Prenatal development of the cochlear nerve in the albino rat

Twenty-eight prenatal (14 to 20 days) Wistar albino rats were studied with Cajal-de Castro's silver reduced stain. The histological sections were oriented in a parasagittal oblique plane, parallel to the cochlear root, in order to observe the origin, course and destination of the cochlear fibres in as few consecutive sections as possible. In all the prenatal days studied, the fibres arising in the first half coil of the cochlea (hook's bundle), show a different orientation than those of the other cochlear nerve fibres, which constitute the spiralized bundle, originating in the basal, medial and apical portions of the cochlea. The hook-bundle does not participate in the curling of the cochlear nerve and it describes a particular course. At first, its fibres are situated in a lateral position in the nerve when it is inside the internal auditive duct. Then, the hook-fibres take a postero-inferior position just at the entry of the bulbar cochlear nuclei region. Furthermore, we have seen no hook's afferents branching in the ventral cochlear nucleus, and it could be suggested that these fibres project directly to the superficial dorso-medial area of the postero-ventral cochlear nucleus.