The first, most anterior pharyngeal arch gives rise to the oral Jaw.

http://en.wikipedia.org/wiki/Pharyngeal_slit

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 brachial 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 jaws in their throat, known as pharyngeal jaws, which develop using the same genetic pathways involved in oral jaw formation.