user157: The book Breath by Breath by Larry Rosenberg splits the Anapanasati Sutta into 4 tetrads. The wildmind website does a similar thing. In the second tetrad there is a verse that is rendered

He trains himself to breathe in sensitive to mental processes, and to
  breathe out sensitive to mental processes.

and in the third tetrad there is the verse

He trains himself to breathe in sensitive to the mind, and to breathe
  out sensitive to the mind.

What is the difference between mental processes and the mind? In their English translations they look very similar. What is the original Pali words or phrases? Do they have difference translations or nuances that may make the differences clearer.

user-1: 
He trains himself to breathe in sensitive to mental processes, and to breathe out sensitive to mental processes.
(Cittasaṅkhārapaṭisaṃvedī assasissāmīti sikkhati. Cittasaṅkhārapaṭisaṃvedī passasissāmīti sikkhati.)
He trains himself to breathe in sensitive to the mind, and to breathe out sensitive to the mind.
(Cittapaṭisaṃvedi assasissāmīti sikkhati. Cittapaṭisaṃvedī passasissāmīti sikkhati.)

In MN 44 we find an explanation for cittasaṅkhāra:

"Now, lady, what are fabrications?"
"Perceptions & feelings are mental fabrications." (Thanissaro trans.)
(Saññā ca vedanā ca cittasaṅkhāroti.)

The Visuddhimagga says (VIII, 229ff):

The remaining [three] clauses should be understood in the same
way as to meaning; but there is this difference here.
The experiencing of bliss must be understood to be through three jhanas, and that of the mental formation through four.  The mental formation consists of the two aggregates of feeling and perception. And in the case of the clause, experiencing bliss, it is said in the Paþisambhidá in order to show the plane of insight here [as well]: “‘Bliss’: there are two kinds of bliss, bodily bliss and mental bliss” (Paþis I 188). Tranquilizing the mental formation: tranquilizing the gross mental formation; stopping it, is the meaning. And this should be understood in detail in the same way as given under the bodily formation (see §§176–85). Here, moreover, in the “happiness” clause feeling [which is actually being contemplated in this tetrad] is stated under the heading of “happiness” [which is a formation] but in the “bliss” clause feeling is stated in its own form. In the two “mental-formation” clauses the feeling is that [necessarily] associated with perception because of the words, “Perception and feeling belong to the mind, these things being bound up with the mind are mental formations” (Paþis I 188). So this tetrad should be understood to deal with contemplation of feeling.
(ix) In the third tetrad the experiencing of the [manner of] consciousness must
be understood to be through four jhanas

Ven. Buddhadasa [1] explains that second tetrad as concerned  specifically with pīti and sukha whereas the third is concerned with citta in a broader and deeper way.

[1] - Mindfulness With Breathing: A Manual for Serious Beginners

user143: From the Anapanasati Sutta

"Mindfulness of in-&-out breathing, when developed & pursued, is of great fruit, of great benefit. Mindfulness of in-&-out breathing, when developed & pursued, brings the four frames of reference to their culmination. The four frames of reference, when developed & pursued, bring the seven factors for awakening to their culmination. The seven factors for awakening, when developed & pursued, bring clear knowing & release to their culmination."

The four tetrads correspond to The Four Frames of Reference referred to above. They are (in Pali and English):

Kāyānupassanā satipaṭṭhāna: being mindful of the body as a frame of reference.
Vedanānupassanā satipaṭṭhāna: being mindful of feelings as a frame of reference.
Cittānupassanā satipaṭṭhāna: being mindful of the mind as a frame of reference.
Dhammānupassanā satipaṭṭhāna: being mindful of mental qualities as a frame of reference.

So the second tetrad in your example is mindfulness of feelings (vedanā) and the third is mindfulness of mind (citta).
A basic distinction of these is here:

1: The Body merely as a transient and compounded Form..
2: Feelings just as vanishing Reactions to sense-contact..
3: Mind only as a group of habitual and conditioned Moods..
4: All Phenomena (dhamma) simply as discrete momentary Mental States..


157: <p>The book <a href="https://www.goodreads.com/book/show/148596.Breath_by_Breath" rel="noreferrer">Breath by Breath</a> by Larry Rosenberg splits the Anapanasati Sutta into 4 tetrads. The <a href="http://www.wildmind.org/texts/anapanasati/anapanasati3" rel="noreferrer">wildmind website</a> does a similar thing. In the second tetrad there is a verse that is rendered</p>

<blockquote>
  <p>He trains himself to breathe in sensitive to mental processes, and to
  breathe out sensitive to mental processes.</p>
</blockquote>

<p>and in the third tetrad there is the verse</p>

<blockquote>
  <p>He trains himself to breathe in sensitive to the mind, and to breathe
  out sensitive to the mind.</p>
</blockquote>

