Second branchial arch

Pharyngeal arch
The scheme of the pharyngeal arch - adapted from Gray's anatomy.
Details
Carnegie stage	10
Identifiers
Latin	arcus pharyngei
MeSH	A16.254.160
Code	TE E5.4.2.0.0.0.2
Anatomical terminology []

The pharyngeal arches are structures seen in the development of vertebrates, are recognisable precursors for numerous structures. The arches develop into the branchial arches or gill arches in fish.

In the human embryo, the arches are first seen during the fourth week of development. They appear as a series of outpouchings of mesoderm on both sides of the developing pharynx. The vasculature of the pharyngeal arches is also known as the aortic arches.

In fish, the branchial arches support the gills.

In vertebrates, the pharyngeal arches are derived from all three germ layers.Neural crest cells enter these arches where they contribute to features of the skull and facial skeleton such as bone and cartilage. However, the existence of pharyngeal structures before neural crest cells evolved is indicated by the existence of neural crest-independent mechanisms of pharyngeal arch development. The first, most anterior pharyngeal arch gives rise to the oral jaw. The second arch becomes the hyoid and jaw support. In fish, the other posterior arches contribute to the branchial skeleton, which support the gills; in tetrapods the anterior arches develop into components of the ear, tonsils, and thymus. The genetic and developmental basis of pharyngeal arch development is well characterized. It has been shown that Hox genes and other developmental genes such as DLX are important for patterning the anterior/posterior and dorsal/ventral axes of the branchial arches. Some fish species have a second set of jaws in their throat, known as pharyngeal jaws, which develop using the same genetic pathways involved in oral jaw formation.