n :  a thick superficial muscle on each side that 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 and occipital bone, and that acts esp. to bend, rotate, flex, and extend the head
, adj :  of, relating to, supplying, or being a sternocleidomastoid <the artery>  .
 
 
 
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