Since Babinski's discovery1 of the signe des orteils, in 1896, an extensive literature has grown up concerning the pathologic reflexes of the lower extremities in man. Experimental studies, however, have been few, and because of this Fulton and Keller1 recently undertook to investigate the Babinski reflex in a series of infrahuman primates. Plantar reflexes and motor performance were studied in monkeys, baboons, gibbons and chimpanzees—types which represent ascending stages in the evolutionary scale. They observed, after destruction of the motor area, that a permanent Babinski response could be detected only in the chimpanzee, the highest of the forms examined. Incidentally they found it possible to estimate the degree of cortical dominance in a given form by three criteria: (1) the rate of recovery of voluntary power following ablation of the motor area controlling a limb; (2) the extent of depression of the spinal reflexes produced by such a