The tendency to reduplication does not confine itself to the cerebrospinal axis, but extends to the individual parts of the body, more especially to those accessory parts which, as it were, bud out from the main body.

Polydactylism is the reduplication of the fingers and toes, a somewhat common malformation. The lowest degree is that in which a small appendage is attached by a narrow neck to the outer aspect of the hand or foot. This may or may not have a bony phalanx. In a higher degree the finger has an independent metacarpal bone, and even an added carpal one. In the highest degree the hand or foot has nine or ten fingers or toes. The multiplication may affect one hand or one foot, or both hands or both feet, or all the four members simultaneously. When individual fingers or toes are divided it is most frequently the little one; next to that the thumb or great toe, and very seldom one of the intermediate ones.

These malformations are remarkably subject to hereditary transmission. It is also remarkable that supernumerary digits when amputated are liable to grow again. (See Darwin, " Animals and Plants under Domestication," vol. ii., p. 14).

Multiplication Of Bones And Muscles

The coccyx, composed of three or four ill-formed vertebra, has nine primordial vertebrae in the embryo. " A' persistence of these would give rise to something like a true Tail, but no authentic case has been recorded in man in which bones have been present in the caudal appendage. The vertebrae may be prolonged as a membrane from the coccyx forming a core to a protuberance, but sometimes the appendage is not a proper tail at all, but merely a cutaneous projection.

The ribs are somewhat frequently reduplicated, so that we may have cervical or lumbar ribs.

Reduplication of muscles is frequent, and some anomalies of this kind are so common as to be regarded as mere varieties.

Supernumerary mammae are perhaps doubtfully to be regarded as instances of Reduplication of parts, as they may be rather due to reversion. There are cases of three, four, and five mammse. The extra mammae are usually near the proper ones, and generally under them, but there are cases of very considerable removal, as in the inguinal region, or on the back. The mammae may be represented only by nipples.

Internal organs are sometimes reduplicated, most commonly the spleen, but also the pancreas and other organs.