Jingszo !

For years, the identity of one of the carpal bones in the wrist of birds was a scientific mystery, until researchers proved it was the pisiform. This bone was originally a sesamoid bone like a kneecap, and had moved from its original position in the wrist to replace the ulnare, another carpal bone. Its position in modern birds appears to establish linkages that allow birds to fold their wings automatically when the elbow flexes.

The bone's shape—with a large V-shaped notch—also allows the pisiform of birds to clasp their hand bones to stop them from dislocating during flight. Therefore, this bone is an important part of a bird's forelimb and critical to flight.