sternocleidomastoid /-klī′dōmas″toid/ [Gk, sternon, chest, kleis, key, mastos, breast, eidos, form] , a muscle of the neck that is attached to the mastoid process of the temporal bone and to the superior nuchal line and by separate heads to the sternum and clavicle. They function together to flex the head. Also called sternomastoid.
