366 DP PETTIGREW ON THE PHYSIOLOGY OF WINGS. 



may not be successfully imitated, both in their structure and moveriients, by 

 mechanical appliances in which elasticity plays a very prominent part. On the 

 contrary, I am prepared to show further on, that flight may be regarded as a 

 purely mechanical problem, and that it admits of a mechanical solution. I am, 

 however, desirous of showing in the first place what movements are vital, 

 what vito-mechanical, and what mechanical in natural flight. This done, we 

 will then be in a position to enter upon a consideration of artificial flight. That 

 elasticity of itself will not produce flight may be inferred from the following 

 experiments. If, for instance, we lash light unyielding reeds to the anterior 

 margins of a pigeon's wings so as to prevent flexion at the elbow-joints, we 

 instantly destroy flight. In this experiment the elasticity of the wings, and 

 particularly of the rowing feathers, is in no wise impaired ; in reality the 

 mobility and flexibility of the wings only are interfered with. A still more 

 conclusive proof is to be found in the fact that in insects the most elastic 

 portions of the wings can be altogether removed without destroying the power 

 of flight. Thus I have cut away as much as two-thirds from the posterior 

 margin of either wing of the blow-fly, and yet the insect flew with remarkable 

 buoyancy. I have also removed portions of the tips of the wings with impunity. 

 I made similar experiments with the dragon-fly, butterfly (pages 361 and 362), 

 and sparrow, and with nearly uniform results. 



Analysis of the Down and Up Strokes in the Wing of the Bird and Bat. — 

 What was said of the movements of the wing of the insect holds equally true 

 of those of the bat and bird, if allowance be made for the more vertical direc- 

 tion of the down and up strokes, and for the fact that the wings of the bat and 

 bird are in several pieces and jointed."" The joints, like the muscles, extend in 

 the direction of the length of the wing ; thus, in addition to the shoulder-joint, 

 we have the elbow, wrist, and finger joints. The insect, bat, and bird have the 

 shoulder joint in common, and this joint is so constructed that the wing is 

 free to move in an upward, downward, forward, backward, and oblique direc- 

 tion. It also admits of a certain amount of rotation or torsion in the direction 

 of the length of the wing. The joint is in fact universal in its nature. Another 

 feature possessed in common by insects, bats, and birds, is the elastic ligaments 

 which recover and partly elevate the wing during the up stroke. Those liga- 

 ments in the bat and bird are not confined to the root of the wing, but extend 

 along its margins even to its tip. 



The presence of those ligaments shows that the wing is not elevated exclu- 

 sively by the reaction of the air. There are, moreover, distinct elevator muscles 

 in the wing of the bat and bird. The presence of voluntary muscles, and of 

 elastic and other ligaments, afford important indications in the construction and 



* The beetles have also their wings jointed. 



