The mid portion of the upper lip or prolabium is called "philtrum". The philtrum of
most persons has a vertical groove. This concavity can be used to hold perfumes or
a "Philtron" (Greek for "love potion").

From URL:http://www.consultsos.com/pandora/in210102.htm

Written by a physician who appears to be a serious scholar. Though with a few quidities.