Figure 2.

Total blood flow rate of both ICAs $({\dot{Q}}_{\mathrm{ICA}})$ in relation to brain volume (V_br). ${\dot{Q}}_{\mathrm{ICA}}$ is calculated from ICA foramen radius data with a wall thickness-to-lumen radius ratio (w) of 0.30 and the new empirical equation. The regression equation for 44 species of extant haplorhine primates (blue and black circles) is ${\dot{Q}}_{\mathrm{ICA}}=0.0068$ V_br ^{1.03±0.07 CI} (R² = 0.95), and that for 12 species of fossil hominins (red squares) is ${\dot{Q}}_{\mathrm{ICA}}=0.00028$ V_br^{1.41±0.30 CI} (R² = 0.91). Solid lines are the regression means; dashed lines are 95% confidence bands. Black circles are Pongo, Pan, Gorilla and H. sapiens. See electronic supplementary material, table S3 for data derived from [6,13,15]. (Online version in colour.)