Flexor Pollicis Longus Muscle Beneath the Skin, Medial View

Description

Medial soft tissue has been removed to expose the ulnar-sided forearm and hand skeleton, including the ulna in profile with the radius partly visible, the carpal bones, metacarpals, and the phalanges to the thumb and fingers. Along the anteromedial forearm, the flexor pollicis longus (FPL) is traced as a deep anterior-compartment muscle whose belly lies lateral to the ulna and whose tendon runs distally toward the thumb, passing deep to the flexor retinaculum to reach the base of the distal phalanx. Superficial ulnar-side contour is suggested by the flexor carpi ulnaris, which sits medial to the flexor digitorum mass and frames the deeper line of the FPL from this perspective. Orientation is clear. Proximal-to-distal continuity from elbow to wrist is emphasized. A medial view is an efficient teaching angle for separating what is superficial on the ulnar border from what is functionally dedicated to the thumb, because the FPL is often mislearned as a wrist flexor rather than a long thumb flexor whose tendon acts across the interphalangeal joint. Clinically, this anatomy underpins anterior interosseous nerve palsy, where denervation of FPL (with pronator quadratus and the radial half of flexor digitorum profundus) produces weak thumb IP flexion and a classic pinch deficit. It also helps explain why lacerations or tenosynovitis within the carpal tunnel can limit thumb flexion even when the thenar muscles remain intact. Use this artwork for upper-limb anatomy lab guides, hand surgery teaching files, and rehabilitation texts discussing thumb flexion mechanics and tendon gliding. It also suits exam preparation materials that differentiate anterior compartment layers and correlate them with median nerve and anterior interosseous nerve lesions. Anatomical accuracy verified by SciePro's Medical Advisory Board.