Each hemisphere possesses a lateral ventricle, which is lined with a layer of ependyma and filled with cerebrospinal fluid (CSF). The ventricle has a body located in the parietal lobe, and horns, the anterior, posterior and inferior horns, which extend into the frontal, occipital and temporal lobes respectively. The body of the ventricle has a floor, roof, and a medial wall. The body of the caudate nucleus forms the floor of the ventricle, and the lateral margin of the thalamus and the inferior surface of the corpus callosum form the roof.
The basal nuclei or ganglia are masses of gray matter lying inside each cerebral hemisphere. These masses are the amygdaloid nucleus, claustrum, and the corpus striatum.
The corpus striatum lies lateral to the thalamus and is divided phylogenetically into the neostriatum, which consists of the caudate nucleus and the putamen, and the paleostriatum, which consists of the globus pallidus. The caudate nucleus and the putamen are separated almost completely by a band of fibers called the internal capsule. The caudate nucleus has a large head and a tail, rather like a tadpole, and the tail ends in the amygdaloid nucleus in the temporal lobe. The globus pallidus lies medial to the putamen, and consists of medial and lateral segments.
The putamen and globus pallidus are sometimes referred together as the lentiform nucleus, although in more modern textbooks the term lentiform is being disregarded as archaic terminology. The caudate nucleus lies laterally to the lateral ventricle and to the thalamus.
The corpus striatum has important connections with the substantia nigra, thalamus and the subthalamus. The major afferent inputs to the corpus striatum are from the substantia nigra, the thalamus and the cerebral cortex. Nigrostriatal fibers are dopaminergic, and have both excitatory and inhibitory effects. Degeneration of this system results in Parkinson’s disease. The thalamostriatal projections arise in the intralaminar nuclei of the ipsilateral thalamus. The corticostriatal afferents are extensive; there are afferents from motor areas of the frontal lobe to the putamen. Fibers from cortical association areas project to the caudate nucleus. The most prominent white matter (see also next spread) consists of the association and the commissural fibers connecting the corresponding regions of the hemispheres.