of many interneurons, including axo-axonic cells, bistratified cells, and radial trilaminar cells. stratum lucidum (str. luc.) is one of the thinnest strata in the hippocampus and only found in the ca3 region. mossy fibers from the dentate gyrus granule cells course through this stratum in ca3, though synapses from these fibers can be found in str. pyr. stratum radiatum (str. rad.), like str. oriens, contains septal and commissural fibers. it also contains schaffer collateral fibers, which are the projection forward from ca3 to ca1. some interneurons that can be found in more superficial layers can also be found here, including basket cells, bistratified cells, and radial trilaminar cells. stratum lacunosum (str. lac.) is a thin stratum that too contains schaffer collateral fibers, but it also contains perforant path fibers from the superficial layers of entorhinal cortex. due to its small size, it is often grouped together with stratum moleculare into a single stratum called stratum lacunosum-moleculare (str. l-m.). stratum moleculare (str. mol.) is the most superficial stratum in the hippocampus. here the perforant path fibers form synapses onto the distal, apical dendrites of pyramidal cells. hippocampal sulcus (sulc.) or fissure is a cell-free region that separates the ca1 field from the dentate gyrus. because the phase of recorded theta rhythm varies systematically through the strata, the sulcus is often used as a fixed reference point for recording eeg as it is easily identifiable. dentate gyrus the dentate gyrus is composed of a similar series of strata: the polymorphic layer (poly. lay.) is the most superficial layer of the dentate gyrus and is often considered a separate subfield (as the hilus). this layer contains many interneurons, and the axons of the dentate granule cells pass through this stratum on the way to ca3. stratum granulosum (str. gr.) contains the cell bodies of the dentate granule cells. stratum moleculare, inner third (str. mol. 1/3) is where both commissural fibers from the contralateral dentate gyrus run and form synapses as well as where inputs from the medial septum terminate, both on the proximal dendrites of the granule cells. stratum moleculare, external two thirds (str. mol. 2/3) is the deepest of the strata, sitting just superficial to the hippocampal sulcus across from stratum moleculare in the ca fields. the perforant path fibers run through this strata, making excitatory synapses onto the distal apical dendrites of granule cells. an up-to-date knowledge base of hippocampal formation neuronal types, their biomarker profile, active and passive electrophysiological parameters, and connectivity is supported at the hippocampome website.