238 FACULTIES OF BIRDS. 



bubbles of air which inflated them ; insomuch that, 

 pressing the body of this bird, one heard a little noise 

 like that produced by pressing the membranous parts 

 of an animal which has been inflated. By the assist- 

 ance of the probe arid blowing, we discovered the 

 communication of these membranes witty the lungs *." 



Besides the air-cells filled from the lungs, it appears 

 from several of the preceding details that there are 

 others directly filled from the mouth and nostrils 

 through the windpipe. The latter, particularly in birds 

 of prey and high-flying birds (Alauda, Cico?iia y <$*c.), 

 are very large, ascending beneath the skin of the 

 neck and shoulders and around the skull. " In the 

 stork," says Dr. Macartney, " we find these cells 

 large enough to admit the finger to pass a considera- 

 able way down upon the inside and back of the wing : 

 they are also large in the owl f." 



It is evident that all this extraordinary number and 

 volume of air-cells, as well as the very great strength 

 observable in the bones of birds, is for the express 

 purpose of rendering them light and buoyant, so that 

 they may support themselves in the air with less 

 effort. 



It is but right to add, that the opinion of John 

 Hunter, who has so well elucidated the anatomical 

 structure and extent of the air-cells of birds, is not 

 altogether in accordance with the conclusions which 

 we have been led to draw. 



The following excellent remarks on the structure, 

 which is so admirably adapted for rendering birds 

 light and buoyant, are by Sir Charles Bell: 



" First/' he says, " it is necessary that birds, as 

 they are buoyed in the air, be specifically lighter ; 

 secondly, the circumference of their thorax must be 

 extended, and the motions of their ribs limited, that 



* Hist. Gener. des Voyages, ix. 311. 

 t Rees's Cyclopaedia, Art. Birds. 



