218 



IGREVV 



ON THE MECHANISM OF FLIGHT. 



The Action of the Wing likened by some to that of an Oar 



The effect produced upon 



i he air by the rotating of the wing upon its axis has, I may remark, been likened by many 

 to that produced upon the water by an oar when it is partially rotated (or what is techni- 



__^ ^^^^m m i i ■ 



quarter of a turn. In raising and extending the wing preparatory to the downward stroke, two opposite movements 

 are required, viz. one from before backwards (Diagram 7 «), and another from below upwards (5). As, however, 

 the axes of these movements are at nearly right angles to each other, the spiral or twisting movement is necessary to run 



the one into the other 



') 



Diagram 7. 



i 



described 



Tl 



iments of the shoulder-joint are cross or check ligaments, one set acting to prevent an undue elevation and 

 backward motion, the other an undue depression and forward motion. They also act in preventing undue twisting 

 (it her in a backward or forward direction. The wing of the insect is geared after a similar fashion at the axilla. 



Elbow-joint. — The long axis of the elbow-joint intersects the long axis of the shoulder-joint nearly at right angles. 

 When the humerus is fixed, and the wing is extended and flexed, the proximal ends of the bones of the forearm describe 

 a spiral track on the distal end of the humerus or bone of the arm. This is proved by the conformation of the elbow- 



forearm 



ties, describe an upward curve, so : 



Diagram 8. 



During flexion the elbow and bones referred to describe another and opposite curve, as shown in Diagram 9 : 



Diagram 9. 





S>. 



. ys 



The movements described by the elbow-joint during extension and flexion may consequently be represented by an 



ellipse or ovoid, as under (Diagram 10) : 



Diagram 10. 



Extension. 



---> 



Flexion. 



Jrrist.joint.-7he long axis of the wrist-joint is at nearly right angles to that of the elbow, and nearly parallel 

 with that of the shoulder. In extension of the wrist, the wrist-joint and the metacarpal and phalangeal bones 



describe a downward curve, as at Diagram 11. 



Diagram 11. 





In flexion the wrist and bones alluded to describe another and opposite curve. 



