the 12 earthly branches 子[zi3], 丑[chou3], 寅[yin2], 卯[mao3], 辰[chen2], 巳[si4], 午[wu3], 未[wei4], 申[shen1], 酉[you3], 戌[xu1], 亥[hai4], used cyclically in the calendar and as ordinal numbers I, II etc