The projections of the medial geniculate complex within the sylvian fissure of the rhesus monkey

The projection pattern of the medial geniculate complex (GM) of the rhesus monkey is studied using silver impregnation technique. The results are summarized as follows: 1. (1) Only anterior part of the parvocellular subdivision of the medial geniculate (GMpcA) projects to the auditory koniocortex (primary auditory area - A _I. The anterior GMpcA projects posteriorly in konicortex while the posterior GMpcA projects more anteriorly. The medial portion of GMpcA has connection to medial koniocortex while lateral GMpcA projects more laterally. 2. (2) The posterior portion of the parvocellular medial geniculate (GMpcP) sends projections mainly to the rostal parakoniocortex - 'auditory association area'. 3. (3) The projections to the second auditory area (A_II) originate either from medial GMpcA or from GMmc (magnocellular portion of the medial geniculate nucleus). 4. (4) No specific projections from the suprageniculate subdivision (SG) of the medial geniculate complex to either A_I and A_II or to the remainder of the temporal operculum were found. The possibility of such projections to the insula and the parietal operculum cannot be excluded from the present investigation. 5. (5) GMmc may send projection to the retroinsular parietotemporal cortex (ReIpt), which on anatomical ground can be homologized to the vestibular area of cat. 6. (6) Geniculocortical afferents terminate mainly in and around cortical lamina IV. These terminations reach the greatest density in koniocortex.