The innervation of the trapezius muscle: a cervical motor supply.

Controversy surrounds the nerve supply to the trapezius muscle. Anatomical studies have revealed independent connections from the C3 and C4 roots of the cervical plexus directly to the trapezius muscle. The objective of this study was to determine if these nerve bundles contain motor fibres and thus constitute an additional motor supply to trapezius. From a study of 32 cadavers, a representative example was chosen. Using a high powered operating microscope it was seen that such fibres were traceable to the ventral roots of the spinal cord. It is generally accepted that fibres in the ventral roots of the spinal cord are motor and thus, in this specimen, the trapezius muscle appeared to receive a direct motor supply from the cervical plexus independent of the accessory nerve.