The boy's father showed similar malformations, and in five generations 21 out of 28 individuals were thus malformed, ten females and 11 males.
The deformity was especially transmitted in the female line.
Instances of supernumerary thumbs are cited by Panaroli, Ephemerides, Munconys, as well as in numerous journals since.

This anomaly is not confined to man alone; apes, dogs, and other lower animals possess it.
Bucephalus, the celebrated horse of Alexander, and the horse of Caesar were said to have been cloven-hoofed.
Hypertrophy of the digits is the result of many different processes, and true hypertrophy or gigantism must be differentiated from acromegaly, elephantiasis, leontiasis, and arthritis deformans, for which distinction the reader is referred to an article by Park.

Park also calls attention to the difference between acquired gigantism, particularly of the finger and toes, and another condition of congenital gigantism, in which either after or before birth there is a relatively disproportionate, sometimes enormous, overgrowth of perhaps one finger or two, perhaps of a limited portion of a hand or foot, or possibly of a part of one of the limbs.

The best collection of this kind of specimens is in the College of Surgeons in London.
Curling quotes a most peculiar instance of hypertrophy of the fingers in a sickly girl.

The middle and ring fingers of the right hand were of unusual size, the middle finger measuring 5 1/2 inches in length four inches in circumference.