Anatomy and Location
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. From the medial edge (close to the elbow) to the lateral edge (toward the center), it is positioned 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 muscles of the superficial layer appear as a single muscle mass. Separation into individual muscles becomes distinct 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 merges into the palmar aponeurosis (aponeurosis palmaris).
- Anatomical variation (normal variant) — this muscle is quite frequently absent bilaterally or unilaterally.
Topography and Neighboring Structures
The topography of the muscle varies along the forearm and hand:
- Middle third of the forearm: on a cross-section, the muscle lies anteriorly alongside the flexor digitorum superficialis (m. flexor digitorum superficialis), pronator teres (m. pronator teres), and flexor carpi radialis (m. flexor carpi radialis).
- 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 groove, directly beneath the deep fascia, lies the median nerve (n. medianus).
- 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 fibrous-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), spinal segments C7–Th1 or C8–Th1.
Function
- Wrist flexion (flexio) — the muscle assists in flexing the wrist joint.
- Aponeurosis tension (tensio) — upon contraction, it tenses the palmar aponeurosis.
Clinical Significance
- Surface landmark (visualization) — on the anterior surface, the tendon of m. palmaris longus serves as a key surgical and anatomical landmark for locating the median nerve at the wrist. Three transverse skin creases are also typically found nearby.
- Traumatology (injuries) — the median nerve in the lower third of the forearm lies superficially within the median sulcus, making this area particularly vulnerable to trauma.
- Hand pathology (Dupuytren's contracture) — the palmar aponeurosis, into which the muscle tendon inserts, is directly involved in the pathology of Dupuytren's contracture.