FIGURE 9.

Scaling of the cortical gray matter. (A) Variation in the volume of the cortical gray matter as a function of the total surface area of the gray matter. Power functions for artiodactyls (minus the giraffe), rodents, and primates are plotted and have exponents 1.466 ± 0.036, 1.350 ± 0.037, and 1.165 ± 0.026, respectively. Notice that the artiodactyl cortex has a larger surface area than rodents for a similar gray matter volume. (B) Variation in the thickness of the cortical gray matter as a function of the total surface area of the gray matter. Power functions for artiodactyls (minus the giraffe), rodents, and primates are plotted and have exponents 0.466 ± 0.036, 0.350 ± 0.037, and 0.165 ± 0.026, respectively. For a similar surface area, the artiodactyl cortex is thinner than the rodent cortex. (C) Variation in the thickness of the cortical gray matter as a function of the total number of cortical neurons. Power functions for artiodactyls (minus the giraffe), rodents, and primates are plotted and have exponents 0.562 ± 0.118, 0.413 ± 0.040, and 0.149 ± 0.024, respectively. Again, for a similar number of cortical neurons, the artiodactyl cortex is thinner than the rodent cortex. (D) FI of the cerebral cortex plotted as a function of the average thickness of the cortical gray matter. Notice that for similar cortical thicknesses, both the artiodactyl and the primate cortex are more folded than the rodent cortex. Artiodactyls in black, afrotherians in blue, glires in green, primates in red. Data from Azevedo et al. (2009), Herculano-Houzel et al. (2010), Ribeiro et al. (2013), Ventura-Antunes et al. (2013), and Neves et al. (2014).