White matter tracts of the deep cerebrum. The sagittal stratum is a polygonal white matter crossroad medial to the superior longitudinal fasciculus and lateral to the tapetum of the corpus callosum. The tapetum is directly lateral to the atria of the lateral ventricles. The sagittal stratum contains association fibers of the middle and inferior longitudinal fascicles and the inferior fronto-occipital fasciculus. The fornices are paired curvilinear paramedian structures just median to the lateral ventricles. The thalamus forms the lateral border of the third ventricle, and lies just medial to the internal capsule. (Image courtesy of AL Rhoton, Jr.)