Final answer:
The foramen magnum is the large opening in the occipital bone through which the spinal cord passes and the vertebral arteries enter the cranium.
Step-by-step explanation:
The opening in the occipital bone through which the spinal cord passes is known as the foramen magnum. This large opening not only allows the spinal cord to connect with the brain but also provides entry for the vertebral arteries into the cranium. The forebrain, which includes the cerebrum and diencephalon, develops from the prosencephalon and is situated in the anterior region of the adult brain above this crucial foramen.