The long thumb flexor
Flexor pollicis longus · musculus flexor pollicis longus
The forearm muscle that bends the tip of your thumb.
What it does
The flexor pollicis longus runs from the radius down to the last bone of the thumb. It is the only muscle that bends the tip of your thumb, which you need for a precise pinch, writing or pressing a button.
Surprising fact
A separate long flexor just for the thumb is unusual among primates, and it helps give humans their strong, precise pinch grip.
Why it matters
Texting, writing and buttoning a shirt all depend on it. Damage to its tendon leaves the thumb tip floppy and makes fine pinching very hard.
Nearby
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Sources
Drafted with AI help; awaiting a human fact-check against these sources.
Open in the 3D atlas · Suggest a correction · Not medical advice.
3D models: Z-Anatomy & BodyParts3D (CC BY-SA 4.0 / 2.1 JP). Card text CC BY 4.0.