108 GENERAL ORNITHOLOGY. 
elbow.” The third segment of the wing is agerist or carpus. In adult life, this normally 
consists of two little knobby carpal bones, extremely irregular in shape,called the scapholunar, 
sc, and cuneiform, cu. One being at the end of the radius, the other at that of the ulna, they 
are also called radiale and wlnare. In the embryo, there is at least another carpal bone, that 
early fuses with the next segment. This fourth segment is the hand proper, or metacarpus, 
mc, C to E (exclusive of d 2). The single metacarpal or hand-bone is very composite ; that 
is, compounded of several; for, besides including certain carpal elements, as already said, it 
consists of three bones fused (in all recent birds) in one, corresponding to the three digits or 
fingers that birds possess. In fact it is three metacarpals in one. The metacarpal corre- 
sponding to the principal finger is much the largest of the three; that of the first finger is very 
short, being only the expanded part seen in the figure just above the bone marked d 2; that 
of the third finger is nearly as long as the maim metacarpal, but much slenderer, and usually 
fused only at its two ends, leaving between itself and the main metacarpal a considerable 
space, as seen opposite the letters me in the figure. The wing is finished off with three 
fingers or digits, marked d 2, d3, d4. The middle one of these, H to D in the figure, is 
much the largest, and forms the main continuation of the hand. This digit, d 3, ordinarily 
consists of two bones, called phalanges, placed end to end, as in the example before us; but 
occasionally there is found a third phalanx. The outer or radial digit, d 2, ordinarily con- 
sists of two bones, of which the terminal one is small, and may be wanting. The inner or 
ulnar digit, d 4, consists of a single small phalanx, closely bound to the side of the middle 
finger. Corresponding to the compactness and consolidation of these terminal segments, the 
digits enjoy little individual motion. The outer or radial digit is the most independent one. 
In the Archeopteryx the three metacarpals were free bones, and the whole hand more like 
that of a lizard. No bird now has free metacarpals in adult life; none has more than three 
digits. These three are supposed by some to correspond to the thumb and fore and middle 
fingers of our hands; by others, to the fore, middle, and ring fingers, and being consequently 
the second, third, and fourth digits, as marked in the figure. The digit marked d 2 is com- 
monly ealled a bird’s thumb or pollex. The Apteryx and the cassowary have but one complete 
digit. The resemblance to a lizard’s or quadruped’s digits is increased by the claws which 
many birds possess. These may be borne on the enlarged terminal phalanx of d 2 (k, in 
fig. 29), as is very well shown in the turkey-buzzard and other American Cathartide ; both on 
this and on the terminal phalanx of d 3 (d” in fig. 29), as in the ostrich; on the latter alone, 
as in the Apteryx, cassowary, American ostrich, and swan. The inner finger, d 4 (d’” in 
fig. 29) is not known to ever bear a claw, excepting in Arche@opteryx. The whole segment, 
C to D, is commonly called “ the hand,” “ pinion,” or manus, though, as we have seen, it consists 
of hand proper (metacarpus), and fingers (digits) with their respective phalanges. (Fig. 112 ter.) 
Some other bones are observed in birds’ wings. As already said, there is a little ossicle in 
the shoulder-joint of many birds ; it is called the scapula accessoria (fig. 56, ohs). At the con- 
vexity of the elbow there may be one or more ossicles, not pertaining properly ‘to the wing- 
skeleton, but developed in the tendons of muscles passing over the joint: they are sesamoids, 
like the human patella, or knee-cap. In various birds there is found at the convexity of the 
wrist, on the head of the metacarpal, an ossicle called the os prominens ; apparently a 
sesamoid. Some other ossicles observed in the wrists of young birds are all supposed to be 
carpal elements, the exact homologies of which may be still questioned. 
The Mechanism of these Bones is admirable. The shoulder-joint is free, much like 
our own, permitting the humerus to swing all about; though the principal motions are to and 
from the side of the body (adduction and abduction), and up and down in a vertical plane. 
The elbow-joint is a very strict hinge, permitting motion in one plane, nearly that of the wing 
itself. The finger-bones have little individual motion. The construction of the wrist-joint is 
