Supernumerary mammary gland in the neck consists of a nipple and a small ductal tree in K14-Eda mice.

(A) Macroscopic view of the nipple of mammary gland 1 and two supernumerary nipples in the neck of a pregnant K14-Eda female. (B) Expression of the nipple marker keratin2e was readily observed in the endogenous but not in the supernumerary nipple. (C-E) Carmine alum stained ductal tree of mammary gland 1 and a supernumerary gland of K14-Eda female mouse at age of 5 weeks (C), on pregnancy day 14 (D), and day of parturition (E). (Scale bar: 500 μm)