Twelfth cranial nerve: The hypoglossal nerve. The twelve cranial nerves, including the hypoglossal nerve, emerge from or enter the skull (the cranium). The hypoglossal nerve supplies the muscles of the tongue. Paralysis of the hypoglossal nerve affects the tongue. It impairs speech (it sounds thick) and causes the tongue to deviate toward the paralyzed side. In time, the tongue diminishes in size (atrophies).