The medial geniculate body afferents from the cerebellum in the rabbit as studied with the method of orthograde degeneration.

The brain stems of 10 rabbits subject to operation of several lesions of cerebellar cortex and nuclei were examined. Survival time was 4 to 10 days. The course and termination of degenerating nerve fibres into the medial geniculate nuclei (MGN) of both sides were analyzed in frozen sections of the cerebellum and the brain stem impregnated according to various modifications of Nauta method. Degenerated nerve fibres in the MGN were found only when the fastigial nucleus of heterolateral side, or fibres originating in this nucleus were damaged. Cerebellofugal fibres run in two bundles to their termination spot in the magnocellular part of the medial geniculate nucleus. The first bundle separates from the main trunk of the uncinate fascicle, and running medially to the vestibular nuclei, terminates in the MGN after passing through the lateral lemniscus and the ventral lemniscal nucleus. The second bundle separates from the ascending branch of the uncinate fascicle and after passing through the dorsal lemniscal nucleus, also in composition of the lateral lemniscus, it terminates in the same region of the MGN.