The microscopic and ultrastructural anatomy of the spiral ganglia and osseous spiral laminae (OSL) of the guinea pig were studied using the transmission and scanning electron microscopes. The nerve and vascular elements within the spiral ganglia and OSL are surrounded by distinct perineural and perivascular spaces maintained by a loose meshwork of cells and connective tissue fibers. The connective tissue cells are fibers within the OSL and spiral ganglia are distinctly different from the arachnoid-like reticular cells and elastin fibers of the modiolus described in an earlier study. The present experiment demonstrates a pathway between the perineural spaces of the modiolus, spiral ganglia, and OSL. The perineural spaces of the modiolus were previously shown to communicate with the subarachnoid space; therefore, perineural communication from the cerebrospinal fluid to the perilymph via this route is likely. Using mircosphere tracers injected intrathecally, this communication route between the subarachnoid space and scala tympani was further defined. The tracer experiment suggests that the perineural spaces within the internal acoustic meatus, modiolus, spiral ganglia, and OSL are normally patent and do not represent artifacts induced during tissue processing.