504 WILLIAM A. LOCY AND OLOF LARSELL 



however, as Guido Fischer ('05) has shown, the air-capillaries of 

 adjacent parabronchi cross the boundaries and anastomose. 



By the final anastomosis of these ultimate divisions of the bron- 

 chial circuits there is established the unique feature of the avian 

 lung — the lack of culs-de-sac in any part of the air circuits. 



Figure 46 is a much simplified diagram to show the relation of 

 the air capillaries to the parabronchus and to the hexagonal 

 prism of lung parenchyma in the adult chick. 



Intermingled with the network of air capillaries is a comple- 

 mental network of blood capillaries so that the facilities for rapid 

 aeration are very complete. The lung of birds is not large in 

 extent, but it is highly vascular and the continuous air current 

 from the air-sacs through the recurrent bronchi makes it an ef- 

 fective apparatus for aeration of the blood. 



