Both observers declare that men present the anomaly about twice as frequently as women.

It is impossible to account for the accessory glands on the theory of reversion, as they occur with no regularity in situation, but may develop at odd places on the body.

The most frequent position is on the pectoral surface below the true mammae and somewhat nearer the middle line, but an accessory gland has been observed on the left shoulder over the prominence of the deltoid, on the abdominal surface below the costal cartilages, above the umbilicus, in the axilla, in the groin, on the dorsal surface, on the labium majus, and on the outer aspect of the left thigh.

Ahlfeld explains the presence of mammae on odd parts of the body by the theory that portions of the embryonal material entering into the composition of the mammary gland are carried to and implanted upon any portion of the exterior of the body by means of the amnion." Possibly the greatest number of accessory mammae reported is that of Neugebauer in 1886, who found ten in one person.

Peuch in 1876 collected 77 cases, and since then Hamy, Quinqusud, Whiteford, Engstrom, and Mitchell Bruce have collected cases.