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106 GENERAL ORNITHOLOGY. 
line ; angulated, 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 Fringillide in the 
Synopsis.) 
Il. THE WINGS. 
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 
D 
Fie. 27.— Bones of right wing of a duck, Clangula islandica, from above, 
Zuat. size. (Dr. R. W. Shufeldt, U.S.A.) 4, shoulder, omos; B, elbow, ancon ; 
C, wrist, carpus ; D, end of principal finger ; Z, end of hand proper, metacarpus. 
AB, upper arm, brachium; BC, fore-arm, antibrachium; CD, whole hand 
or pinion, manus; composed of CE, hand proper or metacarpus, excepting d ?; 
ED, br ad? d3, a4, fingers, digits, digiti. h, humerus; rd, radius ; ul, ulna; sc, 
outer carpal, scapholunare or radiale; cu, inner carpal, cuneiforme or ulnare; 
these two composing wrist or carpus. mc, the compound hand-bone, or meta- 
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. «2, the outer or radial digit, commonly called 
the thumb or pollex, composed of two phalanges; a8, the middle digit, of two 
phalanges; d4, 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 (fore-arm), seat of the secondaries ; at B and 
above it in direction of A, seat of tertiarics proper; below A, in direction of B, 
seat of scapularies (upon pteryla humeralis), often called tertiaries. The wing 
shown half-spread: complete extension would bring A BCD into aright line; 
in complete folding C goes to 4, and D 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 ul are two rods connecting Band C; the 
construction of their jointing at Band C, and with each other, is such, that they 
can slide lengthwise a little upon each other. Now when the point C, revolving 
about B, approaches Ain the arc of a circle, rd pushes on sc, while ul pulls back 
cu; the notion is transmitted to D, and makes this point approach B. Con- 
versely, in opening the wing, rd pulls back sc, and wi pushes on cu, making D 
recede from B. In other words, the angle A B C cannot be increased or dimin- 
ished without similarly increasing or diminishing the angle B C D; 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- 
Jated and economized. ‘This latter mechanism is further illustrated in fig. 28, 
where rc and ue 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 
its end projects beyond wl, the ulna; while in the opposite condition of extension, 
shown in the lower figure, rd is pulled back to a corresponding extent. 
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 
Ratite ; greatly reduced in 
the Emeu, Cassowary, and 
Apteryx; also in the Moas 
(Dinornis) ; in the Creta- 
ceous Hesperornis only the 
rudimentary humerus is 
known. 
their structure we must 
notice particularly 
The Bony Framework 
(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- 
To understand ° 
