<prompt> The collaural fistula is an abnormality of1st branchial arch1st branchial cleft2nd branchial arch2nd branchial cleft  <response>: The collaural fistula is a 1st branchial cleft anomaly which arises from the failure of fusion of the ventral pa of the 1st cleftIts upper pa opens into the floor of the external auditory canalIts lower pa opens in the neck between the angle of the mandible and sternocleidomastoid muscleRef: PL Dhingra, Diseases of Ear, Nose Throat, 7th edition, pg no. 53 