i66 



The Bird 



is attested by their distinctness in our ears after the bird 

 has passed beyond the range of vision. A human singer 

 is compelled to put forth all his energy in his vocal ef- 

 forts, and if, while singing, he should start on a run even 

 on level ground, he would become exhausted at once. 

 The apparatus which gives to a duck the "wind" to out- 

 strip an express train, and to a Mockingbird notes which 

 hold us spellbound as by a motif of grand opera, is most 

 interesting, and as easy to understand in its general scheme 

 as it is effective in operation. 



The Trachea, or Windpipe 



Look into the beak of a sparrow or pigeon and directly 

 back of the tongue, on the floor of 

 the mouth, a narrow slit is visible 

 the glottis, or opening of the 

 windpipe. In the gaping yellow 

 mouth of a nestling robin this 

 may be seen to excellent advan- 

 tage, and watched as it widens and 

 narrows with each breath. But 

 give the young bird a mouthful 

 of food, and this air-passage closes 

 instantly and remains so until all 

 danger of an intruding substance 

 is past. No matter how suddenly 

 you may eject a stream of water 

 from a medicine-dropper into the 



FIG. 126 Open glottis of 



bird's mouth, reflex action will a Pelican, 



anticipate the danger of choking and close the aperture. 



