I love the strange names that some things have! Philtrum comes from the Greek word for "to love" or "to kiss", as the Greeks considered the philtrum to be an erogenous zone. The philtrum is also known as the infranasal depression, and is formed when the nasomedial and maxillary processes meet during embryonic development; if they don't fuse properly, the result is a cleft lip, or harelip.
That's a lot of medical terminology!
By the way, philtrum is an anagram of "lip thrum", from the hint!