XVI] ON STRENGTH AND FLEXIBILITY 1013 



While the bird stands/on the ground its backbone is, as in ourselves, 

 its skeletal axis, and it, including the great cantilever associated with 



Fig. 485. a, Sternum and shoulder-girdle of a skua gull, b, section of do., through 

 the hne AB. St, sternum; Ca, its carina or keel; Co, coracoid bone; Sc, 

 scapula; F, merry-thought or furcula. 



it, carries, and transmit^ to the legs, the whole weight of the body. 

 But as soon as a bird spreads its wings and rests upon the air, legs, 



Fig. 487. A flying bird. Sternum, shoulder -girdle and wings combine to 

 support the body; and all the rest lies as a dead weight thereon. 



backbone, cantilever and all become merely so much weight to be 

 carried; and the whole rests, as on a floor, on the strong, stiff 

 platform made of sternum and shoulder-girdle, which the wings (so 



