Two-bellied muscle
Musculus biventer
- Related terms: Twobellied muscle
Definition
A two-bellied muscle is a type of skeletal muscle that consists of two distinct, contractile portions (or muscle bellies) connected by an intermediate tendon. The intervening tendon may pass through a fibrous loop or pulley. This pulley-system allows redirection of the muscle’s pull, enabling complex multidirectional movements.
Examples
Digastric muscle (neck) — has an anterior and a posterior belly connected by an intermediate tendon; it depresses the mandible and elevates the hyoid bone during swallowing.
Omohyoid muscle (neck) — also has two bellies joined by an intermediate tendon; it depresses and stabilizes the hyoid bone.
Note
It is important to distinguish between “two-bellied” and “two-headed” 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.
