Pharyngeal Arches

1️⃣ Big picture (one-line anchor)

Pharyngeal arches = 6 paired embryonic bars (weeks 4–5) that form face, neck, pharynx, larynx, each arch having its own nerve, muscle, artery, cartilage.

Rule of thumb: Nerve of the arch supplies all its muscles.

2️⃣ What each arch contains (THE CORE LIST)

Each pharyngeal arch has:

• Cartilage → skeletal elements
• Muscle → specific muscle group
• Artery → aortic arch derivative
• Nerve → cranial nerve
• Mesenchyme (from neural crest + mesoderm)

3️⃣ Individual arches (HIGH-YIELD TABLE CONTENT)

1st Arch – Mandibular arch

• Nerve: CN V (V2 + V3)
• Muscles:
• Muscles of mastication
• Mylohyoid
• Anterior belly of digastric
• Tensor tympani
• Tensor veli palatini
• Cartilage (Meckel):
• Malleus, incus
• Mandible (membranous)
• Artery: Maxillary artery
• Key defect: Treacher Collins syndrome

2nd Arch – Hyoid arch

• Nerve: CN VII (Facial)
• Muscles:
• Muscles of facial expression
• Stapedius
• Stylohyoid
• Posterior belly of digastric
• Cartilage (Reichert):
• Stapes
• Styloid process
• Lesser horn + upper body of hyoid
• Artery: Stapedial artery (regresses)

3rd Arch

• Nerve: CN IX (Glossopharyngeal)
• Muscle: Stylopharyngeus
• Cartilage:
• Greater horn + lower body of hyoid
• Artery:
• Common carotid
• Proximal internal carotid

4th Arch

• Nerve: CN X (Superior laryngeal branch)
• Muscles:
• Pharyngeal constrictors
• Cricothyroid
• Levator veli palatini
• Cartilage: Laryngeal cartilages (with 6th)
• Artery:
• Left: Arch of aorta
• Right: Proximal right subclavian

5th Arch

• Absent / rudimentary → no derivatives

6th Arch

• Nerve: CN X (Recurrent laryngeal branch)
• Muscles:
• Intrinsic laryngeal muscles (except cricothyroid)
• Cartilage: Laryngeal cartilages
• Artery:
• Pulmonary arteries
• Left: Ductus arteriosus

4️⃣ Pharyngeal clefts (ectoderm)

• 1st cleft: External auditory canal
• 2nd–4th clefts: Overgrown → cervical sinus (normally disappears)

Persistence → branchial cyst/sinus/fistula (usually along anterior border of SCM).

5️⃣ Pharyngeal pouches (endoderm)

• 1st pouch: Middle ear cavity + auditory tube
• 2nd pouch: Palatine tonsil
• 3rd pouch:
• Inferior parathyroids
• Thymus
• 4th pouch:
• Superior parathyroids
• Ultimobranchial body → C cells (calcitonin)

6️⃣ Neural crest contribution (EXAM FAVORITE)

• Forms cartilage, bone, connective tissue of arches.
• Defects → craniofacial anomalies + cardiac outflow defects.

7️⃣ One-look memory locks

• 1–2 → Face & ear
• 3 → Stylopharyngeus + carotids
• 4–6 → Larynx
• CN pattern: V → VII → IX → X

8️⃣ Common exam traps

• Cricothyroid = 4th arch, not 6th
• Stylopharyngeus = only muscle of 3rd arch
• Inferior parathyroids come from 3rd pouch (but descend lower!)