1. Department of Anatomy (H.N, K.K), School of Medicine, Keio University, Tokyo 160, Japan
2. Department of Regulation Biology (K.I), Faculty of Science, Saitama University, Saitama 338, Japan
3. Second Department of Internal Medicine (H.M, A.I, S.K), National Defense Medical College, Saitama 359, Japan
4. Department of Anatomy (S.H), Institute of Basic Medical Sciences, University of Tsukuba, Ibaraki 305, Japan
5. Department of Neurosurgery (M.K), School of Medicine, Keio University, Tokyo 160, Japan