. A manual of zoology for the use of students : with a general introduction on the principles of zoology . Zoology. 4S8 MANUAL OF ZOOLOGY. piece. As in the Reptiles, the lower jaw articulates with the skull, not directly, but through the intervention of a distinct bone—the quadrate bone ontyriipanic bone—which always re-. Fig. 179.—Skull of Spur-winged Goose {Plectra^terus Gambensis). mains permanently movable, and is never anchylosed with the skull. In no bird are teeth ever developed in either jaw, but both mandibles are encased in horn, forming the beak, and the margins bill are some
. A manual of zoology for the use of students : with a general introduction on the principles of zoology . Zoology. 4S8 MANUAL OF ZOOLOGY. piece. As in the Reptiles, the lower jaw articulates with the skull, not directly, but through the intervention of a distinct bone—the quadrate bone ontyriipanic bone—which always re-. Fig. 179.—Skull of Spur-winged Goose {Plectra^terus Gambensis). mains permanently movable, and is never anchylosed with the skull. In no bird are teeth ever developed in either jaw, but both mandibles are encased in horn, forming the beak, and the margins bill are sometimes serrated. The quadrate bone (os, carrd of the French) is in contact at one end with an elongated bone (jugal bone), the other end of which comes against the palate. By the depression of the lower jaw, assisted by proper muscles, the quadrate bone is brought forward, and the jugal bone is thus made to elevate the palate and upper jaw. With one or two exceptions, the upper mandible is thus movable in all birds. The thoracic cavity is bounded by the dorsal vertebrae, which are usually, as before said, anchylosed to one another to a greater or less extent. Laterally, the thorax is bounded by the ribs, which vary in numbfer from six to ten pairs. In most birds each rib carries a peculiar process—the "uncinate pro- cess"—which arises from its posterior margin, is directed up- wards and backwards, and passes over the rib next in succes- sion behind, where it is bound down by ligament. The first and last dorsal ribs carry no uncinate processes, and in some cases the processes continue throughout life as separate pieces (fig. 180, B). Anteriorly, the ribs articulate with,a series of straight bones, which are called the " sternal ribs," but which in reality are to be looked upon as the ossified " costal carti- ; These sternal ribs (fig. 180, B) are in turn movably articulated to the sternum in front, and " they are the centres upon
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