A transient adrenocortical zone present in some rodents at birth, most notably in mice, situated between the zona reticularis and the adrenal medulla; it degenerates in males with the secretion at puberty and in females during their first pregnancy; it slowly enlarges in unmated females after puberty and does not degenerate until middle age; the X zone appears to secrete no hormone.
Synonym: androgenic zone.
Misnomer for the foetal adrenal cortex of primates.
Synonym: foetal reticularis.
(05 Mar 2000)