1. The University Museum, The University of Tokyo, 7-3-1 Hongo, Bunkyo- ku, Tokyo 113-0033, Japan
2. Department of Veterinary Anatomy, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
3. Animal Medical Center, Nihon University, Fujisawa, Kanagawa 252-8510, Japan
4. Laboratory of Veterinary Surgery, Nihon University, Fujisawa, Kanagawa 252-8510, Japan
5. Department of Veterinary Anatomy, Nihon University, Fujisawa, Kanagawa 252-8510, Japan
6. Department of Zoology, National Science Museum, 3-23-1 Hyakunin-cho, Shinjuku-ku, Tokyo 169-0073, Japan
7. Department of Anatomy II, Azabu University School of Veterinary Medicine, Sagamihara, Kanagawa 229-8501, Japan