Overview
It arises on the manubrium of the sternum and runs along the ventrolateral neck to the head. In the horse it has only the mandibular part (sternomandibularis); there is no mastoid part. The two muscles run together at the base of the neck and diverge cranially. Its terminal tendon passes deep to the parotid gland.
Origin
Manubrium of the sternum.
Insertion
Caudal border of the mandibular ramus, near the angle.
Action
Draws the head and neck ventrally or to the same side.
Innervation
Ventral branch of the accessory nerve (n. accessorius).
Clinical relevance
- It forms the ventral border of the jugular groove. In the cranial half of the neck the omohyoideus separates the external jugular vein from the common carotid artery; in the caudal half there is no such barrier, and a misdirected injection can enter the carotid and cause immediate seizures or collapse. Jugular venipuncture is therefore done in the cranial third of the neck.
- Jugular thrombophlebitis is a complication of catheters and of irritant injections outside the vein.
- In surgery for crib-biting (modified Forssell procedure) the ventral branch of the accessory nerve, which supplies this muscle, is cut and the neighbouring infrahyoid muscles are resected.