The pectoral girdle is also strongly developed in all Carinatae, but is much reduced in Ratitae. In some Moas the sternum has no facet for the articulation of the coracoid, and the pectoral girdle appears to have been entirely absent; it is extremely small also in Apteryx. Clavicles are generally well developed in the Carinatae, and small ones are found also in Hesperornis, and in Emeus and Cassowaries. In the other living Ratitae and in Stringops they are absent. In some Parrots, Owls and Toucans they do not meet one another ventrally. Clavicles are especially stout in some of the birds of prey. They do not generally touch the sternum, but sometimes, as in the Pelican (fig. 63, C), Adjutant and Frigate bird, they are fused with it.
In all Ratitae the scapula and coracoid lie almost in the same straight line with one another, in the Carinatae they are nearly at right angles to one another.
Anterior Limb.
In the wing of nearly all birds the ulna is thicker than the radius, but in Archaeopteryx the two bones are equal in size. In the wing of Archaeopteryx there are three long digits with distinct metacarpals. In all other birds the digits are modified, the metacarpals being commonly fused and the phalanges reduced in number. In Palamedea and some other birds the metacarpus bears a bony outgrowth, which when sheathed in horn forms a spur.
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.
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.)