Three muscles connect with its anterior surface — the sternohyoid, the omohyoid, and the sternocleidomastoid muscle; along the inner boundary lies the thyroid vein. The trachea, the common carotid, the thyroid gland with all its vessels, the vena innominata, and the lower section of the larynx all connect with its posterior surface from below upwards, as does the arteria innominata on the right side.
The purpose of the sternothyroid muscle is to depress the larynx. It thus plays an important role in speech production.
Variations on this muscle exist from one person to another. There may, for instance, be a lateral prolongation as far as the hyoid bone. The muscle may not even be present at all; or it may be doubled. It may also be continuous with the thyrohyoid muscle and the inferior constrictor of the pharynx. Accessory slips to the thyrohyoid muscle, the inferior constrictor, or the carotid sheath may also be present.