STRUCTURE OF THE LUNGS OF MAMMALS. 



51 



The calibre of these passages, so far as it is determined by 

 the free borders of the alveolar septa, amounts in adults to 

 0'4 0'2 of a millimeter; in medium-sized Mammals, as the Pig, 



Fig. 125. 



Fig. 125. System of alveolar passages, with infundibula, from the 

 margin of the lung of a Monkey (Cercopithecus), injected with quick- 

 silver. Magnified 10 diameters, a, Terminal bronchial twig ; fr 6, 

 infundibula ; c c, alveolar passages. 



Dog, and Cat, 0'2 0'15 of a millimeter; in the Rat, about 01 ; 

 in the Mouse and Bat (Plecotus auritus), from (H to O06 of a 

 millimeter. The chief trunks are always somewhat larger than 

 the subdivisions. The diameter also, in Man at least, increases 

 with age. 



Fig. 126. 



Fig. 126. Section of the lung of a Cat, injected with alcohol, and 

 hardened. Magnified 12 diameters, a, Terminal bronchial twig ; 

 b 6, infundibula ; c c, transverse section of alveolar passages ; d d, 

 longitudinal section of alveolar passages. 



The alveoli themselves, which on a transverse section of an air 

 passage or infundibulum are seen to be radially arranged, and 

 to vary from four to eight in number, are usually hemispherical 



E 2 



