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64 SECTION I III The Birds

III WHY NOT MANUS OR
CARPOMETACARPUS?

Again, I wish to briefly discuss anatomical terminol-

ogy, in this instance that of the terminal wing elements,
or as I prefer, the carpus, metacarpus, and digits.
Although not universally accepted, the term manus has
appeared in some recent avian publications. In my
view, the term manus, meaning hand, is functionally ill
suited for all but primates. Carpometacarpus is equally
inadequate because it ignores the digits. Consequently,
there is no reason to add this ambiguous and often
confusing term to the current medical lexicon.

Carpus
There are two carpal bones, a radial and an ulnar. As
their names imply, each articulates with the appropri-
ate articular surface of the adjacent radius or ulna.
Unlike the typical primate wrist, the carpus of a bird
serves as more of a mechanical adaptor than a complex
intermediate joint.

Metacarpus
The avian metacarpus is quite distinctive, possessed of
major and minor, proximally and distally fused meta-
carpal bones. The metacarpus is about one third the
length of the radius and ulna, thus the size depends
on the species.

Digits
Avian digits are equally unique, clearly revealing their
adaptation to flight. There are three digits. The fi rst

digit is attached to the leading edge of the proximal
metacarpus as seen when the wing is deployed in

flight and referred to as the alular, which serves as a
winglet similar to the small rudderlike structures
Figure 5-12 • Lateral view of the distal wing bones in a Canadian found on the wingtips of some commercial jetliners.
goose (prepared specimen) from left to right: (1) distal radius, (2)
distal ulna, (3) minor metacarpal bone, (4) second digit, (5) major The second digit resembles a miniature metacarpus
metacarpal bone, (6) third digit comprised of proximal and distal and is attached to the distal aspect of the major meta-
phalanges directly below major metacarpal bone, and (7) fi rst digit. carpal bone. A second phalanx articulates with the tip

of the first, constituting the terminal skeletal element
in the wing. A third digit articulates with the distal
aspect of the minor metacarpal bone.

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