CHARACTERISTICS OF BIRDS. 119 
effectual by sand and small stones, which the Bird swal- 
lows with its food. In Fig. 99 you see the gizzard of a 
Turkey cut open. You observe the two semi-globular 
Fig. 99.—Gizzard of the Turkey. 
masses of muscle, and the lining covering them on the 
inside of the organ. While these grind the food, the 
gastric juice which digests it is all the time trickling 
down upon it from the gullet at a, where it oozes out 
from a great many little openings. 
203. This grinding operation of the gizzard takes the 
place of the mastication which is done by those animals 
