An anomaly in the nerve supply of the trapezius muscle.

Controversy surrounds the nerve supply to the trapezius muscle. We report a single specimen, from a series of dissections designed to study the intradural and peripheral course of the spinal part of the accessory nerve (sp.XI), in which the nerve failed to supply the trapezius muscle, whose supply came entirely from the cervical plexus. This provides anatomical support for the view that the supply from the cervical plexus may contain motor fibers and helps to explain why the sacrifice of the accessory nerve in radical neck dissection does not always produce complete paralysis of the trapezius muscle.