1 Zhongshan School of Medicine, Sun Yat-sen University, No. 74 Zhongshan Road 2, Guangzhou, 510080, People's Republic of China.
2 Department of Anatomy, Zhongshan School of Medicine, Sun Yat-sen University, No. 74 Zhongshan Road 2, Guangzhou, 510080, People's Republic of China.
3 Department of Anatomy, Zhongshan School of Medicine, Sun Yat-sen University, No. 74 Zhongshan Road 2, Guangzhou, 510080, People's Republic of China. zhoulih@mail.sysu.edu.cn.