In most of the Ratitae and in the extinct Dodo (_Didus_) and Solitaire (_Pezophaps_) the wing is very small, but the usual parts are recognisable. In _Hesperornis_ apparently only the humerus is present; in some Moas, in which the wing is imperfectly known, the presence of the humerus is indicated by traces of a glenoid cavity. In most Moas the wing is apparently completely absent. As compared with those in other Ratitae, the wings of the Ostrich and Rhea are well developed. In the Ostrich (fig. 64, B) and Rhea, as in nearly all Carinatae, the manus has three digits, but in _Apteryx_ there is only a single digit, the second. The Penguins (fig. 64, A) too among Carinatae have only two digits, but in their case it is the pollex which is missing. In the Ostrich the third digit has two phalanges, in all other living birds it has only one phalanx.
[Illustration FIG. 64. BONES OF THE RIGHT WING OF
A. A PENGUIN × 1/3. (Camb. Mus.) B. OSTRICH (_Struthio camelus_) × 1/7. (Partly after PARKER.) C. GANNET (_Sula alba_) × 1/3. (Camb. Mus.)
In C the distal phalanges of the pollex and second digit have been omitted.
1. humerus. 2. radius. 3. ulna. 4. second metacarpal. 5. third metacarpal. 6. pollex. 7. second digit. 8. cuneiform. 9. sesamoid bone.]
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.