Fig. S1.
Smaller average fiber caliber in cortex anterior to corpus callosum, defined here as prefrontal cortex. The ratio between VWM and OWM, which approximates the average fiber caliber, is shown for each coronal section along the A-P axis. Filled circles, prefrontal cortex (coronal sections anterior to corpus callosum); triangles, occipital cortex (posterior third of VGM along the A-P axis); and unfilled circles, intermediate regions. Species are shown in order of decreasing gray matter volume.