The opening in the cranial cavity where the spinal cord connects to the brain is the foramen magnum.
The brain stem connects the brain to the spinal cord. Foramen in anatomy refers to an opening. Foramen magnum is the opening in the cranial cavity through which the brain and the spinal cord establish a connection. It is a large opening in the occipital bone which forms the back and the base of the skull and enclircling the spinal cord. Through the foramen magnum passes the medulla oblongata and its membranes, nerves and the arteries.