The cartilage of the first arch, like that of the other arches, is derived from neural crest cells. It is called Meckel’s cartilage and it largely regresses, except for the proximal portion. which gives rise to the malleus and incus of the middle ear.
In the maxillary process, mesenchyme, largely derived from neural crest, undergoes intramembranous ossification to produce:

• maxillary bone
• zygomatic bone
• temporal bone

The mesodermal mesenchyme of the first arch gives rise to eight pairs of muscles of the head region. Four of these pairs of muscles move the mandible during mastication and are called the muscles of mastication. They include the temporalis, masseter and the medial and lateral pterygoids. Four additional pairs of muscles develop from the mesenchyme. Anterior belly of digastric, mylohyoid, tensor velli palatini and tensor tympani.
All of these muscles are innervated by the trigeminal nerve, CN V, the nerve of branchial arch I.

The pharyngeal pouches are lateral out growths of the foregut region. As such, they are lined with endoderm. Each pharyngeal pouch differentiates into separate components of the head and neck. The endoderm of the first pharyngeal pouch forms the lining of the pharyngotympanic tube and middle ear cavity all highlighted in yellow.

The branchial grooves are ectodermally lined spaces between adjacent branchial arches. The ectoderm of the first branchial groove forms the lining of the external auditory meatus and lateral surface of the tympanic membrane all highlighted in blue in the diagram. The tympanic membrane is formed from ectoderm of the branchial groove, endoderm of the branchial pouch and intervening mesoderm.

The cartilage of the second arch, which is derived from neural crest, is known as Reichert's cartilage. It gives rise to the following structures:

• stapes of the middle ear cavity (note that malleus and incus are from Arch I)
• styloid process
• stylohyoid ligament
• lesser horn of hyoid bone
• upper part of the body of the hyoid bone

Several pairs of muscles are derived from the mesenchyme of the second branchial arch. These include:

• stapedius
• stylohyoid
• posterior belly of digastric
• mimetic muscles, including

• • frontalis
• • orbicularis oris
• • orbicularis oculi
• • buccinator

The endoderm of the second pharyngeal pouch forms the lining of the tonsillar fossa for the palatine tonsils.

The cartilage of the third branchial arch gives rise to the greater horn and inferior part of the body of the hyoid bone.

The mesodermal mesenchyme of the third arch forms a single muscle, stylopharyngeus. This muscle is the only muscle innervated by the glossopharyngeal nerve (CN IX), the nerve of the third arch.

The endoderm of the third pharyngeal pouch forms a dorsal bud and a ventral bud. The ventral buds of the third pouches, fuse in the midline and migrate into the superior mediastinum to form the thymus. The dorsal bud of each pouch forms an inferior parathyroid gland located behind the inferior pole of each lobe of the thyroid gland.

The cartilages of the IV through VI arches remain as cartilage and for the skeleton of the larynx. The consist of both paired and unpaired cartilages.

The mesenchyme of the VI through VI branchial arches give rise to many muscles, all of which are innervated by branches of the vagus nerve (CN X) the nerve of these arches. These include the pharyngeal constrictors and the muscles of the larynx.

The fourth pharyngeal pouch forms a dorsal and ventral bud as does the third pouch. The dorsal buds of the fourth pharyngeal pouches form the superior parathyroid glands located behind the superior poles of the thyroid glands. The ventral buds of the fourth pharyngeal pouches interact with the endoderm of the fifth pharyngeal pouches and neural crest cells to form what is called the ultimobranchial body. This contributed to the development of the parafollicular (C-cells) of the thyroid gland.