rhombencephalic isthmus

[rŏm′bĕn-sə-fălĭk]
n.
  1. A narrow portion in the embryonic neural tube delineating the mesencephalon from the rhombencephalon.
  2. The anterior portion of the rhombencephalon that connects with the mesencephalon.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.