What is the textual structure of original Pali versions of the suttas of the Majjhima Nikaya?

We have Nikaya-Memorizers from 0 BE till now. Monks have the rules to memorize Sutta when growing up.

DN Commentary:

etenevupāyena asītibhāṇavāraparimāṇaṃ khandhakaṃ, pañcavīsatibhāṇavāraparimāṇaṃ parivārañca saṅgahaṃ āropetvā ‘‘idaṃ vinayapiṭakaṃ nāmā’’ti ṭhapesuṃ . vinayapiṭakāvasānepi vuttanayeneva mahāpathavikampo ahosi. taṃ āyasmantaṃ upāliṃ paṭicchāpesuṃ – ‘‘āvuso, imaṃ tuyhaṃ nissitake vācehī’’ti.

...

tadanantaraṃ mahāvaggaṃ, tadanantaraṃ pāthikavagganti, evaṃ tivaggasaṅgahaṃ catutiṃsasuttapaṭimaṇḍitaṃ catusaṭṭhibhāṇavāraparimāṇaṃ tantiṃ saṅgāyitvā ‘‘ayaṃ dīghanikāyo nāmā’’ti vatvā āyasmantaṃ ānandaṃ paṭicchāpesuṃ – ‘‘āvuso, imaṃ tuyhaṃ nissitake vācehī’’ti.

tato anantaraṃ asītibhāṇavāraparimāṇaṃ majjhimanikāyaṃ saṅgāyitvā dhammasenāpatisāriputtattherassa nissitake paṭicchāpesuṃ – ‘‘imaṃ tumhe pariharathā’’ti.

tato anantaraṃ satabhāṇavāraparimāṇaṃ saṃyuttanikāyaṃ saṅgāyitvā mahākassapattheraṃ paṭicchāpesuṃ – ‘‘bhante, imaṃ tumhākaṃ nissitake vācethā’’ti.

tato anantaraṃ vīsatibhāṇavārasataparimāṇaṃ aṅguttaranikāyaṃ saṅgāyitvā anuruddhattheraṃ paṭicchāpesuṃ – ‘‘imaṃ tumhākaṃ nissitake vācethā’’ti.

tato anantaraṃ dhammasaṅgahavibhaṅgadhātukathāpuggalapaññattikathāvatthuyamakapaṭṭhānaṃ abhidhammoti vuccati. evaṃ saṃvaṇṇitaṃ sukhumañāṇagocaraṃ tantiṃ saṅgāyitvā – ‘‘idaṃ abhidhammapiṭakaṃ nāmā’’ti vatvā pañca arahantasatāni sajjhāyamakaṃsu. vuttanayeneva pathavikampo ahosīti. Translation:

As I've explained, 500 bhikkhus in first council recited 80 Bhanavara of Khandhaka (VN.Bhikkhu,Bhikkhuni,Maha,Cula) and 25 Bhanavara of Parivara together, then called it Vinaya-Pitaka. At the end of reciting, the land shook. 500 bhikkhus in first council ordered Upali "Teach VinayaPitaka to your students, Avuso".

...

500 bhikkhus in first council recited 64 Bhanavara in systematized language which included 34 Sutta 3 Vagga step by step (SilakkhandhaVagga, Mahavagga, Pathikavagga) together, then called it DigaNikaya and ordered Ananda "Teach DigaNikaya to your students, Avuso".

Then 500 bhikkhus in first council recited MajjhimaNikaya 80 Bhanavara together, and
they ordered Sariputta's students "Keep it, Avuso".

Then 500 bhikkhus in first council recited SamyuttaNikaya 100 Bhanavara together, and
they ordered Kassapa "Teach SamyuttaNikaya to your students, Bhante".

Then 500 bhikkhus in first council recited AnguttaraNikaya 120 Bhanavara together, and
they ordered Anuruddha "Teach AnguttaraNikaya to your students, Avuso".

The Rule

in commentary according to V.N. Mahākhandhaka:**

Qualities of nissayamuccaka-bhikkhu (teaching lay people)

1. Proficient to recite pāṭimokkha-pāli and to understand it's commentary.
2. Proficient to recite and to understand 4 bhāṇavāra (~1,000 syllable) of sutta and their commentary, to teach laymen on uposatha day.
3. Proficient to recite and to understand sutta for bhikkhu's life such as andhakavindasutta, mahālahulovādasutta, ambaṭṭhasutta, etc.
4. Proficient to recite and to understand sutta for teaching in 3 chances: banquet for saṅgha by layman (nidhikaṇdasutta), funeral ceremony (tirokuṭṭasutta), and auspicious ceremony (maṅgalasutta).
5. Enough understand to judge/to decide about saṇgha's ceremony such as uposatha, pavāraṇā, etc.
6. Proficient to recite and to understand his kammaṭṭhānā throughout the nibbāna-course.
7. 5 years experience in monk hood as a monk.

