Scanning electron microscopy of nerve fibers in the dog cochlea

The nerve fiber arrangement inside the organ of Corti in the dog was studied. Thick sections were cut serially from celloidin-embedded cochleas and observed with a scanning electron microscope (SEM). The nerve fibers in the organ of Corti were clearly exposed in sections cut in the horizontal plane. The arrangement of nerve fibers in the dog showed considerable difference from that of other species. The tunnel basilar fibers in the dog curved basalward, and took a long longitudinal course to form a broad bundle in the center of the tunnel floor. This bundle has not been found in adult animals of other species. Two distinct types of tunnel radial fibers, upper tunnel radial fibers and underpassing radial fibers, were recognized. The latter type of radial fibers ran beneath the bundle of basilar fibers, and seemed to be characteristic of the dog cochlea. From the morphological characteristics, these underpassing radial fibers were thought to be efferent in nature.