156 



GENERA L ORNITHOL OGY 



limb of all the higher vertebrates, so that its bones and joints may 

 readily be compared and identified with those of any lizard or 

 mammal, including man. But this member is highly specialised ; 



Fig. 27. — Bones of right wing of a duck, Clangula islandica, from above, § nat. size. (Dr. 

 R. W. Shufeldt, U.S.A.) A, shoulder, omos; B, elbow, ancon; C, wrist, carpus; D, end of 

 principal finger ; E, end of hand proper, metacarpus. A B, upper arm, hrachium ; B C, fore- 

 arm, antehrachium ; C D, whole hand or,pinion, inanus ; compcsed of C E, hand proper or meta- 

 carpus, excepting d^; E D, ox d'^, d^, d^, fingers, digits, digiti. h, humerus; rd, radius ; vl, 

 idiia; sc, outer car-pal, scapholunare or radiale ; cu, mner car]^al, cimeiforme or ulnar c ; these 

 two composing wrist or carims. mc, the compound hand-bone, or metacarpus, composed of three 

 metacarpal bones, bearing as many digits — the outer digit seated upon a protuberance at the 

 head of the metacarpal, the other two situated at the end of the bone, d", the outer or radial 

 digit, commonly called the thumb or pollex, composed of two phalanges ; d^, the middle digit, 

 of two phalanges ; d *, the inner or ulnar digit, of one phalanx ; d'^ is the seat of the feathers of 

 the bastard wing or alula. D to C (whole pinion), seat of the flight-feathers called primaries ; C 

 to B (forearm), seat of the secondaries ; at Band above it in direction of A, seat of tertiarics 

 proper ; below A, in direction of B, seat of snap^daries (upon pteryla humeralis), often called 

 tertiaries. The wing shown half-spread : comxilete extension would bring A BC D into a right 

 line ; in complete folding C goes to A, and D to B ; all these motions nearly in the plane of the 

 paper. The elbow-joint and ^vl■ist are such perfect hinges, that, in opening or closing the wing, 

 C cannot sinlv below the paper, nor D fly up above the paper, as would otherwise be the effect of 

 the pressure of the air upon the flight-featliers. Olaserve also : re? and %d are two rods con- 

 necting B and C ; the construction of their jointing at B and C, and with each other, is such 

 that tliey can slide lengthwise a little upon each other. Now when the point C, revolving about 

 B, approaches A in the arc of a circle, rd pushes on sc, while ul pulls back cu ; the motion is 

 transmitted to D, and makes this point approach B. Conversely, in opening the wing, rd pulls 

 back sc, and ul pushes on cu, making D recede from B. In other words, the angle ABC cannot 

 be increased or diminished without similarly increasing or diminishing the angle BCD; so 

 that no part of the wing can be opened or shut without automatically opening or shutting the 

 rest, — an interesting mechanism by which muscular power is correlated and economised. This 

 latter mechanism is further illustrated in Fig. 28, where re and uc show respectively the size, 

 shape, and position of the radial condyle and ulnar condyle of the humerus. It is evident that 

 in the flexed state of the elbow, as shown in the middle figure, the radius, rf?,'^is so pushed upon 

 that its end projects beyond ul, the ulna ; while in the opposite condition of extension, shown 

 in the lower figure, rd is pulled back to a corresponding extent. 



being fitted for accomplishing flight, not only by the development 

 of feathers, but also by modifications in the bones themselves. The 

 axes of the bones have a special direction with reference to each 



