Magnified view of the base of the cerebrum. The uncus is the medial prominence of the parahippocampal gyrus separated from the crus cerebri of the midbrain by the crural cistern. Prominent midline structures visible here are the posterior perforated substance within the interpeduncular (intercrural) cistern surrounded laterally by the oculomotor nerves and mammillary bodies anteriorly. The pituitary infundibulum is just inferior to the optic chiasm. Medial to the uncus and lateral to the optic tracts is the anterior perforated substance. The olfactory tract courses along the base of the frontal lobe and divides into two striae (the medial and lateral olfactory striae) just anterior to the anterior perforated substance. Posterolateral to the midbrain, prominences of the thalamus include the medial geniculate nucleus and the pulvinar. The pulvinar is the largest thalamic nucleus and contains strong connections with the visual cortex. (Image courtesy of AL Rhoton, Jr.)