3S8 



THE BIOLOGY OF BIRDS 



bone at the end of the tail, the hook-like (uncinate) processes 

 on the ribs are small or absent, the barbs of the feathers do 

 not form a coherent vane, and the sutures of the skull-bones 

 remain for a long time distinct, whereas in Flying Birds they 



almost always disappear 

 very early. 



(b) In support of the 

 view that Running Birds 

 are degenerate Flying 

 Birds, a strong argument 

 is furnished by the Tina- 

 mous or Crypturi, par- 

 tridge-like birds of Mexico 

 and Central and South 

 America. They are great 

 runners, but they have 

 also strong and rapid 

 flight. The breastbone 

 bears a keel, and yet in 

 the skull and in some 

 other skeletal features 

 there is a marked resem- 

 blance to ostriches and 

 their relatives. For the 

 Ratitae differ from all 

 other birds except Tina- 

 mous in the nature of 

 their palate : the pterv- 



-An ostrich feather the barbs jjg form a jointed arti- 

 irom one another, not lorming ° . . ■* 



culation with the palatines, 

 and a close union either 

 by fusion or by overlapping suture with the base of the 

 well-developed vomer. This kind of skull, called dromae- 

 ognathous, is very distinctive. Tinamous are often ranked 

 with Carinatae because they are flying birds with a keel, 

 but their skull is distinctly struthious. This suggests that 

 the struthious Running Birds may have degenerated from 

 flying birds somewhat like Tinamous. The disappearance 



Fig. 55 

 free 

 a vane 



