BIRDS. 



295 



the next place, that there should be some convenient receptacle 

 into which it can be instantaneously transferred, until wanted. 

 In some birds, which, like the Swift, live ui)on insect prey, 

 seized when on the wing, the upper part of the throat is so 

 large as to answer for this purpose. In the Pelican, a pecuhar 

 pouch is attached to the lower jaw (^Fig. 21-7), and in this a 

 goodly store of fish can be carried about. In the Cormorant, 

 the gullet itself is dilated, so that it is not unusual, when the 

 bird has got a fish too large to be swallowed at once, to see 

 the tail hanging for a time out of its mouth. But the plan 

 which is most usual, is that which may be exemplified in the 



liy- 24V.— Pblicas. 



digestive system of a common fowl {Fig. 2 IS). The gullet, 

 {oesophagus) is suddenly expanded, forming a bag or chamber, 

 known as a crop. Beneath this there is a slighter expan- 

 sion, which forms the second or membranous stomach, in 

 which the food is softened by the action of what is called 

 the gastric juice. From this the food passes on to the 

 third stomach, in which the process of digestion is com- 

 pleted. In flesh-eating birds, this stomach is thin and mem- 

 branous ; but in those which feed on grain, the sides of it 

 are of considerable thickness, and, being moved by powerful 

 muscles, act as a mill in grinding down the food. Many who 

 see the gizzard of a fowl at table know that it serves in the 

 economy of the bird as a grinding machine ; but comparatively 



