• Consists of the pharyngeal arches, pouches, grooves, and membranes.

• Are composed of mesoderm and neural crest cells. (They are formed by migration of neural crest cells around cores of mesoderm covered externally by ectoderm and internally by endoderm.) Each arch has its own cartilaginous, muscular, vascular, and nervous components.

1. Pharyngeal arch 1

• Forms the Meckel's cartilage, which develops the malleus and incus and maxilla, zygomatic and temporal squama, and mandible.
• Forms CN V (V2 and V3), which supply muscles of mastication and mylohyoid, digastric anterior belly, tensor veli palatini, and tensor tympani muscles.

2. Pharyngeal arch 2

• Forms the Reichert's cartilage, which develops the stapes, styloid process, lesser cornu, and upper half of the hyoid bone.
• Forms CN VII, which innervates muscles of facial expression and the digastric posterior belly, stylohyoid, and stapedius muscles.

3. Pharyngeal arch 3

• Forms the third arch cartilage, which forms the greater cornu and lower half of the hyoid bone.
• Forms CN IX, which innervates the stylopharyngeus muscle.

4. Pharyngeal arch 4

• Forms the fourth arch cartilage, which forms the laryngeal cartilages.
• Forms CN X (superior laryngeal branch), which innervates the muscles of the soft palate except the tensor veli palatini, muscles of the pharynx except stylopharyngeus, and the cricopharyngeus muscle

5. Pharyngeal arch 6

• Forms the sixth arch cartilage, which forms laryngeal cartilages.
• Forms CN X (recurrent laryngeal branch), which innervates the intrinsic muscles of the larynx, except cricothyroid, and the upper muscles of the esophagus.

• Are evaginations of the foregut endoderm.
• Pharyngeal pouch 1 forms the epithelium of the auditory tube and the middle ear cavity.
• Pharyngeal pouch 2 forms the epithelium and crypts of the palatine tonsil.
• Pharyngeal pouch 3 forms the inferior parathyroid gland and thymus.
• Pharyngeal pouch 4 forms the superior parathyroid gland and ultimobranchial body.

• Are four invaginations of the surface ectoderm between adjacent arches.
• Pharyngeal groove 1 gives rise to the epithelium of the external auditory meatus and skin over the tympanic membrane.
• Pharyngeal grooves 2, 3, and 4 are obliterated.

• Are located at the junction of each pharyngeal groove and pouch.
• Pharyngeal membrane 1 gives rise to the tympanic membrane.
• Pharyngeal membranes 2, 3, and 4 are obliterated.