310 



THE RESPIRATORY SYSTEM 



broader spaces, the alveolar ducts (infundibula of Schultze), which are 

 surrounded by air saccules with pulmonary alveoli. According to Miller 

 the alveolar ducts bear numerous alveoli, and are lined with flattened 

 respiratory epithelium, and contain scattered bundles of smooth muscle 

 which end in a delicate sphincter where the duct passes into the non- 



FIG. 293. FROM A SECTION OF A CHILD'S LUNG. 



A, atrium; B, bronchioles ending in terminal respiratory bronchioles, TB; PA, 

 pulmonary artery; PV, pulmonary vein. Hematein and eosin. Photo. X 50. 



muscular atria, from three to six for each alveolar duct. Each atrium, 

 of more or less circular outline, opens into a variable number (two to 

 five) of irregular and variable alveolar saccules (air sacs). Each sac- 

 cule bears on its periphery numerous pulmonary alveoli. The epithelium 

 of the entire bronchial tree, including the nucleated respiratory cells, con- 

 tains abundant mitochondria (Meves and Tsukaguchi, Anat. Anz., 46, 

 1, 1914). 



