216 ELEMENTARY PHYSIOLOGY. [XX. 



a. Sections of blood-vessels (cp. Lesson xu). 



b. Sections of bronchia. Note that 



The sections of the larger bronchia resemble 

 sections of trachea, except that 



a. The cartilages are irregular in form, and 

 irregularly scattered throughout the 

 fibrous coat. 



/3. The transverse muscular fibres now form 

 a complete ring in the sub-mucous coat. 



From the smaller bronchia the cartilages are 

 absent, but the muscular fibres still con- 

 tinue as scattered fibres arranged trans- 

 versely. 



c. The passage of a small bronchial tube into an 

 infundibulum (this may be seen occasionally 

 in a section). Note that 



a. The columnar ciliated cells become 

 shorter and lose their cilia. 



/?. The muscular fibres apparently cease. 

 7. The longitudinal fibres spread out into 

 an irregular mesh work. 



d. Sections of alveoli. 



a. The outline of the alveoli : the distinct 



basement membrane. 

 /3. The flat, tesselated epithelium 1 . This 



1 The outlines of the epithelium cells of the alveoli may be 

 rendered evident by treatment with silver nitrate in the following 

 manner. In a just killed mammal, a carmula is tied in the trachea, 



