1 Department of Human Anatomy, Histology and Embryology, School of Basic Medicine, Peking Union Medical College, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, Beijing, 100005, China.
2 Joint Laboratory of Anesthesia and Pain, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, 100005, China.
3 Eight-Year MD Program, Peking Union Medical College, Beijing, 100730, China.
4 Department of Human Anatomy, Histology and Embryology, School of Basic Medicine, Peking Union Medical College, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, Beijing, 100005, China. qianxj72@sina.com.