<p>What is the difference between mental processes and the mind? In their English translations they look very similar. What is the original Pali words or phrases? Do they have difference translations or nuances that may make the differences clearer.</p>
 -1: <blockquote>
<p>He trains himself to breathe in sensitive to mental processes, and to breathe out sensitive to mental processes.</p>
<p>(<em>Cittasaṅkhārapaṭisaṃvedī assasissāmīti sikkhati. Cittasaṅkhārapaṭisaṃvedī passasissāmīti sikkhati.</em>)</p>
<p>He trains himself to breathe in sensitive to the mind, and to breathe out sensitive to the mind.</p>
<p>(<em>Cittapaṭisaṃvedi assasissāmīti sikkhati. Cittapaṭisaṃvedī passasissāmīti sikkhati.</em>)</p>
</blockquote>
<p>In <a href="http://www.accesstoinsight.org/tipitaka/mn/mn.044.than.html" rel="noreferrer">MN 44</a> we find an explanation for <em>cittasaṅkhāra</em>:</p>
<blockquote>
<p>&quot;Now, lady, what are fabrications?&quot;</p>
<p>&quot;Perceptions &amp; feelings are mental fabrications.&quot; (Thanissaro trans.)</p>
<p>(<em>Saññā ca vedanā ca cittasaṅkhāroti.</em>)</p>
</blockquote>
<p>The Visuddhimagga says (VIII, 229ff):</p>
<blockquote>
<p>The remaining [three] clauses should be understood in the same
way as to meaning; but there is this difference here.</p>
<p>The <em>experiencing of bliss</em> must be understood to be through three jhanas, and that of the <em>mental formation</em> through four.  The mental formation consists of the two aggregates of feeling and perception. And in the case of the clause, experiencing bliss, it is said in the Paþisambhidá in order to show the plane of insight here [as well]: “‘Bliss’: there are two kinds of bliss, bodily bliss and mental bliss” (Paþis I 188). <em>Tranquilizing the mental formation</em>: tranquilizing the gross mental formation; stopping it, is the meaning. And this should be understood in detail in the same way as given under the bodily formation (see §§176–85). Here, moreover, in the “happiness” clause feeling [which is actually being contemplated in this tetrad] is stated under the heading of “happiness” [which is a formation] but in the “bliss” clause feeling is stated in its own form. In the two “mental-formation” clauses the feeling is that [necessarily] associated with perception because of the words, “Perception and feeling belong to the mind, these things being bound up with the mind are mental formations” (Paþis I 188). So this tetrad should be understood to deal with contemplation of feeling.</p>
<p>(ix) In the third tetrad the <em>experiencing of the [manner of] consciousness</em> must
be understood to be through four jhanas</p>
</blockquote>
<p>Ven. Buddhadasa [1] explains that second tetrad as concerned  specifically with <em>pīti</em> and <em>sukha</em> whereas the third is concerned with <em>citta</em> in a broader and deeper way.</p>
<hr />
<p>[1] - Mindfulness With Breathing: A Manual for Serious Beginners</p>
 143: <p>From the <a href="http://www.accesstoinsight.org/tipitaka/mn/mn.118.than.html" rel="noreferrer">Anapanasati Sutta</a></p>
<blockquote>
<p>&quot;Mindfulness of in-&amp;-out breathing, when developed &amp; pursued, is of great fruit, of great benefit. Mindfulness of in-&amp;-out breathing, when developed &amp; pursued, brings the four frames of reference to their culmination. The four frames of reference, when developed &amp; pursued, bring the seven factors for awakening to their culmination. The seven factors for awakening, when developed &amp; pursued, bring clear knowing &amp; release to their culmination.&quot;</p>
</blockquote>
<p>The four tetrads correspond to The <a href="http://www.accesstoinsight.org/lib/thai/lee/frames.html" rel="noreferrer">Four Frames of Reference</a> referred to above. They are (in Pali and English):</p>
<blockquote>
<p>Kāyānupassanā satipaṭṭhāna: being mindful of the body as a frame of reference.</p>
<p>Vedanānupassanā satipaṭṭhāna: being mindful of feelings as a frame of reference.</p>
<p>Cittānupassanā satipaṭṭhāna: being mindful of the mind as a frame of reference.</p>
<p>Dhammānupassanā satipaṭṭhāna: being mindful of mental qualities as a frame of reference.</p>
</blockquote>
<p>So the second tetrad in your example is mindfulness of feelings (vedanā) and the third is mindfulness of mind (citta).</p>
<p>A basic distinction of these is <a href="http://what-buddha-said.net/drops/III/Straight_View.htm" rel="noreferrer">here</a>:</p>
<blockquote>
<p>1: The Body merely as a transient and compounded Form..</p>
<p>2: Feelings just as vanishing Reactions to sense-contact..</p>
<p>3: Mind only as a group of habitual and conditioned Moods..</p>
<p>4: All Phenomena (dhamma) simply as discrete momentary Mental States..</p>
</blockquote>
