Development of the Face

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Development of the Face
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First Groove
Around the 1st groove there will be 6 lumps
that become the auricular hillocks (form the
ear) Second arch grows down over the other
grooves, joining with the 6th arch, covering the
grooves in between -if not covered all the way
you get a persistent cervical cyst or sinus
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Ridge on upper surface of maxillary process
(yellow) is providing the path of the
nasolacrimal duct from the eye to the nasal
pit. If this doesnt smooth out then we get
oblique facial cleft. The movement of the
maxillary process to the median facilitates the
movement of the medial nasal prominences. Once
in the midlines, the maxillary processes and the
medial nasal prominences fuse together. The
maxillary processes do not fuse together because
of the presence of the nasal prominences thus
giving a normal philtrum anatomy. If the two
medial nasal prominences do not fuse at the
midline, you get median cleft lip (hare lip)
If there is failure of fusion between medial
nasal prominence and the maxillary prominence you
get either unilateral or bilateral cleft lip.
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The primary palate is formed from the joining
of the medial nasal processes -if you had a
median cleft lip it would occur btwn the central
incisors -the lateral cleft would occur btwn the
lateral and canine The remainder of the
palate comes from the developing maxilla
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The tongue is in the way of the lateral
palatine process. The turgor pressure increases
and the palatal shells flip up when the tongue is
depressed. This rhythmic muscular action allows
the tongue to stay out of the way. Once the
lateral palatine processes have flipped up, they
begin fusing starting at the incisive foramen and
working backwards to the posterior of the palate.
The presence of the tongue pressing up on
the palate (once the lateral palatine processes
have flipped up) help facilitate this fusion
process.
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Pharyngeal Apparatus
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Not individual fingerlike projectionsmore
like a webbing Spaces between arches are known
as pouches -membrane between arches are known as
brachial or pharyngeal -ectoderm is outside
endoderm is inside First groove forms external
canal of ear Ear drum is two cell layers
thick -outer cell layer ectoderm -inner cell
layer endoderm Second pouch forms the
palatine tonsil The ectodermal component of
the oral cavity is known as the stomadeum
Thyroid is derived from foramen cecum The
foramen cecum is located on the floor of the
pharynx (yellow portion above)
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Within the mesodermal component (pink area)
the following develops 1) Aortic Arch (blood
vessel) 2) Primitive Cartilage 3) Nerve
Supply -first four cranial arches contain these
nerves ? 5, 7, 9, and 10 -arch 1 contains
nerve V (V2 maxillary V3 mandible) -arch 2
contains nerve VII -arch 3 contains nerve
IX -arch 4 contains nerve X 4) Core of
ectomesenchyme -of neural crest origin -forms
muscle and connective tissue
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Meckels cartilage does NOT form mandible it
acts as a template for mandible - Meckels
cartilage becomes stylomandibular ligament,
Malleus of inner ear, and a small portion of
the auricular portion of the condyle.
Mandible forms from intramembranous ossification!
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Migration of dorsal and ventral tissuesforms
the thymus and thyroid gland and parathyroid
glands There are a total of 4 parathyroid
glands. This is a result of the thyroid getting
in the way during migration causing separation of
these glands. Ultimopharyngeal body will give
rise to thyrocalcitonion (hormone) from the
fourth pouch C-shaped embryo (due to folding)
allows for short distance during migration of
these tissues.
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Thymus is supposed to have two major lobes that
join in the midline and connected via an
isthmus. Can have excess thymic tissue along
the side following the path of decent (persistent
cord of thymic tissue) This figure shows a
parathyroid gland that didnt move properly
(ectopic inferior parathyroid gland) These
tissues are endodermally derived.
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Development of the Tongue
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Lateral lingual swellings (from proliferating
mesenchyme) arise on the internal face of the
mandibular arch. -these swelling grow
towards the midline and over the
tuberculum impar. The future root of the
tongue is represented by a median elevation
formed by the union of the bases of the second
and third pharyngeal arches. -The copulas
grow over the hyporpharyngeal eminence.
Innervation - anterior 2/3
-sensory is from 5th nerve -some
innervation from the chorda tympani
of 7th - posterior 1/3
-glossopharyngeal (9th) - epiglottis
-vagus nerve (10th)