substantia innominata

Defined on the basis of Nissl staining, the substantia innominata is a predominantly grey matter structure of the basal telencephalon whose position is described relative to the anterior commissure. Caudal to that commissure it lies deep to the globus pallidus and dorsal to the amygdala; rostral to it, the structure lies deep to the striatum, and this more rostral portion contains the basal forebrain nucleus. Its status was revised in the late twentieth century, when the region was resegmented on the basis of neurochemistry and connectivity to constitute the striatopallidal system. Under that scheme its caudal portion falls largely within the ventral pallidum and its rostral portion within the ventral striatum, so the older name and the newer parcellation describe overlapping but not identical territory.