CN XII. Hypoglossal Nerve
The hypoglossal nerve as the name indicates can be found below the tongue. It is a somatomotor nerve that innervates all the intrinsic and all but one of the extrinsic muscles of the tongue. The neuronal cell bodies that originate the hypoglossal nerve are found in the dorsal medulla of the brain stem in the hypoglossal nucleus. This nucleus gives rise to axons that exit as rootlets that emerge in the ventrolateral sulcus of the medulla between the olive and pyramid. The rootlets come together to form the hypoglossal nerve and exit the cranium via the hypoglossal canal. The nerve passes laterally and inferiorly between the internal carotid artery and internal jugular vein. The twelfth cranial nerve travels lateral to the bifurcation of the common carotid and loops anteriorly above the greater horn of the hyoid bone to run on the lateral surface of the hyoglossus muscle. It then travels above the edge of the mylohyoid muscle. The hypoglossal nerve then separates into branches that supply the intrinsic muscles and three of the four extrinsic muscles of the tongue.