Absence of cortical fiber tracts in Neurod2/6 double mutants. Dorsal views of freshly dissected brains at P1 show the presence of major brain areas in Neurod2−/−;Neurod6−/− double mutants (DKO; C), Neurod2+/−;Neurod6−/− (A), and Neurod2−/−;Neurod6+/− (B) controls. Hematoxylin and eosin histology of horizontal (A–C) and coronal (D–F) paraffin sections (5 μm) from P1 brains reveal complete absence of AC and CC in double mutants (marked by brackets), whereas the HC is normally developed (C, F). The AC is already absent in brains from Neurod2−/−;Neurod6+/− mutants (E) but present in Neurod2+/−;Neurod6−/− (D) mutants. Scale bars, 1 mm. IC, Internal capsule.