Unbiased stereological methods were used to examine and compare morphometrically the geniculate bodies (GB) in representatives of four mammalian orders (Insectivora, Rodentia, Lagomorpha, and Carnivora). The significant disproportion was observed between the relative sizes of both geniculate nuclei and their neuronal populations in the common shrew and the bank vole. The medial geniculate body (MGB) in the common shrew definitely surpassed the lateral geniculate body (LGB) in terms of percentage volume and percentage number of neurons. The volume of the GB and their nuclei correlated with their mean neuronal populations, whereas the negative correlation was observed between volumes and neuronal density; however, not as distinct as in the non-sensory brain structures. In all examined species, the LGB always had a higher numerical density than the MGB, while the MGB neurons were always distinctly larger than that of the LGB, which clearly differentiated both neuronal complexes. Analysis of these data shows that the GB differs in terms of the morphometric characteristics in the studied species.
