The umbilical is the part of The Veil that is dragged down to the surface of Sanctum.
The umbilical is like a giant Tornado, the winds are harsh and have been known to rip the ears off a Bound, A solid reason why most of the Faith have their ears removed.
The Umbilical doesn't actually touch the Surface, but is stopped by the planets magnetic forces, instead it creates a harsh storm wall known as "The Rim"
The Umbilical can be tall and thin, or short and fat.
In the Darker seasons after a big Daybreak it has even been known to disconnect completely from the planet, just to reform again after a few days.