The external opening of the branchial fistula is nearly always situated in the lower third of the neck near the anterior border of which of the following muscle

Branchial fistula • A branchial sinus or fistula (congenital type) is formed when the 2nd arch fails to fuse with the 5th arch or Epipericardial ridge. It represents a persistent second branchial cleft. • Bursting of the branchial cyst or an inadvertent incision may lead to formation of acquired branchial fistula. • The external opening of the fistula is nearly always situated in the lower third of the neck near the anterior border of the sternomastoid muscle.