3-DIMENSIONAL RECONSTRUCTION OF THE HUMAN FETAL PHILTRUM

The anatomy of the philtrum is incompletely understood because it is d ifficult to analyze three dimensionally. Previous anatomic studies sug gested that the philtral ridges are formed by the dermal insertion of the orbicularis oris muscle and musculis nasalis decussating across th e midline, with the philtral dimple an area of few muscular insertions . This theory is inconsistent with the usual finding of a normal-appea ring philtrum contralateral to the cleft in patients with unilateral c left lip. Using a microcomputer and three-dimensional software, we hav e created a three-dimensional model of the philtrum from digitized ima ges of sequential transverse histological sections from a third-trimes ter fetus. Our studies demonstrate that the philtral ridges ape formed by thickened dermis and dermal appendages. The labial levators are th e predominant muscles associated with the philtrum throughout its leng th; their fibers insert into the dermis lateral to the philtral ridges . Crossing muscle fibers of the orbicularis oris pars marginalis only appear below the vermillion-cutaneous junction, caudal to the philtral ridges.