basal ganglia [Gk, basis + ganglion, knot] , areas of gray matter, largely composed of cell bodies, within each cerebral hemisphere. The most important are the caudate nucleus, the putamen, the substantia nigra, the subthalamic nucleus, and the pallidum. The basal ganglia are surrounded by the rings of the limbic system and lie between the thalamus of the diencephalon and the white matter of the hemisphere.
