The two distinct carpal bones are the radial carpal and the ulnar carpal. The radial carpal (fig. 57, 4) is a small somewhat cubical bone, wedged in between the manus and the radius and ulna. The ulnar carpal (fig. 57, 5) is a somewhat larger, more irregular bone, lying adjacent to the end of the ulna. It is deeply notched to receive the carpo-metacarpus.
The hand. In the adult bird the hand is in a much modified condition; only the first three digits are represented, and the metacarpals are all fused with one another and with the distal carpalia to form the carpo-metacarpus.
The most prominent part of the carpo-metacarpus is formed by the second metacarpal (fig. 57, 7), a stout, straight bone expanded at both ends. The third metacarpal (fig. 57, 8) is a more slender curved bone fused at both ends with the second metacarpal. The first metacarpal forms simply a small projection on the radial side of the proximal end of the second metacarpal.
The phalanges. The first digit or pollex includes two phalanges, the distal one being very small and bearing a claw.
The second digit includes three phalanges, the proximal one being somewhat flattened. The third digit has a single small phalanx.
The Pelvic Girdle.
The bones constituting the pelvic girdle are not only as in other higher vertebrates ankylosed together forming the innominate bones, but are also ankylosed with a series of some seventeen sacral and pseudosacral vertebrae. The acetabulum (fig. 61, 5) with which the head of the femur articulates is incompletely ossified.
The ilium (figs. 58 and 61, 1) is the largest bone of the pelvis. It forms a long flattened plate extending for a considerable distance both in front of and behind the acetabulum, and is fused along its whole length with the transverse processes and neural spines of the sacral and pseudosacral vertebrae. It forms more than half the acetabulum, above and behind which it is produced to form a process, the antitrochanter (fig 61, 8), with which the great trochanter of the femur articulates.
Fig. 61. Lateral view of the pelvis and sacrum of a Duck (Anas boschas) × 2/3.