Laminar distribution of neuronal (A,A′), glial (B,B′,C,C′), synaptic (D,D′) and extracellular matrix (ECM) markers (E,E′) in the neocortical subplate (SP) during the trilaminar organization phase, shown on sections of 23‐ (E′), 24.5‐ (C′) and 25‐ (A′,B′,D′) postconceptional weeks (PCW) old brains. Neuroserpin neurons (A) are concentrated in the cortical plate (CP) and superficial SP (sSP). GFAP architecture (B,C) shows gradual changes in GFAP‐reactive cells from sagittal strata to CP. Note the presence of regularly aligned radial glia fibers in the intermediate portion of the subplate (marked with 2 on C). (C1,C2,C3) Differences in glial architecture of sSP (marked with 1 on C), iSP (marked with 2 on C) and dSP (marked with 3 on C). Synaptic markers show characteristic reactivity in sSP and CP (D) in concordance with distribution of the synapses. ECM marker fibronectin (E,E′) is expressed throughout the SP, with the highest concentration in the sSP of frontal and medial occipital cortex. Rectangles on (A′,B′,C′,D′) correspond to the positions of enlarged images below them. Numbers 1, 2, 3 on (C) correspond approximately to the positions of enlarged (C1,C2,C3). CC, corpus callosum; dSP, deep SP; iSP, intermediate SP; MZ, marginal zone. Scale bars: 500 μm (A–E); 50 μm (C1–C3).