The omohyoid muscle is an infrahyoid muscle of the neck that is innervated by the ansa cervicalis of the cervical plexus receiving fibers from the ventral rami of C1–C3 spinal nerves. The omohyoid is a paired, flat strap of muscle that is made up of superior and inferior bellies joined by an intermediate tendon. The primary function of the omohyoid muscle is to depress and fix the hyoid bone and underlying larynx though it also draws the hyoid bone downwards in phonation and in the terminal phase of swallowing.
- origin: transverse scapular ligament and superior border of scapula medial to the suprascapular notch
- insertion: lateral and inferior border of the hyoid bone
- innervation: anterior rami of C1–C3 spinal nerves from the cervical plexus; the superior and inferior bellies are innervated by separate nerves of the ansa cervicalis
- depresses and fixes the hyoid bone
- draws the hyoid bone and underlying larynx downwards in phonation and the terminal phase of swallowing
- intermediate tendon of the muscle tenses overlying cervical fascia and maintains patency of the internal jugular vein
The omohyoid muscle originates from the superior border of the scapula medial to the suprascapular notch. The muscle may also derive from the transverse scapular ligament.
As the omohyoid muscle courses upwards from an almost horizontal inferior belly and comes to lie over the internal jugular vein it is replaced by a flat (intermediate) tendon (see deep cervical fascia). The muscle continues with the superior belly which courses more vertically upwards and comes to lie on the carotid sheath. The superior belly of omohyoid passes beneath the sternocleidomastoid muscle and finally comes to converge with the sternohyoid muscle. The omohyoid inserts edge to edge with the sternohyoid muscle on the lateral part of the inferior border of the hyoid bone. The omohyoid muscle inserts lateral to the sternohyoid muscle.
The superior belly of the omohyoid muscle forms the anteroinferior border of the carotid triangle vascular area, which houses the upper part of the common carotid artery, carotid sinus and carotid body. The carotid triangle is formed by the anterior border of the sternocleidomastoid muscle posteriorly, the posterior belly of the digastric muscle anterosuperiorly and the superior belly of the omohyoid anteroinferiorly.
The intermediate tendon of the omohyoid muscle lies over the internal jugular vein and is able to slide easily on the underlying vein. The tendon is sometimes used in dissections of the neck to identify the internal jugular vein immediately underneath.
- blood supply from branches of the inferior thyroid artery
- omohyoid muscle is supplied by the anterior rami of C1–C3 spinal nerves from the cervical plexus
- the superior and inferior bellies are innervated by separate nerves of the ansa cervicalis
The omohyoid muscle primarily depresses and fixes the hyoid bone and underlying larynx. The omohyoid muscle has also been thought to depress the larynx and hyoid bone in phonation and in the terminal phase of swallowing. The intermediate tendon of the omohyoid muscle overlies and tenses the cervical fascia ensuring patency of the internal jugular vein.
A number of anatomical variants have been noted regarding the anatomy of the omohyoid muscle which are often clinically relevant given the proximity of the muscle to significant neurovascular structures.
- duplicate or double bellies of both the superior and inferior portions of the muscle have been reported in cadaveric case series
- significant variations in the origin and insertion of the muscle have also been reported in a number of case series likely related to the embryology of the muscle, which is first attached in the fetus to the medial end of the clavicle. The process of migration of the muscle to the superior aspect of the scapula may be arrested at any point.