298 



PRACTICAL HISTOLOGY. 



[XXVII. 



(d.) (H) Study specially the mucous membrane. Note the 

 epithelium, basement membrane, and the longitudinal layer of 

 elastic fibres under it (fig. 2 86). 



5. Vesicular Structure of the Lungs. Make sections of a 

 lung hardened by the freezing method. Let the sections be cut so 

 as to include the pleura and subjacent lung. Stain in haematoxylin, 

 and mount in balsam. 



(a.) (L) Observe the pleura, with its two layers, the deeper 



Fro. 287. V.S. Human Luuff. p. Pleura; a. Epithelium of a bronchus ; b. Blood-vessel; 

 c. Pulmonary vein ; *. Interlobular septum, continuous with deep layer of pleura; 

 v. Air-vesicles ( x 50 and reduced |). 



layer sending fine septa interlobular septa into the lung between 

 its alveoli (fig. 287). 



(b.) The alveoli or air-cells cut in every direction; some appear 

 as an open network, and others with a base. The outline of the 

 alveoli may be somewhat irregular, according to the extent of dis- 

 tension of the lung. Here and there, between groups of alveoli, 

 may be seen a wide passage the infundibulum. 



