Pharyngeal Arches, Pouches & Clefts

Arch derivatives

Arch	Nerve	Muscles	Skeletal and ligament derivatives
1st (mandibular)	Trigeminal (V2, V3; motor in V3)	Muscles of mastication, mylohyoid, anterior belly of digastric, tensor tympani, tensor veli palatini	Meckel's cartilage: malleus, incus, sphenomandibular ligament; the mandible itself forms by intramembranous bone around it
2nd (hyoid)	Facial (VII)	Muscles of facial expression, stapedius, stylohyoid, posterior belly of digastric	Reichert's cartilage: stapes, styloid process, stylohyoid ligament, lesser horn and upper body of hyoid
3rd	Glossopharyngeal (IX)	Stylopharyngeus	Greater horn and lower body of hyoid
4th	Vagus (X), superior laryngeal branch	Cricothyroid, pharyngeal constrictors, most soft palate muscles (levator veli palatini)	Laryngeal cartilages (with the 6th)
6th	Vagus (X), recurrent laryngeal branch	Intrinsic laryngeal muscles except cricothyroid	Laryngeal cartilages

Arches are covered by ectoderm, lined by endoderm and filled with mesoderm plus neural crest cells (which form the cartilage and connective tissue of the face).

Structure	Derivative
1st pouch	Middle ear cavity and auditory (eustachian) tube
2nd pouch	Lining of the palatine tonsil crypts
3rd pouch	Inferior parathyroid glands and thymus
4th pouch	Superior parathyroid glands and the ultimobranchial body (parafollicular C cells)
1st cleft	External auditory meatus
2nd–4th clefts	Overgrown by the 2nd arch (cervical sinus) and normally obliterated

A persistent cervical sinus gives a branchial (lateral cervical) cleft cyst along the anterior border of the sternocleidomastoid.
The thyroid does NOT come from a pouch: it descends from the foramen cecum of the tongue; remnants give a midline thyroglossal duct cyst that moves with swallowing and tongue protrusion.

Treacher Collins syndrome: first-arch neural crest defect (often TCOF1) with mandibular and zygomatic hypoplasia, down-slanting eyes and ear malformations.
22q11.2 deletion (DiGeorge): 3rd and 4th pouch failure, causing hypocalcemia from absent parathyroids, T-cell deficiency from thymic hypoplasia, and heart defects.
Hemifacial microsomia: underdevelopment of first- and second-arch structures on one side.

Saying the mandible is made from Meckel's cartilage: it forms by intramembranous ossification lateral to it.
Assigning the posterior digastric to the first arch: anterior belly = 1st arch (V3), posterior belly = 2nd arch (VII).
Giving the inferior parathyroids to the 4th pouch: inferior = 3rd pouch (they migrate farther down with the thymus).
Putting a branchial cleft cyst in the midline: midline neck cysts are thyroglossal duct cysts.

Pick an answer to see right away whether it is correct and why.

Which muscle develops from the first pharyngeal arch?
The stapes, styloid process and lesser horn of the hyoid come from:
A child has hypocalcemia, recurrent infections and a heart defect. Which embryologic structures failed to develop normally?
A painless mass along the anterior border of the sternocleidomastoid in a young adult is most likely from:
Which nerve supplies the muscles derived from the 2nd pharyngeal arch?

0 of 5 answered

Answer key: 1 A · 2 B · 3 D · 4 D · 5 C

Dental School Map · Original study material, written and checked by our team; always confirm clinical decisions against current guidelines.