CHAP. XXIX.] 



THE HUMAN LUNGS. 



389 



Fiff 204 



veniently designating that series of air-cells, associated by depen- 

 dence on a single terminal air-tube. We shall afterwards show 

 how much difference exists in the isolation of 

 the lobules of the liver even in allied animals, 

 and how unimportant this variety appears to be. 



The superficial lobes derive a covering on 

 one aspect from the pleura, but are separated 

 from it by rather dense areolar tissue, which 

 may be dissected off without rupturing the air- 

 cells. If the interstices between contiguous 

 superficial lobules be explored by the knife, the 

 terminal bronchia are found at the bottom of 

 the fissures, each going to a single lobule, and 

 besides these are seen branches of the pulmonary 

 artery and vein, not running in company, nor 

 limiting themselves to a single lobule, but com- 

 mon to contiguous lobules; so that the air-spaces 

 of one lobule do not communicate with those 

 of another across the interstices, but the blood- 

 vessels do. On the exterior of the lobule we 

 observe bubbles of air of various sizes in its 

 tissue, and if the bronchial tubes be injected, 

 the lobule is distended, and its exterior presents 

 a number of bulgings known as the air-cells, 

 about which much controversy has existed, 

 Their shape seems irregularly polyhedral, like 

 the lobules themselves. The angles, where three 



or more of these cells meet, are the points at 



which the terminal twigs of the pulmonary 



artery and vein penetrate among the cells, after 



meandering more or less over the surface of 



the lobule. In their course in the interior of 



the lobule, these twigs generally run separately 



in the lines of junction of three or more cell- 



walls, branching as they run and breaking up 



into their capillaries on either hand. 



As the superficial lobules are truncated where they form the 



surface of the lung, so the cells are truncated where they form the 



surface of the lobule. This is most decidedly the case where the 



lobules are well defined, and admit of separation; but where 



contiguous lobules are not isolated by areolar tissue (as in most 



parts of the interior of the lungs, and in the lungs of the smaller 



small bronchial tube laid 



fibres e S? C nX ^re- 



