124 HIGH SCHOOL ZOOLOGY. 



there is in all ])irds wliieh luivo that power, while the other, 

 J cldhyornis, had a wing fashioned in the same way as the great 

 majority of our birds, necessitating a keel ui)on the sternum. 

 Tlius at a very early period of the history of the hirds, the 

 distinction which we draw between those with a raft-like and 

 those with a keeled stermim (the Ratitse and the Carinatae) 

 was already established. But this distinction is of a compara- 

 tively unini[)ortant character, because it would a})pear that at 

 various periods of the world's history, members of difterent 

 families of birds have lost the power of flight (and along with 

 this, to a greater or less degree, the keel on the sternum,) by 

 taking exclusively to some other method of locomotion, such, as 

 swimming or running. Nevertheless, when we realize how the 

 structure of a bird is connected with its power of flight, we 

 shall more easily undei'stand how the absence of that power 

 mjiy produce a superficial resemblance. 



5. If we study, then, the structure of any typical carinate 

 bird, we shall soon learn that apart from the plumage there are 

 many other features which are evidently adapted to its mode of 

 locomotion and habits of life, and that the whole structiire of 

 the body is, indeed, modified in connection therewith. Although 

 the common domestic fowl belongs to a family of poor fliers, yet 

 a knowledge of its structure forms a key to that of all the 

 Carinata3. Numerous races are known but all belong to a 

 single species, Gallus domesticus, the nearest wild ally of which is 

 the Gallus hankiva of India. With the pheas.ints, pea-fowl and 

 guinea-fowl they form the family Phasianidae of the order 

 Gallinacei, all of the birds included under which (prairie-fowl, 

 partridge, turkey, etc.,) are indiflTerent fliers, seeking their food 

 on the ground, partly by scraping, for which purpose the feet 

 are provided with strong claws. 



6. Let us now proceed to examine the skeleton of a fowl with 

 the object of seeing in what respects it differs from that of the 

 fossil birds and reptiles The vertebral column presents the five 



