Electric stimulation was performed on the motor cortex of the human brain in 30 cases of epileptics and then histological investigation was made on the removed specimen of the brain. The extent of the center for the upper limb was relatively wide and the extent of the center for the lower limb was hardly discovered by electric stimulation. In the center of the upper limb, the extent for fingers was the widest and responded by the lowest voltage, then following order of the wrist, the elbow and the shoulder joint. The area anteriorly close to the Rolandic fissure, even if without any motor response to electric stimulation, had mostly the giant pyramidal cells of Betz, especially the area close to the midline had always bigger Betz cells. The gyri anteriorly distant from the Rolandic fissure, even if with motor response to electric stimulation, hardly had the Betz cells. No Betz cells were observed in the responded area of the area 6 and posterior to the Rolandic fissure. From these results the theory seems to be not reliable that the motr response caused by electric stimulation is due to the Betz cells.