accessory phrenic nerve

n.
  1. Any of the accessory nerve strands that arise from the fifth cervical nerve, often as branches of the nerve to the subclavius, and pass downward to join the phrenic nerve.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.