Figure 5.

(A) A slice from a 21 pcw fetal brain sectioned in the coronal plane and stained for Nissl; (B) The plane atlas of the 21 pcw fetal cerebrum; the blue frame highlights insular regions; (C) An enlarged view of insular regions highlighted by the blue frame in (A,B). The boundaries of the cortical plane (color and white curves) are manually depicted. Columns, i.e., the red and yellow colored bars between boundaries of the cortical plate, are used as neuron number counting boxes. These columns are perpendicular to the white boundary. The width of each column is 40 μm. Arabic numberals indicate the column IDs; (D) Neuron numbers of the columns in (C). Lower-case Roman numberals indicate local maxima (i, iii) and minima (ii). csr, circular sulcus of Reil; csr-u, upper limiting sulcus; csr-l, lower limiting sulcus.