or into the branches of the 

 pulmonary veins. 



Fig. 253. Scheme of lung lobule 

 after Miller: b. ;-., Respiratory bronchiole ; 

 d. al., alveolar duct (terminal bronchus); 

 a, a, a, atria; s. al., air-sacs; a. p., air- 

 cells or alveoli. 



P ^ 



A 



Fig. 254. Reconstruction in wax of 

 a single atrium and air-sac with the alveoli : 

 V, Surface where atrium was cut from al- 

 veolar duct ; /", cut surface, where another 

 air-sac was removed; A, atrium; S, air-sac 

 with air-cells (alveoli) (after Miller). 



The lymphatics of the lung are classified by Miller as follows : 

 () lymphatics of the bronchi ; (<) lymphatics of the arteries ; (c) 

 lymphatics of the veins; (d} lymphatics of the pleura. The bron- 

 chial lymphatics are arranged in two plexuses as far as cartilage is 

 present in the walls of the bronchi, one internal and one external to 

 the cartilage. Beyond the cartilage only a single plexus is found. 

 In the terminal bronchioles there are found three lymphatic vessels, 

 two of which pass to the vein and one to the artery of the lobules. 

 No lymphatics are found beyond the terminal bronchioles. The 

 larger arteries are accompanied by two lymphatic vessels; the 

 smaller ones, only one. The same is true in general of the lym- 

 phatics accompanying the vein. The bronchial lymphatics and 

 those accompanying the arteries and veins anastomose in the regions 

 of the divisions of the bronchi. The pleura possesses a rich net- 

 work of lymphatics with numerous valves. 



Accompanying the bronchi and bronchial arteries are found 

 numerous nerve-fibers, of the nonmedullated and medullated varie- 

 ties, arranged in bundles of varying size, in the course of which are 

 found sympathetic ganglia. Berkley (94), who has studied the dis- 

 tribution of the nerves of the lung with the chrome-silver method, 

 finds that in the external fibrous layer of the bronchi is found a 



