Answer: Philtrum

The subtle groove between the base of your nose and your upper lip is called a philtrum and in the human body (and that of other primates) no longer serves a function. Among many other mammals that have philtrums, however, the groove does in fact serve a purpose. In the case of dogs, for example, the philtrum extends up to the nose pad itself and both helps keep the nose moist via capillary action and, via the wetting action, helps the dog smell better as a wet nose traps odor particles better than a dry one.

In humans the philtrum is only a vestigial trait that marks where the nasomedial and maxillary growth processes meet during embryonic development in the womb. The philtrum and the process that creates it are practically invisible to us but in rare cases, about 1 to 2 per 1000 births in the developed world, children are born with a cleft lip, cleft palate, or both, failure of the area to properly fuse results in a gap in the upper lip.