From Chapter 11, Meta Modern Era by Shri Mataji Nirmala Devi
#21 Kundalini and Sacrum Bone
There is one more residual energy, which is coiled up and remains potential, in the triangular bone called the sacrum. Residual energy means that it is the basic original energy, which has not gone into division. When the divine energy falls on the brain of the fully developed foetus, then, in the prism-like brain, it falls into three categories. It happens due to refraction. The energy that falls on the sides of the brain cross over to form the sympathetic nervous system. But when the divine energy falls on the summit of the brain, which is like a prism, the original energy, without any refraction, passes through and coils down in the sacrum bone, as Kundalini.
Perhaps the Greeks knew that it was a sacred bone, so they called it the 'sacrum'. This original, complete energy is coiled into three and a half coils, which is in a resting, potential state. The subtle system we have within ourselves is built-in. In the process of our evolution, we have seven main energy centres, in the spinal chord and also in the brain.
When this fourth energy, which is called the Kundalini in the Sanskrit language, is awakened like a plumule in a seed, it passes through six centres and ultimately pierces the sixth centre fontanelle bone area, which is called Brahmarandra, and connects human awareness to the all-pervading power of divine love.
Thus one develops the fourth dimensional awareness. This is how the Kundalini achieves this Yoga.