Your thumb and fingers don't have ANY muscles.
Our fingers themselves do not have muscles in them. This obviously might make you wonder how exactly we can move our fingers. Well, the short answer is by remote control.
You might be thinking that we move everything by remote control, because the brain is what controls everything. But the fingers are special because of their lack of muscle.
Fingers are moved by tendons, pulled by muscles in the forearm. That's why if you flex your fingers, you can feel the muscles in your forearm. You could say that we don't directly control our fingers at all.
The muscles in the forearm and palm are connected to the finger bones by smooth, flexible strings called tendons. The way our finger joints bend is by the muscles pulling on these tendons.
This is partly why many people can't bend their pinkies all the way without also bending their ring fingers. These muscles operate somewhat like strings on a marionette.
The total muscle count involved is 17 in the palm of the hand and 18 in the forearm. It's pretty interesting that the parts of our body that we use so frequently are completely devoid of muscles.