Scarpa's ganglion in the rat and guinea pig.

This study describes the location of the cell-bodies of the primary afferent vestibular neurons (Scarpa's ganglion) in relation to the internal auditory meatus of the temporal bone in rats and guinea pigs. In these species the internal auditory meatus consists of three distinct opening or pores (foramina) into the temporal bone. The superior division of the vestibular nerve emerges from the dorsal-most foramen and the pars superior of Scarpa's ganglion is visible as a ridge or 'frill' which occupies the foramen. The inferior division of the vestibular nerve emerges from the cochlear foramen and the cell-bodies of the pars inferior of Scarpa's ganglion lie in the dorsal and rostral area of this foramen. A thin layer of cell-bodies, the isthmus ganglionaris, stretches across the bony transverse crest separating these two foramen. In the newborn rat Scarpa's ganglion is an ovoid structure lying within the cranial cavity.