1. Department of Veterinary Anatomy, Obihiro University of Agriculture and Veterinary Medicine, Obihiro 080-8555, Japan
2. Department of Veterinary Anatomy, Kasetsart University, Bangkok 10900, Thailand
3. Department of Zoology, National Science Museum, Tokyo 169-0073, Japan
4. Department of Veterinary Anatomy, Nihon University, Fujisawa 252-8510, Japan
5. Department of Veterinary Anatomy, Graduate School of Agriculture and Life Science, The University of Tokyo, Tokyo 113-8657, Japan
6. Laboratory of Anatomy and Physiology, Nihon University, Fujisawa252-8510, Japan