A fan-shaped extrinsic tongue muscle that makes up most of the volume of the tongue. The genioglossus originates from the inside of the anterior base of the mandible. Most of its muscle fibers attach broadly along the intrinsic tongue muscles of the top of the tongue. Some of the lower genioglossal fibers attach along the body of the hyoid bone. The genioglossus pulls the tongue down and forward. It is innervated by cranial nerve XII (hypoglossal nerve).