10. Supplement III: Neuroanatomy Considerations

The laminar neuropil in the phylogenetically older parts of the cerebrum is called allocortex (Mountcastle (ed), Medical physiology, C V Mosby, St Louis, 1974, [1]. Examples include the prepyriform cortex (paleocortex), the hippocampus (archicortex) and parts of the perirhinal and entorhinal cortex (mesocortex) Maclean, The triune brain. Plenum, New York, 1969, [2]; the olfactory bulb is here included as allocortex owing to its similarity to the others in topology and phylogenetic derivation, though not all anatomists accept this taxonomy. Generically allocortex has three layers with differing subdivisions specific to each area. Layer I also called marginal lies under the bounding pial membrane and has input axons and the dendritic trees on which they synapse. Layer II has the cell bodies, often with triangular shapes giving the name pyramidal cells (mitral cells in the bulb). Layer III has output axons with recurrent side branches called collateral branches that synapse on interneurons called stellate cells (internal granule cells in the bulb) but mainly on other pyramidal cells.