Flexor digitorum superficialis arises from the common origin, the medial ligament of the elbow joint, and the sublime tubercle on the medial border of the coronoid process of the ulna (humeroulnar head). From this point a fibrous arch continues the origin across to the radius, where the muscle arises from the whole length of the anterior oblique line (radial head). The fleshy belly is partly hidden above by the other superficial flexors, and is therefore frequently described as being in an intermediate layer. Its oblique origin, in continuity from the medial epicondyle to the insertion of pronator teres, forms the upper limit of the space of Parona. Above the wrist the tendons appear on each side of palmaris longus tendon. The flesh which gives rise to the tendons for the middle and ring fingers is superficial across the wide origin of the muscle. That giving rise to the tendons of the index and little fingers arises more deeply from the common flexor origin and ulnar collateral (medial) ligament of the elbow. It lies beneath the belly for the middle two fingers, and is divided by a transverse tendinous intersection into an upper and two lower bellies. The tendons pass in the above order beneath the flexor retinaculum, i.e. middle and ring fingers superficial to index and little finger. In the forearm the muscle has the median nerve plastered to its deep surface by areolar tissue; the commencing profundus tendon for the index finger can readily be mistaken for the nerve at operation or in a dissection.
Nerve supply of flexor digitorum superficialis:
By the median nerve (C7, 8).
Action of flexor digitorum superficiallis:
The muscle is a flexor of the proximal interphalangeal joints, and secondarily of the metacarpophalangeal and wrist joints.