root filament

n.
  1. Any of the small individual fiber fascicles into which the roots of each spinal nerve and several of the cranial nerves divide in a fanlike fashion before entering or leaving the spinal cord or brainstem.nerve rootlet
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.