The 5-week-old human embryo has external gill slits (grooves). they do not develop into gills, so what happens to them?

As the gills does not develop into gills, they are likely to contribute to the development of the lower jaw of the human embryo though after the embryonic stage, the gill slits won’t be retained or won’t be a part of a human as they only appear during embryonic stage for the development of the lower jaw.