Identification

• This model shows the development of the face from facial prominences, mainly during the 4th to 8th weeks of intrauterine life.
• Facial development occurs around the primitive mouth, called the stomodeum.
• Most facial mesenchyme is derived from neural crest cells.
• The maxillary and mandibular prominences arise from the 1st pharyngeal arch.

Five primary facial prominences

1. One frontonasal prominence - above the stomodeum
2. Two maxillary prominences - one on each side
3. Two mandibular prominences - one on each side

Stage-wise explanation of the model

1. Early stage - end of 4th week

• The frontonasal prominence forms the upper boundary of the stomodeum.
• Paired ectodermal thickenings called nasal or olfactory placodes appear on its lower part.
• The maxillary prominences lie lateral to the stomodeum.
• The mandibular prominences lie below the stomodeum.

2. Fifth week - formation of nasal processes

• The nasal placodes invaginate to form nasal pits.
• The tissue around each nasal pit forms:
  • Medial nasal prominence on the medial side
  • Lateral nasal prominence on the lateral side
• Thus, there are paired medial and paired lateral nasal prominences.

3. Sixth to seventh week - fusion and formation of upper lip

• The maxillary prominences enlarge and grow medially.
• They push the medial nasal prominences toward the midline.
• The right and left medial nasal prominences fuse with each other.
• Each maxillary prominence fuses with the corresponding medial nasal prominence.
• This produces the upper lip.

4. Formation of intermaxillary segment

• Fusion of the two medial nasal prominences forms the intermaxillary segment.
• It gives rise to:
  1. Philtrum of upper lip
  2. Premaxillary part of maxilla, which carries the incisor teeth
  3. Primary palate

5. Formation of lower lip and mandible

• The paired mandibular prominences merge in the midline.
• They form:
  • Lower lip
  • Lower jaw or mandible
  • Lower part of face

6. Nasolacrimal groove and duct

• A groove between the maxillary prominence and lateral nasal prominence is the nasolacrimal groove.
• Ectoderm in its floor forms an epithelial cord.
• This cord canalizes to form:
  • Lacrimal sac
  • Nasolacrimal duct

Derivatives of facial prominences

Important viva points

• Upper lip is formed by: two medial nasal prominences and two maxillary prominences.
• Lateral nasal prominence does not form the upper lip.
• Philtrum is derived from: intermaxillary segment.
• Lower lip and mandible are derived from: mandibular prominences.
• Nasolacrimal duct develops from: ectoderm in the nasolacrimal groove.
• The face is largely completed by: the end of the 8th week.

Clinical correlations

1. Cleft lip
   • Due to failure of fusion of the maxillary prominence with medial nasal prominence.
   • May be unilateral or bilateral.
2. Median cleft upper lip
   • Due to failure of fusion of the two medial nasal prominences.
3. Oblique facial cleft
   • Due to failure of fusion of maxillary prominence with lateral nasal prominence.
   • It follows the line of the nasolacrimal groove.
4. Macrostomia
   • Due to incomplete fusion of maxillary and mandibular prominences at the angle of the mouth.
5. Microstomia
   • Due to excessive fusion of maxillary and mandibular prominences.