Turn your attention to the lower part of the back where the prosectors have performed the laminectomy. The vertebrae have been cut, through the laminae, just posterior to the transverse processes.

Examine the part of the vertebral column that has been removed and identify the ligamenta flava, called the yellow ligament because elastic tissue gives it a yellow appearance. This ligament connects adjacent vertebral lamina. By bending the segments of the removed column back and forth, you can visualize the importance of this ligament. The discussion of the vertebral ligaments in the overview describes their relationships in reference to a midsagittal view of the vertebral column. (Figure 1-6) Here you have a posterior view of the ligaments in their normal positions.

Carefully move the encased spinal cord to one side with a probe to see the posterior longitudinal ligament lying under the cord on the posterior surface of the vertebral bodies. This ligament runs primarily down the center of the vertebral bodies. The posterior surface of the intervertebral discs can be seen just lateral to the posterior longitudinal ligament.

Examine the spinal cord. The cord is surrounded by the dura mater. Posteriorly, the epidural space is visible between the dura mater and the bones of the vertebral canal. There could be some fat and veins in this space.

If the dura mater has been slit, gently pull it away from the cord using forceps. The arachnoid mater may stick to the dura mater or it may remain attached to the cord. If it remains attached to the cord, pull the arachnoid mater gently away from the cord to see if any arachnoid trabeculae adhere to the pia mater.

Find the end of the spinal cord proper. It is called the conus medullaris. Remember this part of the cord is usually found at the L2 level.

The spinal nerves proceed inferiorly from the lower end of the spinal cord through the subarachnoid space. Below L2, they are known collectively as the cauda equina given this name because they resemble a horse tail. (Figures 1-13; 1-14)

Emanating from the conus medullaris and running inferiorly in the middle of the cauda equina is a thin strand of pia mater, the filum terminale. The filum terminale and cauda equina are housed in a large subarachnoid space between L2 and S2. This space is called the lumbar cistern. (Figure 1-13)

Turn your attention to the spinal cord superior to L2. Again, pull the dura and arachnoid laterally from the cord to identify the dorsal and ventral spinal nerve rootlets as they enter and exit the cord.

Continue pulling GENTLY on the dura and arachnoid, look between adjacent spinal rootlets to see the lateral projections of the denticulate ligament . You will not see these below L2.

With a probe, follow a set of dorsal and ventral spinal nerve rootlets until they exit through an intervertebral foramen. If the bone has been chipped away, you can see a dorsal root ganglion (spinal ganglion). You may even see the spinal nerve dividing into dorsal and ventral rami.