Final answer:
The foramen magnum is the opening in the base of the cranium that allows the spinal cord to exit the skull and connects it to the brain.
Step-by-step explanation:
The opening in the base of the cranium that allows the spinal cord to pass out of the skull is known as the foramen magnum. This large opening is located in the occipital bone of the skull and serves as a critical passage not only for the spinal cord to connect with the brain but also for the vertebral arteries to enter the cranium. The foramen magnum is part of the posterior cranial fossa, which is the deepest and houses the brainstem.