Lesions were made at varying levels in the spinal cords of a number of dogfish, rudd, and frogs. After a suitable survival period the resulting fibre degeneration was demonstrated by means of a silver impregnation technique. The findings have provided experimental confirmation of a profuse spinal projection to the reticulair formation of the hindbrain in all three classes examined. These fibres were found to project to a constant sector of the reticular formation which closely corresponded not only between individual specimens of the same species, but between the three species, and which was situated ventrolaterally in the medulla oblongata. The density of this degeneration was always greatest in the caudal brainstelm and became progressively less at more rostra1 levels. All spinal projections to the reticular formation exhibited some degree of bilaterality, including those in specimens with lesions of hemisections or less.A spinotectal pathway was also demonstrated in certain specimens of dogfish. No involvement of cranial nerve nuclei was seen. These findings are discussed.
Spinocerebellar systems have been investigated in three classes of poikilothermic vertebrates. Lesions were made in the spinal cord of a number of dogfish, rudd and frogs which were selected as representatives of their classes. After a postoperative survival period the resulting fibre degeneration was demonstrated by means of a suitable silver impregnation technique. The findings have provided experimental confirmation of a spinocerebellar pathway in each species examined. In the dogfish these fibres form part of a mixed spinal lemniscus, which ascends through the brainstem, and leave it to enter the corpus cerebelli through its peduncles. In the rudd two separate systems were found, one of which corresponds to that seen in the dogfish. The other forms a separate compact fasciculus which lies more dorsally in the brainstem throughout its course. This one can be followed into the cerebellum through the peduncle. Within the corpus cerebelli :it was not possible to distinguish between the two systems. In the frog also two separate systems were seen. These retained their individual identity from the spinal cord to their entrance into the cerebellar peduncle beyond which they appeared to merge. These findings have been compared with the results of other authors, and an attempt has been made to show how and why such systems have evolved.
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