[Cytoarchitecture of the formatio reticularis of the brain stem of the dolphin].

In the present study some qualitative and quantitative features of the reticular formation of the medulla oblongata, pons and midbrain have been elucidated by cytoarchitectonic methods in the dolphin (Tursiops truncatus). The studies have demonstrated that similar to land mammalia, the dolphin has a reticular formation made up of spatially open cell groups lying in the deepest parts of the brain stem. Cytoarchitectonically the component parts of the reticular formation show a number of peculiarities enabling us to distinguish separate nuclei. In the dolphin peculiar architectonics have been observed in the nucleus gigantocellularis medullae oblongatae, nucleus papillioformis or the nucleus reticularis tegmenti Bechterewi and the nucleus centralis superior medialis seu ventralis. Fairly poor in cells are the nucleus centralis caudalis pontis and the nucleus centralis oralis pontis. We failed to single out as autonomous nuclei cell groups corresponding to the nucleus funiculi lateralis and the nucleus paratrochlearis of the land mammalia. The size and density of cells in nuclei have a number of peculiarities. The analysis of the ratios of the brainstem volume to that of reticular structures has shown them to be the smallest in the dolphin as compared with land mammals. The smaller share held by the brain-stem reticular formation and its cytoarchitectonic features can be associated with the functional properties resulting from the greater specialization of some of brain-stem systems (e.g. auditory, vestibular, extrapyramidal etc.) in the dolphin in comparison with land mammals.