We made a thorough observation of the morphology and course of the lingual nerve (LN) and inferior alveolar nerve (IAN) to clarify their topographical relationships in the infratemporal fossa and in the paralingual area. Thirty-two Korean hemi-sectioned heads were dissected macroscopically and microscopically from a clinical viewpoint. On the 32 tracings on the radiograph, the average distance between the retromolar portion and the LN was 7.8 mm, and no case was found where the LN ran above the alveolar crest as passing along the mandibular lingual plate. The bifurcation of the LN and IAN was located around the mandibular notch, inferior to the otic ganglion in 66% of the cases, and a plexiform branching pattern of the mandibular nerve was observed in only two cases. The bifurcation spot of the LN and IAN was located 14.3 mm inferior to the foramen ovale and 16.5 mm superior to the tip of hamulus. Collateral nerve twigs from the LN to the retromolar area were observed in 26 cases (81.2%), with an average of one nerve twig. We observed four types of variations in terms of communication pattern. In four specimens, the mylohyoid nerve passed through the mylohyoid muscle and connected with the LN. In other four specimens, the IAN communicated with the auriculotemporal nerve. We also observed another type of variational communication between the IAN and the nerve to the lateral pterygoid (LPt); this was observed in only one specimen, and it could be predicted that motor innervation from the nerve to the LPt was transmitted via the mental nerve to the depressor anguli oris. Another type was observed where the IAN divided into two branches with the posterior branch being partially entrapped by the LPt muscle fibers.