Summary of facial developmenta
| Week | Description |
|---|---|
| Late 3rd to early 4th | Anterior neuropore closes; oropharyngeal membrane appears |
| Early 4th | Frontonasal process appears; early development of maxillary and mandibular processes creates stomodeum |
| Late 4th | Oropharyngeal membrane disintegrates; nasal (olfactory) placodes appear |
| Early 5th | Lateral nasal processes and then the medial nasal processes appear, forming nasal pit; mandibular processes meet in midline; olfactory epithelium starts to form in upper nasal cavities |
| Late 5th | Nasal sacs form; medial nasal processes fuse with maxillary processes and form nasal fins, separating primitive nasal and oral cavities; nasal sacs migrate more medially and become more slit-like; olfactory nerves form; Meckel cartilage forms |
| Early 6th | Oronasal membrane forms and disintegrates opening posterior nasal choana; medial nasal processes start to form primitive nasal septum and primary palate |
| Late 6th | Lateral palatine processes develop; they are initially directed caudally alongside and above the tongue; naso-optic furrow develops and nasolacrimal duct forms (will become patent at birth); external ear develops; labiogingival laminae appear; lips and gums separate; dental lamina appears; maxilloturbinal (future inferior turbinate) starts to form; remaining nasal turbinals form; eyelids start to form |
| Early 7th | Philtrum and upper lip complete; nasal septum further develops; external olfactory epithelium confined to upper nasal cavities and further develops |
| Late 7th | External ear fully developed; nasal plugs close nostrils (will open again in 16th week); cartilaginous nasal capsule develops; palatal shelves elevate and fuse, forming secondary palate; future nostril now complete; eyes move more to midline; fusion of maxillary and mandibular processes narrows the width of the mouth and completes lower cheeks |
| 8th | Lateral nasal wall well-developed; facial muscle primordia appear (muscles develop by 9th week) |
| 9th–10th | Nasal septum starts to fuse with palate (will be complete by 12th week); ossification of maxillas occurs |
| 10th–11th | Uncinate process arises; infundibulum then develops; tooth buds become cup-shaped (teeth will be near complete in 6th month); eyelids fuse (will open in 26th–28th weeks) |
| 12th | Ossification centers of all facial bones are present |
↵a The timeline of development differs slightly in the references quoted in Parts 1 and 2 of these articles. The timeline in this Table represents a compilation of the various dates in these references, and because some normal variation is to be expected, this Table represents the best averaging of any differences in developmental dates that we could make.