This arises by imperfect closure of the lateral aspects of the branchial arches. There is a small aperture, only sufficient to admit a small probe or bristle, usually situated half an inch to an inch above the sterno-clavicular articulation, more rarely further upwards and outwards, or in the middle line. The aperture leads into a canal which is directed towards the pharynx or oesophagus, and may communicate with one or other of these. It is stated that the fistula may communicate with the larynx, but this is doubtful (Karewski). The fistula is Imed with mucous membrane, and mucus may be discharged at the orifice. There is usually one fistula which is most frequently on the right side or in the middle, but occasionally there are two symmetrically placed.

Occasionally, from a similar origin, we have Cysts in the neck without external, aperture. These may be filled with serous fluid (Congenital hydrocele of the neck), or may have a more epidermic structure and contents, so as to constitute Dermoid cysts. By the bursting of these latter, or after opening by the surgeon, a fistula may remain, this being one of the ways in which the fistula colli congenita may originate.