Sagittal view of brainstem and cerebellum. Most of the brainstem and the cerebellum are contained within the posterior cranial fossa, which is bounded above by the tentorium cerebelli (not labeled) and tentorial notch, anteriorly by the clivus, and inferiorly by the foramen magnum. Superiorly in this image, the anterior commissure, located anterior to the column of the fornix, connects the right and left temporal lobes across the midline. Anterior to this is the lamina terminalis, a thin membrane that extends from the optic chiasm to the anterior commissure forming the anterior wall of the midline third ventricle. Anterior to this is the lamina terminalis cistern containing the anterior cerebral artery (not labeled). Below the lamina terminalis is the stalk of the pituitary gland with the gland resting in the sella turcica. The mammillary body is located on the inferior surface of the hypothalamus. The right oculomotor nerve emerges from the lateral wall of the interpeduncular fossa of the midbrain. The midbrain tegmentum contains the red nucleus and central tegmental tract, while the midbrain tectum includes the superior and inferior colliculi (corpora quadrigemina). Posterior to the midbrain is the quadrigeminal cistern, a dilation of the subarachnoid space between the splenium of the corpus callosum and superior surface of the cerebellum. The pineal gland and great cerebral vein are contained within it. The trochlear nerve emerges from the dorsum of the midbrain and wraps around the cerebral peduncles as it courses towards the lateral wall of the cavernous sinus. The trigeminal nerve leaves the anterolateral pons and crosses the petrous ridge of the temporal bone and expands as the Gasserian ganglion within Meckel's cave. The ophthalmic nerve courses into the lateral wall of the cavernous sinus inferior to the trochlear nerve as does the maxillary nerve, inferior to the ophthalmic. The abducens nerve leaves the pons at the pontomedullary junction anteriorly. It penetrates the clival dura and ascends and enters the cavernous sinus where it courses on the lateral surface of the internal carotid artery. This is seen because the body of the sphenoid has been drilled away. Anteroinferior to the sphenoid body is the nasal cavity. Posterior to the inferior turbinate is the opening of the Eustachian tube. (Image courtesy of PA Rubino)