Digits
The digits or ‘fingers’ of a bird's wing are also reduced in number to three. In the embryonic stage, there is a predisposition of five or possibly six digits, which reveals something about the number of fingers in the ancestors of modern birds (Kaiser 2007).
Remaining are the 1st digit: alula or thumb wing and the 2st digit (large or index finger) and a rudimentary part of the 3rd digit (middle finger).