106 



GENERAL OBNITHOLOGY. 



line ; cmgulated, when they are straight, or nearly so, but do not lie in the same line, and 

 therefore meet at an angle. (An important distinction. See under family FrmgilUdce in the 

 Synopsis.) 



II. THE WJNSS. 



Definition. — Pair of anterior or pectoral limbs organized for flight by means of dermal 

 outgrowths. Used for this purpose by birds in general ; but by ostriches and their allies only 



as outriggers to aid running; 

 by penguins as fins for swim- 

 ming under water; used also 

 in the latter capacity by some 

 birds that fly well, as divers, 

 cormorants, dippers. Want- 

 ing in no recent birds, but 

 imperfect in a few, as all 

 Batitoe ; greatly reduced in 

 the Emeu, Cassowary, and 

 Apteryx ; also in the Moas 

 {TUnornis) ; in the Creta- 

 ceous Hesperornis only the 

 rudimentary humerus is 

 known. To understand 

 their structure we must 

 notice particularly 



Fio. 27. — Bones of right wing of a dnok, Clangula isla/ruUcat from above, 

 } uat. size. (Dr. K.W. Shufeldt, TJ.S.A.) A, shoulder, omos; S, elbow, ancon; 

 C, wrist, carpus ; D, end of principal finger ; E, end of hand proper, riKtacarpus. 

 A B, upper arm, brachium; B C, fore-arm, cmtibrtuihium ; CD, whole hand 

 f-r pinion, manus; composed of CE, hand proper or metacarpus, excepting d^; 

 E D,ov d^ d^,d*, fingers, digits, digiti. h, humerus ; rd, radius ; ul, ulna ; sc, 

 outer carpal, scaphohma/re or radiate ; cu, inner carpal, cwneifoi'mexyT uVnare ; 

 these two composing wrist or campus, mc, the comi»ound haud-bone, or vieta- 

 carpus, 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 2, 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^\& the seat of the 

 feathers of the bastard wing or alula. Dto Ci whole pinion ), seat of the flight- 

 feathers called primaries ; CXoB (fore-arm), seat of the secondaries ; at B and 

 above it in direction otA, seat of tertiaries proper; below A, in direction of .B, 

 seat of acapularies (upon pteryla humeraliB), often called tertiaries. The wing 

 sliown half-spread ; complete extension would bring ABCD into a right line ; 

 in complete folding C goes to A, and Z) to B ,• all these motions nearly in the 

 plane of the paper. The elbow-joint and wrist are such perfect hinges, that, in 

 opening or closing the wing, C cannot sink 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-feathers. Observe also: rd and id are two rods connecting B and C; the 

 construction of their jointing at .Sand C, and with each other, <is such, that they 

 can sHd^ lengthwise a little upon each other. Now when the point C, revolving 

 about B, approaches .4 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, Con- 

 versely, in opening the wing, rd pulls back sc, and ul pushes on cu, making B 

 recede from B. In other words, the angle ABC cannot be increased or dimin- 

 ished without similarly increasing or diminishing the angle BCD; so that no 

 part of the wing can be opened or shut without automatically opening or shut- 

 ting the rest, — an interesting mechanism by which muscular power is corre- 

 lated and economized. This latter mechanism is further illustrated in flg. 28, 

 where rcanduc show respectively the size, shape and position of the radial con- 

 dyle 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, rd, is so pushed upon that 

 i ts end projects beyond u2, the ulna ; while in the opposite condition of extension, 

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



Tbe Bony FrameTvoi^ 



(figs, 27, 28, 29). —The 

 skeleton of a bird's wing is 

 built upon a plan common 

 to the fore or pectoral 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 the 

 member is highly special- 

 ized; being fitted for accom- 

 plishing 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 refer- 

 ence to each other and to 

 the axes of the body; the 

 movements of the joints are 

 peculiar in some respects; 

 and the whole extremity of 

 the wing, from the wrist 

 outward, is peculiarly con- 



