[Features of the neuronal organization of the periaqueductal gray substance of the midbrain in the cat].

On the basis of morphological investigations two areas were distinguished in the periaqueductal grey of the cat midbrain: medial, directly surrounding the sylvius aqueduct and containing small neurons with significant (P less than 0.001) prevalence of fusiform cells and lateral with larger neurons, where triangular cells were significantly (P less than 0.001) prevalent. The neurons of the medial area displayed a significant (P less than 0.001) tendency of their dendrite orientation towards the sylvius aqueduct.