The spinal root of accessory nerve (or part) is firm in texture, and its fibers arise from the motor cells in the lateral part of the anterior column of the gray substance of the medulla spinalis as low as the fifth cervical nerve.

Passing through the lateral funiculus of the medulla spinalis, they emerge on its surface and unite to form a single trunk, which ascends between the ligamentum denticulatum and the posterior roots of the spinal nerves; enters the skull through the foramen magnum, and is then directed to the jugular foramen, through which it passes, lying in the same sheath of dura mater as the vagus, but separated from it by a fold of the arachnoid.

In the jugular foramen, it receives one or two filaments from the cranial part of the nerve, or else joins it for a short distance and then separates from it again.

As it traverses the Sternocleidomastoideus it gives several filaments to the muscle, and joins with branches from the second cervical nerve.

This article incorporates text in the public domain from page 913 of the 20th edition of Gray's Anatomy (1918)