1 10 AVES. 



trachea, which is more strongly developed in Anas fusca and in 

 Clangula. Feeble traces of a double widening of the tube occur in 

 Anas crecca and tadorna ; there are elongated dilatations in Anas 

 rufina, glacialis and Mergus merganser, and a single one in Pala- 

 medea cornuta. In the Emeu a peculiar structure is observed, for 

 in that bird an elongated slit, several inches long, is found above the 

 bifurcation of the trachea, and communicates with a large cellular 

 air-sac situated in the neck. 



In other Birds from the orders just mentioned convolutions occur 

 of the lower part of the trachea, and are situated either free beneath 

 the integument at the commencement of the thoracic cavity, or 

 are enclosed to a greater or less degree of depth within the sternal 

 keel. Thus in Platalea, Penelope, the Cock of the Woods, the 

 Corn-crake, and some Pheasants, especially in the males of these 

 species, and in Anas semipalmata (where it makes the most com- 

 plex convolutions of all), the trachea descends beneath the skin to 

 beneath the level of the anterior border of the sternum, ascends and 

 having made a second curve upon itself, bifurcates into the bronchi 

 for the lungs. In both the male and female of Grus virgo and 

 cinerea, with however certain sexual modifications, the trachea 

 penetrates the keel of the sternum, is enclosed within it as in a bony 

 capsule, and there makes several spiral convolutions upon itself 

 which extend in the male as far as the posterior extremity of the 

 keel. In both the sexes of Cygnus musicus and Bewickii, a loop- 

 shaped coil of the trachea lies within the keel of the sternum ; 

 in the Black Swan however this structure is more feebly developed, 

 and does not exist at all in the mute Swan (Cygnus o\or). It is 

 most strongly indicated in the Trumpeter Swan (C. buccinator), 

 where the tracheal convolution descends as deeply as in the male 

 Crane. In Numida cristata a coil of the trachea is situated between 

 the shafts of the furcular bone. A well-marked sexual difference 

 is observable in the Black Stork, where in the male the bronchi, 

 long and having complete-rings, are always curved in the shape of 

 the letter S ; this is the case also, though in a lesser or scarcely 

 noticeable degree, in the male of the White Stork. A peculiar con- 

 dition of the trachea is met with in the Penguin, by the ridge upon 

 the inner wall of the thyroid cartilage forming a septum, which is 

 prolonged throughout the whole of that tube. A similar structure 

 is found at the inferior extremity of the trachea in Procellaria gla- 

 cialis. 



The existence of an Inferior or Bronchial Larynx, in which the 



