A case of right partial and double internal jugular veins.

We present a very rare case of right partial and double internal jugular veins, found in an 86-year-old Japanese female cadaver during a student dissection practice session in 2002 at Osaka Dental University. In this case, the right internal jugular vein separated into medial and lateral branches at a level with the middle of the fifth cervical vertebra. Both branches had the same thickness as an internal jugular vein and poured into the right subclavian vein. A slender venous space slit was formed by these two branches and the right subclavian vein. The inferior belly of the right omohyoid muscle and the inferior root of the right ansa cervicalis passed through the superior region in this venous space. To our knowledge, this case has never been reported previously. Therefore, we attempted to investigate the incidence based on existing references for similar cases and speculated on the development based on our findings. We considered the medial branch was the right internal jugular vein and the lateral branch was the communicating branch between the external and internal jugular veins.