4 BIRDS. 



than the secondaries. Attached to the little bone 

 which represents the thumb are two or three short 

 and very stiff feathers, called the winglet ; they 

 lie upon the basal part of the first primaries 

 at the very edge of the wing. Corresponding to 

 these series of feathers there are, both on the 

 outer and inner surface of the wing, several rows 

 of smaller ones, called coverts, from their office 

 of covering the basal part of the quills. 



The feathers of the wing, overlapping each other, 

 present a continuous surface of great breadth, 

 with which the repeated strokes upon the air are 

 performed, which constitute flight. Each feather 

 is concave, whether we regard it transversely or 

 longitudinally ; its stem, or midrib, is remarkably 

 strong, though very light, and the beards, which 

 present their edges in the direction of the stroke, 

 are linked to each other by a series of minute 

 hooks. All of these provisions increase the power 

 of the wing in its downward strokes upon the 

 resisting air. 



To use these broad fans with sufficient force 

 to impel the bird through the air, large and 

 vigorous muscles are required. Accordingly, in 

 Birds, particularly those of long and powerful 

 flight, the greatest portion of the whole muscular 

 force of the animal is concentrated upon these 

 organs. The muscles which produce the down- 

 ward stroke of the wing are enormous ; and, for 

 their attachment, the breast-bone is not only 



