The omohyoid is a two-bellied (digastric) infrahyoid strap muscle with an inferior belly from the scapula and a superior belly to the hyoid, connected by an intermediate tendon slung beneath a fibrous loop attached to the clavicle and first rib. It defines the anterior and posterior triangles of the neck by crossing the sternocleidomastoid, making it a key neck dissection landmark.
| Origin | Superior border of the scapula near the suprascapular notch (inferior belly origin) |
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| Insertion | Body of the hyoid bone (superior belly insertion), with an intermediate tendon joining the two bellies constrained by the deep cervical fascia to the clavicle and first rib |
| Nerve Supply | Ansa cervicalis (C1-C3 from the cervical plexus) |
| Blood Supply | Superior thyroid artery and transverse cervical artery branches |
| Actions | Depresses and retracts the hyoid bone (as part of post-swallow hyoid descent); tenses the deep cervical fascia of the anterior neck (compartment-lowering function to reduce venous pressure in the deep cervical veins); minor swallowing role in stage 2 of the oral-pharyngeal transit |
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The omohyoid defines the boundary between the anterior triangle (medial) and the posterior triangle (lateral and inferior) of the neck, making it the key landmark in neck dissection level classification: level IVA nodes are inferior to the omohyoid in the anterior triangle; level V nodes are in the posterior triangle posterior to the SCM and lateral to the omohyoid. Division of the omohyoid at its intermediate tendon allows access to the deep cervical compartment. The muscle may cause a visible pulsatile neck mass when the intermediate tendon compresses the internal jugular vein during neck movements.
The fibrous loop constraining the omohyoid intermediate tendon against the deep cervical fascia can compress the internal jugular vein with neck rotation, producing a pulsatile neck swelling from IJV hypertension distal to the compression; the syndrome is treated by dividing the intermediate tendon and releasing the fascial sling.
