In recent years, the suprasylvian gyrus of the cat has attracted the attention of many neurophysiologists and experimental psychologists and the variety of their interests is reflected in the number of morphological and functional sub divisions which have been made of it. Some of these subdivisions are shown in Fig. 1. Workcrs concerned with t. hc visual system havc made studies of the third visual area (awa to) on the medial aspect. of thc gyrus, and of the latcral supra sylvian area on the lateral aspeet, both of which contain representations of the retina (Clare and Bishop, 1954; Hubel and Wiesel, 1965, 1969; Wright, 1969). However, the full extent of these areas and particularly of the latter, is still not known. Other workers have investigated the extent of the gyrus activated by somatic sensory (Darian. Smith, Isbister, Mok and Yokota, 1966) or auditory (Woolsey, 1961) stimuli. A third field of incrcasing interest is the study of the "polysensory areas" of the cortex, two of which are situated in the middle supra sylvian gyrus. In these areas, in animals anaesthetized with chloralose, conver gence upon single neurons of auditory, somatic and visual impulses has been demonstrated (see ego Thompson, Johnson and Hoopes, 1963; Dubner and Rut ledge, 1964, 1965; Dubner, 1966; Bignall, 1967) and it has been proposed that these areas play an important part in the central processing of sensory information (Buser and Bignall, 1967; Thompson, 1967).