Sternocleidomastoid muscle

The sternocleidomastoid (SCM) is a muscle of the neck. It has two heads that meld to form one insertion. SCM, along with the trapezius muscle, is invested by the superficial layer of the deep cervical fascia, which splits around it. SCM divides the neck into anatomical anterior and posterior triangles

  • sternal head (tendinosus): manubrium of sternum
  • clavicular head (fleshy): medial part of clavicle 
  • when acting unilaterally: lateral flexion, rotates head to opposite side
  • when acting bilaterally: flexes neck, draws head ventrally and elevates chin, draws sternum superiorly in deep inspiration
  • absent mastoid insertion (occipital insertion only)
  • absent clavicular or sternal head
  • fusion with trapezius muscle
  • additional clavicular head
  • separate muscle bellies for sternomastoid and cleidomastoid
  • separate muscle bellies for cleidooccipital and sternocleidomastoid
Anatomy: Head and neck
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Article information

rID: 13075
Section: Anatomy
Synonyms or Alternate Spellings:
  • Sternocleidomastoid
  • SCM
  • Sternomastoid muscle
  • Sternomastoid

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