The tonsils of the cerebellumThis word means the “little brain” and refers to a large part of the brain that sits in lowermost part of the skull, at the back of the head, immediately above the top of the spine. This part of the skull is known as the posterior fossa. are herniated through the foramen magnumThe large, ovoid opening at the base of the skull, measuring about 3 x 3.5cm, through which the spinal cord passes, to continue on as the brain stem., at the base of the skull, as occurs in Chiari type 1 but, in addition, the lower part of the brain stemThis is the most primitive part of the brain, connecting the rest of the brain to the body, via the spinal cord. In addition to feeding signals to and from such “higher centres”, the brain stem contains a number of important control centres, regulating vital functions such as breathing and blood pressure. is lower than normal in position, lying in the upper part of the spinal canalThe individual bones that comprise the spinal column are made up of a weight-bearing “body” and other components which, together, form a ring of bone, behind the body. These individual vertebrae, joined together as the spinal column, therefore, create a canal running down the entire length of the spine..