1. Department of Veterinary Anatomy, The University of Tokyo, Yayoi 1–1–1, Bunkyo-ku, Tokyo 113-8657, Japan
2. Department of Anatomy, Kyorin University School of Medicine, Mitaka, Tokyo 181-8611, Japan
3. Department of Global Agricultural Sciences, The University of Tokyo, Yayoi 1–1–1, Bunkyo-ku, Tokyo 113-8657, Japan