aponeurosis of external abdominal oblique muscle

broad, flat tendinous portion of the external abdominal oblique muscle. The fleshy fibers of the muscle end in the aponeurosis along a line descending vertically from the costochondral joint of the ninth rib then turning laterally just below the level of the umbilicus toward the anterior superior iliac spine. The fibers of the aponeurosis run medially and inferiorly, contributing to the anterior wall of the sheath of the rectus abdominis muscle and decussating with those of the contralateral aponeurosis at the median linea alba. Inferomedially, the aponeurosis is attached to the upper border of the pubic symphysis, the pubic crest and pubic tubercle. Between the anterior superior iliac spine and the pubic tubercle, it is thickened and turned under, forming the inguinal ligaments. The portion of the aponeurosis attached to the pubic bone forms the superficial inguinal ring by splitting into medial and lateral crura. See Also: external spermatic fascia, inguinal ligament, lacunar ligament, pectineal ligament, reflected inguinal ligament, superficial inguinal ring, rectus sheath.