supernumerary organs

su·per·nu·mer·ar·y or·gans

organs exceeding the normal number, which may develop from multiple foci of organization in an organ-formative field larger (originally) than that of the definitive main organ; such organs are aberrant but frequently not a cause of disease; illness may persist if they are left in the body after therapeutic removal of the main organ, for example, accessory spleen.
Synonym(s): accessory organs (2)

su·per·nu·mer·ar·y or·gans

(sū'pĕr-nū'mĕr-ar-ē ōr'gănz)
Organs exceeding the normal number, which may develop from multiple foci or organization in an organ-formative field larger (originally) than that of the definitive main organ; such organs are aberrant but frequently not a cause of disease; illness may persist if they are left in the body after therapeutic removal of the main organ, e.g., accessory spleen.