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Fig. 2 from : Cortical white and gray matter volumes of various species (n = 59) are related by a power law that spans five to six orders of magnitude. Most data points are based on measurement of a single adult animal. The line is the least squares fit, with a slope around 1.23 ± 0.01 (mean ± SD). The average and median deviations of the white matter volumes from the regression line are, respectively, 18% and 13% on a linear scale. Sources of data: If the same species appeared in more than one source below, the one mentioned earlier was used. All 38 species in table 2 in ref. 3 were taken, including 23 primates, 2 tree shrews, and 13 insectivores. Another 11 species were taken from table 2 in ref. 8, including 3 primates, 2 carnivores, 4 ungulates, and 2 rodents. Five additional species came from table 1 in ref. 11, including 1 elephant and 4 cetaceans. The data point for the mouse (G = 112 mm3 and W = 13 mm3) was based on ref. 30, and that for the rat (G = 425 mm3 and W = 59 mm3) was measured from the serial sections in a stereotaxic atlas (42). The estimates for the fisherman bat (Noctilio leporinus, G = 329 mm3 and W = 43 mm3) and the flying fox (Pteropus lylei, G = 2,083 mm3 and W = 341 mm3) were based on refs. 43 and 44, with the ratios of white and gray matters estimated roughly from the section photographs in the papers. The sea lion data (Zalophus californianus, G = 113,200 mm3 and W = 56,100 mm3) were measured from the serial sections at the website given in the legend to Fig. 1, with shrinkage correction.