Kāyānupassanā This section title is omitted by BJT, though it includes the others (Vedanānupassanā, Cittānupassanā, Dhammānupassanā) at their proper places.
Contemplation of the Body

Ānāpānapabbaṁ
The Section about In-breathing and Out-breathing

 

Kathañ-ca, bhikkhave, bhikkhu kāye kāyānupassī viharati?
And how, monks, does a monk dwell contemplating (the nature of) the body in the body?

Idha, bhikkhave, bhikkhu araññagato vā, rukkhamūlagato vā,
Here, monks, a monk who has gone to the wilderness, or has gone to the root of a tree,

suññāgāragato vā, nisīdati.
or has gone to an empty place, sits down.

Pallaṅkaṁ ābhujitvā, The absolutives here and in the next line are connected with the finite verbs assasati and passasati (as in Ñāṇamoli’s translation of MN 10), and not with nisīdati in the preceding line, in which case the folding of the legs, setting the body straight, and establishment of mindfulness would all occur before he sat down! ujuṁ kāyaṁ paṇidhāya,
After folding his legs crosswise, setting his body straight,

parimukhaṁ satiṁ upaṭṭhapetvā, Parimukhaṁ means at the front, or perhaps, around the mouth, i.e. it is a vague area, not meant to be confined to one particular spot or place, which would have been easy to designate if that is what was meant (like specifying oṭṭha, the lip). It is of course the mindfulness that is important in the practice, not the breathing as such, which only provides a basis for the mindfulness.
and establishing mindfulness at the front,

so sato va assasati, sato va passasati.
being very mindful he breathes in, mindful he breathes out.

 

Dīghaṁ vā assasanto “dīghaṁ assasāmī” ti pajānāti,
While breathing in long, he knows “I am breathing in long”,

dīghaṁ vā passasanto “dīghaṁ passasāmī” ti pajānāti;
or, while breathing out long, he knows “I am breathing out long”;

rassaṁ vā assasanto “rassaṁ assasāmī” ti pajānāti,
or, while breathing in short, he knows “I am breathing in short”,

rassaṁ vā passasanto “rassaṁ passasāmī” ti pajānāti.
or, while breathing out short, he knows “I am breathing out short”.

Sabbakāyapaṭisaṁvedī -paṭisaṁvedī, see the note to -anupassī above for a comment on this form and meaning. Paṭisambhidāmagga says: Kāyo ti dve kāyā - nāmakāyo ca rūpakāyo ca; body means the two bodies - the mind-body and the physical body; this would seem to mitigate against breathing meditation being taken solely as a body-based meditation. assasissāmī The instruction here changes from the present tense for breathing to the future tense. The reason for this change is that once the mind is settled on the breath he needs to deliberately cultivate mindfulness to progress further in the practice. ti sikkhati,
Experiencing the whole body I will breathe in, like this he trains,

sabbakāyapaṭisaṁvedī passasissāmī ti sikkhati;
experiencing the whole body I will breathe out, like this he trains;

passambhayaṁ kāyasaṅkhāraṁ assasissāmī ti sikkhati,
calming the bodily process I will breathe in, like this he trains,

passambhayaṁ kāyasaṅkhāraṁ passasissāmī ti sikkhati.
calming the bodily process I will breathe out, like this he trains.

 

Seyyathā pi, bhikkhave, dakkho bhamakāro vā bhamakārantevāsī vā
Just as, monks, a clever turner or turner’s apprentice

dīghaṁ vā añchanto “dīghaṁ añchāmī” ti pajānāti,
while making a long turn knows “I am making a long turn”,

rassaṁ vā añchanto “rassaṁ añchāmī” ti pajānāti, The choice of simile here is surely significant, as the turner knows not just what is happening, but how he is making it happen, so that knowledge of the intention is also included in the practice.
or, while making a short turn knows “I am making a short turn”,

 

evam-eva kho, bhikkhave, bhikkhu dīghaṁ vā assasanto “dīghaṁ assasāmī” ti pajānāti,
just so, monks, a monk while breathing in long, knows “I am breathing in long”,

dīghaṁ vā passasanto “dīghaṁ passasāmī” ti pajānāti;
or, while breathing out long, he knows “I am breathing out long”;

rassaṁ vā assasanto “rassaṁ assasāmī” ti pajānāti,
or, while breathing in short, he knows “I am breathing in short”,

rassaṁ vā passasanto “rassaṁ passasāmī” ti pajānāti.
or, while breathing out short, he knows “I am breathing out short”.

Sabbakāyapaṭisaṁvedī assasissāmī ti sikkhati,
Experiencing the whole body I will breathe in, like this he trains,

sabbakāyapaṭisaṁvedī passasissāmī ti sikkhati;
experiencing the whole body I will breathe out, like this he trains;

passambhayaṁ kāyasaṅkhāraṁ assasissāmī ti sikkhati,
calming the bodily process I will breathe in, like this he trains,

passambhayaṁ kāyasaṅkhāraṁ passasissāmī ti sikkhati.
calming the bodily process I will breathe out, like this he trains.

