166 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 moti? 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 i : 
dropper into the’ 4... 196 = Open glottis of 
bird’s mouth, reflex action will a Pelican, 
anticipate the danger of choking and close the aperture. 
