Medical term:

sternocleidomastoidei

ster·no·clei·do·mas·toid mus·cle

(SCM) (stĕr'nō-klī'dō-mas'toyd mŭs'ĕl)

Origin, by two heads from anterior surface of manubrium of the sternum and sternal end of clavicle; insertion, mastoid process and lateral half of superior nuchal line; action, turns head obliquely to opposite side; when acting together, flex the neck and extend the head; nerve supply, motor by accessory, sensory by cervical plexus.
Synonym(s): musculus sternocleidomastoideus [TA] , sternomastoid muscle.

Medical Dictionary for the Health Professions and Nursing © Farlex 2012

sternocleidomastoid muscle

Neck muscle. Origin: upper edge of manubrium, middle of upper clavicle. Insertion: mastoid process. Nerve: accessory (CN XI), spinal C2. Action: contralaterally rotates head.

See: face and headfor illus.