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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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           ch005-A02527.indd   64                                                                                     2/11/2008   10:53:21 AM
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