system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can’t the ring finger extend independently of its adjacent digits?
gpt
The ring finger and middle finger each have two tendons that connect near the base of the fingers. One of the tendons from the ring finger goes underneath a tendon for the middle finger, while both middle finger tendons are on top. You can lift just your middle finger because nothing is in the way, but when you try to lift just your ring finger one of the tendons is blocked/held down by one of the middle finger tendons.

It can go up a little but it's already under tension and tendons can't stretch very easily, so the ring finger doesn't go very high.