PRIMARY PALATE Figure 6a. Four weeks (3 1/2 mm) b. Five weeks (6 1/2 mm) c. Five and a half weeks (9 mm) Around the end of the 4th week, proliferating mesoderm produces five swellings around the stomodeum. These are the frontonasal process at the upper margin, the paired maxillary processes laterally and the paired mandibular processes at the lower margin.  Also at this time, the nasal (olfactory) placodes are appearing on each side of the frontonasal prominence. In week 5, four subsidiary swellings of the frontonasal process form horseshoe shaped elevations around the nasal placodes recessing them in nasal pits.  These swellings are the paired nasomedial and paired nasolateral swellings. Initially the nasal pits are continuous ventrally with the stomodeum.