Sacral

Svadhisthana is described in the Sat-Cakra-Nirupana as a lotus of six petals at the root of the genitals, bearing the letters bam through lam. Within it is a white crescent, the region of water, with the seed syllable VAM seated on a makara, the composite aquatic creature of Indian iconography; the presiding deity is Vishnu with the shakti Rakini. The name is usually glossed as one's own dwelling place, though the etymology is disputed and other readings are given. As with all the centres, the text describes what the practitioner is to visualise and what is said to follow from steady concentration on it, in a form of practice that belongs within an initiatory lineage and is not fully intelligible apart from it.

The makara seated beneath Svadhisthana's seed syllable is a composite creature, part crocodile and part fish or elephant depending on the region and period, that appears throughout Hindu iconography as the mount of the river goddess Ganga and of the sea god Varuna; its presence here extends that wider association of the makara with water and with the unpredictable, generative force the tradition assigns to rivers and oceans to the second chakra specifically. The chakra's location at the root of the genitals also places it, in the kundalini model, as the second stage the rising serpent power is said to pass on its way from Muladhara toward Sahasrara, still within the lower, more overtly elemental part of the ascent.

The answer is that it depends on the text, and the modern assumption of seven is a simplification. Indian tantric and yogic literature describes systems of four, five, six, seven, nine, twelve and more centres; the Kubjikamata Tantra and other early works give different sets, Buddhist tantric systems generally work with four or five, and Tibetan practice normally uses four principal chakras with a somewhat different distribution. The six-plus-one scheme that Purnananda gives, six centres from the base to the brow plus the thousand-petalled sahasrara above them, became dominant in the west because Woodroffe translated a text that uses it. Geoffrey Samuel and other historians of Indian religion have traced this variety in detail. Anyone who has been told that the seven chakras are an ancient and universal Indian teaching has been told something a little too tidy to be true.

Buddhist tantric literature offers a genuinely different structure rather than a subset of the Hindu one: texts associated with the Chakrasamvara Tantra generally work with four or five centres, head, throat, heart, navel and sometimes the genitals, tied to a scheme of channels and subtle drops rather than to seven chakras and their elements, and used differently, chiefly in completion stage practices aimed at generating the experience of clear light. An earlier Hindu source than Purnananda's, the Kubjikamatatantra, compiled around the tenth or eleventh century, likewise describes a five centre system, further evidence that the six-plus-one scheme was one solution among several before Woodroffe's translation made it the default.