There are, as it happens, multiple renditions of both the Trisiras slaying and the Vritra slaying to be found within the Vedic canon. And there are a few reasons for that. Partially it is the result of having multiple Rsis drawing from the underlying mytheme in order to evocatively express Their take on it. But it is also because many of these renditions actually perform different functional roles for us – the readings of these recountings go along with different rites and rituals. After all, many Indo-European religious rites are actually examples of what Eliade famously termed ‘Eternal Return’ – the re-immanentization of various things contained in the myth out into our world via their strategic re-enactment. 

We have already demonstrated that the Nordic account of the obtaining of the Mead of Poetry is, in effect, this trend going the other way around – wherein what is represented in the Vedic canon via both a mythic account and a set of ritual instructions for the preparation of Soma … is myth-understood in the Nordic transmission of the same elements to instead refer only to a more exciting and fabulous (that is to say, fable-ous) epic quest.

[Which should not, I must emphasize, be misconstrued as a suggestion that the Nordic account is ‘wrong’ – any more than the Vedic mythological presentation is. Both are valid and encode functionally almost identical understanding – it’s just that only the Vedic canon actually contains texts making directly explicit that which is already implicit within both mythic accounts and provides the ‘how-to’ guide, so to speak.]

So, for example, whereas for we in the Hindu end of things have the Soma obtained between the Press-Stones (that is to say – via the pressing together of two stones) that are occasionally referred to as Mountain … in the Nordic recollection we instead find the Mead of Poetry being obtained in the Hnitbjorg, a mountain which opens and closes.

As you can see, this is not a hugely substantive deviation on the part of the Norse – for in both the Vedic and the Eddic, we find mythological, poetic forms utilized to ‘encode’ the ritual process.

It is certainly an eloquent way to transmit, to pass down a complex formula : turning it into a story, that can be memorized, told, yet may conceal its secrets if casually overheard (or, in a latter age, read) from prying ears.

It is just that by the time these verses were actually committed to a form which could be passed down to us – thanks to Snorri Sturluson, writing some decades after the end of the Nordic religion as a truly living entity in his native Iceland – the actual ritual understanding was evidently beyond reach. Of Sturluson, at any rate. Perhaps it was only ‘safe’ to talk about and to recall in mythic-narrativistic terms.

Perhaps the Eddic equivalent to our Brahmana commentary/instructional manual texts for the Vedas which would have directly set out such a ritual understanding and approach, were too closely guarded for Sturluson to come into contact with and thence transmit on down to us.

Perhaps it had been lost (or, at least, lost to non-practitioners). Along, I suspect, with much of the mythology which would have more fully and properly underpinned it.

Now I mention this, because it strikes me as quite cognate with what may have occurred in the Greek sphere, even though the early forms of the relevant scriptural accounts were composed while the Greek mythoreligion was very much a living entity. 

Why do I suspect this? 

Because when we look at the Vedic accounts featuring Trita / Third – we tend to find that Trita is invoked in this ritual context (often alongside the other two Aptyas – named, as you might expect, ‘First’ and ‘Second’ : Ekata and Dvita , respectively) for the transference of the burden of the impurity of sin, error, moral failing. And also, in various further hymnals, for the provision of the power with which to destroy the Demon Dragon – for example, as the preparer of the Soma; as the performer of prayer-songs, and as the recipient of the nourishing, energizing, and sustaining power of food. The latter set of elements, we have already addressed – and it is not hard to see how they relate figuratively to Iolaus’ utilization of fire (which is, after all, a key element in the preparation of Soma, the performance of Vedic prayer, and is represented as the ‘digestive fire’ which enables us to draw energy from food in the Vedic conceptry) as the ‘power’ (the ‘fire-power’, indeed) utilized to secure the Death of the Demon in the Labours of Herakles. 

But the former … this notion of Trita taking on the status of the one who has done wrong, and thence enabling its further distribution away from the actual enactor of the sin – it is both a mythological element, and a metaphysical, a ritual one. And it is these things simultaneously. Something which one would not encounter if only treating the subject mythically – which is what we have in the Greek legendariums. For the ‘ritual’ sense has dropped out near completely, and these tales are understood only as that – tales, perhaps with moral allegories for the listener; rather than replicable patterns within reality which are instructions in the more directly literal rather than merely literary sense. 

Quoting from some of the Vedic source matter may make things clearer. 

Shatapatha Brahmana 1 2 3 
“Thence sprung the Âptya deities, Trita, Dvita, and Ekata.

