A detailed description of the location of kundalini in the human body is found in Sat Cakra Nirupana (1-3, 8-10). It is said that outside the meru, i.e. the vertebral column or backbone, there are two siras, the sasisira on the left and mihira sira on the right. Between them, inside, the spine, is the sushumna, appearing like blooming datura (thorn apple) flowers, extending from the middle of the kanda up to the head. Inside the sushumna there shines the vajra nadi, starting from the genitals and going up to the head. Citrini, which is fine like spider’s thread lies inside the vajra. It pierces through the lotuses situated inside the meru as it passes up. Inside the citrine is the Brahmanadi extending from the mouth of Shiva in the kanda up to the place of Adi-deva inside the head. The mouth of the sushumna which is its starting point in the kanda, is spoken of as the brahma dwara, the door to Brahman, which leads up to the place of Parama Shiva, the Supreme God inside the brain from where the elixir called sudhadhara oozes out. The mouth of the sushumna is also called the granthisthana, i.e the place of the joint between the sushumna and the kanda.
The description continues further by saying that the starting point of the vajra nadi is located two finger-widths above the mouth of the sushumna. This point is little below the genitals. It is inside the pericarp of the muladhara lotus. At that place there is the triangle (trikona) called Tripura. In this triangle dwells the Bhagavan in the form of a phallus, called swayambhu, with its head turned downward, shining like a molten gold. Its shape is like that of a new leaf, broad at the base above and tapering downward. The head of the svayambhu has a depression in the center like a whirlpool.
This swayambhu linga is said to be the seat of the kundalini, which lies on the linga like a serpent making three and a half coils. A coil is called kundala in Sanskrit, and kundalini means the coiled one. It holds the opening of the brahma dwara in its own mouth. This means that the kundalini extends up to the starting point of the sushumna inside the kanda. It is said that the kundalini is extremely slender like a lotus stalk. It shines like lightning. It controls the acts of inspiration and expiration. She is the presiding deity of sound and speech in both the gross and subtle aspects. All these facts are mentioned in the text Shatchakra Nirupana.