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hypoglossal nerve[¦hī·pə¦gläs·əl ′nərv]
the 12th pair of cranial nerves. The hypoglossal nerve originates from the nerve cells that form its motor nucleus, which are located in the brain stem at the medulla oblongata. The appendages of the nerve cells unite in ten to 15 rootlets between the pyramid and the olive. Upon merging in a common trunk, they depart from the skull through the hypoglossal canal into the occipital bone. After leaving the skull, the hypoglossal nerve forms an arch and, at the anterior end of the hyoglossal muscle, branches into terminal branches, which innervate the musculature of the tongue. When a disorder of hypoglossal nerve exists, the corresponding half of the tongue becomes paralyzed, and the tongue muscles atrophy.