Reference for Niddah 48:2

בן ארבעה לדקה בן שמנה לגסה הימנו ולמטה אסור

had not ended, but if the period has ended it is permitted; and from this is excluded one who had two backs and two spinal columns which, even though its period of pregnancy had ended, it is forbidden if it saw the light<span class="x" onmousemove="('comment',' Not being viable it is forbidden as nebelah. ');">²</span>

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