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Anatomy Atlases: Illustrated Encyclopedia of Human Anatomic Variation: Opus III: Nervous System: Cranial Nerves and Ganglia: Spinal Accessory (CN XI) Nerve

Illustrated Encyclopedia of Human Anatomic Variation: Opus III: Nervous System: Cranial Nerves and Ganglia

Spinal Accessory (CN XI) Nerve

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD

Peer Review Status: Internally Peer Reviewed

The following variations in the origin, course, and branches of this nerve have been reported. The lower limit of origin from the anterior horn of the spinal cord may be as high as the third cervical segment (instead of the fifth or sixth segment) or as low as the first thoracic segment.

The nerve may exit from the subdural space below the first cervical nerve and reenter the space at a higher level. It may pass beneath (but never pierce) the sternocleidomastoid muscle.

The nerve sometimes supplies only the sternocleidomastoid muscle, in which case the trapezius is supplied by the third and fourth cervical nerves.

The nerve may provide a branch to the descendens cervicalis.

In about 70% of cases, the accessory nerve crosses anterior to the internal jugular vein, and in about 30% of cases, posterior.

It may pass through an annulus in the internal jugular vein.

Image 42


Balagura, S. and R.G. Katz. (1980) Undecussated innervation to the sternocleidomastoid muscle. A reinstatement. Ann Neurol. 7:84-85.

Kessel, F. (1928) Verlauf des Nervus accessorius durch eine Insel der Vena jugularis interna. Anat. Anz. 65:162-164.

Kopsch, F. (1908) Rauber's Lehrbuch der Anatomie des Menschen. Georg Thieme, Leipzig.

Laux, G., Guerrier, Y. and J. Olivier. (1950) Les rapports du spinal médullaire avec les deux premiers nerfs cervicaux. Assoc. Anatomistes Comptes Rendus 37:262-270.

Latarjet, A. (1948) Testut's Traité d'Anatomie Humaine, 9th ed. G. Doin & Cie., Paris.

Mirto, D. and E. Pulsateri. (1896) Sur les rapports anastomotiques entre le nerf accessoire et la vague. Arch. Ital. Biol. 1896:25:348.

Pearson, A.A., Sauter, R.W. and G.R. Herrin. (1964) The accessory nerve and its relation to the upper spinal nerves. Am. J. Anat. 114:371-391.

Piffer, C.R., Garcia, P.J. and J.C. Soares. (1980) Course of the external branch of the accessory nerve and its relations with the first portion of the internal jugular vein. Anat. Anz. 148:252-257.

Schaefer, E.A., Symington, J, and T.H. Bryce., Eds. (1915) Quain's Anatomy, 11th ed. Longmans, Green, and Co., London

Straus, Jr., W.L. and A.B. Howell. (1936) The spinal accessory nerve and its musculature. Q. Rev. Biol. 11:387-402.

Weigner, K. (1894) Bezeichnungen des Nervus accessorius zu den proximalen Spinalnerven. Anat. Hefte 17:549-587.

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