This subject has a moderately extensive literature and examples have been recorded by various authors for some years. Most of the cases, however, have been the subjects of some pathological lesion, either congenital or acquired. Perhaps the earliest authentic case is the one originally described by Rosinius Lentilius in 1698, and quoted by Critchley, of a female, presumably young, epileptic sinistrad. The sex is not as important as the other factors, but it is a pity that there is no reference to the intellectual capacity. It is, if nothing else, a pointer to the usual type of case studied. In the adults, hemiplegics seem to have proved the most fruitful source for those collecting examples of this phenomenon, although a full list of causes is well known.