Abstract
1. The terminations of the primary trigeminal fibers were studied using Fink-Heimer technique in the rat. 2. Primary trigeminal afferents terminated in the superior and spinal trigeminal nuclei. In three layers of the spinal nucleus (the zonal, gelatinous and proper), no difference of the terminal density was recognized. Terminations to the reticular formation were found in a narrow portion of the lateral reticular formation along the column of the spinal nucleus. At the level of the motor trigeminal nucleus, the presynaptic terminals were recognized in the dorsomedial portion to the superior nucleus. There was no termination in the medial part of the reticular formation, nor terminals in the sensory trigeminal nucleus of the opposite side. A fiber boundle arise d from the mandibular subdivision terminated to the most rostral portion of the solitary nucleus. 3. The topographical organization in the trigeminal nucleus was placed with the dorsoventral direction. The mandibular subdivision occupied the most dorsally, the maxillar occupied the middle and the ophthalmic occupied the most ventrally. The mandibular and maxillar subdivisions took up very large area compared with the ophthalmic one. The same pattern as the dorsoventral direction in the trigeminal nuclei was found in the terminal area of the reticular formation neighbouring with the trigeminal nuclei. 4. In the rat, the above-mention e d topographical localization of the primary fibers did not clearly correspond to the terminal pattern . of the corticofugal fibers from S I and S II face areas reported in the previous paper. 5. It was suggested that cells of a peculiar type in the semilunar ganglion supply their axons to the solitary nucleus via the primary trigeminal nerve in order to conduct the gustatory impulse.
