This section is from the book "The Sushruta Samhita", by Kaviraj Kunja Lal Bhishagratna. Also available from Amazon: The Sushruta Samhita.
There are twenty-four Dhamanies (ducts) in all, and all of them have their origins in the naval region (which includes the whole abdominal region †). Several authorities assert that no arbitrary distinctions should be made among the Siras (veins), Dhamanis (arteries), and the Srotas, (channels), since Dhamanis and Srotas are but different modifications of one original kind of Sirá (vessels). But this opinion is not a sound one inasmuch as they have got different natures, origins and functions and as being described so in the Ayurveda. But owing to their adjacent positions, the existence of several authoritative dicta (Apta-vak) regarding the oneness of their character, similarity of their functions, and the minute nature of their shape, they appear to be homologous in their action, even amidst the real diversities in their work and office. 2.
Of the twenty-four Dhamanis, which (originally) have their roots in the naval region (Nábhi), ten have upward course, ten have downward course, and four flow laterally or transversely. 3.
The ten up-coursing Dhamanis (nerves)
* Sans. Dhama - to be filled with air, so called from the fact of their being distended with air after death.
+ So far, as in foetal life, allantoic arteries and the unbilical veins subserve the purposes of nutrition, excretion, etc , and reflects the rudimentary vascular system.
perform such specific functions of the body, as sound, touch, taste, sight, smell, inspiration, sighing, yawning, sneezing, laughter, speech, and weeping, etc., and tend to maintain the integrity of the body. These Dhamanis, reaching the heart, respectively ramify themselves into three branches, thus making thirty (ramifications in all). Ten of these serve the following purposes, viz , two serve as the channels of the bodily Váyu, two of the Pitta, two of the Kapha, two of the blood, and two of the Rasa (lymph chyle). Eight of the remaining ones (twenty), serve the following functions, viz., two of them carry sound, two sight or colour, two smell, and two taste. Moreover a man speaks with the help of another two, makes sound with the help of another couple, sleeps through the instrumentality of another pair (couple), and wakes up with the help of another couple. Two of the Dhamanis (ducts) carry the fluid of lachry-mation, two of them (ducts), attached to the breasts of a woman, carry milk of her breasts, which, coursing through the breast of a man, convey his seminal fluid. Thus we have described the thirty Dhamanis with their ramifications. These sustain and maintain the integrity (of the limbs and members of the body) above the (line of) umbilicus, such as the Udara, the sides, the back the chest, the neck, the shoulders and the arms. 4.
The up-coursing Dhamanis duly perform the offices stated above. Now I shall describe the specific functions, etc., (i.e., nature, office, and situations, etc.) of the down-coursing ones. 5.
 
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