FEEDING OF POULTRY 403 



explained at present. They are, however, slight with 

 normal rations. In general the color of the shell is deter- 

 mined by the breeding or by the individual characteristics 

 of the fowl. 



493. Digestive apparatus of birds (Fig. 17). — ^The pro- 

 cess of digestion with birds is essentially similar to that with 

 mammals although there are important differences in the 

 apparatus by which it is accomplished. It is necessary 

 to know something of the general arrangement and 

 working of the digestive canal when attempting to estab- 

 lish proper methods of feeding, and for a better selec- 

 tion and combination of suitable foods. 



Although some extinct species of birds were well 

 supplied with teeth, existing forms have the mouth 

 armed only with a horny beak. The common fowls 

 must swallow grains whole but are able to tear some 

 food into small fragments, which they particularly do 

 when feeding the young. Ducks, and geese more especi- 

 ally, have the mouth supplied with laminae which serve 

 to cut soft herbage. 



In birds the salivary glands are small and the lim- 

 ited amount of saliva probably has little effect on the 

 food. 



The esophagus is of great caliber and very expan- 

 sible. It is dilated in the cervical portion in ducks and 

 geese. In gallinaceous birds, instead of this dilatation 

 there is attached to, and forming practically a part of, 

 the esophagus, the reservoir called the crop. The food 

 is temporarily retained in the crop, but is changed very 

 little other than being softened by the water swallowed 

 with it, the small amount of mucus, and the inconse- 

 quential amount of saliva. The high temperature doubt- 

 less assists this softenmg effect, and fermentation also 



