INTRODUCTORY 5 



This provides a firm basis for the Hmb, 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 

 peculiarities of the fowl from the economic 

 point of view are to be found in connection 

 with the reproductive organs of the female. 

 During a normal life- time a bird lays a large 



