Lateral view of the midbrain. The cerebral peduncles are located anteriorly and consist of longitudinal fiber tracts traveling from the cerebral cortex to the brainstem and spinal cord. The oculomotor nerve (CN III) emerges from the interpeduncular fossa between the cerebral peduncles. The lateral mesencephalic sulcus extends from the medial geniculate body of the thalamus to the pontomesencephalic sulcus and separates the cerebral peduncle from the tegmental surface of the midbrain. Posteriorly, the midbrain tectum consists of the superior and inferior colliculi. The inferior brachium carries auditory afferent fibers from the inferior colliculus to the medial geniculate body of the thalamus.  The pineal gland is located in the midline above the superior colliculi, and several components of the thalamus, including the pulvinar, are visible superior to the midbrain.  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 at the pontomesencephalic junction. (Image courtesy of AL Rhoton, Jr.)