Appendix. 85 



The windpipe enters the keel below, at the junction of the furcula or 

 merrythought, passes along just above the edge to the extreme end of the 

 bone, then turns forward, and comes to the front along the upper edge of 

 the keel, where it is connected with the horizontal plate of the sternum ; 

 it then turns back again as far as the middle of the keel, again comes 

 forward for a short length, when, curving sharply upwards on itself, 

 it proceeds backwards, then downwards, then forwards, and finally upwards 

 into the interior of the thorax, where it divides into the two bronchi going 

 to the right and left lungs, the syrinx or organ of voice being situated at the 

 bifurcation. 



S ir John Richardson informs us that the bird flies at such an altitude 

 that its passage is only known by the peculiarly shrill screams it utters — 

 a fact not so remarkable when we consider that the vibrations of sound 

 produced by the syrinx are conveyed through a convoluted trumpet nearly 

 five feet in length. 



So much for the convolutions of the trachea in the adult cranes. 

 I think that this account will in the main bear out my suggestion that the 

 result of these elongated curves corresponds to that of those in a French 

 horn — nameiiy, they increase the depth and sound of the voice : 



With regard to the young birds, Mr T. J. Roberts informs us that, 

 In the embryo crane just about to break the shell the trachea does not enter the 

 sternum at all, and is perfectly simple. But the anterior part of the keel, which is 

 entirely cartilaginous and diminutive, is much thickened, and a cross section of it 

 shows it to consist of two thin walls, separated by a marrow-like substance. In this 

 feature of the sternum we see the only indication in the embryo of the singular 

 structure to be developed later in life. The degree of complexity of the trachea is thus 

 sliown to be dependent upon age, and the variations are no doubt fully accounted for by 

 this fact. 



As might be expected, in the young birds the voice is entirely wanting 

 in resonance, being a mere plaintive cheep ; and just in proportion as the 

 windpipe becomes more and more convoluted in the adult birds, so does 

 the resonance of the voice become more and more marked^ from the feeble 

 tone of the Asiatic white crane, with its straight trachea, through all the 

 various grades up to the resonant clang of the whooping crane of North 

 America. 



The convolutions of the trachea in birds are not confined to the Cranes, 

 but are to be found in many other families. In several of the swans 

 [Oygnua) the trachea enters into the keel of the sternum very much in the 

 same manner as it does in the Cranes. This, however, as might be 

 expected, is not the case in the tame or mute swan {Oygnus olor), which, as 

 its English name implies, is nearly voiceless, and does not even sing as 

 fabled when dying. In other species of the genus, as bhe Hooper, the 

 Oygnus musicus of Bonaparte, the trachea is contained in the keel, as in the 

 Cranes, and the result is that the bird has a loud, melodious, far-reaching, 

 hooping or whooping voice, from which its English name, is derived. 



