Cytoarchitecture of the micro-excitable cortex. Photomicrographs of motor cortex of the right hemisphere in the PMG monkey (A: Nissl staining; C: SMI-32 staining) and in the normal monkey (B: Nissl staining; D: SMI-32 staining). Black arrows show the location of pyramidal cells in layer V, whereas the open arrows show the location of layer III. Note the absence of layer III SMI-32 stained neurons in Mk-PM. Scale bars: 500 microns.