Telencephalon

The telencephalon is the anterior subdivision of the embryonic forebrain and the corresponding territory of the mature brain. Its derivatives include the cerebral hemispheres, with cerebral cortex, deeper basal ganglia and associated structures, including the olfactory bulbs. It is an anatomical and developmental division, rather than a name for one behavior or one type of neuron.^[ref]

The forebrain divides into telencephalon and diencephalon. These names should not be treated as interchangeable: the thalamus belongs to the diencephalon, whereas cerebral cortex belongs to the telencephalon. The large cerebral hemispheres can cover deeper regions in a surface view, so apparent position in a photograph alone is a poor guide to developmental membership.^[ref]

A practical example is classifying structures in a section through the brain. A region of cerebral cortex and a deep basal ganglia nucleus can both be telencephalic even though one is superficial and the other deep. Conversely, an adjacent thalamus is diencephalic. This distinction makes the telencephalon useful as a map of related structures without assuming that everything within that map performs the same computation.