Abductor Pollicis Brevis

The abductor pollicis brevis is often divided into outer and inner parts, or it may receive slips from the navicular bone or styloid process of the radius. A third head arising from opponens pollicis has been reported. An accessory slip is frequently found joining the muscle with abductor pollicis longus. More rarely, accessory slips connect abductor pollicis with palmaris longus, extensor carpi radialis longus, accessory extensor carpi radialis, opponens or flexor pollicis brevis. 

A cutaneous slip is frequently present attached to the skin over the proximal part of the thenar eminence, and inserted distally on the radial side of the first phalanx. The absence of abductor pollicis has been reported. Syn.: m. abductor externus (Sömmerring).

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References

Brottet, -. (1876) Long abducteur du pouce, surnuméraires. Lyon Med. 21:475.

Henle, J. (1871) Handbuch der Muskellehre des Menschen, in Handbuch der systematischen Anatomie. Verlag von Friedrich Vieweg und Sohn., Braunschweig.

Macalister, A. (1875) Additional observations on muscular anomalies in human anatomy (third series), with a catalogue of the principal muscular variations hitherto published. Trans. Roy. Irish Acad. Sci. 25:1- 134.