* * *

Iti ajjhattaṁ vā kāye kāyānupassī viharati, The context seems to indicate that contemplating (the nature of) the body in the body means contemplating the transient, ownerless nature of the body, as is signified by the references to origination and dissolution (samudaya & vaya [= anicca]) on the one hand; and the impersonal knowledge “there is a body” (atthi kāyo [= anattā]) on the other. Dukkha, the other of the three characteristics of existence (tilakkhaṇa) is implied in anicca. And similarly in regard to the other contemplations.
Thus he dwells contemplating (the nature of) the body in the body in regard to himself,

bahiddhā vā kāye kāyānupassī viharati, That we are really talking about others’ bodies, and not the internal and external parts of our own body, is confirmed by the Abhidhamma Satipaṭṭhānavibhaṅga (translated elsewhere on this website), where the grammar excludes any other interpretation.
or he dwells contemplating (the nature of) the body in the body in regard to others,

ajjhattabahiddhā See DP, ajjhattaṁ (and obahiddhā) for these meanings. In Janavasabhasutta (DN 18,26) it says: Idha ... bhikkhu ajjhattaṁ kāye kāyānupassī viharati ātāpī sampajāno satimā vineyya loke abhijjhādomanassaṁ; ajjhattaṁ kāye kāyānupassī viharanto tattha sammā samādhiyati, sammā vippasīdati, so tattha sammā samāhito sammā vippasanno bahiddhā parakāye ñāṇadassanaṁ abhinibbatteti; here ... a monk dwells contemplating (the nature of) the body in the body, ardent, with full awareness, mindfully aware, after removing avarice and sorrow regarding the world; while he dwells contemplating (the nature of) the body in the body there he becomes perfectly concentrated, perfectly clear, and, being perfectly concentrated, perfectly clear, he generates knowledge and insight regarding the external bodies of others. Similarly in regard to the contemplation of vedanā, citta, and dhamm . vā kāye kāyānupassī viharati,
or he dwells contemplating (the nature of) the body in the body in regard to himself and in regard to others,

samudayadhammānupassī vā kāyasmiṁ viharati, Kāye (on the previous line) & kāyasmiṁ are alternative forms of the locative singular of kāya, the former ending being the normal one, and the latter borrowing from the pronominal declension; the same alternation occurs later with citte and cittasmiṁ.
or he dwells contemplating the nature of origination in the body,

vayadhammānupassī vā kāyasmiṁ viharati,
or he dwells contemplating the nature of dissolution in the body,

samudayavayadhammānupassī vā kāyasmiṁ viharati,
or he dwells contemplating the nature of origination and dissolution in the body,

“atthi kāyo” ti vā panassa sati paccupaṭṭhitā hoti Some texts (BJT) and translations (Way, VRI) divide these alternatives into 3 blocks (1: ajjhattaṁ, bahiddhā, ajjhattabahiddhā; 2: samudaya-, vaya-, samudayavaya-; 3: “atthi kāyo”), but this is not justified by the grammar, which connects all the alternatives with vā...vā...
or else mindfulness that “there is a body” is established in him

yāvad-eva ñāṇamattāya patissatimattāya, The translation follows the commentary, which says: Yāvad-evā ti payojanaparicchedavavatthāpanam-etaṁ. Idaṁ vuttaṁ hoti: yā sā sati paccupaṭṭhitā hoti sā na aññad-atthāya. Atha kho yāvad-eva ñāṇamattāya aparāparaṁ uttaruttari ñāṇapamāṇatthāya ceva satipamāṇatthāya ca, satisampajaññānaṁ vuḍḍhatthāyā ti attho; just as far as, this designates, and is limited to, purpose. This is what is said: whatever mindfulness is established is not for another reason. Then the meaning of as far as (is necessary for) a measure of knowledge is so as to increase more and more, further and further, knowledge and mindfulness, for the increase of mindfulness and full awareness. For the same word in Sanskrit having this meaning see SED under mātra. This seems to me to make much better sense than the usual translation of for just knowledge and remembrance (Way); or for mere understanding and mere awareness (VRI). See also MN 22, near the end, where saddhamatta is translated by Ñāṇamoḷi and Bodhi (MLDB) as sufficient faith, and pemamatta as sufficient love.
just as far as (is necessary for) a full measure of knowledge and a full measure of mindfulness,

anissito ca viharati, Comm: taṇhānissayadiṭṭhinissayānaṁ vasena anissito va viharati; he lives independent because he is not dependent on wrong views or craving. na ca kiñci loke upādiyati. Comm: ayaṁ me attā vā attaniyaṁ vā ti na gaṇhāti; he doesn't grasp (anything) thinking: this is my self or this belongs to my self.
and he dwells independent, and without being attached to anything in the world.

Evam-pi kho, bhikkhave, bhikkhu kāye kāyānupassī viharati.
In this way, monks, a monk dwells contemplating (the nature of) the body in the body.

Ānāpānapabbaṁ Niṭṭhitaṁ
The Section about In-breathing and Out-breathing is Finished