Third lumbrical muscle
Musculus lumbricalis tertius
- Related terms: Lumbricals (3)
Definition
Third lumbrical muscle | |||
Origin | From the medial side of the second flexor digitorum profundus tendon to the third digit (middle finger) and the lateral side of the third flexor digitorum profundus tendon to the fourth digit (ring finger) | ||
Insertion | Extensor expansions of the 4th digit (ring finger) | ||
Artery | Superficial palmar arch, deep palmar arch, common palmar digital arteries, dorsal digital artery | ||
Innervation | Deep branch of ulnar nerve | ||
Action | Flexes the metacarpophalangeal joint and extends the proximal and distal interphalangeal joints of the ring finger | ||
The third lumbrical muscle is a bipennate intrinsic muscle of the hand. It originates from the adjacent sides of the second and third flexor digitorum profundus (FDP) tendons. Specifically, its origin includes the ulnar side (and adjacent volar surface) of the FDP tendon going to the middle finger, and the radial side (and adjacent volar surface) of the FDP tendon going to the ring finger.
The muscle then courses distally, passing around the lateral side of the metacarpophalangeal (MCP) joint of the ring finger. It eventually reaches the dorsal aspect of the hand, where it inserts into the dorsal digital expansion (extensor expansion) covering the ring finger. This unique insertion mechanism enables the third lumbrical to flex the MCP joint of the ring finger while simultaneously extending both the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints of that same finger.
References
Valenzuela M, Launico MV, Varacallo MA. Anatomy, Shoulder and Upper Limb, Hand Lumbrical Muscles. [Updated 2023 Nov 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK534876/
