STRUCTURAL MATURATION OF STATO-ACOUSTIC NERVE IN CAT

The maturation of the stato-acoustic nerve in the cat was studied by light microscopy and EM from the fetal stage to the adult. Measurement of the outer diameter of the fibers and the study of the myelination process revealed that myelination began earlier for the vestibular nerve than for the cochlear nerve: by the 53rd day of gestation 64% of the vestibular fibers already passed the promyelin stage; for the cochlear nerve this promyelin stage began for the majority of fibers on the 57th gestation day. Afterward maturation proceeded more rapidly for the cochlear nerve. In the case of both nerves, maturation is still incomplete at 2 mo. of age. Concerning the relationship between the thickness of the myelin sheath and the axoplasmic diameter, there is already a good correlation by the 57th day of gestation in the vestibular nerve; it appears several days after birth in the cochlear nerve.