Omohyoid muscle: origin, insertion, action and innervation

The omohyoid is a long, thin neck muscle with two bellies that runs from the top of the shoulder blade to the hyoid bone. It pulls the hyoid down after swallowing and is supplied by the ansa cervicalis.

Where it is

The omohyoid belongs to the infrahyoid muscles, the four "strap muscles" below the hyoid bone, with the sternohyoid, the sternothyroid and the thyrohyoid. It is the only one that does not stay in the front of the neck: it crosses the whole side of the neck at an angle.

Its course has three parts:

• The inferior belly starts on the scapula, runs forward across the lower neck, above the clavicle.
• An intermediate tendon lies under the sternocleidomastoid, over the internal jugular vein. A band of deep fascia ties this tendon down toward the clavicle, which gives the muscle its bent shape.
• The superior belly climbs almost vertically to the hyoid, next to the sternohyoid.

Because it crosses both triangles of the neck, the omohyoid divides them into smaller ones. In the anterior triangle it separates the carotid triangle from the muscular triangle. In the posterior triangle it separates the occipital triangle above from the small supraclavicular triangle below.

Origin and insertion

• Origin (inferior belly): the upper border of the scapula, just next to the suprascapular notch. Some fibers come from the ligament that bridges the notch.
• Insertion (superior belly): the lower border of the body of the hyoid bone, just lateral to the sternohyoid.

What it does

1. Depresses the hyoid: after the hyoid and larynx have been lifted for swallowing or speech, the omohyoid helps bring them back down.
2. Steadies the hyoid: with the other infrahyoid muscles, it holds the hyoid still so the suprahyoid muscles can open the mouth against it.

Some textbooks add that, through the fascia around its intermediate tendon, it may tense the deep fascia of the neck over the internal jugular vein. That role is not settled, so learn the depressor action first.

Innervation and blood supply

The omohyoid is supplied by the ansa cervicalis, a loop of nerve fibers from C1 to C3 that lies on the front of the carotid sheath. Each belly receives its own small branch from the loop.

Blood reaches the superior belly from the superior thyroid artery. The inferior belly is supplied by branches of the thyrocervical trunk, such as the transverse cervical and suprascapular arteries.

How to remember it

• Omo means shoulder: from the Greek omos. The omohyoid joins the shoulder (blade) to the hyoid.
• The strap that leaves the front: three strap muscles stay in the midline; the omohyoid wanders across the neck to the scapula.
• A bent elbow under the SCM: the tendon is the elbow, the two bellies are the arm and forearm, and the sternocleidomastoid covers the elbow.
• Triangle splitter: if a question asks which muscle divides the anterior and posterior triangles into smaller ones, the answer is the omohyoid.

See the suprascapular notch on the scapula page, then test yourself in the neck quiz.

Frequently asked questions

What is the action of the omohyoid?

It depresses the hyoid bone, usually after it has been raised in swallowing, and helps hold the hyoid steady.

What nerve supplies the omohyoid?

The ansa cervicalis, a loop of fibers from C1 to C3 of the cervical plexus.

Where does the omohyoid originate?

From the upper border of the scapula, close to the suprascapular notch.

Why does the omohyoid have two bellies?

Its intermediate tendon is tied down by fascia near the clavicle, which divides it into an inferior belly and a superior belly and bends its course.

Which triangles does the omohyoid divide?

It splits the anterior triangle into the carotid and muscular triangles, and the posterior triangle into the occipital and supraclavicular triangles.

Sources

• OpenStax, Anatomy and Physiology 2e, 11.3 Axial muscles of the head, neck and back
• OpenStax, Anatomy and Physiology 2e, 8.1 The pectoral girdle
• Z-Anatomy, the libre 3D atlas of anatomy