Patterns of the cranial venous system from the comparative anatomy in vertebrates: Part III. The ventricular system and comparative anatomy of the venous outlet of spinal cord and its homology with the five brain vesicles

Ontogenetically, the ventricular venous system may develop in order to drain the gray matter (cells of the mantle layer of the neural tube) which migrates dorsally. On primitive brain vesicles of submammals especially fish, amphibian and reptile, the ventricular venous system is the major venous collector located on the middorsal surface, in between the meningeal layers comparable to the subarachnoid space in mammals. The ventricular venous system functions as a major drainage system for the brain vesicles in these submammals but its role decreases when the other two venous systems develop. Concerning the route of venous exit from the brain vesicles, we found that it resembles the spinal cord but could not be found all the way along the brain vesicles.