Muladhara is described in the Sat-Cakra-Nirupana, a Sanskrit text of 1577 by Purnananda which is the single source behind most modern accounts of the chakras, as a lotus of four petals at the base of the trunk, bearing the letters vam, sham, shham and sam. Within it is a yellow square, the symbol of the earth element, with the seed syllable LAM; the presiding deity is a child form of Brahma with the shakti Dakini. Inside the square is a triangle in which the kundalini is said to lie coiled three and a half times around a svayambhu linga, sleeping and closing the mouth of the central channel, the sushumna. The whole apparatus, petals with assigned letters, element, seed syllable, deity and animal vehicle, is a visualisation scheme for a specific meditative practice, not a description of anatomy or of energy in any modern sense.
The three principal nadis named throughout Hatha yoga literature, Ida, Pingala and Sushumna, are given their fullest early account in texts such as the Hatha Yoga Pradipika and the Goraksha Samhita, which describe seventy-two thousand nadis in all, with these three, plus eleven others, as paramount; Sushumna, the central channel, is said to run the same course as the chakra system itself, from Muladhara to Sahasrara, with Ida and Pingala winding around it. The elephant given as Muladhara's animal vehicle, vahana, is named in the tradition as Airavata, the mount of the god Indra, chosen for its association with strength and with the earth the root chakra governs.
Sources The Serpent PowerSir John Woodroffe (Arthur Avalon) with Roots of YogaJames Mallinson and Mark Singleton (trans. and eds.)