The sigmoid sinus starts just below the temporal bone on the sides of the head and follows a complex course to the jugular foramen, a hole in the bone at the base of the skull. At this point in its course, the sinus meets with the internal jugular vein.
As the tentorium (the dura mater that separates the cerebellum, located at the back of the head, from the rest of the brain) reaches its end, the sigmoid connects with the petrosal sinus, which is above it in terms of structure. The sigmoid sinus moves in a downward manner through an S-shaped groove. This groove lies behind the middle of the mastoid, an area of bone behind the ear. It is connected through the mastoid and the condylar messenger veins with the pericranial nerves.
The sigmoid and transverse sinus both vary in size.