Anatomical Adaptations for Bipedalism: Cranium

Comparison of foramen magnum placement in a modern human and an extant chimpanzee.

Comparison of foramen magnum placement in a modern human and an extant chimpanzee.

Illustration of the direction of the spinal cord in relation to the foramen magnum.

The placement of the foramen magnum, the large hole at the bottom of the cranium through which the spinal column passes, is directly related to the orientation of the cranium. Consider that a primate holds their mandible (or chin) parallel to the ground. In a quadruped, the spinal column also runs parallel to the ground so the foramen magnum is more dorsally placed (i.e., toward the back of the cranium). In a bidped, the spinal column runs perpendicular to the mandible and the ground. The foramen magnum is located more inferiorly (more on the bottom of the cranium). Australopithecines have a more inferiorly placed foramen magnum.^8-10