[TA] a thin layer of gray matter on the dorsal surface of the corpus callosum in which the medial and lateral longitudinal striae lie embedded. The indusium griseum is a rudimentary component of the hippocampus, continuous caudally around the splenium of the corpus callosum with the fasciolar gyrus, a slender convolution in turn continuous with the dentate gyrus of the hippocampus; rostrally the indusium griseum curves around the genu and rostrum of the corpus callosum and extends ventralward to the olfactory trigone as the tenia tecta or rudimentum hippocampi, hidden in the depth of the posterior parolfactory sulcus that marks the anterior border of the subcallosal gyrus or precommissural septum. SYN: supracallosal gyrus.