Central projections of the spiral ganglion of the squirrel monkey

Abstract For establishing the relationships of the central projections of the spiral ganglion with the cytoarchitectural regions of the cochlear nuclear complex in a primate species, 23 squirrel monkeys, Saimiri sciureus were utilized. Restricted lesions of the cochlea were confirmed histologically and the resulting degeneration was traced to the cochlear nuclei in sections prepared with Nauta (′57) and Fink‐Heimer (′67) technics. By following the course of degeneration, the cochlear root fibers can be seen to bifurcate into ascending and descending branches. The ascending branches from the apical through basal turns of the spiral ganglion terminate in a rostro‐lateral to caudo‐medial gradient in the anteroventral cochlear nucleus. The descending branches from the apical through basal segments of the spiral ganglion terminate in a ventral to dorsal pattern in the posteroventral and dorsal cochlear nuclei. Ascending branches terminate chiefly on large and small spherical cells and globular cells in the anteroventral region. Terminals of descending branches are associated with globular, multipolar and octopus cells of the posteroventral nucleus and cells of the central and granular layers of the dorsal cochlear region.