ORGANS OF RESPIRATION. 



plexus of very fine and of coarser fibers, from which branches are 

 given off which end in the muscle tissue of the bronchi, and others 

 which pass through this layer to form, after further division, a sub- 



Fig. 255. From section of human lung stained in orcein, showing the elastic fibers sur- 

 rounding the alveoli. 



Blood capillaries 

 seen in surface 



Alveolus in cross- 

 section. 



Fig. 256. Section through injected lung of rabbit. 



epithelial plexus from which fibrils may be traced into the connec- 

 tive-tissue folds in the larger bronchi and between the bases of the 

 epithelial cells in the smaller bronchi and bronchioles. Some few 

 fibrils were traced between alveoli situated near bronchi, " termi- 

 nating, apparently, immediately beneath the pavement epithelium in 

 an elongated or rounded minute bulb ; " these may, however, repre- 



