White matter tracts in deep cerebrum and brainstem.  The corpus callosum is the largest collection of commissural fibers in the brain and connects the cerebral hemispheres across the midline. In this view the thalamus has been dissected to expose the mammillothalamic tract, which arises from the mammillary body connecting it with the anterior thalamic nucleus.  Lateral to the thalamus, the internal capsule contains both ascending and descending fibers going to and from the cerebral cortex.  The fornix is a C-shaped bundle of fibers that extend from the hippocampus to the mammillary body, septal nucleus, and nucleus accumbens.  At its anterior end, the anterior commissure separates the fornix into pre-commissural and post-commissural fiber bundles.  The anterior commissure connects the two temporal lobes across the midline. Posterior to the thalamus, the epithalamus consists of the pineal gland, habenula, habenular commissure, and posterior commissure. Below the thalamus, the oculomotor nucleus has been dissected within the midbrain tegmentum. The medial longitudinal fasciculus is a fiber bundle connecting the nuclei of cranial nerves III, IV, and VI within the brainstem and is involved with coordinating eye movements. (Image courtesy of AL Rhoton, Jr.)