At high magnification, the appearance of a normal breast acinus is shown here. Note the epithelial cells lining the lumen demonstrate apocrine secretion with snouting, or cytoplasmic extrusions, into the lumen. A layer of myoepithelial cells, some of which are slightly vacuolated, is seen just around the outside of the acinus. Suckling by the infant signals release of oxytocin which induces myoepithelial cell contraction.