A Litre and a Half of Brains*: Contemporary Survey in Electrophysiology

VI. Cerebral Cortex 

1. Hippocampal Formation.—  A. Anatomical Facets: Long before modern microrecording was devised, details of hippocampal architecture had been worked out (Ramon y Cajal⁴⁴⁵; Lorente de Nó³⁶³). The hippocampal formation is a modified 3-layer pallium rolled into the lateral ventricle from surface cortex along the line of the rhinal fissure. An extension of the subcortical white matter of exposed cortex wraps itself about the ventricular surface of the roll—that through which recording electrodes penetrate into the cellular interior—as a thin sheet of white matter called alveus. The efferent fibers of alveus arise from hippocampal neurones, a modification of the usual cortical pyramids. Somata lie closely packed in a layer of restricted width. Axons pass through alveus and fimbria and into fornix forming the principal outgoing path of the hippocampus. After coursing medially and anteriorly the fornix enters the septum to follow a recurved route to its