Reference for Yevamot 142:8
ומי חיי והתניא כיון שיצא לאויר העולם נפתח הסתום ונסתם הפתוח שאלמלא כן אין יכול לחיות אפילו שעה אחת
'Where, for instance, the child put forth his head out of the forechamber [of the uterus]'.<span class="x" onmousemove="('comment',' Seven days prior to the Passover Eve; while birth was completed on the Passover Eve between the time of the preparation and the time of the eating. As the protrusion of the head constitutes birth in respect of circumcision (v. Nid. 29a) the operation must be performed as soon as birth is completed. ');"><sup>11</sup></span> But can such a child survive? Surely it was taught: As soon as the child emerges into the air of the world the closed organ<span class="x" onmousemove="('comment',' The mouth. ');"><sup>12</sup></span>