The Organs of Digestion 383 



The diiferences in flavor and other qualities which 

 are probably caused by the food cannot be satisfac- 

 torily explained at present. They are, however, slight 

 with normal rations. In general the color of the shell 

 is determined by the breeding or by the individual 

 characteristics of the fowl. 



Digestive apparatus. — The process of digestion with 

 birds is essentially similar to that with mammals, 

 although there are important differences in the ap- 

 paratus by which it is accomplished. It is necessary 

 to know something of the general arrangement and 

 working of the digestive canal when attempting to 

 establish proper methods of feeding, and for a better 

 selection and combination of suitable foods. 



Although some extinct species of birds were well 

 supplied with teeth, existing forms have the mouth 

 armed onh- 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 espe- 

 cially, have the mouth supplied with lamina, 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 oesophagus 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 dila- 

 tation there is attached to, and forming practically a 

 part of, the oesophagus, the reservoir called the crop. 

 The food is temporarily retained in the crop, but is 



