Could you show us which sentences you mean?
First section...
The definition (the four frames of reference) "And what is right mindfulness? There is the case where a monk remains focused on the body in & of itself — ardent, alert, & mindful — putting aside greed & distress with reference to the world. He remains focused on feelings in & of themselves... the mind in & of itself... mental qualities in & of themselves — ardent, alert, & mindful — putting aside greed & distress with reference to the world. This is called right mindfulness...
"This is the direct path for the purification of beings, for the overcoming of sorrow & lamentation, for the disappearance of pain & distress, for the attainment of the right method, & for the realization of Unbinding — in other words, the four frames of reference."
Last section from the Anapanasati which mentions the 4 frames. Note there are 4 enumerated paragraphs too...
Meditation on breathing "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.
"Now how is mindfulness of in-&-out breathing developed & pursued so as to be of great fruit, of great benefit?
"There is the case where a monk, having gone to the wilderness, to the shade of a tree, or to an empty building, sits down folding his legs crosswise, holding his body erect, and setting mindfulness to the fore. Always mindful, he breathes in; mindful he breathes out.
"[1] Breathing in long, he discerns, 'I am breathing in long'; or breathing out long, he discerns, 'I am breathing out long.' [2] Or breathing in short, he discerns, 'I am breathing in short'; or breathing out short, he discerns, 'I am breathing out short.' [3] He trains himself, 'I will breathe in sensitive to the entire body.' He trains himself, 'I will breathe out sensitive to the entire body.' [4] He trains himself, 'I will breathe in calming bodily fabrication.' He trains himself, 'I will breathe out calming bodily fabrication.'
"[5] He trains himself to breathe in sensitive to rapture, and to breathe out sensitive to rapture. [6] He trains himself to breathe in sensitive to pleasure, and to breathe out sensitive to pleasure. [7] He trains himself to breathe in sensitive to mental processes, and to breathe out sensitive to mental processes. [8] He trains himself to breathe in calming mental processes, and to breathe out calming mental processes.
"[9] He trains himself to breathe in sensitive to the mind, and to breathe out sensitive to the mind. [10] He trains himself to breathe in satisfying the mind, and to breathe out satisfying the mind. [11] He trains himself to breathe in steadying the mind, and to breathe out steadying the mind. [12] He trains himself to breathe in releasing the mind, and to breathe out releasing the mind.
"[13] He trains himself to breathe in focusing on inconstancy, and to breathe out focusing on inconstancy. [14] He trains himself to breathe in focusing on dispassion [literally, fading], and to breathe out focusing on dispassion. [15] He trains himself to breathe in focusing on cessation, and to breathe out focusing on cessation. [16] He trains himself to breathe in focusing on relinquishment, and to breathe out focusing on relinquishment."
— MN 118