Reference for Chullin 154:19

לא שנו אלא שאינה קשורה בולד אבל קשורה בולד אין חוששין לולד אחר

viz. , If a woman brought forth an abortion which resembled a beast or a wild animal or a bird, and there was an afterbirth too, if the afterbirth was attached to it we do not apprehend another foetus;<span class="x" onmousemove="('comment',' This woman therefore would be clean if no blood issued from her womb, for the bringing forth of these animal-like abortions is not accounted a birth, in accordance with the view of the Rabbis that whatsoever has not the form of man is not accounted a birth (v. Nid. ');">¹⁰</span>

Jastrow