Qualities of bhikkuparisūpaṭṭhāpaka-bhikkhu (teaching bikkhus)

If above layman's teachers want to teach bhikkhus (ūpajjhā-ācāriya, nissaya-ācāriya), they must increase their skill level to all of the following qualities.

These are for abhivinaya teaching:

1. Proficient to recite mahāvibhagha and bhikkhunivibhaṅga (first 3 books of thai 45 books pali-tipitaka) of vinaya-pitaka-pali. At least, he can relay with the other 3 bhikkhu. Proficient to understand it's commentary, too.
2. Proficient to recite all saṇgha's ceremony in vinaya-pitaka mahāvagga and julavagga.
3. Proficient to recite 14 vatta in vattakhandhaka.

These are for abhidhamma (kammaṭṭhāna) teaching:

4. Proficient to recite one of this suttanta-pali: mūlapaṇṇassa (1st/3 parts of M.N.) for student in M.N. faculty, mahāvagga (2nd/3 parts of D.N.) for student in D.N. faculty, sagāthavagga+nidānavagga+khandhavāravagga of S.N. or mahāvagga of S.N. for student in S.N. faculty, before half of A.N. or after half of A.N. or ekakanipāta+dukanipāta of A.N. for student in A.N. faculty, jātaka+commentary (because kammaṭṭhāna was described in commentary) for student in jātaka faculty.

Qualities of bhikkunovdaka-bhikkhu (teaching bhikkunīs)

If above layman's teachers want to teach bhikkhunī, they must increase their skill level to all of these qualities:

1. Proficient to recite whole tipitaka-pali and commentary-pali. Or at least, he still must recite whole tipitaka, but he can recite just one commentary of suttanta, first 4 parts of commentary of 7 parts of abhidhamma. However, vinaya-commentary is what he must recite it all.

Reference: tipitaka and commentary of vinaya pācittiyakaṇḍa bhikkhunovādakasikkhāpada and vinaya mahāvagga mahākhandhaka.

Related topic: https://buddhism.stackexchange.com/a/22917/10100 https://buddhism.stackexchange.com/a/23663/10100

The Dhamma was traditionally spoken, heard, memorized and recited in unison. It was written down and organized later.

Bhante Sujato has a very useful overview of the challenge of organizing the Dhamma throughout the ages. Notably, Bhante Sujato has himself chosen to organize the Tipitaka into numbered segments, which allows translations to be matched up with their root sources verse by verse.

The Pali suttas were initially transmitted by oral tradition. The composition is in a poetic form, using mnemonic formulae for memorization and recitation. The recitation would have also served a ritualistic or ceremonial purpose. Even the tradition says that in the First Buddhist Council, Ananda and Upali recited the suttas and the vinaya.

So, the answer is that the textual structure of the Pali suttas is irrelevant because they were originally transmitted orally. What is more important is the "oral" structure of the Pali suttas i.e mnemonic formulae.

Please see "Pali Oral Literature" by L.S. Cousins. I quote below:

Early Buddhist literature is an oral literature. Such a literature is not without its own characteristic features. A widespread use of mnemonic formulae is one of the most typical of these. I would refer to the considerable body of research on the nature of oral epic poetry. In such poetry the formulae are used both as an aid to actual performance and to maintain the continuity and form of the epic tradition.

Both these features are certainly present in the sutta literature. In the first place many suttas are clearly designed for chanting. We should assume that, then as now, their chanting would produce a great deal of religious emotion - the pamojja and piti-somanassa of the texts. The difference of course would be that the language of the suttas would still be directly comprehensible to the hearers. In these circumstances suttas would be chanted by individual monks both for edification and for enjoyment. We may compare the recitations attributed to Ananda and Upali in accounts of the First Council. In practice they would have to be tailored to the needs of the particular situation ~ shortened or lengthened as required. An experienced chanter would be able to string together many different traditional episodes and teachings so as to form a coherent, profound and moving composition.

The people at the PTS also divided each sutta in paragraphs, but not numbered. The pali text they work on is this https://obo.genaud.net/dhamma-vinaya/pts_pali/mn/mn.2.077-106.pts_pali.htm where there are already paragraphs

It is really the work of the each translator to find the beginning and end of a paragraph. it is not from a tradition. THe palm leaf itself does not have any paragrpah, like here

EAP1150/1/77/4: Aggikkhandhopama-sutta pāli Description: A canonical text of the discourse of the Buddha warning the monks against sensual pleasures. The text originally belongs to Aṅguttaranikāya collection. Extent: ka [330] - ke [338]. Scribe(s): Monk Varananda. Additional date information: Copied c. 1804 https://eap.bl.uk/archive-file/EAP1150-1-77