The hypoglossal nerve (CN 12) descends from the cranium and crosses the internal carotid artery above the bifurcation It It innervates the hyoglossus, thyrohyoid, and genioglossus muscles
Hypoglossal nerve (CN 12) descending between internal jugular and internal carotid artery before crossing artery to innervated tongue muscles (illus. courtesy Wikipedia)
Injury to the hypoglossal presents in paralysis of one side of the tongue, so that when the patient sticks his tongue out, the tongue deviates toward the damaged nerve because of unopposed action of the contralateral (opposite) genioglossus.
This injury is most common after carotid endarectomy and is the reason why surgeons always ask these patients to stick their tongue out when they have recovered from anesthesia. Most typically, if this injury occurs it is transient as it is usually related to retractor placement and the deviation will resolve over days to weeks.
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