Carlisle in 'Phil. Transact.' 1814 page 94. A. Walker on 'Intermarriage' 1838 page 140 gives a case of five generations; as does Mr. Sedgwick in 'Brit. and Foreign Medico-Chirurg. Review' April 1863 page 462. On the inheritance of other anomalies in the extremities see Dr. H. Dobell in volume 46 of Medico-Chirurg. Transactions 1863; also Mr. Sedgwick in op. cit. April 1863 page 460. With respect to additional digits in the negro see Prichard 'Physical History of Mankind.' Dr. Dieffenbach 'Jour. Royal Geograph. Soc.' 1841 page 208 says this anomaly is not uncommon with the Polynesians of the Chatham Islands; and I have heard of several cases with Hindus and Arabs.)
Additional digits have been observed in negroes as well as in other races of man, and in several of the lower animals, and have been inherited. Six toes have been described on the hind feet of the newt (Salamandra cristata), and are said to have occurred with the frog. It deserves notice, that the six-toed newt, though adult, preserved some of its larval characters; for part of the hyoidal apparatus, which is properly absorbed during the act of metamorphosis, was retained. It is also remarkable that in the case of man various structures in an embryonic or arrested state of development, such as a cleft-palate, bifid uterus, etc., are often accompanied by polydactylism. (12/31. Meckel and Isid G. St. Hilaire insist on this fact. See also M. A. Roujou 'Sur quelques Analogies du Type Humain' page 61 published, I believe, in the 'Journal of the Anthropolog. Soc. of Paris' January 1872.) Six toes on the hinder feet are known to have been inherited for three generations of cats. In several breeds of the fowl the hinder toe is double, and is generally transmitted truly, as is well shown when Dorkings are crossed with common four-toed breeds (12/32. 'The Poultry Chronicle' 1854 page 559.) With animals which have properly less than five digits, the number is sometimes increased to five, especially on the front legs, though rarely carried beyond that number; but this is due to the development of a digit already existing in a more or less rudimentary state. Thus, the dog has properly four toes behind, but in the larger breeds a fifth toe is commonly, though not perfectly, developed. Horses, which properly have one toe alone fully developed with rudiments of the others, have been described with each foot bearing two or three small separate hoofs: analogous facts have been noticed with cows, sheep, goats, and pigs. (12/33. The statements in this paragraph are taken from Isidore Geoffroy St. Hilaire 'Hist. des Anomalies' tome 1 pages 688-693. Mr. Goodman gives, 'Phil. Soc. of Cambridge' November 25, 1872 the case of a cow with three well developed toes on each hind limb, besides the ordinary rudiments; and her calf by an ordinary bull had extra digits. This calf also bore two calves having extra digits.)
There is a famous case described by Mr. White of a child, three years old, with a thumb double from the first joint. He removed the lesser thumb, which was furnished with a nail; but to his astonishment it grew again and reproduced a nail. The child was then taken to an eminent London surgeon, and the newly-grown thumb was removed by its socket-joint, but again it grew and reproduced a nail. Dr. Struthers mentions a case of the partial regrowth of an additional thumb, amputated when a child was three months old; and the late Dr. Falconer communicated to me an analogous instance. In the last edition of this work I also gave a case of the regrowth of a supernumerary little-finger after amputation; but having been informed by Dr. Bachmaier that several eminent surgeons expressed, at a meeting of the Anthropological Society of Munich, great doubt about my statements, I have made more particular inquiries. The full information thus gained, together with a tracing of the hand in its present state, has been laid before Sir J. Paget, and he has come to the conclusion that the degree of regrowth in this case is not greater than sometimes occurs with normal bones, especially with the humerus, when amputated at an early age.