Post‐natal development and maturation of the nerve fibers of the central nervous system

Young ( '45 ; Vizoso and Young, '48) has advanced a theory concerning the maturation of peripheral nerve fibers based on the relation of internodal length and fiber diameter. In peripheral nerves, there is a direct correlation between internodal length and fiber diameter, the largest fibers having the longest interannular segments. Young believes that the linear relationship between internodal length and fiber diameter found in the adult results from the fibers which will ultimately become the largest, being the first to medullate, and their internodes are therefore stretched further by growth after their formation. There is also a linear relationship between internodal length and fiber diameter in the central nervous system (Hess and Young, '49, '52). It was decided to determine if there is a relationship between the ultimate fiber size and time of myelination in the fibers of the central nervous system, in order to compare their course of development with the fibers in peripheral nerves.