Fiber Analysis of the Optic and Cochlear Nerves of Small Cetaceans

Abstract

Cranial nerves of mammals contain relatively constant functional components (Ottoson, 1983). Comparative quantitative analysis of the optic and cochlear nerves in odontocetes may be significant for estimating the function potential of the visual and hearing systems in these highly specialized aquatic mammals. Jacobs and Jensen (1964), Jacobs et al. (1964), Korneliussen et al.(1965), Jacobs (1973), Morgane and Jacobs (1972), Jansen and Jansen (1969) and Dawson (1980) reported the fiber numbers of statoacoustic nerves and optic nerves of several odontocete species. Fiber size distribution of the optic nerve of Tursiops Truncatus was showed by Dawson et al. (1982). Fiber size distribution of statoacoustic nerve of Physeter catodon was reported by Jacobs and Jensen (1964). Data on cochlear nerve fiber analysis are provided recently by Gao and Zhou (1991) in Lipotes vexillifer, Neophocaena phocaenoides, and Sousa chinensis. Although these papers provided very useful data, further studies on fiber analysis of optic and cochlear nerves are needed for comparison among small cetaceans.