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- Origin:
    - superficial head: distal border of the flexor retinaculum;
    - greater multangular bone tuberosity of the trapezium bone deep head;
    - trapezoid and capitate bones;
- Insertion: base of the proximal phalanx of the thumb;

- Action:
    - flexes proximal phalanx of the thumb; continued action flexes first metacarpal and rotates it medially;
- Synergists:  FPL, adductor pollicis;

- Nerve supply: superficial head: Median, C8,  T1
                        deep head:        Ulnar, C8, T1;

- Discussion:
    - FPB is on volar surface of metacarpal and under abductor brevis;
    - one head of the flexor brevis originates from volar carpla ligament and in the region of the Flexor Carpi Radialis tendon;
    - other originates from trapezium and from capitate tendon that inserts into radial sesamoid & radial tubercle of proximal phalanx;
    - this muscle also attaches to an expansion into the extensor mech. and assists in extending the distal phalanx of the thumb