INTRODUCTORY 5 



This provides a firm basis for the Umb, which is 

 all the more necessary since the two hip-bones 

 are not united in the middle line ventrally. 

 The tarsal joint is simplified and the meta- 

 tarsal bones are united into a single rod. 



The digestive apparatus also affords ex- 

 amples of purposive modification. No existing 

 bird possesses teeth, their place being taken 

 by the horny sheaths covering the jaws. 

 Birds like the fowl have a dilatation of the 

 oesophagus into which food is received, and 

 in which it undergoes the preparatory macera- 

 tion rendered necessary because of the absence 

 of the preliminary process of chewing. The 

 stomach is divided into two parts. Within 

 the walls of the first part is a thick and com- 

 plicated layer of glands ; while the second 

 part has powerful muscular walls and a horny 

 lining in its interior. Here the food is sub- 

 jected to a grinding process rendered more 

 effective by the presence of hard substances 

 such as small pebbles. 



Some of the most important structural 

 I peculiarities of the fowl from the economic 

 j point of view are to be found in connection 

 1 with the reproductive organs of the female. 

 ! During a normal life-time a bird lays a large 



