The double omohyoid muscle in humans: report of one case and review of the literature.

An anomalous muscle was found in the right anterior cervical region of a 68-year-old Japanese man. The muscle was investigated anatomically, with special reference to its supply. Few such reports are available. The anomalous muscle arose from the upper margin of the scapula as an aponeurotic sheet, ran medialocranialward and separated into the superficial and profound fasciculi at the lateral edge of the sternohyoid muscle. The former fasciculus was inserted into the lower border of the hyoid bone without fusing with adjacent muscles, or as an independent fasciculus. Meanwhile, the latter fasciculus incompletely fused with the lateral portion of the sternohyoid muscle. This muscle was supplied from its posterior surface and the upper edge by two slender nerves from the ansa cervicalis (roots of origin: C1, C2 and C3). Based on the nerve supply and a review of the literature, the muscle is discussed in terms of its true nature and its mechanism of formation. As a result of the investigation, this muscle is assumed to be a vestigial structure in humans reduced from the M. episterno-cleido-hyoideus sublimis (Fürbringer), which is observed in lower types of vertebrates (reptilies, etc.).