The mesencephalic trigeminal nucleus (Vme) neurons are primary sensory neurons transmitting orofacial proprioceptive sensation. The neurons innervating the periodontal ligaments and the masticatory muscles are intermingled with each other in the caudal part of the Vme. After fluorescent tracers, propridium iodide and bisbenzimide were applied to the inferior alveolar nerve and the masseter nerve on the same side of the rat, and a doubled-labeled neurons were observed in ipilateral Vme, mainly in the caudal part, and a few in the middle, rostral part. This reflects simultaneous innervation of both the periodontal ligaments and the masseter spindles by collaterals of peripheral process of single Vme neurons.