Hyoid bone

Anatomy

The hyoid bone is situated in the anterior triangle of the neck, between the mandible and thyroid cartilage. The bone has three parts: a body, two greater horns and two lesser horns.

• Body: Forms the central portion of the horseshoe-shaped bone and has a vertical median ridge. The anterior surface is convex and directed anterosuperiorly, while the posterior surface is concave and directed posteroinferiorly.
• Greater horns (greater cornua): Two large posterolateral bony extensions from the lateral ends of the body, ending in tubercles.
• Lesser horns (lesser cornua): Two small conical projections extending superiorly from the junction of the body with the greater horns.

The greater horns articulate with the body via fibrocartilage (which ossifies with age), while the lesser horns are connected by fibrous tissue. Synovial joints link the greater and lesser horns.

Relations

• Superior: Suspended from the styloid process of the temporal bone by the stylohyoid ligament.
• Inferior: Attached to the thyroid cartilage via the thyrohyoid membrane.
• Posterior: Lies anterior to the epiglottis.

Muscle attachments

The muscles attaching to the hyoid bone can be classified into:

• Suprahyoid muscles (above the hyoid bone)
• Infrahyoid muscles (below the hyoid bone)
• Other muscles (oral cavity and pharynx)

Suprahyoid muscles

Suprahyoid muscles are located superior to the hyoid bone and are primarily involved in elevating it. They include the:

1. Digastric muscle: The digastric muscle has an anterior and posterior belly. The two muscle bellies unite at an intermediate tendon suspended by a fibrous sling that attaches to the hyoid bone at the junction between the greater horn and the body. Along with elevating the hyoid bone, the digastric muscle depresses the mandible.
2. Mylohyoid muscle: The mylohyoid muscles originate from the mylohyoid line of the mandible and form the floor of the mouth. The anterior fibers insert into the mylohyoid raphe, while the posterior fibers insert into the lower anterior surface of the body of the hyoid bone.
3. Geniohyoid muscle:The geniohyoid muscle originates from the inferior mental spine of the mandible and travels inferiorly to insert into most of the anterior surface of the body of the hyoid bone. In addition to elevating the hyoid bone, it also protracts the bone.
4. Stylohyoid muscle: The stylohyoid muscle originates from the styloid process of the temporal bone and travels inferiorly. Near its insertion, it is pierced by the digastric muscle, splitting the stylohyoid muscle into two tendinous structures which attach to the junction between the greater horn and body of the hyoid bone. This muscle retracts the hyoid bone in addition to elevating it.

Learning the origins and insertions of all these muscles can seem tricky. Remember them easily with our quick muscle anatomy reference charts!

Infrahyoid muscles (strap muscles)

The infrahyoid muscles, also known as strap muscles, are located below the hyoid bone and primarily depress the bone. These muscles include the:

1. Thyrohyoid muscle: The thyrohyoid muscle is a small muscle that originates from the oblique line on the thyroid cartilage lamina. It extends superiorly to insert into the greater horn and body of the hyoid bone.
2. Sternohyoid muscle: The sternohyoid muscle originates from the manubrium of the sternum and medial end of the clavicle to insert into the inferior border of the body of the hyoid bone (medial to the omohyoid insertion).
3. Omohyoid muscle: The omohyoid muscle has a superior and inferior belly. The inferior belly of the omohyoid originates from the scapula and travels superiorly ending in an intermediate tendon. The superior belly originates from the intermediate tendon and inserts into the inferior border of the body of the hyoid bone (lateral to the sternohyoid insertion).

The sternothyroid muscle is also an infrahyoid muscle, however it does not attach to the hyoid bone.

Learn all about the hyoid bone and muscles of the neck with these carefully-designed study units!

Other muscles (oral cavity and pharynx)

Aside from the suprahyoid and infrahyoid muscles, the hyoid bone receives the attachment of three other muscles of the oral cavity and pharynx:

1. Genioglossus muscle: The genioglossus muscle is an extrinsic muscle of the tongue. It originates from the superior mental spine of the mandible and inserts into the tongue and hyoid bone. The superior fibers insert into the tongue, while the inferior fibers insert into the anterosuperior surface of the body of the hyoid bone. Its function is depression and protraction of the tongue.
2. Hyoglossus muscle: The hyoglossus muscle is an intrinsic muscle of the tongue. It originates from the anterior surface of the body and greater horn of the hyoid bone and inserts into the lateral aspect of the tongue. Its action is to retract the tongue.
3. Chondroglossus muscle: The chondroglossus is also an intrinsic muscle of the tongue. It originates from the lesser horn of the hyoid bone and extends superiorly to blend with other intrinsic muscles of the tongue. Its action is to depress the tongue.
4. Middle pharyngeal constrictor: The middle pharyngeal constrictor has fibers that encircle the pharynx constricting it during swallowing. It originates from the greater and lesser horns of the hyoid bone, with some fibers also originating from the stylohyoid ligament. They meet fibers from the opposite side, inserting into the pharyngeal raphe.

Membrane and ligament attachments

In addition to muscles, the hyoid bone receives the attachment of membranes and ligaments such as the:

1. Thyrohyoid membrane: From the superior thyroid cartilage to the body of hyoid. It is separated from the hyoid bone by a bursa and the central fibers of the membrane are thickened to form the thyrohyoid ligament.
2. Hyopepiglottic ligaments: Connects the hyoid bone to the epiglottis.
3. Stylohyoid ligaments: From the styloid process to the lesser horn. The stylohyoid ligament, along with the styloid process and lesser horns of the hyoid bone form the stylohyoid complex or styloid apparatus.

These structures stabilize the hyoid and allow coordinated movement during speech and deglutition (swallowing).

Embryology and ossification

The hyoid bone develops from three embryological sources:

• Lesser horns: Second pharyngeal arch
• Greater horns: Third pharyngeal arch
• Body: Hypobranchial eminence (midline mesenchymal condensation)

It ossifies from six centers: two each for the body, greater horns, and lesser horns.

Memory tip: Think “3s” — 3 parts, 3 muscle groups, 3 ligaments, 3 embryological origins, and 6 ossification centers.

The best way to remember complex anatomy is with spaced repetition. Try it out with this quiz on the hyoid bone!