Embryology · Head and neck: pharyngeal arches

Second pharyngeal arch (hyoid arch) and the facial nerve !

Embryonic structure

The second arch gives the muscles of facial expression, the stapes and part of the hyoid. Its nerve is the facial nerve.

Updated 2026-11-01

See it in 3D: Stapes · Hyoid bone · Temporal bones · Facial nerve (VII) · Facial nerve branches · Stylohyoid · Digastric · Orbicularis oris · Orbicularis oculi · Buccinator · Frontalis · Occipitalis · Platysma · Zygomaticus major · Zygomaticus minor · Risorius · Mentalis · Depressor anguli oris · Levator labii superioris · Nasalis · Procerus

What it is

The second pharyngeal arch, or hyoid arch, holds Reichert's cartilage and is supplied by the facial nerve (VII). It gives every muscle of facial expression, stapedius, the stapes, the styloid process and the upper hyoid. It also grows down over arches 3 and 4: when that closure fails, branchial cysts and fistulas remain.

Key facts

Week 5: the second arch overgrows arches 3 and 4.
Buccinator is a muscle of facial expression (VII), even though it helps with chewing.
Digastric has two bellies from two arches: anterior (1st, V3) and posterior (2nd, VII).

Structure

Reichert's cartilage: the arch's cartilage bar.
Mesenchyme from rhombomere 4 neural crest; it expresses HOXA2.
Nerve: facial (VII), which follows its muscles across the face and scalp.
Artery: the second aortic arch, which regresses and leaves the stapedial and hyoid arteries.
Its caudal edge grows over arches 3 and 4 and joins the epicardial ridge, closing the cervical sinus.

What it becomes

Nerve: facial (VII).
Muscles: all muscles of facial expression (orbicularis oculi and oris, buccinator, frontalis, occipitalis, platysma, zygomatics, auriculars), stapedius, stylohyoid and posterior belly of digastric.
From Reichert's cartilage: stapes, styloid process of the temporal bone, stylohyoid ligament, lesser horn and upper body of the hyoid.
Artery: stapedial and hyoid arteries, which barely persist in the adult.

Markers

HOXA2
Neural crest (R4)
Reichert's cartilage

Clinical notes

Peripheral facial palsy (for example Bell palsy): loss of expression on one side of the face and, if stapedius is involved, hyperacusis.
Failed caudal growth of the 2nd arch: branchial cysts, sinuses or fistulas along the front of sternocleidomastoid.
Fixed or malformed stapes: conductive hearing loss.

Test yourself

Think of the answer, then tap the question to see it.

Which nerve supplies stapedius, and which arch does it come from?

The facial nerve (VII); stapedius comes from the second arch.

What comes from Reichert's cartilage?

The stapes, styloid process, stylohyoid ligament, and the lesser horn with the upper body of the hyoid.

Why does digastric have two different nerve supplies?

Its anterior belly comes from the 1st arch (V3) and its posterior belly from the 2nd arch (VII).

Which developmental failure of the second arch causes lateral branchial cysts?

Failure to grow down over arches 3 and 4, leaving a remnant of the cervical sinus.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

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Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: Embryology, Branchial Arches - StatPearls - NCBI Bookshelf (StatPearls Publishing (NCBI Bookshelf), 2023); Embryology, Face - StatPearls - NCBI Bookshelf (StatPearls Publishing (NCBI Bookshelf), 2024); Langman's Medical Embryology, 13th ed., ch. 17: Head and Neck (Wolters Kluwer, 2015).

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Representative model, for educational purposes only.