JER-FALCON'S WING. 307 



and very firm. It admits of extension till the meta- 

 carpal bones (the whole hand in fact) be nearly in 

 the same line with the fore-arm, but beyond this it 

 cannot be stretched without breaking the wing 1 ; and 

 here the other end of the ulna, together with the 

 bones of the thumb, offer the same resistance against 

 bending in the wrong direction that is offered by the 

 elbow -joint. 



The knuckle-joint, III, has little or no motion in 

 any direction ; and it rather gives a little elasticity 

 to the bone, which is very hard and firm in its texture, 

 than answers any other purpose ; but, though very 

 light, this portion of the wing is, from the way in which 

 the thickened parts are placed, actually stronger in 

 rapid motion than if it were all as thick as these. 



The form of all the bones, indeed, is such as to 

 give them the maximum both of stiffness and of 

 strength. The humerus, which, is the only single 

 bone, is very strong, both from its shape and from 

 the cross pieces inside the tube opposite to the inser- 

 tions of the muscles and tendons ; and even these 

 are additional means of support. This bone, too, is 

 so near the centre of motion, that the resistance of 

 the air acts much less powerfully upon it than upon 

 the others. The fore-arm, having to sustain the 

 broadest part of the wing, is very strong : indeed it is 

 the strongest form which, combined with the same 

 lightness, could be given ; and lightness is as essen- 

 tial as firmness in all the parts of a wing, because 

 weight would be a source both of weakness and 

 fatigue. The radius, or larger bone, has the form of 

 a bow, and the smaller one, the ulna, that of a bow- 

 string ; and any one who places the tips or horns of 

 a bent bow on the ground, and tries to crush it by 

 pressing down the middle of the bend, will find it 

 X2 



