The optic nerve of the Mallard duck: Fiber‐diameter frequency distribution and physiological properties

A correlative study of the anatomy and physiology of the axons of the optic nerve of the Mallard duck was carried out. The principal findings were: Electronmicroscopy used in conjunction with phase contrast microscopy showed the nerve to have a fiber spectrum ranging from 0.3 μ to 6.0 μ with a mode at 1.15 μ. No unmyelinated axons were found. The cross‐sectional area of the nerve was estimated to be 4.38 mm 2 ; assuming a mean fiber density of 350,000 fibers/mm 2 , the total number of axons in the nerve was estimated to be about 1,500,000. The conduction velocities of the fibers were found to range from 21 m/sec to about 3 m/sec. Different recovery cycles were found for each of the different compound action potentials. Using a graphical method, a good correlation could be established between the fiber‐size spectrum and the configuration of the compound action potential.