cauda equina

[ĭ-kwīnə]
n.
  1. The bundle of spinal nerve roots running through the lower part of the subarachnoid space within the vertebral canal below the first lumbar vertebra.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.