Organs of Nutrition 129 
descends after it leaves the mouth. In some birds this 
is a simple tube of the same diameter throughout, always 
moist from the secretion of (mucous) glands which are 
found abundant in its walls, but serving merely as a 
passage for the food on its way to the stomach. 
In another class of birds an enlarged chamber is 
present, called the crop. This serves a somewhat simi- 
lar purpose as the external pouch of the pelican; that 
is, it acts as a receptacle for food. No especial digestive 
glands are found here, and the only agents acting on 
Fic. 102.—Brush, or tube-like tongue of Honey Creeper. Twice natural size. 
the food are water, the secretions of the salivary glands, 
and the heat of the bird’s body. The crop exists only 
superficially in some birds, the dilation being hardly 
noticeable. 
From these we find a succession of more distinctly 
marked permanent crops, until in grain-eating birds this 
organ is very prominent. If we examine an English 
Sparrow after it has made a hearty meal in the chicken- 
yard, we will find the crop filled with grains of wheat, 
some cracked in pieces by the bill, others entire. 
