Axon numbers in rat oculomotor, trochlear and abducent nerves.

In the rat oculomotor, trochlear and abducent nerves, large and small classes of myelinated fibres can be clearly distinguished. Small myelinated axons comprise a larger proportion of the total in the oculomotor nerve than in the other two. Mean counts enable the myelinated preganglionic parasympathetic outflow of the oculomotor nerve to be estimated at 216 fibres. Unmyelinated fibres are most frequent in the abducent nerve and least frequent in the trochlear nerve.