The spine is a very clear and obvious anatomical expression of the midline. Its a fearsomely complicated arrangement of bones, discs, ligaments and muscles. It is intimately related to the functioning of the nervous system. Its connections into the dura mean it is an integral part of the reciprocal tension membrane system. The spine is limited at the top end by the neurocranium via the occiput and at the bottom end by sacrum and coccyx as part of the pelvic bowl; together with these structures and the ribs it forms the axial skeleton.