FIGURE 10.

Distribution of neurons along the anteroposterior axis of the cerebral cortex. Each artiodactyl species is represented in a different color. (A) Cumulative percentage of neurons along the anteroposterior axis of the cerebral cortex plotted as a function of the cumulative mass of the gray matter of the cerebral cortex along the same axis. Anterior is to the left. Each point represents the values for one 6 mm block of cortex along the axis. The plotted line indicates the linear relationship expected for a uniform distribution of neurons in the cortical mass along the anteroposterior axis. While the kudu fits the uniform distribution, the springbok, pig, and giraffe deviate in such a manner that the cumulative distribution of neurons along the cortical mass is better described by a different function (plotted) in the anterior 2/3 of the cortical mass. (B) Variation in neuronal density in each 6 mm block of cerebral cortex along the anteroposterior (A-P) axis. Anterior is to the left. While there is little variation in neuronal density along the cortex of the kudu, densities vary by 4–5× among cortical blocks in the pig, springbok and giraffe. (C) Difference in neuronal densities found in the anterior 2/3 and in the posterior 1/3 of the cerebral cortex in each species. Averages in each group are shown for each species. The largest neuronal densities are found in the posterior 1/3 of the cortex in the giraffe, pig, and springbok. (D) Variation in the surface density of neurons in the cortex (that is, neurons/mm²) in each 6 mm block of cerebral cortex along the anteroposterior axis. Despite the large variation along the cortex of each species, there is no systematic difference in surface density of neurons along the A-P axis.