Bird characteristics: Body always covered with feathers; feet (toes and usually tarsometatarsus) covered with scales (thickened skin). Aquatic birds have webbed toes. No teeth; horny beak. Lightweight skeleton in flying birds (many hollow bones), with keel on sternum for attachment of flight muscles (pectoral muscles). No keel in large flightless birds (ostrich, emu, rhea). Completely bony ribs (no rib cartilage). Clavicles fused into single bone, the furculum (wishbone). Numerous neck vertebrae (number varies by species) provide great neck flexibility. Some of the middle thoracic vertebrae fused in some species (chicken); posterior thoracic, all lumbar, and all sacral vertebrae fused into synsacrum, which in turn is fused to the pelvis. Short, flexible tail terminates in stout bone (pygostyle) for support of highly mobile long tail feathers. Wing (arm) skeleton modified for flying (ostrich and penguins evolved from flying ancestors). Wrist joint automatically straightens when elbow joint is straightened; conversely, wrist joint automatically bends when elbow joint is bent. Individual hand and finger bones reduced in number and largely fused together for support of primaries (outer flight feathers). Three digits present; small third digit nonmovable. Short alular feathers attach to movable first digit. Secondaries (inner flight feathers) attach to rear edge of ulna. Three toes point forward and one points backward in most species (e.g., chicken, hawk, crow), or two toes forward and two back (e.g., woodpecker, parrot). Ostrich has two toes per foot. Toes terminate with claws. Male chicken has bony spur covered with horny sheath on tarsometatarsus.
Oxford Scholarship Online requires a subscription or purchase to access the full text of books within the service. Public users can however freely search the site and view the abstracts and keywords for each book and chapter.
If you think you should have access to this title, please contact your librarian.