The foramen magnum (Latin for 'great hole') is a large, oval-shaped opening in the occipital bone of the skull.

The spinal cord, an extension of the medulla oblongata, passes through the foramen magnum as it exits the cranial cavity.

One of the attributes of a biped's foramen magnum is a forward shift of the anterior border of the cerebellar tentorium; this is caused by the shortening of the cranial base.

Studies on the foramen magnum position have shown a connection to the functional influences of both posture and locomotion.

The forward shift of the foramen magnum is apparent in bipedal hominins, including modern humans, Australopithecus africanus, and Paranthropus boisei.

In humans, men tend to have a larger sized foramen magnum than women, but the overall shape is consistent.

Although not proven, compared to other hominins, the route that blood travels through the foramen magnum in Australopithecus boisei are more straight and direct.

[7] With the enlargement and broadening of the anterior foramen magnum, allow for more venous drainage from the occipital and marginal sinuses.

[8] Although not fully proven, there are many studies that show the possibility[9] that where the foramen magnum is positioned in the cranium is significant in fossils.

The anterior foramen magnum shifts the weight of the body more to the mammals' pelvis and femur, present in some primates, like great apes.

With a posterior foramen magnum, the alignment and weight of the body falls more lateral under the head This allows for humans and other bipedal mammals to be able to walk on two limbs.

The shift in the foramen magnum moving towards a more anterior position in the cranium, gives rise to the idea of possible bipedalism.