Graphs showing the total number of Tbr2+ cells in the ventricular zone (VZ), inner subventricular zone (iSVZ) and outer SVZ (oSVZ) within a 200 µm wide radial unit of macaque, ferret and rat somatosensory cortex.

<p>(<b>a–c</b>) There was a similar number of Tbr2+ cells in the iSVZ of each species, but macaque had a much larger number of Tbr2+ cells in the oSVZ. The stage of development is shown at the bottom of each graph, and the approximate cortical layer generated during each stage of development is indicated along the top of each graph. Legend indicates histological zones: VZ: blue; iSVZ: red; oSVZ: green.