Palmaris longus

Location and anatomy

The palmaris longus muscle belongs to the medial compartment of the forearm (which contains muscles originating from the medial epicondyle) and is part of its first, superficial layer. Ordering the muscles of this layer from the medial edge (closer to the elbow) to the lateral edge (toward the center), it is located second—between the flexor carpi ulnaris and the flexor carpi radialis.

• Origin (origo) — medial epicondyle of the humerus (epicondylus medialis humeri). In the proximal forearm, the superficial layer muscles appear as a single muscle head. Separation into distinct muscles becomes noticeable more distally, at the border of the upper and middle thirds of the forearm.
• Insertion (insertio) — the muscle tendon runs along the midline beneath the deep fascia and continues into the palmar aponeurosis (aponeurosis palmaris).
• Anatomical variation (normal variant) — this muscle is quite frequently absent.

Topography and adjacent structures

The topography of the muscle changes along the course of the forearm and hand:

• At the middle third of the forearm: on a cross-section, the muscle lies anteriorly together with the flexor digitorum superficialis (m. flexor digitorum superficialis), pronator teres (m. pronator teres), and flexor carpi radialis (m. flexor carpi radialis).
• In the lower third of the forearm: the tendons of the palmaris longus and flexor carpi radialis form the borders of the median sulcus (sulcus medianus). Within this sulcus, directly beneath the deep fascia, lies the median nerve (n. medianus).
• In the hand: the tendon blends into the apex of the palmar aponeurosis. The aponeurosis itself is a triangular fibrous plate whose base sends slips to the proximal phalanges of digits II–V. The septa of the aponeurosis form fibro-osseous canals for the flexor tendons.

Blood supply and innervation

• Blood supply (arteriae) — radial artery (a. radialis) and ulnar artery (a. ulnaris).
• Innervation (nervus) — median nerve (n. medianus), segments C7–Th1 or C8–Th1.

What is its function?

• Wrist flexion (flexio) — the muscle assists in flexing the wrist.
• Aponeurosis tension (tensio) — upon contraction, the muscle tightens the palmar aponeurosis.

Clinical significance

• External landmark (visualization) — on the anterior surface, the tendon of m. palmaris longus serves as a landmark for the median nerve at the forearm boundary. Three transverse skin creases are also identifiable nearby.
• Traumatology (injuries) — the median nerve in the lower third of the forearm lies superficially in the median sulcus, making this area particularly vulnerable to trauma.
• Hand pathology (Dupuytren's contracture) — the palmar aponeurosis, into which the muscle tendon inserts, has clinical relevance in Dupuytren's contracture.

Class and exam questions

What else to study on this topic

• Palmar aponeurosis (aponeurosis palmaris)
• Median nerve (n. medianus)
• Flexor carpi radialis (m. flexor carpi radialis)
• Dupuytren's contracture

Other topics in the "Anatomical Structures" section

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