Extra (supernumerary or accessory) nipples or breast tissue

Extra nipples or breast tissue is fairly common (1-6% of women) and is a result of incomplete regression of the mammary ridge (milk line) during the development of the embryo before birth.

Pathology Outlines - Supernumerary / accessory tissue

Accessory Breast Tissue in Pregnancy

Nipple Deformities: What Are They, Signs, Symptoms, and More

Supernumerary nipple - wikidoc

Internet Scientific Publications

If a girl has a third nipple, would it develop into a third breast

25 Breastfeeding Teaching Tools ideas

Supernumerary (Extra) Nipple Removal

Frontiers Ectopic Breast Tissue in the Inguinal Region: A Case Report and Suggestion of Indications for Excision

Third Nipple: Types, Causes, Removal, and More

Atlas of breast cancer early detection

KellyMom