This invites us to investigate, whether or not the ancients had any knowledge of the internal anatomy of the body. Some of the Yogis later than Patanjali, who have described these various exercises to be performed by the student of Yoga for the control of Vayu or nervous impulse, describe in detail, the construction and action of the nervous system. Did they then dissect the human bodies, to find out its internal construction? Certainly their description of the nervous system tallies with our present knowledge of anatomy and physiology. Did they gain this knowledge by some mystic vision? What ever it may be, the fact remains that the anatomy of nerves given in the Tantric manuals canstand comparison with our present knowledge. According to the writers on Yoga there are ten important Vayu-nadis, i.e., nerves of impulse, without a knowledge of which the process and technique of Pranayama is not possible. There are many more, but these have the power of carrying impulses (Prana-vahaka). The following are their names and locations: Ida on the left side of the body; Pingala on the right side; Sushumna in the centre of the body piercing the skull and joining the cerebum (Brahma-chakra); Gandhari in the left eye; Hastajivha in the right eye; Pusha in the right ear; Yashaswini in the left ear; Alambusha in the mouth; Kuhu in the penis; and Shakhini in the perineum (Mulasthana). Of these ten nadis, three are the most important and these are Ida, Pingala, and Sushumna. I will describe them in detail in the same way as is done in Yogic literature. But it must also be borne in mind that the rest of the nadis, from their positions, appear to carry impressions to the brain by means of the five senses.
The first is Ida, the location of which is on the left side of the Meru-danda, i.e., the spinal column and ends in the right nostril. The second is Pingala which is on the right side of the spinal column and ends in the left nostril. From this description, it is clear that these nadis cross each other before their respective endings and have their origin, or mouth as it is called, in the plexus of nerves called Muladhara-chakra which is situated in Mulasthana, that is, the perineum. I think that the Muladhara-chakra is the Pelvic plexus of the sympathetic system. From this description of the nadis, it appears that Ida and Pingala correspond to the gangliated cords of the sympathetic system, which are situated on either side of the spinal column. At the cephalic end, each sympathetic trunk passes into the cranial cavity, arborises with its fellows of the other side and forms a plexus. Through this plexus the sympathetic trunks gain complex relations with the spinal cord (Sushumna-nadi) where it joins the brain. This plexus is called in Yogic literature Bhrukuti-chakra. At the caudal end, both the sympathetic trunks end in the pelvic plexus.
The third nadi, Sushumna, is centrally situated and passes through the Mere-danda, i.e., the spinal column. It originates inside the Kanda, i.e., the sacrum which roughly corresponds with the level of the navel.
It runs, up the body, from this point, pierces the Talu (the base of the skull) and joins Brahma-chakra (the plexus of nerves of a thousand branches or the cerebrum). This nadi, as it ascends and reaches the level of Kantha (region of the larynx), divides into and anterior and a posterior part. The anterior portion goes towards the Ajna-chakra, the plexus of command, which is situated between the two eye-brows and joins the Brahma-randhra (cavity in the brain). The posterior passes from behind the skull and joints the Brahma-randhra which is supposed to be a cavity in the brain from which the Yogi liberates his soul. It is this posterior portion that is to be developed by a student of Yogic science.
This description of the Sushumna nadi concurs with that of the spinal cord and very nearly or almost accurately. It seems that the ancients had a knowledge of the function of the two parts of the spinal cord, the anterior and the posterior, when one reads it described that the anterior division of the nadi goes towards the Ajna-chakra, i.e., to a point in the frontal lobe of the brain (the lobe of intelligence) from which are issued the orders to move the different parts or our voluntary muscles, and which is a plexus controlled by our thought. The Yogi is told to develop the posterior portion of the nadi, which governs all sensations and supplies all the vital organs of the body, a portion which normally is not under our control. Of all the ten nadis these three are the principal, and the three Sushumna is the most important. The importance of this nadi lies in the fact that through it, by certain practices, one can put a stop to the flight of time, by drawing Prana (Vitality) from the Ida and Pingala nadis, i.e., by consciously controlling the incessant working of these sympathetic cords, it is possible to put a stop to the katabolic activity of the body. This conscious control over them, which could only be achieved through the Sushumna nadi, suspends the general wear and tear of the tissues of the vital organs, and helps in the prolongation of life. When the Ida, and Pingala nadis are thus decitalised by the Sushumna nadi, there is said to exist no night or day for a Yogi. Sushumna is said “to devour time.”
It is also through this Sushumna nadi that we obtain knowledge of our relations with the external world. But a knowledge of the self and a control of the vital organs can only be achieved by consciously controlling the Ida and Pingala nadis which form a connecting link between the prevertebral plexuses (Chakras) of the sympathetic system and spinal cord (Sushumna nadi)
All these plexuses, in order to excite Sushumna nadi by their connection with it, must work through the Kundali-chakra. In fact, what the brain or medulla is to the central nervous system, Kundali-chakra is to the sympathetic system. Normally, the central nervous system is well developed as regards its response to external stimuli while the sympathetic nervous system lies dormant. When the latter is made active by Pranayama and by certain other processes prescribed in the Hatha-Yoga, a person develops the power to do certain things which are beyond the scope of an ordinary individual. Actions done by these persons are regarded as miracles, though to a Yogi they are not so. They are due to a latent power within but it requires to be converted into active energy. A Yogi, when he develops his autonomic nervous system, becomes so engrossed that the somatic functions of his Sushumna nadi, and the knowledge of his relations with the external world are held in abeyance and he sees his self pervading the whole universe and becoming one with it.
Before actually, defining Kundalini in terms of our present knowledge of anatomy, one should like to name the six important Lotuses or Chakras (Plexuses) with their present anatomical equivalents.