Abductor Pollicis Brevis
Hand
Raises the thumb away from the palm — the most superficial thenar muscle and the first to atrophy (waste away) in median nerve palsy, causing a flat 'ape hand.'
Function
Abducts thumb at CMC/MCP; assists opposition
Origin
Flexor retinaculum; scaphoid and trapezium tubercles
Insertion
Lateral base of proximal phalanx of thumb
Innervation
Recurrent branch of median nerve (C8-T1)