The infrahyoid muscles are a group of four muscles that are located inferiorly to the hyoid bone in the neck. They can be divided into two groups:
- Superficial plane – omohyoid and sternohyoid muscles.
- Deep plane – sternothyroid and thyrohyoid muscles.
The arterial supply to the infrahyoid muscles is via the superior and inferior thyroid arteries, with venous drainage via the corresponding veins.
In this article, we shall look at the anatomy of the infrahyoid muscles – their attachments, actions and innervations.
Omohyoid
The omohyoid is comprised of two muscle bellies, which are connected by a muscular tendon.
- Attachments:
- Superior belly arises from the hyoid bone and inferior belly arises from the scapula.
- Two muscle bellies are connected by an intermediate tendon, which is anchored to the clavicle by the deep cervical fascia.
- Actions: Depresses the hyoid bone.
- Innervation: Anterior rami of C1-C3, carried by a branch of the ansa cervicalis.
Sternohyoid
The sternohyoid muscle is located in the superficial plane of the neck, along with the omohyoid muscle.
- Attachments: Originates from the sternum and sternoclavicular joint. Ascends to insert onto the hyoid bone.
- Actions: Depresses the hyoid bone.
- Innervation: Anterior rami of C1-C3, carried by a branch of the ansa cervicalis.
Sternothyroid
The sternothyroid muscle is a wide muscle, located underneath the sternohyoid in the deep plane of the neck.
- Attachments: Arises from the manubrium of the sternum and attaches to the thyroid cartilage.
- Actions: Depresses the thyroid cartilage.
- Innervation: Anterior rami of C1-C3, carried by a branch of the ansa cervicalis.
Thyrohyoid
The thyrohyoid is a short band of muscle, thought to be a continuation of the sternothyroid muscle.
- Attachments: Arises from the thyroid cartilage of the larynx and ascends to attach to the hyoid bone.
- Actions: Depresses the hyoid. If the hyoid bone is fixed, it can elevate the larynx.
- Innervation: Anterior ramus of C1, carried within the hypoglossal nerve.
