Reference for Yoma 169:13

וכבר היה ר' ישמעאל ורבי עקיבא ורבי אלעזר בן עזריה מהלכין בדרך ולוי הסדר ורבי ישמעאל בנו של רבי אלעזר בן עזריה מהלכין אחריהן נשאלה שאלה זו בפניהם מניין לפקוח נפש שדוחה את השבת

Abba Saul said: From the navel which sends its roots into every direction!<span class="x" onmousemove="('comment',' Hence the dispute of these Tannaim looks exactly the same as those mentioned above.');">¹⁷</span> You may even say that [the first view is in agreement with] Abba Saul, inasmuch as Abba Saul holds his view only touching the first formation, because 'everything develops from its core [middle]', but regarding the saving of life he would agree that life manifests itself through the nose especially, as it is written: In whose nostrils was the breath the spirit of life.<span class="x" onmousemove="('comment',' Gen. VII, 22.');">¹⁸</span> R'Papa said: The dispute arises only as to from below upwards,<span class="x" onmousemove="('comment',' If the person under the debris has his feet up and his head down. According to one view, one must examine the core, i.e., the heart; according to the other, even though the heart seems to have suspended action, the definitive diagnosis depends on the action or failure of the function of the nose.');">¹⁹</span>

Jastrow