2. They roamed about with Indra, even as nowadays a Brâhman follows in the train of a king. When he slew Visvarûpa, the three-headed son of Tvashtri, they also knew of his going to be killed.; and straightway Trita slew him. […]
3. And the people thereupon said: ‘Let those be guilty of the sin who knew about his going to be killed! ‘How?’ they asked. ‘The sacrifice shall wipe it off upon (shall transfer it to) them!’ they said. Hence the sacrifice thereby wipes off upon them (the guilt or impurity incurred in the preparation of the offering), when they pour out for them the water with which the dish has been rinsed, and that in which he (the Adhvaryu) has washed his fingers.
4. And the Âptyas then said: ‘Let us make this pass on beyond us!’ ‘On whom?’ they asked. ‘On him who shall make an offering without a dakshinâ (gift to the officiating priests)!’ they said. Hence one must not make an offering without a dakshinâ; for the sacrifice wipes (the guilt) off upon the Âptyas, and the Âptyas wipe it off upon him who makes an offering without a dakshinâ.
5. Thereupon the gods ordained this to be the dakshinâ at the new- and full-moon sacrifices, to wit, the Anvâhârya mess of rice , ‘lest the oblation should be without a dakshinâ.’ That (rinsing water) he pours out (for each Âptya) separately: thus he avoids a quarrel among them. He makes it hot (previously) : thus it becomes boiled (drinkable) for them. He pours it out with the formulas, ‘For Trita thee!’ ‘For Dvita thee!’ ‘For Ekata thee!’–Now it is as an animal sacrifice that this sacrificial cake is offered .” 

Now, for those of you who are unfamiliar with how the Vedas work – in addition to the actual Hymnals Themselves, there are several other layers of text associated with each Veda. The Brahmanas are commentaries / ritual manuals , which help ‘bring to life’ what is contained within the hymnals: and turn these from beautiful and beautifully complex poetry, into actual, viable religious ceremonies. In other words, they take the words, and show how the words are actually to be employed; and that means unpacking the mythological referencing going on, in order to explicate the actual metaphysical saliency for the recurrence of them. 

As we can see here, Trita (along with the other two Aptyas, Second and First – Dvita and Ekata) are directly referenced in the context of the removal of the burden of sin from somebody engaged in necessary, albeit morally problematic work … and, potentially, thence passing on said burden to other individuals who are morally impugned themselves. 

The exposition for this takes a mythic occurrence – the slaying of Trisiras – and illustrates how what is going on in that myth actually, metaphysically works. And thence how to emulate it. 

The general thrust of the concept also occurs within the main Vedic texts, as well – 

RV VIII 47 
“13 Each evil deed made manifest, and that which is concealed, O Gods,
The whole thereof remove from us to Trita Āptya far away.
14 Daughter of Heaven, the dream that bodes evil to us or to our kine,
Remove, O Lady of the Light, to Trita Āptya far away.
15 Even if, O Child of Heaven, it make a garland or a chain of gold,
The whole bad dream, whate’er it be, to Trita Āptya we consign.
16 To him whose food and work is this, who comes to take his share therein,
To Trita, and to Dvita, Dawn! bear thou the evil dream away.
17 As we collect the utmost debt, even the eighth and sixteenth part,
So unto Āptya we transfer together all the evil dream.”

AV VI 113: 
“1 This sin the Gods wiped off and laid on Trita, and Trita wiped it off on human beings.
Thence if the female fiend hath made thee captive, the Gods by prayer shall banish her and free thee.
2 Enter the particles of light and vapours, go to the rising fogs or mists, O Evil!
Hence! vanish in the foams of rivers. Pūshan, wipe woes away upon the babe-destroyer!
3 Stored in twelve separate places lies what Trita hath wiped away, the sins of human beings.
Thence if the female fiend hath made thee captive, the Gods by prayer shall banish her and free thee.”

It should be noted that in the latter case, the ‘female fiend’ in question ,  Grahi , is a bestower of disease and weakness – hence, freeing the supplicant from Grahi , is thought of as a curative for this disease. Something which, interestingly enough, is also the role of Lords Indra and Agni in RV X 161 1. In other words, Trita has a role also in the provision of the restoration of Health; and, per RV VIII 47 and AV 19 56, a function connected to sleep as well (in particular, as applies RV VIII 47, the removal of nightmares, bad dreams; as with the Dawn’s breaking dispelling these nocturnal terrors likewise). 

And this is interesting to us, as there is some suggestion that amongst the Greeks, the Cult of Iolaus was connected to such things – the act of sleeping for a protracted period proximate to a particular site sacred to Iolaus furnishing the supplicant with the healing of both physical and psychic malady. There is further suggestion that the appropriately disposed were able to experience a powerfully resonant vision-state akin to a seer or a shaman – with consequent potential mystic powers that may sound suspiciously like some of those attributed to Trita in the Vedas. 

If accurate, this would rather heavily imply that the various surrounding elements to the figure of Trita – the ones that go rather beyond the close association with Indra and the Dragon-Slaying of Trisiras (or, for that matter, Vritra etc.) – have found direct parallel expression in the Greek Iolaos , and point toward an archaic Indo-European underpinning origin for all of these. 

However, even leaving those concepts to one side – it seems difficult to dispute that, in essence, the figures of Iolaos and Trita exhibit strong coterminity. With the main differences between the most prominent mythic occurrences being explicable through a combination of ‘mythic drift’ and garbling (on the part of the Greeks – who, as earlier noted, appear to have effectively run together what are otherwise separate mythic episodes when it comes to the Hydra-slaying) – and prospectively, a different sociological setup significantly influencing the mythinterpretation of legend. And, in relation to both, the difference between the ritual understanding and employment of a myth as a typology versus the mere literary-historical retelling of that same formula, contributing to further dysjunction and further loss down the ages.