The ectoderm which contributes to the formation of the face is well around the stomodeum by the fourth week of embryonic life.

The stomodeum is separated from the foregut by the buccopharyngeal membrane.  Later, this membrane becomes perforated and establishes communication between the amniotic cavity and the foregut.

Frontonasal process (or prominence) - is a median prominence that overhangs the cephalic end of the oral cavity by 6^th week. It becomes the forehead and the dorsum of the nose.

The first arch (Mandibular arch) forms the lateral wall of the stomodeum. This arch gives off a bud from its dorsal end called the maxillary process that grows ventromedially. The main part of the arch continues as mandibular process.

The stomodeum is now bounded cranially by the frontonasal process, the 1^st arch on either sides, and caudally by the pericardium.

Nasal (olfactory) pits are located on either side of the frontonasal prominence and are surrounded by horseshoe-shaped eminences. The medial portion of these eminences is called the medial nasal process. The lateral portion is called the lateral nasal process.

The lateral nasal process is separated from the maxillary process (the more rostral portion of the first branchial arch) by a furrow which reaches the medial aspect of the developing eye. This furrow is called the nasolacrimal groove (naso-optic furrow).

The right and left mandibular processes of the first branchial arch grow medially and fuse with each other and form the inferior boundary of the oral cavity. They form the lower lip and lower jaw.

The maxillary processes grow and as they do so, they crowd the medial nasal processes toward the midline where they unite with one another.

The medial nasal processes also crowd the frontal process upward. The mesoderm of the medial nasal processes (of the frontonasal process) gives rise to the philtrum of the upper lip.

The lateral nasal processes fuse with the maxillary processes, obliterating the nasolacrimal groove. This ectodermal groove gets buried & becomes the nasolacrimal duct and lacrimal sac. Thus, it is understood that the nasolacrimal duct is ectodermal in development.

The parts developed from the Frontonasal process – by the ophthatlmic nerve.

The parts developed from the Maxillary process – by the Maxillary nerve.

Skin over the angle of the mandible – by the great auricular nerve (this part of the face is pulled from the neck region).

    * Frontonasal process - Forehead and the dorsum of the nose

                * Lateral nasal processes - Sides (alae) of the nose

                * Medial nasal processes – Philtrum

    * Maxillary processes - Upper cheek region and most of the upper lip

    * Mandibular processes - Chin, lower lip, and lower cheek regions

·        Muscles of the facial expression – Develop from the 2^nd pharyngeal arch and later migrate to the face. Hence, are supplied by the facial nerve.

Thickening of the surface ectoderm on either side of the frontal process just above the stomodeum is the first indication of the nasal cavity. These are called the nasal (olfactory) placodes.

 The nasal (olfactory) placodes begin to invaginate by the 5th week and form the nasal pits.

The nasal pits invaginate by:

1)      forward growth of the medial and lateral nasal processes, and,

2)      Posteroinferior growth of the pits themselves, the placode tissue comes to line the roof of each pit.

The pits grow and approach the primitive oral cavity. A thin oronasal membrane is located between the pits and the oral cavity.

This membrane then ruptures and forms the primitive choanae.

At the end of the second month, as the maxilla develops, a partition between the primitive nasal chambers and the oral cavity begins to form. This marks the beginning of the formation of the palate.

1. Primary palate -

The anterior aspect of the partition between the nasal cavity and the oral cavity is formed by the medial nasal processes (intermaxillary segment) and is called the primary palate (median palatine process).

2. Secondary palate -

Shelf-like processes originating from the maxillary process called the palatine shelves (lateral palatine processes) grow medially and form most of the palate. This segment of the palate is called the secondary palate.

As the secondary palate is formed, the nasal septum grows inferiorly toward it. The nasal septum and the two palatine shelves unite to form separate right and left nasal chambers, an oral cavity, and the definitive choanae.

Cleft (hare) lip and cleft jaw: the medial nasal processes do not fuse with the maxillary processes.

Median cleft of lower lip: Failure of fusion of 2 mandibular processes.

Cleft palate and/or uvula: the palatine shelves fail to fuse with each other and/or with the primary palate

 Oblique facial cleft: The nasolacrimal duct remains exposed due to the lateral nasal process failing to fuse with the maxillary process. It can occur along with a cleft lip.

Microstomia: Small mouth-due to too much fusion of the maxillary and mandibular processes.

Macrostomia: Wide mouth-due to inadequate fusion of the maxillary and mandibular processes.

Micrognathia- the jaws are small due to underdevelopment of the maxillary and mandibular processes.

1st arch syndrome: or Mandibulofacial dysostosis – The entire 1st arch remain underdeveloped affecting the lower eyelid, the maxilla, the mandible, and the external ear. (Treacher-Collins and Robin’s Sequence)

Rathke’s pouch gives rise to the anterior and intermediate lobes and the infundibulum gives rise to the posterior lobe of the pituitary gland.

Parotid gland:  Ectodermal – Outgrowth from the labiogingival groove.

Submandibular and sublingual glands – Endodermal –  Outgrowth from the linguogingival groove.