BIRD. 



length, and united at both extremities. From the 

 knuckle joint at III to the point at 1, answers to the 

 ringers in the human hand. The fore-finger, from III 

 to 1, consists of two phalanges soldered together. 

 The distal phalanx forms the tip of the wing, and 

 terminates at 1. This phalanx consists of only a 

 single bone. This bone consists of a longer thickened 

 portion, the fore-finger ending at 1, and a shorter, the 

 second finger, ending at 2, with a thinner portion of 

 bone between them. The second phalanx, which is 

 broad and flat, is marked by oblique thickened portions 

 ending at 3 and 4, and answering to the third and 

 fourth fingers, only the whole is one plate of bone, 

 thickened and strengthened by the oblique ridges 

 terminating at 3 and 4, which proceed from a thick- 

 ened portion continued along the other side. 



Jer- falcon's wing. 



It will be seen that all the bones in this wing which 

 have moveable joints are very much enlarged at their 

 extremities ; and that, with the exception of the joint 

 at the head of the humerus, one part only of which 

 is seen, as the socket in which the shoulder joint 

 moves is not shown in the figure, have their motions 

 chiefly in one direction or plane only. 



When the wing is extended, the upper process of 

 the head of the humerus is brought considerably 

 within the centre of motion of the shoulder-joint. To 

 it the tendons of the muscles which raise the wing 

 are attached, and its projection, increased beyond the 

 centre of motion, gives the lever power, by means of 

 which these muscles act. The muscle which depresses 

 the wing, or gives the stroke in flying, has its tendon 

 attached to the under side of the flattened portion of 

 the head of the humeral bone, farther without the 

 centre of motion than the others are within it, and 

 therefore it acts upon a longer lever of power, and 

 has a shorter lever of resistance to overcome than 

 the muscles which elevate the wing. 



All the round bones of the wing are hollow, or 

 tubular, which makes them mnch lighter than if thev 

 had been solid and of the same dimensions, and mucn 

 stronger and stiffer than if they were solid with the 



same quantity of bone. But at all places where 

 there is either a muscle or a tendon inserted, the 

 action of which would be upon one side only of the 

 tube, there is a tie, or septum of bone extending 

 from the one side to the other, so that it may throw 

 the strain equally upon both sides of the tube. If 

 this strain is great, these ties are branched, so that 

 they throw it upon a considerable portion of the 

 bone, and as they are ties in the one direction and 

 struts in the cross one, and all gradually run into the 

 bone by heads enlarging in curves, they give the 

 same strength as if the bone were entirely solid 

 throughout. Indeed, for maximum of strength and 

 stiffness, with minimum of weight, these bones are 

 quite a study. 



The elbow joint, I, is very beautifully constructed. 

 It is a sort of triple hinge ; and when the humerus 

 and radius are brought into the same line in the 

 stretching of the wing, the processes, as may be seen 

 from their form, stop it from having the least flexure 

 in the other direction, while the head of the ulna 

 comes over the centre, between the double processes 

 of the two principal bones, and wedges it against all 

 bending upwards, something in the same manner as 

 the keystone of an arch. 



The wrist-joint at II, is also both very peculiar 

 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 ; and 

 here xhe 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, that 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 those. 



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 

 much stiffer and stronger than a straight stick of twice 

 the thickness. A very portable bridge is often made 

 upon this principle, of a thin plank, bent into the 

 form of a bow by a cord tied to the two ends ; and 

 when tied in this manner, a plank which a man < ui 

 carry without fatigue, will enable him to cross with 

 safety a chasm ten or twelve feet wide. 



But the bow and the bridge arc very impcrt'i ct 



