CORMORANTS. 363 



it could not again ascend, if they were not received upon 

 something more elastic than feathers. But the resources of 

 nature are always true to the purpose, and the gannet is let 

 down, and assisted in again ascending, upon that finest of all 

 springs, the air. 



The cellular tissue immediately beneath the skin, on the 

 under part of the gannet, is formed into air cells : or rather, 

 the skin is attached to the muscles by a number of mem- 

 branous points, so that it can be inflated to a very consider- 

 able extent, or reduced by the contraction of the muscles, at 

 the pleasure of the bird. Those external air cells form a 

 sort of three divisions, one on each side the breast, and one 

 anteriorly of the furcal bone (or merrythought), on the neck 

 of the bird. The two lateral ones have a sort of septum 

 along the keel of the sternum ; and they receive air from the 

 air cells within, through apertures beneath the great pectoral 

 muscles ; but they communicate with each other, so that one 

 side of the bird cannot be inflated or reduced without a 

 similar effect taking place in the other. Such an inflation 

 would, indeed, be very awkward ; as in case of a wound in 

 one side, the bird could not keep its balance. The anterior 

 cell is unconnected with the rest, opens into the interior 

 cells further forward, is globular, and about four inches in 

 diameter when expanded, and has a beautiful fan-shaped 

 muscle for its contraction. 



The particular action by means of which the gannet in- 

 flates those cells, the occasions upon which they are inflated 

 or contracted, and their uses in the economy of the bird, are 

 not perfectly known ; but, as has been already said, they 

 could have the effect of making the bird descend upon the 

 water like an elastic balloon, or rise in like manner when it 

 plunges. 



