The philtrum is the groove between your top lip and your nose. It doesn't have any function that we know of -- except to serve as a clue about how a baby's face forms during the first few months in the womb.
In this amazing clip, the BBC's Michael Mosley talks about facial development and shows this amazing animation, created based on data from high-quality medical scans of a developing embryo, produced especially for an episode of Inside the Human Body.
The time-lapse video below shows how this process happens, from about four weeks to 10 weeks. Among other things, you can see how an embryo's eyes start out on the sides of the head -- like a fish -- and migrate to the front.
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