500 Mr. Brookes on the Formation of the Trachea 



it is almost acute, but having a small indentation inferiorly. It 

 is formed of flattened minute rings (connected by intervening 

 membranes) firmly ossified at their rounded edge. From the 

 lower extremity the bronchi separate ; these decussate each 

 other in a very extraordinary manner, as may be seen in the 

 specimen. The membranous spaces between the rings of the 

 bronchi are very distinct; and I must confess myself at a loss 

 to account for this singular arrangement. The trachea occupies 

 the anterior surface of the oesophagus at the entrance into the 

 thorax. This proceeds to its destination between the bronchi. 



Probably one reason for the compressed figure of the inferior 

 part of the trachea may be for the purpose of allowing large 

 erpetalous animals to descend in deglutition with greater facility 

 than could otherwise happen without impediment to respiration; 

 for in consequence of the ossified structure of this singular por- 

 tion of the aspera arteria, neither the pressure of the individual 

 by its volume, nor by its struggles in articulo mortis, would cause 

 obstruction. 



Perhaps it is not possible for the naturalist to investigate any 

 subject more fraught with interest than the pulmonary organ in 

 birds, the more striking peculiarities of which exist in some of 

 the genera of the order Grallatores ; for instance, in the Gruidce, 

 the Platalea, and, as it now seems, in the Tantalus. They are 

 found also in the Anatidce almost universally; and although the 

 genus Anser is an exception, nevertheless the Anser semipalma- 

 tus, an Australian goose, is singularly furnished with the most 

 contorted trachea of the whole aquatic tribe. 



The species of the genus Cygnus are remarkable for the con- 

 tortions of the trachea within the carina of the sternum, but the 

 domestic swan is altogether an exception, and presents another 

 discrepancy in the number of the ribs. The form of the trachea 

 in the Fuligula nigra (Black Scoter) is the most simple among 



