Prenatal morphogenesis of the human incisive canal

The literature describing the formation of the incisive canal is very bizarre. The fusion of the primary and secondary palatal processes leads to formation of a triangular seam, which erroneously has been taken for the future incisive canal. If so, the nasopalatine (incisive) nerve and its accompanying vessels were to run through the primary oronasal cavity, which is not compatible with our biological experience. This study was undertaken to shed light on this region of fusion. We focus on the formation of the incisive canal; the neighboring nasopalatine ducts, which are a transient formation, are mentioned where present. A series of seven horizontal cross-sections of human embryos and fetuses from the 7th to the 24th week of pregnancy (between 25 and 225 mm CRL, crown-rump-length) were examined histologically and partly reconstructed in 3D applying the software analySIS (Soft Imaging Systems, Münster, Germany). The incisive canal did not develop at the junction of the primary and the secondary palate, but within the primary palate rostral to that location. The nasopalatine nerve and the nasopalatine artery are structures that exist before ossification starts in the area of the future incisive canal. The neighboring nasopalatine ducts were found in regions laterally and anterolaterally of the nasopalatine nerve, and it was mostly separated from it by bone. In advanced stages of development, the nasopalatine duct only existed as single epithelial remnants and was prone to obliteration.