The Lines upon the palm, or creases formed in closing the hand, differ a little in different persons. In former times, when men were addicted to the arts of divination, and thought more about the connection between the physical world and the world of spirits, and strove, by a close observation of the former, to penetrate the mysteries of the latter, much attention was paid to these lines. They were named with the names of the Planets and the signs of the Zodiac; and a science grew up akin to Astrology and Physiognomy. Cheiromancy was the name given to it; and numerous and voluminous treatises were written upon it.
Source: wiktionary