Noun
sternocleidomastoid muscle (plural sternocleidomastoid muscles)
(anatomy) A long thick superficial muscles on each side of the anterior neck which arises by one head from the first segment of the sternum and by a second from the inner part of the clavicle, that inserts into the mastoid process of the temporal bone and that acts especially to bend, flex, rotate and extend the head.
Synonyms: sternomastoid muscle, sternomastoid