Flexor Pollicis Longus: Function & 3D Anatomy

Educational draft · anatomical review pendingSources checked 19 October 2026. Prepared with AI assistance; not yet reviewed by a qualified anatomist. Not for diagnosis or treatment.

Region: Deep anterior forearm
Digit: Thumb
Distal attachment: Distal thumb phalanx
Abbreviation: FPL

The thumb, rather than the other four fingers

Flexor pollicis longus is the long thumb flexor. Its distal destination differs from that of flexor digitorum profundus, which reaches the other four digits.

Both are now available in the same forearm subset. Use the structure list to compare them when overlapping surfaces are difficult to pick directly.

Sources: Loyola anatomy · Anatomy tables

Radius and membrane to the thumb tip bone

Its origin lies on the anterior radius and adjacent interosseous membrane. Its distal attachment reaches the base of the thumb’s distal phalanx.

Only the radius is loaded among those attachment structures. The membrane and thumb phalanx cannot be selected, and the distal end is not an attachment to the radius.

Sources: Loyola anatomy

Bending the thumb’s interphalangeal joint

FPL flexes the distal phalanx of the thumb at its interphalangeal joint.

The source pose is fixed. Camera rotation does not bend the fingers or thumb, and the model does not simulate tendon gliding, grip or muscle contraction. Muscle and tendon are not separately selectable tissues.

This guide names one action; it does not reconstruct the complete muscles or joints of the thumb. An isolated surface cannot demonstrate a pinch mechanism or assess tendon integrity.

Sources: Loyola anatomy

Anterior interosseous nerve

The anterior interosseous nerve, a branch of the median nerve, supplies FPL.

Nerves and vessels are not loaded in this subset, so the text describes connections you cannot select in the viewer.

Compare the named supply with FDP, but do not infer nerve branching or sensory territories from model color or surface shape.

Sources: Anatomy tables

Read the model

Explore flexor pollicis longus in 3D

Inspect the long course. Choose Front or Oblique and follow the isolated surface. Focus selection restores useful framing without changing the source pose.
Restore the radius. Choose Show context, enable Fade others and alternate Radius with Flexor pollicis longus. Do not expect a thumb-bone layer: those bones are not loaded.
Compare fingers with thumb. Select Flexor digitorum profundus, then open its title. Both pages keep the same source coordinates and offer reciprocal related links.

What this model can—and cannot—show

BodyParts3D provides this right-sided surface model, not every anatomical variant. Colors distinguish structures; they are not tissue textures.

This forearm subset includes radius, ulna and the two deep digital flexors, but not the hand bones, interosseous membrane, flexor retinaculum, tendon sheaths, nerves or vessels. Flexor digitorum superficialis is not loaded. Distal mesh ends extend into a hand region without its bones; they must not be read as attachments to the forearm bones.

FPL is one mesh with no separate muscle/tendon controls. The short thumb muscles and other hand structures are not loaded. The arm and elbow subsets do not contain this FPL mesh.

The experimental Section tool is available in the regional forearm study, not on this isolated-structure page. Its flat cut surfaces are geometric aids, not CT images or tissue sections.

Sources and editorial status

This guide uses independently written explanations with links to the evidence behind them. Source checking and specialist anatomical review are separate steps; the latter is still pending.

Loyola University Chicago — LUMEN, Flexor pollicis longus
Radial/membrane origin, distal thumb attachment and flexion action. No illustrations reproduced.
Texas Tech University Health Sciences Center El Paso — Forearm & Wrist anatomy tables
FPL and anterior interosseous nerve rows: muscle identity and median-nerve branch relationship.

3D geometry and its separate license are credited beneath the viewer. References do not imply endorsement of this site.

Flexor pollicis longus