THE BRONCHI, THEIR BRANCHES, AND THE BRONCHIOLES. 311 



The trachea contains numerous branched tubulo-alveolar glands 

 of the mucous variety containing here and there crescents of 

 Gianuzzi. The glands are especially numerous where the tracheal 

 wall is devoid of cartilage. 



The larynx and trachea receive their nerve supply from sensory 

 nerve-fibers and sympathetic neurones. These have been described 

 by Ploschko (97) working in Arnstein's laboratory. According to 

 this observer, the sensory fibers divide in the mucosa, forming sub- 

 epithelial plexuses from which fibrils are given off which enter the 

 epithelium of the larynx and trachea and, after further division, end 

 on the epithelial cells in small nodules, or small clusters of nodules. 

 In the trachea of the dog, such fibrils were traced to the ciliary 

 border of the columnar ciliated cells before terminating. Numerous 

 sympathetic ganglia are found in the larynx and trachea. In the 

 latter they are especially numerous in the posterior wall. The 

 neuraxes of the sympathetic neurones forming these ganglia were 

 traced to the nonstriated muscular tissue of the trachea. The cell- 

 bodies of these sympathetic neurones are surrounded by end-baskets 

 of small medullated fibers terminating in the ganglia. Medullated 



Fig. 246. From longitudinal section of human trachea, stained in orcein : a, Layer of 

 elastic fibers ; b, cartilage. 



nerve-fibers, ending in the musculature of the trachea in peculiar 

 end-brushes, were also described by Ploschko. 



C THE BRONCHI, THEIR BRANCHES, AND THE 

 BRONCHIOLES. 



The primary bronchi and their branches show the same general 

 structure as the trachea, showing, however, irregular plates and 

 platelets of cartilage instead of half- rings, which surround the 

 bronchi. The cartilage is absent in bronchial twigs of less than 



