Q5 LONG ANSWER 10M ★ High-yield

Describe the development of the face and the palate. Add a note on cleft lip and cleft palate.

Anatomy · 1st Professional — Pre-Clinical

The Facial Primordia

The face develops between the 4th and 8th weeks from five primordia surrounding the stomodeum, all containing neural crest mesenchyme.

Primordium	Number	Derivatives
Frontonasal prominence	One	Forehead, bridge of the nose
Medial nasal prominences	Two	Tip and septum of the nose, philtrum of the upper lip, premaxilla carrying the four incisor teeth, and the primary palate
Lateral nasal prominences	Two	Alae (sides) of the nose
Maxillary prominences	Two (1st arch)	Cheeks, lateral parts of the upper lip, most of the maxilla, secondary palate
Mandibular prominences	Two (1st arch)	Lower lip, chin and mandible

The lower lip forms from a single pair fusing in the midline, which is why cleft lower lip is very rare while cleft upper lip is common
The nasolacrimal duct forms in the groove between the lateral nasal and maxillary prominences, which is why its congenital obstruction is common

Development of the Palate

The incisive foramen is the landmark separating the primary from the secondary palate, and clefts are classified by their relation to it
Palatal closure occurs about a week later in the female, which is why isolated cleft palate is commoner in girls while cleft lip is commoner in boys

Classification of Clefts

Type	Position	Embryological failure
Cleft lip	Anterior to the incisive foramen	Failure of the maxillary prominence to fuse with the medial nasal prominence
Cleft of the primary palate	Anterior to the incisive foramen; involves the alveolus	Same as above, extending back
Cleft palate (isolated)	Posterior to the incisive foramen	Failure of the palatine shelves to fuse with each other
Combined	Both	Both mechanisms
Median cleft lip	Midline of the upper lip — rare	Failure of the two medial nasal prominences to merge; associated with holoprosencephaly
Oblique facial cleft	From the lip to the eye	Failure of the maxillary and lateral nasal prominences to fuse

Cleft lip is commoner in boys, more often on the left, and more often unilateral
Incidence about 1 in 700; multifactorial, with phenytoin, valproate, smoking and folate deficiency as risk factors

Development of the Tongue

Part	Origin	Nerve supply follows
Anterior two-thirds	Two lingual swellings and the tuberculum impar — first arch	General sensation — lingual (V3); taste — chorda tympani (VII, second arch)
Posterior one-third	Copula and hypobranchial eminence — third arch overgrows the second	Glossopharyngeal (IX)
Posterior-most part	Fourth arch	Internal laryngeal branch of the vagus
Muscles	Occipital myotomes that migrate in	Hypoglossal (XII) — except palatoglossus (vagus)

Taste in the anterior two-thirds is carried by the second arch nerve although the mucosa is first arch — a mismatch explained by the second arch contribution being overgrown
The third arch overgrows the second posteriorly, which is why the vallate papillae lie in front of the sulcus terminalis but are supplied by IX

Development of the Teeth, Salivary Glands and Nose

Structure	Origin	Note
Enamel	Ectoderm — ameloblasts of the enamel organ	The only dental tissue not of mesodermal origin; cannot regenerate
Dentine, pulp, cementum	Neural crest mesenchyme of the dental papilla and sac	Odontoblasts survive and can lay down secondary dentine
Parotid gland	Ectoderm	Encapsulated late, after the lymphatics form — which is why it contains lymph nodes
Submandibular and sublingual glands	Endoderm	Encapsulated early; contain no lymph nodes
Nasal cavities	Nasal placodes deepen into nasal pits, then sacs	Separated from the mouth by the oronasal membrane, which breaks down
Paranasal sinuses	Outgrowths of the nasal cavity	Only the maxillary and ethmoid are present at birth; the frontal and sphenoid develop in childhood

Two dentitions develop from the same dental lamina — 20 deciduous teeth from the 6th week and 32 permanent teeth from buds lingual to them
Choanal atresia — failure of the oronasal membrane to break down; a neonate is an obligate nose-breather, so bilateral atresia causes cyclical cyanosis relieved by crying
The frontal sinus is absent at birth, which is why frontal sinusitis does not occur in young children

Applied Aspects

Cleft lip repair at about 3 months, cleft palate at 9 to 12 months — the "rule of tens" (10 weeks, 10 pounds, haemoglobin 10) is a traditional guide to fitness for lip repair
Feeding difficulty is immediate — the infant cannot generate suction; special teats and positioning are needed, and nutrition must be secured before surgery
Otitis media with effusion is almost universal in cleft palate, because the tensor veli palatini cannot open the auditory tube; hearing must be monitored
Speech requires velopharyngeal competence; a cleft causes a nasal escape and needs long-term speech therapy
Management is by a multidisciplinary team — surgeon, orthodontist, ENT surgeon, speech therapist, audiologist and psychologist — over many years
Periconceptional folic acid reduces the risk, as it does for neural tube defects
Dental development is disturbed when the alveolus is involved, and orthodontic care with alveolar bone grafting is needed around 9 to 11 years
Choanal atresia presents as cyclical cyanosis in the neonate, relieved by crying, because the newborn breathes through the nose
The nasolacrimal duct forms in the groove between the lateral nasal and maxillary prominences; its lower end is the last to canalise, which is why congenital obstruction with a watering eye is so common and usually resolves spontaneously
Frontonasal dysplasia and holoprosencephaly represent a spectrum in which failure of the forebrain to divide is mirrored in the face — "the face predicts the brain"
Antenatal ultrasound detects most clefts of the lip from about 18 weeks, allowing counselling and planned delivery in a centre with the necessary team

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