PHYSICAL FEATURES OF BIRDS. 269 



the horizontal body level. In the bird, we have an 

 upright quadruped, or a biped with the front limbs used 

 as wings, and the head considerably above the rest of the 

 parts of the body. This narrows the base within which 

 the center of equilibrium falls while the bird stands 

 upright; but when the bird spreads its wings it bends 

 forward, and thus widens its base and places itself in 

 more stable equilibrium. Yet, skill in flight has its 

 degrees of excellence of development in the different 

 sorts of birds. The birds just mentioned are the most 

 notable fliers among the aquatic birds. Among the land 

 birds of North America, the buzzards and certain of the 

 hawks come the nearest to being tireless on the wing. The 

 most familiar feature of the landscape, in some parts of 

 the continent, is the vulture, or buzzard, as he and his 

 comrades soar above the land expanse beneath, no part of 

 it hidden from their observing eyes, searching for a carcass, 

 soaring till they find it, apparently alighting only when 

 feeding. The hen hawk, the familiar red tail, was 

 watched by one observer from seven in the morning till 

 four in the afternoon, during which time it kept aloft in 

 the air. 



The skeleton of the bird's wing has much the same 

 construction as our arm; insomuch so that we call the 

 large bone articulating with the shoulder the humerus; 

 the two smaller bones below it and articulating partly 

 with each other, the radius and the ulna; while the still 

 smaller bones or series of bones on beyond the radius and 

 the ulna are called the fingers, the one just at the turn 

 of the wing corresponding to our thumb, the middle and 

 longest finger corresponding to the middle or main exten- 

 sion of our hand. 



As organs of flight, the wings are provided with 



