238 



THE KESPIKATORY SYSTEM 



edges encircle the entire tube. In the lower mammals, e. g., the 

 pig, these overlapping cartilages are so highly developed that the 

 plates often lie three or four deep ; in man they are rarely more 



FlG. 201. A BRONCHUS FROM THE HUMAN LUNG. 



a, lining epithelium ; J, duct of a mucous gland ; c, muscularis mucosee ; d, accumu- 

 lated mucus, etc., bathing the surface of the epithelium; , mucous glands;/, hyaline 

 cartilage ; ^, outer fibrous coat ; A, pulmonary alveoli. Hematein and eosin. Photo. 

 x 34 



