Palm readers say all vertical lines can be considered as pipelines or electrical circuits that carry the energy in and out of you to the people around you. By "energy" I mean your positive personality characteristics that drive your daily interests, activities, and life purpose.
The location of the lines on the hands reveals the type of energy flowing. Thumb energies are related to physically doing things to shape, control, and dominate one's environment. For example, thumb energies deal with making tools work and getting results in the material world.
The Mercury finger is on the opposite side of the hand from the thumb. Mercury energies are very different from thumb energies. Mercury energies are much more subtle than thumb energies, but in the long run, Mercury energies are more powerful and meaningful to some people. It just depends on where one is on his or her karmic path.
Vertical lines on the Mercury tip indicate excellent psychic communication and sensitivity with spiritual realms. The deeper, longer, and clearer the vertical lines, the better the flow of psychic energy. The energy in the Mercury tip is related to the most subtle personality characteristics such as spirituality, planning for a meaningful future, creating eloquence in your life, communicating meaningfully and creating the highest levels of intimacy.
Here is a Mercury finger with good psychic lines on the tip and abundant lines on the lower two zones. The tip shape is conic and does not indicate as much psychic energy as a pointy tip would.
Not all hands have psychic vertical lines. In fact, some hands show only the major lines (heart, head, and life). People with very few lines on their hands will be very guarded about showing their emotions. It does not mean that they do not have emotions, it just means they keep them very tightly controlled and hidden.