Enumerate the derivatives of first branchial arch. What are the head and neck structure which develop from 3rd pharyngeal arch and pouch?

In the early embryo, the fore-gut develops between the brain above and the primitive heart below.

The mouth is separated from the pharynx by the buccopharyngeal membrane which disappears around the end of 3^rd week when a series of arches appears in the wall of pharynx. These arches are formed by mesodermal condensations and are known as the branchial arches.The arches fuse ventrally, thus forming u-shaped structures which support the pharynx. Initially there are 6 of these arches, but the 5^th is vestigial and rapidly disappear.

There are 4  branchial pouches internally, 4 branchial grooves externally. These separate the remaining five branchial arches.

Each branchial pouch is lined by endoderm and branchial grooves by endoderm. These pouches and grooves are separated by a thin layer of mesoderm. If this endoderm, mesoderm & ectoderm layers break down a branchial fistula is formed.

A central core of cartilage develop in each arch and muscles differentiate from the surrounding mesoderm.
Each arch is supplied by Cranial Nerve and by an artery.

1^st Branchial arch –

• Maxilla, Incus, Malleus, Anterior ligament of malleus, sphenomandibular ligament, Mandible
• Muscles- Muscles of mastication
• Nerve- Mandibular Branch of the Trigeminal Nerve
• Artery- Maxillary artery

2^nd Branchial arch-

• Stapes, styloid process, stylohyoid ligament, lesser cornua and upper part of the body of the hyoid bone.
• Muscles of facial expression, Posterior belly of Diagastric
• Stylohyoid muscle
• Auricles muscles stapedius muscles
• Nerve- Facial
• Artery- 2^nd aortic arch Rarely persist as stapedial

3^rd Branchial arch

• Greater cornua and lower part of the body of the hyoid bone
• Muscles- Stylopharyngeus
• Nerve- Glossopharyngeal Nerve
• Artery – 3^rd aortic artery which persist as part of the Internal Carotid Artery

4^th Branchial arch

• Thyroid and epiglottis
• Muscles- cricothyroid, all  muscles of palate except tensor veli palatini
• Artery- left aorta, Rt- subclavian artery

5^th Brachial arch

• Cricoid, Arytenoid, corniculate, cuneiform
• Muscles:  All muscles of pharynx except cricothyroid
• Artery- Pulmonary

1^ST Branchial Pouch:

Growth laterally to form: The Eustachian tube and the middle ear.

2^nd Branchial Groove:

Deepens to form (only Dorsal part) External auditory meatus and remaining disappear but if it persist collaural fistula is formed.

Pinna

Number of tubercles appear at the dorsal each of the first and 2^nd branchial arches. These tubercles surrounds the dorsal end of the 1^st groove which is to be form the External Auditory Canal.

2^nd /3^rd /4^th  Branchial pouches and grooves

2^nd pouch –Dorsal part contribute to middle ear

ventral part – supra tonsillar fossa.

Externally 2^nd Branchial arch grow caudally and covers over 3^rd 4^th 6^th arch

3^rd pouch –Dorsal part Inferior parathyroid gland

Ventral part- Thymic part

Deep pit/sinus lined by ectoderm. Its lip fuse and ectoderm lining cystic space is produced which disappear later.