STRUCTURE OF THE LUXGS. 



191 



Fig. 59-* 



and subdivides ; its walls, at the same time, becoming 

 thinner and thinner, until at length they are formed only 

 of a thin membrane of areolar and elastic tissue, lined by 

 a layer of squamous epithelium, not provided with cilia. At 

 the same time, they are altered in shape; each of the 

 minute terminal branches widening out funnel-wise, and 

 its walls being pouched out irregularly into small saccular 

 dilatations, called air-cells (fig. 59). Such a funnel-shaped 

 terminal branch of the bronchial tube, with its group of 

 pouches or air-cells, has -been called an wfundibulum 

 (fig. 59), and the irregular oblong space in its centre, 

 with which the air-cells communicate, an intercellular 

 passage. 



The air-cells may be 

 placed singly, like recesses 

 from the intercellular pas- 

 sage, but more often they 

 are arranged in groups or 

 even in rows, like minute 

 sacculated tubes; so that 

 a short series of cells, 

 all communicating with 

 one another, open by a 

 common orifice into the 

 tube. The cells are of 

 various forms, according 

 to the mutual pressure to 

 which they are subject ; 

 their walls are nearly in contact, and they vary from. 

 .I Q to -f~ of an inch in diameter. Their walls are formed 

 of fine membrane, similar to that of the intercellular 

 passages, and continuous with it, which membrane is 



* Fig. 59. Two small groups of air-cells, or infundibula, a a, with 

 air-cells, b b, and the ultimate bronchial tubes, c c, with which the air- 

 cells communicate. From a new-born child (after Kolliker). 



