define sternocleidomastoid
Sternocleidomastoid muscle. In human anatomy, the sternocleidomastoid muscle (/ËstÉËrnoÊËklaÉªdÉËmÃ¦sËtÉÉªd, -nÉ-, -doÊ-/[1][2]), also known as sternomastoid and commonly abbreviated as SCM, is a paired muscle in the superficial layers of the side of the neck. It is one of the largest and most superficial cervical muscles.