1. Laboratory of Microanatomy, School of Veterinary Medicine, Rakuno Gakuen University, Ebetsu, Hokkiado 069-8501, Japan
2. Department of Veterinary Anatomy, Faculty of Veterinary Medicine, Khon Kaen University, Khon Kaen 40002, Thailand
3. College of Agriculture, Department of Food and Environment Science, Rakuno Gakuen University, Ebetsu, Hokkaido 069-8501, Japan