6 



INTRODUCTION. 



to explain the principal modifications observable in 

 these admirable structures. 



Fig. 2.— figure of wing, showing the origins of the quill-feathers. 



(h) The humerus ; (r) the radius ; (e) the cubital bone, the outer side of 

 which is entirely occupied by the insertion of the secondary quiUs (S), which 

 are separated by a small space from the primaries (P), all of which take 

 their origin from the metacarpal bone representing the hand. The joint 

 (x) representing the wrist-joint, indicates the point of separation between 

 the primary and the secondary quills. The bastard quills, or those attached 

 to the thumb, are indicated by the letter b. 



The formation of the wing in reference to its 

 office depends almost entirely upon the arrange- 

 mentj the proportions, and the shape of the quills ; 

 and these again determine the powers of flight. 



The principal modifications in the structure of 

 these important organs are therefore briefly ex- 

 pressed by simple epithets, the precise meaning of 

 which it will be necessary to remember. 



In regard to their comparative length, a wiug, 

 however otherwise constructed, is termed long when 



