198 



FIRST LESSONS IN ZOOLOGY. 



posite direction the air would force for itself an easy pas- 

 sage by bending the long barbs of the feathers, which 



Fro. _ 203. -Right wing-bones of a young chicken. X, shoulder; /?, elbow; C, 

 wrist or carpus; D, tip of third finger; <i, hiuiierus; 6, ulna; c, radius; d. 

 scapholunar bone ; e, cuneiform bone ; f, g, epiphyses of metacaipal bones, 7, k, 

 respectively; h, metacarpal and its digit i. 



would no longer sustain each other/' The wing acts on 

 the air like a wedge or an inclined plane, "in order to pro- 

 duce a reaction against this resistance which 

 impels the body of the bird upward and for- 

 ward.'" 



The wings are moved by the two pectoral 

 muscles, one of which is much larger than 

 the other, and lowers the wings, causing it to 

 make the downward strokes, while the wings 

 are raised by the smaller pectoral muscle. A 

 long sharp wing like that of the swallow or 

 tern is best adapted for continued flight, 

 while a short, rounded wing is least so. 



Certain birds have the >ower of soaring, 

 i.e., of moving in the air on motionless 

 wings, no muscular power being apparently 

 used to overcome the bird's weight or the re- 

 sistance of the air. While crows, hawks, and 

 gulls can soar, yet they flap their wings at 



FIG. 304. Wing- i J . , . , . . 



bones of Penguin, intervals; but "frigate-birds live in the air 

 night and day for a week at a time without touching a 

 voost. Their congeners, the buzzards, spend the day in the 



