The skull diploe are located between the inner and outer plates of the skull and where the diploic veins are located.
The sutures are special joints that link the bones of the skull together. They were called sutures by early anatomists because they looked like stitches used by surgeons and tailors. The design of the sutures is a reflection of the forces that act on them. One of the main forces comes from the diploic veins that pass through the diploic space located beneath the sutures.
The diploic veins, like most of the veins of the head called cranial veins, have no valves so that the water within them sloshes back and forth with upright posture and walking and other movement. The affect is similar to carrying water in a bucket while walking. It’s impossible to keep the water still. The same thing happens in the head. Walking amplifies the waves with each step. Musculoskeletal stress, combined with cardiorespiratory and neurological stress in the form of circulatory and electrical waves also affect the shapes of the sutures.
As a result of upright posture, the veins, venous blood volume and venous pressure tends to be greater toward the back and base of the skull. Consequently, the amplitude of the wave-like shapes of the sutures are larger.
The affects of venous volume and pressure are much lower at the top of the head. As a result, the amplitude, that is the size of the waves of the sutures are much smaller.
Venous drainage problems in the brain causes the sutures to stay open in certain pathological (abnormal) crania. In some cases the sutures stay open due to design problems in the crania such as a small jugular foramen or small, or sometimes almost absent extra venous outlets to drain into the vertebral veins.
Interestingly, Dr. Franz Schelling began his research into the role of venous drainage problems in multiple sclerosis after he noticed significant discrepancies in the size of the venous jugular foramen from one side of the crania to the other in many MS patients.