A
keel or
carina (plural carinae) in
bird anatomy is an extension of the
sternum (breastbone) which runs axially along the midline of the sternum and extends outward, perpendicular to the plane of the
ribs. The keel provides an anchor to which a bird's wing muscles attach, thereby providing adequate
leverage for
flight. Keels do not exist on all birds; in particular, some
flightless birds lack a keel structure.