Neurosurgery is predicated on the knowledge of the structure-function relationship of the brain. When the topic is broached in its historiography, it begins with Fritch and Hitzig's report on the localization of motor function in the cortex of the dog and skips rapidly to Wilder Penfield's homunculus. In that gap are found the origins of modern neurosurgery in 3 papers published by Jean-Martin Charcot and Albert Pitres between 1877 and 1879 in which they describe the somatotopic organization of the human motor cortex and draw the first human brain map. Their findings, obtained through the clinicopathological method, gave relevance to David Ferrier's observations in animals. Their work was extensively cited, and their illustrations reproduced by Ferrier in his landmark lecture to the Royal College of Physicians in 1878. It was known to William Macewen, who used localization to guide him in resecting intracranial mass lesions, and to William Osler and John Hughlings Jackson, who were early advocates of intracranial surgery. This paper describes Charcot and Pitres' discovery of the cortical origin of human voluntary movement and its somatotopic organization, and their influence on 19th-century intracranial surgery. It fills a gap in the historiography of cerebral localization and neurosurgery.