THE RESP1XA TOR Y A PPA RA TUS. I / t 



are crowded to one side, and their contents are 

 apparently transformed into a homogeneous mu- 

 cous mass. Scattered here and there among the 

 glands and between the cartilaginous rings, lie larger 

 and smaller clusters of fat-cells. 



The blood-vessels, passing through the outer lay- 

 ers, furnish an abundant capillary net-work to the 

 mucous glands ; and spread out in a rich capillary 

 plexus beneath the basal membrane. 



Although the larger and medium-sized bronchi 

 have the same general structure as the trachea, still 

 we find, aside from a decrease in the thickness of 

 the walls, certain noteworthy structural modifica- 

 tions which chiefly concern the cartilaginous and 

 muscular elements. The cartilage occurs in the 

 form of regular, incomplete rings, only in the upper 

 portion of the larger bronchi. As the tubes become 

 smaller the cartilage occurs in the form of scattered, 

 irregular-shaped, often angular plates, which become 

 gradually smaller and thinner. Furthermore, a dis- 

 tinct layer of smooth muscular tissue, in the form of 

 transverse rings, connected with each other by in- 

 terlacing cells, appears between the mucosa and the 

 submucosa. We find, also, that the longitudinal 

 bundles of fibrillar and elastic connective tissue in 

 the mucosa are more strongly developed as the 

 bronchi becomes smaller, so as to throw the mucous 

 membrane into pronounced longitudinal folds. 



Following the bronchi now down toward their 



