Internal orifice of branchial Fistula is located at:
Branchial festula represents 2nd branchial cleft:

Internal orifice: Anterior aspect of posterior tonsillar pillar.
External orifice: Lower third of neck over anterior border of sternocleidomastoid.
Lower third of neck over anterior border of starnocleidomastoid
Floor of external auditory canal
Posterior tonsillar pillar
Anterior to tragus on the ipsilateral side