Layers of the abdominal wall as seen on high frequency ultrasound. Fat (F); external oblique muscle (EO); internal oblique muscle (IO); transversus abdominis muscle (TA); rectus abdominis (RA); peritoneum (arrow); aponeurosis of external oblique (white arrowhead) and anterior part of the aponeurosis of internal oblique contributing to the rectus sheath (black arrowhead).