The term ventral pallidum refers to a composite structure primarily of forebrain with arguable extension into the midbrain. It is part of the striatopallidal system, which is defined on the basis of neurochemistry and connectivity. It includes the portions of the globus pallidus and the substantia innominata located ventral to the anterior commissure; it extends into the olfactory tubercle and, in some respects, pars reticulata of the substantia nigra. Its boundary with the dorsal pallidum is indistinct in sections stained for Nissl substance ( Heimer-1995 ).