The genioglossus is a flat, fan-shaped muscle that originates from the superior mental spine of the mandible (chin bone) and inserts onto the undersurface of the tongue and the hyoid bone. Its main functions include extending, protruding, and depressing the tongue. The genioglossus muscle is innervated by the hypoglossal nerve (cranial nerve XII). Its contraction helps stabilize and enlarge the upper airway, particularly during sleep, and is implicated in obstructive sleep apnea.