2. The pharyngeal (Branchial)
apparatus :
It consists of :
1-pharyngeal arches.
2-pharyngeal pouches.
3-pharyngeal grooves.
4-pharyngeal membranes.
These embryonic structures contribute to
the development of the head & neck
regions.
3. Drawings illustrating the
human pharyngeal apparatus.
A, dorsal view of cranial part of an
embryo.
B to D, lateral views showing later
development of pharyngeal arches.
E to G, ventral or facial views,
illustrating the relationship of the first
pharyngeal arch to the stomodeum.
-Maxillary prominence of 1st arch lies
lateral to stomodeum.
-Mandibular prominence of
1st arch lies caudal to stomodeum.
H,horizontal S.of cranial part of emb.
I, horizontal S. illustrating the arch
components + floor of pharynx.
J, sagittal S.illustrating the openings
of pharyngeal pouches in the lateral
wall of the primordial pharynx.
4. Pharyngeal arches
They begin to develop early in the
4th week as neural crest cells migrate
into the future head & neck regions.
By the end of 4th week, 4 pairs of
pharyngeal arches are visible externally
The 5th & 6th arches are rudimentary
and not visible on surface of embryo.
Fronto-nasal
prominence
Pharyngeal arches are separated
externally by fissures- the pharyngeal
grooves, which numbered craniocaudally as the arches.
The arches appear along lateral wall
of primordial pharynx.
The primordial mouth (stomodeum)
is temporarily closed by oropharyngeal
bilaminar membrane (ectoderm &
endoderm), which ruptures at about 26
th
5. Pharyngeal arches
1st pharyngeal arch (mandibular
arch), the primordium of jaws
consists of :
1- A dorsal portion, the
maxillary process, which gives rise to
the maxilla (upper jaw), zygomatic
bone, and squamous part of temporal
bone.
2- A ventral portion, the mandibular
process, which gives rise the mandible
( lower jaw).
-1st pair of pharyngeal arches plays a
major role in facial development.
2nd pharyngeal arch (hyoid arch) :
contributes to the formation of hyoid
bone.
6. Pharyngeal Arches
A, By the end of the 4th week (28days),
4 pairs of pharyngeal arches are developed.
B, Drawing showing pharyngeal pouches
+ aortic arches, that supplies the
pharyngeal arches and arise from truncus
arteriosus, then enter the dorsal aorta.
The derivatives of aortic arches : are the
adult arteries of head & neck.
C, Horizontal section showing the floor
of primordial pharynx and germ layer
derivatives of the pharyngeal arch
components : each arch consists of
a core of mesenchyme, which is covered
externally by ectoderm and internally by
endoderm.
7. Pharyngeal Arch
Components arch consists of a core of mesenchyme that is
Each
covered externally by ectoderm and internally by
endoderm.
A core of mesenchyme derived from the original
mesenchyme - mesoderm during 3rd week + neural
crest cells (neuroecto-dermal origin) during 4th week
that migrate into the arches.
Skeletal musculature & vascular endothelia are
derived from the original mesenchyme in the
arches.
A typical pharyngeal arch contains :
1-an aortic arch artery : arises from
truncus arteriosus of primordial heart to enter the
dorsal aorta.
2-a cartilaginous rod : that forms the skeleton of arch.
3-a muscular components : to give ms. of head
& neck.
8. Fate of Pharyngeal
Arches
A, lateral view of embryo at 5
week
(32 days) showing pharyngreal arches
+ cervical sinus.
th
B, section illustrating growth of 2nd
arch over 3rd & 4rth arches.
C, embryo of about 33 days.
D, section illustrating early closure
of the cervical sinus during 5th week.
E, embryo of 41 days (end of 6th w.).
F, section showing the transitory
cystic remnant of cervical sinus.
G, drawing of 20-week fetus
illustrating the area of face derived
from the 1st pair of pharyngeal arches.
9. Fate of Pharyngeal
Arches
They contribute to the development of
face, nasal cavities, mouth,larynx, pharynx,
and neck.
During 5th week, 2nd arch enlarges to
overgrow the 3rd & 4th arches, forming
ectodermal depression- the cervical sinus.
B,D
By the end of 7th week, 2nd to 4th
pharyngeal grooves + the cervical sinus
have disappeared, giving the smooth
contour to the neck
10. Derivatives of Pharyngeal
Arch Cartilages :
A, lateral view of 4-week embryo, illustrating location of cartilages in pharyngeal arches.
B, 24-week fetus illustrating adult dreivatives of arch cartilages :
1-Note development of mandible by intramembranous ossification of
mesenchymal tissue surrounding the ventral part of 1st arch cartilage (Meckel’s
cartilage) + development of malleus & incus (middle ear bones) dorsally + anterior
ligament of malleus & sphenomandibular ligament in the middle part. 2-Note, the 2nd
arch cartilage (hyoid or Reichert’s cartilage) gives rise dorsally stapes & styloid
process, in the middle stylohyoid ligament, and ventrally lesser cornu + upper part of
11. Derivatives of Pharyngeal
Arch Cartilages :
B, 3- Note also derivatives of the 3rd arch cartilage which ossifies to form :
greater cornu (horn) + inferior part of the body of hyoid bone.
4- Cartilaginous components of 4th & 6th pharyngeal arches fuse to
form most of laryngeal cartilages (thyroid + cricoid + arytenoid + corniculate +
cuneiform), EXCEPT the cartilage of epiglottis which develops from the mesenchyme
of the caudal part of hypopharyngeal eminence lying in the floor of primordial
pharynx and derived from 3rd & 4th pharyngeal arches.
The 5th arch is often absent, if present it is rudimentary and has No derivatives.
12. Derivatives of Pharyngeal
Arch Muscles :
A, lateral view of 4-week embryo showing the muscles derived from the
pharyngeal arches, the arrow showing the pathway of myoblasts from the occipital
myotomes to form the muscles of tongue.
B, sketch of head & neck of 20-week fetus, showing the 1st pharyngeal arch
forms ms. of mastication & other ms./ 2nd arch forms ms. of facial expression,
post.belly of digastric & other ms. / 3rd arch forms stylopharyngeus./ 4th arch forms
cricothyroid, levator veli palatini + constrictors of pharynx. / 6th arch forms
interinsic ms. of larynx + striated ms of esophagus.
14. Derivatives of Pharyngeal Arch
Nerves
A, lateral view of head &neck and thorax of
4-week embryo showing the cranial nerves :
Trigeminal N.(V), Facial N.(VII),
Glossopharyngeal N.(IX), and Vagus N.(X)—
supplying 1st ,2nd , 3rd & caudal (4th + 6th )
pharyngeal arches, respectively.
B, sketch of head & neck of 20-week fetus
showing the 2 branches of 1st arch nerve (CNV),
maxillary & mandibular branches of trigeminal N
C, Sagittal section of fetal head & neck
showing the sensory nerves of trigeminal N.,
which is the principal sensory N. of head & neck
supplying face, teeth & m.m. of nasal cavity,
palate, mouth & tongue, and is the motor N. for
ms. of mastication.
C, The nerves from 2nd to 6th pharyngeal arches
have little sensory nerves, however, they
innervate m.m. of post.tongue, pharynx & larynx.