Synonyms for Musculus Sternocleidomastoideus (same or very similar meaning)
WordNet sense 1 (one of two thick muscles running from the sternum and clavicle to the mastoid and occipital bone; turns head obliquely to the opposite side; when acting together they flex the neck and extend the head):
sternocleidomastoid, sternocleido mastoideus, sternocleidomastoid muscleFrom the ODE community, based on WordNetadd/edit