The globus pallidus is characterized by a high iron content and the distribution of the ferric iron in the rat brain provides evidence that globus pallidus extends rostroventrally below the anterior commissure and into the olfactory tubercle. The extension of the globus pallidus into the olfactory tubercle is consistent with the notion of the ventral striatum,14 in the sense that it provides for an expected close proximity between the striatum and the globus pallidus throughout the dorsoventral extent of the corpus striatum. The distribution of enkephalin, and of acetylcholinesterase- and succinate dehydrogenase-positive neurons is also consistent with an extension of the ventral part of globus pallidus to the base of the forebrain in the rat. Since part of the ventral pallidum corresponds to a region that is usually referred to as the subcommissural part of the substantia innominata, it seems reasonable to restrict the term substantia innominata to the more caudally-located sublenticular part of the substantia innominata.