Anatomy · Embryology and Genetics

Development of pharyngeal arches, pouches and clefts

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  • Pharyngeal apparatus: arches, internal pouches, external clefts, and intervening membranes in the primitive pharynx's lateral wall.
  • Develops early in the fourth week; five arches remain after the rudimentary fifth disappears (1 to 4, 6).

Pharyngeal Arches: Formation and Components

Organization

  • Each arch: core of mesoderm, covered externally by ectoderm and internally by endoderm.
  • Four components per arch: cartilage bar, muscle mass, artery, and nerve.
  • Cartilage derives from neural crest mesenchyme; muscle from the arch's mesodermal cord; the artery connects the aortic sac to the dorsal aorta; the nerve arises from the hindbrain.
  • Paraxial-mesoderm-derived arch mesoderm forms most head and neck muscles; neural-crest-derived mesoderm forms skeletal and connective tissue elements.
  • Nerve of the arch gives motor supply to muscles derived from it and sensory supply to overlying skin and mucosa; nerve supply thus indicates a muscle's arch of origin.