The foramen magnum is a large oval opening in the occipital bone of the human skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla, passes through the foramen magnum as it exits the cranial vault. Apart from the transmission of the medulla oblongata and its membranes, the foramen magnum transmits the vertebral arteries, the anterior and posterior spinal arteries, the tectorial membranes and alar ligaments. It also transmits the spinal component of the accessory nerve into the skull.