branchial cleft
nounMedical Definition of branchial cleft
: one of the open or potentially open clefts that occur on each side of the neck region of a vertebrate embryo between the branchial arches, are formed by the meeting of an external furrow in the ectoderm with a pharyngeal pouch, may or may not extend through from the exterior to the cavity of the mouth and pharynx, and correspond to the gill slits of fishes and amphibians
— called also pharyngeal cleft, pharyngeal slit, visceral cleft