stratum spongiosum

[spŏn′jē-ōsəm]
n.
  1. The middle layer of the endometrium, formed chiefly of dilated glandular structures and flanked by the stratum compactum on the luminal side and by the basal layer on the myometrial side.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.