Signals derived from the mNEc records. A. I-MI signals. Each value corresponds to the distance between two adjacent mNEcs. B. Mitotic density signals. Each value corresponds to the density of mNEcs (number of mNEcs/100 μm2) in successive spatial windows along the D-V axis (window length = mean I-MI length). C. Binary signals. Represent the mNEcs distribution as stochastic point process. “1 s”: indicate the position of the centre of each mNEcs along the D-V axis; “0 s”: represents the absence of mNEcs. In all cases the D-V axis position coincides with the abscissa and the dorsal midline corresponds to the position “0” of the “x” axis. The blue subseries correspond to the alar plate (OT), light blue subseries correspond to the ventralized region of the dorsal midbrain and the green subseries to the ventral midbrain. Arrows: indicate the original dorsal/ventral midbrain boundary.