CYGNUS BEWICK1I. 



portion longer and more slender than that of the Hooper. In the internal 

 conformation of the two species, particularly as regards the trachea and 

 sternum, the differences are more striking. In the Common Wild Swan, 

 it is well known, that the trachea, previous to entering the thorax, makes 

 a curious convolution or duplicature, within a cavity prepared for it in 

 the keel or projecting part of the sternum. This cavity in most speci- 

 mens does not extend in depth more than 3 or 3£ inches, and the flexure 

 of the trachea is always vertical. In the new species, the cavity frequently 

 extends to the depth of 5^ or 6 inches, and after reaching the posterior 

 extremity of the keel, occupies in addition a portion of the lateral part of 

 the sternum itself, where the trachea, instead of making a vertical flexure 

 like that of the Hooper, is obliged to take a horizontal bend, and to form, 

 as it were, a loop in that portion of the sternum which is excavated. 

 The keel of the new kind is also not so deep as that of the Hooper ; and, 

 in consequence, the two portions of the trachea within the hollowed cavity 

 are brought closer together. Other marked differences are observable in 

 the trachea of the new species, after its egress from the hollowed cavity of 

 the keel, as compared with the corresponding parts of the Hooper. In the 

 former, the trachea after describing the arch on its egress from the keel, 

 enters the cavity of the thorax itself, for upwards of two inches, and is 

 there attached by the inferior larynx, or bone of divarication, which hangs 

 vertically within the thorax, to the bronchial tubes ; in the Hooper, on the 

 contrary, no portion of the trachea enters within the thorax, but the in- 

 ferior larynx, to which it is attached, reaches just as far as the anterior 

 ridge of the sternum, upon which it rests obliquely. The dimensions of 

 trachea, where it joins the inferior larynx, and this part itself, are very 

 dissimilar in the two species. In the one, the diameter is greater at this 

 part than at any other, the larynx broad, and not so much compressed ; 

 in the Hooper, the trachea is greatly contracted and compressed where it 

 joins the larynx, which is not one-half the diameter of that of the other. 

 In the size and form of the bronchii also, there is a marked difference, 

 those of C.ferus measure nearly 4 inches in length, and possess a large 

 diameter ; whereas those of the other are not more than two inches long, 

 and their greatest diameter scarcely half that of the Hooper, while the 

 form of the rings which compose the tubes are also of different shapes. 

 In addition, the sternum of the new kind is much broader in comparison 

 to the relative size of the bird, and the ridge of the keel, instead of nar- 

 rowing downwards as in the Hooper, gains breadth as it approaches the 

 posterior extremity of the keel, or where the cavity widens, and occupies 



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