Posterior oblique view of the midbrain. The posterior temporal and occipital lobes of the cerebrum have been removed to reveal the posterior aspect of the midbrain, thalamus, and epithalamus. The pineal gland and habenula are components of the epithalamus, which is located superior to the midbrain and medial to the thalami. The pulvinar are large nuclei forming the posterior aspect of the thalamus. The third ventricle separates the two thalami with the exception of a small variable mass of gray matter called the massa intermedia. The superior and inferior colliculi comprise the tectum of the midbrain. The brachium of the inferior colliculus carries auditory afferent fibers from the inferior colliculus to the medial geniculate nucleus of the thalamus. The trochlear nerve (CN IV) emerges from the dorsal aspect of the midbrain below the inferior colliculus and courses around the lateral aspect of the brainstem. The posterior cerebral artery also courses around the lateral aspect of the brainstem to supply the occipital lobes of the cerebrum. Inferior to the midbrain a portion of the cerebellar vermis has been resected to reveal the superior cerebellar peduncle which projects from the deep cerebellar nuclei to the midbrain and thalamus. (Image courtesy of AL Rhoton, Jr.)