[Aspects of facial morphogenesis in the rat].

The facial morphogenesis of the rat has been observed by scanning microscopy on embryos taken every day from the 10th post-coitum day to term. Three points should be noted. Firstly the muzzle has at the beginning of the development an individuality which tends to diminish later. Secondly the vibrissae, whose primary elements are grouped in plates, are of great importance in the development of the muzzle. Finally, the opening between the internal parts of the nasal ridges is elevated with at the top a sharp angle, contrary to that of man which is little elevated and is arched. This could express the difference relating in each of the two cases the mesenchymatous naso-dorsal center, to which divergence between the two types of face, one with muzzle and the other without, would be linked. The primates presenting these two types, the tendency at the moment is to classify them using this discrimination. The study of the two corresponding aspects would supply a precious addition to these observations.