152 THE WAYS OF BREATHING 



" air-cells " in the bones and muscular interstices 

 of birds in 1774, simultaneously with Camper. 

 The abdominal air-sacs of birds are appendages 

 of the lungs, and although there exists a general 

 homology between lungs and the air -sac of 

 fishes, there is no special homology between the 

 abdominal extensions of the lungs in birds and 

 the latter. 



