Some thirty years ago, the late Prof. S. W. Ranson and his colleagues, at the Institute of Neurology of Northwestern University Medical School, revived the use of the stereotaxic instrument in the study of the anatomy and functions of the central nervous systems of animals, particularly cats and monkeys. Horsley and Clarke had described a stereotaxic instrument in 1908, one which was used in England and brought to this country by Dr. Ernest Sachs. Dr. Edward Fincher and Dr. Sachs used this instrument at Washington University in the late 1920's in some experiments on monkeys. The experiments described in the first three volumes of the Institute of Neurology at Northwestern (1929, 1930, 1931), conducted chiefly by Ranson and Hinsey, intensified the need for this instrument, which they had seen used in Dr. Sachs' laboratory while they were in St. Louis. In 1932, Ingram, Ranson, Hannett, Zeiss, and Terwilliger published the