Measurements:
(1) external cranial volume in mL
(2) head circumference in mm
The external cranial volume is measured by displacement of water by the cranium from a hemispherical bowl into a funnel running into a fluid cylinder. The subject is lying supine with the head and neck overlying the edge of the table. The head is placed in the bowl up to the a horizontal plane connecting the glabella and inion (external occipital protuberance).
The head circumference is taken around the cranium to include the glabella and inion, using a metal tape.
brain volume in mL over external cranial volume of 1,000 to 2,800 mL =
= (0.25 * (cranial volume in mL)) + 840
brain volume in mL over external cranial circumference of 45 to 70 cm =
= (36 * (circumference in cm)) – 700
The data shown in Figures 2 and 3 can be approximated in JMP to cover measurements below those covered by the linear equations.
brain volume in mL over external cranial volume of 300 to 1,400 mL =
= (-0.000339 * ((cranial volume in mL)^2)) + (1.4390135 * (cranial volume in mL)) - 169.1596
brain volume in mL over external cranial circumference of 24 to 45 cm =
= (42.410065 * (circumference in cm)) – 998.4251
Limitations:
• The person’s hair has to be closely cropped to prevent error.
• The method is subject to error in head placement, so multiple readings should be averaged.
• The method assumes no cranial bone disease.
• Hydrocephalus may be associated with errors in the estimates.
• The subjects for the study were Danes, so racial variation should be expected.
