In May, 1914, an intracranial operation for exposing chiasmal lesions was devised and successfully performed on a patient with an hypophysial cyst. It was unlike the procedure of Krause, McArthur and the earlier operation of Frazier, in that it was an intradural rather than an extradural approach. It antedated the later operation of Frazier and the procedure of Adson—operations which, although differing in some details, are in principle the same. It has been consistently employed in lesions suitable for its use, first, because, at the time it was devised a serious trial of an intracranial approach had never been made, and second, because of the desire to learn whether such an approach offered more in the treatment of chiasmal lesions than does the popular nasal approach. Between 1914 and 1918, thirty-seven patients with chiasmal lesions have come to us for treatment. Six patients were not treated, either because operation did