The Omohyoid Muscle is a muscle located in the anterior neck that depresses the hyoid bone. Composed of two bellies (superior and inferior), this muscle serves as an anatomical landmark for defining the boundaries of the neck triangles.

Anatomy

Morphology and Connection Points

The Omohyoid Muscle is a thin, long, and obliquely oriented muscle located between the infrahyoid muscles. It consists of two distinct parts: the superior and inferior belly. The inferior belly originates from the superior border of the scapula and lateral to the transverse scapular ligament, and is attached to the clavicle by a fibrous ligament. The superior belly originates from the intermediate tendon, courses lateral to the sternohyoid muscle, and inserts onto the inferior border of the hyoid bone. The intermediate tendon, located between the two bellies, forms the muscle's characteristic structure. The intermediate tendon of the omohyoid muscle is tightly wrapped in deep cervical fascia and anchors to the clavicle or first rib. The intermediate tendon lies just anterior to the internal jugular vein. The inferior belly originates from the scapula and the transverse scapular ligament, while the superior belly inserts onto the hyoid bone.

Embryological Origin and Classification

The Omohyoid Muscle belongs to the infrahyoid muscle group and develops from cervical somites (myotomes). Functionally and anatomically, the muscle is among the infrahyoid muscles involved in the movement of the hyoid bone during swallowing and speech.

Nerve Innervation and Vascular Supply

The muscle is innervated by the ansa cervicalis (cervical plexus). The inferior part is innervated by spinal nerves C1-C3, while the superior part is innervated only by C1 fibers. Its blood supply is provided by branches of the superior thyroid artery and the transverse cervical artery.

Function and Clinical Relationships

The Omohyoid Muscle is a slender, long muscle within the infrahyoid muscle group, consisting of two bellies (venter superior and venter inferior). It stabilizes the position of the hyoid bone during swallowing and speech by pulling it downward, thus facilitating effective suprahyoid muscle function and controlled laryngeal movements. It also prevents excessive distension of the internal jugular vein by stretching the deep cervical fascia on the lateral side of the neck, thus facilitating venous return. Anatomically, it is an important reference point for defining the borders of the neck triangles and is a structure that requires careful evaluation, particularly in head and neck surgery (e.g., thyroidectomy, lymph node dissection, and tracheotomy). Variations of the muscle may include congenital absence, duplication, anomalous fibers originating from the clavicle, and differences in the placement of the intermediate tendon. These variations can lead to diagnostic difficulties during surgery or imaging studies, and excessive tension of the intermediate tendon can cause venous drainage disorders due to compression of the internal jugular vein. Due to its structural and functional properties, the omohyoid muscle is taken into consideration both in the evaluation of anatomical structures and in the planning of certain clinical and surgical situations.