Lessons

Cranium

The placement of the foramen magnum, the large hole on 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). Australopiths have a more inferiorly placed foramen magnum8-10.

 

Comparision of the spinal cord direction
between a biped and a quadruped.

Comparison of the relative positions of the foramen magnum in modern humans and extant chimpanzee.