BRANCHIAL ARCHES

The human head and neck structures are derived from discrete evolutionary
precursors (ancient gill apparatus)
 5 pairs of arches form on either side of the pharyngeal foregut
 Begins on Day 22 (week 3)
 Layers
1) outer ectoderm
2) inner endoderm
3) mesenchyme core derived from lateral plate mesoderm with contributions
from adjacent somites/somitomeres and neural crest
 Each arch separated by
1. ectodermally lined cleft
2. mesodermal pharyngeal membrane
3. endodermal pharyngeal pouch
2. Arch 5 never forms in humans or promptly regresses
3. Only first cleft forms a definitive structure - Clefts 2-4 are obliterated
 Constituents
1) cartilaginous support
2) aortic arch artery
3) cranial nerve
Branchial Arch 1
Artery:
Maxillary artery
Skeletal:
From maxillary cartilage
1) sphenoid
2) incus
From mandibular cartilage (Meckel’s)
1) malleus
2) sphenomandibular ligament
From direct ossification of dermal mesenchyme
1) maxilla
2) zygoma
3) squamous portion of temporal bone
4) mandible
Muscles (from cranial somitomere 4)
1) temporalis
2) masseter
3) lateral pterygoid
4) medial pterygoid
5) mylohyoid
6) anterior belly digastric
7) tensor tympani
8) tensor palate
Cranial Nerve
1) Maxillary and mandibular divisions of trigeminal nerve
Pouch
1) Tubotympanic recess – tympanic cavity and Eustachian tube
2) Anterior 2/3rd tongue
1st Branchial cyst
 Located inferior or ventral to external acoustic meatus
 May drain thru a cervical aural fistula which usually opens into the EAM
Branchial Arch 2
Artery:
Stapedial artery
Skeletal – Reichert’s cartilage
1) Stapes
2) Styloid process
3) Hyoid bone – lesser horn and superior rim of body
4) Stylohyoid ligament
Muscles (from cranial somitomere 6)
1) Muscles of facial expression
2) Posterior belly digastric
3) Fronto-occipitalis
4) Stylohyoid
5) Stapedius
Cranial Nerve
1) Facial nerve
Cleft
1) External acoustic meatus
Pouch
1) Palatine tonsils
2) Copula tongue (overgrown)
2nd Branchial cyst
 Located just ventral to the ventral border of sternomastoid
 May have external and/or internal fistula
 Internal fistula travels through carotid bifurcation to open into palatine tonsils
Branchial Arch 3
Artery:
Common carotid artery
Skeletal
1) Hyoid – greater horn and inferior rim of body
Muscles (from cranial somitomere 7)
1) stylopharyngeus
Cranial Nerve
1) Glossopharngeal nerve
Pouch
1) thymus gland
2) inferior parathyroid glands
Branchial Arch 4
Artery:
Arch Aorta
Skeletal
1) Laryngeal cartilages
Muscles (from occipital somites 2-4)
1) Pharyngeal constrictors
2) Cricothyroid
3) Levator veli palatini
Cranial Nerve
1) Superior laryngeal branch of Vagus nerve
Pouch
1) Superior parathyroid glands
Branchial Arch 6
Artery:
Ductus arteriosus
Skeletal
1) Laryngeal cartilages
Muscles (from occipital somites 1-2)
1) Intrinsic muscles larynx
Cranial Nerve
2) recurrent laryngeal branch of Vagus nerve
Pouch
Ultimobranchial bodies
– differentiate into C cells (parafollicular) of thyroid
– produce calcitonin
Origins of craniofacial muscles
Mesodermal Origin
Somitomeres 1, 2
Somitomere 3
Somitomere 4
Somitomere 5
Somitomere 6
Somitomere 7
Somites 1, 2
Somites 2-5
Muscles
Superior, medial and ventral recti
Superior oblique
Muscles of mastication
Lateral rectus
2nd arch muscles
Stylopharyngeus
Intrinsic laryngeals
Tongue muscles
Innervation
CN III
CN IV
CN V
CN VI
CN VII
CN IX
CN X
CN XII