The hippocampal formation (hippocampus and dentate gyrus), if traced backwards alongside the choroidal fissure of the descending horn of the lateral ventricle, is found to curve round the splenium of the corpus callosum and apparently to disappear. Actually, however, it is continued in very rudimentary form forwards along the upper surface of the corpus callosum, as a thin film of grey matter called indusium. This section (from a monkey’s brain) shows the hippocampal rudiment on either side of the mid-line. Below is the corpus callosum (C.C.) in transverse section, and above the longitudinal fissure between the medial surfaces of the cerebral hemispheres. Magnification X 70. 

Original card