Cytoarchitectonic features of the non-primary motor cortex (Brodmann’s area 6) that rostrally abuts on area 4 are an absent inner granular layer (layer IV; hence the term “agranular cortex”) and fairly large and elongated pyramidal cells in lower layer III. Giant pyramidal (or Betz) cells, the most prominent feature of the primary motor cortex (Brodmann’s area 4), are scattered throughout the caudal sector of area 6 close to the border with area 4. They are absent in the rostral part of area 6. At the rostral border of area 6 with the prefrontal cortex (PFC) the large and elongated pyramids in lower layer III decrease in size (Fig. 1). The most important feature of the border between area 6 and the PFC is an emerging inner granular layer (layer IV; arrowheads in Fig. 1). In the caudal sector of the PFC, layer IV is discreet and barely detectable (dysgranular cortex). Further rostral, layer IV gradually increases in width and cell density. Hence, the features of the “typical” granular cortex emerge gradually rather than abruptly.
KeywordsGranular Layer Primary Motor Cortex Sagittal Section Profile Index Posterior Commissure
Unable to display preview. Download preview PDF.