PETTIGREW ON THE MECHANISM OF FLIGHT 



2 11) 



cally called "feathered") between the effective and non-effective strokes. Tin- analogy, how- 

 ever, is more apparent than real, since the flat of t he oar is applied in an opposite direction 

 to that in which the boat is impelled, whereas the wing is applied obliquely in (he same 



Diagram 12. 



t" 



---N 



The movements described by the wrist-joint during extension and flexion may therefore be represented as in the 



adjoining woodcut (Diagram 13). 



Diagram 13. 



Flexion. 



Extension. 



The movements of the wrist-joint are always the reverse of those occurring at the elbow-joint. Thus, daring ex- 

 tension, the elbow and bones of the forearm are elevated, and describe one side of an ellipse ; while the wrist and bones 

 of the hand are depressed, and describe the side of another and opposite ellipse, as shown at Diagrams 14 & 1ft. 



Diagram 14, — Extension of the wing. 



Elbow and forearm. 



Wrist and hand. 



These movements, I need scarcely observe, are reversed during flexion 



Diagram 15. 



of the Wing. 



Wrist and hand. 



V 



Elbow and forearm 



ft 



wards, and vice versa. 



Similar remarks may be made regarding the disposition of the articular surfaces, and the movement, of the 



and reciprocate.— The alternating and opposite movements de- 



metacarpal and phalangeal bones. 



Wrist 



scribed by the elbow- and wrist-joints are occasioned by the bones of the elbow and wrist bong .p.rally arranged, 

 and from each making a quarter of a turn or so during extension, and the same amount during flexion. As a 

 consequence, the wing, as has been explained in the text, may be shot out or extended, and withdrawn or flexed, 10 ■ 

 nearly straight line, the modus operandi or principle of action being not inadequately represented by the componem 

 parts of an auger or gimlet,-the axis of the instrument representing the action of the vvmg as a .hole, the sp.ral 

 flanges the movements of the component bones and of the feathers (Diag. 16). 



Diagram 16. 



Extension (elbow) 



Flexion (wrist) 



Line along which the wing travels during extension and flexion 



Flexion (elbow). 



Extension (wrist). 



- , rrr- i «»J Th^ nhiect df the alternatim: and reciprocating movements 



Elevation and Depression of the Wing, how caused.— I he object oi tue aiiti g i B 



