CLASS AVES. 



Ill 



bone of the bird of flight," says Owen, " was first solid, next 

 a maiTow-bone, and finally became the case of an air-cell." 



The Plumage is a model of adaptation. The quills are 

 hollow, and like the bones, filled with air. They are compos- 

 ed of the same substance, chemically, as the hair of mammals 

 and the scales of fishes. The delicate filaments of a feather 

 are covered with grasping barbs of a microscopic fineness. 

 The under side of a feather is concave, to resist an upward 



Plumage op a Bird.— I, crown ; 2^ forehead ; 3, nostrils ; 4, upper mandible : 5, lower 

 do. ; 6, throat ; 7, neck ; 8, spurious quUls ; 9, occiput ; 10, ear ; 11, nape ; M, 

 breast; 13, middle coverts ; lU, large do. ; 15,l>dly; 16, tibia; 17, farms; 18, inner 

 toe ; IS, middle do. ; 20, outer do. ; Zl, thumb ; H2, under taU-coverta; 2S, tail; U, 

 primaries ; H5, secondaries ; 26, tertiaries. 



pressure. On the tail is a gland containing oil, with' which 

 the bird lubricates its plumage and makes it waterproof. The 

 whole plumage is renewed (molted) once or twice a year. 



The Wing has a motion somewhat like the stroke of an 

 oar ; it strikes the air with the broad side, but, in returning, 

 presents only the sharp edge. The flight of a bird offers 



