Flexor digitorum superficialis tendon

Four long tendons come off flexor digitorum superficialis muscle near the wrist and travel through the carpal tunnel formed by the flexor retinaculum. These tendons, along with those of flexor digitorum profundus, are enclosed by a common flexor sheath.  

At the level of the fingers, each flexor digitorum superficialis (FDS) tendon is volar and superficial to the flexor digitorum profundus (FDP) tendon up to the level of the distal A2 pulley, where it splits into radial and ulnar slips that rotate around the FDP tendon to become deep to the tendon. After the split, decussation of FDS fibers (Camper chiasm) transiently joins the two slips to form an opening through which the FDP tendon passes to become superficial. Each FDS slip continues distally to insert separately on the volar middle phalangeal base.