The flexor digitorum superficialis is the single muscle which makes up the intermediate layer of the muscles of the anterior compartment of the forearm.

It has two heads:

  • humero-ulnar head
  • radial head

Origin
  • Humeroulnar head: medial epicondyle of humerus (primary origin), and coronoid process of ulna
  • Radial head: anterior oblique line of radius
Insertion

Margins of the base of the middle phalanges of the index, middle, ring and little fingers.

 

Four tendons are formed within the distal forearm, which pass through the carpal tunnel along with the tendons of its counterpart muscle, the flexor digitorum superficialis (also 4 tendons), the flexor pollicis longus and the median nerve.

The tendons of the flexor digitorum superficialis split to insert onto the margins of the base of the middle phalanges, allowing the deeper tendons of the flexor digitorum profundus to pass through and inserting more distally on the bases of the distal phalanges. This can be remembered with the mnemonic superficialis splits, profundus passes through.

The tendons of the flexor digitorum profundus within the palm of the hand provide the origin for the lumbrical muscles, which arise from the sides of these tendons.

Innervation

Median Nerve

Blood Supply

Ulnar artery

Antagonist

Extensor digitorum

Action

The flexor digitorum superficialis produces flexion at the following joints:

  • Proximal interphalangeal joints: flexes digits 2-5 (primary action due to insertion)
  • Metacarpophalangeal joints (2-5)
  • Wrist