Dr. Aymen Ahmed Warille

Dr. Nermeen Noor El-Dien

Pharyngeal arches

• most typical feature in development of the head and neck is formed by the pharyngeal or branchial arches. These arches appear in the fourth and fifth weeks of development and contribute to the characteristic external appearance of the embryo.

• Initially, they consist of bars of mesenchymal tissue separated by deep clefts known as pharyngeal (branchial) clefts

4 –week

embryo

Pharyngeal

arch

Pharyngeal

cleft

Scanning electron micrograph of a human

embryo

Nasal placode

2nd &3rd

Pharyngeal

arches

• Simultaneously, with development of the arches and clefts, a number of outpocketings, the pharyngeal pouches, appear along the lateral walls of the pharyngeal gut, the most cranial part of the foregut.

• Pharyngeal arches not only contribute to formation of the neck, but also play an important role in formation of the face.

.

Pharyngeal pouches as outpocketings of the foregut and the primordium of the thyroid gland and aortic arches

Development of the pharyngeal arches. A. 25 days. B. 28 days. C. 5 weeks.

• Six pharyngeal arches develop by thickening of the mesoderm on each side of the primitive pharynx.

• These arches are separated externally by grooves covered by ectoderm called pharyngeal cleft , and are separated internally by grooves covered by endoderm called pharyngeal pouches.

• The 5th pair of pharyngeal arches degenerates completely .

*Four

ectodermal

clefts.

*Five

endodermal

pouches.

*Six

mesodermal

arches

• The following structures develop from the mesoderm of each arch of the remaining 5 pairs :

1) a bar of cartilage which may change to bone

2) striated muscles.

3) an aortic ( pharyngeal) arch artery.

• Each arch receives a nerve from the hindbrain ( pons and medulla oblongata)that supplies the muscles of the arch.

Pharyngeal arches and

their derivatives

The first pharyngeal arch • consists of a dorsal portion, the maxillary process,

which extends forward beneath the region of the eye, and a ventral portion, the mandibular process, which contains Meckel’s cartilage

• During further development, Meckel’s cartilage disappears except for two small portions at its dorsal end that persist and form the incus and malleus

• Mesenchyme of the maxillary process gives rise to the premaxilla, maxilla, zygomatic bone, and part of the temporal bone through membranous ossification

• The mandible is also formed by membranous ossification of mesenchymal tissue surrounding Meckel’s cartilage.

Arch Bones and ligaments

from cartilage

Striated muscles

Arch artery Nerve

First arch 1) Mallus 2)Incus 3)Spheno-mandibular ligament. 4)Mandible & maxilla . 5) Palatine bone 6)Squamous temporal bone .

1) Muscles of mastication . 2) Tensor palati. 3) Tensor tympani. 4) Mylohyoid . 5) Anterior belly of digastric.

Maxillary artery

Mandibular nerve

( trigeminal )

SECOND PHARYNGEAL ARCH

• The cartilage of the second or hyoid arch (Reichert’s

cartilage) gives rise to the stapes, styloid process of the temporal bone, stylohyoid ligament, and ventrally, the lesser horn and upper part of the body of the hyoid bone .

• Muscles of the hyoid arch are the stapedius, stylohyoid, posterior belly of the digastric, and muscles of facial expression.

• The facial nerve, the nerve of the second arch, supplies all of these muscles.

Arch Bones and ligaments

Striated muscles

Arch artery Nerve

Second arch -Stapes -Styloid process -Lesser horn and upper ½ of hyoid bone

-Ms of face . -Occipitofrontalis muscle -Platysma -Post .belly of digastric. -Stylohyoid. -stapedius.

Stapedial artery Facial nerve.

Third arch -Greater horn and lower ½ of hyoid bone

Stylo-pharyngeus. Common and internal carotid artery

Glosso-pharyngeal nerve.

Fourth arch -Thyroid cartilage -Cuniform cartilage.

Cricothyroid Arch of aorta Rt subclavian artery.

Superior laryngeal nerve

Sixth arch Other cartilage of larynx

Other interinisc muscles of larynx

Pulmonary arteries.

Recurrent laryngeal nerve.

Pharyngeal pouches 1- first pouch :

• gives rise to a diverticulum called tubotympanic recess that forms the mucous membrane of middle ear and auditory tube .

Second pouch:

• Palatine tonsils.

Third pouch :

• Most of thymus gland ,

• inferior parathyroid gland .

Fourth pouch :

• Superior parathyroid gland

• A small part of the thymus gland.

Pharyngeal pouches

Pharyngeal clefts

first cleft :

• It deepens to become the external auditory meatus . Its bottom forms the outer layer of the ear drum.

2nd , 3rd & 4th clefts :

• These clefts become buried by the 2nd pharyngeal arch , which grows inferiorly in the neck leaving a cervical sinus lined with ectoderm.

• Later on , cervical sinus becomes obliterated & the neck becomes smooth.

Congenital anomalies of the branchial arches

1- branchial fistula :

• When the 2nd pharyngeal arch fails to grow caudally over the 3rd &4th arches.

• the 2nd , 3rd &4th clefts remain in contact with the surface by a narrow canal . It usually lies along the anterior border of sternomastoid muscle.

2- branchial (cervical ) cyst :

• Due to persistence of the cervical sinus . It lies usually below the angle of the jaw.

Patient with a lateral

cervical cyst. These cysts

are always on the lateral

side of the neck in front of

the sternocleidomastoid

muscle