Comparative embryology has shown that all vertebrate embryos have folds in the neck region called?

The folds in the neck region of the mammalian embryo, that are erroneously called "gills", are not gills in any sense of the word and never have anything to do with breathing. They are merely flexion folds, or wrinkles, in the neck region resulting from the sharply down turned head and protruding heart of the developing embryo. These folds eventually develop into a portion of the face, inner ear, tonsils, parathyroid and thymus. No reputable medical embryology text claims that there are "gill slits" in mammals.