The weight of the mammals brain in a comparative anatomical order

Comparing and establishing the ability to think between different organisms and the weight of their brains is a difficult task. Some studies have reported attempts to draw cross-species correlations between brain size and cognitive abilities, but no unambiguous data have been obtained. The purpose of this study was analysis of changings of the weight of the brain of animals and the cytoarchitectonic organization of its cortical formations in a comparative anatomical series. Brain preparations from the collection of the Laboratory of Cytoarchitectonics and Brain Evolution of the Institute of the Brain of the Scientific Center of Neurology were studied. The brain weight of 401 mammals was studied. The material was taken within 24 hours after the death of the animal, the brain was fixed in a 10% solution of neutral formalin, and photographed. Separate areas of the brain were cut in the frontal plane for microscopic examination. The section thickness was 20 µm, the preparations were stained with cresyl-violet according to the Nissl method. In the comparative anatomical series, the development and complication of the structural organization of the brain of animals is noted, which manifests itself primarily in the differentiation of the new cortex into separate cytoarchitectonic areas and cortical fields. As a result of the study, it was found that the brain of rodents has a more primitive structure, and in carnivores, in comparison with the brain of rodents, well-defined large arcuate grooves and convolutions are determined, the structure of the new cortex is more complex. The cortical formations of the brain of carnivores are represented by the main areas. There are significant features in the structure of the cortical formations of the brain of primates. The brain of monkeys is clearly divided into separate regions, and the regions into separate cortical fields, all cytoarchitectonic layers are clearly distinguished. In general, the study showed that in the comparative anatomical series, the weight of the brain of animals increases, while the decisive role in the formation and complication of cognitive functions, apparently, is played by the complication of the structural organization of the cortical formations of the brain, its differentiation into separate areas, fields and subfields, as well as changes in their neural composition.