FACE DEVELOPMENT (1)

• Morphology of face is developed from 5 prominences:1. Frontonasal process2. 2 maxillary swelling3. 2 mandibular swelling

• These process cause furrows between processes, and fusion of prominences involves elimination of furrows.

• Oral cavity (primitive stomatodeum) is at first bounded:I. Above: frontal prominenceII. Below: developing heartIII. Laterally: first branchial arch

• With the spread of arches together, the cardiac plate is eliminated from stomatodeum.

• Thus, epithelial covering the mesechyme of 1st, 2nd and 3rd branchial arches forms floor of the mouth.

• Week 4: (position of stomatodeum)-The stomatodeum is limited cranially by the frontal process, laterally by the maxillary process and ventrally by the mandibular process. • Week 5: (olfactory placode and lower lip forms)-The frontal prominence, just rostral to the stomatodeum, form olfactory placode due to the rapid proliferation of underlying mesenchyme.-The ectoderm at the center of placodes invaginated to form an oral nasal pit-This devides the raised rim of placode into lateral and medial nasal process.-The groove between the lateral nasal process and the adjacent maxillary swelling is called the nasolarimal groove. Later the ectoderm of this groove invaginated into the underlying mesenchyme to form the nasolacrimal duct.-The mandibular swellings come together and fuse to form the lower lip.

• Week 6: (septum and philtrum formation)-At the beginning of week 6, the lateral part of the face expands and broadens. This causes the eyes and maxillary process which where initially located at the side of the face to come to the front of the face. -The medial nasal process migrates towards each other and fuse to form the septum of the nose.-The inferior tips of the medial nasal process expand laterally and inferiorly and fuse to form the intermaxillary process. The tip of the maxillary swelling grows to meet the intermaxillary process and fuse. This gives rise to the philtrum.

-By the time of face development, the epithelium at the inferior border of maxillary process and superior border of mandibular process proliferate and thickens. -When fuse they form a single primary epithelium band, joining the upper and lower jaw.

Nasal passage and palate formation (2)

Nasal passage:

At the end of 6th week:-The nasal pits deepens and fuse to form a single, enlarged,

ectodermal nasal sac lying super posterior to the intermaxillary process.

At the end of 6th week to the beginning of the 7th week:

-The floor and the posterior wall of the nasal sac proliferate to form the nasal fin separating the nasal sac from oral cavity.

-Vacuoles develop in the nasal fin and fuse with nasal sac, the sac enlarges and thinning the fin to a thin membrane called the oronasal membrane.

-oral nasal membrane separate the sac from oral cavity.

During the 7th week:-Oronasal membrane ruptures to form an opening called

primitive choana.-The floor of the nasal cavity (primary palate) is formed by the

Posterior extension of the Intermaxillary process.

Secondary palate formation (week7-8):

-Formation involves the fusion of:i. Right and left maxillary processes

(palatine shelf)ii. Median nasal process

-The median nasal process grows downward and forward to form the nasal septum.

-The palatine shelves, at first grows downward to the elevated the tongue.-As a result of the enlargement of the mandible, the tongue drops to the floor of the stomatodeum.

-When the tongue is moved from the growing lateral palatine processes, the processes are straightened to a horizontal position and grows medially towards and fuse with each other with primary palate to form the secondary palate

-The nasal septum fuse with the upper surface of the primary and secondary palates along the midline.

-Now nasal cavity opens into the pharynx behind the secondary palate through an opening called the definitive choana

Tongue formation (3)

Tongue development:• Pharyngeal arch: 1, 3, and 4• Occipital Somite Mesoderm

Begins late of 4th week1st arch: -Forms a median swelling called tuberculum impar.-A pair of lateral swellings, the distal tongue buds. The lateral swellings quickly enlarge

and merge with each other and also with median swelling and form the anterior two-third of the tongue.

2nd arch:-Develop a midline swelling calledcopula.

5th and 6th week:a midline swelling of the 3rd and 4th arches called hypopharyngeal eminence overgrows the copulawhich disappears. Thus, forms the posterior one-third of the tongue.(Hypo pharyngeal eminence expand mainly by the growth of 3rd arch endoderm.)A depression called foramen cecum is visible where the median and terminal sulcus intersect.

4th arch:-Marks the development of epiglottis.

-Tongue separates from the floor of the mouth by a downward growth of ectoderm around its periphery, subsequently degenerates to form lingual sulcus and gives the tongue mobility.

Muscles of the tongue: -Different origin. -Arise from the mesoderm of the occipital somites, which have migrated forward

into the tongue area. -With their nerve- 12th cranial nerve Hypoglossal nerve (motor).

Nerve supply (sensory) correspond to their origin:i. 1st arch nerve 5th cranial (trigeminal) nerve supply anterior two-third.ii. 3rd arch nerve 9th cranial nerve (glossopharyngeal) supply the posterior

one third.

Mandibular formation (4)

Formation of mandible (week 6-10):-Cartilage of 1st arch (meckel’s cartilage) is associated to this formation but makes no contribution to it.

6th week: (meckel’s cartilage)-Cartilage extend as a hyaline cartilagenous rod, surronded by fibrocellular capsule.

-The 2 cartilage (from left and right) do not meet at midline but are separated by a thin band of mesenchyme.

-Mandibular nerve comes along 2/3 of the way along the length of cartilage. At this point, it divides into lingual branch (medial) and inferior alveolar branch (lateral) which run along medial and lateral aspect of the cartilage.

-Inferior alveolar further divides into incisor and mental branches anteriorly.

-In the angle between incisor and mental branch, condensation of mesenchyme occurs.

7th week:• First bone-Intramembranous ossification begins in this condensation forming first bone.-From this center, the bone spreads anteriorly to the midline and posteriorly to the point where mandibular nerve divides.-As it spreads anteriorly to midline, the bone forms a trough (drain) that consist of lateral and medial plates that unite beneath the incisor nerve.-It then comes into close approximation with similar trough formed in the adjoining mandibular process. -Trough is converted to a canal as bone form over the nerve , joining lateral and medial plate.

• Backward extension of ossification-Similar as forward but backward, it forms a trough at the lateral aspect of meckel’s cartilage.-It is then converted to a canal that contains inferior alveolar nerve.

• Ramus of mandible -Developed by a rapid spread of ossification posteriorly into mesenchyme of 1st branchial arch, turning away from the meckel’s cartilage.-This point of diverge is marked by the lingula.

Fate of meckel’s cartilage:

1. Posterior extremity: Incus and malleus of inner ear.2. Posterior extremity Sphenomalleolar ligament.3. From sphenoid to the division of the mandibular nerve, cartilage is lost totally.

But its fibrous cellular capsule persist as the Sphenomandibular ligament.4. From lingula forward to the division of the alveolar nerve: degrade, space

replace by new bone.

Further growth of mandible:

Three secondary growth cartilages appeared (Compare to primary cartilage):i. Cells are largerii. Less intercellular matrix formed.

1. Condylar cartilage: appears during 12th week. Converted quickly to bone by endochondral ossification.

2. Coronoid cartilage: anterior border and top of the condylar cartilage. Disappears long before birth.

3. Symphyseal cartilage: two end of Meckel’s cartilage. Obliterated within the 1st year after birth.

• Conclusion:

-Membrane bone is developed in relation to the nerve of 1st branchial arch and entirely independent of meckel’s cartilage.-It consist of neural, alveolar, and muscular element.--It’s growth is assisted by development of secondary cartilage.