Foramen magnum

In anatomy, the foramen magnum is the large hole through the occipital bone in the base of the skull, through which the medulla oblongata (an extension of the spinal cord) exits the skull vault.

In humans the foramen magnum is farther underneath the head than in great apes. Thus, the neck muscles do not need to be as robust in order to hold the head upright. Comparisons of the position of the foramen magnum in early hominid species are useful to determine how comfortable a particular species was when walking on two limbs ( bipedality) rather than four.