Internodal length of nerve fibres in dorsal roots of cat spinal cord.

Internodal length of myelinated fibres adjacent to the borderline between the central and the peripheral nervous system in S1 dorsal roots of cats during development was determined. Numerical data was obtained from reconstructions of individual nerve fibres as recorded on scale using several long series of consecutive sections. At the initiation of myelination (foetus 60 days), the internodal length was approximately 100 microns. During the period 7-30 days, internodes shorter than 50 microns occurred. In older cats the shortest internodes were about 100 microns in length. In the adult cat a linear relationship between axon diameter and internodal length was not found.