Reference for Yevamot 205:14
מן הארכובה ולמעלה: מתיב רב כהנא (דברים כח, נז) ובשליתה היוצאת מבין רגליה אמר אביי בשעה שכורעת לילד נועצת עקביה בירכותיה ויולדת
R. Ashi, however, said: It may even be said that it is disconnected, but any part adjacent to the foot is legally regarded as the foot itself.<span class="x" onmousemove="('comment',' Hence any part between it and the knee may be legally regarded as directly above the foot. ');"><sup>35</sup></span> ABOVE THE KNEE. R. Kahana raised an objection: And against her afterbirth that cometh out from between her feet!<span class="x" onmousemove="('comment',' Deut. XXVIII, 57; which shews that the region of the thighs is also included in the term of feet. ');"><sup>36</sup></span> — Abaye replied: When a woman kneels down to give birth she presses her heels against her thighs and thus gives birth. Come and hear: He had neither dressed his feet nor trimmed his beard!<span class="x" onmousemove="('comment',' II Sam. XIX, 25. Cf. supra n. 13. ');"><sup>37</sup></span>