A re-evaluation of the premaxillary bone in humans.

The discovery of the premaxillary bone (os incisivum, os intermaxillare or premaxilla) in humans has been attributed to Goethe, and it has also been named os Goethei. However, Broussonet (1779) and Vicq d'Azyr (1780) came to the same result with different methods. The first anatomists described this medial part of the upper jaw as a separate bone in the vertebrate skull, and, as we know, Coiter (1573) was the first to present an illustration of the sutura incisiva in the human. This fact, and furthermore its development from three parts:-(1) the alveolar part with the facial process, (2) the palatine process, and (3) the processus Stenonianus-can no longer be found in modern textbooks of developmental biology. At the end of the nineteenth and in the early twentieth century a vehement discussion focused on the number and position of its ossification centers and its sutures. Therefore, it is hard to believe that the elaborate work of the old embryologists is ignored and that the existence of a premaxillary bone in humans is even denied by many authors. Therefore this re-evaluation was done to demonstrate the early development of the premaxillary bone using the reconstructions of Felber (1919), Jarmer (1922) and data from our own observations on SEM micrographs and serial sections from 16 mm embryo to 68 mm fetus. Ossification of a separate premaxilla was first observed in a 16 mm embryo. We agree with Jarmer (1922), Peter (1924), and Shepherd and McCarthy (1955) that it develops from three anlagen, which are, however, not fully separated. The predominant sutura incisiva (rudimentarily seen on the facial side in a prematurely born child) and a shorter sutura intraincisiva argue in this sense. The later growth of this bone and its processes establish an important structure in the middle of the facial skull. Its architecture fits well with the functional test of others. We also focused on the relation of the developing premaxilla to the forming nasal septum moving from ventral to dorsal and the intercalation of the vomer. Thus the premaxilla acts as a stabilizing element within the facial skeleton comparable with the keystone of a Roman arch. Furthermore, the significance of the premaxillary anlage for the closure of the palatine was documented by a synopsis made from a stage 16, 10.2 mm GL embryo to a 49 mm GL fetus. Finally the growth of the premaxilla is closely related to the development of the human face. Abnormal growth may be correlated to characteristic malformations such as protrusion, closed bite and prognathism. Concerning the relation of the premaxillary bone to cleft lip and palate we agree with others that the position of the clefts is not always identical with the incisive suture. This is proved by the double anlagen of an upper-outer incisor in a 55 mm fetus and an adult.