Topographical variations of the incisive canal and nasopalatine duct in human fetuses.

The incisive canal for nerves and vessels is generally thought to run along a suture between the incisive bone (IN) and maxilla. In contrast, there was a report saying the canal passes through the IN or primary palate in human fetuses. Examination of sagittal and frontal sections from 69 fetuses (31 of gestational age [GA] 9-15 weeks and 38 of GA 26-34 weeks) showed that the canal often penetrated the IN at the nasal half of its course and that, in other fetuses, the canal penetrated the IN along its entire course, irrespective of involvement of the nasopalatine duct. Canals developing in and corresponding to parts of the suture resulted in partial enlargement of the thin and tight sutures, which contained loose tissue, vessels, nerves and even a duct. Small processes of the IN were identified as upper irregular parts continuous with inferior main masses of bone in frontal sections but as bone fragments in sagittal sections. In some sections, a thin layer of the maxilla along the canal covered the medial or inferior aspect of the IN. Therefore, the incisive canal with or without duct exhibited a spectrum of variations in topographical relation to the IN-maxillary border. Because the primitive oronasal communication passes through the suture, the nasopalatine duct may have originated from the secondary developed elongation of the nasal epithelium at midterm. A large incisive fossa along the midline on the oral surface of the palate might make a macroscopic finding of variants difficult even in adults.