With ventricular landmarks in mind, return to the the brain stem. Identify the various brain stem components on a hemisected brain. (Figure 7-12) See how many can be found on the whole brain. (Figure 7-3)

The inferior end of the brain stem is called the medulla. It begins at the inferior border of the cerebellum (your specimen may have a small amount of spinal cord inferior to the medulla). It runs superiorly to the prominent anterior, inferior pontine sulcus . (Figure 7-8)

The pons is the next most superior brain stem structure. Running superiorly from the inferior pontine sulcus it's characterized anteriorly by bulging massive transversely running fibers. The pons is limited superiorly by yet another transverse sulcus, the superior pontine sulcus . (Figure 7-8)

Moving more superiorly the next brain stem structure we encounter is the midbrain (mesencephalon). The midbrain extends from the superior pontine nucleus to an area just inferior to the paired mammillary bodies of the diencephalon. Look for the mammillary bodies just lateral to the midline. (Figure 7-3)

The last and superior most brain stem structure is the diencephalon. The diencephalon is a paired structure lying on either side of the third ventricle. So the view we have of the diencephalon from a hemisected brain is really its medial surface. The diencephalon is subdivided into a superior thalamus and an inferior hypothalamus. Look for the shallow groove on the lateral wall of the third ventricle that separates these two parts of the diencephalon, the hypothalamic sulcus .

The thalamus is bounded superiorly by the floor of the lateral ventricle, inferiorly by the hypothalamic sulcus, anteriorly by the interventricular foramen and medially by the third ventricle. The thalamus also forms the superior part of the lateral wall of the third ventricle.

The hypothalamus is bounded superiorly by the hypothalamic sulcus, inferiorly by the mammillary bodies, anteriorly by the optic chiasm. It forms the floor and inferior part of the lateral wall of the third ventricle.

See if you can now locate the mammillary bodies and the infundibulum or stalk of the pituitary gland (hypophysis).

Using a whole brain, now see if you can find some of the cranial nerves that emerge from the brain stem. If you're lucky, you can identify the stubs of cranial nerves IX, X, XI and XII as they emerge from the lateral surface of the medulla. Cranial nerves VI, VII and VIII emerge near the inferior end of the pons in the inferior pontine sulcus, while cranial nerve V emerges on the superior lateral surface of the pons. Cranial nerves III and IV emerge near the superior boundary of the pons at the superior pontine sulcus. Also emerging from the lateral superior pontine sulcus, find the optic tracts, optic chiasm and optic nerves. Just posterior to the optic chiasm locate the infundibulum and the more posteriorly placed mammillary bodies. You should also be able to see the olfactory tracts.