268 Analytical Notices of Books. 



Cygiiusferus, Meyer, and Cygnus Bewickii, Yarrell, are clearly made out, 

 especially as regards the structure of the trachea and sternum in the new 

 species, which is explained in two plates, the latter of which represents 

 these parts in three stages of their progressive developement. In the adult 

 state of the new species, the trachea, of equal diameter throughout, 

 enters tlie keel of the sternum, through which it passes to the end, 

 where, inclining upwards and outwards, it passes into a cavity formed in 

 the body of the bone by the separation of the bony plates, and produ- 

 cing a convex protuberance on the inner surface of the sternum. In this 

 cavity the trachea assumes a horizontal direction, and makes a considerable 

 curve reaching within half an inch of the posterior edge of the sternum. 

 It then returns to the keel, along the upper part of which it passes to the 

 exterior edge of the bone, over which it is reflected to enter the body of 

 the bird and become attached to the lungs. In a less perfect state of 

 developement the trachea occupies one side only of the cavity in the 

 body of the sternum; and at a still earlier period, it is found in the keel 

 alone, not having yet passed into the horizontal portion of the bone, in 

 which, however, the projection indicating the cavity is already strongly 

 marked. 



In these particulars the new species differs materially from the Wild 

 Swan, in which the trachea never assumes a horizontal direction, and does 

 not even penetrate within the keel to the extent of one half of the length 

 of the sternum. In the comparative length of the bronchi, and of the 

 bone of divarication, in the form of the latter, in the uniform calibre 

 of the tube of the trachea of the new species, and in other particulars, 

 additional differences exist. These are clearly explained by Mr. Yarrell, 

 who has also given comparative measurements of both species ; and, in 

 further illustration of his subject has indicated some differences in habit 

 and in voice, the latter agreeing with the variation in the structure of the 

 trachea. 



To the organs of voice in Birds Mr. Yarrell has for many years been 

 especially attentive, and the result of his enquiries respecting them 

 forms the subject of another communication in the present part. In this 

 truly valuable paper Mr. Yarrell describes the organ as consisting of four 

 parts: the glottis, or superior larynx; the tube of the trachea; the in- 

 ferior larynx, with its muscles ; and the bronchi. These parts are noticed 



