The course of the sigmoid sulcus is variable. It may be different on both sides in thesame person. In the investigation of 150 Chinese skulls by projecting the sulcus onthe surface of the skull three types could be classified. The first type is that the sulcuskeeps a certain distance from the crista supramastodea or the posterior border of theporus acusticus externus. Out of 300 sides, 244 belong to this type. The second type isthat the sulcus is very close to the lower border of the crista supramastoidea, the distancebeing only a few millimeters from the upper border of the crista supramastoidea. Outof 300 sides, 41 belong to this type. In the third type, the distance between the posteriorborder of the porus acusticus externus and the anterior border of the sigmoid sulcus is lessthan 5 mm. Only 15 cases out of 300 sides belong to this type. In all cases no sexual difference could be found. There is a tendency of the rightside deeper and also nearer to the crista supramastoidea and the posterior border of theporus acusticus externus than the left.