eli5: Why can we bend our index finger’s first joint freely but we can’t bend our other fingers first joint(thumb excluded) without the others slightly retracting?

Question

eli5: Why can we bend our index finger’s first joint freely but we can’t bend our other fingers first joint(thumb excluded) without the others slightly retracting?

In: Biology

Answer 1

The ring finger shares a muscle with the pinky and shares a muscle with the middle finger. You can’t move your ring finger if the middle finger is restrained and when you move your pinky or middle finger the muscle pulls on the ring finger. The middle finger more so than the pinky.