The superficial layer of the anterior compartment of the forearm is characterized by different morphological variations. During standard anatomical dissection, two morphological variations in the superficial compartment of the forearm were observed. The first one was the palmaris profundus, which originated from the radius and distally fused with the tendon to 3rd digit (from the flexor digitorum superficialis muscle) inserted on the medial phalanx of the third digit. The second variation was a distinct superficial flexor of the 4th digit represented by one muscle belly with originated from a common mass from the medial humeral epicondyle, passes through the carpal tunnel, and is inserted into the medial phalanx of the fourth digit. The flexor digitorum superficialis muscle was located deeply to it and it was divided only into three tendons (to 2nd, 3rd, and 5th digits). Tendons connected to the 2nd and 3rd digits were crossed with each other at the level of carpal tunnel. From the humeroulnar head of the flexor digitorum superficialis muscle, an additional muscle belly was arising and its tendon was fused with the superficial flexor of the fourth digit. Knowledge about morphological variations in this region is clinically important because of the direct correlation with the median nerve, and the possibility to cause carpal tunnel syndrome.
Keywords: accessory structure; accessory tendon to the fourth finger; carpal tunnel; flexor digitorum superficialis; median nerve entrapment; neuropathy; palmaris profundus; ulnar artery.