<P> As the thorax is compressed by the flight muscles during 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 furcula for a bird of its size, there are many species where the furcula is completely absent, for instance scrubbirds, some toucans and New World barbets, some owls, some parrots, turacos, and mesites . 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 falcons, the arms of the furcula are large, hollow and quite rigid . </P> <P> In birds, the furcula also may aid in respiration by helping to pump air through the air sacs . </P> <P> Several groups of theropod dinosaurs have also been found with furculae, including dromaeosaurids, oviraptorids, tyrannosaurids, troodontids, coelophysids and allosauroids . </P> <P> 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 . </P>

Where is the wishbone located on a turkey