Marc Dax and the discovery of the lateralisation of language in the left cerebral hemisphere.

In 1836, Marc Dax presented a revolutionary conclusion based on both his clinical observations and reports from the literature: the localisation of language in the left hemisphere. Twenty-seven years later, his son, Gustave Dax, extended and enriched his work. Their involvement in 19th century neuropsychology is impressive and recognition should have been considerable. However, according to the vast majority of historians of neurology, neuropsychology and aphasiology, the priority in establishing the dominance of the left brain hemisphere for speech goes to Paul Broca in an undivided way. Is it possible that Marc Dax's and his son, Gustave Dax's works were entirely unknown? Were they known and utterly forgotten? Were they ignored? How did we get to know that they existed? The aim of the present paper is to try to answer those and other questions and to demonstrate that there is abundance of data pointing out that the priority of the discovery of left hemisphere dominance for speech ought to be, at least, shared by Dax and Broca.