208 



MICROSCOPIC ANATOMY OF THE ORGANS. 



of the lung and its relation to the blood-vessels. The following 

 notes are based on his work. He speaks of the last division of 

 the bronchus before it breaks up into the lung parenchyma ;is 

 the terminal bronchus. From this a number of other passages 



FIG. 160. 



Alveolar ( """ 

 ducts \ ^ 



Blood- 

 vessel 



Respiratory 



bronchiole 



Alveoli"?: 



Bronchiole 



Section through the lung of a cat. The respiratory bronchiole divides to form two alveolar 



ducts. X 50. 



lead, which are connected by a central chamber, known as the 

 vestibulum (Fig. 161). These passages open into the atria, 

 which communicate by means of the air-sac passages with the 

 various air sacs. Around the periphery of the air sacs are the 

 air cells. This can be seen in Fig. 161. 



The terminal bronchus (average diameter, 0.4 mm.) con- 

 tains smooth muscle cells in its walls. It is lined with 

 columnar epithelium. Between this and the atria are the 



