The Cortical Projection of the Medial Geniculate Body.

THERE are but few accounts of the study of the cortical distribution of the auditory radiation by means of lesions of the medial geniculate body. Apart from clinico-pathological studies in man, most of the investigations have been made by means of cortical stimulation and ablation. In man and the monkeys there is general agreement that the auditory radiation ends in the superior temporal gyrus within the Sylvian fissure. The only point at issue is how much, if any, of the exposed surface of this convolution is reached by the radiation. The results, however, in the common laboratory animals-the dog, the cat, and the rabbit-are uncertain and discrepant. Ferrier (1876) studied the cortical localization of hearing in monkeys, dogs, cats, and rabbits both by stimulation and extirpation. Amongst the several responses that occurred from stimulation he regarded pricking of the ears as the one most indicative of the auditory area. Bilateral cortical extirpation was performed, and taking every precaution to prevent arousing the animal's awareness through some other channel, hearing was tested by sounds made in various ways. Ferrier placed in the cat the auditory receptive zone, to which he gave in his account the number 14, in the superior part of the second arcuate gyrus, or gyrus ectosylvius medius, i.e. between the upper end of the pseudo-sylvian and the suprasylvian sulcus. Munk (1878, 1881) removed in dogs the posterior portions of the second, third, and fourth arcuate gyri (or posterior suprasylvian and posterior lateral gyri), i.e. the cortical region immediately in front and behind the posterior limb of the superior sylvian fissure (the post-sylvian fissure of Owen). The dog is described as being in such a state that for three or four weeks after the operation it is deaf. It then becomes able to hear, but does not understand what it hears. In the cortical zone immediately above the pseudo-sylvian sulcus Munk placed " tactile awareness " of the ear. Mann (1896) stimulated the cortex in cats and rabbits. The area from which movements of the ear were most easily elicited corresponded with Ferrier's localization of the auditory zone. Luciani (1884), who was very critical of the work of Munk, used, however, 35