The philtrum (Greek φιλτρον philtron, from φιλειν philein 'to love; to kiss'), also known as the infranasal depression, is the vertical groove in the upper lip, formed where the nasomedial and maxillary processes meet during embryonic development. It has no apparent function besides its visual prominence . Pathology When these processes fail to fuse fully, a cleft lip (sometimes called a "hare lip") can result. A flattened or smo… (More on Philtrum)