sigmoid sulcus sigmoid sulcus the inner surface of the mastoid portion of the temporal bone presents a deep, curved groove, the sigmoid sulcus, which lodges part of the transverse sinus; in it may be seen the opening of the mastoid foramen. sigmoid sulcusleft temporal bone. inner surface. (sigmoid sulcus visible at center left.)base of the skull. upper surface. (sigmoid sulcus not labeled, but is visible near mastoid foramen.)detailsidentifierslatinsulcus sinus sigmoidei ossis temporalista98a02.1.06.006ta2456fma55499anatomical terms of bone