Size and shape of the cerebral cortex in mammals. II. The cortical volume.

The geometry of the brain and cerebral cortex in mammals has been studied from an evolutionary perspective and is described in mathematical terms. The volume of the cerebral cortex, in contrast to the cortical surface area, scales to brain volume in a similar way, irrespective of the degree of cortical folding. Among mammals, Cetacea form a subgroup, in that their volumetric data fit an isometric model better than an allometric model. An index of corticalization is presented which contains information about both the mass of interconnective nerve fibers and the degree of intracortical processing. It is shown, furthermore, that a semilogarithmic equation appropriately describes the relationship between mean cortical thickness and brain volume. Finally, allometric equations between brain volume and cortical parameters, which can be used for predictive purposes, are presented.