BIRDS 273 



the sparrow sleeps, the more securely it sits upon its perch. 

 In addition to this arrangement, there are muscles by 

 which the bird can voluntarily cling to a support. 



The head and neck. — The head is small and light and 

 the neck is long and muscular. Any animal that stands 

 high from the ground must have a long neck with which to 

 reach its food. At the same time the head must be as 

 light as possible to enable such a long neck to support it 

 without fatigue. The anterior part of the head is pro- 

 longed into a hard, horny beak, the grasping organ of the 

 sparrow. The beak consists of an upper and a lower man- 

 dible, but is not furnished with teeth. No living bird has 

 teeth. The beak is made to withstand the wear of picking 

 food from the hard ground or other surface. Besides, it is 

 used as a weapon of defense. 



The alimentary canal. — The gullet leads directly to a 

 large pouch, the crop, in which the hastily procured food is 

 stored for a time. The walls of the crop are provided with 

 bands of muscles which, by their contractions, set up a slow 

 churning movement. Following the crop is the slightly 

 dilated and glandular stomach. Situated just a little be- 

 yond and below the stomach is the thick-walled gizzard. 

 The intestine immediately follows, forming, at first, a long 

 loop, the duodenum, and then passing on toward the anal 

 aperture, expands at its terminal part into a wide, saclike 

 portion, the cloaca. Situated within the loop forming the 

 duodenum is the pancreas which is directly connected with 

 this part of the intestine. The gall bladder of the over- 

 lying liver is also connected with the duodenum (Fig. 187). 



The digestive process. — The process of digestion is begun 

 in the crop. Here the food is slowly churned and moistened 

 by the juices given out by the glands of the crop. Passing 



herkick's zool. — 18 



