Origin and Insertion
The muscle originates from several bony structures:
- Medial epicondyle of the humerus;
- Coronoid process of the ulna (processus coronoideus);
- Proximal part of the radius (radius).
As it extends toward the hand, the muscle belly transitions into tendons that insert onto the middle phalanges of digits II–V.
⚙️ Structural Feature: At the level of the proximal phalanges, each tendon splits into two slips, creating a bifid tendon. The tendon of the flexor digitorum profundus (m. flexor digitorum profundus) passes through the resulting gap. This anatomical arrangement is called the tendinous chiasm (chiasma tendineum).
Topography in the Forearm
The flexor digitorum superficialis forms the second layer of the medial flexor compartment of the forearm.
- Anteriorly (superficially): The muscle is covered by the first layer, which includes (from medial to lateral): the flexor carpi ulnaris, palmaris longus, flexor carpi radialis, and pronator teres. In the middle and lower thirds of the forearm, its belly may be visible in the intervals between the muscles and tendons of the first layer.
- Posteriorly (deeply): The deep surface of the muscle is related to the deep lamina of the forearm fascia, which separates the first and second layers from the third, deep layer.
- Vessels and Nerves: The ulnar artery (a. ulnaris) runs between the flexor digitorum superficialis and flexor digitorum profundus. In the middle and lower thirds of the forearm, it travels in the groove between the flexor carpi ulnaris and the flexor digitorum superficialis. The median nerve (n. medianus) lies centrally.
Topography in the Hand and Digits
In the digits, the tendon of the flexor digitorum superficialis attaches to the middle phalanx (phalanx media). The tendon of the flexor digitorum profundus extends further to attach to the distal phalanx (phalanx distalis).
The fibrous digital sheath (vagina fibrosa tendinis flexoris) consists of annular (pars anularis) and cruciform (pars cruciformis) parts. Additionally, the synovial sheath of the flexor tendon (vagina synovialis tendinis flexoris) is present.
Function, Blood Supply, and Innervation
- Function: Flexes the middle phalanges of digits II–V and assists in wrist flexion.
- Innervation: Supplied by the median nerve (n. medianus), spinal segments C7–T1.
- Blood Supply: Supplied by the radial (a. radialis) and ulnar (a. ulnaris) arteries.