G, Enlarged view of the lentiform nucleus and amygdala. The extreme capsule separates the claustrum and insula, and the external capsule separates the claustrum and lentiform nucleus. The lateral medullary lamina separates the putamen from the outer segment of the globus pallidus and the medial medullary lamina separates the medial and lateral segments of the globus pallidus. H, The cross section of the right hemisphere has been extended behind the cerebral peduncle and across the terminal part of the optic tract and the lateral and medial geniculate bodies. The section of the midbrain extends through the cerebral peduncle and substantia nigra. The inferior choroidal point, the lower end of the choroidal fissure and attachment of the choroid plexus in the temporal horn, is located just behind the head of the hippocampus. The oculomotor nerve arises on the medial side of the cerebral peduncle. I, The thalamus has been removed on the right side. The choroid plexus is attached along the choroidal fissure located between the fornix and thalamus. The tail of the caudate nucleus courses in the roof of the temporal horn above the hippocampus. J, The axial section on the left side has been extended through the midportion of the cerebral peduncle and the coronal section through the thalamus. The thalamus forms the floor of the body of the ventricle. At the midthalamic level, the lentiform nucleus is reduced markedly in size as compared with the more anterior levels where it forms a prominent part of the deep gray matter. As the cross section moves posteriorly, the thalamus forms a progressively greater part of the central core of the hemisphere located between the insula and ventricular surface. The temporal horn is located below the lentiform nucleus. The posterior segment of the uncus faces the cerebral peduncle. The bulb of the corpus callosum overlying the forceps major and the calcar avis overlying the calcarine sulcus are exposed in the medial wall of the atrium. K, All of the right thalamus and the medial part of the left thalamus have been removed to expose the crural, ambient, and quadrigeminal cisterns. The midbrain forms the medial wall and the parahippocampal and dentate gyri form the lateral wall of the ambient cistern. The crural cistern is located between the posterior uncus segment and the cerebral peduncle. The left lateral geniculate body has been preserved. The optic radiations arise in the lateral geniculate body and pass laterally above the temporal horn. L, Enlarged view. The body of the fornix is in the lower medial part of the wall of the body of the lateral ventricles. The crus of the fornix forms part of the anterior wall of the atrium and the fimbria sits on the upper surface of the hippocampus in the floor of the temporal horn. The amygdala fills most of the anterior segment of the uncus and the hippocampal head extends into the posterior segment. The posterior commissure, aqueduct, and mamillary bodies are exposed in the walls of the third ventricle. The anterior part of the third ventricular floor between the mamillary bodies and the infundibular recess is quite thin and is the site frequently selected for a third ventriculostomy. (Images courtesy of AL Rhoton, Jr.)