1. Department of Laboratory Animal Science, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Osaka 598-8531, Japan.
2. Department of Veterinary Anatomy, Division of Veterinary Science, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Osaka 598-8531, Japan.
3. Department of Veterinary Anatomy, Faculty of Common Veterinary Medicine, University of Yamaguchi, Yamaguchi 753-8515, Japan.