The furcula ("little fork" in Latin) or wishbone is a forked bone found in birds and some other animals, and is formed by the fusion of the two clavicles. In birds, its primary function is in the strengthening of the thoracic skeleton to withstand the rigors of flight.
The furcula works as a strut between a bird's shoulders, and articulates to each of the bird's scapulae. In conjunction with the coracoid and the scapula, it forms a unique structure called the triosseal canal, which houses a strong tendon that connects the supracoracoideus muscles to the humerus. This system is responsible for lifting the wings during the recovery stroke.
As the thorax is compressed by the flight muscles during up- and downstroke, the upper ends of the furcula spread apart, expanding by as much as 50% of its resting width, and then contracts. X-ray films of starlings in flight have shown that in addition to strengthening the thorax, the furcula acts like a spring in the pectoral girdle during flight. It expands when the wings are pulled downward and snaps back as they are raised. Acting like a spring, the furcula is able to store some of the energy generated by contraction in the breast muscles, expanding the shoulders laterally, and then releasing the energy during upstroke as the furcula snaps back to the normal position. This, in turn, draws the shoulders toward the midline of the body. While the starling has a moderately large and strong forcula for a bird of its size, there are many species where the furcula is completely absent, for instance Australian scrubbirds and bush birds, some toucans and South American barbets, some owls, some parrots, turacos from Africa and mesites of Madagascar. These birds are still fully capable of flying. They also have close relatives where the furcula is vestigal, reduced to a thin strap of ossified ligament, seemingly purposeless. Other species have evolved the furcula in the opposite direction, where it has increased in size and become too stiff or massive to act as a spring. In strong flyers like cranes and falcones, the arms of the furcula are large, hollow and quite rigid.
In other animals
Several groups of theropod dinosaurs have also been found with furculae, including dromaeosaurids (including a new North American species of Velociraptor), oviraptorids, tyrannosaurids, troodontids, coelophysids and allosauroids.
Seeing the occurrence in diplodocid dinosaurs of interclavicles, Tschopp and Mateus (2013)  proposed that furcula is a transformed and divided interclavicle, rather than a fused clavicle.
In popular culture
In 15th Century Europe it was thought that the wishbone could be used to predict the weather. Nowadays, once removed from the turkey or chicken, the wishbone is dried and then held between the little fingers of two opposing "wishers". Once the wish has been made the bone is pulled by each person. The wisher who breaks off a larger section of bone is assumed to have their wish granted. Alternatively, the winner of this contest may choose to transfer the fragment of the wishbone, along with the wish, to a person of his or her choosing.
- Gill, Frank B. (2007). Ornithology. New York: W. H. Freeman and Company. pp. 134–136. ISBN 0-7167-4983-1.
- Proctor, Noble S.; Lynch, Patrick J. (October 1998). Manual of Ornithology: Avian Structure and Function. Yale University Press. p. 214. ISBN 0-300-07619-3.
- The Inner Bird: Anatomy and Evolution, by Gary W. Kaiser
- Currie, Philip J.; Padian, Kevin (October 1997). Encyclopedia of Dinosaurs. Academic Press. pp. 530–535. ISBN 0-12-226810-5.
- Carpenter, Kenneth (July 2005). The Carnivorous Dinosaurs. Indiana University Press. pp. 247–255. ISBN 0-253-34539-1.
- Tykoski, Ronald S. et al (September 2002). "A Furcula in the Coelophysid Theropod Syntarsis". Journal of Vertebrate Paleontology 22 (3): 728–733.
- Tschopp, E., & Mateus O. (2013). "Clavicles, interclavicles, gastralia, and sternal ribs in sauropod dinosaurs: new reports from Diplodocidae and their morphological, functional and evolutionary implications". Journal of Anatomy 222: 321–340.
- Davis, Marcia. "Wishbone myth has long history". Knoxville News Sentinel. Retrieved 27 September 2012.