There are 27 verebrae between the head and the sacrum. With the exception of the first two, these vertebrae are separated from each other by intervertebral discs which are very closely connected to the vertebral bodies. Immediately dorsal to the vertebral bodies is the vertebral canal which houses the spinal cord and its investing membranes. Between the outermost of these membranes (dura mater) and the vertebral bodies, is the dorsal longitudinal ligament which starts at the odontoid process of the second cervical vertebrae and ends at the body of the first coccygeal vertebrae. As it passes over each intervertebral disc it expands laterally and blends with the disc tissue. In the thoracic region a series of ligaments, the conjugal ligaments, are interposed between the discs and the dorsal longitudinal ligament.