商民族根据玄鸟生商的传说，用一种特殊符号记载他们祖先契十月孕育的过程，这就是甲乙丙丁戊己庚辛壬癸，后来人们称之为天干。
The nation of Shang recorded the ten months process of conceiving of their ancestors with the special symbols which were called the Ten Heavenly Stems .
玄鸟生商