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Anatomy
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Suprahyoid and Infrahyoid Muscles

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Introduction

The hyoid muscles are superficial muscles in the neck which attach to the hyoid bone. They are grouped according to their position to the hyoid bone, the suprahyoid muscles lie above the hyoid bone and the infrahyoid muscles lie beneath it. These muscles act to stabilise the trachea and play a vital part in swallowing and speech.

When the infrahyoid muscles contract, they depress the hyoid bone, allowing the suprahyoid muscles to contract and depress the mandible. If the suprahyoid muscles contract when the infrahyoid muscles are relaxed, the hyoid bone is elevated.1,2

This article will further explore the suprahyoid and infrahyoid muscles individually, showing their function, origins and insertions, as well as their innervation and vasculature.

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Suprahyoid muscles

The suprahyoid muscles act to depress the mandible when the infrahyoid muscles are contracted and to elevate the hyoid bone when the mandible is fixed.

The suprahyoid muscles consist of four muscles: digastric, stylohyoid, mylohyoid and geniohyoid muscles. These muscles contribute to swallowing and mastication, therefore they are commonly referred to as accessory muscles of mastication. Digastric, mylohyoid and geniohyoid also contribute to the floor of the mouth.

The suprahyoid muscles are primarily supplied by branches of the facial artery, with the occipital and lingual arteries also contributing.1,2

Digastric

The digastric muscle has two bellies; the anterior and posterior bellies which are separated by the intermediate tendon.

Function

Functions of the digastric muscle include:

  • elevation of the hyoid bone during swallowing
  • depression of the mandible

Attachments

Origin of the digastric muscle:

  • the anterior belly originates from the digastric fossa of the mandible
  • the posterior belly originates from the mastoid notch of the temporal bone

Insertion of the digastric muscle:

  • both bellies join via the intermediate tendon which runs through the stylohyoid muscle and then inserts onto the body and greater cornu of the hyoid bone via a fibrous sling.

Innervation

As the bellies of the digastric muscle have different embryological origins, they are innervated by different nerves:

  • the anterior belly is derived from the first pharyngeal arch and is therefore innervated by the mylohyoid nerve, a branch of the mandibular nerve, which itself is a branch of the trigeminal nerve.
  • the posterior belly is derived from the second pharyngeal arch and is therefore supplied by the digastric nerve, a branch of the facial nerve.
Digastric muscle
Figure 1. Digastric muscle.5

Stylohyoid

The stylohyoid muscle is a thin strip of muscle, located superior to the posterior belly of the digastric muscle.

Function

Functions of the stylohyoid muscle include:

  • elevation of the hyoid bone superiorly and posteriorly during swallowing
  • depression of the mandible

Attachments

Origin of the stylohyoid muscle:

  • the styloid process of the temporal bone

Insertion of the stylohyoid muscle:

  • the body of the hyoid bone

Innervation

Innervation of the stylohyoid muscle:

  • the stylohyoid branch of the facial nerve which arises posterior to the parotid gland
Stylohyoid muscle
Figure 2. Stylohyoid muscle.5

Mylohyoid

Mylohyoid is a broad and triangular muscle which meets its partner from the other side to form the floor of the oral cavity, as well as supporting the floor of the mouth.

Function

Functions of the mylohyoid muscle include:

  • forms the oral diaphragm
  • elevation of the floor of the mouth
  • elevation of the hyoid bone
  • depression of the mandible
  • aids the elevation of the tongue

Attachments

Origin of the mylohyoid muscle:

  • the mylohyoid line of the mandible

Insertion of the mylohyoid muscle:

  • both parts of the muscles meet at a median tendon, known as the mylohyoid raphe, which then inserts onto the body of the hyoid bone

Innervation

Innervation of the mylohyoid muscle:

  • the mylohyoid nerve, a branch of the mandibular nerve
Mylohyoid muscle
Figure 3. Mylohyoid muscle.5

Geniohyoid

The geniohyoid muscle lies deep to mylohyoid muscle, near to the midline of the neck.

Function

Functions of the geniohyoid muscle include:

  • elevation of the hyoid bone
  • depression of the mandible
  • supports the lateral movement of the mandible

Attachments

Origin of the geniohyoid muscle:

  • the inferior mental spine on the internal surface of the mandible

Insertion of the geniohyoid muscle:

  • the body of the hyoid bone

Innervation

Innervation of the geniohyoid muscle:

  • the C1 nerve roots from the cervical plexus that run within the hypoglossal nerve
Geniohyoid muscle
Figure 4. Geniohyoid muscle.6

Infrahyoid muscles

There are four infrahyoid muscles: omohyoid, sternohyoid, sternothyroid and thyrohyoid. In general, they act to depress the hyoid bone and play an important role in the position of the larynx and swallowing.

The infrahyoid muscles lie in two planes; the superficial plane (omohyoid and sternohyoid muscles) and the deep plane (sternothyroid and thyrohyoid muscles). They are supplied by the superior and inferior thyroid arteries and drained by the corresponding veins.1,2

Omohyoid

The omohyoid muscle consists of a superior and inferior belly, which are connected by a muscular tendon.

