Many anatomical variants on the sternocleidomastoid muscle have been reported. In this study, supernumerary clavicular heads of sternocleidomastoid muscle in a Korean female cadaver were bilaterally displayed. The observed supernumerary heads were classified as follows: one sterno-mastoid, one cleido-occipital and one cleido-mastoid on the right side, and one sterno-mastoid-occipital, four cleido-occipitals, and one cleido-mastoid on the left side. The sterno-mastoid and sterno-mastoid-occipital and the cleido-occipital made the superficial layer of the sternocleidomastoid muscle, while others made deep layer. We discussed clinical relevance and developmental basis of these muscular variations important for clinicians and anatomists.
Keywords: Development; Sternocleidomastoid; Superficial layer; Variation.