English: Principal hippocampal subdivisions in the marmoset (Callithrix jacchus). (A) Major hippocampal subdivisions in Giemsa-stained marmoset mid-septotemporal hippocampus. Arrows mark the boundaries between subdivisions at the level of the cell layer(s). (B) Definitions of the principal cell population in the marmoset mid-septotemporal hippocampus. (C) Complex hilar cytoarchitecture of the marmoset dentate gyrus that is common in non-rodent species. (D) Definitions of the regions that have been used to define CA3 and hilar cell populations within the dentate gyrus; 1: CA3 or CA3o (outer CA3, Houser et al., 1990), 2: reflected blade of CA3 (Lorente De Nó, 1934) or CA3h (used in this study; Lim et al., 1997; Ding and Van Hoesen, 2015) or CA3i (inner CA3, Houser et al., 1990) or CA4 (Rosene and Van Hoesen, 1987), 3: polymorphic cell layer (2+3: CA4 of Lorente De Nó, 1934), and 4: plexiform layer (Cajal, 1968), 5: dentate granule cells. Stratum radiatum (6) and stratum oriens (7) insert themselves superficial and deep to CA3h. The separation between CA3h and the hilar polymorphic layer is variable in different species and at different septotemporal levels. When the CA3h and the polymorphic cell layer merge, we cannot reliably distinguish CA3h cells from hilar polymorphic cells in Nissl-stained preparations. Scale bars: 250 μm.

From: Front. Neuroanat., 09 March 2016 | https://doi.org/10.3389/fnana.2016.00022 Taxonomic Separation of Hippocampal Networks: Principal Cell Populations and Adult Neurogenesis

R. Maarten van Dijk, Shih-Hui Huang, Lutz Slomianka and Irmgard Amrein