The term area 4a of Geyer refers to the more anterior of two parts of primary motor cortex defined on the basis of cytoarchitecture and neurotransmitter binding in the human ( Matelli-2004 ). The other part is area 4p of Geyer. The relation of area 4a to the rostral sector of primary motor cortex, which is defined in the macaque on the basis of function and connectivity, is undetermined. It is not related to area 4a of Vogts, which is one of three subdivisions defined by other criteria.