This paper describes an ultrasonic array system by analyzing data for visualizing brain image under skull. We perform the experiment with a cow scapula as a skull and a steel sulcus as a lateral cerebral sulcus. We employ 1.0MHz and 0.5MHz ultrasonic array probes. The waves of them have some superiority, respectively. The 0.5MHz waves have higher penetration and the 1.0MHz waves have higher resolution. With taking each advantage of them, we synthesize with the waves of 1.0MHz and 0.5MHz. After that, we visualize the sulcus and skull. We calculate the thickness of the bone from the synthesized waves. The thickness is determined from the surface and the bottom points. The surface point is easily determined from the wave. The bottom point is determined by using fuzzy inference. The sulcus surface was extracted from a B-mode image made from the synthesized waves. As the result, we have calculated the best result of the weight of 0.4. Moreover, we extracted the steel sulcus images of the highest efficiency with the weight of 0.5.