CHAP, XXIX.] 



THE HUMAN LUNGS. 



391 





perform the same function. They are a series of branched cellulated 

 air-passages, not lined with epithelium, or coated with muscular 

 tissue, but highly extensible and elastic, of much larger aggregate 

 capacity than the terminal bronchia which lead to them, and re- 

 sembling closely, in general conformation, the reptilian lung. In- 

 deed, an admirable notion of the essential arrangement of the lobules 

 of the mammalian lung may be derived from an examination of the 

 terminal parts of the sacculated bronchia of the lung of the turtle. 

 The lobular passages are wider than the terminal bronchia of which 

 they are the continuations, and than the cells which pullulate on 

 their walls. They also branch again and again in order to spread 

 from the terminal bronchial tube on every hand throughout the 

 whole area of the lobule, and as their ramifications observe no 

 certain order or course, it happens that sections carried through the 

 lobules are rarely found to follow any single passage far, so as to 

 display, in a happy manner, its mode of distribution. Sometimes, 

 however, this is better seen than at others. 



M. Eossignol has recently given an elaborate description of the 

 pulmonary structure. He insists particularly on the ultimate bron- 

 chial ramifications being in shape like an inverted funnel, and he 

 terms them the infundibula. The cells, forming a honeycomb on 

 their interior, he calls the alveoli (figs. 205 and 206). Emphysema, 



Fig. 205. 



Thin slice from the pleural surface of a cat's lung, considerably magnified. At the thin edge, 

 bed, alveoli are seen. In the centre (as a), where the slice is thicker, alveoli are seen on the 

 walls of infundibula. From Rossignol. 



according to this author, seems to consist in a distension of the 

 passages and cells, and a breaking down and obliteration of the 

 septa, first between the cells of the same passage, and then 



