mammary gland epithelial cell differentiation peripheral mammary gland bud epithelial cell differentiation The process in which a relatively unspecialized epithelial cell of the mammary placode becomes an epithelial cell at the periphery of the mammary gland bud. Cells at the periphery of the bud are larger that those of the surrounding epithelium and are arranged concentrically. biological_process dph GO:0060645 2009-05-29T08:06:16Z