Merudanda is a term used in Hatha Yoga and is the vertrebal column in the human body. In ancient yoga texts it is also called vajradanda or Vinadansa. Danda means staff, vajra means very hard, and vina is a string instrument having a long shaft (the human body is quite often compared with the vina, the divine lute). In Shiva Samhita (11.17), the word prsthavamsa is used for the vertebral column. Prstha means the back side, and vamsa means a bamboo or a pipe. It is said in Yoga Shikha Upanishad (1.119) that “the vajradansa contains 21 pieces of bone surrounding the sushumna nadi (spinal cord), like beads woven around a thread”. This statement corroborates modern physiology, as the spinal cord is known to extend from the neck down to the second lumbar vertebra, thus passing through the seven cervical, twelve thoracic and two lumbar vertebrae.
The whole merudanda, however, contains 33 vertebrae in which five pieces of bone are fused, forming the triangular sacrum bone (called trikona, yoni, and kanda in Yoga texts) and four pieces together forming the coccyx. From the kanda various nadis (channels) are said to emerge. The most important among them is the susumna nadi, which is located inside the merudanda. All other nadis arising from the kanda run outside the merudanda, and ultimately reach different organs of the human body.
Merudanda must be called one of the most vital parts in Yoga physiology, not only because it is the place from which all nadis originate, but more importantly, it is the inner path (called brahmanadi or Madhya marga) which forms the innermost cavity running through the merudanda up to the brain.
In Hatha Yoga Pradipika (I.28-29), this path is called pascima marga (the dorsal path). This path is clogged by impurities in all of us. For attaining enlightenment and emancipation it is necessary to remove all impurities from it and make it clean, so that the prana (vital air) along with kundalini can rise upward through it.
For achieving this result, various practices are recommended in hatha yoga.
These are
- The posture called pascimatana
- Mudras of hatha yoga, especially mahamudra, mahabandha and mahavedha
- Kumbhaka (holding of breath), along with the application of three locks, namely, jalandhara – bandha (the chin lock), uddiyana bandha (the abdominal lock) and mula bandha (the anal lock).
In all these practices there is a stretch produced on the merudanda. It is the main factor responsible for promoting the arousal of kundalini. Pranayama (control over breath) brings about cleansing of all nadis, especially the inner path.
Thus it may be said that the merudanda plays a very important role in hatha yoga insofar as it provides the site for the happenings which lead to the goal of mukti (liberation).