In C the distal phalanges of the pollex and second digit have been omitted.
| 1. humerus. | 6. pollex. |
| 2. radius. | 7. second digit. |
| 3. ulna. | 8. cuneiform. |
| 4. second metacarpal. | 9. sesamoid bone. |
| 5. third metacarpal. |
Pelvic Girdle.
Birds have a very large pelvis and its characters are constant throughout almost the whole group. The ilium is very large, and is united along its whole length with the sacral and pseudosacral vertebrae. The ischium is broad and extends back parallel to the ilium with which in most birds it fuses posteriorly, further forward the ilio-sciatic foramen separates the two bones. In Tinamus, Hesperornis, Apteryx (fig. 65, B, 2), and Struthio, the ischia are separate from the ilia along their whole length except at the acetabulum; in Phororhacos, on the other hand, the two bones are fused along almost their whole length. The bone usually called the pubis in birds corresponds to the post-pubis of Dinosaurs and forms a long slender rod (fig. 65, 3) lying parallel to the ischium. In many birds the ischia and pubes are united at their distal ends. This is the case in the Ostrich (fig. 65, D), in which the ilia and ischia are widely separated. In many birds the pubis is drawn out in front into the pectineal process, this is specially large in Apteryx (fig. 65, B, 5), and in the embryos of many birds. It is probably homologous with the pre-pubis of Dinosaurs but in some birds is formed in part by the ilium. The acetabulum in birds is always perforate.
Fig. 65. Pelvic girdle and sacrum of
A. Cassowary (Casuarius galeatus) × 1/8.
B. Owen's Apteryx (A. oweni) × ½.
C. Broad billed Rhea (R. macrorhyncha) × 1/6.