The hippocampal formation develops on the medial wall of the hemispheres, dorsally to the choroid fissure and behind the interventricular foramen. It is also involved in the rotation of the hemispheres and so extends in posterior and inferior directions to form a C-shape. The pre-commissural and supra-commissural hippocampus (located in front of and above the corpus callosum) remain rudimentary. The retrocommissural hippocampus develops inside the temporal lobe into the cornu ammonis, dentate gyrus, subiculum and into the accompanying nerve fibres. It rolls up and thereby forms the hippocampal sulcus that runs dorsally and parallel to the choroid fissure.