CorpusHuman Anatomy
MuscularMuscle group

Infrahyoid (strap) muscles

Musculi infrahyoidei

Also known as: strap muscles, sternohyoid, sternothyroid, thyrohyoid, ansa cervicalis

Four flat "strap" muscles below the hyoid (sternohyoid, omohyoid, sternothyroid and thyrohyoid). They depress and steady the hyoid and larynx.

Show on body map

Overview

The infrahyoid muscles lie in the muscular triangle of the anterior neck, in front of the thyroid gland, larynx and trachea. There are two layers. The superficial layer is sternohyoid (manubrium → body of hyoid) and omohyoid (scapula → hyoid; two bellies). The deep layer is sternothyroid (manubrium → oblique line of the thyroid cartilage) and thyrohyoid (oblique line → greater horn and body of the hyoid). Sternothyroid limits upward enlargement of the thyroid gland, so goitres tend to extend downward behind the sternum.

They lower the hyoid and larynx after swallowing and during speech or singing, and they fix the hyoid so that the suprahyoid muscles can depress the mandible. Thyrohyoid can also raise the larynx when the hyoid is fixed. All are supplied by C1–C3 through the ansa cervicalis, except thyrohyoid, which receives C1 fibres travelling with CN XII.

Parts & subdivisions

  1. Sternohyoid
    Manubrium and medial clavicle → body of the hyoid. Ansa cervicalis (C1–C3).
  2. Omohyoid
    Two bellies joined by an intermediate tendon.
  3. Sternothyroid
    Posterior manubrium → oblique line of the thyroid cartilage. Ansa cervicalis (C2–C3).
  4. Thyrohyoid
    Oblique line of the thyroid cartilage → greater horn of the hyoid. C1 via CN XII.

Anatomy

Innervation

Ansa cervicalis (superior and inferior roots) of the cervical plexus; thyrohyoid by C1 via the hypoglossal nerve.

Nerve roots

C1–C3

Arterial supply

Superior thyroid artery (external carotid) and inferior thyroid artery (thyrocervical trunk).

Relations

Overlie the thyroid gland, larynx and trachea. Lie deep to SCM laterally and superficial to the pretracheal fascia.

Function

  • Depress the hyoid and larynx
  • Fix the hyoid during mandibular depression
  • Fine-tune laryngeal position in phonation

Clinical significance

Thyroidectomy

The strap muscles are separated in the midline (or divided high up, to preserve the ansa cervicalis nerve supply that enters their lower parts) to expose the thyroid gland.

Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.