This section is slightly anterior to Section 9. The optic chiasm is still visible at the base of the brain, and the lateral olfactory tract is prominent ventral and laterally, overlying the olfactory cortex. The stria medullaris thalami lies slightly offset from the dorsal midline, and is cut through obliquely. The corpus callosum and fornix are both large fiber bundles at this level. The internal capsule forms a stub at the medial edge of the caudate.
This section has three prominent white matter bundles, almost in parallel. Dorsal most is the corpus callosum, overriding the septal nuclei. Below the septum is the anterior commissure, which is traveling mainly medial-lateral at this level, and therefore is prominent in the coronal section plane. The optic nerves and their crossing in the optic chiasm can be seen at the base of the brain. The lateral olfactory tract is visible, but slightly reduced in size (relative to sections 12 and 13), since fibers have started to terminate in the piriform cortex.
This level is dominated by the basal ganglia and overlying cerebral hemispheres. The cortical white matter consists of incoming and outgoing fibers, and interhemispheric fibers crossing in the corpus callosum. Diffusely spread fibers in the midline, below the corpus callosum, correspond to the precommissural fornix, containing fibers from the hippocampus traveling to the septum and nucleus accumbens. The anterior commissure is prominent as two “spots,” resulting from a cross sectional cut through fibers that are traveling largely in the anterior-posterior direction. The lateral olfactory tract is located at the ventral surface.
With this section, the series has reached the far anterior level of the brain, in front of the corpus callosum and in front of the basal ganglia. The dorsal part of the section, above the rhinal fissure, contains frontal cortex. At this most anterior tip, there is no longer a white matter core, and the section is cutting tangentially through the cortical gray matter. Olfactory areas are located below the rhinal fissure. The large white matter tracts, lateral and medial, correspond to olfactory nerve fibers. The lateral tract continues posteriorly, to terminate within the piriform cortex.
