Final answer:
The veins in the epidural space near the posterior longitudinal ligament are part of the internal vertebral venous plexus and drain into the vertebral veins.
Step-by-step explanation:
In the epidural space near the posterior longitudinal ligament, the veins observed are part of the extensive internal vertebral venous plexus. This plexus contains veins that run in the epidural space around the spinal cord and are crucial in draining blood from the spinal cord and vertebral bodies. Specifically, the posterior parts of this plexus are found near the posterior longitudinal ligament, which is situated anterior to the spinal cord, attached to the posterior sides of the vertebral bodies.
The plexus facilitates venous return to larger systemic veins such as the vertebral veins, which in turn connect to the brachiocephalic veins and eventually the superior vena cava, completing systemic circulation.