A<unk>  is an additional<unk>  occurring in mammals, including humans. They are often mistaken for moles. Studies variously report the prevalence of<unk> s as approximately 1 in 18 and 1 in 40. The<unk> s appear along the two vertical "milk lines", which start in the armpit on each side, run down through the typical<unk> s and end at the groin. They are classified into eight levels of completeness from a simple patch of hair to a milk-bearing breast in miniature.
Supernumerary nipple
Inverted nipple
Cracked nipple
Accessory breast
Bifid penis
Genital wart
Genu recurvatum
Webbed penis