THE CORTICAL PROJECTION OF THE MEDIAL GENICULATE BODY

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Abstract
In 2 cats electrolytic lesions were placed, by means of the Clarke-Horsley stereotaxic instrument, in the hilus of the medial geniculate body. The brains were prepared by the Marchi method. The auditory radiation runs cranialwards and ventralwards from the medial geniculate to lie ventro-caudal to the lateral geniculate body. The fibres then pass lateralwards to enter the internal capsule, in which the auditory lies ventral to the optic radiation. The ventral fibres traverse the peduncle. Many of the fibres reach the cortex, passing directly caudal to the lenticular nucleus and the claustrum, but a considerable proportion traverse the caudal part of the globus pallidus and putamen, deviating to pass caudal, dorsal and ventral to the caudal extremity of the claustrum. The cortical audito-sensory area has a homogeneous cytoarchitecture and is bounded caudally by the posterior ectosylvian sulcus, dorsally by the middle part of the suprasylvian sulcus, and cranially approximately by the anterior ectosylvian sulcus (since dorsally it extends just cranial to and ventrally stops just caudal to this sulcus). Ventrally the area ends a short distance dorsal to the rhinal fissure. There is a point to point homolateral relationship between the medial geniculate and the cortex. No other fibres were found arising from the medial geniculate. The adjusting of the stereotaxic apparatus produced a lesion in the cuneate nucleus in each cat. The fibres from this run in the medial half of the medial lemniscus and terminate in the medial part of the pars externa of the ventral nucleus of the thalamus.