184 Bird Comrades 



graceful tapering point to the wing, and giving to it 

 the symmetry and proportion that are required for effect- 

 ive use. When the wing is folded, the hand extends 

 obliquely downward and backward. 



Now, these bones and their attendant ligatures are 

 wonderfully and wisely contrived. The humerus moves 

 freely in its socket in the shoulder, so that it can be swung 

 in every required direction, and yet, as should be the- case, 

 its principal movement is -up and down in a vertical line 

 - the precise movement required for the effective wing- 

 strokes in flight. But note further. The elbow joint, 

 unlike that of the shoulder, is a rigid hinge, permitting 

 motion in only one plane, that of the wing itself, or nearly 

 so. The same is true of the wrist joint, which holds the 

 hand firmly, allowing no motion save that which opens 

 and closes the wing. The wisdom of this arrangement 

 will be seen at a glance. 



In the human arm the hand can be moved in every 

 direction with the greatest freedom, and, moreover, the 

 wrist may be turned and the hand laid on its back, its 

 palm, its edge, or at almost any conceivable angle. This 

 is a very convenient contrivance for man, but it would 

 be a great misfortune for our avian friends if their wings 

 would rotate so readily; for in that case they would not 

 have sufficient rigidity to answer the purposes of flight, 

 but would be' twisted into every position by the assaults 

 of the air currents. Besides, even in ordinary flight it 

 would require a constant muscular effort to keep the wings 

 in the proper position. How wisely Nature has devised 



