It was upright posture that caused a forward migration of the foramen magnum in the skull to a place beneath the center and the mass of the brain. The foramen magnum contains the spinal cord. Among other things it can also contain extra venous drainage outlets as well. It’s central location makes for near perfect balance of the head on the neck. It’s particular location also makes the foramen magnum the lowest point inside the cranial vault in the base of the skull.
The condyles of the skull are joints shaped like kidney beans that attach the skull to the first cervical certebral call atlas or C1. They are located along the perimeter of the left and right sides of the formen magnum beneath the skull. The condyles are actually the lowest point in the formen magnum. Picture a sink with drain in the bottom. Typically the bottom of the basin contains a slight depression that contains the drain. The ring of the foramen magnum and the condyles are similar to the depression in the bottom of the basin of the sink.
According to a study by Dr. Dean Falk, an expert physical anthropologist with a background in brain evolution, and others, such as the world renowned Andrew Tobias from Australia, humans and hominids developed additional venous drainage routes to handle the increase in brain blood flow that comes from upright posture. Those extra routes drain the bottom of the cranial vault and empty into the veins of the vertebral venous plexus of the spine.
The extra venous drainage routes tend to be located around the foramen magnum, which as was mentioned above, is the lowest point inside the cranial vault. Some veins actually enter the foramen magnum and exit through openings called the condylar and hypoglossal canals. In fact, there are numerous variations in the drainage system used by humans to empty the bottom of the vault. The subject is complex because it has never been studied in humans in detail. But considering the fact that drainage issues in the skull may lead to answers to finding the cause of neurodegenerative diseases which are some of the most critical and costly health care issues of the day this subject should not be overlooked.
The bottom line, however, is that those extra venous routes, which specifically evolved to handle the increase in brain blood flow that comes from upright posture, as well as to drain the lowest point of the cranial vault, drain into the vertebral venous plexus of the spine, not the internal jugular foramen and veins.
Dr. Zamboni is currently using stents and balloons to open up veins that improve drainage through the internal jugular veins, and possibly other alternative venous pathways as well. Nonetheless, to drain the lowest point of the skull his procedure would have to cause a venous shift upwards toward the jugular foramen and away from its normal flow downwards toward the foramen magnum and alternative outlets located lower down in the bottom of the vault.
While this may work, and it may be the best answer in certain cases, it isn’t the best route for completely draining the lowest point of the cranial vault. The most efficienct route is the one nature intended; that route is into the vertebral venous plexus of the spine not the internal jugular veins. Whatever the cause, the best method to drain the lowest point in the cranial vault would be to remove the source of stenosis and back pressure against the vertebral venous plexus. I’ll address that issue in future posts.