122 



ANIMAL LOCOMOTION. 



of separate and opposite movements acting upon an instru- 

 ment so designed, that a movement applied at one part in- 

 creases in rapidity as the point of contact is receded from, as 

 happens in the wing. In the piston movement the motion is 

 uniform, or nearly so; all parts of the piston travelling at 

 very much the same speed. In the wing movements, on the 

 contrary, the motion is gradually accelerated towards the tip 

 of the pinion, where the pinion is most effective as an elevator, 

 and decreased towards the root, where it is least effective — 

 an arrangement calculated to reduce the number of muscular 

 contractions, while it contributes to the actual power of the 

 wing. This hypothesis, it will be observed, guarantees to the 

 wing a very high speed, with comparatively few reversals and 

 comparatively few muscular contractions. 



In the bat and bird the wings do not vibrate with the 

 same rapidity as in the insect, and this is accounted for by 

 the circumstance, that in them the muscles do not act exclu- 

 sively at the root of the wing. In the bat and bird the 

 muscles run along the wing towards the tip for the pur- 

 pose of flexing or folding the wing prior to the up stroke, 

 and for opening out and expanding it prior to the down 

 stroke. 



As the wing must be folded or flexed and opened out or 

 expanded every time the wing rises and falls, and as the 

 muscles producing flexion and extension are long muscles 

 with long tendons, which act at long distances as long levers, 

 and comparatively slowly, it follows that the great short 

 muscles (pectorals, etc.) situated at the root of the wing must 

 act slovvdy likewise, as the muscles of the thorax and wing of 

 necessity act together to produce one pulsation or vibration 

 of the wing. What the wing of the bat and bird loses in 

 speed it gains in power, the muscles of the bat and bird's 

 wing acting directly upon the points to be moved, and under 

 the most favourable conditions. In the insect, on the con- 

 trary, the muscles act indirectly, and consequently at a dis- 

 advantage. If the pectorals only moved, they would act as 

 short levers, and confer on the wing of the bat and bird the 

 rapidity peculiar to the Aving of the insect. 



Tlie tones emitted by the bird's wing would in this case 