Function

Function of the omohyoid muscle:

  • depression of the hyoid bone

Attachments

Origin of the omohyoid muscle:

  • the inferior belly of the omohyoid muscle originates from the scapula and runs supromedially deep to the sternocleidomastoid

Insertion of the omohyoid muscle:

  • the superior belly of the omohyoid muscle inserts onto the inferior belly via an intermediate tendon
  • the intermediate tendon is anchored to the clavicle via the deep cervical fascia
  • the superior belly then ascends and attaches on the lateral border of the body of the hyoid bone.

Innervation

Innervation of the omohyoid muscle:

  • the anterior rami of C1-C3 which is carried by a branch of the ansa cervicalis, part of the cervical plexus.
Omohyoid muscle
Figure 5. Omohyoid muscle.5

Sternohyoid

The sternohyoid muscle is located within the superficial plane, medial to the omohyoid.

Function

Function of the sternohyoid muscle:

  • depression of the hyoid bone

Attachments

Origin of the sternohyoid muscle:

  • the sternum and sternoclavicular joint

Insertion of the sternohyoid muscle:

  • the body of the hyoid bone

Innervation

Innervation of the sternohyoid muscle:

  • the anterior rami of C1-C3 which is carried by a branch of the ansa cervicalis
Sternohyoid muscle
Figure 6. Sternohyoid muscle.6

Sternothyroid

The sternothyroid muscle lies posterior to the sternohyoid within the deep plane.

Function

Function of the sternothyroid muscle:

  • depression of the thyroid cartilage and larynx

Attachments

Origin of the sternothyroid muscle:

  • manubrium of the sternum

Insertion of the sternothyroid muscle:

  • thyroid cartilage

Innervation

Innervation of the sternothyroid muscle:

  • the anterior rami of C1-C3 which is carried by a branch of the ansa cervicalis
Sternothyroid muscle
Figure 7. Sternothyroid muscle.6

Thyrohyoid

The thyrohyoid muscle is short and superior to the sternothyroid. It is considered to be a continuation of the sternothyroid muscle.

Function

Functions of the thyrohyoid muscle:

  • depression of the hyoid bone
  • elevation of the thyroid cartilage and larynx when the hyoid bone is fixed

Attachments

Origin of the thyrohyoid muscle:

  • the thyroid cartilage

Insertion of the thyrohyoid muscle:

  • the body and greater cornu of the hyoid bone

Innervation

Innervation of  the thyrohyoid muscle:

  • anterior ramus of C1 which is carried within the hypoglossal nerve
Thyrohyoid muscle
Figure 8. Thyrohyoid muscle.6
Clinical relevance: Ludwig’s angina

Ludwig’s angina is a rare but serious complication from caries, gingivitis and tonsillitis.

Ludwig’s angina occurs in the floor of the mouth and is an example of phlegmon, which is a term for inflammation of soft tissue that spreads under the skin, usually producing pus.

Bacteria spread within the connective tissue of the floor of the mouth and through the pharynx, causing symptoms such as difficulty swallowing, pain on swallowing and fever. The pathogens can easily migrate through the connective tissue of the mylohyoid muscles into the submandibular region. This can become more serious if the pathogens spread cranially into the skull or caudally into the mediastinum.3

Clinical relevance: Infrahyoid muscle paralysis

Infrahyoid muscles paralysis typically presents with swallowing difficulties and a hoarse voice. Paralysis of these muscles usually occurs secondary to cervical spine trauma and resulting damage to the ansa cervicalis. 

The majority of the infrahyoid muscles are innervated by the ansa cervicalis in their lower half, therefore, if access is required to the deeper structures in the neck, these muscles are divided in the upper half. Neck dissection to excise malignant tumours commonly results in damage to the ansa cervicalis.4

Key points

  • There are eight hyoid muscles, four suprahyoid and four infrahyoid muscles.
  • The suprahyoid muscles include digastric, stylohyoid, mylohyoid and geniohyoid.
  • The infrahyoid muscles include omohyoid, sternohyoid, sternothyroid and thyrohyoid.
  • The hyoid muscles act to stabilise the trachea and play a vital part in swallowing and speech.
  • Damage to the hyoid muscles can result in difficulty speaking and swallowing and sometimes a hoarse voice.

Reviewer

Professor Ingrid Goldsborough

Head of Anatomy and Histology

University of Manchester

References

  1. Richard L. Drake, A. Wayne Vogyl, Adam W.M. Mitchell. Gray’s Anatomy for Students. s.l. Elsevier. Published in 2015.
  2. Margaret J. Fehrenbach, Susan W. Herring. Illustrated Anatomy of the Head and Neck. Elsevier. Published in 2017.
  3. Achudhan Karunaharamoorthy, Dimitrios Mytilinaios. Suprahyoid muscles. Kenhub, 2020.
  4. Achudhan Karunaharamoorthy, Dimitrios Mytilinaios. Infrahyoid muscles. Kenhub, 2020.
  5. Adapted by Geeky Medics. Olek Remesz. Hyoid muscles. Licence: [CC BY-SA].
  6. Dr Lewis Potter. Geeky Medics. Hyoid muscles. 

 

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