[TA] intermediate muscle of anterior (flexor) compartment of forearm; origin, via a humeroulnar head from the medial epicondyle of the humerus, the medial border of the coronoid process, and a tendinous arch between these points, and a radial head from the oblique line and middle third of the lateral border of the radius; insertion, by four split tendons, passing to either side of the flexor digitorum profundus tendons, into sides of middle phalanx of each finger; action, flexes proximal interphalangeal joint of the fingers; nerve supply, median. SYN: musculus flexor digitorum superficialis [TA], musculus flexor digitorum sublimis, musculus flexor sublimis, superficial flexor (muscle) of fingers.