CHAPTER FORTY-EIGHT 



BIRDS 



I. ALL birds have feathers, and in this they differ Characters 

 from every other group of animals. In common with 

 the reptiles, they lay hard-shelled eggs and have scaly 

 feet, but they resemble mammals in having warm blood. 

 The blood is, indeed, warmer than that of mammals ; 

 in the small, active, singing birds it is at least 10 degrees 

 (Fahrenheit) above that of man. In all zoological 

 arrangements the birds (Aves, from the Latin avis, a 

 bird) follow the reptiles and are followed by the mam- 

 mals ; but no zoologist believes this to have been the 

 course of evolution. The mammals and birds arose 

 independently from reptilian ancestors, and today the 

 birds are much more reptilian than mammalian in 

 structure. The feathers must be regarded as greatly 

 modified scales, and the single occipital condyle at the 

 base of the skull is a reptilian feature. Although 



From Thompson's "Zoology" 



FIG. 150. Wing of a dove, showing the bones and important feathers : h, humerus ; 

 r, radius; u, ulna; c, carpals; m.c., carpo-metacarpals ; s.f., secondary feathers; 

 p.f., primary feathers. 



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