The furcula or wishbone is a forked bone found in most birds and some species of non-avian dinosaurs, 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.
Wishbone of a chicken
New Year postcard from around 1909 featuring a wishbone as a lucky symbol
Bird anatomy, or the physiological structure of birds' bodies, shows many unique adaptations, mostly aiding flight. Birds have a light skeletal system and light but powerful musculature which, along with circulatory and respiratory systems capable of very high metabolic rates and oxygen supply, permit the bird to fly. The development of a beak has led to evolution of a specially adapted digestive system.
Highlighted in red is an intact keeled sternum of a dissected pigeon. In flying birds the sternum is enlarged for increased muscle attachment.
Ostrich foot integument (podotheca)
The anatomy of bird's respiratory system, showing the relationships of the trachea, primary and intra-pulmonary bronchi, the dorso- and ventro-bronchi, with the parabronchi running between the two. The posterior and anterior air sacs are also indicated, but not to scale.
The cross-current respiratory gas exchanger in the lungs of birds. Air is forced from the air sacs unidirectionally (from right to left in the diagram) through the parabronchi. The pulmonary capillaries surround the parabronchi in the manner shown (blood flowing from below the parabronchus to above it in the diagram). Blood or air with a high oxygen content is shown in red; oxygen-poor air or blood is shown in various shades of purple-blue.