748 



CAPILLARIES OF LUNGS. 



of Blood-vessels, which does not seem to be covered by any limiting 

 membrane, but which admits air from the central cavity freely 

 between its meshes ; and thus its Capillaries are in immediate 



relation with air on 



Fig. 400. 



all sides, a provision 

 that is obviously very 

 favourable to the com- 

 plete and rapid aera- 

 tion of the blood they 

 contain. — In the Lung 

 of Man and Mam- 

 mals, again, the plan 

 of structure differs 

 from the foregoing, 

 though the general 

 effect of it is the same. 

 For its whole interior 

 is divided -up into 

 minute Air-cells, which 

 freely communicate 

 with each other, and 

 with the ultimate ra- 

 mifications of the air- 

 tubes into which the 

 Trachea subdivides ; and the network of Blood-vessels (Fig. 402) 

 is so disposed in the partitions between these cavities, that the 



Fig. 401. 



Interior of upper part of Lung of Frog. 



Interior structure of Lung of Fowl, as displayed by a section, 

 a, passing in the direction of a bronchial tube, and by another 

 section, b, cutting it across. 



