All the venous channels of spinal cord, like arteries, are longitudinal in position being parallel to long-axis of spinal cord. These are six in number with fixed position as follows:

1. One anteromedian: It run along anterior median fissure of spinal cord.
2. Two anterolateral: They run along anterolateral sulcus in front of attachment of anterior nerve roots. These three veins are named anterior spinal veins.
3. One posteromedian: It runs along posterior median sulcus of spinal cord.
4. Two posterolateral: These veins run along posterolateral sulcus of spinal cord, posterior to attachment of posterior roots of spinal nerve. These three veins are named as posterior spinal veins.

Communication Network
All the six veins receive tributaries from spinal cord. These tributaries form a fine network on the pial surface of spinal cord which is called venous vasocorona.
Drainage: Spinal veins form a plexus inside vertebral canal called internal vertebral venous plexus.
Radicular veins arising from it join to form segmental veins which come out through intervertebral foramen to drain in regional veins of cervical, thoracic and lumbar regions.

Communication with Intracranial Veins
Upper end of internal vertebral venous plexus ascend through foramen magnum to communicate with basilar venous plexus which in turn, establishes communication with intracranial venous sinuses.

Source: P. McKee, J. Calonje – McKee’s Pathology of the Skin (Elsevier)