Locate the region of the vestibulocochlear nerve, at the junction of the brain stem, the pons, and the cerebellum. Counting from medial to lateral, the vestibulocochlear nerve is the third of six cranial nerves that enter the brain at this junction (Nieuwenhuys figure 17, page 22; Nauta page 164). To get a good view, you may have to move aside the basilar artery and its two offshoots, the spinal arteries. Do this gently, with a probe, and avoid poking or tearing the tissue. Since the vestibulocochlear nerve is small and delicate, it may not be present on your specimen. On the dorsal aspect of this section, observe the area just medial to the inferior cerebellar peduncle (a.k.a. the restiform body). This region contains the dorsal and ventral cochlear nuclei. Again on the ventral aspect (the side that includes the pons), locate two bulges on either side of the superior extent of the brain stem. These are the inferior olives. Just superior to these are two smaller bulges, the superior olives. As you learned in class, the superior olives help to localise low-frequency sounds by computing interaural phase differences.

From the midbrain, auditory signals go to the medial geniculate nucleus of the thalamus. The medial geniculate is small and rather nondescript, and therefore difficult to locate. It's just medial to the lateral geniculate nucleus, which you observed as part of your laboratory exercise on the gross anatomy of the visual system. The medial geniculate body projects to primary auditory cortex in the superior temporal gyrus, just below the Sylvian fissure. Locate the superior temporal gyrus on a coronal section.

Gently lift the spinal cord so and, if it hasn't already been cut horizontally, cut it now. Notice the butterfly-shaped grey matter surrounding the central canal. The longest extents of the `wings' of this butterfly shape are the dorsal horns, containing the substantia gelatinosa. This is the first synapse of somatosensory signals, and the entry point to the central nervous system. The surrounding white matter contains ascending and descending axons.

On a coronal section at the level of the mammillary bodies, locate the ventrobasal nucleus of the thalamus (Nauta page 255; Nieuwenhuys figure 35, page 41). This diagonal, oblong clump of grey matter is sandwiched between the mediodorsal nucleus of the thalamus and the white matter of the internal capsule. Between the ventrobasal nucleus and the mediodorsal nucleus are the intralaminar nuclei. The ventrobasal and intralaminar nuclei relay afferent somatosensory signals to the cerebral cortex.

On a section of cerebral cortex immediately posterior to the central sulcus, locate the postcentral gyrus. This is the most anterior portion of the parietal lobe, and is the location of somatosensory cortex.