TirE PLUMAGE AND FLTOm' OF BIRDS. 15 



liv I'irds wliosc wiugs arc nearly horizontal, as tlio lark and the quail. " In general," 

 he says, " the wings arc iilaecd ohiiquely ; this is principally owing to the length of then- 

 feathers, the fixed point of whic^h is at the root. AMu<n birds fly horizontally, theii- 

 motion is not in a straight Hne, but obliquely upwards, and they allow the body to conic 

 do\^ai to a lower level before a second stroke is made by the wings, so that they move in 

 a succession of cui'ves. To ascend obliquely, the wmgs must repeat their strokes upon 

 the ail- in quick succession ; and in descending obliquely, these actions are proportionally 

 slower. 



" In birds of prey the form of the wings is very oblique, so that they cannot rise in the 

 air perpendicularly luiless they fly against the wind; they have, however, a greater 

 power of horizontal motion than other birds, because the extreme parts of the -wings 

 are long, and the ends of the feathers lap over each other, which opposes a uniform 

 resistance to the air ; while, in other birds, the air passes through between the feathers, 

 which lessens the power of keeping the wing oblique. To enable themselves to tm'u to 

 the right or left, they move one wing more rapidly than the other. This is attended 

 with chlficulty when the flight is rapid ; they, therefore, make a large sweep before they 

 can tm-n roimd." 



The tail of the bird serves as a rudder. The last bone of the caudal veiichm is larger 

 than the rest, and of a difl'erent figure. The development of this bone is necessary, as it 

 supports the tail-feathers, the quills of which are fixed in capsules, as well as powerful 

 muscles. Thus they are capable of being closed, elevated, or depressed, and also of being 

 expanded, as in the turkey-cock. The tail-feathers vary in size, length, shape, and 

 strength, in various groups or genera. Their usual number is twelve, sometimes they 

 amount to fom-teen, and in the gallinaceous tribes to eighteen, and even more. When 

 the tail is short, the office of directing the flight is performed by the legs, which are 

 then generally very long. In many birds, as in the woodpecker, the tail is much 

 emploj'ed as a support to the body in climbing trees. 



There are yet several cii-cimistances respecting the structure and action of the wings 

 which remain to be noticed. Thus, if we attend to the mode of their articulation with 

 the scapula, we find it producing a motion oblique with regard to the axis of the body, so 

 that the stroke which they give to the aii- is directed both do^\^nvards and backwards, 

 and the bird, while moving forwards, is at the same tiiue supported in opposition to the 

 force of gra^-ity. 



The different portions of the wing are likewise so disposed as to be contracted and 

 folded together when the wing is dravm up, and fully expanded when it descends in 

 order to strilie the air. Without this provision, a great part of the motion acquired by 

 the resistance of the air against the wing in its descent, would have been lost by a coun- 

 teracting resistance during its ascent. The disposition of the great feathers is such that 

 they stri e the air mth their flat sides, but present only their edges in rising ; what is 

 called " feathering the oar," in rowing, is a similar operation, and derives its name from 

 tlus resemblance. 



As the inclination of the wing is chiefly backwards, the greatest part of the eff'ect pro- 

 duced by its action is to move the' body forwards. Birds of prey ha\'e a great obliquity 

 of wing, and are consequently better adapted to horizontal progressive motion, which they 

 chiefly practise ia pursuing their prey, than for a rapid perpendicular flight. Those 

 birds, on the contrary, wdiich rise to great heights, in a direction nearly vertical, such as 

 tlie quail and the lark, have the wings so disposed as to strilie directly downwards, 

 without any obliquity whatever. 



The flight of a bird in the air is conducted on similar principles to that of a fish swim- 

 ming in the water, except that the bird is heavier in comparison with the air than the 

 fish when compared with the water. Some of the inhabitants of the deep are of enormous 



