Anatomy of the extensor pollicis brevis muscle.

52 hands have been dissected to check the anatomy and function of the extensor pollicis brevis. Various abnormalities were found: absence of the E.P.B. (two), insertion on the distal phalanx (four), absence of bony insertion on the base of the first phalanx and insertion on the extensor hood (36). In ten cases (in addition to the two with absence of E.P.B.), no function was elicited by pulling the tendon which inserted upon the extensor hood.