Fig. 2. Scattered Pdgfra⁺ cells spread into the cerebral cortex in lateral-to-medial and ventral-to-dorsal directions. (A-C) Coronal sections through the neocortex at different ages, hybrized in situ with a probe for Pdgfra. (A) At E14.5, there are no Pdgfra⁺ cells in the developing cortex. (B) By E17.5, intensely labelled Pdgfra⁺ cells are present within the developing cortical plate and presumptive sub-cortical white matter at the lateral margin of the cortex as well as the medial cortex (arrowheads in B). (C) By E20.5, there are numerous Pdgfra⁺ cells in the cortex, especially in the sub-cortical white matter. At all stages, Pdgfra is also expressed by the meninges and skull.