500 Mr. Bnooxzs 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 cesophagus 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 Gruide, 
the Platalea, and, as it now seems, in the Tantalus. They are 
found also in the Anatide 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 
the 
