Oral Histology & Development

Oral Cavity

Formation of the secondary palate

Formation of secondary palate starts between week 7 and 8, and ends at around the third month of gestation.

Oral Cavity mainly consists of three outgrowths:

  • The nasal septum grows downward from Frontonasal process along the midline

  • The two palatine shelves, one at each side and extends from the maxilla towards the midline

Week 7:
  • The two palatine shelves which arise from the bilateral maxillary processes, grow downward in a vertical direction on both sides of the tongue 

  • The tongue is withdrawn from between the shelves, and moves forward 

  • The intermaxillary segment and the maxillary prominence fuse together forming the upper lip

Week 8:
  • The tongue and mandible are small relative to the upper facial complex.

  • The lower lip is positioned behind the upper one

  • The tongue occupies an elevated position between the palatine shelves

  • The tongue has been depressed and the palatine shelves are elevated but not fused yet

  • The palatine shelves slide over the tongue in a process called the palatine shelves elevation

  • The facial complex (head) is folded into the developing thorax region

Week 9:
  • The lower lip is positioned in advance to the upper lip

  • The tongue is situated below the palatine shelves

  • The tongue and lower jaw can grow forward, because the facial complex has lifted away from the thorax

  • The palatine shelves continue to grow medially until they meet; this process is known as the palatine shelf closure

  • A second fusion occurs between these two fused shelves and the primary palate at the midline of the nasal septum

  • This fusion will lead to the separation of the primitive oral cavity into the oral cavity and nasal cavity

  • Closure of the secondary palate proceeds from the primary palate

The Tongue

  • Tongue formation starts at week 4 until week 12

  • It is formed from the first, second, third and fourth pharyngeal arches, and from the occipital bone 

  • The anterior two thirds of the tongue are called the body, while the posterior third is called the base

  • The body of the tongue is the movable part and it is made of:

1) Muscles
2) Connective Tissue
3) Epithelium tissue

Stages of tongue development:
  • A swelling (tuberculum impar) arises in the midline of the Mandibular process, and in between two lingual swellings.

  • Then these three swellings (tuberculum impar + two lingual swellings) fuse together forming the anterior two thirds of the tongue.

  • The large midline swelling which forms the root of the tongue is formed from the 2nd, 3rd, and 4th pharyngeal arches.

  • The large midline swelling consists of:

            a.  Copula (2nd arch)

            b.  Large hypobranchial eminence (3rd + 4th arches)

  • The hypobranchial eminence overgrows the copula causing it to disappear

  • The posterior of the 4th arch develop the epiglottis

  • Tongue is separated from the floor of the mouth after the formation of the lingual sulcus