Bird Flight 185 



the bird's flying apparatus! When outstretched, it is 

 held firmly by the power of its own mechanism, with its 

 broad under surface lying horizontally, and no breezy 

 current can bend or twist it from its normal position. 



The set of muscles that open the wing are called the 

 extensors, and those that close it, the flexors. The former 

 lie upon the back of the upper arm and the front of the 

 forearm and the hand, their tendons passing over the 

 convexities of the elbow and wrist, while the flexors 

 occupy the opposite sides, and their tendons run up into 

 the concavities of the joints. There are several powerful 

 pectoral muscles which run out from the shoulder and 

 breast, and operate upon the upper end of the humerus, 

 and with these the wing is lifted and the strokes are made 

 during flight. 



Another mechanical contrivance deserves attention. 

 An extremely elastic cord reaches over from the shoulder 

 to the wrist joint, supporting a fold of skin that occupies 

 the deep angle of the elbow, and that is covered with short, 

 fluffy feathers. When the bird is flying, this cord is 

 stretched and forms the front edge of that section of the 

 wing. But, now, suppose the wing is closed, will not this 

 cord make a cumbersome fold, flapping loosely in the 

 angle of the elbow? Such would, indeed, be the case, did 

 not its extreme elasticity enable it to contract to the 

 proper length, so as to keep the wing's border straight 

 and smooth. 



Without the feathers the wing would be useless as an 

 instrument of flight. The shorter plumes that shield the 



