Two-headed muscle
Musculus biceps
- Related terms: Twoheaded muscle
Definition
A two-headed muscle is a type of skeletal muscle that has two distinct heads of origin, each arising from a different anatomical site. These heads typically merge into a single muscle belly before inserting onto a common tendon. The dual origins allow the muscle to cross multiple joints or perform combined actions, depending on which head is active.
Examples
Biceps brachii (arm) — long and short heads flex the elbow and supinate the forearm.
Biceps femoris (posterior thigh) — long and short heads extend the hip and flex the knee.
Gastrocnemius (calf) — medial and lateral heads contribute to plantar flexion of the foot.
Note
It is important to distinguish between “two-headed” and “two-bellied” muscles, which are related but anatomically distinct terms.
Feature | Two-headed muscle | Two-bellied muscle |
Definition | A skeletal muscle with two separate heads (origins) that merge into a single muscle belly before inserting on a common tendon. | A skeletal muscle with two distinct muscle bellies, connected by an intermediate tendon. |
Number of origins | Two separate origins (hence “two-headed”). | Usually a single origin shared by both bellies. |
Direction of pull | Fibres usually pull in one direction, producing a unified movement. | The line of pull may change due to the intermediate tendon or pulley mechanism. |
Examples | Biceps brachii (arm), biceps femoris (thigh), gastrocnemius (leg). | Digastric (neck), omohyoid (neck). |
Tendon structure | Single terminal tendon of insertion. | Intermediate tendon connecting two bellies. |
References
Gray, H. (2016) Gray’s anatomy the anatomical basis of clinical practice. 41st edition. Edited by S. Standring. New York: Elsevier.
