Furcula

The furcula, commonly known as the wishbone, is a forked bone at the front of the chest in birds and some extinct dinosaurs. It forms from the fusion of the left and right clavicles (collarbones) and is part of the pectoral girdle. In most birds it appears as a V- or U-shaped arch spanning the midline, with its two arms extending toward the shoulders.

Functionally, the furcula acts as a spring during flight. When the wings move during the downbeat, the furcula is compressed, storing elastic energy that is released during the upstroke to aid wingbeat. This elasticity also helps stabilize the thorax against the bending forces of flapping and can contribute to respiration by influencing the movement of the rib cage and sternum.

Development and variation: The furcula develops early in embryonic life through the fusion of the clavicles. Across bird species, its size and robustness vary with flight style and ecological demands. Strong fliers often have a more substantial furcula, while birds that fly less or are flightless may have a smaller or less pronounced structure.

Evolution and paleontology: The furcula is not unique to modern birds; it has been identified in a range of theropod dinosaurs, indicating a shared ancestral feature of the group that gave rise to birds. In paleontological contexts, the presence and condition of the furcula can inform reconstructions of pectoral muscle attachments and flight capability.